Board warpage identification system

Abstract

The substrate bow identification system includes at least three first support devices and at least three second support devices forming first and second substrate support areas configured to support a substrate, an actuator configured to vertically move the at least three second support devices, and a controller for driving the actuator, the controller configured to determine a force applied by the actuator, compare the determined force applied by the actuator at a position in the vertical direction of the second substrate support area relative to the first substrate support area with a predetermined force at a predetermined position in the vertical direction of the second substrate support area relative to the first substrate support area, and determine a bow of the substrate from the comparison.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application No. 22166063.2, filed March 31, 2022, the entire contents of which are incorporated by reference herein.

[0002] The present invention relates to a substrate warpage identification system and a lithography apparatus including the substrate warpage identification system. [Background technology]

[0003]

[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 (often called a "design layout" or "design") in a patterning device (e.g., mask) onto a layer of radiation-sensitive material (resist) provided on the substrate (e.g., wafer).

[0004]

[0004] As semiconductor manufacturing processes continue to evolve, the dimensions of circuit elements have been continually scaled down, while the amount of functional elements, such as transistors, per device has been steadily increasing for decades, following a trend colloquially known as "Moore's Law". To accommodate Moore's Law, the semiconductor industry is pursuing technologies that allow it to create smaller and smaller features. To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features that are patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. To form smaller features on a substrate than a lithographic apparatus using radiation with a wavelength of, for example, 193 nm, a lithographic apparatus using extreme ultraviolet (EUV) radiation with a wavelength in the range of 4 nm to 20 nm, for example, 6.7 nm or 13.5 nm, may be used.

[0005]

[0005] A wafer, or more generally a substrate onto which a pattern will be projected, is held on a substrate support such as a wafer table. Preferably, the substrate is flat, so that the projection surface onto which the pattern is projected by the lithographic apparatus is flat. However, the substrate may tend to exhibit some degree of non-flatness, such as warping. Warping may result in non-flatness of the substrate, which may be translated into overlay errors when projecting the pattern onto the substrate. Substrate warping may result from various causes, such as the application of a coating on the surface of the substrate, or other processing steps performed on the surface of the substrate. This warping can be counteracted by clamping the substrate on the substrate table, for example by electrostatic clamping. In contrast, it may be desirable to obtain information about the warping of the substrate before clamping. The deformation of the substrate can be reduced by adjusting the clamping force so that the clamping can flatten the warping of the substrate. Summary of the Invention

[0006]

[0006] In view of the above, the present invention aims to provide a means for measuring the warpage of a substrate.

[0007] According to one embodiment of the present invention, a substrate warpage identification system is provided, the system comprising: at least three first support devices forming a first substrate support area configured to support a substrate; at least three second support devices forming a second substrate support area configured to support a substrate; an actuator configured to vertically move the at least three second support devices; a controller configured to drive the actuator, the controller comprising: -determining the force applied by the actuator; - determining a vertical position of a second substrate support area relative to a first substrate support area; -Drive the actuator a lower position in which the second substrate support area is lower than the first substrate support area in a vertical direction to support a substrate by the first substrate support area; and moving the at least three second support devices from one of an upper position, in which the second substrate support areas are above the first substrate support areas, to another of an upper position and a lower position, in a vertical direction, for supporting the substrate by the second substrate support areas; - determining a force applied by an actuator at a vertical position of the second substrate support area relative to the first substrate support area when the at least three second support devices move from one of a lower position and an upper position to another of a lower position and an upper position; - comparing the determined force applied by the actuator at a vertical position of the second substrate support area relative to the first substrate support area with a predetermined force at a predetermined vertical position of the second substrate support area relative to the first substrate support area; - determining a warpage of the substrate from the comparison.

[0008] According to a further embodiment of the present invention there is provided a lithographic apparatus comprising the substrate bow identification system as described above. [Brief description of the drawings]

[0009]

[0009] An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0010] [Figure 1] 1 is a schematic overview of a lithographic apparatus that may be employed in accordance with an embodiment of the present invention; [Diagram 2] 2 shows a detailed view of a portion of the lithographic apparatus of FIG. 1; [Diagram 3] 2 illustrates generally a position control system as part of a positioning system that may be employed in accordance with an embodiment of the present invention; [Figure 4]1A and 1B are schematic diagrams illustrating a side view of a substrate warpage identification system; [Figure 5A] 1A and 1B are schematic diagrams illustrating a side view of a substrate bow identification system in a continuous state; [Figure 5B] 1A and 1B are schematic diagrams illustrating a side view of a substrate bow identification system in a continuous state; [Figure 5C] 1A and 1B are schematic diagrams illustrating a side view of a substrate bow identification system in a continuous state; [Figure 6A] 1 shows perspective views of a substrate in various positions of a second support device relative to a first support device. [Figure 6B] 1 shows perspective views of a substrate in various positions of a second support device relative to a first support device. [Figure 6C] 1 shows perspective views of a substrate in various positions of a second support device relative to a first support device. [Figure 6D] 1 shows perspective views of a substrate in various positions of a second support device relative to a first support device. [Figure 6E] 1 shows perspective views of a substrate in various positions of a second support device relative to a first support device. [Figure 7] 11 is a graph showing actuator force versus second support device position for various levels of substrate bow. [Figure 8] 13 is another graph showing actuator force versus second support device position at various levels of substrate bow. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011]

[0010] In this specification, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet (e.g., having wavelengths of 365, 248, 193, 157 or 126 nm) and EUV (e.g., extreme ultraviolet radiation having wavelengths in the range of about 5 to 100 nm).

[0012]

[0011] As used herein, the terms "reticle," "mask," or "patterning device" may be broadly interpreted to refer to a general patterning device that can be used to impart an incident radiation beam with a patterned cross-section that corresponds to a pattern to be created on a target portion of a substrate. The term "light valve" may also be used in this context. In addition to typical masks (transmissive or reflective; binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0013] 1 illustrates a lithographic apparatus LA, which includes an illumination system (also called illuminator) IL configured to condition a radiation beam B (e.g. UV, DUV or EUV radiation), a mask support (e.g. mask table) MT constructed to support a patterning device (e.g. mask) MA and coupled to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. wafer table) WT constructed to hold a substrate (e.g. resist coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate support according to certain parameters, and a projection system (e.g. 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.

[0014]

[0013] In operation, the illumination system IL receives a radiation beam from the radiation source SO, for example via the beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, to direct, shape and / or control the radiation. The illuminator IL can be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section in the plane of the patterning device MA.

[0015]

[0014] The term "projection system" PS as used herein should be interpreted broadly as embracing any type of projection system including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optics, or any combination thereof, appropriate for the exposure radiation being used and / or other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" as used herein should be considered as synonymous with the more general term "projection system" PS.

[0016]

[0015] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g. water) so as to fill a space between the projection system PS and the substrate W, which is also referred to as immersion lithography. More detailed information about immersion techniques is found in US Pat. No. 6,952,253, which is incorporated herein by reference.

[0017] The lithographic apparatus LA may be of a type having two or more substrate supports WT (also called dual stage). In such a "multi-stage" machine, multiple substrate supports WT may be used in parallel and / or steps in preparation for a subsequent exposure of a substrate W may be performed on a substrate W located on one of the substrate supports WT, while a pattern is exposed on another substrate W on another substrate support WT using that another substrate support.

[0018]

[0017] In addition to the substrate support WT, the lithographic apparatus LA may include a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold a number 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 a system for providing immersion liquid. When the substrate support WT is away from the projection system PS, the measurement stage may be moved below the projection system PS.

[0019]

[0018] In operation, a radiation beam B is incident on a patterning device (e.g. mask MA) held on a mask support MT and is patterned by a pattern (design layout) on the patterning device MA. After passing through the patterning device MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. Using the second positioner PW and the position measurement system IF, the substrate support WT can be accurately moved, for example to position different target portions C in the path of the radiation beam B at focused and aligned positions. Similarly, the patterning device MA can be accurately positioned with respect to the path of the radiation beam B using the first positioner PM and possibly further position sensors (not explicitly shown in Figure 1). The patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 as illustrated occupy dedicated target portions, they may be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-lane alignment marks.

[0020]

[0019] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely, the x-axis, the y-axis, and the z-axis. Each of the three axes is orthogonal to the other two axes. Rotation about the x-axis is called Rx-rotation. Rotation about the y-axis is called Ry-rotation. Rotation about the z-axis is called Rz-rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is vertical. The Cartesian coordinate system is used for clarity purposes only, without limiting the invention. Instead of Cartesian coordinates, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The Cartesian coordinate system may have a different orientation, for example, the z-axis has a component along the horizontal plane.

[0021]

[0020] Figure 2 shows a more detailed view of a part of the lithographic apparatus LA of Figure 1. The lithographic apparatus LA may be provided with a base frame BF, a balance mass BM, a metrology frame MF, and a vibration isolation system IS. The metrology frame MF supports the projection system PS. In addition, the metrology frame MF may support part of the position measurement system PMS. The metrology frame MF is supported by the base frame BF via the vibration isolation system IS. The vibration isolation system IS is arranged to prevent or reduce the propagation of vibrations from the base frame BF to the metrology frame MF.

[0022]

[0021] The second positioner PW is arranged to accelerate the substrate support WT by providing a driving force between the substrate support WT and the balance mass BM. The driving force accelerates the substrate support WT in a desired direction. Due to conservation of momentum, this driving force is also applied to the balance mass BM with an equal magnitude, but in a direction opposite to said desired direction. Typically, the mass of the balance mass BM is significantly larger than the mass of the second positioner PW and the moving parts of the substrate support WT.

[0023]

[0022] In one embodiment, the second positioner PW is supported by the balance mass BM. For example, the second positioner PW comprises a planar motor for levitating the substrate support WT above the balance mass BM. In another embodiment, the second positioner PW is supported by the base frame BF. For example, the second positioner PW comprises a linear motor, and the second positioner PW comprises a bearing, such as a gas bearing, for levitating the substrate support WT above the base frame BF.

[0024]

[0023] The position measurement system PMS may comprise any type of sensor suitable for determining the position of the substrate support WT. The position measurement system PMS may comprise any type of sensor suitable for determining the position of the mask support MT. The sensor may be an optical sensor, such as an interferometer or an encoder. The position measurement system PMS may comprise a combined interferometer and encoder system. The sensor may be another type of sensor, such as a magnetic sensor, a capacitive sensor, an inductive sensor, etc. The position measurement system PMS may determine the position relative to a reference, for example a metrology frame MF or a projection system PS. The position measurement system PMS may determine the position of the substrate table WT and / or the mask support MT by measuring the position or by measuring a time derivative of the position, such as the velocity or the acceleration.

[0025]

[0024] The position measurement system PMS may comprise an encoder system. Encoder systems are known, for example, from US Patent Application Publication No. 2007 / 00581731 A1, filed 7 September 2006, which is incorporated herein by reference. The encoder system comprises an encoder head, a grating and a sensor. The encoder system may receive a primary radiation beam and a secondary radiation beam. Both the primary radiation beam and the secondary radiation beam originate from the same radiation beam (i.e. the original radiation beam). At least one of the primary radiation beam and the secondary radiation beam is generated by diffracting the original radiation beam by a grating. If both the primary radiation beam and the secondary radiation beam are generated by diffracting the original radiation beam by a grating, the primary radiation beam should have a different diffraction order than the secondary radiation beam. The different diffraction orders are, for example, +1, -1, +2 and -2. The encoder system optically combines the primary radiation beam and the secondary radiation beam into a combined radiation beam. A sensor in the encoder head determines the phase or phase difference of the combined radiation beam. The sensor generates a signal based on the phase or phase difference. The signal represents the position of the encoder head relative to the grating. One of the encoder head and the grating may be located on the substrate structure WT. The other of the encoder head and the grating may be located on the metrology frame MF or the base frame BF. For example, the encoder heads are located on the metrology frame MF while the grating is located on a top surface of the substrate support WT. In another example, the grating is located on a bottom surface of the substrate support WT and the encoder head is located below the substrate support WT.

[0026]

[0025] The position measurement system PMS may comprise an interferometer system. Interferometer systems are known, for example, from US Pat. No. 6,020,964, filed Jul. 13, 1998, which is incorporated herein by reference. The interferometer system may comprise a beam splitter, a mirror, a reference mirror, and a sensor. The radiation beam is split into a reference beam and a measurement beam by the beam splitter. The measurement beam propagates to the mirror and is reflected by the mirror to the beam splitter. The reference beam propagates to the reference mirror and is reflected by the reference mirror to the beam splitter. At the beam splitter, the measurement beam and the reference beam are combined into a combined radiation beam. The combined radiation beam is incident on a sensor. The sensor determines the phase or frequency of the combined radiation beam. The sensor generates a signal based on the phase or frequency. This signal represents the displacement of the mirror. In one embodiment, the mirror is connected to the substrate support WT. The reference mirror may be connected to a metrology frame MF. In one embodiment, the measurement and reference beams are combined into a combined radiation beam by an additional optical component instead of a beam splitter.

[0027]

[0026] The first positioner PM may comprise a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the mask support MT relative to the long-stroke module with high accuracy over a small range of movement. The long-stroke module is arranged to move the short-stroke module relative to the projection system PS with relatively low accuracy over a large range of movement. By combining the long-stroke module and the short-stroke module, the first positioner PM can move the mask support MT relative to the projection system PS with high accuracy over a large range of movement. Similarly, the second positioner PW may comprise a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the substrate support WT relative to the long-stroke module with high accuracy over a small range of movement. The long-stroke module is arranged to move the short-stroke module relative to the projection system PS with relatively low accuracy over a large range of movement. By combining the long-stroke module and the short-stroke module, the second positioner PW can move the substrate support WT relative to the projection system PS with high accuracy over a large range of movement.

[0028]

[0027] The first positioner PM and the second positioner PW are each provided with an actuator for moving the mask support MT and the substrate support WT, respectively. The actuator may be a linear actuator providing a driving force along a single axis, for example the y-axis. Multiple linear actuators may be applied to provide driving forces along multiple axes. The actuator may be a planar actuator providing driving forces along multiple axes. For example, the planar actuator may be arranged to move the substrate support WT in six degrees of freedom. The actuator may be an electromagnetic actuator comprising at least one coil and at least one magnet. The actuator is arranged to move the at least one coil relative to the at least one magnet by applying a current to the at least one coil. The actuator may be a moving magnet type actuator, which has at least one magnet coupled to the mask support MT and the substrate support WT, respectively. The actuator may be a moving coil type actuator, which has at least one coil coupled to the mask support MT and the substrate support WT, respectively. The actuator may be a voice coil actuator, a reluctance actuator, a Lorentz actuator, or a piezo actuator, or any other suitable actuator.

[0029]

[0028] The lithographic apparatus LA comprises a position control system PCS, as shown diagrammatically in Fig. 3. The position control system PCS comprises a setpoint generator SP, a feedforward controller FF, and a feedback controller FB. The position control system PCS provides a drive signal to an actuator ACT. The actuator ACT may be an actuator of the first positioner PM or the second positioner PW. The actuator ACT drives a plant P, which may comprise a substrate support WT or a mask support MT. An output of the plant P is a position quantity, such as a position or a velocity or an acceleration. The position quantity is measured by a position measurement system PMS. The position measurement system PMS generates a signal, which is a position signal representative of a position quantity of the plant P. The setpoint generator SP generates a signal, which is a reference signal representative of a desired position quantity of the plant P. For example, the reference signal represents a desired trajectory of the substrate support WT. The difference between the reference signal and the position signal forms an input to the feedback controller FB. Based on this input, the feedback controller FB provides at least a part of the drive signal for the actuator ACT. The reference signal may form an input to a feedforward controller FF, based on which the feedforward controller FF provides at least a portion of the drive signal for the actuator ACT. The feedforward controller FF may utilize information about dynamic properties such as mass, stiffness, resonant modes, and natural frequencies of the plant P.

[0030]

[0029] FIG. 4 illustrates a substrate W, such as a wafer, supported by a substrate transfer robot SLR. More specifically, the substrate is supported by a first support device FSD, which supports the substrate. The first support device presents an upper surface identified as a first support area FSA. The upper surface of the first support device supports a bottom surface of the substrate W. The first support device FSD is included in a substrate transfer robot. The substrate transfer robot can, for example, load the substrate into a lithographic apparatus. The substrate is also supported by a second support device SSD, which is included in a substrate support WT, such as a wafer table. The substrate support can be included in the lithographic apparatus. The second support device can, for example, be formed by a number of pins extending from the substrate support. The second support device presents an upper surface identified as a second support area SSA. The upper surface of the second support device supports a bottom surface of the substrate.

[0031]

[0030] The substrate support is provided with an actuator ACT configured to move the second support device in a vertical direction. This actuator can be formed by any suitable actuator, such as one or more piezo actuators or linear motors. The actuator is driven by a control device CON, such as a suitably programmed microcontroller, microprocessor or other control device. The control device is further provided with an actuator force magnitude as input, which is representative of the force exerted by the actuator on the substrate via the second support device. The actuator force magnitude can be derived by any suitable method. For example, the control device can measure the current or power supplied to the actuator. The current or power can be representative of the force applied by the actuator on the substrate. In case of an electric motor, such as a linear motor, the actuator force can be proportional to the motor current. In another example, the force exerted by the second support device is measured by a suitable force measuring sensor and a sensor signal representative of the measured force is provided to the control device.

[0032] As will be described below with reference to Figures 5A-5C, the control device is configured to drive the actuator to move the second support device in a vertical direction.

[0033]

[0032] Figures 5A-5C respectively show a substrate, a substrate transport robot, and a substrate support as shown in Figure 4. In Figure 5A, the second support device is in a lower position. That is, the substrate is supported by the first support device, but not by the second support device. Thus, the substrate is supported by the first support area of ​​the first support device. In this example, the force exerted by the actuator on the substrate via the second support device is zero. Thus, the weight of the substrate is supported by the first support device.

[0034]

[0033] As shown in Fig. 5B, when the actuator is driven by the control device to move the second support device upward, the first and second support devices support the substrate. The substrate is supported by the first support area of ​​the first support device and the second support area of ​​the second support device. When the second support device moves upward, the weight of the substrate supported by the second support device gradually increases, so that the actuator force through the second support device tends to increase.

[0035]

[0034] As shown in Figure 5C, when the actuator is further driven by the control device to move the second support device further upward, the second support device supports the substrate while the first support device is released from the substrate. That is, the first support device no longer supports the substrate. The substrate is supported by the second support area of ​​the second support device.

[0036] 6A-6E show perspective views of a substrate supported by first and / or second support devices and exhibiting some degree of warping.

[0037]

[0036] As shown in FIG. 6A, the substrate is supported by three first support devices FSD, more specifically by the first substrate support areas of these first support devices. In this state, the second support devices SSD are released from the substrate. That is, the second support devices SSD do not support the substrate. In this example, the second support surface of the second support devices is 200 micrometers below the first support surface of the first support devices. Due to the warping of the substrate itself and possibly also due to gravity, the substrate shows some degree of warping, so that the bottom of the substrate surface is shown as the deepest point DP. In FIG. 6A-6E, the white lines represent "height lines", i.e., the same amount of deflection of the substrate in the vertical direction is shown by a specific number.

[0038] In FIG. 6B, the actuator has moved the second support device upwards by 100 micrometers, so that the first support device is still supporting the majority of the weight of the substrate.

[0039] 6C, the actuator again moves the second support device upwards by 100 micrometers, so that both the first support area of ​​the first support device and the second support area of ​​the second support device support the weight of the substrate. The substrate tends to flatten to some extent.

[0040] In Figure 6D, the actuator again moves the second support device upwards by 100 micrometers, resulting in an increase in the weight of the substrate being supported by the second support area of ​​the second support device, and the bow and / or deformation of the substrate again changes relative to the bow in Figure 6C.

[0041]

[0040] In Figure 6E, the actuator has again moved the second support device upwards by 100 micrometers, so that the second support area of ​​the second support device supports the substrate while the first support device is released from the substrate.

[0042]

[0041] Thus, in the sequence of Figures 6A to 6E, the top surface of the second support device is at -200 micrometers, -100 micrometers, 0 micrometers, +100 micrometers, and +200 micrometers relative to the top surface of the first support device.

[0043]

[0042] Figure 7 is a graph showing the force exerted by the second support device along the vertical axis of the figure versus the relative position of the second support device relative to the first support device along the horizontal axis of the figure. As with Figures 4, 5A-5C, and 6A-6E, the relative position of the second support device relative to the first support device is understood to be the position of the top surface of the second support device relative to the top surface of the first support device as viewed vertically.

[0044]

[0043] Generally, as the second support device is moved upwards by the actuator, the force from the actuator increases until the entire load of the substrate is supported by the second support device, although the handover between the first and second support devices depends on the bowing of the substrate, as illustrated in Figure 7 and described in more detail below.

[0045]

[0044] Figure 7 shows the (modeled) actuator forces with respect to the position of the top surface of the second support device relative to the position of the top surface of the first support device. At a relative position of 0, the top surfaces of the first and second support devices are at the same level, i.e., at the same vertical height. At a relative position of -100 micrometers, the top surface of the second support device is 100 micrometers below the top surface of the first support device. Correspondingly, at a relative position of +100 micrometers, the top surface of the second support device is 100 micrometers above the top surface of the first support device.

[0046]

[0045] For flat substrates, the takeover of the second support device, i.e. the change in actuator force, tends to occur around the 0 micrometer relative position, as illustrated by curve FL. For umbrella-shaped substrates, i.e. the substrate has an "umbrella-shaped" bow, the change in actuator force tends to occur above the 0 micrometer relative position, as illustrated by curves UM100 and UM200, which represent the actuator force at 100 micrometer and 200 micrometer umbrella shapes, respectively. For bowl-shaped substrates, i.e. the substrate has a "bowl-shaped" bow, the change in actuator force tends to occur below the 0 micrometer relative position, as illustrated by curves BL100 and BL200, which represent the actuator force at 100 micrometer and 200 micrometer bowl shapes, respectively.

[0047] The control device is configured to determine forces applied by the actuators at vertical positions of the second substrate support areas relative to the first substrate support areas when the at least three second support devices move from the lower position to the upper position, the control device being provided with the forces applied (i.e., applied) by the actuators and the positions of the top surfaces of the second support devices relative to the top surface of the first support devices.

[0048]

[0047] The control device is provided with calibration data that allows the bow of the substrate to be derived from the measured forces and positions. For example, the control device is provided with a predetermined force at a predetermined position in the vertical direction of the second substrate support area relative to the first substrate support area. The bow of the substrate can be derived by comparing the determined force applied by the actuator at the position in the vertical direction of the second substrate support area relative to the first substrate support area with the predetermined force at the predetermined position in the vertical direction of the second substrate support area relative to the first substrate support area. For example, if the determined force at the determined position is equal to the determined force at the predetermined position, the bow of the substrate may be the same as the predetermined bow based on which the determined force at the predetermined position was determined. As another example, if the determined force (both at the same position) exceeds the predetermined force, the bow of the substrate may differ from the predetermined bow in that the substrate is more bowl-shaped. In this example, the first support device is positioned closer to the outer periphery of the substrate compared to the second support device. In this case, if the identified force (both at the same vertical position of the second support device relative to the first support device) exceeds the predetermined force, the warp of the substrate may differ from the predetermined warp in that the substrate may be bowl-shaped. In another example, the bow of the substrate may differ from the predetermined bow in that if the specified force is less than the predetermined force (both at the same vertical position of the second support device relative to the first support device), the substrate may be umbrella-shaped. The greater the deviation between the specified force and the predetermined force, the greater the deviation of the shape from the predetermined shape. As described above, the control device thus determines the bow of the substrate from the comparison.

[0049]

[0048] Returning to Fig. 7, the above-mentioned situation where the force exerted by the actuator at a given position is above or below a given force can be illustrated as multiple points (i.e., points showing different forces at the same position) arranged vertically one above the other. Thus, for example, at position 0, the different curves UM200, UM100, FL, BW100, BW200 are arranged above each other.

[0050]

[0049] As another example, such determination can be performed at a predefined force, whereby the control device determines the position at which the actuator force is equal to the predefined force.

[0051]

[0050] For example, if the specified force at a given location is equal to the predetermined force at the given location, the warpage of the substrate may be the same as the predetermined warpage that was the basis for determining the predetermined force at the given location. As another example, if the predetermined force is reached at a location above the given location, the warpage of the substrate may differ from the predetermined warpage in that the substrate is more umbrella-shaped. As another example, if the predetermined force is reached at a location below the given location, the warpage of the substrate may differ from the predetermined warpage in that the substrate is more bowl-shaped. The greater the difference between the specified force and the predetermined force, the greater the difference in shape from the predetermined shape may be.

[0052]

[0051] Returning to Figure 7, the above-mentioned situation where the position is above or below a given position at a given force can be illustrated as points aligned horizontally (i.e., points at the same position indicating different positions). Thus, for example, the different curves UM200, UM100, FL, BW100, BW200 at force 1 are spaced horizontally from each other.

[0053]

[0052] Figure 8 shows another example of the relationship between the (measured) actuator force and the second support device position at various levels of substrate bowing. More specifically, in this example, the second support device is moved upwards at a constant speed. Instead of showing the vertical position of the second support area relative to the first support area, time is shown. In Figure 8, a curve FL based on a flat substrate, a curve BW200 based on a bowl-shaped substrate with a bowing of 200 micrometers, and a curve UM200 based on an umbrella-shaped substrate with a bowing of 200 micrometers are shown. As described above with reference to Figure 7, the determination of bowing can be based on the actuator force and / or the vertical position (i.e., represented by time in this example). For example, the time difference TDIFF represents the time difference to reach a given actuator force.

[0054]

[0053] A 100 micrometer or 200 micrometer bow as in the above example can be understood as the height difference between the center of the substrate (or the other pole in the height direction) and the edge of the substrate. The bow of the substrate can be determined in an undisturbed state (i.e., unaffected by forces such as gravity, clamps, etc.).

[0055] The actuator force applied to the substrate by the secondary support devices may be specified as the sum of forces applied to the substrate by at least three secondary support devices.

[0056]

[0055] The lower position of the second support device can be understood as a position in which the second support device is not supporting a substrate, and the upper position of the second support device can be understood as a position in which the second support device is supporting a substrate.

[0057]

[0056] The control device may be a separate control device, such as a microprocessor or microcontroller with suitable software instructions. The control device may be implemented as software instructions on a microprocessor, microcontroller, or other control device in a multitasking environment.

[0058]

[0057] In accordance with the above example, the controller can be configured to determine the bow of the substrate from a vertical position of the second substrate support area relative to the first substrate support area, where the force applied by the actuator changes when the at least three second support devices move from one of the lower position and the upper position to the other of the lower position and the upper position. Any suitable change in actuator force may be considered. By determining the bow of the substrate from a vertical position of the second substrate support area relative to the first substrate support area, where the force applied by the actuator changes to a predetermined percentage (e.g., 60% to 90%, more preferably 80% of the upper position) of the force applied by the actuator when the at least three second support devices are in the upper position, the bow can be accurately determined.

[0059]

[0058] The position of the second support device can be controlled to change at a constant velocity, whereby the relative position of the second substrate support area is derived from the constant velocity and the time elapsed while moving the second substrate support area.

[0060]

[0059] The above-mentioned determination can be performed by an upward movement (i.e., from a lower position to an upper position) or by a downward movement (i.e., from an upper position to a lower position). When an upward movement is utilized, the determination of the warpage can be derived using a lifting action in which the substrate table lifts the substrate from the substrate transport robot. Thus, the warpage can be determined based on the handling of the substrate performed when loading the substrate. That is, the warpage can be determined without requiring any additional action when loading the substrate. Similarly, as another example, the warpage can also be determined when the substrate is unloaded from the lithographic apparatus by the substrate transport robot. The determined warpage may be used in another tool to which the substrate unloaded from the lithographic apparatus is provided.

[0061]

[0060] As shown in Figures 6A-6E, at least three first support devices may be arranged on a first circle extending in a horizontal plane, and at least three second support devices may be arranged on a second circle extending in a horizontal plane. The inventors have noticed that the warpage of the substrate is mainly circularly symmetric, and therefore, arranging the first and second support devices on the first and second circles, respectively, facilitates the identification of the circular warpage. The diameter of the first circle may be different from the diameter of the second circle, which increases the accuracy of the identification of the warpage. If the second support device is included in a substrate table for lifting the substrate from a substrate transfer robot, a known and existing structure may be applied to support the substrate. Thus, additional hardware may not be required in an existing lithography apparatus.

[0062]

[0061] The first support devices may be distributed such that there is one plane of symmetry. For example, the second support devices may be arranged on a circle such that the angle between the first and second support devices and the angle between the second and third support devices are the same, less than 120° or more than 120°.

[0063]

[0062] The second support devices may be distributed so that there are three planes of symmetry. For example, the second support devices may be arranged on a circle with a mutual angle of 120°. This arrangement of the second support devices makes the shape of the substrate under gravity closer to (axis) symmetry.

[0064]

[0063] The above-mentioned substrate bow identification system may be included in a lithographic apparatus. The lithographic apparatus may further comprise a substrate support configured to hold a substrate and a substrate transport robot configured to load and / or unload the substrate. The at least three first support devices are included in the substrate transport robot and the at least three second support devices are included in the substrate support of the lithographic apparatus. The determination of the bow can be derived when loading or unloading the substrate, i.e. when the substrate table lifts the substrate from the substrate transport robot to load the substrate or when the substrate table transfers the substrate from the substrate support to the substrate transport robot to unload the substrate. Thus, the bow can be determined based on the substrate handling performed when loading or unloading the substrate. That is, no additional actions are required when loading or unloading the substrate. The force and position applied by the actuators are measured when the substrate support lifts the substrate from the substrate transport robot. Comparison with the predetermined force and the predetermined position and the determination of the bow of the substrate can then be performed when the substrate is loaded. For example, the determination of the bow may be performed prior to clamping the substrate on the substrate support. The determined substrate bow may then be used to adjust the clamping force sequence to take the substrate bow into account. The at least three second support devices may be formed by e-pins on the substrate support.

[0065]

[0064] Although specific reference is made in this specification to the use of lithographic apparatus in IC manufacture, it should be understood 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.

[0066]

[0065] Although specific reference has been made herein to embodiments of the invention in the context of 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 objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus may be generally referred to as lithography tools. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0067]

[0066] Although specific reference has 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 is not limited to optical lithography and may be used in other applications, such as imprint lithography, where circumstances permit.

[0068]

[0067] Where circumstances permit, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium and readable and executable 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 a read-only memory (ROM), a random access memory (RAM), a magnetic disk storage medium, an optical storage medium, a flash memory device, or an electrical, optical, acoustic, or other form of propagated signal (e.g., carrier wave, infrared signal, digital signal, etc.). Also, firmware, software, routines, instructions may be described herein as performing certain operations. However, it should be understood that such description is merely for convenience and that such operations are in fact due to a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., thereby enabling an actuator or other device to interact with the material world.

[0069]

[0068] Although specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The foregoing description is intended to be illustrative, not limiting.

Claims

1. A substrate warpage identification system, at least three first support devices forming a first substrate support area configured to support a substrate; at least three second support devices forming a second substrate support area configured to support the substrate; an actuator configured to vertically move the at least three second support devices; a controller configured to drive the actuator, the controller comprising: - determining the force exerted by said actuator; - determining the vertical position of the second substrate support area relative to the first substrate support area; - driving the actuator, a lower position in which the second substrate support area is lower than the first substrate support area in a vertical direction so as to support the substrate by the first substrate support area; and moving the at least three second support devices from one of an upper position, in which the second substrate support area is above the first substrate support area, to the other of the upper position and the lower position, in a vertical direction, for supporting the substrate by the second substrate support area; - determining the forces exerted by the actuators at the positions in the vertical direction of the second substrate support area relative to the first substrate support area when the at least three second support devices move from the one of the lower position and the upper position to the other of the lower position and the upper position; - comparing the determined force applied by the actuator at the position in the vertical direction of the second substrate support area relative to the first substrate support area with a predetermined force at a predetermined position in the vertical direction of the second substrate support area relative to the first substrate support area; - determining a warpage of the substrate from said comparison; Board warpage identification system.

2. 2. The substrate warpage identification system of claim 1, wherein the controller is configured to identify the warpage of the substrate from the position in the vertical direction of the second substrate support area relative to the first substrate support area, where the force applied by the actuators changes when the at least three second support devices move from the one of the lower position and the upper position to the other of the lower position and the upper position.

3. 3. The substrate warpage identification system of claim 2, wherein the controller is configured to identify the warpage of the substrate from the position in the vertical direction of the second substrate support area relative to the first substrate support area, where the force applied by the actuator changes to a predetermined percentage of the force applied by the actuator at the upper position of the at least three second support devices.

4. The substrate warpage identification system according to any one of claims 1 to 3, wherein the predetermined percentage of the force applied by the actuator at the upper position of the at least three second support devices is between 60% and 90%, more preferably 80%.

5. The substrate warpage identification system of any one of claims 2 to 4, wherein the controller is configured to move the at least three second support devices from one of the lower position and the upper position to the other of the lower position and the upper position at a constant speed, and the controller is configured to derive the position of the second substrate support area from the constant speed and a time elapsed while the second substrate support area moves.

6. 6. The substrate warpage identifying system according to claim 1, wherein the one of the lower position and the upper position is the lower position, and the other of the lower position and the upper position is the upper position.

7. The substrate warpage identification system of any one of claims 1 to 6, wherein the at least three first support devices are arranged on a first circle extending in the horizontal plane, and the at least three second support devices are arranged on a second circle extending in the horizontal plane.

8. The system for identifying substrate warpage according to claim 7 , wherein a diameter of the first circle is greater than a diameter of the second circle.

9. The system for identifying substrate warpage according to claim 7 , wherein a diameter of the second circle is greater than a diameter of the first circle.

10. The system for identifying substrate warpage according to any one of claims 7 to 9, wherein the first support devices are distributed such that there is one plane of symmetry.

11. The system for identifying substrate warpage according to any one of claims 7 to 10, wherein the second support devices are distributed such that there are three planes of symmetry.

12. A lithographic apparatus comprising the substrate bow identification system according to any one of the preceding claims.

13. 13. The lithographic apparatus of claim 12, further comprising a substrate support configured to support the substrate and a substrate transport robot configured to load or unload the substrate, wherein the at least three first support devices are comprised in the substrate transport robot and the at least three second support devices are comprised in the substrate support of the lithographic apparatus.

14. 14. The lithographic apparatus of claim 13, wherein the controller is configured to measure the force applied by the actuator when the substrate is transferred from the substrate transport robot to the substrate support or when the substrate is transferred from the substrate support to the substrate transport robot, and to identify the bow of the substrate before clamping the substrate on the substrate support.

15. The lithographic apparatus of claim 14, wherein the at least three second support devices are e-pins of the substrate support.

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