NL2009338A - Support, method to load a plate-shape object on the support, lithographic apparatus and method to load a substrate on the substrate table of the lithographic apparatus. - Google Patents

Description

SUPPORT, METHOD TO LOAD A PLATE-SHAPE OBJECT ON THE SUPPORT, LITHOGRAPHIC APPARATUS AND METHOD TO LOAD A SUBSTRATE ON THE SUBSTRATE TABLE OF THE LITHOGRAPHIC

APPARATUS

BACKGROUND

Field of the Invention

[0001] The invention relates to a support to support a plate-shaped object, a method to load a plate-shaped object on the support, a lithographic apparatus, and a method to load a substrate on a substrate table of the lithographic apparatus.

Description of the Related Art

[0002] 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.

[0003] In a known embodiment of a lithographic apparatus, a substrate is loaded on a support surface of a substrate table by a robot which holds the substrate at the bottom side of the substrate. To make loading of the substrate on a substantially horizontal support surface possible, three E-pins are provided in the substrate table. The e-pins are movable between an extended position, wherein the upper ends of the e-pins extend above the substrate table, and a retracted position, wherein the upper ends of the e-pins are retracted in the substrate table.

[0004] During the loading of the substrate on the substrate table, the robot loads the substrate on the three e-pins in the extended position. Since the substrate will be received on the e-pins extending above the support surface, the robot can be withdrawn leaving the substrate on the e-pins.

[0005] Then, the E-pins can be moved to the retracted position to place the substrate on the support surface.

[0006] The shape of the substrate during the loading sequence is defined by the gravity sag of the substrate. Other influences such as the influence of squeeze film damping effects caused by an air flow below the substrate may also have an effect on the shape of the substrate. There is limited freedom to manipulate the final substrate shape while it touches the substrate table.

[0007] Substrates with increasing sizes are to be handled in a lithographic apparatus. Presently substrate sizes up to 300 mm are used in lithographic processes. It is desirable to increase substrate diameters, for example to a diameter of approximately 450 mm. These larger substrates will have a smaller thickness to diameter ratio, resulting in a reduced bending stiffness. As a result, the substrates will have a larger gravitational deflection on the three e-pins in the extended position, which could inherently lead to larger substrate load grid errors and potentially also overlay errors.

SUMMARY

[0008] This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions may be made to avoid obscuring the purpose of the section. Such simplifications or omissions are not intended to limit the scope of the present invention.

[0009] It is desirable to provide a substrate stage having means for reliably placing a substrate on a support surface of the substrate table, in particular for substrates having relatively low bending stiffness.

[0010] According to an embodiment of the invention, there is provided a support to support a plate-shaped object, comprising: a substantially horizontal support surface configured to support the object, a set of first pins, wherein each first pin is movable between a retracted position, wherein an upper end of the first pin is arranged below the support surface and an extended position wherein the upper end of the first pin extends above the support surface, a set of second pins, wherein each second pin is movable between a retracted position, wherein an upper end of the second pin is arranged below the support surface and an extended position wherein the upper end of the second pin extends above the support surface, wherein the upper ends of the first pins in the extended position are substantially further spaced from the support surface than the upper ends of the second pins in the extended position.

[0011] According to an embodiment of the invention, there is provided a method to load a plate-shaped object on the support of clause 1, comprising the steps of: moving the first pins to the extended position, moving the second pins to the extended position, placing the object on the first pins with an external object holding device, placing the object on the second pins by moving the first pins towards the retracted position, and placing the object on the support surface by moving the second pins to the retracted position.

[0012] According to an embodiment of the invention, there is provided a lithographic apparatus 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 substrate table comprises a substantially horizontal support surface configured to support the substrate, and wherein the lithographic apparatus further comprises: a set of first pins, wherein each first pin is movable between a retracted position, wherein an upper end of the first pin is arranged below the support surface and an extended position wherein the upper end of the first pin extends above the support surface, a set of second pins, wherein each second pin is movable between a retracted position, wherein an upper end of the second pin is arranged below the support surface and an extended position wherein the upper end of the second pin extends above the support surface, wherein the upper ends of the first pins in the extended position are substantially further spaced from the support surface than the upper ends of the second pins in the extended position.

[0013] According to an embodiment of the invention, there is provided a method to load a substrate on the substrate table in the lithographic apparatus of clause 13, comprising the steps of: moving the first pins to the extended position, moving the second pins to the extended position, placing the substrate on the first pins, placing the substrate on the second pins by moving the first pins towards the retracted position, and placing the substrate on the support surface by moving the second pins to the retracted position. Further features and advantages of the invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. The invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. The Summary and Abstract sections of this patent document may describe one or more, but not all exemplary embodiments of the invention as contemplated by the inventor(s).

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. In the drawings, like reference numbers may indicate identical or functionally similar elements. The drawing in which an element first appears is generally indicated by the left-most digit in the corresponding reference number. The accompanying drawings, which are incorporated in and constitute part of the specification, illustrate embodiments of the invention and, together with the general description given above and the detailed descriptions of embodiments given below, serve to explain the principles of the present invention.

[0015] 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:

[0016] Figure 1 depicts a lithographic apparatus comprising a substrate stage according to an embodiment of the invention;

[0017] Figure 2 depicts a cross section (II-II) of the substrate stage of the lithographic apparatus of Figure 1;

[0018] Figure 3 depicts a top view of the substrate stage of Figure 2; and

[0019] Figures 4-7 depict steps in placing a substrate on a support surface of a substrate stage according to the invention.

[0020] Features and advantages of the present invention 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.

DETAILED DESCRIPTION

[0021] References in the specification to "one embodiment", "an embodiment", "an example embodiment", etc., indicate that the embodiment 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. Further, 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.

[0022] It should be understood that spatial descriptions (e.g., "above", "below", "left," "right," "up", "down", "top", "bottom", etc.) used herein are for purposes of illustration only, and that practical implementations of the structures described herein can be spatially arranged in any orientation or manner.

[0023] The invention will be better understood from the following descriptions of various embodiments of the invention. Thus, specific embodiments are views of the invention, but each does not itself represent the whole invention. In many cases individual elements from one particular embodiment may be substituted for different elements in another embodiment carrying out a similar or corresponding function.

[0024] 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.

[0025] 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.

[0026] 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 stmcture 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.”

[0027] 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.

[0028] 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.

[0029] 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”.

[0030] 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).

[0031] 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 stages” 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.

[0032] 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.

[0033] 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.

[0034] 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 C.O. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.

[0035] 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.

[0036] The depicted apparatus could be used in at least one of the following modes:

[0037] 1. 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.

[0038] 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.

[0039] 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.

[0040] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

[0041] The lithographic apparatus comprises a substrate table WT. An upper part of the substrate table WT is shown in more detail in Figures 2 and 3 in cross-section and top view, respectively.

[0042] The substrate table WT comprises a support surface S configured to support the substrate W on the substrate table WT. The support surface S may be a flat surface, but can also be defined by a quantity of burls or other objects extending from the substrate table WT to a supporting height. The support surface S may also be defined in any other suitable way.

[0043] The substrate table WT is configured to receive the substrate W at a predefined area on the support surface S. This predefined area is indicated by a dashed circle in Figure 3. This predefined area comprises a center CE. This center CE will receive the center of a substrate W to be placed on the substrate table WT.

[0044] The predefined area may be designed to receive a substrate of relatively large size, for example a substrate of 450 mm in diameter. Such large size substrate will have a smaller thickness to diameter ratio, resulting in a reduced bending stiffness.

[0045] To make controlled placing of a substrate W on the substrate table WT possible, the substrate table WT is provided with a set of inner pins IP and a set of outer pins OP each configured to receive and support the substrate W.

[0046] The set of inner pins IP comprises three pins extending substantially vertically and being arranged equally divided about the circumference of a first circle. The center of this circle corresponds with the center CE of the support surface S. Each inner pin IP is movable between a retracted position, wherein an upper end of the inner pin IP is arranged below the support surface S and an extended position wherein the upper end of the inner pin IP extends above the support surface S. In figure 2 the inner pins IP are shown in the extended position.

[0047] In an embodiment, the set of outer pins OP comprises six pins extending substantially vertically and being arranged equally divided about the circumference of a second circle, concentrically with the first circle. Each outer pin OP is movable between a retracted position, wherein an upper end of the outer pin OP is arranged below the support surface S and an extended position wherein the upper end of the outer pin OP extends above the support surface S. In figure 2 the outer pins OP are shown in the extended position.

[0048] The diameter of the first circle is smaller than the diameter of the second circle. Thus the inner pins IP are arranged closer to the center CE than the outer pins OP. For example, the support surface S is designed to support a substrate W having a diameter of approximately 450 mm, and the diameter of the first circle is for example about 170 mm and the diameter of the second circle is for example 400 mm.

[0049] The upper ends of the inner pins IP in the extended position are substantially further spaced from the support surface S than the upper ends of the outer pins OP in the extended position. For example, the height IPH of the upper ends of the inner pins IP in the extended position above the support surface is minimally 5 mm, preferably in the range of 8 -15 mm, while the height OPH of the upper end of the outer pins OP in the extended position above the support surface is maximally 5 mm, preferably in the range of 0.1 mm - 2 mm.

[0050] In this embodiment, the inner pins IP are used to receive a substrate from a substrate loading device, for instance a loading robot, whereas the outer pins OP are used to place the substrate W on the support surface. Thus, between receiving the substrate W on the inner pins IP and placing the substrate W on the support surface S, the substrate W is transferred from the inner pins IP to the outer pins OP.

[0051] An advantage of this embodiment is that a smaller number of inner pins IP with a large travel distance have to be provided, while the substrate can be placed on the support surface with great accuracy on the support surface due to the presence of the larger number of outer pins OP. It is desirable that there are only a small number of pins with a large travel range, since this results in lower costs and in a smaller clause on volume required in the substrate stage for the pins. For example, the volumes VO in the substrate table WT would not be completely available when the outer pins OP would have the same travel distance as the inner pins IP.

[0052] The outer pins OP are arranged at a relatively large diameter. This relatively large diameter is selected such that a substrate W supported on the outer pins OP will bend convexly with respect to the support surface S. When the substrate W is lowered in this position first the center part of the substrate W will come into contact with the support surface S at the center CE thereof. Then the rest of the substrate W will be placed on the support surface from the center to the circumference of the wafer W. This will lead to reduced stress in the substrate W placed on the support surface S.

[0053] Since the inner pins IP are arranged at the first circle with smaller diameter a centralized motor design, having a single actuator for actuation of all three inner pins IP may be used. However, each inner pin IP may also have its own actuator.

[0054] The outer pins OP may be actuated by any suitable actuator, for instance an electromagnetic actuator, such as a Lorentz type actuator or a 3 phase linear motor, or a piezoelectric driven actuator, such as a direct driven, mechanical amplified or inertial slider-type piezoelectric driven actuator. Other possible piezoelectric actuators could be a bimorph or a piezoelectric stack type actuator possibly with an amplifying mechanism.

[0055] The upper ends of the inner pins IP are provided with holding means HM to hold the substrate at substantially the same location, in particular during transfer of the substrate W from the inner pins IP to the outer pins OP.

[0056] These holding means HM may comprise clamping means such as a vacuum clamp or an electrostatic clamp. In addition thereto or as an alternative, the upper ends of the inner pins may be provided with friction increasing material and/or the upper ends of the outer pins may be provided with friction reducing material, so that the substrate will slide easier over the upper ends of the outer pins OP than over the upper ends of the inner pins IP. As a result, the substrate W will remain centered with respect to the center CE of the support surface S.

[0057] As another addition or a an alternative embodiment, the outer pins OP may be mounted on a flexible mounting means which provides flexibility to the outer pins OP in a radial direction, i.e. in direction of a line between the center CE and the respective outer pin OP. Such construction will increase the stability of the position of the substrate W with respect to the support surface S. In yet another addition or alternative embodiment, the outer pins are tilted in at least the radial direction, i.e. tilted towards the center CE.

[0058] The upper ends of the outer pins are provided with sensors SE to determine a distance between the upper ends of the outer pins OP and the substrate W. The sensors SE may be any sensors suitable to determine a distance between the sensor SE and a substrate W arranged within a measurement range of the sensor, for example an electromagnetic, electrostatic sensor or optical sensor.

[0059] A control device may be configured to adapt a height of the upper ends of the outer pins OP in the extended position in dependence of the distance measured by the sensor. This height control of the outer pins OP may for instance be used to position the outer pins OP such that the substrate will simultaneously be placed on the outer pins OP, even when the substrate W is not perfectly flat. In such embodiment, the height of the outer pins OP can be adjusted, while the substrate W is lowered towards the outer pins OP, such that the substrate W comes to rest at the same time on all the outer pins OP.

[0060] It is remarked that in addition to or as an alternative for the sensors SE, a deflection measuring device may be used which is configured to determine the deflection or shape of the complete substrate, for example a camera or scanning device configured for this goal.

[0061] A method to place a substrate W on a substrate table WT will now be discussed referring to Figures 4-7.

[0062] Figure 4 shows a substrate W supported by the inner pins IP in the extended position. The substrate W is placed on the inner pins IP by a loading robot (not shown). Since the inner pins IP are arranged at relative small distance from the center of the substrate W the outer circumference of the substrate W sags due to the gravity force acting on the substrate W. It is remarked that the sagging of the substrate is shown exaggerated with respect to the actual vertical deviation. In practice, the vertical deviation of the outer circumference caused by sagging may for instance be in the range of 0.1 - 1 mm.

[0063] When the inner pins IP would be lowered to the retracted position and the outer pins would not have been provided, the substrate W would be placed on the support surface S first with the outer circumference and subsequently with the rest of the substrate W towards the center. As this could lead to undesired stress in the substrate W, the outer pins OP are provided and arranged in the extended position as shown in Figure 5.

[0064] To place the substrate W on the support surface S, the inner pins IP are moved towards the retracted position therewith lowering the substrate W towards the upper ends of the outer pins OP.

[0065] In Figure 5, the substrate W is shown in a position where it is supported on both the inner pins IP and the outer pins OP. Since in this position the substrate W is supported at the radial distance of the first circle of the inner pins IP and the second circle of the outer pins OP, the substrate W shows relative little sagging at the center and/or at the outer circumference of the substrate W. The maximal vertical deflection of the substrate W may for instance be lower than 0.05 mm

[0066] To prevent sliding of the substrate W during the placement of the substrate W on the outer pins OP, the substrate W may be held by the holding means of the inner pins IP, so that the substrate W does not slip with respect to the inner pins IP. Further measures as described above may be taken to avoid slip of the substrate W with respect to the inner pins IP.

[0067] Further, the sensors SE as previously described may be used to measure the distance between the outer pins OP and the substrate W to determine the distance between the outer pins OP and the substrate W. The height of the outer pins OP may be adjusted so that the substrate W comes to rest on the outer pins OP in a desired order, for instance substantially simultaneously.

[0068] When it is desired that the substrate W is placed on the support surface S as flat as possible, the inner pins IP and the outer pins OP may be lowered simultaneously to the retracted position, so that the substrate is supported by the inner pins TP and the outer pins OP when it comes into contact with the support surface S. As a result, the complete surface of the substrate W will substantially simultaneously come to rest on the support surface S.

[0069] In the present embodiment, it is however desired that the center of the substrate W first comes into contact with the support surface S, and thereafter the rest of the substrate W starting from the center towards the outer circumference of the substrate W.

[0070] For this reason the inner pins IP are moved towards the retracted position. Figure 6 shows the inner pins IP in the retracted position. The upper ends of the inner pins IP are now below the support surface S, and the substrate W is only supported by the six outer pins OP. Due to the gravity force on the substrate W, the middle part of the substrate W sags. The vertical deflection of the substrate W in the center with respect to the outer pin may for instance be in the range of 0.05 mm - 0.5 mm. Lowering of the outer pins OP will result in lowering of the substrate W wherein first the center of the substrate W comes to rest on the center of the support surface S, and subsequently the rest of the substrate W from the center towards the outer circumference of the substrate W.

[0071] Figure 7 shows the substrate table WT with the inner pins IP and the outer pins OP in the retracted positions, wherein the upper ends are arranged below the support surface S. The substrate W is now completely supported by the support surface S.

[0072] Hereinabove an embodiment of a substrate table WT is described and shown wherein two sets of pins are used to place a substrate W on the support surface S of the substrate stage WT. The first set of pins, preferably having three pins, has a relatively large travel range, while the second set of pins has a relatively small travel range. The height of the first pins is selected to make loading of a substrate on the first pins with an external loading device possible, in particular when the loading device holds the substrate at its bottom side. The height of the second pins is selected to place the substrate in a predefined way on the support surface, for example starting from the center of the substrate.

[0073] In the shown embodiment, the first set of pins is arranged in a small circle while the second set of pins is arranged in a relatively large circle. Alternative configurations of the first set of pins and the second set of pins are also possible.

[0074] For example, the first set of pins and the second set of pins may each consist of three pins which are alternately arranged on a single circle having a relative large diameter, for example 400 mm diameter for a 450 mm substrate. To receive a substrate the pins of the first set of pins are moved to the extended position. The pins of the second set are also positioned in the extended position. When a substrate W has been loaded on the pins of the first set, these pins of the first set are lowered until the substrate comes to rest on the pins of both the first set of pins and the second set of pins. Since all the pins are arranged in a relatively large circle the substrate will sag in the middle. To place the substrate on the support surface, the substrate is further lowered by simultaneous lowering of all the pins of the first and second set towards the retracted position. In this embodiment, only three pins with large travel range are required, while the substrate is securely placed on the support surface with the use of six pins arranged in a single circle.

[0075] Hereinabove, the set of first pins and the set of second pins are described as being arranged on the substrate table of a lithographic apparatus. In an alternative embodiment, the set of first pins and the set of second pins may also be located on any other suitable location, for instance another part of a substrate stage. For example, the set of first pins may be arranged on a long-stroke module that forms part of the second positioning device PW. In an alternative embodiment the set of first pins may be arranged on a support frame supporting the second positioning device PW, for example a base frame.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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 support for a plate-shaped object, comprising: a substantially horizontal support surface configured to support the object, a set of first pins, each first pin being movable between a retracted position at which its upper end is arranged below the support surface and an extended position at which its upper end extends above the support surface, a set of second pins, wherein each second pin is movable between a retracted position, wherein an upper end of the second pin is arranged below the support surface and an extended position wherein the upper end of the second pin extends above the support surface, wherein the upper ends of the first pins in the extended position are substantially further spaced from the support surface than the upper ends of the second pins in the extended position.

2. The support of clause 1, wherein the support surface comprises a center, the first pins being arranged closer to the center than the second pins.

3. The support of clause 1, wherein the first pins are arranged in a first circle having a first diameter, and the second pins are arranged in a second circle concentric with the first circle and having a larger diameter than the first circle.

4. The support of clause 1, wherein the set of first pins consists of three first pins.

5. The support of clause 1, wherein the upper ends of the first pins comprise holding means to hold the substrate.

6. The support of clause 1, wherein the second pins are mounted on a flexible mounting means providing flexibility in a direction of a line between the center and the respective second pin.

7. The support of clause 1, wherein the support further comprises measurement device to determine a distance between the upper ends of the second pins and a substrate part to be supported by the respective second pin.

8. The support of clause 7, wherein a control device is configured to adapt a height of the upper ends of the second pins in the extended position in dependence of the distance measured by the measurement device.

9. The support of clause 3, wherein the diameter of the second circle is selected such that a substrate supported on the second pins will bend convexly with respect to the support surface.

10. A method to load a plate-shaped object on the support of clause 1, comprising the steps of: moving the first pins to the extended position, moving the second pins to the extended position, placing the object on the first pins with an external object holding device, placing the object on the second pins by moving the first pins towards the retracted position, and placing the object on the support surface by moving the second pins to the retracted position.

11. The method of clause 10, wherein the step of placing the object on the support surface comprises placing the object on the support surface from the center to the outer rim.

12. The method of clause 10, wherein the step of placing the object on the second pins comprises measuring, for each second pin, a distance between the upper end of the second pin and a substrate part to be supported by the respective second pin, and optionally adjusting the height of the second pin in dependence of the measured distance.

13. A lithographic apparatus 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 substrate table comprises a substantially horizontal support surface configured to support the substrate, and wherein the lithographic apparatus further comprises: a set of first pins, wherein each first pin is movable between a retracted position, wherein an upper end of the first pin is arranged below the support surface and an extended position wherein the upper end of the first pin extends above the support surface, a set of second pins, wherein each second pin is movable between a retracted position, wherein an upper end of the second pin is arranged below the support surface and an extended position wherein the upper end of the second pin extends above the support surface, wherein the upper ends of the first pins in the extended position are substantially further spaced from the support surface than the upper ends of the second pins in the extended position.

14. The lithographic apparatus, wherein the support surface has a center, the first pins being arranged closer to the center than the second pins.

15. A method to load a substrate on the substrate table in the lithographic apparatus of clause 13, comprising the steps of: moving the first pins to the extended position, moving the second pins to the extended position, placing the substrate on the first pins, placing the substrate on the second pins by moving the first pins towards the retracted position, and placing the substrate on the support surface by moving the second pins to the retracted position.

Claims (1)

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.