WO2020001750A1 - Distance sensor for measuring a distance to a ferromagnetic element, magnetical levitation system and method for measuring a distance to a ferromagnetic element - Google Patents

Distance sensor for measuring a distance to a ferromagnetic element, magnetical levitation system and method for measuring a distance to a ferromagnetic element Download PDF

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Publication number
WO2020001750A1
WO2020001750A1 PCT/EP2018/067109 EP2018067109W WO2020001750A1 WO 2020001750 A1 WO2020001750 A1 WO 2020001750A1 EP 2018067109 W EP2018067109 W EP 2018067109W WO 2020001750 A1 WO2020001750 A1 WO 2020001750A1
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WIPO (PCT)
Prior art keywords
distance
distance sensor
magnetic
magnetic field
electromagnetic actuator
Prior art date
Application number
PCT/EP2018/067109
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French (fr)
Inventor
Christian Wolfgang Ehmann
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Applied Materials, Inc.
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Filing date
Publication date
Application filed by Applied Materials, Inc. filed Critical Applied Materials, Inc.
Priority to JP2019571061A priority Critical patent/JP2020533781A/en
Priority to PCT/EP2018/067109 priority patent/WO2020001750A1/en
Priority to CN201880030816.5A priority patent/CN110859042A/en
Priority to KR1020197027160A priority patent/KR102324106B1/en
Priority to TW108122397A priority patent/TW202001274A/en
Publication of WO2020001750A1 publication Critical patent/WO2020001750A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67242—Apparatus for monitoring, sorting or marking
    • H01L21/67259—Position monitoring, e.g. misposition detection or presence detection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/003—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring position, not involving coordinate determination
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
    • G01B7/023—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring distance between sensor and object
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67242—Apparatus for monitoring, sorting or marking
    • H01L21/67253—Process monitoring, e.g. flow or thickness monitoring
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/677—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations
    • H01L21/67703—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations between different workstations
    • H01L21/67709—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations between different workstations using magnetic elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/677—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations
    • H01L21/67703—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations between different workstations
    • H01L21/67712—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations between different workstations the substrate being handled substantially vertically
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/677—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations
    • H01L21/67703—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations between different workstations
    • H01L21/6773—Conveying cassettes, containers or carriers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/677—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations
    • H01L21/67739—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations into and out of processing chamber
    • H01L21/67751—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations into and out of processing chamber vertical transfer of a single workpiece
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
    • B65G54/00—Non-mechanical conveyors not otherwise provided for
    • B65G54/02—Non-mechanical conveyors not otherwise provided for electrostatic, electric, or magnetic
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/142—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices
    • G01D5/147—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices influenced by the movement of a third element, the position of Hall device and the source of magnetic field being fixed in respect to each other

Definitions

  • Embodiments of the present disclosure relate to a distance sensor for measuring a distance to a ferromagnetic element. More specifically, embodiments of the present disclosure particularly relate to a magnetic levitation system for magnetically levitating a ferromagnetic element and a method for compensating stray magnetic fields in a distance sensor.
  • Systems are known for performing various processes, e.g. coating of a substrate in a processing chamber.
  • Several methods are known for depositing a material on a substrate.
  • substrates may be coated by using an evaporation process, a physical vapor deposition (PVD) process, such as a sputtering process, a spraying process, etc., or a chemical vapor deposition (CVD) process.
  • PVD physical vapor deposition
  • CVD chemical vapor deposition
  • the process can be performed in a processing chamber of a deposition apparatus, where the substrate to be coated is located.
  • a deposition material is provided in the processing chamber.
  • a plurality of materials such as small molecules, metals, oxides, nitrides, and carbides may be used for deposition on a substrate.
  • other processes like etching, structuring, annealing, or the like can be conducted in processing chambers.
  • Coated substrates can be used in several applications and in several technical fields.
  • an application can be organic light emitting diode (OLED) panels.
  • Further applications include insulating panels, microelectronics, such as semiconductor devices, substrates with thin film transistors (TFTs), color filters or the like.
  • OLEDs are solid-state devices composed of thin films of (organic) molecules that create light with the application of electricity.
  • OLED displays can provide bright displays on electronic devices and use reduced power compared to, for example, liquid crystal displays (LCDs).
  • the organic molecules are generated (e.g., evaporated, sputtered, or sprayed etc.) and deposited as layers on the substrates.
  • the particles can for example pass through a mask having a boundary or a specific pattern to deposit material at specific positions on the substrate, e.g. to form an OLED pattern on the substrate.
  • a processing system can include a magnetic levitation system for guiding a carrier in the processing chamber, e.g. during a coating process.
  • a magnetic levitation system may be adapted for providing the carrier in a processing position and/or for transporting the carrier within the processing chamber.
  • the magnetic levitation system may include one or more levitation units having electromagnetic actuators, sensors, signal processors and power amplifiers to form a closed control loop, such that the levitated carrier is maintained at a predetermined distance from the magnetic bearing.
  • One aspect of a magnetic levitation system is to position the electromagnetic actuators and distance sensors close to each other within the levitation unit to achieve a minimized size of the magnetic levitation system and improved control behavior through collocation of the actuator and the sensor.
  • an aspect of the present disclosure to provide a distance sensor and method for operation thereof that overcome at least some of the problems in the art.
  • a distance sensor for measuring a distance to a ferromagnetic element.
  • the distance sensor comprises at least a first permanent magnet element, at least a first hall element, and at least a second hall element, wherein the first permanent magnet element generates a first magnetic field, and the direction of the first magnetic field at the position of the first hall element is substantially opposite to the direction of the first magnetic field at the position of the second hall element.
  • a magnetic levitation system for magnetically levitating a ferromagnetic element.
  • the magnetic levitation system comprises at least one electromagnetic actuator and at least one distance sensor according to the first embodiment, wherein the at least one distance sensor is configured to measure a distance to the ferromagnetic element.
  • a method for measuring a distance to a ferromagnetic element includes providing a distance sensor comprising a first hall element and a second hall element, detecting a first signal of the first hall element and a second signal of the second hall element, and subtracting the second signal from the first signal.
  • a use of a distance sensor according to the first embodiment is provided.
  • the distance sensor is used in a magnetic levitation apparatus, wherein the distance sensor is configured to measure a distance to a levitated body.
  • Embodiments are also directed at apparatuses for carrying out the disclosed methods and include apparatus parts for performing each described method step. These method steps may be performed by way of hardware components, a computer programmed by appropriate software, by any combination of the two or in any other manner. Furthermore, embodiments according to the disclosure are also directed at methods by which the described apparatus operates. It includes method steps for carrying out every function of the apparatus.
  • Fig. 1 shows a schematic front view of a magnetic levitation system according to embodiments described herein;
  • Fig. 2a shows a cross-sectional side view of a magnetic levitation system according to embodiments described herein;
  • Fig. 2b shows a cross-sectional front view of a magnetic levitation system according to embodiments described herein;
  • Fig. 3a, 3b show cross-sectional side views of a distance sensor according to embodiments described herein;
  • Fig. 4 shows a flowchart of a method for measuring a distance to a ferromagnetic element according to embodiments described herein;
  • Fig. 5 shows a flowchart of a method for further compensation of an erroneous component of a distance signal according to embodiments described herein.
  • Embodiments described herein involve magnetic levitation and/or transportation of a carrier, e.g. a substrate carrier.
  • a carrier e.g. a substrate carrier.
  • the magnetic levitation of a carrier may be contactless.
  • the term “contactless” as used throughout the present disclosure can be understood in the sense that a weight of the carrier is not held by a mechanical contact or mechanical forces, but is held by a magnetic force.
  • the carrier may be held in a levitating or floating state using magnetic forces instead of mechanical forces.
  • An advantage as compared to mechanical devices for guiding a carrier in a processing system, is that a contactless levitation does not suffer from friction affecting the linearity and/or precision of the movement of the carrier.
  • the contactless transportation of the carrier allows for a frictionless movement of the carrier, wherein a position of the carrier, e.g. relative to a mask in a deposition process, can be controlled and maintained with high precision. Further, the levitation allows for fast acceleration or deceleration of the carrier and/or a fine adjustment of the carrier speed.
  • a contactless levitation or transportation of a carrier during a deposition process is beneficial in that no particles are generated due to a mechanical contact between the carrier and sections of the apparatus, such as mechanical rails, during the transport of the carrier. Accordingly, a contactless magnetic levitation system provides for an improved purity and uniformity of the layers deposited on the substrate, in particular since a particle generation is minimized when using contactless magnetic levitation.
  • the magnetic levitation system may be configured to be operated in a vacuum environment.
  • the processing system may include at least one vacuum chamber, wherein a deposition process is performed on a substrate.
  • the at least one vacuum chamber may include one or more vacuum pumps, such as turbo pumps and/or cryo-pumps, connected to the vacuum chamber for generation of a vacuum inside the vacuum chamber.
  • the magnetic levitation system may be configured to transport a substrate into, out of or through the vacuum chamber.
  • the magnetic levitation system may be used to transport a carrier.
  • a carrier may be adapted for carrying a substrate, a plurality of substrates and/or a mask.
  • a carrier may be a substrate carrier, for example, adapted for carrying a large area substrate and/or a plurality of large area substrates.
  • a carrier may be a mask carrier, for example, adapted for carrying an edge exclusion mask for preventing the edges of a substrate to be coated in a deposition process.
  • a carrier according to embodiments described herein need not be limited to a substrate carrier or mask carrier. The methods described herein also apply to other types of carriers, i.e. carriers adapted for carrying objects or devices other than, e.g., substrates or masks.
  • substrate as used herein embraces both inflexible substrates, e.g., a glass substrate, a wafer, slices of transparent crystal such as sapphire or the like, or a glass plate, and flexible substrates, such as a web or a foil. According to embodiments, which can be combined with other embodiments described herein, embodiments described herein can be utilized for Display PVD, i.e. sputter deposition on large area substrates for the display market.
  • a large area substrate or a respective carrier may have a size of at least 0.67 m 2 .
  • the size may be from about 0.67m (0.73x0.92m - Gen 4.5) to about 8 m 2 , more specifically from about 2 m 2 to about 9 m 2 or even up to 12 m 2 .
  • a large area substrate or carrier can be GEN 4.5, which corresponds to about 0.67 m 2 substrates (0.73x0.92m), GEN 5, which corresponds to about 1.4 m 2 substrates (1.1 m x 1.3 m), GEN 7.5, which corresponds to about 4.29 m 2 substrates (1.95 m x 2.2 m), GEN 8.5, which corresponds to about 5.7m 2 substrates (2.2 m x 2.5 m), or even GEN 10, which corresponds to about 8.7 m 2 substrates (2.85 m x 3.05 m). Even larger generations such as GEN 11 and GEN 12 and corresponding substrate areas can similarly be implemented.
  • FIG. 1 The figures show a vertically oriented carrier.
  • carrier 110 supporting substrate 120 is oriented in a plane defined by first direction 192 and second direction 194, wherein first direction 192 is oriented substantially in the carrier transport direction and second direction 194 is oriented substantially parallel to the gravitational direction.
  • First direction 192 is oriented substantially perpendicular to second direction 194.
  • embodiments described herein are not limited to vertically oriented carriers. Other orientations, e.g. a horizontal orientation, of the carrier can also be provided.
  • substantially parallel directions may include directions which form a small angle of up to 10 degrees with each other, or even up to 15 degrees.
  • the terminology of “substantially perpendicular” directions may include directions which form an angle of less than 90 degrees with each other, e.g. at least 80 degrees or at least 75 degrees. Similar considerations apply to the notions of substantially parallel or perpendicular axes, planes, areas, orientations or the like.
  • a vertical direction is considered a direction parallel or substantially parallel to the direction along which the force of gravity extends.
  • a vertical direction may deviate from exact verticality (the latter being defined by the gravitational force) by an angle of, e.g., up to 15 degrees.
  • Embodiments described herein may further involve the notion of a“horizontal direction”.
  • a horizontal direction is to be understood to distinguish over a vertical direction.
  • a horizontal direction may be perpendicular or substantially perpendicular to the exact vertical direction defined by gravity.
  • Embodiments described herein relate to a distance sensor for measuring a distance to a ferromagnetic element, as well as a magnetic levitation system for magnetically levitating a ferromagnetic element.
  • a distance sensor for measuring a distance to a ferromagnetic element
  • a magnetic levitation system for magnetically levitating a ferromagnetic element.
  • the magnetic levitation system 100 shown in Fig. 1 includes a carrier 110.
  • the carrier 110 supports a substrate 120.
  • the carrier 110 includes a ferromagnetic element 150, e.g. a bar of ferromagnetic material.
  • the magnetic levitation system 100 includes a plurality of levitation units 170 comprising e.g. active magnetic units such as electromagnetic devices, solenoids, coils or superconducting magnets. Individual levitation units of the plurality of levitation units 170 are indicated with reference numeral 175.
  • the plurality of levitation units 170 extends in a first direction 192.
  • the carrier 110 is movable along the plurality of levitation units 170.
  • the ferromagnetic element 150 and the plurality of levitation units 170 are configured for providing a magnetic levitation force for levitating the carrier 110.
  • the magnetic levitation force extends in a second direction 194.
  • the magnetic levitation system 100 shown in Fig. 1 may include a plurality of distance sensors (not shown) provided at the plurality of levitation units 170.
  • a distance sensor may be provided at each levitation unit 175.
  • a distance sensor may be provided within each levitation unit 175.
  • the distance sensors may be configured for measuring the distances between the plurality of levitation units 170 and the carrier 110 during contactless levitation of the carrier 110.
  • the magnetic levitation system 100 shown in Fig. 1 includes a magnetic drive structure 180.
  • the magnetic drive structure 180 includes a plurality of magnetic drive units. Individual magnetic drive units of the magnetic drive structure 180 are indicated with reference numeral 185.
  • the carrier 110 can include a second ferromagnetic element 160 to interact with the magnetic drive units 185 of the magnetic drive structure 180.
  • the magnetic drive units 185 of the magnetic drive structure 180 drive the carrier within the processing system, for example along the first direction 192.
  • the second ferromagnetic element 160 can include a plurality of permanent magnets, which are arranged with an alternating polarity. The resulting magnetic fields of the second ferromagnetic element 160 can interact with the plurality of magnetic drive units 185 of the magnetic drive structure 180 to move the carrier 110 in the first direction 192 while being levitated.
  • the magnetic levitation system 100 includes a control unit 130.
  • the control unit 130 may be connected to the plurality of levitation units 170 and/or to the distance sensors.
  • the control unit 130 may be configured for controlling the magnetic levitation of the carrier 110.
  • the control unit 130 may be configured for controlling the distance between the carrier 110 and the plurality of magnetic units 170 during levitation of the carrier 110, e.g. based on measured distances supplied to the control unit 130 by the distance sensors.
  • the magnetic drive structure 180 may drive the carrier 110 under the control of the control unit 130.
  • FIG. 2a is a cross-sectional view in the first direction 192, or in the carrier transport direction
  • Fig. 2b is a cross-sectional view in the third direction 196 being perpendicular to the first direction 192 and the second direction 194, or in the direction transverse to the carrier transport direction.
  • levitation unit 175 comprises at least an electromagnetic actuator 178.
  • Electromagnetic actuator 178 may comprise at least a coil l78a and at least a ferromagnetic core 178b, and generates a magnetic field upon application of an electric current to coil l78a.
  • the magnetic field generated by electromagnetic actuator 178 applies a magnetic levitation force to the ferromagnetic element 150 in the second direction 194, causing the carrier 110, to which ferromagnetic element 150 is attached, to be levitated.
  • the at least one electromagnetic actuator, the at least one distance sensor and the controller may be contained within an airtight enclosure. Due to the operation of the magnetic levitation system 100 in high or ultra-high vacuum applications, the various components of the levitation unit 175 are shielded from the surrounding vacuum environment.
  • levitation unit 175 may further comprise housing 176 which encloses the components of the levitation unit 175, shielding the components of the levitation unit 175 from the surrounding vacuum environment.
  • Housing 176 may be an airtight enclosure which encloses internal volume 177 such that internal volume 177 is separate from the surrounding vacuum environment. Separating internal volume 177 from the surrounding vacuum environment avoids contamination of the surrounding vacuum environment.
  • Housing 176 may comprise a non-ferromagnetic material, allowing for the at least one distance sensor 200 being located within housing 176 to detect the magnetic field through housing 176.
  • housing 176 may comprise a metal, in particular an aluminium alloy or a non-ferromagnetic stainless steel.
  • Internal volume 177 may be maintained at the same pressure as the surrounding vacuum environment, or at a different pressure as the surrounding vacuum environment.
  • internal volume 177 may be maintained at a higher pressure than the surrounding vacuum environment. This feature allows for the components of levitation unit 175 contained within housing 176 to be cooled via convection, or to modify the mean free path of the internal volume 177 such that electrical arcing between electrical or electronic components contained within housing 176 is avoided.
  • internal volume 177 may contain a gas composition that is the same as the surrounding vacuum environment, or different to the surrounding vacuum environment.
  • levitation unit 176 may further comprise controller 179.
  • Controller 179 is electrically attached at least a distance sensor 200 and at least an electromagnetic actuator 178.
  • Controller 179 may acquire a distance signal from at least a distance sensor 200 corresponding to distance X between distance sensor 200 and ferromagnetic element 150. Based on the acquired distance signal, controller 179 outputs an actuator signal corresponding to a target actuator force to be applied by electromagnetic actuator 178.
  • controller 179 may be configured for closed-loop control of the at least one electromagnetic actuator to control the distance to the ferromagnetic element 150.
  • controller 179 may implement a closed-loop control mechanism for maintaining a target distance.
  • the closed-loop control mechanism may include a PI controller, a PID controller, or any other closed-loop controller in the art.
  • the closed-loop control mechanism may take at least one distance signal as an input, and may generate a control signal for at least one electromagnetic actuator as an output.
  • the closed-loop control mechanism may be configured to receive further input signals. For example, an estimated current signal of at least one electromagnetic actuator may be used as an additional input signal.
  • controller 179 may be a component of levitation unit 175.
  • each levitation unit 175 in the plurality of levitation units 170 may each have a separate controller 179 which may control each levitation unit 175 independently.
  • each separate controller 179 disposed in each levitation unit 175 may be electrically attached to control unit 130, as exemplarily shown in Fig. 1.
  • controller 179 may be a component of control unit 130, where each controller 179 for each levitation unit 175 in the plurality of levitation units 170 are integrated into a single control unit 130.
  • levitation unit 176 further comprises at least a distance sensor 200.
  • levitation unit 176 may comprise two distance sensors 200 arranged on either side of electromagnetic actuator 178.
  • the number of distance sensors 200 may be at least one distance sensor for each electromagnetic actuator 178, in particular two distance sensors 200 for each electromagnetic actuator 178.
  • Distance sensor 200 may include at least one transducer that varies its output voltage in response to a magnetic field.
  • distance sensor 200 may include a hall effect sensor or a giant magnetoresistive (GMR) sensor.
  • GMR giant magnetoresistive
  • Distance sensor 200 is configured for detecting the magnetic field of ferromagnetic element 150 such that the distance X between distance sensor 200 and ferromagnetic element 150 may be determined. Distance sensor 200 is therefore able to be used to contactlessly determine the distance between levitation unit 175 and carrier 110, to which ferromagnetic element 150 is attached. Further, since the magnetic field of ferromagnetic element 150 is detected, the presence of non-ferromagnetic elements between distance sensor 200 and ferromagnetic element 150 does not hinder the operation of distance sensor 200.
  • Distance sensor 200 may be located in an appropriate position so as to reliably measure the distance X to ferromagnetic element 150.
  • Distance sensor 200 may be mounted to levitation unit 175, or may be positioned within levitation unit 175.
  • distance sensor 200 may be positioned inline with electromagnetic actuator 178. Collocation of sensor and actuator in a sensor/actuator pair is preferable in order to achieve reliable and high-performance control of the levitation unit 175. Therefore it is preferred that distance sensor 200 is positioned in close proximity to electromagnetic actuator 178. Further, positioning distance sensor 200 in close proximity to electromagnetic actuator 178 has the additional effect of allowing for the levitation unit 175 to be more compact.
  • electromagnetic actuator 178 since electromagnetic actuator 178 generates an electromagnetic field to levitate the carrier 110, positioning distance sensor 200 in close proximity to electromagnetic actuator 178 becomes problematic. Stray magnetic fields generated by electromagnetic actuator 178 may be detected by distance sensor 200, such that an undesirable cross-coupling between the electromagnetic actuator 178 is generated. This cross-coupling due to stray magnetic fields impacts the reliable determination of distance X between distance sensor 200 and ferromagnetic element 150, and hence impacts the reliable determination of the distance between the carrier and the magnetic levitation system.
  • a distance sensor 200 for measuring a distance X to a ferromagnetic element 150 comprises at least a first permanent magnet element 201, at least a first hall element 203 and at least a second hall element 204, wherein the first permanent magnet element 201 generates a first magnetic field 205.
  • the first and second hall elements 203, 204 are oriented such that the direction of the first magnetic field 205 at the position of the first hall element 203 is substantially opposite to the direction of the first magnetic field 205 at the position of the second hall element 204.
  • Second magnetic field 206 may be generated by electromagnetic actuator 178 as an unwanted effect of levitating a carrier 110.
  • Second magnetic field 206 may comprise a stray magnetic field. Since the magnitude of second magnetic field 206 is dependent on the levitation force applied to the carrier 110, the effect of second magnetic field 206 on distance sensor 200 creates an undesirable cross-coupling between electromagnetic actuator 178 and distance sensor 200. By providing a distance sensor 200 according to the present disclosure, this undesirable cross-coupling can be compensated.
  • Providing a distance sensor 200 with at least a first permanent magnet 201 and first and second hall elements 203, 204 allows for distance X between ferromagnetic element 150 and distance sensor 200 to be determined by detecting first magnetic field 205, while also allowing for a second magnetic field 206 to be compensated.
  • First magnetic field 205 generates a positive voltage component across first hall element 201 and a negative voltage component across second hall element 202.
  • Second magnetic field 206 meanwhile, generates positive voltage components across both first and second hall elements 201, 201.
  • First and second hall elements 203, 204 generate a voltage based on the magnetic field applied thereto.
  • First and second hall elements 203, 204 are positioned such that first magnetic field 205 induces a voltage in the first and second hall elements 203, 204.
  • the strength of first magnetic field 205 is affected by the presence of ferromagnetic element 150 such that a difference in first magnetic field 205 occurs between when ferromagnetic element 150 is closer to or farther from distance sensor 200.
  • By positioning hall elements 203, 204 such that first magnetic field 205 generates a voltage therein, the distance between distance sensor 200 and ferromagnetic element 150 can be measured.
  • First magnetic field 205 is generated by at least a first permanent magnet element 201.
  • distance sensor 200 comprises first permanent magnet element 201.
  • First permanent magnet element 201 is positioned such that a magnetic field loop is generated so that the magnetic flux direction on one side of distance sensor 200 is in a first flux direction away from ferromagnetic element 150 and the magnetic flux direction on the other side of distance sensor 200 is in a second flux direction towards ferromagnetic element 150.
  • Distance sensor 200 may further comprise core elements 202 positioned to direct the first magnetic field 205.
  • First and second hall elements 203, 204 are positioned in first magnetic field 205 such that first hall element 203 is in a region of magnetic flux in the first flux direction and second hall element 204 is in a region of magnetic flux in the second flux direction.
  • a first permanent magnet element 20 la and a second permanent magnet element 20 lb are provided.
  • the polarities of the first and second permanent magnet elements 20 la, 20 lb are arranged opposite to each other, such that a magnetic field loop is generated so that the magnetic flux direction on one side of distance sensor 200 is in a first flux direction away from ferromagnetic element 150 and the magnetic flux direction on the other side of distance sensor 200 is in a second flux direction towards ferromagnetic element 150.
  • Distance sensor 200 may further comprise core element 202 positioned to direct the first magnetic field 205.
  • First and second hall elements 203, 204 are positioned in first magnetic field 205 such that first hall element 203 is in a region of magnetic flux in the first flux direction and second hall element 204 is in a region of magnetic flux in the second flux direction.
  • the at least first permanent magnet elements 201 may be included in a plurality of permanent magnet elements.
  • distance sensor 200 may comprise at least two first permanent magnet elements, or may comprise at least two first permanent magnet elements and at least two second magnet elements.
  • the plurality of permanent magnet elements may be oriented such that they form a Halbach array, so that the magnetic field generated by the plurality of permanent magnet elements is strong on a side facing ferromagnetic element 150 and weak on the side opposite ferromagnetic element 150.
  • a Halbach array has the advantage of not generating a magnetic field on its rear surface, such that other components located within a levitation unit, which may be sensitive to magnetic interference, are affected by first magnetic field to a lesser extent compared to conventional magnet elements.
  • first and second hall elements 203, 204 are oriented inversely to one another such that first magnetic field 205 generates a positive voltage in the first and second hall elements 203, 204.
  • first and second hall elements 203, 204 are oriented such that first hall element 203 positioned in a region of magnetic flux in the first flux direction is oriented in the first flux direction, and second hall element 204 positioned in a region of magnetic flux in the second flux direction is oriented in the second flux direction.
  • first hall element 203 is oriented upwards and second hall element 204 is oriented downwards.
  • first magnetic field 205 generates a positive voltage in both first hall element 203 and second hall element 204, so that the magnitudes of each voltage are substantially equal to each other.
  • second magnetic field 206 generates a positive voltage in one of the first or second hall elements 203, 204 and a negative voltage in the other one of the first and second hall elements 203, 204, so that the magnitudes of each voltage are substantially equal to each other.
  • the voltages generated by each of the first and second hall elements 203, 204 may be added such that the voltages generated by the first magnetic field 205 are retained and the voltages generated by the second magnetic field 206 are cancelled, compensating the measured voltage of any effect of second magnetic field 206 on the output voltage of distance sensor 200.
  • first and second hall elements 203, 204 may be oriented in the same direction as each other such that the first magnetic field 205 generates a positive voltage in one hall element and generates a negative voltage in the other hall element.
  • first and second hall elements 203, 204 are both oriented upwards or both oriented downwards.
  • first magnetic field 205 generates a positive voltage in first hall element 203 and a negative voltage in second hall element 204, so that the magnitudes of each voltage are substantially equal to each other.
  • second magnetic field 206 generates a positive voltage in both first and second hall elements 203, 204, so that the magnitudes of each voltage are substantially equal to each other. It follows that the voltages generated by each of the first and second hall elements 203, 204 may be subtracted such that the voltages generated by the first magnetic field 205 are retained and the voltages generated by the second magnetic field 206 are cancelled, compensating the measured voltage of any effect of second magnetic field 206 on the output voltage of distance sensor 200.
  • stray magnetic fields can be compensated.
  • the stray magnetic fields may be generated by, for example, an electromagnetic actuator, a magnetic element on a substrate carrier, or a cathode target. Compensating the stray magnetic fields allows for distance sensor 200 to be positioned closer to an electromagnetic actuator, so that improved performance of the magnetic levitation system can be achieved through collocation of sensor and actuator. Further, by compensating for stray magnetic fields, distance sensor 200 can produce a more reliable and accurate distance measurement, such that the distance between a carrier and a magnetic levitation system can be more reliably and more accurately maintained.
  • controller 179 as shown in Figs. 2a and 2b may be configured for compensating stray magnetic fields generated by at least one electromagnetic actuator and acting on the at least one distance sensor.
  • Controller 179 may be electrically attached to the at least one distance sensor 200, such that controller 179 may receive first and second signals from first and second hall elements, respectively.
  • Controller 179 may be configured to subtract first and second signals from each other, such that the signal components generated by a stray magnetic field generated by the at least one electromagnetic actuator are compensated.
  • a method for measuring a distance to a ferromagnetic element includes providing a distance sensor comprising a first hall element and a second hall element, detecting a first signal of the first hall element and a second signal of the second hall element, and subtracting the second signal from the first signal.
  • Fig. 5 shows a flowchart for a method 500 for measuring a distance to a ferromagnetic element according to embodiments of the present disclosure. Method 500 begins at start 510.
  • a distance sensor comprising a first hall element and a second hall element.
  • the distance sensor may be a distance sensor according to embodiments described herein, wherein the distance sensor is capable of measuring a distance to a ferromagnetic element.
  • the distance sensor may be, for example, provided in proximity with an electromagnetic actuator. An undesired stray magnetic field generated by the electromagnetic actuator may affect the distance sensor such that a cross-coupling between the electromagnetic actuator and the distance sensor is caused.
  • a first signal of the first hall element is detected, while at block 513, a second signal of the second hall element is detected.
  • the first and second signals of the first and second hall elements may each comprise a component of a distance measurement signal and a stray magnetic field signal.
  • the distance measurement signal components of each of the first and second signals may be substantially equal in magnitude, but opposite in polarity, whereas the stray magnetic field signal components of each of the first and second signals may be substantially equal in magnitude and may have the same polarity.
  • the first signal of the first hall element and the second signal of the second hall element are subtracted from each other. Since the stray magnetic field signal components of each of the first and second signals are substantially equal in magnitude and have the same polarity, subtracting the first and second signals from each other cancels each of the stray magnetic field signal components of the first and second signals. The stray magnetic field signal components are therefore compensated, so that a distance signal which remains unaffected by the undesired stray magnetic field may be generated. Finally, the method 500 concludes at end 520.
  • the distance sensor provided at block 511 may further comprise at least a first permanent magnet element for generating a first magnetic field, wherein the direction of the first magnetic field at the position of the first hall element is substantially opposite to the direction of the first magnetic field at the position of the second hall element.
  • the distance sensor provided at block 511 may further comprise at least a first permanent magnet element and at least a second permanent magnet element for generating a first magnetic field, wherein the direction of the first magnetic field at the position of the first hall element is substantially opposite to the direction of the first magnetic field at the position of the second hall element.
  • the first magnetic field therefore causes first hall element to generate a first distance measurement signal component and second hall element to generate a second distance measurement signal component, wherein the polarity of the first distance measurement signal component is opposite to that of the second distance measurement signal component.
  • first magnetic field may cause first hall element to generate a positive voltage component and second hall element to generate a negative voltage component.
  • the magnitude of first and second distance measurement signal components generated by first and second hall elements, respectively may be substantially equal such that when the first and second signals of the first and second hall elements, respectively, are subtracted from each other in block 514, the first and second distance measurement signal components do not cancel each other, and first and second stray magnetic field components are compensated.
  • a distance signal which remains unaffected by the effects of a stray magnetic field can be generated.
  • Method 500 may be carried out using a controller.
  • controller 179 which may be a component of a levitation unit 175.
  • Controller 179 may be electrically attached to at least a distance sensor 200, such that controller 179 receives a first signal and a second signal as input.
  • one aspect of a magnetic levitation system is to position the electromagnetic actuators and distance sensors close to each other within the levitation unit to achieve a minimized size of the magnetic levitation system and improved control behavior through collocation of the actuator and the sensor.
  • One undesirable effect of the closer proximity between the electromagnetic actuators and distance sensors is that stray magnetic fields generated by the electromagnetic actuators introduce a cross-coupling effect with the distance sensors.
  • Embodiments described herein solve this problem by, for example, using a first and second hall element and subtracting their signals to compensate for stray magnetic fields.
  • the stray magnetic field may not affect the first and second hall elements within the distance sensor equally.
  • the curvature of the stray magnetic field may be higher in a region where a distance sensor is positioned, or the magnitude of the stray magnetic field may not be uniform.
  • method 501 further comprises the additional steps of detecting a coil current of at least one electromagnetic actuator, using the coil current to estimate the magnetic flux generated by the at least one electromagnetic actuator, and compensating an erroneous component of a distance signal measured by the distance sensor.
  • the method 501 begins at start 510.
  • Method 501 which comprises blocks 511, 512, 513 and 514 according to method 500 described above, further comprises in block 515 detecting a coil current of at least one electromagnetic actuator.
  • the coil current in an electromagnetic actuator is proportional to the magnetic flux generated by the electromagnetic actuator.
  • the coil current may be detected from a current signal being sent to an electromagnetic actuator, or by using a current sensor configured to measure the current in the coil of an electromagnetic actuator.
  • the magnetic flux generated by the at least one electromagnetic actuator is estimated.
  • the estimation of the magnetic flux generated is based on the coil current of the at least one electromagnetic actuator as detected in block 515.
  • Estimating the magnetic flux includes generating a magnetic flux compensation signal which may be used to compensate an erroneous component of the distance signal generated by the distance sensor.
  • an erroneous component of the distance signal measured by the distance sensor is compensated. Compensation is performed by subtracting the magnetic flux compensation signal generated in block 516 from the distance signal detected by the distance sensor such that further effects of cross-coupling between the electromagnetic actuator and the distance sensor not already compensated for by block 514 are compensated.
  • Carrying out method 501 as described above allows for further compensation of stray magnetic fields, such as non-uniform or high-curvature stray magnetic fields, or stray magnetic fields from adjacent electromagnetic actuators such that distance sensors may be positioned in even closer proximity to electromagnetic actuators, further improving the performance of the magnetic levitation system.
  • stray magnetic fields such as non-uniform or high-curvature stray magnetic fields, or stray magnetic fields from adjacent electromagnetic actuators such that distance sensors may be positioned in even closer proximity to electromagnetic actuators, further improving the performance of the magnetic levitation system.
  • estimating the magnetic flux in block 516 comprises calculating a model of the magnetic flux based on the magnitude and/or frequency of the coil current.
  • the coil current may, for example, induce eddy currents in housing 176, or may generate a given flux magnitude which is dependent on frequency.
  • ferromagnetic element 150 may be a non-laminated element, which may introduce a frequency dependence.
  • the model may include a predetermined or pre-calculated model of the magnetic flux generated by an electromagnetic actuator for a given coil current magnitude and/or frequency.
  • the model may include a lookup table of pre-calculated values.
  • the model may be calculated in real-time based on a mathematical approximation of the magnetic flux generated by an electromagnetic actuator for a given coil current magnitude and/or frequency.
  • a model of the magnetic flux may be determined by measuring the magnetic flux behavior of an electromagnetic actuator in response to an applied coil current and determining its effect on the distance signal.
  • the ferromagnetic element is fixed at a known distance from the distance sensor, and a coil current is applied to the electromagnetic actuator, generating a distance signal from the distance sensor.
  • Changing the coil current applied to the electromagnetic actuator generates a change in the magnetic flux, which changes the distance signal from the distance sensor under the influence of the magnetic flux.
  • the model may take into account further parameters for estimating the magnetic flux generated by the at least one electromagnetic actuator.
  • the model may include parameters relating to the coil current of at least one neighboring electromagnetic actuator. If an electromagnetic actuator is positioned in close proximity to its neighbors, the stray magnetic flux generated by a neighboring electromagnetic actuator may also cross-couple with neighboring distance sensors. The erroneous component of the distance signal generated by the distance sensor, caused by the stray magnetic flux acting on the distance sensor, may therefore be further compensated.
  • a digital signal processor typically comprises an analog-digital converter (ADC), a digital signal processing unit, and a digital-analog converter (DAC), allowing for analog signals to be manipulated in real-time.
  • the digital signal processor may be a separate component provided in a levitation unit, or may be integrated into a controller for a levitation unit. Carrying out the estimation of the magnetic flux on a digital signal processor allows for real-time estimation of the magnetic flux, allowing for faster acquisition of the distance signal, and allowing for higher performance of the levitation system in maintaining a target distance between a carrier and the levitation system.

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Abstract

The present disclosure relates to a distance sensor for measuring a distance to a ferromagnetic element, a magnetic levitation system for magnetically levitating a ferromagnetic element and a method for compensating stray magnetic fields in a distance sensor. According to a first aspect, a distance sensor for measuring a distance to a ferromagnetic element is provided. According to a second aspect, a magnetic levitation system for magnetically levitating a ferromagnetic element is provided, comprising at least one electromagnetic actuator and at least one distance sensor according to the first aspect, wherein the at least one distance sensor is configured to measure a distance to the ferromagnetic element. According to a third aspect, a method for measuring a distance to a ferromagnetic element is provided, the method comprising providing a distance sensor comprising a first hall element and a second hall element, detecting a first signal of the first hall element and a second signal of the second hall element, and subtracting the second signal from the first signal. According to a fourth embodiment, a use of a distance sensor according to the first aspect is provided, wherein the distance sensor is used in a magnetic levitation apparatus, wherein the distance sensor is configured to measure a distance to a levitated body.

Description

DISTANCE SENSOR FOR MEASURING A DISTANCE TO A FERROMAGNETIC ELEMENT, MAGNETICAL LEVITATION SYSTEM AND METHOD FOR
MEASURING A DISTANCE TO A FERROMAGNETIC ELEMENT
TECHNICAL FIELD OF THE DISCLOSURE
[0001] Embodiments of the present disclosure relate to a distance sensor for measuring a distance to a ferromagnetic element. More specifically, embodiments of the present disclosure particularly relate to a magnetic levitation system for magnetically levitating a ferromagnetic element and a method for compensating stray magnetic fields in a distance sensor.
BACKGROUND OF THE DISCLOSURE
[0002] Systems are known for performing various processes, e.g. coating of a substrate in a processing chamber. Several methods are known for depositing a material on a substrate. As an example, substrates may be coated by using an evaporation process, a physical vapor deposition (PVD) process, such as a sputtering process, a spraying process, etc., or a chemical vapor deposition (CVD) process. The process can be performed in a processing chamber of a deposition apparatus, where the substrate to be coated is located. A deposition material is provided in the processing chamber. A plurality of materials, such as small molecules, metals, oxides, nitrides, and carbides may be used for deposition on a substrate. Further, other processes like etching, structuring, annealing, or the like can be conducted in processing chambers.
[0003] For example, coating processes may be considered for large area substrates, e.g. in display manufacturing technology. Coated substrates can be used in several applications and in several technical fields. For instance, an application can be organic light emitting diode (OLED) panels. Further applications include insulating panels, microelectronics, such as semiconductor devices, substrates with thin film transistors (TFTs), color filters or the like. OLEDs are solid-state devices composed of thin films of (organic) molecules that create light with the application of electricity. As an example, OLED displays can provide bright displays on electronic devices and use reduced power compared to, for example, liquid crystal displays (LCDs). In the processing chamber, the organic molecules are generated (e.g., evaporated, sputtered, or sprayed etc.) and deposited as layers on the substrates. The particles can for example pass through a mask having a boundary or a specific pattern to deposit material at specific positions on the substrate, e.g. to form an OLED pattern on the substrate.
[0004] A processing system can include a magnetic levitation system for guiding a carrier in the processing chamber, e.g. during a coating process. A magnetic levitation system may be adapted for providing the carrier in a processing position and/or for transporting the carrier within the processing chamber. The magnetic levitation system may include one or more levitation units having electromagnetic actuators, sensors, signal processors and power amplifiers to form a closed control loop, such that the levitated carrier is maintained at a predetermined distance from the magnetic bearing.
[0005] In applications where substrates are processed in high vacuum, metallic shielding of actuators, sensors and other components prevents the use of several types of distance sensors. In such applications, distance sensors based on magnetic effects, such as hall effect sensors, are used since they are able to measure distances through a non-ferrous metallic shielding.
[0006] One aspect of a magnetic levitation system is to position the electromagnetic actuators and distance sensors close to each other within the levitation unit to achieve a minimized size of the magnetic levitation system and improved control behavior through collocation of the actuator and the sensor.
[0007] In view of the above, an aspect of the present disclosure to provide a distance sensor and method for operation thereof that overcome at least some of the problems in the art.
SUMMARY OF THE DISCLOSURE
[0008] According to a first embodiment, a distance sensor for measuring a distance to a ferromagnetic element is provided. The distance sensor comprises at least a first permanent magnet element, at least a first hall element, and at least a second hall element, wherein the first permanent magnet element generates a first magnetic field, and the direction of the first magnetic field at the position of the first hall element is substantially opposite to the direction of the first magnetic field at the position of the second hall element.
[0009] According to a second embodiment, a magnetic levitation system for magnetically levitating a ferromagnetic element is provided. The magnetic levitation system comprises at least one electromagnetic actuator and at least one distance sensor according to the first embodiment, wherein the at least one distance sensor is configured to measure a distance to the ferromagnetic element.
[0010] According to a third embodiment, a method for measuring a distance to a ferromagnetic element is provided. The method includes providing a distance sensor comprising a first hall element and a second hall element, detecting a first signal of the first hall element and a second signal of the second hall element, and subtracting the second signal from the first signal.
[0011] According to a fourth embodiment, a use of a distance sensor according to the first embodiment is provided. The distance sensor is used in a magnetic levitation apparatus, wherein the distance sensor is configured to measure a distance to a levitated body.
[0012] Embodiments are also directed at apparatuses for carrying out the disclosed methods and include apparatus parts for performing each described method step. These method steps may be performed by way of hardware components, a computer programmed by appropriate software, by any combination of the two or in any other manner. Furthermore, embodiments according to the disclosure are also directed at methods by which the described apparatus operates. It includes method steps for carrying out every function of the apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the disclosure and are described in the following: Fig. 1 shows a schematic front view of a magnetic levitation system according to embodiments described herein;
Fig. 2a shows a cross-sectional side view of a magnetic levitation system according to embodiments described herein;
Fig. 2b shows a cross-sectional front view of a magnetic levitation system according to embodiments described herein;
Fig. 3a, 3b show cross-sectional side views of a distance sensor according to embodiments described herein;
Fig. 4 shows a flowchart of a method for measuring a distance to a ferromagnetic element according to embodiments described herein; and
Fig. 5 shows a flowchart of a method for further compensation of an erroneous component of a distance signal according to embodiments described herein.
DETAILED DESCRIPTION OF EMBODIMENTS
[0014] Reference will now be made in detail to the various embodiments of the disclosure, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to same components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the disclosure and is not meant as a limitation of the disclosure.
Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.
[0015] Embodiments described herein involve magnetic levitation and/or transportation of a carrier, e.g. a substrate carrier. As such, the magnetic levitation of a carrier may be contactless. The term “contactless” as used throughout the present disclosure can be understood in the sense that a weight of the carrier is not held by a mechanical contact or mechanical forces, but is held by a magnetic force. Specifically, the carrier may be held in a levitating or floating state using magnetic forces instead of mechanical forces. In some implementations, there may be no mechanical contact between the carrier and the rest of the apparatus at all during levitation, and for example movement, of the carrier in the system.
[0016] An advantage, as compared to mechanical devices for guiding a carrier in a processing system, is that a contactless levitation does not suffer from friction affecting the linearity and/or precision of the movement of the carrier. The contactless transportation of the carrier allows for a frictionless movement of the carrier, wherein a position of the carrier, e.g. relative to a mask in a deposition process, can be controlled and maintained with high precision. Further, the levitation allows for fast acceleration or deceleration of the carrier and/or a fine adjustment of the carrier speed.
[0017] For example, a contactless levitation or transportation of a carrier during a deposition process is beneficial in that no particles are generated due to a mechanical contact between the carrier and sections of the apparatus, such as mechanical rails, during the transport of the carrier. Accordingly, a contactless magnetic levitation system provides for an improved purity and uniformity of the layers deposited on the substrate, in particular since a particle generation is minimized when using contactless magnetic levitation.
[0018] The magnetic levitation system may be configured to be operated in a vacuum environment. The processing system may include at least one vacuum chamber, wherein a deposition process is performed on a substrate. The at least one vacuum chamber may include one or more vacuum pumps, such as turbo pumps and/or cryo-pumps, connected to the vacuum chamber for generation of a vacuum inside the vacuum chamber. The magnetic levitation system may be configured to transport a substrate into, out of or through the vacuum chamber.
[0019] The magnetic levitation system may be used to transport a carrier. A carrier may be adapted for carrying a substrate, a plurality of substrates and/or a mask. A carrier may be a substrate carrier, for example, adapted for carrying a large area substrate and/or a plurality of large area substrates. Alternatively, a carrier may be a mask carrier, for example, adapted for carrying an edge exclusion mask for preventing the edges of a substrate to be coated in a deposition process. [0020] A carrier according to embodiments described herein need not be limited to a substrate carrier or mask carrier. The methods described herein also apply to other types of carriers, i.e. carriers adapted for carrying objects or devices other than, e.g., substrates or masks.
[0021] The term“substrate” as used herein embraces both inflexible substrates, e.g., a glass substrate, a wafer, slices of transparent crystal such as sapphire or the like, or a glass plate, and flexible substrates, such as a web or a foil. According to embodiments, which can be combined with other embodiments described herein, embodiments described herein can be utilized for Display PVD, i.e. sputter deposition on large area substrates for the display market.
[0022] According to embodiments, a large area substrate or a respective carrier may have a size of at least 0.67 m2. The size may be from about 0.67m (0.73x0.92m - Gen 4.5) to about 8 m2, more specifically from about 2 m2 to about 9 m2 or even up to 12 m2. For instance, a large area substrate or carrier can be GEN 4.5, which corresponds to about 0.67 m2 substrates (0.73x0.92m), GEN 5, which corresponds to about 1.4 m2 substrates (1.1 m x 1.3 m), GEN 7.5, which corresponds to about 4.29 m2 substrates (1.95 m x 2.2 m), GEN 8.5, which corresponds to about 5.7m2 substrates (2.2 m x 2.5 m), or even GEN 10, which corresponds to about 8.7 m2 substrates (2.85 m x 3.05 m). Even larger generations such as GEN 11 and GEN 12 and corresponding substrate areas can similarly be implemented.
[0023] The figures show a vertically oriented carrier. As exemplarily shown in Fig. 1, carrier 110 supporting substrate 120 is oriented in a plane defined by first direction 192 and second direction 194, wherein first direction 192 is oriented substantially in the carrier transport direction and second direction 194 is oriented substantially parallel to the gravitational direction. First direction 192 is oriented substantially perpendicular to second direction 194. However, embodiments described herein are not limited to vertically oriented carriers. Other orientations, e.g. a horizontal orientation, of the carrier can also be provided.
[0024] In the present disclosure, the terminology of“substantially parallel” directions may include directions which form a small angle of up to 10 degrees with each other, or even up to 15 degrees. The terminology of “substantially perpendicular” directions may include directions which form an angle of less than 90 degrees with each other, e.g. at least 80 degrees or at least 75 degrees. Similar considerations apply to the notions of substantially parallel or perpendicular axes, planes, areas, orientations or the like.
[0025] Some embodiments described herein involve the notion of a“vertical direction”. A vertical direction is considered a direction parallel or substantially parallel to the direction along which the force of gravity extends. A vertical direction may deviate from exact verticality (the latter being defined by the gravitational force) by an angle of, e.g., up to 15 degrees.
[0026] Embodiments described herein may further involve the notion of a“horizontal direction”. A horizontal direction is to be understood to distinguish over a vertical direction. A horizontal direction may be perpendicular or substantially perpendicular to the exact vertical direction defined by gravity.
[0027] Embodiments described herein relate to a distance sensor for measuring a distance to a ferromagnetic element, as well as a magnetic levitation system for magnetically levitating a ferromagnetic element. Reference is first made to Fig. 1 showing an example of a magnetic levitation system 100 according to embodiments described herein.
[0028] The magnetic levitation system 100 shown in Fig. 1 includes a carrier 110. The carrier 110 supports a substrate 120. The carrier 110 includes a ferromagnetic element 150, e.g. a bar of ferromagnetic material. The magnetic levitation system 100 includes a plurality of levitation units 170 comprising e.g. active magnetic units such as electromagnetic devices, solenoids, coils or superconducting magnets. Individual levitation units of the plurality of levitation units 170 are indicated with reference numeral 175. The plurality of levitation units 170 extends in a first direction 192. The carrier 110 is movable along the plurality of levitation units 170. The ferromagnetic element 150 and the plurality of levitation units 170 are configured for providing a magnetic levitation force for levitating the carrier 110. The magnetic levitation force extends in a second direction 194.
[0029] The magnetic levitation system 100 shown in Fig. 1 may include a plurality of distance sensors (not shown) provided at the plurality of levitation units 170. A distance sensor may be provided at each levitation unit 175. Alternatively, a distance sensor may be provided within each levitation unit 175. The distance sensors may be configured for measuring the distances between the plurality of levitation units 170 and the carrier 110 during contactless levitation of the carrier 110.
[0030] The magnetic levitation system 100 shown in Fig. 1 includes a magnetic drive structure 180. The magnetic drive structure 180 includes a plurality of magnetic drive units. Individual magnetic drive units of the magnetic drive structure 180 are indicated with reference numeral 185. The carrier 110 can include a second ferromagnetic element 160 to interact with the magnetic drive units 185 of the magnetic drive structure 180. The magnetic drive units 185 of the magnetic drive structure 180 drive the carrier within the processing system, for example along the first direction 192. For example, the second ferromagnetic element 160 can include a plurality of permanent magnets, which are arranged with an alternating polarity. The resulting magnetic fields of the second ferromagnetic element 160 can interact with the plurality of magnetic drive units 185 of the magnetic drive structure 180 to move the carrier 110 in the first direction 192 while being levitated.
[0031] The magnetic levitation system 100 includes a control unit 130. The control unit 130 may be connected to the plurality of levitation units 170 and/or to the distance sensors. The control unit 130 may be configured for controlling the magnetic levitation of the carrier 110. The control unit 130 may be configured for controlling the distance between the carrier 110 and the plurality of magnetic units 170 during levitation of the carrier 110, e.g. based on measured distances supplied to the control unit 130 by the distance sensors. The magnetic drive structure 180 may drive the carrier 110 under the control of the control unit 130.
[0032] Reference is now made to Figs. 2a and 2b showing cross-sectional views of a levitation unit 175. Fig. 2a is a cross-sectional view in the first direction 192, or in the carrier transport direction, and Fig. 2b is a cross-sectional view in the third direction 196 being perpendicular to the first direction 192 and the second direction 194, or in the direction transverse to the carrier transport direction.
[0033] According to embodiments of the present disclosure, which may be combined with other embodiments described herein, levitation unit 175 comprises at least an electromagnetic actuator 178. Electromagnetic actuator 178 may comprise at least a coil l78a and at least a ferromagnetic core 178b, and generates a magnetic field upon application of an electric current to coil l78a. The magnetic field generated by electromagnetic actuator 178 applies a magnetic levitation force to the ferromagnetic element 150 in the second direction 194, causing the carrier 110, to which ferromagnetic element 150 is attached, to be levitated.
[0034] According to embodiments of the present disclosure, which may be combined with other embodiments described herein, the at least one electromagnetic actuator, the at least one distance sensor and the controller may be contained within an airtight enclosure. Due to the operation of the magnetic levitation system 100 in high or ultra-high vacuum applications, the various components of the levitation unit 175 are shielded from the surrounding vacuum environment. For this purpose, levitation unit 175 may further comprise housing 176 which encloses the components of the levitation unit 175, shielding the components of the levitation unit 175 from the surrounding vacuum environment. Housing 176 may be an airtight enclosure which encloses internal volume 177 such that internal volume 177 is separate from the surrounding vacuum environment. Separating internal volume 177 from the surrounding vacuum environment avoids contamination of the surrounding vacuum environment.
[0035] Housing 176 may comprise a non-ferromagnetic material, allowing for the at least one distance sensor 200 being located within housing 176 to detect the magnetic field through housing 176. For example, housing 176 may comprise a metal, in particular an aluminium alloy or a non-ferromagnetic stainless steel.
[0036] Internal volume 177 may be maintained at the same pressure as the surrounding vacuum environment, or at a different pressure as the surrounding vacuum environment. For example, internal volume 177 may be maintained at a higher pressure than the surrounding vacuum environment. This feature allows for the components of levitation unit 175 contained within housing 176 to be cooled via convection, or to modify the mean free path of the internal volume 177 such that electrical arcing between electrical or electronic components contained within housing 176 is avoided. Further, internal volume 177 may contain a gas composition that is the same as the surrounding vacuum environment, or different to the surrounding vacuum environment.
[0037] According to embodiments of the present disclosure, which may be combined with other embodiments described herein, levitation unit 176 may further comprise controller 179. Controller 179 is electrically attached at least a distance sensor 200 and at least an electromagnetic actuator 178. Controller 179 may acquire a distance signal from at least a distance sensor 200 corresponding to distance X between distance sensor 200 and ferromagnetic element 150. Based on the acquired distance signal, controller 179 outputs an actuator signal corresponding to a target actuator force to be applied by electromagnetic actuator 178. [0038] According to an embodiment of the present disclosure, which may be combined with other embodiments described herein, controller 179 may be configured for closed-loop control of the at least one electromagnetic actuator to control the distance to the ferromagnetic element 150. For example, controller 179 may implement a closed-loop control mechanism for maintaining a target distance. The closed-loop control mechanism may include a PI controller, a PID controller, or any other closed-loop controller in the art. The closed-loop control mechanism may take at least one distance signal as an input, and may generate a control signal for at least one electromagnetic actuator as an output. The closed-loop control mechanism may be configured to receive further input signals. For example, an estimated current signal of at least one electromagnetic actuator may be used as an additional input signal.
[0039] As exemplarily shown in Figs. 2a and 2b, controller 179 may be a component of levitation unit 175. In this case, each levitation unit 175 in the plurality of levitation units 170 may each have a separate controller 179 which may control each levitation unit 175 independently. Optionally, each separate controller 179 disposed in each levitation unit 175 may be electrically attached to control unit 130, as exemplarily shown in Fig. 1. Alternatively, controller 179 may be a component of control unit 130, where each controller 179 for each levitation unit 175 in the plurality of levitation units 170 are integrated into a single control unit 130.
[0040] According to embodiments of the present disclosure, which may be combined with other embodiments described herein, levitation unit 176 further comprises at least a distance sensor 200. As exemplarily shown in Fig. 2a, levitation unit 176 may comprise two distance sensors 200 arranged on either side of electromagnetic actuator 178. The number of distance sensors 200 may be at least one distance sensor for each electromagnetic actuator 178, in particular two distance sensors 200 for each electromagnetic actuator 178. [0041] Distance sensor 200 may include at least one transducer that varies its output voltage in response to a magnetic field. For example, distance sensor 200 may include a hall effect sensor or a giant magnetoresistive (GMR) sensor. Distance sensor 200 is configured for detecting the magnetic field of ferromagnetic element 150 such that the distance X between distance sensor 200 and ferromagnetic element 150 may be determined. Distance sensor 200 is therefore able to be used to contactlessly determine the distance between levitation unit 175 and carrier 110, to which ferromagnetic element 150 is attached. Further, since the magnetic field of ferromagnetic element 150 is detected, the presence of non-ferromagnetic elements between distance sensor 200 and ferromagnetic element 150 does not hinder the operation of distance sensor 200.
[0042] Distance sensor 200 may be located in an appropriate position so as to reliably measure the distance X to ferromagnetic element 150. Distance sensor 200 may be mounted to levitation unit 175, or may be positioned within levitation unit 175. As exemplarily shown in Figs. 2a and 2b, distance sensor 200 may be positioned inline with electromagnetic actuator 178. Collocation of sensor and actuator in a sensor/actuator pair is preferable in order to achieve reliable and high-performance control of the levitation unit 175. Therefore it is preferred that distance sensor 200 is positioned in close proximity to electromagnetic actuator 178. Further, positioning distance sensor 200 in close proximity to electromagnetic actuator 178 has the additional effect of allowing for the levitation unit 175 to be more compact.
[0043] However, since electromagnetic actuator 178 generates an electromagnetic field to levitate the carrier 110, positioning distance sensor 200 in close proximity to electromagnetic actuator 178 becomes problematic. Stray magnetic fields generated by electromagnetic actuator 178 may be detected by distance sensor 200, such that an undesirable cross-coupling between the electromagnetic actuator 178 is generated. This cross-coupling due to stray magnetic fields impacts the reliable determination of distance X between distance sensor 200 and ferromagnetic element 150, and hence impacts the reliable determination of the distance between the carrier and the magnetic levitation system.
[0044] Reference is now made to Figs. 3a and 3b showing side cross-sectional views of distance sensor 200 according to embodiments of the present disclosure. Therein, a distance sensor 200 for measuring a distance X to a ferromagnetic element 150 is provided. Distance sensor 200 comprises at least a first permanent magnet element 201, at least a first hall element 203 and at least a second hall element 204, wherein the first permanent magnet element 201 generates a first magnetic field 205. The first and second hall elements 203, 204 are oriented such that the direction of the first magnetic field 205 at the position of the first hall element 203 is substantially opposite to the direction of the first magnetic field 205 at the position of the second hall element 204.
[0045] Second magnetic field 206 may be generated by electromagnetic actuator 178 as an unwanted effect of levitating a carrier 110. Second magnetic field 206 may comprise a stray magnetic field. Since the magnitude of second magnetic field 206 is dependent on the levitation force applied to the carrier 110, the effect of second magnetic field 206 on distance sensor 200 creates an undesirable cross-coupling between electromagnetic actuator 178 and distance sensor 200. By providing a distance sensor 200 according to the present disclosure, this undesirable cross-coupling can be compensated.
[0046] Providing a distance sensor 200 with at least a first permanent magnet 201 and first and second hall elements 203, 204 allows for distance X between ferromagnetic element 150 and distance sensor 200 to be determined by detecting first magnetic field 205, while also allowing for a second magnetic field 206 to be compensated. First magnetic field 205 generates a positive voltage component across first hall element 201 and a negative voltage component across second hall element 202. Second magnetic field 206, meanwhile, generates positive voltage components across both first and second hall elements 201, 201. By subtracting the voltage generated by second hall element 204 from the voltage generated by first hall element 203, the voltage component generated across first and second hall elements 201, 202 by second magnetic field 206 is cancelled out, and the voltage components generated across first and second hall elements 201, 202 by first magnetic field 205 remain.
[0047] First and second hall elements 203, 204 generate a voltage based on the magnetic field applied thereto. First and second hall elements 203, 204 are positioned such that first magnetic field 205 induces a voltage in the first and second hall elements 203, 204. The strength of first magnetic field 205 is affected by the presence of ferromagnetic element 150 such that a difference in first magnetic field 205 occurs between when ferromagnetic element 150 is closer to or farther from distance sensor 200. By positioning hall elements 203, 204 such that first magnetic field 205 generates a voltage therein, the distance between distance sensor 200 and ferromagnetic element 150 can be measured. [0048] First magnetic field 205 is generated by at least a first permanent magnet element 201. Referring firstly to the embodiment exemplarily shown in Fig. 3 a, distance sensor 200 comprises first permanent magnet element 201. First permanent magnet element 201 is positioned such that a magnetic field loop is generated so that the magnetic flux direction on one side of distance sensor 200 is in a first flux direction away from ferromagnetic element 150 and the magnetic flux direction on the other side of distance sensor 200 is in a second flux direction towards ferromagnetic element 150. Distance sensor 200 may further comprise core elements 202 positioned to direct the first magnetic field 205. First and second hall elements 203, 204 are positioned in first magnetic field 205 such that first hall element 203 is in a region of magnetic flux in the first flux direction and second hall element 204 is in a region of magnetic flux in the second flux direction.
[0049] An alternative arrangement is exemplarily shown in Fig. 3b. In this embodiment, a first permanent magnet element 20 la and a second permanent magnet element 20 lb are provided. The polarities of the first and second permanent magnet elements 20 la, 20 lb are arranged opposite to each other, such that a magnetic field loop is generated so that the magnetic flux direction on one side of distance sensor 200 is in a first flux direction away from ferromagnetic element 150 and the magnetic flux direction on the other side of distance sensor 200 is in a second flux direction towards ferromagnetic element 150. Distance sensor 200 may further comprise core element 202 positioned to direct the first magnetic field 205. First and second hall elements 203, 204 are positioned in first magnetic field 205 such that first hall element 203 is in a region of magnetic flux in the first flux direction and second hall element 204 is in a region of magnetic flux in the second flux direction.
[0050] The at least first permanent magnet elements 201 may be included in a plurality of permanent magnet elements. For example, distance sensor 200 may comprise at least two first permanent magnet elements, or may comprise at least two first permanent magnet elements and at least two second magnet elements. The plurality of permanent magnet elements may be oriented such that they form a Halbach array, so that the magnetic field generated by the plurality of permanent magnet elements is strong on a side facing ferromagnetic element 150 and weak on the side opposite ferromagnetic element 150. A Halbach array has the advantage of not generating a magnetic field on its rear surface, such that other components located within a levitation unit, which may be sensitive to magnetic interference, are affected by first magnetic field to a lesser extent compared to conventional magnet elements.
[0051] According to embodiments of the present disclosure, first and second hall elements 203, 204 are oriented inversely to one another such that first magnetic field 205 generates a positive voltage in the first and second hall elements 203, 204. This means that the first and second hall elements 203, 204 are oriented such that first hall element 203 positioned in a region of magnetic flux in the first flux direction is oriented in the first flux direction, and second hall element 204 positioned in a region of magnetic flux in the second flux direction is oriented in the second flux direction. In the cross-sectional side views shown in Figs. 3a and 3b, it follows that first hall element 203 is oriented upwards and second hall element 204 is oriented downwards.
[0052] In the case where first and second hall elements 203, 204 are oriented inversely to one another, first magnetic field 205 generates a positive voltage in both first hall element 203 and second hall element 204, so that the magnitudes of each voltage are substantially equal to each other. However, second magnetic field 206 generates a positive voltage in one of the first or second hall elements 203, 204 and a negative voltage in the other one of the first and second hall elements 203, 204, so that the magnitudes of each voltage are substantially equal to each other. It follows that the voltages generated by each of the first and second hall elements 203, 204 may be added such that the voltages generated by the first magnetic field 205 are retained and the voltages generated by the second magnetic field 206 are cancelled, compensating the measured voltage of any effect of second magnetic field 206 on the output voltage of distance sensor 200.
[0053] As an alternative embodiment, first and second hall elements 203, 204 may be oriented in the same direction as each other such that the first magnetic field 205 generates a positive voltage in one hall element and generates a negative voltage in the other hall element. In the cross-sectional side views shown in Figs. 3a and 3b, it follows that in this case, first and second hall elements 203, 204 are both oriented upwards or both oriented downwards.
[0054] In the case where first and second hall elements 203, 204 are oriented in the same direction as each other, first magnetic field 205 generates a positive voltage in first hall element 203 and a negative voltage in second hall element 204, so that the magnitudes of each voltage are substantially equal to each other. However, second magnetic field 206 generates a positive voltage in both first and second hall elements 203, 204, so that the magnitudes of each voltage are substantially equal to each other. It follows that the voltages generated by each of the first and second hall elements 203, 204 may be subtracted such that the voltages generated by the first magnetic field 205 are retained and the voltages generated by the second magnetic field 206 are cancelled, compensating the measured voltage of any effect of second magnetic field 206 on the output voltage of distance sensor 200.
[0055] By configuring distance sensor 200 according to the present disclosure, stray magnetic fields can be compensated. The stray magnetic fields may be generated by, for example, an electromagnetic actuator, a magnetic element on a substrate carrier, or a cathode target. Compensating the stray magnetic fields allows for distance sensor 200 to be positioned closer to an electromagnetic actuator, so that improved performance of the magnetic levitation system can be achieved through collocation of sensor and actuator. Further, by compensating for stray magnetic fields, distance sensor 200 can produce a more reliable and accurate distance measurement, such that the distance between a carrier and a magnetic levitation system can be more reliably and more accurately maintained.
[0056] According to an embodiment of the present disclosure, which may be combined with other embodiments described herein, controller 179 as shown in Figs. 2a and 2b may be configured for compensating stray magnetic fields generated by at least one electromagnetic actuator and acting on the at least one distance sensor. Controller 179 may be electrically attached to the at least one distance sensor 200, such that controller 179 may receive first and second signals from first and second hall elements, respectively. Controller 179 may be configured to subtract first and second signals from each other, such that the signal components generated by a stray magnetic field generated by the at least one electromagnetic actuator are compensated.
[0057] According to a third embodiment of the present disclosure, a method for measuring a distance to a ferromagnetic element is provided. The method includes providing a distance sensor comprising a first hall element and a second hall element, detecting a first signal of the first hall element and a second signal of the second hall element, and subtracting the second signal from the first signal. [0058] Reference is now made to Fig. 5, which shows a flowchart for a method 500 for measuring a distance to a ferromagnetic element according to embodiments of the present disclosure. Method 500 begins at start 510.
[0059] At block 511, a distance sensor comprising a first hall element and a second hall element is provided. The distance sensor may be a distance sensor according to embodiments described herein, wherein the distance sensor is capable of measuring a distance to a ferromagnetic element. The distance sensor may be, for example, provided in proximity with an electromagnetic actuator. An undesired stray magnetic field generated by the electromagnetic actuator may affect the distance sensor such that a cross-coupling between the electromagnetic actuator and the distance sensor is caused.
[0060] At block 512, a first signal of the first hall element is detected, while at block 513, a second signal of the second hall element is detected. The first and second signals of the first and second hall elements, respectively, may each comprise a component of a distance measurement signal and a stray magnetic field signal. The distance measurement signal components of each of the first and second signals may be substantially equal in magnitude, but opposite in polarity, whereas the stray magnetic field signal components of each of the first and second signals may be substantially equal in magnitude and may have the same polarity.
[0061] At block 514, the first signal of the first hall element and the second signal of the second hall element are subtracted from each other. Since the stray magnetic field signal components of each of the first and second signals are substantially equal in magnitude and have the same polarity, subtracting the first and second signals from each other cancels each of the stray magnetic field signal components of the first and second signals. The stray magnetic field signal components are therefore compensated, so that a distance signal which remains unaffected by the undesired stray magnetic field may be generated. Finally, the method 500 concludes at end 520.
[0062] According to further embodiments, which may be combined with other embodiments described herein, the distance sensor provided at block 511 may further comprise at least a first permanent magnet element for generating a first magnetic field, wherein the direction of the first magnetic field at the position of the first hall element is substantially opposite to the direction of the first magnetic field at the position of the second hall element. Alternatively, the distance sensor provided at block 511 may further comprise at least a first permanent magnet element and at least a second permanent magnet element for generating a first magnetic field, wherein the direction of the first magnetic field at the position of the first hall element is substantially opposite to the direction of the first magnetic field at the position of the second hall element. The first magnetic field therefore causes first hall element to generate a first distance measurement signal component and second hall element to generate a second distance measurement signal component, wherein the polarity of the first distance measurement signal component is opposite to that of the second distance measurement signal component. For example, first magnetic field may cause first hall element to generate a positive voltage component and second hall element to generate a negative voltage component. The magnitude of first and second distance measurement signal components generated by first and second hall elements, respectively, may be substantially equal such that when the first and second signals of the first and second hall elements, respectively, are subtracted from each other in block 514, the first and second distance measurement signal components do not cancel each other, and first and second stray magnetic field components are compensated. Thus, a distance signal which remains unaffected by the effects of a stray magnetic field can be generated.
[0063] Method 500 may be carried out using a controller. For example, referring again to Figs. 2a and 2b, method 500 may be carried out by controller 179, which may be a component of a levitation unit 175. Controller 179 may be electrically attached to at least a distance sensor 200, such that controller 179 receives a first signal and a second signal as input.
[0064] As discussed above, one aspect of a magnetic levitation system is to position the electromagnetic actuators and distance sensors close to each other within the levitation unit to achieve a minimized size of the magnetic levitation system and improved control behavior through collocation of the actuator and the sensor. One undesirable effect of the closer proximity between the electromagnetic actuators and distance sensors is that stray magnetic fields generated by the electromagnetic actuators introduce a cross-coupling effect with the distance sensors. Embodiments described herein solve this problem by, for example, using a first and second hall element and subtracting their signals to compensate for stray magnetic fields. [0065] However, a further undesirable effect is introduced when the distance sensor is positioned in even closer proximity to the electromagnetic actuators, in that the stray magnetic field may not affect the first and second hall elements within the distance sensor equally. For example, the curvature of the stray magnetic field may be higher in a region where a distance sensor is positioned, or the magnitude of the stray magnetic field may not be uniform. These effects are particularly problematic for distance sensors which may be, for example, positioned between electromagnetic actuators. In such cases, the first and second magnetic field signal components may not be sufficiently equal in magnitude for the second magnetic field signal to be completely compensated through subtraction. Therefore, additional compensation of these effects may be advantageous.
[0066] Reference is now made to Fig. 6, which shows a flowchart for a method 501 for measuring a distance to a ferromagnetic element. According to embodiments of the present disclosure, which may be combined with other embodiments described herein, method 501 further comprises the additional steps of detecting a coil current of at least one electromagnetic actuator, using the coil current to estimate the magnetic flux generated by the at least one electromagnetic actuator, and compensating an erroneous component of a distance signal measured by the distance sensor. The method 501 begins at start 510.
[0067] Method 501, which comprises blocks 511, 512, 513 and 514 according to method 500 described above, further comprises in block 515 detecting a coil current of at least one electromagnetic actuator. The coil current in an electromagnetic actuator is proportional to the magnetic flux generated by the electromagnetic actuator. The coil current may be detected from a current signal being sent to an electromagnetic actuator, or by using a current sensor configured to measure the current in the coil of an electromagnetic actuator.
[0068] Further, in block 516, the magnetic flux generated by the at least one electromagnetic actuator is estimated. The estimation of the magnetic flux generated is based on the coil current of the at least one electromagnetic actuator as detected in block 515. Estimating the magnetic flux includes generating a magnetic flux compensation signal which may be used to compensate an erroneous component of the distance signal generated by the distance sensor. [0069] Finally, in block 517, an erroneous component of the distance signal measured by the distance sensor is compensated. Compensation is performed by subtracting the magnetic flux compensation signal generated in block 516 from the distance signal detected by the distance sensor such that further effects of cross-coupling between the electromagnetic actuator and the distance sensor not already compensated for by block 514 are compensated.
[0070] Carrying out method 501 as described above allows for further compensation of stray magnetic fields, such as non-uniform or high-curvature stray magnetic fields, or stray magnetic fields from adjacent electromagnetic actuators such that distance sensors may be positioned in even closer proximity to electromagnetic actuators, further improving the performance of the magnetic levitation system.
[0071] According to embodiments of the present disclosure, which may be combined with other embodiments described herein, estimating the magnetic flux in block 516 comprises calculating a model of the magnetic flux based on the magnitude and/or frequency of the coil current. The coil current may, for example, induce eddy currents in housing 176, or may generate a given flux magnitude which is dependent on frequency. Further, ferromagnetic element 150 may be a non-laminated element, which may introduce a frequency dependence. The model may include a predetermined or pre-calculated model of the magnetic flux generated by an electromagnetic actuator for a given coil current magnitude and/or frequency. For example, the model may include a lookup table of pre-calculated values. Alternatively, the model may be calculated in real-time based on a mathematical approximation of the magnetic flux generated by an electromagnetic actuator for a given coil current magnitude and/or frequency.
[0072] A model of the magnetic flux may be determined by measuring the magnetic flux behavior of an electromagnetic actuator in response to an applied coil current and determining its effect on the distance signal. The ferromagnetic element is fixed at a known distance from the distance sensor, and a coil current is applied to the electromagnetic actuator, generating a distance signal from the distance sensor. Changing the coil current applied to the electromagnetic actuator generates a change in the magnetic flux, which changes the distance signal from the distance sensor under the influence of the magnetic flux. By measuring the change in the distance signal based on the coil current, a model can be calculated for estimating the effect that the magnetic flux of the electromagnetic actuator has on distance signal based on the coil current.
[0073] The model may take into account further parameters for estimating the magnetic flux generated by the at least one electromagnetic actuator. For example, the model may include parameters relating to the coil current of at least one neighboring electromagnetic actuator. If an electromagnetic actuator is positioned in close proximity to its neighbors, the stray magnetic flux generated by a neighboring electromagnetic actuator may also cross-couple with neighboring distance sensors. The erroneous component of the distance signal generated by the distance sensor, caused by the stray magnetic flux acting on the distance sensor, may therefore be further compensated.
[0074] According to embodiments of the present disclosure, which may be combined with other embodiments described herein, estimating the magnetic flux is performed on a digital signal processor. A digital signal processor typically comprises an analog-digital converter (ADC), a digital signal processing unit, and a digital-analog converter (DAC), allowing for analog signals to be manipulated in real-time. The digital signal processor may be a separate component provided in a levitation unit, or may be integrated into a controller for a levitation unit. Carrying out the estimation of the magnetic flux on a digital signal processor allows for real-time estimation of the magnetic flux, allowing for faster acquisition of the distance signal, and allowing for higher performance of the levitation system in maintaining a target distance between a carrier and the levitation system.
[0075] While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. Distance sensor (200) for measuring a distance to a ferromagnetic element (150), comprising:
at least a first permanent magnet element (201, 20 la);
at least a first hall element (203); and
at least a second hall element (204),
wherein the first permanent magnet (201, 20 la) element generates a first magnetic field (205), and the direction of the first magnetic field (205) at the position of the first hall element (203) is substantially opposite to the direction of the first magnetic field (205) at the position of the second hall element (204).
2. Distance sensor (200) according to claim 1, further comprising at least a second permanent magnet element (20 lb) arranged parallel to and with opposite polarity to the first permanent magnet element (20 la), wherein the first and second permanent magnet elements (20 la, 20 lb) generate the first magnetic field (205).
3. Distance sensor (200) according to any of claims 1 and 2, wherein the first and second hall elements (203, 204) are oriented inversely to one another such that the first magnetic field (205) generates a positive voltage in the first and second hall elements (203, 204).
4. Magnetic levitation system (100) for magnetically levitating a ferromagnetic element (150), comprising:
at least one electromagnetic actuator (178); and
at least one distance sensor (200) according to any of claims 1 to 3,
wherein the at least one distance sensor (200) is configured to measure a distance (X) to the ferromagnetic element (150).
5. Magnetic levitation system (100) according to claim 4, further comprising a controller (130, 179) configured for closed-loop control of the at least one electromagnetic actuator (178) to control the distance (X) to the ferromagnetic element (150).
6. Magnetic levitation system according to claim 5, wherein the controller (130, 179) is configured for compensating magnetic fields generated by the at least one electromagnetic actuator (178) and acting on the at least one distance sensor (200).
7. Magnetic levitation system (100) according to any of claims 4 to 6, wherein the at least one electromagnetic actuator (178) is configured for transporting the ferromagnetic element (150) in a transport direction (192).
8. Magnetic levitation system (100) according to any of claims 4 to 7, wherein the ferromagnetic element is a substrate carrier (110).
9. Magnetic levitation system (100) according to any of claims 5 to 8, wherein the at least one electromagnetic actuator (178), the at least one distance sensor (200) and the controller (179) are contained within an airtight housing (176).
10. Magnetic levitation system (100) according to any of claims 4 to 9, wherein the magnetic levitation system (100) is configured for operation in a vacuum.
11. Method for measuring a distance (X) to a ferromagnetic element (150), the method comprising:
providing a distance sensor (200) comprising a first hall element (203) and a second hall element (204);
detecting a first signal of the first hall element (203) and a second signal of the second hall element (204); and
subtracting the second signal from the first signal.
12. Method according to claim 11, wherein the distance sensor (200) further comprises at least a first permanent magnet element (201, 20 la) for generating a first magnetic field (205), wherein the direction of the first magnetic field (205) at the position of the first hall element (203) is substantially opposite to the direction of the first magnetic field (205) at the position of the second hall element (204).
13. Method according to any of claims 11 and 12, further comprising: detecting a coil current of at least one electromagnetic actuator (178); using the coil current, estimating the magnetic flux generated by the at least one electromagnetic actuator (178); and
compensating an erroneous component of a distance signal measured by the distance sensor (200).
14. Method according to claim 13, wherein estimating the magnetic flux comprises calculating a model of the magnetic flux based on the magnitude and/or frequency of the coil current.
15. Method according to any of claims 13 or 14, wherein estimating the stray magnetic flux is performed on a digital signal processor.
16. Use of a distance sensor (200) according to any of claims 1 to 3 in a magnetic levitation apparatus (100), wherein the distance sensor (200) is configured to measure a distance (X) to a levitated body.
PCT/EP2018/067109 2018-06-26 2018-06-26 Distance sensor for measuring a distance to a ferromagnetic element, magnetical levitation system and method for measuring a distance to a ferromagnetic element WO2020001750A1 (en)

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CN201880030816.5A CN110859042A (en) 2018-06-26 2018-06-26 Distance sensor for measuring a distance to a ferromagnetic element, magnetic levitation system and method for measuring a distance to a ferromagnetic element
KR1020197027160A KR102324106B1 (en) 2018-06-26 2018-06-26 A distance sensor for measuring a distance to a ferromagnetic element, a magnetic levitation system, and a method for measuring a distance to a ferromagnetic element
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