Substrate handling system for a lithographic apparatus and method thereof - Patents.com

Abstract

The substrate handling system comprises a substrate holder comprising a body having a body surface and a plurality of burls protruding from the body surface for supporting a substrate at a distance from the body surface, clamping means configured to clamp and / or unclamp the substrate on the substrate holder, and transport means configured to load and / or unload the substrate on the substrate holder, the transport means further configured to physically contact the substrate during clamping and / or unclamping to the substrate holder. A method for clamping and unclamping a substrate, a computer program, a computer readable medium and a lithographic apparatus are also described.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of European Application No. 19183180.9, filed June 28, 2019, which is incorporated herein by reference in its entirety.

[0002] [Technical field] The present invention relates to a substrate handling system of a lithographic apparatus and to a method for reducing wear or erosion on a substrate holder during unloading and loading of a substrate. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern in a patterning device (e.g. mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4-20 nm, e.g., 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than lithographic apparatus using radiation having a wavelength of, e.g., 193 nm.

[0005] Substrate holders with multiple burls for supporting a substrate are commonly used in lithographic apparatus. The substrate is typically clamped to the substrate holder during exposure. Clamping may be performed by using electrostatic or vacuum forces. An example of a substrate may be a wafer. Other substrates such as patterning devices may also be clamped to the support structure using the clamping technique.

[0006] In some systems, the clamping and unclamping of the substrate on the substrate holder may be hard and undamped. The clamping surface may be the surface on which the substrate is clamped and / or unclamped. The clamping process requires low friction and high friction during clamping. Low friction is necessary to minimize the applied stresses and deformations that can cause overlay issues. High friction is necessary to maximize the gripping force and prevent the substrate from slipping relative to the clamping surface during scanning acceleration of the substrate holder.

[0007] Furthermore, during clamping or unclamping of the substrate, vibrations may occur that cause wear or erosion of the substrate holder. More specifically, the burls may be worn or eroded. This wear or erosion reduces the flatness of the clamping force. If the clamping force is not flat, the number of focus errors and overlay between patterned layers on the wafer will increase. Summary of the Invention [Problem to be solved by the invention]

[0008] It is an object of the present invention to provide an improved substrate handling system which reduces wear or erosion of components of the substrate handling system.

[0009] Another object of the present invention is to reduce the number of focus errors during exposure, thereby reducing overlay between patterned layers. [Means for solving the problem]

[0010] In a first aspect of the invention, there is provided a substrate handling system comprising a substrate holder comprising a body having a body surface and a plurality of burls protruding from the body surface for supporting a substrate at a space from the body surface, clamping means configured to clamp and / or unclamp the substrate on the substrate holder, and transport means configured to load and / or unload the substrate on the substrate holder, the transport means further configured to physically contact the substrate during clamping and / or unclamping to the substrate holder.

[0011] The transport means may be movable at least between an extended position, in which its upper end extends above the substrate holder, and a retracted position, in which its upper end is retracted inside the substrate holder. Either the retracted position or the extended position is a different position relative to the position in which the transport means contacts the substrate. For ease of understanding, this latter position of the transport means may be referred to as the contact position.

[0012] The transport means is therefore configured to be positioned during clamping and / or unclamping to the substrate holder in a contact position, in which the transport means physically contacts the wafer.

[0013] When loading the substrate onto the substrate holder, the robot may load the substrate onto the transport means arranged in the extended position. The substrate is received on the transport means extending above the plurality of burls so that the robot can withdraw the substrate while leaving it on the transport means. The transport means may then be moved to a storage position in order to place the substrate onto the plurality of burls. In the storage position, the transport means is not in contact with the substrate.

[0014] After loading, the substrate is clamped to the substrate holder by a clamping means to avoid any shifting of the substrate during exposure. The surface of the substrate holder to which the substrate is clamped is the clamping surface. Once the exposure is completed, the substrate is unclamped from the substrate holder, which means that the clamping means releases the substrate. Finally, the substrate is unloaded from the substrate holder by the transport means. In particular, the transport means may move to an extended position.

[0015] When a substrate is clamped or unclamped to the substrate holder, the substrate may vibrate on the burls. The vibration may wear or erode the burls and reduce the flatness of the clamping surface. It is noted that clamping and unclamping a substrate is a different process than loading and unloading a substrate. Thus, the clamping and unclamping process is performed until the substrate vibration stops or is significantly reduced.

[0016] Advantageously, the system of the present invention reduces such vibrations through the transport means during the clamping and / or unclamping process. Furthermore, during clamping, the transport means is configured to counter gravity and provide zero load or normal force on the burls during clamping. Furthermore, the present invention reduces wear or erosion on the substrate holder. The substrate holder may be used in a lithographic apparatus.

[0017] The substrate may be a wafer or a reticle. The invention may also be useful for a reflective reticle placed on a substrate holder. In such an embodiment, the substrate holder may be the reticle holder of the mask holder.

[0018] In an embodiment, the transport means is configured to detect vibrations on the substrate caused by clamping and / or unclamping the substrate to the substrate holder.

[0019] In an embodiment, the transport means is further configured to position the substrate during unclamping in a vibration position in which the substrate is located away from the burls. In the vibration position the substrate may be in free space, meaning that the substrate is not in contact with the burls.

[0020] Either the retracted position or the extended position or the contact position is a different position relative to the vibration position or the position of vibration of the substrate. For ease of understanding, the extended position may be referred to as a first position, the retracted position may be referred to as a second position, the contact position may be referred to as a third position, and the vibration position may be referred to as a fourth position.

[0021] In this embodiment, the substrate vibrates away from the burls, meaning that the substrate vibrates in free space without interacting with the burls, which advantageously avoids wear or erosion of the burls, which helps maintain the flatness of the clamping surface.

[0022] In one embodiment, the substrate is electrostatically clamped to the substrate holder. In this embodiment, the clamping means provides an electrostatic force between the body surface and the substrate. The electrostatic force clamps the substrate to the substrate holder. The electrostatic force may be exerted on the body surface, and more specifically, in spaces between burls on the body surface.

[0023] In one embodiment, the unclamping occurs during the gradual weakening (during ramp-down) of the electrostatic force clamping device. Thus, the clamping means is the electrostatic force clamping device. During said ramp-down, if the substrate loosens from the body, it may start to vibrate due to internal stresses and lack of damping. Thus, during ramp-down, the transport means is configured to contact the substrate to reduce vibration. Furthermore, during said ramp-down in this embodiment, the transport means is further configured to continuously push the substrate up. When the electrostatic force generating device is switched off, the substrate is released and is moved continuously to said vibration position by the transport means. In said vibration position or in the fourth position, the substrate may remain subject to the unclamping, such as vibration.

[0024] In one embodiment, the transport means comprises a force feedback sensor means. In another embodiment, the transport means is configured to position the substrate in a vibration position when the force feedback sensor means detects a force caused by unclamping. In an alternative or additional embodiment, the transport means comprises a transport means controller, the transport means configured to position the substrate in a vibration position when the transport means controller detects a force caused by unclamping. In another embodiment, the force detected may be a release of the substrate, and thus the transport means may be configured to detect the release of the substrate by using the force feedback sensor means and / or the transport means controller.

[0025] The vibration of the substrate mechanically transmits a force to the transport means, and by detecting the force caused by unclamping on the substrate, the above embodiment advantageously reduces the time that the substrate vibrates on the burls, and therefore the embodiment reduces wear or erosion of the burls.

[0026] In one embodiment, the transport means is configured to detect a reduction in vibration of the substrate in the clamp and move the transport means away from the substrate. In another embodiment, the force feedback sensor means is configured to detect the reduction in vibration. In a different embodiment, the transport means controller is configured to detect the reduction in vibration.

[0027] In the above embodiment, the reduction in the force from the substrate to the transport means is detected, which allows the transport means to move away from the substrate at the right moment, reducing unwanted stresses on the surface of the substrate that may damage it.

[0028] In one embodiment, the transport means comprises a plurality of pins and a motor means, preferably the transport means comprises at least three pins. In another embodiment, the motor means comprises a servo actuator configured to provide force feedback control of at least 100 Hz. In an additional embodiment, the plurality of pins are coated with a damping material, preferably the damping material is polyetheretherketone, or PEEK. In an embodiment, the system further comprises a gas dispenser means configured to dispense at least one gas onto at least the body surface, preferably the gas is hydrogen or nitrogen. In another embodiment, the gas dispenser means is configured to fill a volume between the clamping surface and the substrate with gas. In another embodiment, the system comprises a damping means for damping contact of the plurality of burls with the substrate, preferably the damping means may comprise a gas damper and / or a magnetic damper.

[0029] The above embodiment advantageously reduces vibrations experienced by the substrate and increases the reduction in wear or erosion of the burls. Regarding the gas used in the gas dispenser means, hydrogen is preferred in EUV lithography apparatus due to its cleaning properties. Regarding nitrogen, it is preferred in deep ultraviolet (DUV) lithography apparatus as it is an inert gas and is not flammable.

[0030] In a second aspect of the invention there is provided a method of declamping a substrate comprising declamping the substrate and contacting the substrate with a transport means during declamping, and moving the substrate by the transport means during declamping to a vibration position where the substrate is spaced from a plurality of burls.

[0031] Vibrations caused by unclamping occur in free space without interacting with the burls, reducing wear or erosion of the burls.

[0032] In one embodiment, the method further comprises detecting the release of the substrate before moving the substrate into the vibration position. In an additional embodiment, the detection is performed by using a force feedback measurement or by a transport means controller. The transport means controller may be connected to the transport means and may therefore have the same functionality as the transport means controller described in the embodiment of the first aspect of the invention.

[0033] If the transport means moves the substrate to the vibration position before unclamping, the substrate may be subjected to stresses that would damage its surface. Advantageously, the above embodiment releases the substrate from the burls at the right moment, avoiding damage to the substrate.

[0034] In one embodiment, the speed of movement to the vibration position is greater than or equal to 10 mm / s. Advantageously, this embodiment reduces the time that the substrate is vibrated over the burls, reducing wear or erosion thereof.

[0035] Furthermore, any of the embodiments of the method according to the second aspect of the invention may use a substrate handling system according to any of the embodiments of the first aspect of the invention.

[0036] In a third aspect of the present invention, there is provided a method for clamping a substrate, the method comprising clamping the substrate and contacting a transport means with the substrate during clamping.

[0037] Advantageously, contacting the transport means during unclamping reduces vibrations experienced by the substrate and reduces wear or erosion of the burls.

[0038] In one embodiment, the method further comprises detecting a reduction in vibration of the substrate by the transport means and moving the transport means away from the substrate, hi another embodiment, the reduction in vibration of the substrate is detected by force feedback measurement or a transport means controller.

[0039] The reduced vibrations experienced by the substrate during clamping also reduces the risk of wear or erosion of the burls. In the above embodiment, the reduction in the force from the substrate to the transport means is detected. This allows the transport means to be released from the substrate at the right moment, reducing unwanted stresses on the surface of the substrate that may damage it.

[0040] Furthermore, any of the embodiments of the method according to the third aspect of the invention may use a substrate processing system according to any of the embodiments of the first aspect of the invention.

[0041] In a fourth aspect of the invention there is provided a computer program comprising instructions for causing a system of any embodiment of the first aspect of the invention to carry out the steps of any of the method embodiments of any of the second and third aspects of the invention. In a fifth aspect of the invention there is provided a computer readable medium having stored thereon a computer program according to the fourth aspect of the invention.

[0042] In a sixth aspect of the present invention, there is provided a lithographic apparatus comprising a system according to any of the embodiments of the first aspect of the present invention and / or a computer readable medium according to the fifth aspect of the present invention.

[0043] Further aspects, features, and advantages of the present 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. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are shown herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the relevant art based on the teachings contained herein. [Brief description of the drawings]

[0044] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which: [Figure 1] FIG. 1 depicts a lithography system comprising a lithographic apparatus and a radiation source. [Diagram 2] 1 illustrates a cross-sectional view of a substrate holder and a substrate in a conventional lithographic apparatus; [Diagram 3] 11 is a cross-sectional view showing the working operation of the transport means during loading. FIG. [Figure 4a] 3 is a cross-sectional view illustrating wear or erosion of multiple burls of the substrate holder of FIG. 2 due to clamping and unclamping of the substrate. [Figure 4b] 3 is a cross-sectional view illustrating wear or erosion of multiple burls of the substrate holder of FIG. 2 due to clamping and unclamping of the substrate. [Diagram 5] 4A-4C are cross-sectional views illustrating the working operation of the substrate handling system of the present invention during clamping; [Figure 6] 11A-11C are cross-sectional views illustrating the working operation of the substrate handling system of the present invention during unclamping. [Figure 7] FIG. 2 illustrates another embodiment of a substrate handling system of the present invention. [Figure 8a] FIG. 4 shows another embodiment of the transport means of the substrate handling system of the present invention; [Figure 8b] FIG. 4 shows another embodiment of the transport means of the substrate handling system of the present invention; [Figure 9a]4 is a flow chart illustrating a method for reducing wear or erosion during clamping and unclamping of the present invention. [Figure 9b] 1 is a flow chart illustrating a method for reducing wear or erosion during clamping and unclamping of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] 1 shows a lithography system comprising a radiation source SO and a lithographic apparatus LA. The source SO is configured to generate a beam of EUV radiation B and to provide the beam of EUV radiation B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS, and a substrate holder WT configured to support a substrate W.

[0046] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. To that end, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The facetted field mirror device 10 and the facetted pupil mirror device 11 together provide an EUV radiation beam B having a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0047] After being conditioned in this way, the EUV radiation beam B interacts with the patterning device MA. This interaction results in a pattern EUV radiation beam B'. The projection system PS is configured to project the pattern EUV radiation beam B' onto the substrate W. To that end, the projection system PS may comprise a number of mirrors 13, 14 configured to project the pattern EUV radiation beam B' onto the substrate W held by a substrate holder WT. The projection system PS may apply a demagnification factor to the pattern EUV radiation beam B' to form an image having smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of 4 or 8 may be applied. Although the projection system PS is illustrated in Figure 1 as having only two mirrors 13, 14, the projection system PS may include a different number of mirrors, for example 6 or 8 mirrors.

[0048] Substrate W may include a previously formed pattern, in which case lithographic apparatus LA aligns the image formed by patterned EUV radiation beam B' with the previously formed pattern on substrate W.

[0049] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure may be provided to the source SO, illumination system IL and / or projection system PS.

[0050] The source SO may be a laser-produced plasma (LPP) source, a discharge-produced plasma (DPP) source, a free-electron laser (FEL) or any other source capable of producing EUV radiation.

[0051] FIG. 2 shows a substrate holder WT forming part of the lithographic apparatus LA. The substrate holder WT has the same shape as the substrate in plan view, e.g. circular, and is substantially the same size as the substrate, e.g. 300 mm or 450 mm in diameter. The substrate holder WT comprises a body 21 having a body surface 22 and a number of burls 20 protruding from the body surface 22. At least one section 210 of the body surface 22 arranged between the burls 20 may be configured to clamp and / or unclamp the substrate W. In an embodiment, the burls 20 have a height in the range of 100 μm to 500 μm, e.g. about 150 μm. The substrate W may be supported by distal end surfaces of the burls 20 that correspond to a substantially flat support surface for supporting the substrate W in a flat state. For example, the body 21 and the burls 20 may be formed of SiSiC, a ceramic material having silicon carbide (SiC) grains in a silicon matrix.

[0052] A number of through holes are formed in the body 21. Through holes 89 allow a transport means (not shown in FIG. 2) to protrude through the substrate holder WT to receive the substrate W, and allow the space between the substrate W and the substrate holder WT to be evacuated by connecting to a clamping negative pressure. Other structures may be provided, for example to control gas flow and / or thermal conductivity between the substrate holder WT and the substrate W.

[0053] In an embodiment in which the substrate holder WT is configured to perform vacuum clamping of the substrate W against the plurality of burls 20, an edge seal 85 is provided near the periphery of the substrate holder WT. The clamping means is therefore configured to provide vacuum clamping by modifying the pressure applied to the area around the substrate W. The substrate W is clamped to the substrate holder WT by connecting the clamping opening 89 to a clamping vacuum such that the space 201 is at a lower pressure than the space 202 above the substrate W. In this way, the clamping means is configured to modify the pressure in the spaces 201 and 202. The air pressure above the substrate W therefore holds the substrate W tightly to the substrate holder WT.

[0054] Thus, a clamping force (in this case a vacuum force) can be generated in the body surface, more specifically in the space 201 between the burls 20 of the body surface. The section 210 represents an area of ​​the body surface where the clamping force can be performed. Thus, at least one section 210 of the body surface 22 located between the burls 20 is configured to clamp and / or unclamp the substrate. The edge seals 85a, 85b protrude upwards from the substrate holder WT to minimize the gap between the substrate holder WT and the substrate W, and to minimize the inflow of air from the surroundings into the space directly below the substrate W, thereby reducing the load on the clamping negative pressure. The burls 20 can be provided in the area between the edge seals 85a, 85b.

[0055] The edge seal 85 is a pair of protruding edge seal ridges 85a, 85b around the outside of the substrate holder WT. The edge seal ridges 85a, 85b have a height slightly less than the burls 20, for example by about 10 μm, to prevent them from contacting the substrate W but to reduce gas inflow into the space between the substrate W and the substrate holder WT for improved vacuum clamping. The burls 20 may be provided in the region between the edge seal ridges 85a, 85b and although not shown in FIG. 2, there may be one or more rows of burls in this region. The substrate holder WT may also include electronic components, for example heaters and sensors for controlling the temperature of the substrate holder WT and the substrate W.

[0056] The openings 81 and 82 are configured to accommodate transport means (not shown in FIG. 2) intended to load and unload a substrate onto the substrate holder WT.

[0057] As an alternative to providing a vacuum clamp, the substrate holder is configured to electrostatically clamp the substrate W to the burls 20. In this case, a voltage provided by the clamping means is applied to the body surface 22. More specifically, the clamping means applies an electrostatic force in the space between the burls of the body. The section 210 represents an area of ​​the body surface where the clamping force can be performed. Thus, at least one section 210 of the body surface 22 located between the burls 20 is configured to clamp and / or unclamp the substrate. This section 210 may be named burl-free area 210. At least one section 210 or burl-free area of ​​the body surface 22 located between the burls 20 electrostatically attracts and clamps the substrate W. Thus, at least one section 210 or burl-free area of ​​the body surface 22 located between the burls 20 is configured to electrostatically clamp and / or unclamp the substrate. This electrostatic clamping method can also be used in the embodiment of FIG. 2.

[0058] The at least one section of the body surface located between the burls may be understood as a section or area of ​​the body surface where the burls do not protrude from the body surface, in other words, the at least one section of the body surface located between the burls is a section or area of ​​the body surface where the burls are not present.

[0059] Fig. 3 shows how the substrate W is loaded onto the substrate table WT. It can also be seen that the transport means is in an extended or first position. After receiving the substrate W by the transport means 30, the transport means 30 may be moved to a stored or second position for placing the substrate on the plurality of burls 20. In Fig. 4b the transport means is in the stored or second position and is housed inside the substrate holder WT. Then, before exposure the substrate W is clamped and after exposure the substrate W is unclamped for unloading from the substrate WT.

[0060] Especially during clamping as well as unclamping, the substrate experiences high friction which may wear the burls, more specifically the burls located under the outer portion of the substrate as shown in Fig. 4b. Due to the stiff and undamped wafer clamping system, this change in wafer shape may be accompanied by wafer vibrations as shown in Fig. 4a, which may lead to deformation problems at the surface of the substrate W. This will lead to overlay problems between its layers if the substrate W is a wafer.

[0061] In Figures 5 and 6, a substrate handling system 100 according to an embodiment of the present invention is shown, which prevents the wear shown in Figures 4a and 4b. In this embodiment, the substrate W is a wafer, but this example does not limit the invention to this type of substrate. Furthermore, the substrate handling system 100 is configured to electrostatically clamp and / or unclamp the substrate W.

[0062] The substrate handling system 100 of Figures 5 and 6 comprises a substrate holder WT. The substrate holder WT comprises a body 21 having a body surface 22. Further, the substrate holder WT comprises a plurality of burls 20 protruding from the body surface 22 for supporting a substrate W at a distance from the body surface 22. At least one section 210 of the body surface 22 located between the plurality of burls 20 may be configured to clamp and unclamp a substrate.

[0063] Furthermore, the substrate handling system 100 comprises a clamping means configured to clamp and / or unclamp the substrate to the substrate holder WT, and the substrate handling system 100 also comprises a transport means 30 configured to load and / or unload the substrate W to the substrate holder WT and configured to detect vibrations of the substrate W. The transport means 30 is configured to physically contact the substrate W during electrostatic clamping and / or unclamping to the substrate holder WT.

[0064] As shown in Figure 5, the conveying means is positioned in a contact or third position, which is different from the conventional extended and retracted positions shown in Figures 3 and 4b, respectively.

[0065] Advantageously, the present invention reduces vibration of the substrate W during clamping and / or unclamping. During electrostatic clamping as shown on the right hand side of Fig. 5, the transport means 30 is configured to maintain physical contact with the substrate W and gently push the backside as shown on the left hand side of Fig. 5.

[0066] During electrostatic clamp release, i.e. during the gradual decrease (ramp down) of the clamp voltage as shown on the right side of Fig. 6, the transport means 30 is configured to contact the substrate W and gently push the backside. Furthermore, the transport means 30 is configured to detect the release of the substrate by measuring the vibration of the substrate also during the ramp down of the clamp voltage, after which the transport means 30 pushes the substrate W up, so that the vibration of the substrate edge occurs in free space and not on the multiple burls 20. In one embodiment, the release of the substrate starts when the clamp voltage is reduced.

[0067] More specifically, the transport means 30 is configured to position the substrate W during unclamping in the vibration position 110 or in the fourth position, where the substrate is located away from the burls 20. This may be said to be the substrate being located in a space free from the burls 20, as shown in Fig. 6. The speed of moving to the vibration position is 10 mm / s or more. Once the substrate W is totally released, e.g. when the clamping voltage reaches 0 volts, the transport means is configured to maintain the substrate W in the vibration position until a reduction in vibration is detected and / or until the vibration has stopped, i.e. until unclamping is completed.

[0068] Figure 7 shows another embodiment of a substrate handling system 100 according to the invention. As can be seen, this embodiment comprises some elements of the systems of figures 5 and 6, which for simplicity of explanation will not be described again.

[0069] The transport means 30 of the substrate handling system 100 of Figure 7 comprises three pins 31, three electric motors 40, one force feedback sensor 50 and a transport means controller or motor controller 41. Also in this embodiment, the electric motors 40 are configured to position the substrate W through the pins 31 at the vibration position 110 when the force feedback sensor 50 detects a force or vibration caused by unclamping.

[0070] In another embodiment, the motor controller 41 is configured to detect the force or vibration caused by electrostatic clamping release and is configured to send a command to the electric motor 40 to position the substrate W through the pins 31 at the vibration position 110 .

[0071] It is further proposed to introduce additional damping into the pin by making the pin from a damping material such as PEEK, or by introducing electromagnetic damping into the actuating portion of the pin, or by servo action configured to provide force feedback control at least at 100 Hz. Alternatively, dedicated damping pins, rings or other shapes or structures can be used for this purpose.

[0072] These embodiments may be implemented in any case where there is backfill gas between the burls 20. To that end, in the embodiment of Fig. 7, the substrate processing system 100 further comprises a gas dispenser 60. The gas dispenser 60 is configured to dispense at least one gas at least to the body surface. In other words, the gas dispenser 60 is configured to fill a volume 70 between the clamping surface and the substrate with hydrogen 61. Advantageously, the backfill gas 61 may be beneficial to provide some additional damping immediately after unclamping.

[0073] In an alternative embodiment, the transport means may be an external device. Fig. 8a shows an overhead view of such an embodiment. The transport means comprises an external robot 80 having a gripper hand 81 configured to load and unload the substrate W onto the substrate holder WT. In another embodiment, the external robot is configured to load and unload the substrate onto the pins 31. In an additional embodiment, the external robot 80 is configured to load and unload the substrate onto the burls 20.

[0074] Also, in the embodiment of Fig. 8a, the position where the gripping hand 81 is at the same height as the substrate W is shown by a dashed line, i.e. it may be located in a plane parallel to the substrate or in the same plane as the substrate. In this embodiment, the external robot 80 is configured to grip the substrate W from said plane. The gripping hand 81 may also grip the substrate W by physical contact, preferably using at least one wedge, or by electrostatic forces.

[0075] In the embodiment of Fig. 8b, the gripping hand 81 is positioned above the substrate W. In this embodiment, the external robot 80 is configured to grip the substrate W from said position. In particular, the gripping hand 81 may grip the substrate W by physical contact, preferably by means of at least one wedge, or by electrostatic forces.

[0076] In any of the embodiments in which the transport means 30 comprises an external robot 80, the external robot 80 may be used in any of the handling systems shown in Figures 5 to 7. As shown in particular in Figure 8b, the external robot 80 may be connected to a motor controller 41 and a force feedback sensor 50. The motor controller 41 is also configured to detect forces or vibrations caused by unclamping, and to send commands to the external robot 80 to position the substrate at a vibration position 110 during unclamping. As in the previous embodiment, at said vibration position 110 the substrate is spaced apart relative to the burls 20.

[0077] Furthermore, the motor controller 41 is also configured to detect forces or vibrations caused by the clamping and to send commands to the external robot 80 to contact the substrate and reduce vibrations of the substrate W. Advantageously, the external robot 80 allows for the implementation of more complex clamping schemes (e.g. differential forces over time at different positions) without overly complicating the primary function of the substrate holder WT.

[0078] In any of the embodiments of Figures 5 to 8b, the transport means 30, either pins 31 or an external robot 80 with gripping hands 81, is configured to keep the substrate W at zero normal load force during clamping.

[0079] Fig. 9a shows a flow chart of a method 300 for unclamping a substrate W. The method 300 is executed during electrical unclamping as represented in the right part of Fig. 9a. The method 300 comprises electrically unclamping 301 the substrate W and contacting 301 the substrate W with the transport means 30 during said unclamping. This means contacting the substrate W with the transport means 30 during a gradual decrease (ramp down) of the clamping voltage. Furthermore, the release of the substrate W is detected 302 by using a force feedback measurement or by the transport means control device 40. When it is released during unclamping, i.e. when the clamping voltage is close to 0V but still clamped, the substrate W is moved 303 by the transport means 30 to a substrate vibration position 110 where the substrate W moves away from the burls 20.

[0080] Fig. 9b shows a flow chart of a method 400 for reducing clamping of the substrate W. The method 400 is executed during electrical clamping, as represented in the right part of Fig. 9b. The method 400 comprises a step 401 of electrically clamping the substrate W and simultaneously bringing the transport means 30 into contact with the substrate W during clamping. This means bringing the transport means into contact with the substrate W while increasing the clamping voltage (during ramp-up). Furthermore, the reduction of vibration is detected 402 by using force feedback measurement or by the transport means control device 40. When it is detected during clamping, i.e. when the clamping voltage approaches the optimal clamping voltage, the transport means 30 is moved away 403 from the substrate W.

[0081] In this text specific reference may be made to the use of lithographic apparatus in the manufacture of ICs, however it will be appreciated that the lithographic apparatus described herein may have other applications including 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.

[0082] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other patterning device). These apparatus may be generally referred to as lithography tools. Such lithography tools may use vacuum or atmospheric (non-vacuum) conditions.

[0083] 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, where the context permits, the invention is not limited to optical lithography and may be used in other applications, such as, for example, imprint lithography.

[0084] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Also, embodiments of the present invention may be implemented as instructions stored on a machine-readable medium that may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical, optical, acoustic or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, instructions may be described herein as performing certain actions. However, it will be understood that such description is merely for convenience and that such actions may in fact result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., which in turn may cause actuators or other devices to interact with the physical world.

[0085] While specific embodiments of the invention have been described above, it will be understood that the invention may be embodied in other ways than as described. The above description is intended to be illustrative and 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 claims set forth below. Other aspects of the invention are presented in the following numbered paragraphs: (Item 1) A substrate holder comprising a body having a body surface and a plurality of burls protruding from the body surface to support a substrate at a distance from the body surface; clamping means configured to clamp and / or unclamp the substrate on the substrate holder; a transport means configured to load and / or unload the substrate on the substrate holder, A substrate handling system, wherein the transport means is further configured to physically contact the substrate during the clamping and / or unclamping to the substrate holder. (Item 2) The system described in Item 1, wherein the transport means is further configured to position the substrate in a vibration position during the unclamping, wherein the substrate is positioned away from the plurality of burls in the vibration position. (Item 3) The system described in item 1 or 2, wherein the conveying means is equipped with a force feedback sensor means. (Item 4) The system described in Item 3, wherein the transport means is configured to position the substrate at the vibration position when the force feedback sensor means detects a force caused by the unclamping. (Item 5) The conveying means includes a conveying means control device, 5. The system of any one of claims 1 to 4, wherein the transport means is configured to position the substrate in a vibration position when the transport means control device detects a force caused by the unclamping. (Item 6) The system of any one of items 1 to 5, wherein the transport means comprises a plurality of pins and a motor means. (Item 7) The system described in Item 6, wherein the motor means comprises a servo actuator configured to provide force feedback control of at least 100 Hz. (Item 8) The system described in item 6 or item 7, wherein the plurality of pins are coated with a damping material, preferably the damping material is polyetheretherketone. (Item 9) The system described in any one of items 1 to 8, further comprising a gas dispenser means configured to eject at least one gas onto at least the body surface, preferably the gas being hydrogen or nitrogen. (Item 10) The system described in any one of items 1 to 9, further comprising a damping means for damping contact between the substrate and the plurality of burls, preferably the damping means being a gas damper and / or a magnetic damper. (Item 11) A system described in any one of items 1 to 10, wherein the transport means is further configured to detect a reduction in vibration of the substrate while in the clamp and move the transport means away from the substrate. (Item 12) The system described in items 3 and 11, wherein the force feedback sensor means is configured to detect a reduction in the vibration. (Item 13) The system described in items 5 and 11, wherein the conveying means control device is configured to detect a reduction in the vibration. (Item 14) A method for unclamping a substrate, comprising: unclamping the substrate and contacting a transport means with the substrate during the unclamping; and moving the substrate by the transport means to a vibration position during the unclamping, In the vibration position, the substrate is spaced from a plurality of burls. (Item 15) The method of item 14, further comprising detecting release of the substrate before moving the substrate to the vibration position. (Item 16) The method according to item 15, wherein the detection is performed by using force feedback measurements or by a transport means control device. (Item 17) The method according to any one of items 14 to 16, wherein the speed of moving to the vibration position is 10 mm / s or more. (Item 18) A method for clamping a substrate, comprising: clamping the substrate; and contacting a transport means with the substrate during the clamping. (Item 19) Detecting a decrease in vibration of the substrate by the transport means; 20. The method of claim 18, further comprising: moving the transport means away from the substrate. (Item 20) The method according to item 18 or 19, wherein the reduction in vibration of the substrate is detected by using force feedback measurement or by a transport means control device. (Item 21) A computer program comprising instructions for causing a system according to any one of items 1 to 13 to perform the steps of the method according to any one of items 14 to 20. (Item 22) A computer-readable medium on which the computer program according to item 21 is stored. (Item 23) A lithographic apparatus comprising the system according to any one of items 1 to 13 and / or the computer-readable medium according to item 22.

Claims

1. a substrate holder comprising a body having a body surface and a plurality of burls projecting from the body surface for supporting a substrate at a spaced distance from the body surface; clamping means configured to clamp and / or unclamp the substrate on the substrate holder; a transport means configured to load and / or unload the substrate on the substrate holder, the transport means is further configured to physically contact the substrate during the unclamping from the substrate holder; A substrate handling system, wherein the transport means is further configured to position the substrate at a vibration position midway through the unclamping when a force caused by the unclamping is detected, wherein the substrate is positioned away from a plurality of burls at the vibration position.

2. The conveying means includes a force feedback sensor means, The substrate handling system of claim 1 , wherein the force feedback sensor means is configured to detect the force caused by the unclamping.

3. The conveying means includes a conveying means control device, The substrate handling system of claim 1 , wherein the transport means control device is configured to detect the force caused by the unclamping.

4. A substrate handling system as described in any one of claims 1 to 3, wherein the transport means comprises a plurality of pins and a motor means.

5. 5. The substrate handling system of claim 4, wherein the motor means comprises a servo actuator configured to provide force feedback control of at least 100 Hz.

6. The substrate handling system of claim 4 or 5, wherein the pins are coated with a damping material.

7. 7. The substrate handling system of claim 1, further comprising a gas dispenser means configured to dispense at least one gas onto at least the body surface.

8. and / or a damping means for damping contact between the substrate and the plurality of burls; 8. A substrate handling system according to claim 1, wherein the transport means is further configured to detect a reduction in vibration of the substrate while in the clamp and to move the transport means away from the substrate.

9. The transport means is further configured to detect a reduction in vibration of the substrate during clamping and move the transport means away from the substrate; The substrate handling system of claim 2 , wherein the force feedback sensor means is configured to detect a reduction in the vibration.

10. The transport means further configured to detect a reduction in vibration of the substrate while in the clamp and move the transport means away from the substrate; The substrate handling system of claim 3 , wherein the transport means control device is configured to detect a reduction in the vibration.

11. 1. A method for unclamping a substrate, comprising: unclamping the substrate and contacting a transport means with the substrate during the unclamping; moving the substrate to a vibration position by the transport means during the unclamping; detecting release of the substrate during the unclamping prior to moving the substrate to the vibration position; In the vibration position, the substrate is spaced from a plurality of burls.

12. The method of claim 11, wherein the detection is performed by using force feedback measurements or by a conveying means control device.

13. 13. The method according to claim 11, wherein the speed of moving to the vibration position is 10 mm / s or more.

14. A lithographic apparatus comprising a substrate handling system according to any one of the preceding claims.

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