Wafer Bending Measurement System

Abstract

This disclosure provides a metrology system for measuring the curvature of a wafer. For example, the metrology system may include a wafer support configured to position a wafer for wafer curvature measurement, a first light source configured to illuminate a first side of the wafer during the wafer curvature measurement, and a first pinhole mask disposed between the first light source and the wafer support. The first pinhole mask may include a plurality of first pinholes arranged to allow first light from the first light source to pass through and project a plurality of first light spots corresponding to these first pinholes onto the first side of the wafer. The metrology system may also include a first camera arranged to capture images of these first light spots from the first side of the wafer during the wafer curvature measurement.

Description

Cross-references to related applications

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 592,914, filed October 24, 2023, and U.S. Non-Provisional Patent Application No. 18 / 621,827, filed March 29, 2024, which are incorporated herein by reference in their entirety. Technical Field

[0002] This disclosure relates to semiconductor wafer fabrication, and more specifically to a system for measuring the curvature of semiconductor wafers. Background Technology

[0003] The background description provided herein is intended to present the general context of this disclosure. The work of the present inventors, to the extent described in this background section, and aspects of this description that might not have been considered prior art at the time of submission, neither expressly nor implicitly acknowledges that it is prior art to this disclosure.

[0004] Semiconductor wafers require numerous processing steps to form semiconductor devices. During these processing steps, a crucial factor determining the success rate and yield of many steps is the degree of wafer deflating (i.e., out-of-plane bending) before, during, and after the processing steps.

[0005] For example, in wafer-to-wafer bonding (a packaging technology used in the production of microelectronics, microelectromechanical systems (MEMS), nanoelectromechanical systems (NEMS), optoelectronics, etc.), two wafers are bonded together, with the exposed surface of one wafer bonded to the exposed surface of another wafer. These two wafers constitute a semiconductor device or part of a semiconductor device. At the wafer bonding interface, multiple materials may be present, such as dielectric materials and metal interconnects, where the metal interconnects form electrical contacts with matching metal interconnects on the second wafer to be bonded. This bonding process, where multiple materials are present at the bonding interface, is called hybrid bonding.

[0006] The quality of hybrid bonding between two wafers depends on many factors, which can be broadly categorized into wafer characteristics and process conditions. Among the former, wafer flatness, wafer smoothness, wafer cleanliness, and the wafer materials used all affect the final result of the bonding process.

[0007] With the increasing use of hybrid bonding in fabricating heterogeneous devices from multiple wafers and / or chips, ensuring wafer curvature meets specifications before hybrid bonding can significantly reduce the number of bonding defects and improve device yield. Currently, various metrology systems are available for measuring wafer curvature, such as optical interferometers and various types of capacitive sensors. In practice, it is necessary to plot the out-of-plane curvature of the entire wafer, requiring the measurement of out-of-plane displacement at numerous points on the wafer surface. When the number of measurement points per wafer is large, the throughput of most metrology systems decreases significantly; that is, the number of wafers that the metrology system can plot per unit time (e.g., one hour) decreases significantly. This, in turn, leads to a decrease in the overall throughput of the bonding process itself.

[0008] While the previous discussion focused on hybrid bonding, many other semiconductor manufacturing processes also require wafer curvature to be within specified limits, such as various photolithography, patterning, and thin-film processes. Some of these processes utilize active methods to control wafer curvature, which requires measuring the curvature profile of the feed wafer and then measuring the actively controlled wafer curvature profile.

[0009] Therefore, a wafer curvature metrology system is needed that can rapidly generate an out-of-plane curvature map of the entire wafer within a short time. Such a system would be particularly suitable for inclusion in semiconductor processing tools for in-line wafer inspection between processing steps. Furthermore, it would be advantageous if the cost of the in-line metrology system were lower than that of a typical wafer curvature metrology system. A wafer curvature metrology system with high throughput and low cost could also be advantageously used in stand-alone metrology systems. Summary of the Invention

[0010] This disclosure provides a metrology system for measuring the curvature of a wafer. For example, the metrology system may include a wafer support configured to position a wafer for wafer curvature measurement, a first light source configured to illuminate a first side of the wafer during the wafer curvature measurement, and a first pinhole mask disposed between the first light source and the wafer support. The first pinhole mask may include a plurality of first pinholes arranged to allow first light from the first light source to pass through and project a plurality of first light spots corresponding to these first pinholes onto the first side of the wafer. The metrology system may also include a first camera arranged to capture images of these first light spots from the first side of the wafer during the wafer curvature measurement.

[0011] In one embodiment, the metrology system may further include one or more modules configured to process the wafer. In another embodiment, the metrology system may further include a measurement and control system coupled to the first light source and the first camera. The measurement and control system may be configured to measure the wafer curvature of the target wafer by comparing an image of a target light spot captured for the target wafer with an image of a reference light spot captured for a reference wafer. In some embodiments, the first pinholes in the first pinhole mask may be arranged according to a linear pattern. In various embodiments, the first pinholes may be equidistantly spaced in a first direction of the linear pattern and equidistantly spaced in a second direction of the linear pattern. The second direction may be orthogonal to the first direction.

[0012] In one embodiment, the first pinhole mask may include a first opening for transmitting first reflected light from a first side of the wafer to the first camera. For example, the first opening may be centrally located relative to the wafer and the first light spots in the first pinhole mask.

[0013] In one embodiment, the wafer support can orient the wafer horizontally relative to the direction of gravity. In another embodiment, the wafer support can orient the wafer vertically relative to the direction of gravity. In some embodiments, the wafer can be oriented with a certain tilt relative to the vertical direction. In various embodiments, the deviation of this tilt from the vertical orientation can be within 15 degrees.

[0014] In one embodiment, the metrology system may further include a second light source configured to illuminate a second side of the wafer during the wafer curvature measurement. This second side may be opposite to a first side of the wafer. The metrology system may further include a second pinhole mask disposed between the second light source and the wafer support. The second pinhole mask may include a plurality of second pinholes arranged to allow second light from the second light source to pass through and project a plurality of second light spots corresponding to these second pinholes onto the second side of the wafer. The metrology system may further include a second camera configured to capture images of these second light spots from the second side of the wafer during the wafer curvature measurement.

[0015] In one embodiment, the metrology system may further include a wafer flipper configured to receive the wafer from the wafer support, flip the wafer, and return the wafer to the wafer support to perform the wafer curvature measurement on a second side of the wafer. In another embodiment, the wafer support may be configured to flip the wafer and reposition the wafer to perform the wafer curvature measurement on a second side of the wafer. In some embodiments, the metrology system may be configured to perform the wafer curvature measurement in less than 10 seconds. In various embodiments, the metrology system may be configured to calculate the wafer curvature based on images of these first light spots captured by the first camera in less than 30 seconds.

[0016] In one embodiment, the wafer support may support the wafer at its center. In another embodiment, the wafer support may support the wafer at its edge. In some embodiments, the first light source may be further configured to illuminate a second side of the wafer during the wafer curvature measurement, the first pinholes of the first pinhole mask may be further arranged to allow second light from the first light source to pass through and project a plurality of second light spots corresponding to the first pinholes onto the second side of the wafer, the first camera may be further arranged to capture images of the second light spots from the second side of the wafer, and the wafer curvature measurement may be performed on both the first and second sides of the wafer to correct for gravitational effects.

[0017] In an embodiment, the metrology system may further include an alignment system configured to align the wafer on the wafer support for measuring the wafer curvature.

[0018] It should be noted that the Summary of this Exploration does not specify every embodiment and / or additional novel aspect of the invention disclosed herein or claimed. Rather, the Summary provides only a preliminary discussion of different embodiments and corresponding points of novelty. For additional details and / or possible perspectives on the invention and embodiments, the reader is directed to the Detailed Description of this Exploration and the corresponding drawings, which are discussed further below. Attached Figure Description

[0019] Different embodiments of this disclosure presented as examples will be described in detail with reference to the following accompanying drawings, wherein the same reference numerals refer to the same elements, and wherein:

[0020] Figure 1 An exemplary metrology system for measuring wafer curvature according to an embodiment of this disclosure is shown;

[0021] Figure 2 It shows in Figure 1Exemplary pinhole masks used in metering systems according to embodiments of this disclosure;

[0022] Figure 3 It shows in Figure 1 A schematic diagram of an exemplary array of reference and target light spots captured in an image of a wafer during operation of a metrology system according to an embodiment of this disclosure;

[0023] Figure 4 It shows the use of Figure 1 A comparison chart of wafer curvature measured by the metrology system and the standard stand-alone optical interferometry wafer curvature metrology system; and

[0024] Figure 5 Another exemplary metrology system for measuring wafer curvature according to an embodiment of this disclosure is shown. Detailed Implementation

[0025] The following disclosure provides numerous different embodiments or examples for implementing various features of the provided subject matter. Specific examples of components and arrangements are described below to simplify this disclosure. Of course, these are merely examples and are not intended to be limiting. For example, forming a first feature on or on a second feature in the following description may include embodiments where the first and second features are in direct contact, and may also include embodiments where additional features may be formed between the first and second features, such that the first and second features are not in direct contact. Furthermore, reference numerals and / or letters may be repeated in various examples in this disclosure. Such repetition is for simplicity and clarity and does not in itself define the relationship between the various embodiments and / or configurations discussed. Further, for ease of description, spatial relative terms such as “top,” “bottom,” “below,” “under,” “lower,” “above,” “upper,” etc., may be used herein to describe the relationship between one element or feature as shown in the figures and another element or feature. In addition to the orientations depicted in the figures, spatial relative terms are intended to encompass different orientations of the device during use or operation. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and therefore the spatial relative descriptors used herein may also be interpreted accordingly.

[0026] For clarity, the order of discussion of the different steps described herein has been presented. In general, these steps can be performed in any suitable order. Additionally, although each of the different features, techniques, configurations, etc., herein may be discussed in different places within this disclosure, it is intended that each of the concepts can be performed independently of or in combination with each other. Therefore, the invention can be embodied and viewed in many different ways.

[0027] This disclosure relates to a wafer curvature measurement system for achieving high throughput, for example, the wafer curvature measurement system having the ability to plot the wafer curvature of the entire feed wafer in as little as 30 seconds or even less.

[0028] Figure 1 An exemplary (wafer curvature) metrology system 100 for measuring the wafer curvature of wafer 110 during wafer curvature measurement, according to an embodiment of this disclosure, is shown. The metrology system 100 may be part of a stand-alone wafer measurement workstation. Wafer 110 may be held horizontally oriented on wafer support 120 such that gravity exerts an out-of-plane pull on wafer 110 during wafer curvature measurement. In one embodiment, wafer 110 has no wafer curvature and may serve as a reference wafer 110. In another embodiment, wafer 110 has arbitrary and unknown wafer curvature and is the test (or target) wafer 110 whose curvature is to be measured. An alignment system 160 may be included, and this alignment system is used to align wafer 110 on wafer support 120. The diameter of the wafer support 120 can be small, for example, about 30 mm or less, so most of the wafer 110 will be affected by gravity. In addition to the inherent out-of-plane curvature of the wafer 110 itself, gravity may cause the wafer 110 to sag downwards (due to...). Figure 1 (Indicated by the drooping wafer line 110' in the middle).

[0029] In an embodiment, the metering system 100 may use a light source 140 (e.g., a planar light source) to illuminate the wafer 110 through a pinhole mask 130. The planar light source 140 may include an array of optical units, such as LEDs or other suitable discrete point sources or linear light sources, which is equipped with a diffuser or other optical components to make the light intensity distribution on the discrete optical unit array uniform.

[0030] like Figure 2 As shown, an opening 134 can be formed at the center of the light source 140 and the pinhole mask 130 to transmit light reflected from the wafer 110 to a camera 150 mounted above the light source 140, thereby allowing the camera 150 to acquire an image of the entire upper surface of the wafer 110. In an embodiment, a standard CMOS or CCD camera with a resolution of, for example, 4500 × 4500 pixels can be used as the camera 150. Figure 2As shown, the pinhole mask 130 may include a pinhole array 132, which may be drilled in a linear array or other suitable array (e.g., a polar coordinate array, etc.). In embodiments, the linear pinhole array 132 may have equal spacing in both directions, approximately 0.5 mm to 4 mm. In other embodiments, a non-linear pinhole array 132 may be used, the spacing of which is adjusted on the pinhole mask 130 to maintain a substantially uniform density of the pinhole pattern. The diameter of at least one pinhole in the pinhole 132 may be from 50 mm to 1 mm. In some embodiments, one or more modules (e.g., etching modules, developing modules, etc.) configured for processing a wafer (e.g., wafer 110) may be integrated with the metrology system 100 on a common platform.

[0031] During operation of the metrology system 100, the light source 140 projects a spot pattern onto the upper surface of the wafer 110 through the pinhole array 132 of the pinhole mask 130. The sizes of the light source 140 and the pinhole mask 130 can be selected to ensure complete illumination of the wafer 110 with the projected spot pattern. In an embodiment, the diameter of the pinhole mask 130 can be approximately 600 mm (approximately twice the diameter of the wafer 110), and the distance FL between the pinhole mask 130 and the wafer 110 can be set to approximately 400 mm.

[0032] Figure 3 A schematic diagram of an exemplary reference spot array 210 captured in an image of wafer 110 (e.g., reference wafer 110) is shown, acquired by camera 150 during operation of metrology system 100 when a light spot pattern (corresponding to pinhole array 132) is projected by light source 140 onto the upper surface of reference wafer 110 through pinhole array 132 of pinhole mask 130. The reference spots 210 in the image of reference wafer 110 are spaced dx and dy in the two directions X and Y, respectively. For any other wafer (e.g., wafer 110 under test) with arbitrary and unknown wafer curvature (both inherent curvature and additional curvature due to gravity), the projection target spot array 220 of the curved wafer 110 under test will typically be displaced from the reference spot array 210 in the image of reference wafer 110.

[0033] Assuming that the out-of-plane displacement z at the center of wafer 110 (e.g., the wafer under test, which is resting on wafer support 120) is equal to 0, the slope of the out-of-plane displacement z in the X direction can be determined as dz / dx = -(dx – xdz / FL) / FL, where dx is the displacement of the reference spot array 210 in the X direction (i.e., the displacement from the reference spot array 210 to the target spot array 220). Similarly, the slope of the out-of-plane displacement z in the Y direction can be determined as dz / dy = -(dy – ydz / FL) / FL, where dy is the displacement of the reference spot array 210 in the Y direction (i.e., the displacement from the reference spot array 210 to the target spot array 220). The two equations for the slopes of the out-of-plane displacement z in the X and Y directions can be easily and efficiently integrated numerically to produce a distribution on wafer 110 (e.g., the wafer under test), i.e., a graph of the out-of-plane displacement dz(x,y). For a small portion of wafer 110 (e.g., the central portion of wafer 110 corresponding to the opening 134 of the pinhole mask 130), which rests on wafer support 120 and is not illuminated by the spot pattern (corresponding to the pinhole array 132) due to the opening 134, interpolation can be used to determine the wafer curvature.

[0034] To correct for the effects of gravity, after a complete wafer curvature measurement (with the first wafer side of wafer 110 facing upwards), a second measurement can be performed on wafer 110, which has been flipped and placed back on wafer support 120, with the second wafer side of wafer 110 facing upwards. When calculating wafer curvature, the average displacement of the reference spot array 210 in both orientations (i.e., the displacement from the reference spot array 210 to the measurement spot array 220) is used to eliminate the effects of gravity and gravitational sag on the curvature measurement. To facilitate the flipping of wafer 110, wafer support 120 may include means for flipping wafer 110, or a separate wafer flipper 170 may be included in the metrology system 100.

[0035] The operation of the metrology system 100 is controlled by a measurement and control system 180, which is coupled to the wafer support 120, the light source 140, the camera 150, the alignment system 160, and the wafer flipper 170. The wafer support 120 may optionally be equipped with one or more XY, rθ, or similar platforms (not shown) to move the wafer 110 during wafer loading and measurement, if necessary.

[0036] When the camera 150 acquires an image of the wafer 110, conventional image processing methods (such as finding the centroid of the light spot in the acquired image) can be used to determine the position of each light spot in the measurement spot array 220. It has been shown that accurate positioning of the light spots in the image can improve the accuracy of the measured wafer curvature. Further corrections that can be applied to the acquired image may include correction for lens distortion, particularly the barrel distortion inherent in each lens. To perform this correction, an image of a reference plate with an engraved pattern can be acquired, and these images can then be used to correct the pixel positions in the acquired image, thereby correcting the lens distortion. Alternatively, the pinhole mask 130 itself can be detached from its normal position and placed on the wafer support 120 to create a lens distortion-corrected image. In the latter case, an accurate pinhole 132 straight line pattern can act as a set of straight lines, "straightening" the acquired image distorted by the lens of the camera 150. Another type of correction that can be advantageously applied to the acquired image is brightness correction, used to correct for brightness non-uniformity in the image, which may stem from: (a) brightness non-uniformity of light source 140; (b) non-uniform illumination of wafer 110 due to variations in the incident angle of light emitted from pinhole mask 130; and (c) brightness variations due to curvature of wafer 110 (associated with wafer bending), which causes preferential reflection and scattering of light towards and away from camera 150. Brightness correction improves the measured wafer bending data by allowing for more accurate localization of light spots in the acquired image, because reduced variations in image brightness lead to reduced variations in the apparent size of light spots in the acquired image (i.e., reduced expansion and contraction of light spots in different regions of the image), thereby achieving more accurate light spot localization.

[0037] It has been found that the metrology system 100 can capture the desired image of wafer 110 in less than 10 seconds (e.g., about 5 seconds), and can calculate the wafer curvature based on the acquired image in an additional 25 seconds, thus requiring a total of 30 seconds for each wafer curvature measurement. This represents a significant reduction in wafer curvature measurement time compared to conventional wafer curvature metrology systems. Furthermore, as in... Figure 4 As can be seen, the measured wafer curvature is in good agreement with that measured using a standard stand-alone optical interferometry wafer curvature metrology system. However, the process can be completed in only a fraction of the original time, and the cost of metrology system 100 is only a fraction of the cost of optical interferometry system.

[0038] exist Figure 1In the example embodiment shown, the wafer support 120 has a small diameter, resulting in most of the wafer 110 not being supported by the wafer support 120 and being subject to gravity. In addition to the inherent out-of-plane curvature of the wafer itself, gravity may cause the wafer 110 to sag downwards. In some embodiments, the diameter of the wafer support 120 can be large enough to support the entire wafer 110. Therefore, the effects of gravity can be eliminated, and it is not necessary to flip the wafer 110.

[0039] Figure 5 An alternative embodiment of the metrology system 500 is shown, wherein the wafer 310 is oriented vertically, or alternatively, nearly vertically, i.e., deviating from the vertical orientation by less than 15 degrees (e.g., 10 degrees) (not shown). Orienting the wafer 310 in a vertical or nearly vertical orientation reduces or eliminates the effect of gravity on wafer curvature measurement. A major advantage of the metrology system 500 over the metrology system 100 is that it eliminates the need to flip the wafer 310 to eliminate the effects of gravity, resulting in increased throughput due to the elimination of a second measurement. The wafer support 320 will take the form of, for example, a clamp or holder for holding the edge of the wafer 310. The alignment system 360 can still be used to align the wafer 310 on the wafer support 320. The metrology system 300 can be configured to perform single-sided or double-sided wafer curvature measurement by including a single set of pinhole masks 330A, a light source 340A, and a camera 350A, or by adding a second set of pinhole masks 330B, a light source 340B, and a camera 350B, respectively. Using a second set of pinhole masks 330B, light source 340B, and camera 350B allows for simultaneous measurement of wafer curvature on both sides of wafer 310 without flipping wafer 310. This not only increases the throughput of the metrology system but also potentially improves accuracy because it eliminates the need to reposition wafer 310. The single-sided metrology system 300 may include an optional wafer flipper 370 for flipping wafer 310 after wafer curvature measurement on one side, thereby measuring the wafer curvature on the other side of wafer 310. In all other respects, the operation of metrology system 300 is identical to that of metrology system 100, and all image and data processing steps are also exactly the same. Metrology system 300 may be controlled by metrology control system 380, which communicates with wafer support 320, alignment system 360, optional wafer flipper 370, light source 340A, camera 350A, and optionally light source 340B and camera 350B.

[0040] In the foregoing description, specific details, such as the particular geometry of the machining system and the description of the various components and processes used therein, have been set forth. However, it should be understood that the techniques described herein can be practiced in other embodiments departing from these specific details, and such details are for illustrative purposes rather than limiting. The embodiments disclosed herein have been described with reference to the accompanying drawings. Similarly, specific figures, materials, and configurations have been set forth for illustrative purposes to provide a thorough understanding. However, embodiments can be practiced without such specific details. Components having substantially the same functional construction are indicated by similar reference numerals, and therefore any redundant descriptions may be omitted.

[0041] Various techniques have been described as multiple discontinuous operations to aid in understanding the various embodiments. The order of description should not be construed as implying that these operations must be performed in sequence. In fact, these operations do not need to be performed in the presented order. The described operations may be performed in an order different from the order of the described embodiments. In additional embodiments, various additional operations may be performed and / or the described operations may be omitted.

[0042] As used herein, “substrate” or “target substrate” generally refers to the object being processed according to this disclosure. A substrate may include any material portion or structure of a device (particularly a semiconductor or other electronic device) and may be, for example, a base substrate structure (such as a semiconductor wafer, a photomask), or a dielectric layer on or overlying a base substrate structure (such as a thin film). Therefore, a substrate is not limited to any particular base structure, underlying dielectric layer, or overlying dielectric layer, whether patterned or unpatterned, but is contemplated to include any such dielectric layer or base structure, and any combination of dielectric layers and / or base structures. This description may refer to specific types of substrates, but this is for illustrative purposes only.

[0043] Those skilled in the art will also understand that many changes can be made to the operation of the techniques explained above while still achieving the same purpose of this disclosure. The scope of this disclosure is intended to cover such changes. Therefore, the above description of embodiments of the invention is not intended to be limiting. Rather, any limitations on embodiments of the invention are set forth in the appended claims.

Claims

1. A metrology system for measuring the wafer curvature, the metrology system comprising: A wafer support configured to position a wafer for wafer curvature measurement; A first light source is configured to illuminate a first side of the wafer during the wafer curvature measurement; A first pinhole mask is disposed between the first light source and the wafer support. The first pinhole mask includes a plurality of first pinholes, which are arranged to allow first light from the first light source to pass through and project a plurality of first light spots corresponding to the first pinholes in the first pinhole mask onto a first side of the wafer. as well as A first camera is configured to capture images of these first light spots from a first side of the wafer during the wafer curvature measurement.

2. The metering system as claimed in claim 1, further comprising: One or more modules configured to process the wafer.

3. The metering system as described in claim 1, further comprising: A measurement control system coupled to the first light source and the first camera is configured to measure the wafer curvature of the target wafer by comparing an image of a target light spot captured for the target wafer with an image of a reference light spot captured for the reference wafer.

4. The metering system as described in claim 3, wherein, The first pinholes in the first pinhole mask are arranged according to a straight line pattern.

5. The metering system as described in claim 4, wherein, These first pinholes are equidistantly spaced in a first direction of the straight line pattern and equidistantly spaced in a second direction of the straight line pattern, the second direction being orthogonal to the first direction.

6. The metering system as described in claim 1, wherein, The first pinhole mask includes a first opening for transmitting first reflected light from a first side of the wafer to the first camera.

7. The metering system as described in claim 6, wherein, The first opening is located at the center relative to the first light spots in the wafer and the first pinhole mask.

8. The metering system as described in claim 1, wherein, The wafer support orients the wafer in a horizontal position relative to the direction of gravity.

9. The metering system as described in claim 1, wherein, The wafer support orients the wafer in a vertical position relative to the direction of gravity.

10. The metering system as claimed in claim 9, wherein, The wafer is oriented at a certain angle relative to the vertical direction.

11. The metering system as claimed in claim 10, wherein, The deviation of the inclination from the vertical orientation is within 15 degrees.

12. The metering system of claim 1, further comprising: A second light source is configured to illuminate a second side of the wafer, which is opposite to the first side of the wafer, during the wafer curvature measurement. A second pinhole mask is disposed between the second light source and the wafer support. The second pinhole mask includes a plurality of second pinholes, which are arranged to allow second light from the second light source to pass through and project a plurality of second light spots corresponding to the second pinholes in the second pinhole mask onto the second side of the wafer. as well as A second camera is configured to capture images of these second light spots from a second side of the wafer during the wafer curvature measurement.

13. The metering system of claim 1, further comprising: A wafer flipper configured to receive the wafer from the wafer support, flip the wafer, and return the wafer to the wafer support to perform a wafer curvature measurement on a second side of the wafer, the second side being opposite to the first side of the wafer.

14. The metering system as claimed in claim 1, wherein, The wafer support is configured to flip and reposition the wafer to perform wafer curvature measurement on a second side of the wafer, which is opposite to the first side of the wafer.

15. The metrology system of claim 1, wherein the metrology system is configured to perform the wafer curvature measurement in less than 10 seconds.

16. The metrology system of claim 15, wherein the metrology system is configured to calculate the wafer curvature of the wafer in less than 30 seconds based on images of the first light spots captured by the first camera.

17. The metering system as claimed in claim 1, wherein, The wafer support supports the wafer at its center.

18. The metering system as claimed in claim 1, wherein, The wafer support supports the wafer at its edge.

19. The metering system as claimed in claim 1, wherein, The first light source is further configured to illuminate a second side of the wafer, opposite to the first side of the wafer, during the wafer curvature measurement. The first pinholes in the first pinhole mask are further arranged to allow second light from the first light source to pass through and project a plurality of second light spots corresponding to these first pinholes onto the second side of the wafer. The first camera is further arranged to capture images of these second light spots from the second side of the wafer, and The wafer curvature measurement is performed on the first and second sides of the wafer to correct for the effects of gravity.

20. The metering system of claim 1, further comprising: An alignment system configured to align the wafer on the wafer support for measuring the wafer curvature.

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