CN116762041A - Intensity level difference based measurement system, lithographic apparatus and method thereof - Google Patents

Abstract

The system includes a radiation source, a diffraction element, an optical system, a detector, and a processor. The radiation source generates radiation. The diffraction element diffracts radiation to generate a first beam and a second beam. The first beam includes a first non-zero diffraction order and the second beam includes a second non-zero diffraction order different from the first non-zero diffraction order. An optical system receives the first and second scattered radiation beams from the target structure and directs the first and second scattered radiation beams toward the detector. The detector generates a detection signal. The processor analyzes the detection signal to determine a target structure property based at least on the detection signal. The first beam is attenuated relative to the second beam, or the first scattered beam is intentionally attenuated relative to the second scattered beam.

Description

Intensity level difference based measurement system, lithographic apparatus and method thereof

Cross Reference to Related Applications

The present application claims priority from (1) U.S. provisional patent application No. 63/123,548, filed on 12/10/2020, and (2) U.S. provisional patent application No. 63/216,355, filed on 29/6/2021, both of which are incorporated herein by reference in their entireties.

Technical Field

The present disclosure relates to lithographic systems, e.g., systems and methods for overlay measurement.

Background

A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of Integrated Circuits (ICs). In this case, a patterning device (alternatively referred to as a mask or a reticle) may be used to generate a circuit pattern to be formed on an individual layer of the IC. The pattern may be transferred onto a target portion (e.g., comprising a portion of one or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a set of consecutively patterned adjacent target portions. Known lithographic apparatus include: a so-called stepper in which each target portion is irradiated by exposing the entire pattern onto the target portion at one time; and so-called scanners in which each target portion is irradiated by scanning the target portion in a given direction (the "scanning" direction) through a radiation beam scanning pattern while simultaneously scanning the target portion parallel or anti-parallel to the scanning direction. The pattern may also be transferred from the patterning device to the substrate by imprinting the pattern onto the substrate.

During lithographic operations, different processing steps typically require different layers to be sequentially formed on the substrate. Thus, a high degree of accuracy may be required to position the substrate relative to the existing pattern formed thereon. Alignment devices may be used to detect the position of alignment marks placed on a substrate. Misalignment between alignment marks as two different layers is measured as overlay error.

Errors in wafer alignment in a lithographic apparatus result in reduced quality, unreliable performance, and reduced yield of manufactured devices, which in turn increases the time and cost of manufacturing the devices.

Disclosure of Invention

There is a need to provide improved techniques for overlay measurement.

In some embodiments, the system includes a radiation source, a diffraction element, an optical system, a detector, and a processor. The radiation source generates radiation. The diffraction element diffracts radiation to generate a first beam and a second beam. The first beam includes a first non-zero diffraction order and the second beam includes a second non-zero diffraction order different from the first non-zero diffraction order. The optical element attenuates one of the first beam or the second beam. An optical system receives the first and second scattered beams of radiation from the target structure and directs the first and second scattered beams toward the detector. The detector generates a detection signal. The processor analyzes the detection signal to determine a property of the target structure based at least on the detection signal.

In some embodiments, a method comprises: diffracting the beam of radiation to generate a first beam and a second beam; apodization one of the first beam or the second beam; irradiating the target structure with a first beam and a second beam; a first and a second scattered beam of radiation received from a target structure; generating, by the imaging detector, a detection signal based on the first scattered beam and the second scattered beam; and analyzing the detection signal to determine a property of the target structure based on an intensity imbalance between the first scattered beam and the second scattered beam. The first beam includes a first non-zero diffraction order and the second beam includes a second non-zero diffraction order different from the first non-zero diffraction order.

In some embodiments, a method comprises: the method includes irradiating a target structure with a radiation beam, receiving a first scattered beam and a second scattered beam of radiation from the target structure, generating detection signals based on the first scattered beam and the second scattered beam using an imaging detector, and analyzing the detection signals to determine at least one characteristic of the target structure. The target structure has an enhanced optical response that creates an intensity imbalance between the first scattered beam and the second scattered beam.

In some embodiments, a system includes a radiation source, an optical element, an optical system, a detector, and a processor. The radiation source is configured to generate radiation. The optical element is configured to generate a first beam and a second beam. The first beam includes a first non-zero diffraction order and the second beam includes a second non-zero diffraction order different from the first non-zero diffraction order. The first beam is attenuated relative to the second beam. The optical system is configured to direct the first and second beams toward the target structure, receive the first and second scattered beams of radiation from the target structure, and direct the first and second scattered beams toward the detector. The detector is configured to generate a detection signal. The processor is configured to analyze the detection signal to determine a property of the target structure based at least on the detection signal.

Further features of the present disclosure, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the particular embodiments described herein. These embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the relevant art based on the teachings contained herein.

Drawings

The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the disclosure and to enable a person skilled in the pertinent art(s) to make and use the embodiments described herein.

FIG. 1A depicts a schematic diagram of a reflective lithographic apparatus according to some embodiments.

FIG. 1B depicts a schematic diagram of a transmissive lithographic apparatus according to some embodiments.

FIG. 2 depicts a more detailed schematic of a reflective lithographic apparatus according to some embodiments.

FIG. 3 depicts a schematic of a lithographic cell according to some embodiments.

Fig. 4A-4B illustrate schematic diagrams of metrology systems according to some embodiments.

FIG. 5 illustrates a schematic diagram of a metrology system according to some embodiments.

FIG. 6 illustrates a schematic diagram of an asymmetric marker, according to some embodiments.

FIG. 7 illustrates a schematic diagram of a metrology system according to some embodiments.

FIG. 8 illustrates a schematic diagram of an alignment mark, according to some embodiments.

Fig. 9 illustrates a process for performing functions related to determining an intensity difference, in accordance with some embodiments.

Fig. 10 illustrates a process for performing functions related to determining an intensity difference, in accordance with some embodiments.

Features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the figure in which the reference number first appears. The drawings provided throughout this disclosure should not be construed as being drawn to scale unless otherwise indicated.

Detailed Description

The present specification discloses one or more embodiments that incorporate the features of the present disclosure. The disclosed embodiment(s) are provided as examples. The scope of the present disclosure is not limited to the embodiment(s) disclosed. The claimed features are defined by the appended claims.

References in the specification to "one embodiment," "an example embodiment," etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Spatially relative terms, such as "below," "beneath," "lower," "above," "on … …," "upper" and the like, may be used herein to facilitate the description of one element or feature as illustrated in the figures as a relationship to another element(s) or feature. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

The term "about" as used herein indicates a given amount of value that may vary based on a particular technology. Based on a particular technology, the term "about" may indicate a value of a given amount that varies within, for example, 10-30% of the value (e.g., ±10%, ±20% or ±30% of the value).

Embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include Read Only Memory (ROM); random Access Memory (RAM); a magnetic disk storage medium; an optical storage medium; a flash memory device; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, and/or instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term "non-transitory" may be used herein to characterize a computer readable medium used to store data, information, instructions, etc., with the sole exception of a transitory propagating signal.

Before describing these embodiments in more detail, however, it is beneficial to present an example environment in which embodiments of the present disclosure may be implemented.

Example lithography System

FIGS. 1A and 1B illustrate schematic diagrams of a lithographic apparatus 100 and a lithographic apparatus 100', respectively, in which embodiments of the present disclosure may be implemented. The lithographic apparatus 100 and the lithographic apparatus 100' each comprise the following: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask, reticle or dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and a substrate table (e.g., a wafer table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. The lithographic apparatus 100 and 100' also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. In lithographic apparatus 100, patterning device MA and projection system PS are reflective. In lithographic apparatus 100', patterning device MA and projection system PS are transmissive.

The illumination system IL may include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to the reference frame, the design of at least one of the lithographic apparatus 100 and 100', and other conditions, such as for example whether or not the patterning device MA is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be a frame or a table, for example, which may be fixed or movable as required. By using a sensor, the support structure MT may ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS.

The term "patterning device" MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section such as to create a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C to create an integrated circuit.

Patterning device MA may be transmissive (as in lithographic apparatus 100' of fig. 1B) or reflective (as in lithographic apparatus 100 of fig. 1A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, or attenuated phase-shift, as well as various hybrid mask types. One example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam B which is reflected by the small mirror matrix.

The term "projection system" PS can include any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, depending on the exposure radiation being used, or on other factors such as the use of an immersion liquid on a substrate W, or the use of a vacuum. Vacuum environments may be used for EUV or electron beam radiation, as other gases may absorb too much radiation or electrons. A vacuum environment can thus be provided for the entire beam path by means of the vacuum wall and the vacuum pump.

The lithographic apparatus 100 and/or the lithographic apparatus 100' may be of a type having two (dual stage) or more substrate tables WT (and/or two or more mask tables). In such "multiple stage" machines the additional substrate tables WT may be used in parallel, or the preparatory steps may be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some cases, the additional table may not be the substrate table WT.

The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g. water), so as to fill a space between the projection system and the substrate. The immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.

Referring to fig. 1A and 1B, the illuminator IL receives a radiation beam from a radiation source SO. For example, when the source SO is an excimer laser, the source SO and the lithographic apparatus 100, 100' may be separate physical entities. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100' and the radiation beam B is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD (in FIG. 1B), the beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100', for example when the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD (in FIG. 1B) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as "σouter" and "σinner", respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. IN addition, the illuminator IL may comprise various other components (IN FIG. 1B), such as an integrator IN and a condenser CO. The illuminator IL may be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

Referring to FIG. 1A, a radiation beam B is incident on, and is patterned by, a patterning device (e.g., mask) MA, which is held on a support structure (e.g., mask table) MT. In the lithographic apparatus 100, the radiation beam B is reflected from a patterning device (e.g., mask) MA. After being reflected from the patterning device (e.g., mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (e.g., an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately (e.g., so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B. The patterning device (e.g., mask) MA and the substrate W may be aligned using the mask alignment marks M1, M2 and the substrate alignment marks P1, P2.

Referring to FIG. 1B, the radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the support structure (e.g., mask table MT), and is patterned by the patterning device. After passing through the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate (PPU) with respect to an illumination system pupil (IPU). Part of the radiation, without being affected by diffraction at the mask pattern, emanates from the intensity distribution at the illumination system pupil IPU and passes through the mask pattern, and an image of the intensity distribution is produced at the illumination system pupil IPU.

The projection system PS projects an image MP 'of the mask pattern MP onto a photoresist layer coated on the substrate W, wherein the image MP' is formed by a diffracted beam of the mask pattern MP by radiation from the intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Diffraction of radiation at the array and other than zero order diffraction generates a diverted diffracted beam having a change of direction in a direction perpendicular to the line. The undiffracted beam (i.e. the so-called zero-order diffracted beam) passes through the pattern without any change in the propagation direction. The zero-order diffracted beam passes through an upper lens or upper lens group of the projection system PS upstream of the pupil conjugate PPU of the projection system PS to reach the pupil conjugate PPU. The portion of the intensity distribution associated with the zero-order diffracted beam in the plane of the pupil conjugate PPU is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture arrangement PD is for example arranged at or substantially at a plane comprising the pupil conjugate PPU of the projection system PS.

The projection system PS is arranged to capture not only the zero order diffracted beam, but also the first order or first and higher order diffracted beams (not shown) by means of a lens or lens group L. In some embodiments, dipole illumination for imaging a line pattern extending in a direction perpendicular to the line may be used to take advantage of the resolution enhancement effect of dipole illumination. For example, the first order diffracted beams interfere with the corresponding zero order diffracted beams at the level of the wafer W to produce an image of the line pattern MP at the highest possible resolution and process window (i.e., available depth of focus combined with allowable exposure dose deviation). In some embodiments, astigmatic aberration can be reduced by providing a radiation emitter (not shown) in opposite quadrants of the illumination system pupil IPU. Furthermore, in some embodiments, astigmatic aberration can be reduced by blocking a zero order beam in a pupil conjugate PPU of the projection system associated with an emitter in an opposite quadrant. This is described in more detail in US 7,511,799 B2 published 3/31/2009, which is incorporated herein by reference in its entirety.

By means of the second positioner PW and position sensor IF (e.g., an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately (e.g., so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (which is not shown in fig. 1B) can be used to accurately position the mask MA with respect to the path of the radiation beam B (e.g., after mechanical retrieval from a mask library or during a scan).

In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks (as shown) occupy dedicated target portions, they may be located in spaces between target portions (referred to as scribe-lane alignment marks). Similarly, where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

The mask table MT and the patterning device MA can be in a vacuum chamber V, wherein an in-vacuum robot IVR can be used to move a patterning device, such as a mask, in and out of the vacuum chamber. Alternatively, when the mask table MT and the patterning device MA are outside the vacuum chamber, various transport operations may be performed using an external vacuum robot, similar to the internal vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for smooth transfer of any payload (e.g., mask) to the fixed motion mounts of the transfer station.

The lithographic apparatus 100 and 100' may be used in at least one of the following modes:

1. in step mode, the support structure (e.g., mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at the same time (i.e., a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed.

2. In scan mode, the support structure (e.g., mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS.

3. In another mode, the support structure (e.g., mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. The pulsed radiation source SO may be used and the programmable patterning device updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array.

Combinations and/or variations on the described modes of use or entirely different modes of use may also be employed.

In some embodiments, the lithographic apparatus may generate DUV and/or EUV radiation. For example, the lithographic apparatus 100' may be configured to operate using a DUV source. In another example, the lithographic apparatus 100 includes an Extreme Ultraviolet (EUV) source configured to generate an EUV radiation beam for EUV lithography. Generally, an EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition an EUV radiation beam of the EUV source.

FIG. 2 depicts lithographic apparatus 100 in more detail, lithographic apparatus 100 comprising source collector device SO, illumination system IL and projection system PS. The source collector device SO is constructed and arranged such that a vacuum environment can be maintained in the enclosure 220 of the source collector device SO. The EUV radiation emitting plasma 210 may be formed by a discharge generated plasma source. EUV radiation may be generated from a gas or vapor, such as xenon (Xe) gas, lithium (Li) vapor, or tin (Sn) vapor, wherein a very hot plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. For example, a very hot plasma 210 is generated by a discharge that causes an at least partially ionized plasma. For efficient generation of radiation, a partial pressure of Xe, li, sn vapor, or any other suitable gas or vapor, for example, of 10Pa, may be required. In some embodiments, a plasma of excited tin (Sn) is provided to generate EUV radiation.

Radiation emitted by the thermal plasma 210 is transferred from the source chamber 211 into the collector chamber 212 via an optional gas barrier or contaminant trap 230 (also referred to as a contaminant barrier or foil trap in some cases), which gas barrier or contaminant trap 230 is positioned in or after an opening in the source chamber 211. Contaminant trap 230 may include a channel structure. Contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230, as further indicated herein, includes at least a channel structure.

The collector chamber 212 may comprise a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation passing through the collector CO may be reflected from the grating spectral filter 240 to be focused in the virtual source point IF. The virtual source point IF is commonly referred to as an intermediate focus and the source collector means is arranged such that the intermediate focus IF is located at or near the opening 219 in the enclosure 220. The virtual source point IF is an image of the radiation-emitting plasma 210. The grating spectral filter 240 is particularly useful for suppressing Infrared (IR) radiation.

The radiation then passes through an illumination system IL, which may include a facet field mirror device 222 and a facet pupil mirror device 224, the facet field mirror device 222 and the facet pupil mirror device 224 being arranged to provide a desired angular distribution of the radiation beam 221 at the patterning device MA, and a desired uniformity of the radiation intensity at the patterning device MA. When the radiation beam 221 is reflected at the patterning device MA, which is held by the support structure MT, a patterned beam 226 is formed, and the patterned beam 226 is imaged by the projection system PS via reflective elements 228, 229 onto a substrate W held by a wafer or substrate table WT.

There may generally be more elements in the illumination optical unit IL and the projection system PS than shown. Alternatively, the grating spectral filter 240 may be present depending on the type of lithographic apparatus. Furthermore, there may be more mirrors than those shown in fig. 2, for example there may be 1 to 6 additional reflective elements in the projection system PS compared to that shown in fig. 2.

As illustrated in fig. 2, the collector optics CO are depicted as nested collectors with grazing incidence reflectors 253, 254, and 255, as just one example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged axisymmetrically around the optical axis O and this type of collector optics CO is preferably used in combination with a discharge-generated plasma source, commonly referred to as DPP source.

Exemplary lithography Unit

FIG. 3 illustrates a lithography unit 300, sometimes referred to as a lithography cell or cluster, according to some embodiments. The lithographic apparatus 100 or 100' may form part of a lithographic cell 300. The lithography unit 300 may also include one or more apparatuses for performing pre-exposure and post-exposure processes on the substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH, and a bake plate BK. The substrate handler or robot RO picks up substrates from the input/output ports I/O1, I/O2, moves them between different processing apparatuses and delivers them to the load lock LB of the lithographic apparatus 100 or 100'. These devices, often collectively referred to as tracks, are under the control of a track control unit TCU, which itself is controlled by a supervisory control system SCS, which also controls the lithographic apparatus via a lithographic control unit LACU. Thus, different equipment can be operated to maximize throughput and processing efficiency.

Exemplary metrology apparatus

FIG. 4A depicts a schematic cross-sectional view of an inspection apparatus 400 that may be implemented as part of a lithographic apparatus 100 or 100', according to some embodiments. In some embodiments, inspection device 400 may be configured to align a substrate (e.g., substrate W) relative to a patterning device (e.g., patterning device MA). The inspection apparatus 400 may also be configured to detect the position of the alignment marks on the substrate and use the detected position of the alignment marks to align the substrate relative to the patterning device or other component of the lithographic apparatus 100 or 100'. Such alignment of the substrate may ensure accurate exposure of one or more patterns on the substrate.

In some embodiments, inspection apparatus 400 may include illumination system 412, beam splitter 414, interferometer 426, detector 428, beam analyzer 430, and overlay calculation processor 432. The illumination system 412 may be configured to provide an electromagnetic narrowband radiation beam 413 having one or more passbands. In one example, the one or more pass bands may be within a wavelength spectrum between about 500nm and about 900 nm. In another example, the one or more pass bands may be discrete narrow pass bands within a wavelength spectrum between about 500nm to about 900 nm. The illumination system 412 may also be configured to provide one or more pass bands having a substantially constant Center Wavelength (CWL) value over a long period of time (e.g., over the lifetime of the illumination system 412). As discussed above, in the current alignment system, this configuration of the illumination system 412 may help prevent the actual CWL value from shifting from the desired CWL value. As a result, using a constant CWL value may improve the long term stability and accuracy of the alignment system (e.g., inspection apparatus 400) compared to current alignment apparatuses.

In some embodiments, beam splitter 414 may be configured to receive radiation beam 413 and split radiation beam 413 into at least two radiation sub-beams. For example, radiation beam 413 may be split into radiation sub-beams 415 and 417, as shown in FIG. 4A. The beam splitter 414 can also be configured to direct the radiation sub-beams 415 onto a substrate 420 that is placed on a stage 422. In one example, the stage 422 can move along the direction 424. The radiation beamlets 415 may be configured to illuminate alignment marks or targets 418 located on the substrate 420. The alignment marks or targets 418 may be coated with a radiation sensitive film. In some embodiments, the alignment marks or targets 418 may have 180 degree (i.e., 180 °) symmetry. That is, when alignment mark or target 418 is rotated 180 ° about an axis of symmetry perpendicular to the plane of alignment mark or target 418, rotated alignment mark or target 418 may be substantially identical to non-rotated alignment mark or target 418. The targets 418 on the substrate 420 may be: (a) a resist layer grating comprising strips formed of solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlaid target structure comprising resist gratings overlaid or staggered on the product layer grating. Alternatively, the strips may be etched into the substrate. The pattern is sensitive to chromatic aberration in the lithographic projection apparatus, particularly the projection system PL, and the symmetry of the illumination and the presence of such chromatic aberration will manifest themselves in variations in the printed grating. An in-line method used in device fabrication to measure line width, pitch, and critical dimensions utilizes a technique known as "scatterometry". Methods of scatterometry are described in Raymond et al, "Multiparameter Grating Metrology Using Optical Scatterometry" (J.Vac.Sci.Tech.B, vol.15, vol.2, pp.361-368 (1997)) and Niu et al, "Specular Spectroscopic Scatterometry in DUV Lithography" (SPIE, vol.3677 (1999)), both of which are incorporated herein by reference in their entirety. In scatterometry, light is reflected by periodic structures in a target, and the resulting reflection spectrum at a given angle is detected. The structure that produces the reflection spectrum is reconstructed, for example, using Rigorous Coupled Wave Analysis (RCWA) or by comparison with a library of patterns derived from simulation. Thus, the scatterometry data of the printed grating is used to reconstruct the grating. Parameters of the grating, such as line width and shape, may be input to the reconstruction process performed by the processing unit PU based on knowledge of the printing step and/or other scatterometry processes.

In some embodiments, according to one embodiment, the beam splitter 414 may also be configured to receive the diffracted beam 419 and divide the diffracted beam 419 into at least two sub-beams of radiation. As shown in fig. 4A, the diffracted radiation beam 419 may be divided into diffracted radiation sub-beams 429 and 439.

It should be noted that although beam splitter 414 is shown as directing radiation sub-beam 415 toward alignment mark or target 418 and diffracted radiation sub-beam 429 toward interferometer 426, the disclosure is not so limited. It will be apparent to those skilled in the relevant arts that other optical arrangements may be used to obtain similar results for illuminating alignment marks or targets 418 on substrate 420 and detecting images of alignment marks or targets 418.

As illustrated in fig. 4A, interferometer 426 may be configured to receive radiation sub-beam 417 and diffracted radiation sub-beam 429 through beam splitter 414. In an example embodiment, the diffracted radiation sub-beam 429 may be at least a portion of the radiation sub-beam 415 that may be reflected from the alignment mark or target 418. In one example of this embodiment, interferometer 426 comprises any suitable set of optical elements, such as a combination of prisms, which can be configured to form two images of alignment mark or target 418 based on received diffracted radiation beamlets 429. It should be appreciated that high quality images need not be formed, but that the features of the alignment marks 418 should be resolved. Interferometer 426 may also be configured to rotate one of the two images 180 ° relative to the other of the two images, and interferometrically recombine the rotated and un-rotated images.

In some embodiments, detector 428 may be configured to receive the recombined image via interferometer signal 427 and detect interference as a result of the recombined image when alignment axis 421 of inspection apparatus 400 passes through the center of symmetry (not shown) of alignment mark or target 418. According to one example embodiment, this interference may be due to the alignment marks or targets 418 being 180 ° symmetrical and the recombined images constructively or destructively interfering. Based on the detected interference, detector 428 may also be configured to determine the location of the center of symmetry of alignment mark or target 418 and thus detect the location of substrate 420. According to one example, the alignment axis 421 may be aligned with a beam perpendicular to the substrate 420 and passing through the center of the image rotation interferometer 426. Detector 428 may also be configured to estimate the position of alignment mark or target 418 by implementing sensor characteristics and interacting with wafer mark process variations.

In another embodiment, detector 428 determines the location of the center of symmetry of alignment mark or target 418 by performing one or more of the following measurements:

1. measuring positional changes (positional shifts between colors) of the various wavelengths;

2. Measuring the positional change of each stage (positional shift between diffraction orders); and

3. the positional changes of the various polarizations (positional shifts between the polarizations) were measured.

For example, this data may be obtained using any type of alignment sensor, such as the SMASH (smart alignment sensor mix) sensor described in us patent No. 6,961,116, which employs a self-referencing interferometer with a single detector and four different wavelengths, and extracts the alignment signal in software or Athena (advanced techniques using higher order alignment enhancement), as described in us patent No. 6,297,876, which directs each of the seven diffraction orders to a dedicated detector, both of which are incorporated herein by reference in their entirety.

In some embodiments, the beam analyzer 430 may be configured to receive and determine the optical state of the diffracted radiation beamlets 439. The optical state may be a measure of the beam wavelength, polarization or beam profile. Beam analyzer 430 may also be configured to determine the position of stage 422 and correlate the position of stage 422 to the position of the center of symmetry of alignment mark or target 418. In this manner, the position of the alignment mark or target 418, and thus the position of the substrate 420, can be accurately known with reference to the stage 422. Alternatively, beam analyzer 430 may be configured to determine the position of inspection device 400 or any other reference element such that the center of symmetry of alignment mark or target 418 may be known with reference to inspection device 400 or any other reference element. The beam analyzer 430 may be a spot or imaging polarimeter with some form of wavelength band selectivity. In some embodiments, the beam analyzer 430 may be integrated directly into the inspection apparatus 400, or according to other embodiments, connected via several types of fiber optics: polarization preserving single mode, multimode or imaging.

In some embodiments, beam analyzer 430 may also be configured to determine overlay data between two patterns on substrate 420. One of these patterns may be a reference pattern on the reference layer. The other pattern may be an exposure pattern on the exposure layer. The reference layer may be an etched layer that is already present on the substrate 420. The reference layer may be generated by a reference pattern exposed on the substrate by the lithographic apparatus 100 and/or 100'. The exposure layer may be a resist layer exposed adjacent to the reference layer. The exposure layer may be generated by an exposure pattern that is exposed by the lithographic apparatus 100 or 100' on the substrate 420. The exposure pattern on the substrate 420 may correspond to movement of the stage 422 relative to the substrate 420. In some embodiments, the measured overlay data may also indicate an offset between the reference pattern and the exposure pattern. The measured overlay data may be used as calibration data to calibrate the exposure pattern exposed by the lithographic apparatus 100 or 100' such that, after calibration, the offset between the exposure layer and the reference layer may be minimized.

In some embodiments, beam analyzer 430 may also be configured to determine a model of the product stack profile of substrate 420, and may be configured to measure the overlap, critical dimension, and focus of target 418 in a single measurement. The product stack profile contains information about the stacked product, such as alignment marks, targets 418, or substrates 420, and may include marking process variation induced optical feature measurements as a function of illumination variation. The product stack profile may also include product grating profile, mark stack profile, and mark asymmetry information. One example of beam analyzer 430 is Yieldstar manufactured by ASML of veldhaven, the netherlands ^TM As described in U.S. patent No. 8,706,442, which is incorporated by reference herein in its entirety. The beam analyzer 430 may also be configured to process information related to specific properties of the exposure pattern in the layer. For example, beam analyzer 430 may process overlay parameters (an indication of the positional accuracy of a layer relative to a previous layer on a substrate or an indication of the positional accuracy of a first layer relative to a mark on a substrate), focus parameters, and/or critical dimension parameters (e.g., line width and variations thereof) of images depicted in the layer. Other parameters are image parameters related to the quality of the depicted image of the exposure pattern.

In some embodiments, a detector array (not shown) may be connected to the beam analyzer 430 and allow for the possibility of accurate bottom profile detection, as discussed below. For example, detector 428 may be a detector array. For a detector array, many options are possible: multimode fiber bundles, discrete pin detectors per channel, or CCD or CMOS (linear) arrays. The use of multimode optical fiber bundles enables any dissipative element to be remotely located for stability reasons. Discrete PIN detectors offer a large dynamic range, but each detector requires a separate preamplifier. Therefore, the number of elements is limited. CCD linear arrays provide many elements that can be read out at high speed and are of particular interest if phase stepping detection is used.

In some embodiments, the second beam analyzer 430' may be configured to receive and determine the optical state of the diffracted radiation sub-beam 429, as shown in fig. 4B. The optical state may be a measure of the beam wavelength, polarization or beam profile. The second beam analyzer 430' may be identical to the beam analyzer 430. Alternatively, the second beam analyzer 430' may be configured to perform at least all functions of the beam analyzer 430, such as determining the position of the stage 422 and correlating the position of the stage 422 with the position of the center of symmetry of the alignment mark or target 418. In this manner, the position of the alignment mark or target 418, and thus the position of the substrate 420, can be accurately known with reference to the stage 422. The second beam analyzer 430' may also be configured to determine the position of the inspection apparatus 400 or any other reference element such that the center of symmetry of the alignment mark or target 418 may be known with reference to the inspection apparatus 400 or any other reference element. The second beam analyzer 430' may also be configured to determine overlay data between the two patterns and a model of the product stack profile of the substrate 420. The second beam analyzer 430' may also be configured to measure the overlap, critical dimension, and focus of the target 418 in a single measurement.

In some embodiments, the second beam analyzer 430' may be integrated directly into the inspection apparatus 400, or according to other embodiments, it may be connected via several types of fiber optics: polarization preserving single mode, multimode or imaging. Alternatively, the second beam analyzer 430' and the beam analyzer 430 may be combined to form a single analyzer (not shown) configured to receive and determine the optical states of the two diffracted radiation sub-beams 429 and 439.

In some embodiments, processor 432 receives information from detector 428 and beam analyzer 430. For example, processor 432 may be an overlap computation processor. The information may include a model of the product stack profile constructed by the beam analyzer 430. Alternatively, processor 432 may use the received information about the product markers to construct a model of the product marker profile. In either case, processor 432 uses or incorporates a model of the product marking profile to build a model of the stacked product and overlapping marking profiles. The overlay offset is then determined using the overlay model and the spectral impact of the overlay offset measurement is minimized. Processor 432 may generate basic correction algorithms based on information received from detector 428 and beam analyzer 430, including but not limited to optical states of the illumination beam, alignment signals, associated position estimates, and optical states in the pupil, image, and additional planes. The pupil plane is a plane in which the radial position of the radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. Processor 432 may utilize a basic correction algorithm to characterize inspection device 400 with reference to wafer marks and/or alignment marks 418.

In some embodiments, processor 432 may be further configured to determine a print pattern positional offset error relative to the sensor estimates for each mark based on information received from detector 428 and beam analyzer 430. This information includes, but is not limited to, the product stack profile, overlay measurements, critical dimensions, and focus of each alignment mark or target 418 on substrate 420. Processor 432 may utilize a clustering algorithm to group the markers into a set of similar constant offset errors and create an alignment error offset correction table based on this information. The clustering algorithm may be based on the overlay measurements, position estimates, and additional optical stacking process information associated with each set of offset errors. Overlap is calculated for many different markers, for example, overlap targets with positive and negative bias around the programmed overlap offset. The target that measures the smallest overlap is taken as a reference (since it is measured with the best accuracy). From the small overlap of the measurements and the known programmed overlap of their corresponding targets, an overlap error can be deduced. Table 1 shows how this can be performed. The minimum measurement overlap in the example shown is-1 nm. However, this is relevant for targets with a programmed overlap of-30 nm. Thus, this process necessarily introduces an overlay error of 29 nm.

The minimum value may be taken as a reference point and, in relation thereto, an offset between the measured overlap and the overlap expected due to the programmed overlap may be calculated. This offset determines the overlay error for each mark or set of marks having similar offsets. Thus, in the example of Table 1, the minimum measurement overlap is-1 nm, with a programmed overlap of 30nm at the target location. The difference between the expected overlap and the measured overlap at the other targets is compared to the reference. A table such as table 1 may also be obtained from the mark and target 418 at different illumination settings, and the illumination setting and its corresponding calibration factor that results in the smallest overlay error may be determined and selected. After this, processor 432 may group the markers into a set of similar overlay errors. The criteria for grouping the markers may be adjusted based on different process controls (e.g., different error margins for different processes).

In some embodiments, the processor 432 may confirm that all or most members of the group have similar offset errors and apply individual offset corrections from the clustering algorithm to each marker based on their additional optical stack-up measurements. Processor 432 may determine a correction for each mark and feed the correction back to lithographic apparatus 100 or 100' for correcting errors in the overlay, for example by feeding the correction into inspection device 400.

Intensity imbalance determination

Asymmetric marks (e.g., the marks shown in fig. 6) may cause an imbalance between the positive and negative intensity diffraction orders, which may reduce the accuracy of overlay and alignment measurements. The intensity difference between the positive and negative mark diffraction orders can be used to improve overlay accuracy and robustness, especially for process-induced alignment mark asymmetry. In some aspects, the intensity imbalance between conjugate diffraction orders may be used for asymmetry correction applications. An exemplary application is described in WO publication No. 2020057900, the entire contents of which are incorporated herein by reference.

In some embodiments, a filter may be used to create a transmission imbalance between diffraction orders. In some aspects, one of the diffraction orders may be apodized by transmission factor α (or order transmission) relative to the conjugate order (e.g., diffraction order +1 relative to diffraction order-1, otherwise referred to as the opposite portion of the diffraction spectrum). The transmission imbalance between diffraction orders is used to determine the intensity imbalance caused by mark asymmetry from the alignment interferogram. In some aspects, the intensity imbalance may be determined from fringe visibility of the interference pattern. In some embodiments, the filter may be at a pupil plane of the metrology system or in an illumination branch of the metrology system, as described further below.

An implementation for measuring intensity differences is illustrated in fig. 5, which is provided with a filter in front of one of the diffraction orders in order to attenuate one diffraction order while allowing the other diffraction order to pass unmodified.

FIG. 5 illustrates a schematic diagram of a metrology system 500 according to some embodiments. In some embodiments, the metrology system 500 may also represent a more detailed view of the inspection apparatus 400 (fig. 4A and 4B). For example, fig. 5 illustrates a more detailed view of the illumination system 412 and its functions.

In some embodiments, the metrology system 500 includes an illumination system 502, an optical system 504, a detector system 506, and a processor 508. The illumination system 502 may include a radiation source 510, a polarizer 512, a retarder 514 (e.g., a wave plate), a first optical element(s) 516 (e.g., a lens or lens system), a reflective element 518 (e.g., a total internal reflection prism), a field stop 520, a second optical element(s) 522, a wave plate 524, and an aperture stop 526. The optical system 504 may include a reflective element 528 (e.g., a point mirror) and an optical element 530 (e.g., an objective lens). Reflective element 528 may act as a field stop for zero order diffracted radiation.

FIG. 5 shows a non-limiting depiction of a metrology system 500 inspecting a target 532 (also referred to as a "target structure") on a substrate 534. The substrate 534 is disposed on an adjustable stage 536 (e.g., a movable support structure). It should be appreciated that the structures depicted within illumination system 502 and optical system 504 are not limited to the locations they depict. The location of the structure may be changed as desired, for example, as designed for a modular assembly.

In some embodiments, the target 532 may include a diffractive structure (e.g., grating(s) as shown in fig. 6). The target 532 may reflect, refract, diffract, scatter, etc., the radiation. For ease of discussion, and not limitation, radiation that interacts with the target is referred to throughout as scattered radiation. Scattered radiation is collected by the optical element 530.

In some embodiments, system 500 includes a filter 540 that is used to obtain additional information about the asymmetry. The filter 540 may be an attenuating filter (e.g., a neutral density filter). The filter 540 may be an amplitude and/or phase apodization filter. The filter 540 may be placed on either the negative or positive diffraction orders. Filter 540 produces a bias between the positive and negative diffraction orders. The filter 540 may be positioned in a pupil plane of the detection system 506. In other embodiments, the filter 540 may be positioned near the pupil or in the illumination path.

In some embodiments, the filter 540 may be replaceable. For example, filters having different intensity transmission coefficients may be used, and the filter that provides the best performance (i.e., poor intensity accuracy) may be selected.

In some embodiments, the filter 540 may be rotatable. For example, the orientation of the filter may be based on the target structure. For symmetric fine wafer alignment (SF) or bi-directional fine wafer alignment (BF) marks, the orientation may be 45 degrees or 0 degrees, respectively. Other angles may also be useful. For example, an angle of 22 degrees may be used for the hybrid mark. Furthermore, depending on the current handle wafer, the filter 540 may be removed when needed.

The inset 552 shows the positioning of the filter relative to the optical signal. The inset 552 shows a partial filter for the negative SF mark sequence.

The detection system 506 may include a self-referencing interferometer 538 and one or more detectors. The scattered radiation then passes through filter 540 and reaches self-referencing interferometer 538.

Another beam splitter 542 splits the optical signal into two paths a and B. One path contains the sum of the two rotating fields and the other contains the difference. Similarly, the beam splitter 544 splits the optical signal into two paths C and D, each representing the sum and difference of the rotating fields. The radiation of each path A, B, C and D is collected by a respective lens assembly 546A, 546B, 546C and 546D. It then passes through apertures 548A, 548B, 548C or 548D which eliminate most of the radiation from outside the spot on the substrate. Lens assemblies 546A, 546B, 546C and 546D focus the radiation field into each detector 550A, 550B, 550C and 550D, respectively. Each detector provides a time-varying signal (waveform) that is synchronized with the physical scanning movement between the system 500 and the target 532. The signal from the detector is processed by a processor 508.

Fig. 6 is a schematic diagram illustrating an asymmetric marker 600 according to one example. In some embodiments, the processing step may result in asymmetric marks (e.g., deformed alignment marks such as top tilt, bottom tilt, sidewall angle). Asymmetric marks can create an asymmetric imbalance between positive and negative diffraction orders that is a function of wavelength and polarization.

In some embodiments, apodization can be applied on the illumination side of the metrology system.

FIG. 7 illustrates a metrology system 700 according to some embodiments. In some embodiments, the metrology system 700 may also represent a more detailed view of the inspection apparatus 400 (fig. 4A and 4B). For example, fig. 7 illustrates a more detailed view of the illumination system 412 and its functions. Elements of fig. 7 having similar reference numbers (e.g., reference numbers sharing the right-most two digits) to elements of fig. 4A and 4B may have similar structure and function unless otherwise indicated.

In some embodiments, the metrology system 700 includes an illumination system 712, an optical system 710, a detector 728, and a processor 732. The illumination system 712 may include a radiation source 702, an optical fiber 704 (e.g., a multimode optical fiber), an optical element(s) 706 (e.g., a lens or lens system), a reflective element 734, and a diffractive element 708 (e.g., a grating, a tunable grating, etc.). The optical system 710 may include one or more of an optical element 706, a blocking element 736, a reflective element 738 (e.g., a point mirror), and an optical element 740 (e.g., an objective lens). FIG. 7 shows a non-limiting depiction of a metrology system 700 inspecting a target 718 (also referred to as a "target structure") on a substrate 720. The substrate 720 is disposed on an adjustable stage 722 (e.g., a movable support structure). It should be appreciated that the structures depicted within illumination system 712 and optical system 710 are not limited to the locations where they are depicted. For example, the diffraction element 708 may be within the optical system 710. The location of the structure may be changed as desired, for example, as designed for a modular assembly.

In some embodiments, the radiation source 702 may generate radiation 716. The radiation 716 may be spatially incoherent. Because the output of the radiation source 702 cannot be directed directly toward downstream optical structures, the optical fiber 704 can direct radiation 716 to downstream optical structures. The optical element(s) 706 can direct or condition the radiation 716 (e.g., focus, collimate, parallel, etc.). The diffraction element 708 may diffract the radiation 716 to generate radiation beams 713 and 713' (also first and second radiation beams). The radiation beam 713 may include a first non-zero diffraction order (e.g., the +1 order) from the diffraction element 708. The radiation beam 713' may include a second non-zero diffraction order (e.g., -1 order) from the diffraction element 708 that is different from the first non-zero diffraction order. The diffraction element 708 may also generate a zero order beam (not labeled). The blocking element 736 may block the zero order beam to allow for dark field measurements. Reflective element 738 can direct radiation beams 713 and 713' toward target 718. The optical element 740 focuses the radiation beams 713 and 713' onto the target 718 such that the irradiation points of the two beams overlap. The irradiation points may under-fill or overfill the target 718.

In some embodiments, the target 718 may include a diffractive structure (e.g., grating(s) as shown in fig. 6). The target 718 may reflect, refract, diffract, scatter, etc., radiation. For ease of discussion, and not limitation, radiation that interacts with the target is referred to throughout as scattered radiation. The target 718 may scatter incident radiation, represented by scattered radiation beams 719 and 719' (also first and second scattered radiation beams). The scattered radiation beam 719 may represent radiation from a radiation beam 713 that has been scattered by the target 718. Similarly, scattered radiation beam 719 'may represent radiation from radiation beam 713' that has been scattered by target 718. Optical element 742 focuses scattered radiation beams 719 and 719 'such that scattered radiation beams 719 and 719' interfere at detector 728. The optical element 740 directs the radiation beams 713 and 713' such that they are incident on the target 718 at a non-zero angle of incidence (e.g., off-axis). The terms "off-axis" and "wide angle" as used herein refer to directions of propagation that are oblique to a surface, particularly to a plane of a target. The image at the detector 728 may be an interference pattern. Detector 728 may generate a detection signal based on the received scattered radiation beams 719 and 719'. The detector 728 may be an imaging detector (e.g., CCD, CMOS, etc.). In such a scenario, the detection signal may include a digital or analog representation of an image containing the interference pattern, which is sent to the processor 732. In some aspects, the image may correspond to a region of interest.

In some embodiments, the metrology system 700 may include an optical filter 744. The filter 744 may be similar to the filter 540 of fig. 5. In some aspects, the filter 744 may be positioned between the blocking element 736 and the reflective element 738. The inset 746 shows a partial filter with an apodization factor alpha. An inset 748 shows the detection pupil.

In some embodiments, the processor 732 may analyze the detection signal to determine a property of the target 718. It should be appreciated that the measurement process may vary depending on the particular properties of the target 718 being determined. For example, where the determined attribute of the target 718 is an alignment position, measurements are performed only on the target 718. In another example, where the determined attribute of the target 718 is an overlay error, the measurement compares the target 718 to a second target. Overlay error determination is the process of comparing a first target (on a first layer of manufacture) to a second target (on a second layer of manufacture different from the first layer) and determining whether the first and second layers are properly overlaid on top of each other. The first and second targets may for example be stacked on top of each other or manufactured side by side. It is contemplated that other properties of the target 718 (e.g., line width, pitch, critical dimension, etc.) may be determined from the target 718 alone or in combination with another target. Furthermore, while radiation beams 713 and 713' are described above as both being incident on target 718 (i.e., alignment measurement), embodiments are contemplated in which the radiation beams are directed to another target to allow, for example, overlay error measurement. For example, the radiation beam 713 and/or 713' may be replicated (e.g., using a beam splitter) for transmission to another target. For example, the targets 718 may include four targets (e.g., gratings) that are closely positioned together such that they are all within a measurement point formed by the optical system 710. The target may be illuminated and imaged on detector 728 simultaneously. The four targets may be composite gratings formed by overlapping gratings patterned in different layers on a device formed on the substrate 720. In some aspects, the targets may have different orientations relative to each other in order to diffract incident radiation in the X and Y directions.

In some embodiments, the analysis performed by the processor 732 may be based on the target 718 having been irradiated by radiation beams 713 and 713' (e.g., alignment measurements) having different diffraction orders (e.g., +1 and-1). Analysis includes, for example, calculating the intensity differences between the different diffraction orders (e.g., +1 and-1), as previously described herein. In some aspects, a mixing stage may be used. For example, a first image may be obtained using diffraction orders (+1 and-2) and a second image may be obtained using diffraction orders (-1 and +2). In another example, the first image may use diffraction orders (+1 and +2) and the second image may use diffraction orders (-1 and-2).

In some embodiments, the intensity imbalance may be measured at the pixel level based on the image captured at the detector 728. In some aspects, the metrology system 700 can provide intra-mark fringe visibility. The intensity imbalance is determined based on the visibility of the fringes within the mark. Thus, the asymmetry of each pixel (e.g., asymmetric mark 600) is detected from the stripe visibility. In some aspects, the intra-marker variation may be corrected based on the determined intensity imbalance. Amplitude and DC components are locally extracted and fringe visibility is calculated from AC and DC, as described further below.

In some embodiments, the apodization can be generated using a transmissive plate, a Spatial Light Modulator (SLM), or a strongly asymmetric off-axis beam grating. For example, the diffraction element 708 may comprise an asymmetric off-axis beam grating. In some aspects, the asymmetric off-axis beam grating may generate the radiation beams 713 and/or 713 'such that one of the radiation beams 713 or 713' is apodized relative to the other beam. In this case, the filter 744 may be omitted.

In some embodiments, the filter 744 may have different apodization factors in the x and y directions. In some aspects, the filter may have spatially patterned apodization.

In some embodiments, the intensity difference between the positive and negative order diffraction signals is determined. Information from the intensity differences may be used to compensate for alignment mark asymmetry. In some embodiments, information from the intensity differences may be used to compensate for overlay mark asymmetry. For example, the overlay mark may include one or more structures on multiple layers. In some aspects, the images captured by detector 728 may show structures positioned proximate to each other.

In some embodiments, a correlation between fringe visibility and intensity imbalance may be determined.

The intensity imbalance Q can be expressed as:

i+ can be expressed as a function of intensity imbalance as follows:

fringe visibility f can be expressed as

If the positive stage is apodized, thenAnd I ₂ ＝I _- And fringe visibility f (for small Q) can be expressed as:

in some embodiments, fringe visibility of an ideal grating in the presence of a filter is calculated. The intensity imbalance after calibration can be expressed as:

in some embodiments, an apodization factor alpha is selected for the filter that can result in a maximum sensitivity of fringe visibility. For example, the sensitivity of fringe visibility to normalized intensity variation Q as a function of the apodization factor is determined. In some aspects, for an apodization factor equal to 0.17,

in some embodiments, the metrology systems (e.g., metrology system 500 and metrology system 700) may be calibrated. For example, the hardware is calibrated for each system state (e.g., grating period, wavelength, polarization, scan direction, mark type). In some aspects, calibration of the target is performed to determine f _ref To account for coherence loss due to speckle clipping and polarization mismatch. In some embodiments, calibration may be required due to DC signal bias. For example, the DC signal may also be biased by unwanted stray light from the blocked zero order (e.g., by blocking element 736).

In some embodiments, the DC and AC components may be predicted (e.g., isolated from the detection signal) prior to final calibration. An intensity ratio is determined for each mark.

In some embodiments, two similar high markers with significantly different degrees of asymmetry are used in the calibration. Signals of 0 and 180 degrees of wafer rotation are measured.

In some embodiments, amplitude modulation may be used at an appropriate frequency (i.e., greater than the sweep signal frequency) to minimize DC drift.

In some embodiments, the processor 508 may analyze the detection signal to determine the properties of the target 532. For example, the processor 508 may determine the intensity difference based on equation (7). In some aspects, the processor 508 may determine the intensity imbalance based on equation (12).

In some embodiments, radiation source 510 may include one or more sources to provide radiation having different radiation wavelengths.

In some embodiments, one or more demultiplexers may separate each path into multiple signals corresponding to different radiation wavelengths.

While the examples described herein focus on the +/-1 st order diffraction signal, it should be understood that the present disclosure extends to capture and analysis of higher orders (e.g., +/-2 nd order/+/-3 rd order, etc.).

In some embodiments, intentional asymmetry in the mark 600 (e.g., an alignment mark or an overlay mark) is introduced. For example, enhanced optical response is produced by controlling sub-segments in the marker 600. In some aspects, the marks may introduce intensity asymmetry between diffraction orders. Thus, intensity asymmetry can be interpreted as an intentional transmission deviation between diffraction orders (e.g., scattered radiation beams 719 and 719'). In some aspects, the apodization factor can be based upon the asymmetry of the marker. For example, the apodization factor can depend on the type of sub-segment, stack, and/or illumination profile (e.g., polarization, wavelength). Thus, the transfer function between the interferogram and the intensity imbalance may depend on the illumination profile and the stack profile.

In some embodiments, the intensity imbalance may be determined from fringe visibility of the interference pattern. In some aspects, the intensity imbalance for a nominal symmetric marker (i.e., no process asymmetry) may be due to sub-segments rather than zero. The sub-segments may unbalance the intensity by about 0.3.

Fig. 8 illustrates a tag 800 according to one example. The indicia 800 may have a periodic pattern including lines 802, spaces 804, and a pitch P, as shown in fig. 8.

In some aspects, each of the lines 802 has a plurality of subsections 806-816. The markers may include a different number of subsections. For example, fig. 8 shows six subsections, however, as will be appreciated by those of ordinary skill in the art, line 802 may include fewer or more than 6 subsections. The term "pitch" as used herein refers to the distance from a given point on one of the lines to the same point on an adjacent line, as shown (e.g., from subsection 806 to subsection 818).

In some aspects, each sub-segment has a different width. For example, the width of each of the subsections 806-816 has a different width from each other. The width of the subsections 806 may be less than the width of the subsections 816. In one example, the width of the subsections increases in a first direction "X". The above-mentioned spaces in the pattern of marks may be empty. Marks may be formed on the stack (device) and/or on the resist.

In some embodiments, the markers 800 described herein have an enhanced optical response that results in an intensity imbalance due to the artificial asymmetry introduced by controlling the sub-segments and/or creating deformed markers. The artificial asymmetry can be made much stronger than the unwanted mark asymmetry, providing the desired intensity imbalance between diffraction orders.

In one example, the mark 800 is etched at an angle to produce a deformed mark. Other types of sub-segmented labels may also be used. In some aspects, the marks may have a periodic rectangular pattern with different duty cycles. In some aspects, the marks may have subsections of different widths. In some embodiments, a combination of two or more different types of labels may be used. In some aspects, two or more markers may be selected, such as a first marker having a strong response at a first wavelength and a second marker having a strong response at a second wavelength, in order to optimize sensitivity of fringe visibility at the first wavelength and the second wavelength.

In some embodiments, the methods described herein may be implemented in an integrated optical system (e.g., alignment sensor, overlay sensor). For example, the optical filter may be disposed on a photonic integrated circuit that includes an illumination system and a detection system.

Fig. 9 illustrates method steps for performing the functions described herein, according to some embodiments. The method steps of fig. 9 may be performed in any conceivable order, and not all steps are required to be performed. Furthermore, the method steps of fig. 9 described below reflect only one example of a step and are not limiting. That is, additional method steps and functions may be envisaged based on the embodiments described with reference to fig. 1-8.

At step 902, a radiation beam is diffracted to generate a first beam and a second beam. The first beam includes a first non-zero diffraction order and the second beam includes a second non-zero diffraction order different from the first non-zero diffraction order.

At step 904, one of the first beam or the second beam is apodized.

At step 906, the target structure is irradiated with the first beam and the second beam.

At step 908, a first and second scattered beam of radiation is received at an imaging detector from a target structure.

At step 910, the imaging detector may generate a detection signal based on the first scattered beam and the second scattered beam.

At step 912, the detection signal is analyzed to determine a property of the target structure based on the intensity imbalance between the first scattered beam and the second scattered beam.

Fig. 10 illustrates method steps for performing the functions described herein, according to some embodiments. The method steps of fig. 10 may be performed in any conceivable order, and not all steps are required to be performed. Furthermore, the method steps of fig. 10 described below reflect only one example of a step and are not limiting. That is, additional method steps and functions may be envisaged based on the embodiments described with reference to fig. 1-8.

At step 1002, a target structure is irradiated with a radiation beam.

At step 1004, a first and second scattered beam of radiation is received at an imaging detector from a target structure.

At step 1006, a detection signal is generated using an imaging detector based on the first and second scattered beams.

At step 1008, the detection signal is analyzed to determine at least one characteristic of the target structure. The target structure has an enhanced optical response that creates an intensity imbalance between the first scattered beam and the second scattered beam.

These embodiments may be further described using the following clauses:

1. a system, comprising:

a radiation source configured to generate radiation;

a diffraction element configured to diffract the radiation to generate a first beam and a second beam, wherein the first beam comprises a first non-zero diffraction order and the second beam comprises a second non-zero diffraction order different from the first non-zero diffraction order;

an optical system configured to:

directing the first beam and the second beam towards a target structure,

first and second scattered beams of radiation received from the target structure, and

directing the first and second scattered beams toward a detector;

The detector is configured to generate a detection signal;

a processor configured to analyze the detection signal to determine a property of the target structure based at least on the detection signal; and

an optical element configured to attenuate the first beam relative to the second beam or attenuate the first scattered beam relative to the second scattered beam.

2. The system of clause 1, wherein the optical element is positioned between the radiation source and the optical system and is configured to attenuate the first beam relative to the second beam.

3. The system of clause 1, wherein the optical element is positioned in the optical path of the first scattered beam between the target structure and the detector and is configured to attenuate the first scattered beam relative to the second scattered beam.

4. The system of clause 1, wherein the analyzing comprises determining an intensity imbalance between the first scattered beam and the second scattered beam.

5. The system of clause 4, wherein the intensity imbalance is based on an AC component and a DC component of the detection signal.

6. The system of clause 5, wherein the analyzing comprises determining streak visibility based on the AC component and the DC component of the detection signal.

7. The system of clause 1, wherein the attribute of the target structure comprises metrology mark symmetry.

8. The system of clause 1, wherein the first beam is associated with a positive diffraction order and the second beam is associated with a negative diffraction order.

9. A method, comprising:

diffracting a beam of radiation to generate a first beam and a second beam, wherein the first beam comprises a first non-zero diffraction order and the second beam comprises a second non-zero diffraction order different from the first non-zero diffraction order;

apodization one of the first beam or the second beam;

irradiating a target structure with the first beam and the second beam;

a first and a second scattered beam of radiation received from the target structure;

generating, by an imaging detector, a detection signal based on the first scattered beam and the second scattered beam; and

the detection signal is analyzed to determine a property of the target structure based on an intensity imbalance between the first scattered beam and the second scattered beam.

10. The method of clause 9, wherein the analyzing comprises determining the intensity imbalance based on the visibility of fringes within the mark.

11. The method of clause 10, further comprising determining the in-mark fringe visibility based on determining the AC component and the DC component of the detection signal at the pixel level of the imaging detector.

12. The method of clause 9, wherein the apodizing comprises:

one of the first beam or the second beam is passed through a filter.

13. The method of clause 12, wherein the passing comprises passing one of the first or second scattered beams through an amplitude and/or phase apodization filter.

14. The method of clause 9, further comprising filtering the detection signal to isolate an AC component and a DC component.

15. The method of clause 9, further comprising:

the radiation beam is generated from an incoherent radiation source.

16. A method, comprising:

irradiating the target structure with a radiation beam;

a first and a second scattered beam of radiation received from the target structure;

generating a detection signal using an imaging detector based on the first and second scattered beams; and

analyzing the detection signal to determine at least one characteristic of the target structure, wherein the target structure has an enhanced optical response that creates an intensity imbalance between the first scattered beam and the second scattered beam.

17. The method of clause 16, wherein the enhanced optical response is achieved by providing sub-segment metrology marks, the target structure comprising the sub-segment metrology marks.

18. The method of clause 16, wherein the analyzing further comprises determining an intensity imbalance based on the AC component and the DC component of the detection signal.

19. The method of clause 18, further comprising:

a model between the intensity imbalance and AC and DC components of the detection signal is identified based at least on an illumination profile of the radiation beam.

20. A system, comprising:

a radiation source configured to generate radiation;

a diffraction element configured to diffract the radiation to generate a first beam and a second beam, wherein the first beam comprises a first non-zero diffraction order and the second beam comprises a second non-zero diffraction order different from the first non-zero diffraction order;

an optical system configured to:

directing the first beam and the second beam towards a target structure,

first and second scattered beams of radiation received from the target structure, and

directing the first and second scattered beams toward a detector;

The detector is configured to generate a detection signal; and

a processor configured to analyze the detection signal to determine a property of the target structure based at least on the detection signal, wherein the target structure has an enhanced optical response that creates an intensity imbalance between the first and second scattered beams.

In some embodiments, the metrology systems (alignment sensors and/or overlay sensors) described herein can be implemented in larger systems, e.g., within a lithographic apparatus.

Although specific reference may be made in this text to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, magnetic domain memory guidance and detection patterns, flat-panel displays, LCDs, thin-film magnetic heads, etc. Those skilled in the art will appreciate that any use of the terms "wafer" or "die" herein may be considered synonymous with the more general terms "substrate" or "target portion", respectively, in the context of such alternative applications. The substrate referred to herein may be processed, before or after exposure, in for example a tracking unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology unit and/or an inspection unit. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Furthermore, the substrate may be processed more than once, for example, in order to create a multi-layer IC, such that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

Although specific reference may have been made above to the use of embodiments of the disclosure in the context of optical lithography, it will be appreciated that the disclosure may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist has cured.

It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present disclosure is to be interpreted by the skilled artisan in light of the teachings herein.

The term "substrate" as used herein describes a material to which a layer of material is added. In some embodiments, the substrate itself may be patterned, and the material added on top of it may also be patterned, or may remain unpatterned.

Although specific reference may be made in this text to the use of devices and/or systems according to the present disclosure in the manufacture of ICs, it should be clearly understood that such devices and/or systems have many other possible applications. For example, it may be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, LCD panels, thin film magnetic heads, etc. Those skilled in the art will appreciate that any use of the terms "reticle," "wafer," or "die" herein, in the context of such alternative applications, should be considered to be replaced by the more general terms "mask," "substrate," or "target portion," respectively.

While specific embodiments of the disclosure have been described above, it should be appreciated that the disclosure may be practiced otherwise than as described. The description is not intended to limit the present disclosure.

It should be appreciated that the detailed description section (and not the summary and abstract sections) is intended to be used to interpret the claims. The summary and abstract sections may set forth one or more, but not all exemplary embodiments of the disclosure as contemplated by the inventor(s), and are therefore not intended to limit the disclosure and appended claims in any way.

The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specific functions and relationships thereof. For ease of description, the boundaries of these functional building blocks are arbitrarily defined herein. Alternate boundaries may be defined so long as the specified functions and relationships thereof are appropriately performed.

The foregoing description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments without undue experimentation without departing from the general concept of the present disclosure. Accordingly, such alterations and modifications are intended to be within the meaning and scope of equivalents of the disclosed embodiments based on the teachings and guidance presented herein.

The breadth and scope of the claimed subject matter should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims (20)

1. A system, comprising:

a radiation source configured to generate radiation;

a diffraction element configured to diffract the radiation to generate a first beam and a second beam, wherein the first beam comprises a first non-zero diffraction order and the second beam comprises a second non-zero diffraction order different from the first non-zero diffraction order;

an optical system configured to:

directing the first beam and the second beam towards a target structure,

first and second scattered beams of radiation received from the target structure, and

directing the first and second scattered beams toward a detector;

the detector is configured to generate a detection signal;

a processor configured to analyze the detection signal to determine a property of the target structure based at least on the detection signal; and

an optical element configured to attenuate the first beam relative to the second beam or attenuate the first scattered beam relative to the second scattered beam.

2. The system of claim 1, wherein the optical element is positioned between the radiation source and the optical system and is configured to attenuate the first beam relative to the second beam.

3. The system of claim 1, wherein the optical element is positioned in an optical path of the first scattered beam between the target structure and the detector and is configured to attenuate the first scattered beam relative to the second scattered beam.

4. The system of claim 1, wherein the analyzing comprises determining an intensity imbalance between the first scattered beam and the second scattered beam.

5. The system of claim 4, wherein the intensity imbalance is based on an AC component and a DC component of the detection signal.

6. The system of claim 5, wherein the analyzing comprises determining streak visibility based on the AC component and the DC component of the detection signal.

7. The system of claim 1, wherein the attribute of the target structure comprises metrology mark symmetry.

8. The system of claim 1, wherein the first beam is associated with a positive diffraction order and the second beam is associated with a negative diffraction order.

9. A method, comprising:

diffracting a beam of radiation to generate a first beam and a second beam, wherein the first beam comprises a first non-zero diffraction order and the second beam comprises a second non-zero diffraction order different from the first non-zero diffraction order;

apodization one of the first beam or the second beam;

irradiating a target structure with the first beam and the second beam;

a first and a second scattered beam of radiation received from the target structure;

generating, by an imaging detector, a detection signal based on the first scattered beam and the second scattered beam; and

the detection signal is analyzed to determine a property of the target structure based on an intensity imbalance between the first scattered beam and the second scattered beam.

10. The method of claim 9, wherein the analyzing comprises determining the intensity imbalance based on a visibility of fringes within the mark.

11. The method of claim 10, further comprising determining the intra-mark fringe visibility based on determining AC and DC components of the detection signal at a pixel level of the imaging detector.

12. The method of claim 9, wherein the apodization comprises:

One of the first beam or the second beam is passed through a filter.

13. The method of claim 12, wherein the passing comprises passing one of the first or second scattered beams through an amplitude and/or phase apodization filter.

14. The method of claim 9, further comprising filtering the detection signal to isolate an AC component from a DC component.

15. The method of claim 9, further comprising:

the radiation beam is generated from an incoherent radiation source.

16. A method, comprising:

irradiating the target structure with a radiation beam;

a first and a second scattered beam of radiation received from the target structure;

generating a detection signal using an imaging detector based on the first and second scattered beams; and

analyzing the detection signal to determine at least one characteristic of the target structure, wherein the target structure has an enhanced optical response that creates an intensity imbalance between the first scattered beam and the second scattered beam.

17. The method of claim 16, wherein the enhanced optical response is achieved by providing sub-segment metrology marks, the target structure comprising the sub-segment metrology marks.

18. The method of claim 16, wherein the analyzing further comprises determining an intensity imbalance based on the AC component and the DC component of the detection signal.

19. The method of claim 18, further comprising:

a model between the intensity imbalance and AC and DC components of the detection signal is identified based at least on an illumination profile of the radiation beam.

20. A system, comprising:

a radiation source configured to generate radiation;

a diffraction element configured to diffract the radiation to generate a first beam and a second beam, wherein the first beam comprises a first non-zero diffraction order and the second beam comprises a second non-zero diffraction order different from the first non-zero diffraction order;

an optical system configured to:

directing the first beam and the second beam towards a target structure,

first and second scattered beams of radiation received from the target structure, and

directing the first and second scattered beams toward a detector;

the detector is configured to generate a detection signal; and

a processor configured to analyze the detection signal to determine a property of the target structure based at least on the detection signal, wherein the target structure has an enhanced optical response that creates an intensity imbalance between the first and second scattered beams.