WO2024193945A1

WO2024193945A1 - System and method for aligning a substrate

Info

Publication number: WO2024193945A1
Application number: PCT/EP2024/054655
Authority: WO
Inventors: Arjan Gijsbertsen; Aart Adrianus VAN BEUZEKOM; Joost LOBBEZOO; Sebastianus Johannes ARTS; Josephus Johannes Petrus VAN AERT
Original assignee: Asml Netherlands B.V.
Priority date: 2023-03-17
Filing date: 2024-02-23
Publication date: 2024-09-26
Also published as: TW202505296A

Abstract

The present disclosure provides a system and a method for aligning a substrate. The system comprises a rotatable support unit movable in a vertical direction; and an alignment support which is co-located with the rotatable support unit. Optionally the alignment support unit at least partially encloses the rotatable support unit.

Description

SYSTEM AND METHOD FOR ALIGNING A SUBSTRATE

CROSS-REFERENCE TO RELATED APLICATION

[0001] The application claims priority of EP application 23162524.5 which was filed on 17 March, 2023 and EP application 23167034.0 which was filed on 06 April, 2023, and which are incorporated herein in their entirety by reference.

FIELD

[0002] The present invention relates to a system and method for aligning a substrate. The system may be regarded as a component for correcting a position of a range of sizes of substrates. The centering of substrates may be processing as part of, for instance, a substrate handler or stage in for instance an exposure apparatus, metrology tool or inspection tool. The substrate may be a wafer, mask or reticle as used in a lithographic process and/or a lithographic apparatus.

BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as “design layout” or “design”) of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually been reduced while the amount of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as ‘Moore’s law’. To keep up with Moore’s law the semiconductor industry is chasing technologies that enable to create increasingly smaller features. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which are patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm and 13.5 nm. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within a range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] During the lithographic process, multiple patterned layers will typically have to be irradiated and deposited on the same substrate. Herein, the substrate (such as a wafer) will typically have to be moved multiple times from a storage location to the irradiation location in the lithographic apparatus. The lithographic apparatus typically includes one or more dedicated substrate handlers to ensure that the movement of the substrates is dealt with a required accuracy. [0006] In a typical lithography arrangement, substrates are transported to the substrate stage of a lithographic projection apparatus via a substrate track and a substrate handler. In the substrate track, the surface of the substrate is pre-treated. The pre-treatment of the substrate may typically include at least partially covering the substrate by a layer of radiation sensitive material (resist). Further, prior to the imaging step, the substrate may undergo various other pre-treatment procedures, such as priming, soft-bake, or thermal conditioning. After the pre-treatment of the substrate, the substrate is transported from the substrate track to the substrate stage via the substrate handler. The substrate handler typically is adapted to accurately position the substrate on the substrate table of the substrate stage and may also control the temperature of the substrate.

[0007] Thus, loading and unloading of wafers onto a wafer table of the lithography machine is supported by a wafer handling (WH) unit. The unit typically includes a pre-alignment (PA) and conditioning unit (conditioning herein may include temperature stabilization) to align and condition the wafers before transferring them. Pre-alignment ensures that the wafers have limited eccentricity and that the temperature profile of the substrate is substantially uniform.

[0008] US-7307695-B2 describes a method and device for alignment of a substrate. The device includes a (pre-)alignment support located near to the edge of a substrate.

[0009] US-2019/0390335 discloses an aligner for a substrate. The aligner is configured to perform a centering operation of moving and rotating the centering stage until the center of the substrate on the centering stage is located on a central axis of a processing stage. The aligner is configured to calculate a distance by which the centering stage is to be moved and an angle through which the centering stage is to be rotated, based on an initial relative position of the central axis of the centering stage with respect to the central axis of the processing stage, the amount of eccentricity, and the eccentricity direction.

[0010] US-1118512-B2 discloses a Stocker comprising an aligner configured to align wafers. The aligner comprises a rotating member configured to align the wafers by supporting and rotating the wafers. Centering members are arranged radially with respect to the rotating member, each being configured to be movable toward the rotating member, and to move the wafer positioned on the rotating member to align a center of the wafer with respect to a center of the rotating member.

[0011] CN- 104111595- A discloses a pre-alignment device used for lithography equipment. The device comprises a centering unit used for bearing a silicon chip to carry out linear movement to compensate the eccentricity of the silicon chip; an orientation unit used for rotating the silicon chip and determining the gap position of the silicon chip; an image acquisition unit used for acquiring the edge and gap information of the silicon chip; and a data processing unit used for processing the acquired information and filtering out interference information in the acquired information. The invention also discloses a pre-alignment method used for the lithography equipment.

[0012] Processing of layers onto a wafer can give rise to stresses which result in warpage of the wafer. Bowl-shaped wafers result in edges that are located too far away from the centering unit. The current pre-alignment (PA) and conditioning units, as exemplified above, cannot handle strongly warped wafers, which limits processing capabilities. The definition of a strongly warped substrate herein may differ per application, but may for instance imply a height differential exceeding about 500 pm over a top surface of the substrate. Typically, for warped substrates, the conventional prealignment units can only operate if thermal conditioning (such as an air bearing) is active. A workaround is to center using a gripper, also known as an end effector, rather than the centering unit, but this is less accurate and much slower, and consequently comes at throughput loss.

[0013] It is an aim of the present disclosure to provide an improved pre-alignment system and method.

SUMMARY

[0014] The disclosure provides a system for aligning a substrate, comprising: a rotatable support unit movable in a vertical direction along its longitudinal axis; and an alignment support which is co-located with the rotatable support unit.

[0015] In an embodiment, the alignment support at least partially encloses the rotatable support unit. The alignment support may circumferentially enclose the rotatable support unit.

[0016] In an embodiment, the alignment support is operatively decoupled from the rotatable support unit.

[0017] In an embodiment, the alignment support is movable in a vertical and a horizontal direction with respect to the rotatable support unit.

[0018] The alignment support may be arranged at a mutual horizontal distance with respect to the rotatable support unit. The mutual horizontal distance may extend circumferentially. The mutual horizontal distance can be of the order of about 0.5 to 2 cm.

[0019] In an embodiment, the alignment support has a top end provided with at least three protrusions for supporting the substrate. The at least three protrusions together may form at least part of a circular shape.

[0020] A top end of the rotatable support unit may be provided with a suction unit to clamp the substrate.

[0021] In an embodiment, the system further comprises a support table for supporting the substrate and having a centrally located opening, wherein the rotatable support unit is moveable in a vertical direction through the centrally located opening.

[0022] In an embodiment, the support table comprises a thermal conditioning unit.

[0023] According to another aspect, the disclosure provides a method for aligning a substrate, the method comprising the steps of: supporting the substrate on rotatable support unit; moving the rotatable support unit in a vertical direction along its longitudinal axis to lift and rotate the substrate to a predetermined orientation; retracting the rotatable support unit; moving an alignment support, which is co-located with the rotatable support unit, in a vertical direction with respect to the rotatable support unit to move the substrate laterally with respect to the rotatable support unit.

[0024] In an embodiment, the alignment support at least partially encloses the rotatable support unit. The alignment support may be arranged at a mutual horizontal distance with respect to the rotatable support unit.

[0025] In an embodiment, the alignment support is operatively decoupled from the rotatable support unit.

[0026] According to yet another aspect, the disclosure provides a method for aligning a substrate, the method comprising the steps of: supporting the substrate on a substrate table having a centrally located opening; moving a rotatable support unit in a vertical direction through the centrally located opening of the support table to lift and rotate the substrate to a predetermined orientation; retracting the rotatable support unit; moving an alignment support, which is co-located with the rotatable support unit, in a vertical direction with respect to the rotatable support unit to move the substrate laterally with respect to the rotatable support unit.

[0027] In an embodiment, the alignment support at least partially encloses the rotatable support unit. The alignment support may be arranged at a mutual horizontal distance with respect to the rotatable support unit.

[0028] In an embodiment, the alignment support is operatively decoupled from the rotatable support unit.

[0029] According to yet another aspect, the disclosure provides a lithographic apparatus, comprising at least one system as described above.

[0030] According to another aspect, the disclosure provides the use of the system as described above in one or more of a metrology tool, an exposure apparatus, a lithographic apparatus, and a substrate handler.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 depicts a schematic overview of a lithographic apparatus;

Figure 2 depicts a cross-sectional side view of an aligner system;

Figure 3 depicts a cross-sectional side view of an embodiment of a system of the disclosure;

Figure 4 depicts a cross-sectional side view of a further embodiment of a system of the disclosure;

Figure 5 depicts a perspective view of an embodiment of a system of the disclosure;

Figure 6 depicts a perspective view of a further embodiment of a system of the disclosure; Figures 7A to 7D depict cross-sectional side views of respective steps of an embodiment of a method according to the disclosure; and

Figures 8A to 8D depict cross-sectional side views of respective steps of a further embodiment of a method according to the disclosure.

DETAILED DESCRIPTION

[0032] In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation. Radiation may include (deep) ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g. having a wavelength in the range of about 5 to 100 nm).

[0033] The term “reticle”, “mask” or “patterning device” as employed in this text may be broadly interpreted as referring to a generic patterning device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate. The term “light valve” can also be used in this context. Besides the classic mask (transmissive or reflective, binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include a programmable mirror array and a programmable LCD array.

[0034] Figure 1 schematically depicts a lithographic apparatus LA. The lithographic apparatus LA includes an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation or EUV radiation), a mask support (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA in accordance with certain parameters, a substrate support (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support in accordance with 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 patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. [0035] In operation, the illumination system IL receives a radiation beam from a radiation source SO, e.g. via a 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, for directing, shaping, and/or controlling radiation. 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 a plane of the patterning device MA.

[0036] The term “projection system” PS used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and/or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and/or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system” PS.

[0037] The lithographic apparatus LA may be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system PS and the substrate W - which is also referred to as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0038] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also named “dual stage”). In such “multiple stage” machine, the substrate supports WT may be used in parallel, and/or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the substrate support WT while another substrate W on the other substrate support WT is being used for exposing a pattern on the other substrate W. [0039] In addition to the substrate support WT, the lithographic apparatus LA may comprise 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 multiple sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example a part of the projection system PS or a part of a system that provides the immersion liquid. The measurement stage may move beneath the projection system PS when the substrate support WT is away from the projection system PS.

[0040] In operation, the radiation beam B is incident on the patterning device, e.g. mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and a position measurement system IF, the substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor (which is not explicitly depicted in Figure 1) may be used to accurately position the patterning device MA with respect to the path of the radiation beam B. Patterning device MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks Pl, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions. Substrate alignment marks Pl, P2 are known as scribe-lane alignment marks when these are located between the target portions C.

[0041] To clarify the invention, 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 referred to as an Rx-rotation. A rotation around the y- axis is referred to as an Ry -rotation. A rotation around about the z-axis is referred to as an Rz-rotation. The x-axis and the y-axis define a horizontal plane, whereas the z-axis is in a vertical direction. The Cartesian coordinate system is not limiting the invention and is used for clarification only. Instead, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane.

[0042] Figure 2 shows a system 10 for aligning a substrate W. The system comprises a support table 12 for supporting the substrate. The table has a centrally located opening 14. A rotatable support unit 16 is movable in vertical direction through the centrally located opening 14 of the support table 14. The table is provided with at least one second opening 18. An alignment support 20 at least partially extends through said second opening 18 and is moveable in radial direction with respect to the rotatable unit 16. An edge support unit 22 may be provided, comprising a sensor 24. The sensor may be a CCD camera or comparable optical sensor.

[0043] A top surface of the support table 12 may be provided with openings 26, 28. The openings 26, 28 may be connected to respective pumps, allowing to expel gas or suck in gas respectively. The first openings 26, connected to a first pump 30 expelling air through the respective openings, allow to create an air bearing allowing the substrate to float on the support table. The second openings 28, connected to a second pump 32 for sucking in air or gas, allow to clamp the substrate to the support table 12 using pressure reduction. The air bearing created by the air expelled out of openings 26 allows the wafer W to be rotated while clamped (for instance due to the vacuum created by openings 28) and conditioned.

[0044] In use, typically, the substrate W is rotated while the edge is measured using the optical sensor 24. Herein, an edge of the substrate may typically be provided with characterizing features, such as a notch, allowing crude positioning based on optical sensing. Using the information provided by the optical sensor 24, the wafer alignment (x, y, Rz) is calculated and can be corrected. The prealigner in the wafer handler may have a measurement accuracy of a few pm. The centering unit 20 moves the wafer in radial direction. The centering unit may have an accuracy in the order of tens of pm. An alignment residue is then measured via the edge scan unit 22 and may be solved at wafer stage level. After the measurement, the substrate W can be rotated using the rotatable unit 16, such that the notch will be directed in a predetermined orientation.

[0045] There are many commercial pre-alignment units for sale from multiple companies, such as Kensington Laboratories, LLC [USA] or Wafer-Handling.com [California, USA].

[0046] The pre-aligner in a practical embodiment may provide high accuracy measurement (few pm), enabling substrate load in the lithographic apparatus LA within the range of the wafer stage positioning system. In other words, accurate orientation at the wafer handler limits errors at the wafer stage and thus increases throughput. Optionally, the support table 12 may include a Thermal Stabilization Unit (TSU). The latter allows to set a temperature profile of the substrate, typically a substantially uniform temperature across the entire substrate, during pre-alignment. [0047] The main disadvantage of the design of Figure 2 is the limited capability to handle warped wafers. Substrates may have a height differential, or warpage, between their highest and lowest point at the top surface of about 350 pm, maybe up to 500 pm at most. In general, clamping substrates having a height differential exceeding 500 pm is difficult. Using additional tricks, it may be able to clamp warped substrates up to 700 pm warpage. In practice however, the substrates may be warped up to 1 mm, with a roadmap for future substrate specifications extending to 1.3 mm. Warped substrates need to be brought into the air bearing and float at a distance of, typically, tens of pm above the surface of the support table 12. For bowl shaped wafers it is particularly difficult to clamp them. Bowl and umbrella shaped substrates may touch the support table while being flattened and clamped. With state of the art hardware, substrates up to 500 pm warpage may be clamped. Wafers that are warped more than said maximum typically fail and lead to a lot of aborted jobs, and thus reduced yield. Note that warped wafers can be rotated and measured when not clamped in the air bearing. However, the centering unit 20 can only move the wafer if it is supported by the air bearing.

[0048] Generally referring to Figure 3, an embodiment of the system 40 of the disclosure comprises a rotatable support unit 44, which is movable in vertical along its longitudinal axis. An alignment support 46 is co-located with the rotatable support unit 44. Co-located is to be understood as sharing a location. Shown in figure 3 in cross-section, alignment support 46 is positioned at least partially around the rotatable support unit 44, so as to at least partially enclose the rotatable support unit. In operation, the alignment support 46 and the rotatable support unit 44 may be decoupled, thus the two may be operatively decoupled.

[0049] The rotatable support unit 44 may be a telescopic support unit, moveable in a vertical direction by virtue of application of over- or under-pressure for example via pneumatic lines, with or without additional air paths to remove contamination. An advantage of a telescopic support unit is that the upper surface of the support unit may be raised to a predetermined level to allow for calibration by sensing or detecting the telescopic support unit. For example, via one or more sensors located on e.g. one or more end effectors, or via a detection signal at a controller.

[0050] In an embodiment, the alignment support 46 comprises a cylindrical section 48. This is illustrated in Figure 5. Said first cylindrical section 48 at least partially encloses a second cylindrical section 50 of the rotatable support unit 44. The cylindrical section 48 of the alignment support at least partly encloses, and preferably circumferentially encloses, the cylindrical section 50 of the rotatable support unit. The cylindrical section 50 of the rotatable support unit can also move in vertical direction, along its longitudinal axis and with respect to the cylindrical section 48 of the alignment support unit 46. The alignment support 46 is movable in vertical direction and horizontal direction with respect to the rotatable support unit 44.

[0051] In an embodiment, the alignment support is arranged at a horizontal distance with respect to the rotatable support unit. In particular, the cylindrical section 48 may be arranged at a lateral or radial distance with respect to the cylindrical section 50 of the rotatable support unit. Said lateral or radial distance, i.e. distance along the horizontal plane, may be in the order of 0.5 to 5 cm, for instance about 1 cm. For instance, said radial distance may be open between the first cylinder 48 and the second cylinder 50, allowing the first cylinder 48 to move in either horizontal direction with respect to said second cylinder within the range set by said radial distance. The mutual horizontal distance may extend circumferentially. The mutual horizontal distance may be in the order of about 0.5 to 2 cm. [0052] The alignment support 46, typically the cylindrical section 48 thereof, can be provided with a top end provided with at least three protrusions 52 for supporting the substrate W. This is illustrated in Figure 6. The at least three protrusions 52 together may constitute at least part of a circular shape.

[0053] A top end 54 of the rotatable support unit 44 can be provided with a suction unit (not shown) to clamp the substrate. The suction unit herein may typically comprise an opening for gas, connected to a third pump. The pump can reduce the pressure by sucking in air or gas, thus reducing the pressure between the opening and the substrate and thereby clamping the substrate to the top end 54 of the rotatable support 44. As an alternative to the aforementioned vacuum clamp mechanism, any other appropriate clamping mechanism such as e.g. electrostatic clamping, may be provided.

[0054] In the aforementioned embodiments, generally illustrated in Figure 3, the centering of a substrate is completely decoupled from any substrate support table or temperature conditioning unit. Accordingly, a substrate may be aligned separately to any conditioning process in preparation for a subsequent processing step, in e.g. a lithographic process.

[0055] Generally referring to Figure 4, in an embodiment of the disclosure, the system 40 further comprises a support table 12 for supporting the substrate W, having a centrally located opening 42. The rotatable support unit 44 is moveable in a vertical direction along its longitudinal axis through the centrally located opening 42. As described in previous embodiments in relation to Figure 3, an alignment support 46 is co-located with the rotatable support unit, and also arranged to move through the centrally located opening 42 of the support table 12, to enable alignment of substrate W.

[0056] Shown in Figure 4 in cross-section, alignment support 46 is positioned at least partially around the rotatable support unit 44, so as to at least partially enclose the rotatable support unit. In operation, the alignment support 46 and the rotatable support unit 44 may be decoupled, thus the two may be operatively decoupled.

[0057] In an embodiment, the rotatable support unit 44 may also be a telescopic support unit as described above.

[0058] In an embodiment, the alignment support 46 comprises a cylindrical section 48 (see Figure 5) extending through the central opening. Said first cylindrical section 48 at least partially encloses a second cylindrical section 50 of the rotatable support unit 44, which also extends through the same opening 42 of the support table 12. The cylindrical section 48 of the alignment support at least partly encloses, and preferably circumferentially encloses, the cylindrical section 50 of the rotatable support unit. The cylindrical section 50 of the rotatable support unit can also move in vertical direction, with respect to the support table 12 and with respect to the cylindrical section 48 of the alignment support unit 46. The alignment support 46 is movable in vertical direction and horizontal direction with respect to the rotatable support unit 44.

[0059] In an embodiment, the alignment support is arranged at a horizontal distance with respect to the rotatable support unit. In particular, the cylindrical section 48 may be arranged at a lateral or radial distance with respect to the cylindrical section 50 of the rotatable support unit. Said lateral or radial distance, i.e. distance along the horizontal plane, may be in the order of 0.5 to 5 cm, for instance about 1 cm. For instance, said radial distance may be open between the first cylinder 48 and the second cylinder 50, allowing the first cylinder 48 to move in either horizontal direction with respect to said second cylinder within the range set by said radial distance. The mutual horizontal distance may extend circumferentially. The mutual horizontal distance may be in the order of about 0.5 to 2 cm. [0060] The alignment support 46, typically the cylindrical section 48 thereof, can be provided with a top end provided with at least three protrusions 52 for supporting the substrate W. This is illustrated in Figure 6. The at least three protrusions 52 together may constitute at least part of a circular shape.

[0061] A top end 54 of the rotatable support unit 44 can be provided with a suction unit (not shown) to clamp the substrate. The suction unit herein may typically comprise an opening for gas, connected to a third pump. The pump can reduce the pressure by sucking in air or gas, thus reducing the pressure between the opening and the substrate and thereby clamping the substrate to the top end 54 of the rotatable support 44. As an alternative to the aforementioned vacuum clamp mechanism, any other appropriate clamping mechanism such as e.g. electrostatic clamping, may be provided.

[0062] Optionally, the substrate table 12 may comprise a thermal conditioning unit. In such an embodiment, the system of the disclosure allows to condition the temperature profile of the substrate while positioning the substrate and preparing for a subsequent processing step in, e.g. a lithographic process.

[0063] The cylindrical sections 48 and 50 of the alignment unit 46 and the rotation unit 44 respectively may be connected to encoder motors 60, 62 respectively. Due to the micrometer scale accuracy required for a lithographic process, the encoder motors 60, 62 are relatively large. As a result, it is relatively difficult to co-locate the respective functions of alignment and rotation. In an embodiment, the first encoder 62 of the rotatable support unit 44 is relatively bulky. The second encoder 60 may be position on top of, or attached to one of the sides of, the first encoder 62. The alignment unit 44 may comprise an arm 64 which is connected to the cylindrical section 48. The second encoder 60 can move the cylindrical section in both vertical and one or more horizontal directions by moving the arm 64.

[0064] It will be appreciated that while the specific examples described herein are directed to cylindrically-shaped features, i.e. a cylindrical rotation unit and a corresponding cylindrical alignment/centering unit, the disclosure herein is not limited to such shapes. Any functional shape, including substantially cuboidal, may be used for an embodiment according to the invention.

[0065] Generally referring to Figures 7A to 7D, a method for aligning a substrate according to the disclosure may comprise the steps of supporting the substrate W on one of the rotatable support unit 44 and the alignment support 46. The support of the substrate W according to the method of this aspect is independent of and thus decoupled from a support table or conditioning unit. In a first step, see Fig. 7A, the alignment unit 44 is in a lowered position, wherein its top surface is disengaged from the substrate.

[0066] The rotation unit 44 rotates the substrate W to a pre-determined orientation. This step may involve edge measurement using the sensor 24 (not illustrated), as described above. When rotating the substrate, the eccentricity of the substrate can be determined.

[0067] Next, see Figure 7B, the alignment support unit 46 is moved upwards, i.e. vertically along its longitudinal axis, until an upper end thereof engages the substrate W. Herein, the upper end(s) of the alignment unit may be provided with respective vacuum openings to clamp the substrate, or any other appropriate alternative clamping means e.g. electrostatic clamping.

[0068] When the alignment unit 46 has suitably engaged the substrate W, the alignment unit moves the substrate W in a horizontal direction in a plane, i.e. laterally with respect to the rotatable unit 44, to correct the eccentricity of the substrate within a set range and accuracy. See Figure 7C. [0069] Subsequently, see Fig. 7D, the alignment unit 46 is lowered with respect to the rotatable unit 44. If required, the rotation (also referred to as orientation) of the substrate may be corrected by rotation of the rotatable unit 44.

[0070] Finally, the system of the disclosure can transfer the substrate W to a subsequent step or unit in the lithographic process. Transfer of the substrate W may involve a griper or end-effector to relocate the substrate.

[0071] Thus, the method of the disclosure may include moving the rotatable support unit in a vertical direction along its longitudinal axis to lift and rotate the substrate to a predetermined orientation. Optionally, the method may include retracting the rotatable support unit. Next, the method includes moving the alignment support, which is co-located with the rotatable support unit, in a vertical direction with respect to the rotatable support unit to enable subsequent movement of the substrate in a horizontal direction, e.g. radially, with respect to the rotatable support unit.

[0072] Generally referring to Figures 8A to 8D, a method for aligning a substrate according to the disclosure may comprise the steps of supporting the substrate W on a support table 12. In a first step, see Fig. 8A, the alignment unit 44 is in a lowered position, wherein its top surface is disengaged from the substrate. Air bearings 26 and/or the vacuum clamping units 28 may typically be activated. [0073] While the substrate is floating on the air bearings 26, the rotation unit 44 rotated the substrate W into a pre-determined orientation. This step may involve edge measurement using the sensor 24, as described above. [0074] Next, see Figure 8B, the alignment support unit 46 is moved upwards with respect to the support table, until an upper end thereof engages the substrate W. Herein, the upper end(s) of the alignment unit may be provided with respective vacuum openings to clamp the substrate. It will be appreciated that any other appropriate clamping mechanism such as e.g. electrostatic clamping, may be provided.

[0075] When the alignment unit 46 has suitably engaged the substrate W, the alignment unit moves the substrate W in a horizontal direction in a plane, i.e. radially with respect to the rotatable unit 44, to correct the eccentricity of the substrate within a set range and accuracy. See Figure 8C. [0076] Subsequently, see Fig. 8D, the alignment unit 46 is lowered with respect to the rotatable unit 44. If required, the rotation (also referred to as orientation) of the substrate may be corrected by rotation of the rotatable unit 44.

[0077] Finally, the system of the disclosure can transfer the substrate W to a subsequent step or unit in the lithographic process.

[0078] Thus, the method of the disclosure may include moving the rotatable support unit in the vertical direction through the centrally located opening of the support table to lift and rotate the substrate to a predetermined orientation. Optionally, the method may include retracting the rotatable support unit. Next, the method includes moving the alignment support, which is co-located with and operatively decoupled from the rotatable support unit, in a vertical direction with respect to the rotatable support unit to enable subsequent movement of the substrate in a horizontal direction, e.g. radially, with respect to the rotatable support unit.

[0079] During pre-alignment according to either of the above methods, a rotation unit clamps onto a substrate to be aligned, and rotates, thereby rotating the substrate. During this rotation, a separate sensor 24 (such as a CCD camera) may scan the substrate edge during rotation to determine eccentricity. The rotation unit 44 then releases the substrate and the centering unit 46 clamps to the substrate, and moves the substrate and TSU relative to each other to correct for the measured eccentricity. The substrate handler is designed to position the substrate within pre-set thresholds on a target location, such as the wafer table. The position thresholds herein typically relate to rotation and eccentricity.

[0080] The centering unit design of the disclosure includes a centering unit which is co-located with the rotatable unit at the center of a support table, where a support table is present. Such a support table may be a conditioning unit, for instance a thermal stabilization unit (TSU). As the arrangement may be used separately from air-bearing based conditioning, any or no support table could be used. Embodiments of the invention without a support table have been described. As an example, a burl table can be used for conditioning, wherein the alignment and conditioning are typically done sequentially. With an air bearing table it can be done in parallel. In the system according to embodiments of the disclosure, the centering unit and rotation unit are co-located but independently operable. [0081] The present centering unit can handle highly warped wafers, as the local angle of warpage is least at such a center location. At the center location, the substrate is relatively flat. The centering unit and rotatable unit engage with the substrate in the center only. Further benefits include a high- accuracy encoder on the centering unit for more accurate measurements. The system may include a leaf spring mechanism for faster actuation.

[0082] In a practical embodiment, the system of the disclosure can handle substrates with warpage exceeding 1000 pm, up to warpage of 2000 pm or even more. Herein, as the substrates are substantially flat in the center, the alignment and rotation units can correctly position virtually any substrate.

[0083] The system and method of the disclosure can be used in, for instance, one or more of a metrology tool, an exposure apparatus, a lithographic apparatus, and a substrate handler.

[0084] Although specific reference may be made in this text to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include 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.

[0085] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.

[0086] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention, where the context allows, is not limited to optical lithography and may be used in other applications, for example imprint lithography.

[0087] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine -readable medium, which may be read and executed by one or more processors. A machine -readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine -readable medium may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g. carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause actuators or other devices to interact with the physical world.

[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. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. A system for aligning a substrate, comprising: a rotatable support unit movable in a vertical direction along its longitudinal axis; and an alignment support which is co-located with the rotatable support unit.

2. The system of claim 1, wherein the alignment support at least partially encloses the rotatable support unit, and/or wherein the alignment support circumferentially encloses the rotatable support unit, and/or wherein the alignment support is operatively decoupled from the rotatable support unit, and/or wherein the alignment support is movable in a vertical and a horizontal direction with respect to the rotatable support unit, and/or the alignment support being arranged at a mutual horizontal distance with respect to the rotatable support unit, desirably wherein the mutual horizontal distance extends circumferentially, or desirably wherein the mutual horizontal distance is in the order of about 0.5 to 2 cm.

3. The system of claim 1 or 2, the alignment support having a top end provided with at least three protrusions for supporting the substrate, desirably the at least three protrusions together forming at least part of a circular shape.

4. The system of any of the preceding claims, a top end of the rotatable support unit being provided with a suction unit to clamp the substrate, and/or further comprising a support table for supporting the substrate and having a centrally located opening, wherein the rotatable support unit is moveable in a vertical direction through the centrally located opening, desirably wherein the support table comprises a thermal conditioning unit.

5. A method for aligning a substrate, the method comprising the steps of: supporting the substrate on a rotatable support unit; moving the rotatable support unit in a vertical direction along its longitudinal axis to lift and rotate the substrate to a predetermined orientation; retracting the rotatable support unit; moving an alignment support, which is co-located with the rotatable support unit, in a vertical direction with respect to the rotatable support unit to move the substrate laterally with respect to the rotatable support unit.

6. The method of claim 5, wherein the alignment support at least partially encloses the rotatable support unit, and/or the alignment support being arranged at a mutual horizontal distance with respect to the rotatable support unit, and/or the alignment support being operatively decoupled from the rotatable support unit.

7. A method for aligning a substrate, the method comprising the steps of: supporting the substrate on a substrate table having a centrally located opening; moving a rotatable support unit in a vertical direction through the centrally located opening of the support table to lift and rotate the substrate to a predetermined orientation; retracting the rotatable support unit; moving an alignment support, which is co-located with the rotatable support unit, in a vertical direction with respect to the rotatable support unit to move the substrate laterally with respect to the rotatable support unit.

8. The method of claim 7, wherein the alignment support at least partially encloses the rotatable support unit, and/or the alignment support being arranged at a mutual horizontal distance with respect to the rotatable support unit, and/or the alignment support being operatively decoupled from the rotatable support unit.

9. A lithographic apparatus, comprising at least one system according to any of claims 1-4.

10. Use of the system of any of claims 1-4 in one or more of a metrology tool, an exposure apparatus, a lithographic apparatus, and a substrate handler.