NL2012966A - Stage apparatus, lithographic apparatus and device manufacturing method. - Google Patents

Description

STAGE APPARATUS, LITHOGRAPHIC APPARATUS AND DEVICE MANUFACTURING METHOD

BACKGROUND

Field of the Invention

The present invention relates to a stage apparatus for positioning an object, a lithographic apparatus comprising such a stage apparatus, and a device manufacturing method.

Description of the Related Art A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is 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. This pattern can be transferred onto a target portion (e.g. including part 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 network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

Hence, it will be apparent that in the lithographic apparatus there are one or more objects that need to be accurately positioned, e.g. the patterning device may need to be accurately positioned relative to a substrate. This may be achieved using one or more stage apparatus comprising an object table to receive an object, actuators to apply positioning forces between the object table and a base supporting the object table. A recent development is that the actuators of the stage apparatus are variable reluctance devices which have an improved force density while at the same time the (moving) mass and the dissipation level are reduced compared to for instance Lorentz devices.

Variable reluctance devices may also have a bearing function. When designing a magnetic bearing, available options are a traditional moving coil design in which the coil is arranged on the object table of the stage apparatus or a traditional stationary coil design in which the coil is arranged on the base of the stage apparatus.

A disadvantage of the traditional moving coil design is that the coil dissipates heat and that this heat is generated close to the object on the object table of the stage apparatus. Hence, not only power cables, but also coolant hoses need to be supplied to the moving part of the stage apparatus, thereby introducing disturbance forces.

A disadvantage of the traditional stationary coil design is that the mass on the object table of the stage apparatus is increased with respect to the traditional moving coil design, and that the location where the variable reluctance devices apply the corresponding forces depends on the position of the object table relative to the base.

SUMMARY

It is desirable to provide an improved stage apparatus with reduced heat generation on the object table and reduced mass on the object table.

According to an embodiment of the invention, there is provided a stage apparatus for positioning an object in at least a first direction and a second direction, said first and second direction being orthogonal to each other, the stage apparatus comprising: an object table configured to receive the object; a base configured to support the object table; and a variable reluctance device configured to apply a force between the object table and the base in the second direction, the variable reluctance device comprising: a combination of a first magnetic member and a coil arranged on the base; a second magnetic member arranged on the object table; and a control unit, wherein the first magnetic member and the second magnetic member provide a magnetic circuit having a variable reluctance in dependency of their relative position in the second direction, wherein the coil is configured to receive a current and arranged to generate a magnetic flux through the magnetic circuit, wherein the control unit is configured to control an amplitude of the current through the coil in order to control the force applied between the object table and the base, and wherein a dimension of the second magnetic member in the first direction is significantly smaller than a dimension of the first magnetic member in the first direction.

According to another embodiment of the invention, there is provided a lithographic apparatus arranged to transfer a pattern from a patterning device onto a substrate, comprising a stage apparatus according to the invention to position an object within the lithographic apparatus.

According to a further embodiment of the invention, there is provided a device manufacturing method comprising transferring a pattern from a patterning device onto a substrate, wherein the patterning device or the substrate is positioned using a stage apparatus according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figure 1 depicts a lithographic apparatus according to an embodiment of the invention; Figure 2A and 2B respectively depict a schematic side view and a schematic perspective view of a stage apparatus according to an embodiment of the invention, which can be used in the lithographic apparatus of Fig. 1;

Figure 3 depicts two possible combinations of coil and first magnetic member that may be used in the stage apparatus according to the invention;

Figure 4 schematically depicts a possible control scheme of the stage apparatus according to the invention;

Figure 5 schematically depicts in cross sectional view a stage apparatus according to another embodiment of the invention;

Figure 6 schematically depicts in cross sectional view a stage apparatus according to yet another embodiment of the invention;

Figure 7 schematically depicts in cross sectional view a stage apparatus according to a further embodiment of the invention;

Figure 8 schematically depicts a top view of a part of a stage apparatus according to another embodiment of the invention;

Figure 9 schematically depicts a stage apparatus according to yet another embodiment of the invention.

DETAILED DESCRIPTION

Figure 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or any other suitable radiation), a mask support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioning device PM configured to accurately position the patterning device in accordance with certain parameters. The apparatus also includes a substrate table (e.g. a wafer table) WT or "substrate support" constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioning device PW configured to accurately position the substrate in accordance with certain parameters. The apparatus further includes a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W.

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

The mask support structure supports, i.e. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment.. The mask support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The mask support structure may be a frame or a table, for example, which may be fixed or movable as required. The mask support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An 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 which is reflected by the mirror matrix.

The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) or more substrate tables or "substrate supports" (and/or two or more mask tables or "mask supports"). In such “multiple stage” machines the additional tables or supports may be used in parallel, or preparatory steps may be carried out on one or more tables or supports while one or more other tables or supports are being used for exposure.

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. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques can be used to increase 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 a liquid is located between the projection system and the substrate during exposure.

Referring to figure 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source 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 include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.

The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the mask support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed 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. With the aid of the second positioning device 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 positioning device PM and another position sensor (which is not explicitly depicted in Figure 1) 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 positioning device PM. Similarly, movement of the substrate table WT or "substrate support" 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 Ml, M2 and substrate alignment marks PI, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the following modes: f. In step mode, the mask table MT or "mask support" and the substrate table WT or "substrate support" are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT or "substrate support" is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT or "mask support" and the substrate table WT or "substrate support" are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT or "substrate support" relative to the mask table MT or "mask support" may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.

3. In another mode, the mask table MT or "mask support" is kept essentially stationary holding a programmable patterning device, and the substrate table WT or "substrate support" is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or "substrate support" 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 of a type as referred to above.

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

The lithographic apparatus of Fig. 1 comprises a stage apparatus according to the present invention for positioning an object such as a patterning device or a substrate. Note however that other applications of a stage apparatus according to the present invention are feasible as well. As an example, the stage apparatus according to the present invention can e.g. be applied for positioning reticle masking blades, optical components of the projection system, etc.

Below, more details are provided on the stage apparatus according to the present invention.

Fig. 2A schematically depicts a side view of a stage apparatus SA for positioning an object (not shown). Fig. 2B depicts a schematic perspective view of the stage apparatus SA in which some components of the stage apparatus are not shown for clarification. The stage apparatus SA of Fig. 2A and Fig. 2B is configured to position the object in at least a first direction corresponding in this embodiment to the y-direction (see Fig. 2B) and a second direction corresponding in this embodiment to the x-direction, wherein the x- and y-direction are orthogonal to each other. The object may also be positionable in a third direction orthogonal to the x- and y-direction, i.e. the z-direction, but this is not shown in this embodiment.

The stage apparatus SA comprises an object table OT configured to receive the object. In this embodiment, the object table OT is configured to receive the object on a top surface TS of the object table OT, but it will be clear to the skilled person that the object table can be embodied in many different forms depending on the object to be supported by the object table.

The object table OT is moveably supported by a base BA, which means that the object table OT is at least moveable in the first and second direction, i.e. respectively the y- and x-direction, relative to the base.

The first direction may alternatively be referred to as the traveling direction of the object table, and the second direction may alternatively be referred to as the guiding direction of the object table. Hence, a positioning range of the object table in the first direction may be larger, e.g. much larger, than a positioning range of the object table in the second direction.

The base may be a substantially stationary element, but the invention also applies to a base that in turn is moveable relative to a reference frame, e.g. using multiple stages on top of each other, for instance a long stroke stage and a short stroke stage.

In order to be able to position the object table OT relative to the base, the stage apparatus SA comprises one or more variable reluctance devices VRD. In this embodiment, four variable reluctance devices are used as shown in the partial view of Fig. 2B, but only two can be seen in the view of Fig. 2A.

Each variable reluctance device VRD comprises a first magnetic member FMM arranged on the base BA, a second magnetic member SMM arranged on the object table OT, a coil associated with the first magnetic member FMM, and a control unit. Because the first magnetic member FMM is arranged on the base, it may alternatively be referred to as stator, and because the second magnetic member SMM is arranged on the object table, it may alternatively be referred to as rotor.

The first and second magnetic member FMM, SMM of each variable reluctance device VRD provide a magnetic circuit having a variable reluctance.

An advantage of the coil being associated with the first magnetic member, which is arranged on the base, is that heat generated in the coil is not directly supplied to the object table OT. A further advantage is that no electrical power supply cables need to be connected to the object table OT. Another advantage may be that as less heat is generated on the object table OT, no coolant supply hoses may be required between base BA and object table OT. If a sensor is present on the object table, a sensor cable may still be present between the base BA and the object table OT, but the absence of power cables and hoses reduces the introduction of disturbance forces significantly.

The coil is configured to receive a current and to generate a magnetic flux through the magnetic circuit. Fig. 3 shows two examples of how a coil C and first magnetic member FMM may be configured, i.e. combined, to generate a magnetic flux through the magnetic circuit.

Fig. 3 depicts a cross section A of the first magnetic member FMM, wherein the first magnetic member comprises a base element MB and legs LEI, LE2 extending therefrom. The coil C in cross section A is wound around the base element MB.

Fig. 3 further depicts a cross section B of the first magnetic member FMM, wherein the first magnetic member comprises a base element MB and legs LEI, LE2 extending therefrom. The coil C in this example comprises a first coil Cl and a second coil C2 being wound about legs LEI, LE2 of the first magnetic member FMM respectively.

The coil C may also be mounted on other positions on the first magnetic member FMM.

The magnetic members FMM, SMM, can e.g. manufactured using ferrous materials having a comparatively high permeability such as ferrites or sintered materials comprising rare earth materials.

A variable reluctance device VRD may further comprise a measurement coil MC as shown in Fig. 3 at B, for generating a measurement signal. The measurement signal can for instance be a voltage induced in the measurement coil MC due to the magnetic flux that is generated in the magnetic circuit. The measurement coil is arranged to substantially enclose the magnetic flux through the magnetic circuit. A measurement signal representative of the magnetic flux through the magnetic circuit enables an accurate prediction of the generated force, substantially without the requirement for additional measurements of e.g. the flux density in a device airgap e.g. using Hall sensors. The measurement coil MC is provided to an input terminal of a control unit CU of the device as depicted in Fig. 4.

Although in cross section B of Fig. 3, the measurement coil MC is arranged on the first magnetic member, it is noted that the measurement coil MC can also be arranged on or near the second magnetic member.

Instead of using a measurement coil other sensors may also be used, such as a gap sensor or other flux sensor, e.g. a Hall sensor.

In case of a measurement coil, the control unit CU preferably comprises an integrator (not shown) for obtaining a signal representative of the magnetic flux through the magnetic circuit from the measurement signal (e.g. the induced voltage).

The control unit CU is adapted to generate, in this case based on the measurement signal of the measurement coil MC, a control signal at an output terminal of the control unit, wherein the control signal can be applied for controlling the amplitude of the current provided to the coil C. As such, the control signal can e.g. be provided to a power supply PU to control the current as provided by the power supply PU to the coil C.

In general, in a reluctance type of device, the force between stator and rotor is dependent on the relative position of the first and second magnetic members FMM, SMM and the magnetic flux through the magnetic circuit. By properly controlling the magnetic flux through the magnetic circuit using the current through the coil C, the force being applied in the second direction (x-direction) between the object table and the base by the variable reluctance device VRD can be controlled, thereby allowing to control the relative position of the object table with respect to the base in the second direction.

As shown in Fig. 2B, the first magnetic member FMM of each variable reluctance device extends in the first direction (y-direction) to cover at least a positioning range in the first direction of the object table. The associated second magnetic member SMM has a dimension in the first direction (y-direction) which is significant smaller than the positioning range of the object table in the first direction (y-direction) and thus significant smaller than the dimension of the first magnetic member in the first direction. It is to he noted that the first magnetic member extending in the first direction to cover at least a positioning range in the first direction of the object table is to be understood as that the second magnetic member always faces the first magnetic member within the positioning range of the object table in the first direction.

It is to be noted that a second magnetic member having a dimension in the first direction which is significant smaller than the dimension of the first magnetic member in the first direction also falls within the scope of the invention. When the dimension of the first magnetic member in the first direction does not cover the entire positioning range of the object table in the first direction, there is preferably another bearing to rely on when the second magnetic member does not face the first magnetic member anymore, i.e. the second magnetic member does not form a closed magnetic circuit with the first magnetic member anymore.

Due to the dimensional relationship between the first and second magnetic members, the position of the force applied to the object table by the variable reluctance device is substantially independent of the position of the object table in the first direction within the positioning range of the object table in the first direction. Hence, the dynamics and control characteristics are also substantially the same throughout the positioning range of the object table in the first direction, thereby making the positioning control of the object table easier. This is different from prior art stationary coil designs, where the stator used to have a small dimension in the first direction compared to the rotor, so that the position of the force applied to the object table was dependent on the position of the object table within its positioning range in the first direction. Hence, positioning control of the object table in prior art systems was much more complex.

Another advantage of the dimensional relationship between the first and second magnetic members is that the rotor part of the variable reluctance device can be much smaller than in prior art designs, so that the weight of the rotor can be reduced.

Fig. 2B only shows the object table OT with four second magnetic members SMM and two first magnetic members FMM associated with two of the four second magnetic members SMM at one side of the object table OT. From Fig. 2B it can thus be clearly derived that the described embodiment of Fig. 2A comprises four variable reluctance devices VRD. These four variable reluctance devices are all configured to apply a force in the second direction (x-direction) and thus may cooperate in positioning the object table OT in the second direction (x-direction). Due to fact that two of the variable reluctance devices are spaced in the first direction (y-direction) with respect to the other two variable reluctance devices, the four reluctance devices may also be used to position the object table in a rotational direction around the third direction (z-direction).

Fig. 2B further clearly shows how the first magnetic members extend in the first direction (y-direction). Fig. 2B also clearly shows the dimension of the second magnetic members SMM in the first direction, which is smaller than the dimension of the first magnetic members FMM in the first direction, preferably smaller than the positioning range of the object table OT in the first direction.

In Fig. 2B, one of the variable reluctance devices VRD will also be denoted as a first variable reluctance device VRD1. The other variable reluctance device VRD at the same side of the object table will also be denoted as a second variable reluctance device VRD2. The first and second variable reluctance devices have first and second magnetic members which will also be denoted by respectively FMM1, FMM2, and SMM1, SMM2.

Each variable reluctance device VRD1, VRD2 is preferably controlled using a separate control unit.

In the embodiment shown in Fig. 2B, the second magnetic member SMM1 preferably forms a magnetic circuit with first magnetic member FMM1 in the entire positioning range of the object table OT in the first direction, and preferably the second magnetic member SMM2 forms a magnetic circuit with first magnetic member FMM2 in the entire positioning range of the object table OT in the first direction. This means that the positioning range of the object table is limited by the distance DI between the second magnetic members SMM1 and SMM2.

In an alternative embodiment, when the positioning range of the object table OT exceeds the distance DI between the second magnetic members SMM1, SMM2, the first magnetic members FMM1 may overlap and be integrated such that a portion thereof is part of both variable reluctance devices. In such case, the overlapping portion forms a separate segment of the first magnetic members having its own coil, so that control can easily switch between using this segment to control the first variable reluctance device VRD1 and using this segment to control the second variable reluctance device VRD2 depending on the position of the object table OT relative to the base BA. Preferably, a positioning sensor is provided to measure the position of the object table OT relative to the base BA in order to determine if said segment has to be used and if it has to be used for which variable reluctance device it should be used.

In the embodiment of Figs. 2A and 2B and the embodiment shown in Fig. 3, the first magnetic member FMM has a C-shape, i.e. a C-shaped cross section, wherein the legs of the C-shape extend towards the second magnetic member. Other cross-sectional shapes are also possible. One example is an E-shaped cross section. An advantage of the E-shaped first magnetic member may be that the thickness of the second magnetic member may be reduced compared to using a C-shaped cross section of the first magnetic member. This further reduces the mass of the mover on the object table OT.

Fig. 3 at B further shows that a permanent magnet member PMM may be arranged on the first magnetic member FMM. This permanent magnet member PMM provides an attractive force when the second magnetic member is provided to form the magnetic circuit with the first magnetic member. The attractive force applied by the permanent magnet member may be used as a bias force, so that the force generated using the coil can be reduced. As a result thereof, the thermal load of the coil can be reduced. The attractive force may be used as gravity compensation.

Fig. 5 depicts a cross section of a configuration of a stage apparatus according to another embodiment of the invention in which an object table OT is positionable in a first direction corresponding to a y-direction (not shown) which is orthogonal to the shown x- and z-direction, in a second direction corresponding to the x-direction, and in a third direction corresponding to the z-direction.

The configuration of Fig. 5 comprises at least six variable reluctance devices respectively denoted VRD1, VRD2, VRD3, VRD4, VRD5 and VRD6, wherein the variable reluctance devices are similar to the ones shown in the embodiment of Figs. 2A and 2B, although not all components are explicitly shown. For instance, the coils associated with the first magnetic members are not shown and the base is not shown. However, it will be apparent to the skilled person that all first magnetic members FMM1, FMM2, FMM3, FMM4, FMM5 and FMM6 are arranged on the base, and that the second magnetic members SMM1, SMM2, SMM3, SMM4, SMM5 and SMM6 are arranged on the object table OT.

Variable reluctance devices VRD1 and VRD2 are used to apply forces in the second direction (x-direction) to position the object table OT in the x-direction. Additional variable reluctance devices may be provided, which additional variable reluctance devices are spaced in the first direction (y-direction) relative to the variable reluctance devices VRD1 and VRD2 as shown in the embodiment of Figs. 2A and 2B. In that case, the additional variable reluctance devices are also capable of applying forces in the x-direction and thus to position the object table OT in the x-direclion. An advantage of the additional variable reluctance devices is that the object table OT can also be positioned in a rotational direction around the third direction (z-direction).

Hence, in total there may be up to twelve variable reluctance devices.

The variable reluctance devices VRD3, VRD4, VRD5 and VRD6 are rotated 90 degrees clockwise or anti-clockwise relative to the variable reluctance devices VRD1, VRD2, so that they are configured to apply a force in the third direction (z-direction) to position the object table OT in the third direction.

In an embodiment, the variable reluctance devices VRD4 and VRD6 may be omitted as gravity provides a natural pull force in the same direction as the variable reluctance devices VRD4, VRD6. However, the presence of the variable reluctance devices VRD4, VRD6 allows to apply higher forces than provided for by gravity and thus allows to increase the stiffness of the control system and thus the obtainable bandwidth, because the variable reluctance devices VRD4, VRD6 can be used to apply a pretension force.

Where for the second direction (x-direction) at least three variable reluctance devices are required to position the object table in a rotational direction about the third direction (z-direction), there are at least two variable reluctance devices required to position the object table in a rotational direction about the first direction (y-direction). In the embodiment, these two variable reluctance devices are variable reluctance devices VRD3, VRD5. However, when present, the variable reluctance device VRD4, VRD6 may also be used to position the object table in a rotational direction about the first direction.

For variable reluctance devices VRD3, VRD5 the described embodiment of Fig. 3 at B with the permanent magnet member may be beneficial for gravity compensation, so that the weight of the object table is at least partially carried by the permanent magnet member thereby reducing the required current in the coils of variable reluctance devices.

Fig. 6 depicts a cross section of a configuration of a stage apparatus according to yet another embodiment of the invention in which an object table OT is positionable in a first direction corresponding to a y-direction (not shown) which is orthogonal to the shown x- and z-direction, in a second direction corresponding to the x-direclion, and in a third direction corresponding to the z-direction.

The configuration of Fig. 6 comprises at least four variable reluctance devices VRD1, VRD2, VRD3 and VRD4. Multiple similarly arranged variable reluctance devices may be provided, which are in that case preferably spaced in the first direction (y-direction).

In the configuration of Fig. 5 the variable reluctance devices are arranged so that the directions of the to be applied forces are parallel to the chosen coordinate system, i.e. parallel to the x- and z-direction. In the configuration of Fig. 6, the to be applied forces by the variable reluctance devices are rotated 45 degrees relative to the chosen x- and z-direction. However, the direction of the to be applied forces of variable reluctance devices VRD1 and VRD3 are orthogonal to the direction of the to be applied forces of variable reluctance devices VRD2 and VRD4. Hence, the configuration is in essence similar to the one described in Fig. 5.

Fig. 7 depicts a cross section of a configuration of a stage apparatus according to a further embodiment of the invention in which an object table OT is positionable in a first direction corresponding to a y-direction (not shown) which is orthogonal to the shown x- and z-direction, in a second direction corresponding to the x-direction, and in a third direction corresponding to the z-direction.

The configuration of Fig. 7 comprises at least six variable reluctance devices VRD1, VRD2, VRD3, VRD4, VRD5 and VRD6, wherein the variable reluctance devices are arranged in pairs and each pair shares a single second magnetic member.

Variable reluctance devices VRD1 and VRD2 are arranged to provide a force in the x-direction. The first magnetic members FMM1 and FMM2 are arranged on the base (not shown) supporting the object table OT and both form a separate magnetic circuit with second magnetic member SMMA which is shared by both variable reluctance devices VRD1 and VRD2. The same applies to variable reluctance devices VRD3 and VRD4 where first magnetic members FMM3 and FMM4 are arranged on the base and together form a separate magnetic circuit with second magnetic member SMMB which is shared by both variable reluctance devices VRD3 and VRD4. The same also applies to variable reluctance devices VRD5 and VRD6 where first magnetic members FMM5 and FMM6 are arranged on the base and together form a separate magnetic circuit with second magnetic member SMMC which is shared by both variable reluctance devices VRD5 and VRD6.

The variable reluctance devices VRD3-VRD6 are arranged to provide a force in the z-direction. An advantage of this configuration is that the applied forces are applied outside the object table OT, i.e. the line of action of the force that can be applied by the variable reluctance device does not cross the object table, and thus have less effect on the deformation of the object table OT.

In Fig. 8 a schematic top view is shown of a part of a stage apparatus according to another embodiment of the invention. Fig. 8 shows an object table OT and two variable reluctance devices VRD1 and VRD2 configured to apply forces between the object table and a base (not shown) in a second direction corresponding to the x-direction. The object table may also be moveable in a first direction corresponding to the y-direction.

The variable reluctance devices VRD1 and VRD2 comprise second magnetic members SMM1 and SMM2 respectively, which second magnetic members are arranged on the object table OT. The second magnetic members SMM1, SMM2 are arranged to fonn a magnetic circuit with a combination of a first magnetic member FMM and a coil (not shown). Due to the stroke of the object table in the first direction, the variable reluctance devices share the first magnetic member FMM. The first magnetic member FMM is divided into first magnetic member segments of which only four are denoted with reference symbols SGI, SG2, SG3 and SG4 respectively. Each segment is provided with a coil which is separately controllable by a control unit.

The embodiment of Fig. 8 also comprises a positioning sensor SE configured to measure the position of the object table in the first direction relative to the base, so that the position of the second magnetic members SMM1 and SMM2 relative to the segments of the first magnetic member FMM can be derived from an output signal of the sensor SE. The coils in the segments can then be controlled by the control unit based on the output signal of the sensor, such that the segments act as a single first magnetic members seen from the second magnetic member point of view. Hence, if second magnetic member SMM1 forms a magnetic circuit with segments SGI and SG2, and e.g. 60% thereof can be contributed to segment SGI and 40% thereof can be contributed to SG2, the coils in the segments SGI and SG2 should be controlled accordingly, so that they act as a single first magnetic member towards the second magnetic member.

The sensor SE may also be arranged differently depending on the sensor used, e.g. the sensor SE may be an interferometer or encoder.

Figure 9 schematically depicts a stage apparatus according to yet another embodiment of the invention. This embodiment shows that an object table OT may be positionable in a first direction and a second direction that are orthogonal to each other, but not necessarily both need to be translational directions. The object table OT of Figure 9 is moveable in a first direction corresponding to the rotational direction R and in a second direction corresponding to a radial direction RD, which may be part of a cylindrical coordinate system.

The stage apparatus comprises four variable reluctance devices VRD1, VRD2, VRD3 and VRD4, all sharing a first magnetic member FMM, and each comprising a second magnetic member SMM1, SMM2, SMM3, SMM4 respectively that form a corresponding magnetic circuit with the first magnetic member. The first magnetic member FMM is divided into segments, of which some are indicated by reference symbol SG, wherein each segment comprises a coil which can be controlled by a control unit, so that the radial forces applied to the object table by the variable reluctance devices VRD1, VRD2, VRD3 and VRD4 can be controlled. The first magnetic member covers the entire positioning range of the object table in the rotational direction R while a dimension of the respective second magnetic members is significant smaller.

Although specific reference may be made in this text to the use of 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, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so 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 invention in the context of optical lithography, it will be appreciated that the invention 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 is cured.

The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein.

The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the clauses set out below. Other aspects of the invention are set out as in the following numbered clauses: 1. A stage apparatus for positioning an object in at least a first direction and a second direction, said first and second direction being orthogonal to each other, the stage apparatus comprising: an object table configured to receive the object; a base configured to support the object table; and a variable reluctance device configured to apply a force between the object table and the base in the second direction, the variable reluctance device comprising: a combination of a first magnetic member and a coil arranged on the base; a second magnetic member arranged on the object table; and a control unit, wherein the first magnetic member and the second magnetic member provide a magnetic circuit having a variable reluctance in dependency of their relative position in the second direction, wherein the coil is configured to receive a current and arranged to generate a magnetic flux through the magnetic circuit, wherein the control unit is configured to control an amplitude of the current through the coil in order to control the force applied between the object table and the base, and wherein a dimension of the second magnetic member in the first direction is significantly smaller than a dimension of the first magnetic member in the first direction.

2. The stage apparatus according to clause 1, wherein the first magnetic member extends in the first direction to cover at least a positioning range of the object table in the first direction.

3. The stage apparatus according to clause 1, wherein a dimension of the first magnetic member in the first direction is at least the positioning range of the object table in the first direction plus the dimension of the second magnetic member in the first direction.

4. The stage apparatus according to clause 1, wherein the first magnetic member has a C-or E-shaped cross section, wherein legs of the C- or E-shape extend towards the second magnetic member.

5. The stage apparatus according to clause 1, wherein the first magnetic member comprises multiple segments, each segment comprising a coil to generate a magnetic flux through the magnetic circuit.

6. The stage apparatus according to clause 5, further comprising a positioning sensor for measuring a position of the object table relative to the base in the first direction, and wherein the control unit is configured to control the amplitude of the current through each coil of each segment based on an output signal of the positioning sensor.

7. The stage apparatus according to clause 1, further comprising an additional variable reluctance device configured to apply a force between the object table and the base in the second direction, the additional variable reluctance device comprising: a combination of a first magnetic member and a coil arranged on the base; a second magnetic member arranged on the object table; and a control unit, wherein the first magnetic member and the second magnetic members of the additional variable reluctance device provide a magnetic circuit having a variable reluctance in dependency of their relative position in the second direction, wherein the coil of the additional variable reluctance device is configured to receive a current and arranged to generate a magnetic flux through the magnetic circuit, wherein the control unit of the additional variable reluctance device is configured to control an amplitude of the current through the coil of the additional variable reluctance device in order to control the force applied between the object table and the base, wherein the first magnetic member of the additional variable reluctance device extends in the first direction to cover at least a positioning range of the object table in the first direction, and wherein a dimension of the second magnetic member of the variable reluctance device in the first direction is smaller than the positioning range of the object table in the first direction.

8. The stage apparatus according to clause 7, wherein the first magnetic member of the variable reluctance device and the first magnetic member of the additional variable reluctance device are integrated to form integrated first magnetic members, such that at least a portion of the integrated first magnetic members form part of both the variable reluctance device and the additional variable reluctance device.

9. The stage apparatus according to clause 7, wherein the variable reluctance device and the additional variable reluctance device share the same second magnetic member.

10. A stage apparatus according to clause 1, further comprising a measurement coil configured to generate a measurement signal representative of the magnetic flux through the magnetic circuit, wherein the measurement coil is arranged to substantially enclose the magnetic flux through the magnetic circuit, and wherein the control unit is arranged to receive the measurement signal at an input terminal and to provide a control signal based on the measurement signal at an output terminal for controlling an amplitude of the current through the coil.

11. The stage apparatus according to clause 1, wherein a line of action of the force that can be applied by the variable reluctance device does not cross the object table.

12. The stage apparatus according to clause 1, wherein the first magnetic member comprises a permanent magnet for applying an attractive force to the second magnetic member.

13. A lithographic apparatus arranged to transfer a pattern from a patterning device onto a substrate, comprising a stage apparatus according to clause 1 to position the object within the lithographic apparatus.

14. The lithographic apparatus according to clause 13, further comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, wherein the object to be positioned by the stage apparatus is the patterning device or the substrate.

15. A device manufacturing method comprising transferring a pattern from a patterning device onto a substrate, wherein the patterning device or the substrate is positioned using a stage apparatus according to clause 1.

Claims (1)

1. Een lithografieinrichting omvattende: een belichtinginrichting ingericht voor het leveren van een stralingsbundel; een drager geconstrueerd voor het dragen van een patroneerinrichting, welke patroneerinrichting in staat is een patroon aan te brengen in een doorsnede van de stralingsbundel ter vorming van een gepatroneerde stralingsbundel; een substraattafel geconstrueerd om een substraat te dragen; en een projectieinrichting ingericht voor het projecteren van de gepatroneerde stralingsbundel op een doelgebied van het substraat, met het kenmerk, dat de substraattafel is ingericht voor het positioneren van het doelgebied van het substraat in een brandpuntsvlak van de proj ectieinrichting.A lithography device comprising: an illumination device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.