Substrate holder, lithographic apparatus, computer program and method

Abstract

A substrate holding system for supporting a substrate, the substrate holding system comprising a substrate holder and an evacuation conduit wherein: the substrate holder comprises: a body having a surface; a plurality of tabs protruding from the surface and having a distal end forming a support surface for the substrate; and an extraction channel in fluid communication with the evacuation conduit and a space between the surface and the substrate supported by the burls to form an evacuation flow path; and a proportional valve is arranged in the emptying flow path.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 22184122.4 filed on July 11, 2022 and EP application 23151317.7 filed on January 12, 2023, which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates to a substrate holder for supporting a substrate, a lithography apparatus comprising the substrate holder, a method for supporting a substrate on the substrate holder, and a method for clamping a substrate on the substrate holder. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. For example, a lithographic apparatus may be used in the manufacture of integrated circuits (ICs). For example, a lithographic apparatus may project a pattern (also often referred to as a "design layout" or "design") of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer).

[0005] As semiconductor manufacturing processes continue to advance, the size of circuit elements has continued to decrease, while the number of functional elements (such as transistors) per device has been steadily increasing for decades, following a trend often referred to as "Moore's Law." To keep up with Moore's Law, the semiconductor industry has been pursuing technologies that can create smaller and smaller features. To project a pattern on a substrate, a lithography device can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths used today are 365nm (i-line), 248 nm, 193 nm, and 13.5 nm.

[0006] The lithographic apparatus may include an illumination system for providing a projection radiation beam and a support structure for supporting a pattern forming device. The pattern forming device may be used to impart a pattern to the projection beam in a cross-section of the projection beam. The apparatus may also include a projection system for projecting the patterned beam onto a target portion of the substrate.

[0007] In a lithographic apparatus, a substrate to be exposed (which may be referred to as a production substrate) may be held on a substrate holder (sometimes referred to as a wafer stage). The substrate holder may be movable relative to a projection system. The substrate holder typically comprises a solid portion made of a rigid material having dimensions in a plane similar to those of the production substrate to be supported. The surface of the solid portion facing the substrate may be provided with a plurality of protrusions (referred to as burls). The distal surfaces of the burls may coincide with a flat plane and support the substrate. The burls may provide several advantages: contaminant particles on the substrate holder or on the substrate may fall between the burls and therefore do not cause deformation of the substrate; it is easier to machine the burls so that their ends coincide with a plane than to flatten the surface of the solid portion; and the properties of the burls may be adjusted, for example to control the clamping of the substrate to the substrate holder.

[0008] During the process of manufacturing a device, in particular when structures with significant heights are formed (e.g., so-called 3D-NAND), the production substrate may deform. Typically, the substrate may become "bowl-shaped," i.e., concave when viewed from above, or "umbrella-shaped," i.e., convex when viewed from above. For the purposes of this disclosure, the surface on which the device structure is formed is referred to as the top surface. In this context, "height" is measured in a perpendicular direction to the nominal surface of the substrate, which direction may be referred to as the Z direction. Bowl-shaped and umbrella-shaped substrates are flattened to some extent when clamped to a substrate holder, for example, by partially emptying the space between the substrate and the substrate holder. However, if the amount of deformation is too large, which is typically measured by the height difference between the lowest point on the substrate surface and the highest point on the substrate surface, various problems may arise. In particular, it may be difficult to adequately clamp the substrate, so that there may be excessive wear of the burls during loading and unloading of the substrate, and the remaining height variations in the substrate surface may be too large to achieve correct patterning on all parts of the substrate, especially on parts close to the edges. Summary of the invention

[0009] An object of the present invention is to provide a substrate holding system that enables efficient pattern formation on a substrate. A substrate holding system according to an embodiment may enable a more consistent substrate loading and clamping process, thereby reducing overlay errors.

[0010] In a first embodiment, a substrate holding system for supporting a substrate is provided, the substrate holding system comprising a substrate holder and an exhaust conduit, wherein the substrate holder comprises: a body having a surface; a plurality of burls protruding from the surface and having distal ends forming a supporting surface for the substrate; and an extraction channel in fluid communication with the exhaust conduit and a space between the surface and the substrate supported by the burls to form an exhaust flow path; and

[0011] A proportional valve is provided in the exhaust flow path.

[0012] According to the first embodiment, a method for clamping a substrate to a substrate holder is also provided, wherein the substrate holder comprises: a main body having a surface; a plurality of protrusions protruding from the surface and having a distal end forming a supporting surface for the substrate; and an extraction channel, the extraction channel being fluidly connected to the exhaust duct and the space between the surface and the substrate supported by the protrusions to form an exhaust flow path, the method comprising: positioning the substrate on the supporting surface; extracting fluid from the space between the surface and the substrate through the exhaust flow path; and controlling the clamping variables so that the substrate is in full contact with the supporting surface within a substantially predetermined time period.

[0013] According to a second embodiment, a device manufacturing method is provided, comprising: first clamping a substrate having a first radiation-sensitive layer to a first substrate holder of a first lithographic device; performing a first exposure to the radiation-sensitive layer with a first pattern; performing a first processing on the substrate to form a first layer based on the first pattern; second clamping a substrate having a second radiation-sensitive layer to a second substrate holder of a second lithographic device; performing a second exposure to the radiation-sensitive layer with a second pattern; and performing a second processing on the substrate to form a second layer based on the second pattern; wherein the clamping variables applied during the first clamping and the second clamping are determined to minimize the overlap error between the first layer and the second layer.

[0014] According to the present invention, there is also provided a lithographic apparatus comprising a substrate holder.

[0015] Other embodiments, features, and advantages of the present invention, as well as the structure and operation of various embodiments, 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which corresponding reference numerals indicate corresponding parts, and in which:

[0017] Figure 1 A schematic diagram of a lithographic apparatus is depicted;

[0018] Figure 2 depicts a cross section of a portion of a substrate holder of a first embodiment;

[0019] Figure 3 Depicted Figure 2 A plan view of a substrate holder;

[0020] Figure 4depicts a substrate holding system according to a first embodiment;

[0021] Figure 5 is a flow chart of the calibration method in the first embodiment;

[0022] Figure 6 is a flow chart of the clamping method in the first embodiment;

[0023] Figure 7 depicts a model for determining flow settings in a second embodiment;

[0024] Figure 8 Depicted Figure 7 Variations of the model;

[0025] Fig. 9 Depicted Figure 7 Another variation of the model;

[0026] Fig. 10A and Fig. 10B depicts a proportional valve useful in embodiments of the present invention in a closed state (A) and an open state (B); and

[0027] Fig.11 A pneumatic system of an embodiment of the present invention is schematically depicted.

[0028] The features shown in the drawings are not necessarily drawn to scale, and the sizes and / or arrangements depicted are not limiting. It should be understood that the drawings include optional features that may not be essential to the present invention. In addition, not all features of the substrate holder are depicted in each of the drawings, and the drawings may only show some of the components relevant to describing a particular feature. DETAILED DESCRIPTION

[0029] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 436 nm, 405 nm, 365 nm, 248 nm, 193 nm, 157 nm, 126 nm, or 13.5 nm).

[0030] The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to the pattern to be created in a target portion of the substrate. The term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective masks, binary masks, phase-shift masks, hybrid masks, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0031] Figure 1A lithographic apparatus LA is schematically depicted. The lithographic apparatus comprises an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., UV radiation or DUV radiation), a mask support (e.g., mask table) MT configured to support a patterning device (e.g., mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g., substrate table or substrate holder) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate support WT according to certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0032] In operation, the illumination system IL receives a radiation beam B from a radiation source SO, for example via a beam transport system BD. The illumination system IL may include various types of optical components for directing, shaping and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0033] The term "projection system" PS as used herein should be broadly interpreted as covering various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems or any combination thereof, as appropriate for the exposure radiation used, and / or other factors, such as the use of immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0034] The lithographic apparatus may be of a type in which at least a portion of the substrate W may be covered by an immersion liquid having a relatively high refractive index, such as water, so as to fill an immersion space between the projection system PS and the substrate W, which is also referred to as immersion lithography. More information on immersion techniques is given in US 6,952,253, which is incorporated herein by reference.

[0035] The lithographic apparatus may be of a type having two or more substrate supports WT (also known as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or a step of preparing a substrate W for subsequent exposure may be performed on a substrate W on one of the substrate supports WT, while another substrate W on another substrate support WT is being used to expose a pattern on another substrate W.

[0036] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement platform (not depicted in the drawings). The measurement platform is arranged to hold sensors and / or cleaning devices. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measurement platform may hold a plurality of sensors. The cleaning device may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of the system for providing immersion liquid. The measurement platform may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0037] In operation, a radiation beam B is incident on a patterning device (e.g. a mask MA) held on a mask support MT and is patterned by a pattern (design layout) present on the patterning device MA. Having passed through the mask MA, the radiation beam B passes through a 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 the position measurement system PMS, the substrate support WT can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, the first positioning device PM and possibly a further position sensor (the further position sensor not being in position) are arranged to move the substrate support WT accurately. Figure 1 The patterning device MA may be accurately positioned relative to the path of the radiation beam B using the mask alignment marks M1, M2 and the substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 occupy dedicated target portions as illustrated, they may be located in spaces between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe line alignment marks.

[0038] In this application document, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, i.e., an x-axis, a y-axis, and a z-axis. Each of the three axes is orthogonal to the other two axes. A rotation around the x-axis is called an Rx rotation. A rotation around the y-axis is called an Ry rotation. A rotation around the z-axis is called an Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in the vertical direction. The Cartesian coordinate system does not limit the present invention, but is only used for illustration. Alternatively, another coordinate system (such as a cylindrical coordinate system) may be used to illustrate the present invention. The orientation of the Cartesian coordinate system may be different, for example, so that the z-axis has a component along the horizontal plane.

[0039] In a lithographic apparatus, it is necessary to position the upper surface of the substrate to be exposed in the best focus plane of the aerial image of the pattern projected by the projection system with high accuracy. To achieve this, the substrate can be held on a substrate holder. The surface of the substrate holder supporting the substrate can be provided with a plurality of burls, the distal ends of which can be coplanar in a nominal support plane. Although there are many burls, they may be very small in cross-sectional area parallel to the support plane, so that the total cross-sectional area of ​​their distal ends is a few percent of the surface area of ​​the substrate, for example less than 5%. The gas pressure in the space between the substrate holder and the substrate can be reduced relative to the pressure above the substrate to generate a force that clamps the substrate to the substrate holder.

[0040] Figure 2 A partial cross section of a substrate holder 1 of a first embodiment is shown. Figure 3 1 shows a plan view of a substrate holder 1. The substrate holder 1 comprises a body 10 having a surface 11. The body 10 may form an integral part of the substrate holder 1. Figure 2 When positioned as shown, surface 11 can be the top surface of body 10. Therefore, as shown, the top surface can be the upper surface in the Z direction.

[0041] The substrate holder 1 comprises a plurality of support pins 20 connected to the surface 11 of the body 10. In addition, the support pins 20 can be referred to as protuberances, as described above. The plurality of support pins 20 have a proximal end 21 and a distal end 22, wherein the proximal end 21 is located near the body 10 when in place. The distal end 22 is located at the end of the plurality of support pins 20 opposite to the proximal end 21, i.e., at the end of the support pins 20 away from the body 10.

[0042] The plurality of support pins 20 have a central longitudinal axis 23, wherein the proximal end 21 is located at one end of the support pin 20 along the central longitudinal axis 23, and the distal end 22 is located at the other end of the support pin 20 along the central longitudinal axis 23. Therefore, each of the plurality of support pins 20 may have a central longitudinal axis 23 from the proximal end 21 to the distal end 22.

[0043] The distal ends 22 of the plurality of support pins 20 form a support surface for the substrate W. The distal ends 22 of the plurality of support pins 20 may be arranged in a plane. Preferably, the support surface is formed in a substantially flat plane, i.e., the distal surfaces of the support pins 20 may coincide with the flat plane and support the substrate W. This is beneficial because the substrate W may be positioned on the support surface so as to also be substantially flat, which may reduce errors when the substrate W is patterned.

[0044] like Figure 2 and Figure 3As shown, the shape of the plurality of support pins 20 may be generally truncated cone (i.e., truncated cone), or may be conical. Alternatively, the plurality of support pins 20 may be generally cylindrical. The truncated cone support pins 20 may be stronger than cylindrical pins, and therefore less likely to break. Preferably, the plurality of support pins 20 have the same shape as each other.

[0045] The plurality of support pins 20 may be connected to the surface 11 of the body 10 in any suitable manner. The plurality of support pins 20 may be separate components attached to the surface 11 of the body 10. Alternatively, the plurality of support pins 20 may be integrally formed with the body 10. In other words, the plurality of support pins 20 may be formed as protrusions from the surface 11 of the body 10, i.e., the plurality of support pins 20 may be formed as a single component with the body 10.

[0046] The substrate holder 1 may be configured to be able to extract fluid from between a substrate W supported on a support surface and the surface 11. Fluid at the edge of the substrate W may be sucked under the substrate and may flow along the substrate. Figure 2 . When the fluid is extracted, the pressure below the substrate W is reduced relative to the pressure above the substrate W, and the edge of the substrate W will drop toward the substrate holder 1. The substrate W can be clamped by extracting the fluid in the space below the substrate W to provide a reduced relative pressure in the space between the substrate holder 1 and the substrate W.

[0047] The body 10 may include at least one extraction opening 12 through which fluid is extracted. There may be a plurality of extraction openings 12. By way of example only, Figure 3 As shown, there may be three extraction openings 12 (but there may be more or fewer extraction openings).

[0048] When the substrate W is clamped, it is beneficial to reduce the leakage of fluid into the space between the substrate W and the body 10. Therefore, it may be beneficial to provide a physical boundary located near the edge of the substrate holder 1. The physical boundary may be formed towards the edge of the body 10, such as Figure 2 and Figure 3 The physical boundary may be formed by a sealing member 40. The sealing member 40 may be a wall-type protrusion formed around the edge of the body 10 (e.g., around the periphery of the body 10). The sealing member 40 may be formed to provide a seal between the underside of the substrate W and the substrate holder 1 around the edge of the substrate W. The seal provided by the sealing member 40 need not be a complete seal, but may be a partial seal, which reduces the flow of fluid to the space between the substrate holder 1 and the substrate W, but does not eliminate the flow.

[0049] The fixed sealing member 40 may surround the plurality of supporting pins 20. The fixed sealing member 40 may protrude from the surface 11 of the body 10. The fixed sealing member 40 may be connected to the body 10 in any manner. The fixed sealing member 40 may be an integral part of the body 10.

[0050] A pressure sensor (not depicted in the drawings) may be used to measure the pressure between the substrate W and the surface 11 of the body 10. Various sensors are known for measuring the pressure in the space below the substrate W. For example, the pressure sensor disclosed in WO 2017 / 137129 A1 (which is incorporated herein by reference in its entirety) provides an example of a suitable pressure sensor that may be used.

[0051] A flow sensor (not depicted in the drawings) may be used to measure the flow rate of the fluid extracted via the extraction opening 12. Various sensors for measuring the flow rate from the space below the substrate W are known.

[0052] In a first embodiment, a lithographic apparatus may be provided, the lithographic apparatus comprising a substrate holding system as described above. The lithographic apparatus may have the substrate holding system described above and / or with respect to Figure 1 any features shown.

[0053] In a conventional lithographic apparatus, for a given configuration, the flow rate of the gas extracted from the space below the substrate W is predetermined. The lithographic apparatus may have several (e.g., 2 or 3) predetermined flow rates, between which a selection may be made. For example, a known lithographic apparatus allows a selection between 7.0 Nl / min, 2.7 Nl / min, and 1.3 Nl / min, but other flow rates are also possible. For a given configuration, the flow rate is selected to provide a compromise between throughput, average overlap, and overlap variation between substrates. A high flow rate provides increased throughput through a faster clamping process and lower overlap variation between substrates, while a low flow rate provides a smaller average overlap.

[0054] The inventors have determined that for a given evacuation flow rate, changes in the substrate holder will result in changes in the time required to complete the clamping process, resulting in overlap changes. The clamping process can be considered to be completed when the bottom of the substrate contacts the outermost ring protrusion on the substrate holder, thereby achieving full contact with the support surface. The time required to complete the clamping process is referred to as the clamping time in this article. During the clamping process, especially the clamping process of the bowl-shaped substrate, the pressure gradient across the substrate changes over time. This means that during the clamping process, the local stress in the substrate W changes over time. This may cause local changes in the virtual slip (hysteresis) that depends on friction, and may cause local inaccuracies in the substrate position. In other words, the speed at which the clamping is performed affects the clamping behavior and may cause inaccuracies in the substrate position.

[0055] Ideally, the present invention aims to provide greater flexibility in the selection of the evacuation flow rate by providing a proportional valve in the evacuation flow path, and calibrating a specific substrate holder so that the evacuation flow rate can be set to achieve a clamping process within a substantially predetermined time. This means that different flow rates can be set in different lithographic apparatuses when the same configuration is performed on different lithographic apparatuses, and for a lithographic apparatus with two substrate tables, different flow rates can be set depending on which substrate holder 1 and which substrate table the substrate W is being clamped to.

[0056] Experiments and simulations have shown that achieving consistent clamping times results in more consistent overlap between a batch of substrates, allowing compensation for overlap to be performed (e.g., in a subsequent exposure step). It is believed that a consistent clamping process results in more consistent stresses within the clamped substrates, resulting in more consistent substrate deformation. A consistent duration of the clamping process may also have advantages in terms of scheduling activities in a lithographic apparatus.

[0057] Figure 4 , a substrate holding system according to an embodiment of the present invention is depicted in FIG. An exhaust system 50 is connected to the extraction opening 12 via an extraction channel so as to extract fluid from the space between the substrate W and the substrate holder 1. The exhaust system 50 includes a vacuum pump 52 connected to the extraction opening 12 via an exhaust conduit 56. The exhaust conduit 56 and the extraction opening 12 form an exhaust flow path. Other conduits and devices may be included in the exhaust flow path. A proportional valve 51 is disposed in the exhaust flow path, for example, in the exhaust conduit 56, so as to control the flow resistance of the exhaust flow path when the exhaust pump 52 is working, thereby controlling the exhaust flow rate.

[0058] Various types of valves, such as butterfly valves, disk valves, and diaphragm valves, can be used as the proportional valve 51. Ideally, the opening amount of the proportional valve 51 is controlled by an actuator 53. Any suitable type of actuator 53 can be used, such as a piezoelectric actuator, a solenoid, or a stepper motor.

[0059] although Figure 4 Only a single exhaust duct 56 is shown in the figure, but a plurality of parallel branches of the exhaust duct 56 and / or a plurality of extraction openings 12 may be provided to form an exhaust flow path between the exhaust pump 52 and the space between the substrate W and the substrate holder 1. Different branches of the exhaust duct 56 may be provided with respective proportional valves 51 and may have different sizes to increase the range over which the exhaust flow can be controlled.

[0060] Actuator 53 is controlled by controller 54. Controller 54 obtains the set point for (multiple) proportional valve 51 from calibration data memory 55, so that specific substrate holder 1 is used to realize the predetermined clamping time. The process for obtaining calibration data is described below. Ideally, calibration data is obtained from the calibration measurement performed on the actual substrate holder 1 for clamping substrate W for device manufacturing. In some cases, substrate holders can be grouped into groups with similar characteristics (e.g., the type of substrate holder, the type of coating, age, usage), and calibration data obtained from one or more samples of the group can be used. Controller 54 can also consider additional parameters, and calibration data for specific substrate holder 1 to be used, to determine the set point of proportional valve 51, so as to realize the desired predetermined clamping time. Additional parameters can be related to substrate holder 1, such as the length of time from obtaining calibration data or the number of uses of substrate holder 1 from obtaining calibration data, which can take into account the wear of substrate holder 1. Additional parameters may be related to the configuration for the device being manufactured and / or the specific substrate W to be clamped, such as its shape, which may affect the clamping time.

[0061] The shape of the substrate W may be estimated. The estimated shape of the substrate W may be predicted based on previously performed measurements. For example, measurements may be taken of a previously patterned substrate when a particular process is performed or a particular layer is formed. The prediction may be made based on previous measurements, for example by generating an average shape from these measurements. The shape of the substrate W may be measured using at least one sensor (not shown in the figures). Any suitable sensor and / or system for measuring the shape of the substrate W may be used, such as an apparatus for measuring the bow and / or warpage of a substrate W from MTI Instruments, Inc., for example, https: / / www.mtiinstruments.com / applications / wafer-bow-and-warp / Data relating to the measured shape of the substrate W from the sensor may be provided to the controller 54 as feedback.

[0062] Figure 5 The process of obtaining calibration data for the substrate holder 1 is depicted in FIG. The process can be performed in a lithographic apparatus or a device having Figure 4The test bench of the substrate holding system shown is carried out. The substrate W is loaded S1 into the substrate holder 1 in a conventional manner (e.g. using a gripper robot and an e-nail). The proportional valve 51 is set at a set point S2 and the substrate W is clamped S3 by evacuating the space between the substrate holder 1 and the substrate W. The time required to complete the clamping process is determined S4 (e.g. by determining the time when the outermost protuberance 20 is in contact with the substrate W). The calibration data (e.g. including the set point and the time required to complete the clamping process) is stored in association with data identifying the specific substrate holder 1 and / or its related characteristics (e.g., the type of substrate holder, the type of coating, age, amount of use) and optionally data related to the substrate W used (e.g., the degree of warpage and the nature of the backside coating). It is then determined S6 whether sufficient data is available, and if not, the process is repeated with different set points and / or different substrates. The steps of the process do not necessarily need to be performed in the order indicated. For example, S2 can be performed before S1 or in parallel with S1, and S6 can be performed before S5 or in parallel with S5.

[0063] Figure 6 , a clamping process according to an embodiment is depicted in . First, the substrate holder 1 to be used and / or its related features are identified S10. Based on this information, appropriate calibration data is found S11 from the calibration data memory 55. The desired clamping time is determined S12, and the valve set point is determined S13 based on the calibration data, and the proportional valve 51 is set. The substrate W is loaded S14 and clamped S15 by evacuating the space between the substrate holder 1 and the substrate W. The steps of the process do not necessarily need to be performed in the order shown. For example, S10 to S13 can be performed after S14 or in parallel with S14.

[0064] When manufacturing some devices with relatively high features (e.g., DRAM and so-called 3D-NAND), the shape of the substrate W may change significantly between the initial layer and the final layer, such as becoming more warped or changing from a bowl shape to an umbrella shape. The traditional practice is to select the evacuation flow rate according to the shape of the substrate W to be clamped to minimize the deformation. Different evacuation flows may produce different clamping deformation patterns (which are sometimes called "fingerprints"). Therefore, if the shape of the substrate W changes between patterning two layers, different evacuation flows can be selected for clamping to pattern the two layers.

[0065] The inventors have noted that this approach may not be advantageous in all cases. For example, it may be suboptimal in cases where the overlap between a first layer (which is lower in the stack, but not necessarily the first-most layer to be patterned) and a second layer (which is higher in the stack) is important or critical. If the substrate W changes shape between patterning the first layer and patterning the second layer, so that different evacuation flows are selected for these patterning steps, the resulting different clamping deformation patterns may increase the overlay error between the first and second layers.

[0066] Therefore, in a second embodiment, it is proposed to select an evacuation flow and / or an evacuation pressure for clamping the substrate before patterning the first layer and before patterning the second layer together in such a way that the overlay error between the first layer and the second layer is minimized. The selection of the evacuation flow can take into account the expected substrate shape before the two patterning steps and other relevant parameters, such as the substrate holder to be used in each step.

[0067] In a lithographic apparatus having a small number of discrete exhaust flows to choose from, the second embodiment may select the same exhaust flow rate for clamping before two patterning steps, even though this may result in large clamping deformation of one or both of the first and second layers.

[0068] Where a large number of evacuation flow rates can be selected from or the evacuation flow rate can be continuously controlled (e.g., because a proportional valve 51 is provided), the evacuation flow rate used for clamping prior to patterning the first layer may be different from the evacuation flow rate prior to patterning the second layer, but the two flow rates may be more similar than if the two flow rates were selected independently.

[0069] In the second embodiment, it is also desirable to take into account corrections that can be made by other means (e.g., automated process control in the lithographic apparatus). Thus, selection of the evacuation flow rate can be used to minimize overlapped patterns that cannot be corrected by other means. Alternatively, selection of the evacuation flow rate for clamping can be part of an overall control strategy utilizing all controllable parameters of the patterning process.

[0070] Of course, there may be multiple layer pairs in the stack, and overlap is important at this time. Therefore, the optimization method of the second embodiment can be performed multiple times for multiple layer pairs, and the multiple layer pairs can be in any order or can be staggered in the stack. The first layer can be patterned using a first lithographic apparatus, and the second layer can be patterned using a second lithographic apparatus. The second lithographic apparatus can be the same lithographic apparatus as the first lithographic apparatus, or it can be a different lithographic apparatus. In the case of using the same lithographic apparatus for two layers, the first substrate holder and the second substrate holder used can be the same or different.

[0071] Figure 7A system of a second embodiment for determining clamping parameters (such as evacuation flow) for different layers is depicted. The substrate model takes as input a substrate loading shape that is associated with a fingerprint (clamping deformation pattern) and other substrate properties (such as stiffness, thickness, diameter, and backside coating). The substrate holder (WT) model has inputs such as: diameter of substrate W; number of extraction openings 12 (clamping holes); support pin (burl) layout, e-pin position; clamping hole geometry; and support pin (burl) roughness. The substrate model provides substrate parameters, and the substrate holder model provides substrate holder parameters to the flow model. The flow model may have additional inputs such as: number of clamping holes; layout of extraction openings 12 (nozzles) in the substrate holder 1; throughput (TPT) and substrate loading time (timing). The flow model determines the flow settings (e.g., flow and timing) applied to clamp the substrate W before patterning different layers.

[0072] Figure 8 An alternative model for the second embodiment is depicted in . The substrate model takes inputs including: shape, thickness, stiffness and diameter; and the substrate model models the behavior of the substrate W. The inputs to the substrate holder (WT) model include: WT support pin (burl) roughness; number of extraction openings 12 (clamping holes); extraction opening layout; burl layout; E-pin position; geometry of extraction openings 12. The substrate holder model models the behavior of the substrate holder 1 and outputs related parameters. The flow model takes inputs including substrate holder parameters and other parameters such as: extraction hole position; clamping flow; time series of flow; number of extraction openings 12; extraction opening layout; geometry of extraction openings 12. The flow model models the flow of fluid during clamping and its output is provided together with the output of the substrate model to a substrate loading shape model, which predicts the shape that the substrate W adopts when it is loaded on the substrate holder 1. The substrate loading shape, the substrate stage model, and data related to the substrate backside roughness are then used to predict the fingerprint (clamping deformation pattern).

[0073] Fig. 9 Another simpler model of the second embodiment is depicted. The model has a substrate model and a substrate holder model, which provides input to the flow model, which outputs the desired flow settings (also known as yield and time information). The substrate model has inputs of relevant substrate parameters, such as shape, stiffness, and diameter. The inputs to the substrate holder model include substrate diameter, layout of extraction openings 12, and support pin (burl) layout.

[0074] It should be understood that the first and second embodiments may be combined and the flow settings (including flow rates) optimized to provide both consistent clamping time and consistent fingerprints between matching layers.

[0075] In both the first and second embodiments, a curve defining the variation of the flow rate over time may be provided instead of a single set point for the flow rate during the clamping process.

[0076] Fig. 10A and Fig. 10B An example of a proportional valve 51 that may be used with an embodiment of the present invention is shown in FIG. Fig. 10A The proportional valve 51 is shown in a closed configuration, Fig. 10B A proportional valve 51 is shown in an open configuration. In the proportional valve 51, a proportional piezoelectric valve 511 is used to control a control pressure in an input channel 512 connected to a control chamber 513. The control chamber 513 is divided into two isolated parts 513a, 513b by a flexible diaphragm 514, which may be watertight. An input conduit 512 is connected to a first part 513a of the control chamber 513, such that the control pressure controls the position of the flexible diaphragm 514. When the control pressure is high, as in Fig. 10A As shown, the flexible diaphragm 514 is forced into a closed position so that an inlet 515 connected to the evacuation system 50 and a vacuum source (such as, Figure 4 The outlet 517 of the vacuum pump 52 is shown covered. In this configuration, the vacuum source is isolated from the evacuation system 50, so no clamping vacuum is applied in the substrate holder 1.

[0077] If the control pressure is reduced, the flexible diaphragm 514 moves away from the inlet 515 and the outlet 517 so that the fluid communication between the vacuum source and the evacuation system 50 is reestablished. The control pressure is reduced by partially or completely closing the piezoelectric proportional valve 511. The gas in the first part 513a of the control chamber 513 can be discharged (for example, discharged to the atmosphere) through the outlet 516, thereby reducing the pressure in the first part 513a of the control chamber 513. The position of the flexible diaphragm 514 depends on the pressure difference between the first part 513a and the second part 513b of the control chamber 513, any elasticity of the flexible diaphragm 514 and / or any additional biasing device (not shown) that may be provided. Ideally, if the pressures in the first part 513a and the second part 513b of the control chamber 513 are balanced, the flexible diaphragm 514 is biased to a position that fluidly connects the vacuum source to the evacuation system 50 by its own elasticity and / or additional biasing devices. When the flexible diaphragm 514 does not completely block the inlet 515 and the outlet 517, the position of the flexible diaphragm 514 affects the flow resistance between the inlet 515 and the outlet 517, thereby providing a variable flow resistance when the emptying system 50 is emptied by changing the control pressure, and thus a variable clamping pressure can be applied in the emptying system 50.

[0078] The described proportional diaphragm valve has various advantages. In particular, it can operate reliably while incorporated on a substrate stage that experiences high accelerations and may be subject to varying and strong magnetic fields. The flexible diaphragm 514 can be selected to be impermeable to liquids (e.g. water) so that if any immersion liquid is extracted, no damage will occur. High flow rates, e.g. greater than 50 lpm, can be easily accommodated.

[0079] For example, pressure sensors (not shown) may be provided in the first portion 513 a and the second portion 513 b of the control chamber 515 to monitor the proper operation of the proportional valve 51 .

[0080] Fig.11 A simplified schematic diagram of a pneumatic system for controlling the clamping of a substrate is depicted.The pneumatic system comprises several different channels supplying or extracting fluids to or from different parts of the substrate holder 1 .

[0081] The first channel 61 provides clean dry air during substrate loading and is connected to the ambient environment 615 when required. The piezo valve 611 controls the supply of extremely clean dry air (extreme clean dry air, XCDA) to an outlet 616 near the edge of the substrate W to control the edge of the substrate W during loading and unloading operations (known as edge lifting). The piezo valve 613 controls the connection to the ambient environment 615. These valves can be replaced with proportional diaphragm valves as described above to provide additional control over edge lifting and ambient flow, as described in EP22179329.2, which is incorporated herein by reference. Pressure sensors 612, 614 are provided to measure the pressure in the ambient environment and extraction channel to confirm that appropriate operation is being performed.

[0082] The second channel 62 provides extraction near the e-pin 32 under the control of a solenoid valve 623 and is monitored by a pressure sensor 622. Extraction of fluid (e.g., a mixture of liquid and gas) from near the edge of the substrate W is performed through an outlet 628a, which is permanently connected to an extraction vacuum 628b and is monitored by a pressure sensor 627. There is also a connection 626 for a clean dry air supply (e.g., XCDA) monitored by a pressure sensor 625 and a conventional wet vacuum connection 629 monitored by a pressure sensor 624.

[0083] The third channel 63 provides a clamping vacuum to the extraction opening 12 under proportional control provided by the piezo valve 631 and the diaphragm valve 632. A pressure sensor 633 provides monitoring.

[0084] The fourth channel 64 provides proportionally controlled extraction during the loading and unloading process, often referred to as "pre-clamping". Proportional control is provided by a piezo valve 641 and a diaphragm valve 642, while two piezo valves 644 and 645 provide a preset extraction flow rate. Pressure sensors 643, 646 and 647 provide monitoring. The fourth channel 64 is shown as being connected to the extraction opening 12, but may also or alternatively be connected to other dedicated openings (not shown) in the substrate holder 1.

[0085] It will also be appreciated that the principles of the present invention may be applied to lithography tools and clamping systems employing an electrostatic clamp. In this case, other relevant parameters (such as the voltage applied to the electrostatic clamp) may be controlled rather than the flow rate of the evacuation stream.

[0086] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications, such as manufacturing integrated optical systems, guide and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. Those skilled in the art will understand that in the context of such alternative applications, any use of the term "wafer" or "die" herein may be considered synonymous with the more general term "substrate" or "target portion", respectively. The substrates referred to herein may be processed in, for example, a track (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool before or after exposure. Where applicable, the disclosure herein may be applied to these and other substrate processing tools. In addition, the substrate may be processed more than once, for example to form a multi-layer IC, so that the term "substrate" used herein may also refer to a substrate that already contains multiple processed layers.

[0087] Although specific reference may have been made above to the use of embodiments of the present invention in the context of optical lithography, it will be appreciated that the present invention may be used in other applications.

[0088] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0089] The above description is intended to be illustrative rather than limiting. Accordingly, those skilled in the art will appreciate that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A substrate holding system for supporting a substrate, the substrate holding system comprising a substrate holder and an evacuation conduit, wherein: The substrate holder includes: a body having a surface; a plurality of burls protruding from the surface and having distal ends forming a support surface for the substrate; and an extraction channel in fluid communication with the evacuation conduit and a space between the surface and the substrate supported by the burls to form an evacuation flow path; and A proportional valve is provided in the exhaust flow path.

2. A substrate holding system according to claim 1, wherein the exhaust flow path has a first branch and a second branch parallel to the first branch, and the proportional valve is arranged in the first branch, and / or the substrate holding system also includes an actuator, which is connected to the proportional valve and configured to control the opening amount of the proportional valve.

3. The substrate holding system according to claim 2 further includes an additional proportional valve in the second branch, and / or further includes a controller, which is configured to control the actuator during the substrate clamping process so that the time required for the substrate clamping process is substantially equal to a predetermined time period.

4. The substrate holding system of claim 2 or 3, wherein one of the first branch and the second branch is configured to allow a greater flow rate therethrough than the other of the first branch and the second branch.

5. A substrate holding system according to claim 3 or 4, wherein the controller includes a set point storage device, which stores one or more set points for the actuator, ideally, the set points are derived from the calibration of the particular substrate holder.

6. A substrate holding system according to any one of the preceding claims, wherein the proportional valve comprises a diaphragm valve.

7. A lithographic apparatus, comprising the substrate holding system according to any one of claims 1 to 6.

8. A method of clamping a substrate to a substrate holder, wherein the substrate holder comprises: a body having a surface; a plurality of burls projecting from the surface and having distal ends forming a support surface for the substrate; and an extraction channel in fluid communication with the evacuation conduit and a space between the surface and a substrate supported by the burls to form an evacuation flow path, the method comprising: positioning the substrate on the support surface; extracting fluid from the space between the surface and the substrate through the evacuation flow path; and The clamping variables are controlled so that the substrate is in full contact with the support surface for a substantially predetermined period of time.

9. The method of claim 8, wherein the clamping variable is a flow resistance of the evacuation flow path, and optionally, controlling the clamping variable comprises: The position of one or more proportional valves in the purge flow path is controlled.

10. The method according to claim 8 or 9, wherein the controlling comprises: A control set point is looked up in a set point storage device storing one or more set points, ideally representing the position of the one or more proportional valves, ideally derived from a calibration for the particular substrate holder.

11. A computer program for controlling a substrate holding system, the substrate holding system comprising a substrate holder and an evacuation flow path for extracting a fluid from a space between the substrate holder and a substrate, the evacuation flow path having a proportional valve, to perform a clamping method, the method comprising: obtaining a set point associated with the particular substrate holder of the substrate holding system; and The proportional valve is controlled based on the set point.

12. A device manufacturing method, comprising: first clamping a substrate having a first radiation-sensitive layer to a first substrate holder of a first lithographic apparatus; performing a first exposure of the radiation-sensitive layer in a first pattern; performing a first process on the substrate to form a first layer based on the first pattern; secondly clamping the substrate having the second radiation-sensitive layer to a second substrate holder of a second lithographic apparatus; exposing the radiation-sensitive layer to a second pattern; as well as performing a second process on the substrate to form a second layer based on the second pattern; Wherein clamping variables applied during the first clamping and the second clamping are determined to minimize an overlay error between the first layer and the second layer.

13. The method according to claim 12, wherein the clamping variable is an evacuation flow rate, an evacuation pressure, a time of the clamping process or a clamping voltage, and / or wherein the clamping variable is the same during the first clamping and the second clamping.

14. A method according to claim 12 or 13, wherein the clamping variable is determined based on the value of a parameter of the substrate before the first clamping and the value of a parameter of the substrate before the second clamping; optionally, the parameter is selected from the group consisting of substrate shape, substrate warpage, substrate material, substrate stiffness, substrate diameter, substrate back side properties, and / or wherein the clamping variable is determined so that the substrate deformation caused during the first clamping is similar to the substrate deformation caused during the second clamping.

15. The method according to any one of claims 12 to 14, wherein the first lithographic apparatus and the second lithographic apparatus are the same lithographic apparatus, and / or wherein the first substrate holder and the second substrate holder are the same substrate holder.

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