Large size wafer topography measurement device

Abstract

The large-size wafer topography measuring device provided in the application comprises a light source, a beam splitter, a reference mirror, a beam combiner, a detector and a control unit. Parallel light beams emitted by the light source form reference light and test light after being split by the beam splitter. The reference light enters the beam combiner after being reflected by the reference mirror. The test light enters the beam combiner after being reflected by the surface of one side of the wafer to be measured. The beam combiner combines the incident reference light and test light and then converges them to the detector to generate an interference fringe image. The control unit controls the movement of the wafer to be measured and / or the reference mirror to change the optical path difference between the wafer to be measured and the reference mirror, so as to determine the wafer surface topography, improve the test yield and precision of large warping pieces.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and in particular to a large-size wafer morphology measurement device. Background Technology

[0002] In semiconductor manufacturing, wafer morphology inspection is a crucial step, and effective inspection directly affects the quality and performance of the wafer.

[0003] Common methods for inspecting the morphology of large-size wafers include white light interferometry, which offers high accuracy but suffers from a small field of view, requiring multi-field testing and result stitching, leading to stitching errors and low yield. It also limits the testing to a single side. Another method uses a double Fizeau interferometer, allowing simultaneous inspection of both wafer surfaces. This provides comprehensive morphological and dimensional information for the entire wafer in a single test. However, the principle of the Fizeau interferometer dictates a small interference cavity distance between the test and reference surfaces; otherwise, system accuracy will be reduced. Furthermore, the perpendicular incidence of the test light limits the maximum warpage range of the wafer in a single test. Summary of the Invention

[0004] In view of this, the present invention provides a large-size wafer morphology measurement device to improve the measurement accuracy and yield of large-size wafer morphology.

[0005] To solve the above problems, this application adopts the following technical solution:

[0006] One objective of this application is to provide a large-size, large-warpage wafer topography measurement device, comprising:

[0007] A light source, which is used to emit a parallel light beam;

[0008] A first interferometric system, comprising a beam splitter, a reference mirror, a beam combiner, and a detector; and

[0009] The control unit is used to control the movement of the wafer under test and to control the deflection of the wafer under test to a preset tilt angle; wherein:

[0010] The parallel beam emitted from the light source is split by the beam splitter to form a reference beam and a test beam;

[0011] The reference light is reflected by the reference mirror and then enters the beam combiner; the test light is reflected by the surface of one side of the wafer under test and then enters the beam combiner.

[0012] The beam combiner combines the incident reference light and the test light and then focuses them onto the detector, which generates an interference fringe image.

[0013] The control unit controls the movement of the wafer under test and / or the reference mirror to change the optical path difference between the wafer under test and the reference mirror, and determines the surface morphology of the wafer based on the generated interference fringe image.

[0014] In some embodiments, the testing apparatus further includes a stress-free clamping device that vertically clamps the wafer under test, and the control unit can control the movement of the stress-free clamping device to drive the wafer under test to translate and / or deflect.

[0015] In some embodiments, the testing apparatus further includes a wafer stage on which the wafer under test is fixed, and the control unit can control the wafer stage to move to cause the wafer under test to translate and / or deflect.

[0016] In some embodiments, the wafer under test and one of the reference mirrors are moved toward or away from each other.

[0017] In some embodiments, the measuring device further includes a second interference system, which has the same optical path structure as the first interference system and is symmetrically arranged on both sides of the wafer under test.

[0018] In some embodiments, the wafer under test is moved horizontally along the line connecting the two reference mirrors.

[0019] In some embodiments, the light source is a single light source and is split into two laser beams by a beam splitter, which are respectively used as the incident light for the first interference system and the second interference system.

[0020] In some embodiments, the light source is two light sources, which serve as the incident light for the first interference system and the second interference system, respectively.

[0021] In some embodiments, the incident angle of the test light on the wafer under test ranges from 20° to 60°.

[0022] In some embodiments, the wavelength of the parallel beam emitted by the light source can be switched between a first wavelength and a second wavelength, wherein the first wavelength is greater than the second wavelength.

[0023] In some embodiments, the first wavelength is an infrared wavelength, and the second wavelength is a visible or ultraviolet wavelength.

[0024] In some embodiments, the control unit controls the light source to emit a first wavelength beam to obtain the warpage of each sub-region of the wafer under test; divides the wafer into N test regions according to the warpage, and ensures that the warpage of each test region is within the test range of the second wavelength beam, where N is a natural number greater than or equal to 2; the control unit switches the light source to emit a second wavelength beam and sequentially performs morphological measurements on the N test regions.

[0025] In some embodiments, the warpage of the test area of ​​the wafer under test falls within the wavelength test range of the corresponding light beam within a preset tilt angle.

[0026] In some embodiments, the wafer stage deflection angle is determined based on the warpage measured by a first wavelength beam.

[0027] The present application adopts the above technical solution, and its beneficial effects are as follows:

[0028] The large-size wafer morphology measurement device provided in this application splits a parallel beam emitted from a light source into a reference beam and a test beam. The reference beam is reflected by a reference mirror and then enters a beam combiner. The test beam is reflected by the surface of one side of the wafer under test and then enters the beam combiner. The beam combiner combines the incident reference beam and the test beam and then converges them to a detector to generate an interference fringe image. The control unit controls the movement of the wafer under test and / or the reference mirror to change the optical path difference between the wafer under test and the reference mirror, thereby determining the wafer surface morphology and improving the testing yield and accuracy of large warpage wafers. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the structure of the large-size wafer morphology measurement device provided in the embodiments of this application.

[0031] Figure 2 This is a schematic diagram illustrating the generation of the interference fringe image provided in an embodiment of this application.

[0032] Figure 3 This is a schematic diagram illustrating the relationship between the incident angle of light on the wafer under test and the optical path difference, provided in an embodiment of this application.

[0033] Figure 4 This is a flowchart of the steps of the large-size wafer morphology measurement method provided in the embodiments of this application. Detailed Implementation

[0034] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0035] In the description of this application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0038] Please see Figure 1 This is a schematic diagram of the structure of a large-size wafer morphology measurement device provided in an embodiment of this application, including a light source 100, a first interference system 200, and a control unit (not shown). The technical solution for its implementation is described in detail below.

[0039] Light source 100 is used to emit a parallel beam.

[0040] It is understandable that the specific structure of the light source 100 is not limited. It can be a single light source or multiple light sources. The beam emitted from the light source 100 can be split or combined to meet the optical path requirements, thereby ensuring the flexibility of the entire system.

[0041] The first interferometric system 200 includes a beam splitter 210, a reference mirror 220, a beam combiner 230, and a detector 240. The detector 240 can be a charge-coupled device (CCD) or a camera.

[0042] It is understood that the first interference system 200 is not limited to the above-mentioned optical structure. For example, a reflector 250 can be set between the light source 100 and the beam combiner 230, a relay mirror 260 can be set between the beam combiner 230 and the detector 240, or other optical components can be set to fine-tune the optical path. The main optical functions are all within the protection scope of this embodiment.

[0043] The control unit is used to control the movement of the wafer under test 400 and to control the wafer under test to tilt to a preset range of tilt angles. The warpage of the wafer under test within the preset range of tilt angles all fall within the wavelength testing range of the parallel beam emitted by the light source.

[0044] The large-size wafer morphology measurement device provided in the above embodiments of this application operates as follows:

[0045] The parallel beam emitted from the light source 110 is split by the beam splitter 210 to form a reference beam and a test beam;

[0046] The reference light is reflected by the reference mirror 220 and then enters the beam combiner 230. The test light is reflected by the surface of one side of the wafer 400 under test and then enters the beam combiner 230.

[0047] The beam combiner 230 combines the incident reference light and the test light and then focuses them onto the detector 240, which generates an interference fringe image.

[0048] The control unit changes the optical path difference between the wafer under test 400 and the reference mirror 220 by controlling the movement of the wafer under test 400 and / or the reference mirror 220, and determines the surface morphology of the wafer based on the generated interference fringe image.

[0049] Please see Figure 2 This is a schematic diagram illustrating the generation of the interference fringe image provided in this embodiment. Based on the Mach-Zehnder interference principle, the morphological difference between the surface of the tested wafer 400 and the surface of the reference mirror 220 introduces an optical path difference between the reference and test optical paths. When the two beams are combined, interference occurs, and the detector 240 receives the interference fringe image. The control unit controls the movement of the tested wafer 400 and / or the reference mirror 220 to change the optical path difference between the tested wafer 400 and the reference mirror 220. This causes a phase shift in the interference pattern, resulting in a set of interference patterns, from which the surface morphology of the tested silicon wafer can be obtained.

[0050] Please see Figure 3 When the incident angle of light on the wafer 400 under test is θ, and there is angular reflection so that the surface shape of the wafer 400 under test is reflected in the optical path difference, it needs to be multiplied by cosθ. Under the same CCD resolution and wavelength conditions, the vertical range that can be tested increases, and the maximum warpage range of the wafer that can be tested at one time increases accordingly.

[0051] For example, when the incident angle θ is 45°, a 300mm silicon wafer is tested using a 7000x7000 camera with a 633nm test wavelength. Without a tilting system, the maximum testable wafer size is 0.783mm. Using the same 633nm wavelength and camera conditions, a vertically incident interferometer such as a Fiso or Teyman Green can measure a maximum wafer size of 0.554mm. The single-shot warp test range is increased by 41%. The larger the incident angle, the greater the testable warp range. Considering vertical accuracy and spatial layout, the ideal range for the incident angle is between 20° and 60°.

[0052] In this embodiment, the testing apparatus further includes a stress-free clamping device 500 that vertically clamps the wafer 400 under test. The control unit can control the movement of the stress-free clamping device to drive the wafer 400 under test to translate and / or deflect. In this embodiment, the testing apparatus also includes a wafer stage (not shown), on which the wafer 400 under test is fixed. The control unit can control the movement of the wafer stage to drive the wafer 400 under test to translate and / or deflect.

[0053] It is understood that by controlling the movement of the stress-free clamping device and / or the wafer stage through the control unit, the wafer under test 400 is translated, causing one of the wafer under test 400 and the reference mirror 220 to move closer to or away from the other, thereby changing the optical path difference between the wafer under test 400 and the reference mirror 220, and determining the wafer surface morphology based on the generated interference fringe image. The translation of the wafer under test 400 changes the optical path difference between the wafer under test 400 and the reference mirror 220. It is understood that in this embodiment, by controlling the movement of the stress-free clamping device and / or the wafer stage through the control unit, the stress-free clamping device, the transport, and the wafer stage have more movement space, expanding the placement space of the wafer under test 400, removing the distance limitation between the wafer under test 400 and the reference mirror 220, making the adjustment range of the optical path difference between the wafer under test 400 and the reference mirror 220 wider, the testing range larger, and the application scenarios more extensive.

[0054] It is understandable that the wafer under test 400 is deflected to control the wafer under test to be deflected to a preset range of tilt angle, so that the warpage of the wafer under test 400 within the preset range of tilt angle falls within the wavelength test range of the corresponding beam, thereby improving the detection accuracy.

[0055] In this embodiment, the wavelength of the parallel light beam emitted from the light source 110 can be switched between a first wavelength and a second wavelength, with the first wavelength being longer than the second wavelength. For example, the first wavelength is an infrared wavelength, and the second wavelength is a visible or ultraviolet wavelength.

[0056] It is understandable that in practical applications, in order to improve the testing range of the maximum warp of the system without sacrificing vertical sensitivity, this embodiment is designed to use two or more testing wavelengths. The control unit is used to control the wavelength of the laser beam emitted by the light source to switch between the first wavelength and the second wavelength. The control unit also determines the warp of the wafer under test based on the interference fringe image obtained from the first detection, and controls the light source to emit a first wavelength beam and / or a second wavelength beam for a second detection based on the warp amount. Then, the wafer surface topography data is determined based on the interference fringe image obtained from the second detection. Depending on the actual application scenario, for example, based on the warp range or measurement accuracy, it can be divided into small warp measurement mode, high yield measurement mode, high precision measurement mode, and intelligent mode. The following provides a detailed description of the above four modes.

[0057] For a small warped wafer with a pre-determined warp amount of less than or equal to 600 μm, the small warp mode control unit can be used to control the light source 100 to emit a second wavelength beam, directly acquiring the surface morphology of the wafer 400 under test, thus realizing the rapid measurement of high-precision morphology data of the small warped wafer.

[0058] For a large warp wafer with a pre-determined warp amount greater than 600µm, a high-yield mode control unit can be used to control the light source 100 to emit a first wavelength beam, directly acquiring the surface morphology of the wafer 400 under test, thus achieving high-yield measurement of high-precision morphology data for large warp wafers.

[0059] In manufacturing processes that require high precision in wafer surface morphology, a high-precision measurement mode can be adopted. The control unit controls the light source 100 to emit a first wavelength beam to obtain the warpage of the wafer 400 under test based on the interference fringe image obtained from the first detection. Then, the control unit controls the light source 100 to emit a second wavelength beam, and the wafer surface morphology data is determined based on the interference fringe image obtained from the second detection, thereby achieving rapid measurement of high-precision wafer morphology data.

[0060] It should be noted that in practical applications, the control unit can first control the light source 100 to emit a first wavelength beam and then control the light source 100 to emit a second wavelength beam, thereby achieving rapid measurement of high-precision topographic data of the wafer. However, if the overall warpage of the wafer exceeds the testing range of the second wavelength beam, then a partitioning approach can be adopted, as follows:

[0061] First, the control unit controls the light source 100 to emit a first wavelength beam to obtain the warpage amount of each sub-region of the wafer 400 under test. Then, based on the warpage amount, N test regions are divided, and the warpage amount of each test region is placed within the test range of a second wavelength beam, where N is a natural number greater than or equal to 2. The light source is then controlled to emit the second wavelength beam, and the N test regions are measured sequentially to obtain the warpage amount of each test region, thereby achieving rapid measurement of high-precision morphology data of the wafer. The smaller the test region division, the higher the achievable test accuracy.

[0062] Furthermore, in the high-precision measurement mode, after dividing the test area into N test regions based on the warpage, a path is planned, the light source is controlled to emit a second wavelength beam, and the morphology of the N test regions is measured sequentially. By dividing the area and combining it with the path for measurement, high-precision wafer measurement is achieved more scientifically, effectively improving yield and measurement accuracy.

[0063] It is understandable that in the above three measurement modes, the warpage of the wafer 400 under test within the preset tilt angle falls within the wavelength test range of the corresponding beam, thereby ensuring the accuracy of the measurement.

[0064] Furthermore, in practical applications, when no specific mode is specified, the measurement device provided in this embodiment defaults to intelligent mode, i.e., it is configured with at least two different wavelengths, including either the first or second beam wavelength used in the high-yield measurement mode, or the first and second beam wavelengths used in the high-precision measurement mode. A control system can also be configured to adjust the intelligent mode. For example, a longer wavelength can be used preferentially to obtain warpage results. If the warpage is within the maximum testable range of a shorter wavelength, the measurement is switched to a shorter wavelength for morphology measurement. Similarly, a shorter wavelength can be used preferentially for morphology measurement. The control unit controls the light source 100 to emit a second wavelength beam to obtain the warpage amount or range of the wafer 400 under test based on the interference fringe image acquired by the second detection. When the short-wave test results in warpage exceeding the limit, i.e., there is an area where the wafer morphology cannot be detected, the measurement is automatically switched to the first wavelength beam for morphology measurement, further improving measurement yield and testing accuracy.

[0065] Furthermore, in performing the above four measurement modes, it is not limited to using the first wavelength, the second wavelength, or the first wavelength followed by the second wavelength. New wavelengths can be added according to application needs. For example, in high-precision measurement mode, the first wavelength can be used to obtain the warp result, and then the light source can be switched to the second or third wavelength, or even more wavelengths, depending on the warp range. For example, the first wavelength could be infrared, the second visible, and the third ultraviolet. The smaller the wafer warp, the smaller the wavelength can be, thus selecting a suitable wavelength based on the degree of wafer warp. As another example, the wavelength can be selected according to testing requirements. The higher the testing accuracy requirement, the larger the wavelength can be used. The first wavelength can be used to obtain the warp result, and then N test areas can be divided according to the warp amount, ensuring that the warp amount of each test area is within the test range of the required wavelength beam.

[0066] It should be noted that when using the above four testing modes, the selection of wavelength should also take into account the material and process characteristics of the wafer. For example, if the wafer material has a very low reflectivity for certain wavelengths, then the wavelength of light in that band cannot be used for testing.

[0067] Furthermore, the control unit can control the deflection of the wafer stage so that the wafer under test reaches a preset tilt angle, thereby ensuring that the warpage of the wafer under test 400 within the preset tilt angle falls within the wavelength testing range of the corresponding beam.

[0068] Specifically, in the high-yield measurement mode or the small warpage mode, the control unit drives the wafer stage to deflect so that the wafer under test reaches a preset tilt angle. The warpage of the wafer under test 400 within the preset tilt angle falls within the wavelength test range of the first wavelength or the second wavelength. Then, the first wavelength or the second wavelength beam is used for measurement. At this time, the tilt angle of the wafer under test is between 0 degrees and 2 degrees.

[0069] Specifically, in the high-precision measurement mode, the control unit drives the wafer stage to deflect so that the wafer under test reaches a preset tilt angle. After the warpage of the wafer under test 400 within the preset tilt angle falls within the first wavelength test range, it is measured using a beam of the first wavelength. Then, a beam of the second wavelength is used to measure the morphology of the corresponding test area.

[0070] Furthermore, in the high-precision measurement mode, there is another situation where, when the warpage exceeds the maximum range of a single test of the second wavelength, the control unit drives the wafer stage to deflect so that the test area of ​​the wafer under test reaches a preset tilt angle, thereby ensuring that the warpage of each test area is within the test range of the second wavelength beam, and the morphology of the corresponding test area is measured using the second wavelength beam.

[0071] Specifically, the wafer stage is driven to deflect so that the wafer under test reaches the tilt angle corresponding to the first test area, and the morphology is measured using a second wavelength beam; the wafer stage is driven to deflect so that the wafer under test reaches the tilt angle corresponding to the second test area, and the morphology is measured using a second wavelength beam; the wafer stage is driven to deflect so that the wafer under test reaches the tilt angle corresponding to the Nth test area, and the morphology is measured using a second wavelength beam, thereby realizing the zonal measurement of the wafer under test and effectively improving the detection accuracy.

[0072] For example, path planning is performed based on warpage during zonal measurement. First, N test areas are divided according to the warpage and labeled as 1, 2...N; then, the control unit drives the wafer stage to deflect so that the N test areas of the wafer under test reach a preset tilt angle, and the tilt angles corresponding to the N test areas are sequentially labeled as A1, A2...A... N The control unit tilts the first test area of ​​the wafer to a tilt angle of A1, and then uses the second wavelength to measure the morphology; the control unit tilts the second test area of ​​the wafer to a tilt angle of A2, and then uses the second wavelength to measure the morphology; all test areas are completed sequentially according to the path plan, thereby completing the overall measurement of the wafer under test.

[0073] Understandably, in practice, test paths can be planned according to requirements, and measurements can be taken in some test areas. For example, in N test areas, some areas can be tested using high-volume mode, while other areas can be measured using high-precision mode. When using high-precision mode for measurement, the second wavelength can be used directly, or the measurement can be performed according to the partitioned planned path. For specific measurement modes, please refer to the above description, which will not be repeated here.

[0074] It should be noted that traditional Fizeau interferometer systems often use perpendicular reflection to calculate the optical path difference between the silicon wafer surface and the reference mirror surface. To improve the vertical ranging accuracy and reduce errors, a smaller interferometric cavity length is required, which is theoretically the original optical path difference between the two beams. However, if the interferometric cavity distance is too small, the structural space is limited, making it inconvenient to place the wafer under test. Especially for the measurement of wafers with large warpage, it is necessary to coordinate with wafer tilt adjustment for regional measurement and then stitch the measurement results together. In this embodiment, the control unit controls the deflection of the wafer stage or stress-free clamping device, giving the wafer stage or stress-free clamping device more room to move, expanding the placement space of the wafer under test, and further increasing the warpage measurement range of the wafer under test. For wafers under test with the same amount of warpage, compared with tilt measurement by perpendicular incident interferometers such as Fizeau or Thyman Green, the placement space of the wafer under test is larger and the movement is more flexible, effectively reducing the number of times the wafer under test needs to be measured in sections for regional measurement and then stitched together, resulting in higher detection accuracy and efficiency.

[0075] In this embodiment, the measuring device further includes a second interference system 300, which has the same optical path structure as the first interference system 200 and is symmetrically arranged on both sides of the wafer 400 being measured.

[0076] It is understandable that when the optical paths on both sides of the wafer 400 being measured are measured simultaneously, the overall morphological characteristics of the wafer 400 being measured can be obtained based on the coordinate information calibrated by the optical system. These characteristics include, but are not limited to, parameters such as warpage, twist, flatness, thickness, edge roll-off, and nano-morphology.

[0077] It is understood that this embodiment uses a dual-reflection structure, allowing the wafer 400 under test to move horizontally along the line connecting the two reference mirrors. This further removes the distance limitation between the wafer 400 under test and the reference mirrors, giving the stress-free clamping device or wafer stage more room to move, further expanding the placement space of the wafer 400 under test, and further improving the detection accuracy and efficiency.

[0078] It is understood that the reference optical path and the optical path under test designed in this embodiment can have the same optical path length or a specific initial optical path difference can be designed according to system requirements. The methods that can be used include, but are not limited to, using beam splitters or beam splitters of different thicknesses or materials, adding phase delay elements such as phase plates in the optical path, etc., all of which are within the scope of protection of this application.

[0079] In some embodiments, the light source 100 is a single light source and forms two laser beams through a beam splitter, which are respectively used as the incident light of the first interference system 200 and the second interference system 300; or the light source 100 includes two separate sub-light sources, which are respectively used as the incident light of the first interference system 200 and the second interference system 300.

[0080] The large-size wafer morphology measurement device provided in this application splits a parallel beam emitted from a light source into a reference beam and a test beam. The reference beam is reflected by a reference mirror and then enters a beam combiner. The test beam is reflected by the surface of one side of the wafer 400 under test and then enters the beam combiner. The beam combiner combines the incident reference beam and the test beam and then converges them to a detector to generate an interference fringe image. The control unit controls the movement of the wafer 400 under test and / or the reference mirror to change the optical path difference between the wafer 400 under test and the reference mirror, thereby determining the wafer surface morphology and improving the testing yield and accuracy of large warpage wafers.

[0081] Please see Figure 4 This is a flowchart illustrating the steps of a large-size wafer morphology measurement method provided in this application embodiment. Applied to the large-size wafer morphology measurement device provided in any of the above embodiments, it includes the following steps:

[0082] Step S410: The parallel beam emitted from the light source 110 is split by the beam splitter 210 to form a reference beam and a test beam;

[0083] Step S420: The reference light is reflected by the reference mirror 220 and enters the beam combiner 230; the test light is reflected by the surface of one side of the wafer 400 under test and enters the beam combiner 230.

[0084] Step S430: The beam combiner 230 combines the incident reference light and the test light and then focuses them onto the detector 240, which generates an interference fringe image. The control unit controls the movement of the wafer under test 400 and / or the reference mirror 220 to change the optical path difference between the wafer under test 400 and the reference mirror 220, and determines the wafer surface morphology based on the generated interference fringe image.

[0085] It is understood that, according to the Mach-Zehnder interference principle, the morphological difference between the surface of the wafer under test 400 and the surface of the reference mirror 220 will introduce an optical path difference between the reference optical path and the test optical path. After the two beams are combined, interference will occur, and the detector 240 will receive an interference fringe image. The control unit controls the movement of the wafer under test 400 and / or the reference mirror 220 to change the optical path difference between the wafer under test 400 and the reference mirror 220. The interference pattern will undergo a phase shift change, and a set of interference patterns will be obtained, thus obtaining the surface morphology of the silicon wafer under test.

[0086] In this embodiment, the control unit can control the movement of the stress-free clamping device to cause the tested wafer 400 to translate and / or deflect. In this embodiment, the control unit can control the wafer stage and / or the wafer stage to move to cause the tested wafer 400 to translate and / or deflect.

[0087] It is understood that by controlling the movement of the stress-free clamping device and / or the wafer stage by the control unit, the wafer under test 400 is deflected, thereby controlling the wafer under test to be deflected to a preset tilt angle, so that the warpage of the wafer under test 400 within the preset tilt angle falls within the wavelength test range of the corresponding beam.

[0088] It can be understood that by controlling the movement of the stress-free clamping device and / or the wafer stage by the control unit, the wafer under test 400 is translated, so that one of the wafer under test 400 and the reference mirror 220 moves toward or away from the other, thereby changing the optical path difference between the wafer under test 400 and the reference mirror 220, and determining the wafer surface morphology based on the generated interference fringe image.

[0089] It is understood that in this embodiment, the control unit controls the movement of the stress-free clamping device and / or the wafer stage, thereby providing more space for the stress-free clamping device, the transporter, and the wafer stage to move. This expands the placement space of the wafer under test 400, removes the distance limitation between the wafer under test 400 and the reference mirror 220, and allows for a wider range of adjustment of the optical path difference between the wafer under test 400 and the reference mirror 220, resulting in a larger testing range and a wider range of applications.

[0090] In this embodiment, the wavelength of the parallel light beam emitted from the light source 110 can be switched between a first wavelength and a second wavelength, with the first wavelength being longer than the second wavelength. For example, the first wavelength is an infrared wavelength, and the second wavelength is a visible or ultraviolet wavelength.

[0091] It is understandable that in practical applications, in order to improve the test range of the maximum warp of the system without sacrificing vertical sensitivity, this embodiment is designed to use two or more test wavelengths. The first wavelength is an infrared wavelength, and the second wavelength is a visible or ultraviolet wavelength. Depending on the actual application scenario, such as according to the warp range or measurement accuracy, it can be divided into small warp measurement mode, high yield measurement mode, high precision measurement mode and intelligent mode. The above four modes are described in detail below.

[0092] For a small warped wafer with a pre-determined warp amount of less than or equal to 600 μm, the small warp mode control unit can be used to control the light source 100 to emit a second wavelength beam, directly acquiring the surface morphology of the wafer 400 under test, thus realizing the rapid measurement of high-precision morphology data of the small warped wafer.

[0093] For a large warp wafer with a pre-determined warp amount greater than 600µm, a high-yield mode control unit can be used to control the light source 100 to emit a first wavelength beam, directly acquiring the surface morphology of the wafer 400 under test, thus achieving high-yield measurement of high-precision morphology data for large warp wafers.

[0094] In manufacturing processes that require high precision in wafer surface morphology, a high-precision measurement mode can be adopted. The control unit controls the light source 100 to emit a first wavelength beam to obtain the warpage of the wafer 400 under test based on the interference fringe image obtained from the first detection. Then, the control unit controls the light source 100 to emit a second wavelength beam, and the wafer surface morphology data is determined based on the interference fringe image obtained from the second detection, thereby achieving rapid measurement of high-precision wafer morphology data.

[0095] It should be noted that in practical applications, the control unit can first control the light source 100 to emit a first wavelength beam and then control the light source 100 to emit a second wavelength beam, thereby achieving rapid measurement of high-precision topographic data of the wafer. However, if the overall warpage of the wafer exceeds the testing range of the second wavelength beam, then a partitioning approach can be adopted, as follows:

[0096] First, the control unit controls the light source 100 to emit a first wavelength beam to obtain the warpage amount of each sub-region of the wafer 400 under test. Then, based on the warpage amount, N test regions are divided, and the warpage amount of each test region is placed within the test range of a second wavelength beam, where N is a natural number greater than or equal to 2. The light source is then controlled to emit the second wavelength beam, and the N test regions are measured sequentially to obtain the warpage amount of each test region, thereby achieving rapid measurement of high-precision morphology data of the wafer. The smaller the test region division, the higher the achievable test accuracy.

[0097] Furthermore, in the high-precision measurement mode, after dividing the test area into N test regions based on the warpage, a path is planned, the light source is controlled to emit a second wavelength beam, and the morphology of the N test regions is measured sequentially. By dividing the area and combining it with the path for measurement, high-precision wafer measurement is achieved more scientifically, effectively improving yield and measurement accuracy.

[0098] It is understandable that in the above three measurement modes, the warpage of the wafer 400 under test within the preset tilt angle falls within the wavelength test range of the corresponding beam, thereby ensuring the accuracy of the measurement.

[0099] Furthermore, in practical applications, when no specific mode is specified, the measurement device provided in this embodiment defaults to intelligent mode, i.e., it is configured with at least two different wavelengths, including either the first or second beam wavelength used in the high-yield measurement mode, or the first and second beam wavelengths used in the high-precision measurement mode. A control system can also be configured to adjust the intelligent mode. For example, a longer wavelength can be used preferentially to obtain warpage results. If the warpage is within the maximum testable range of a shorter wavelength, the measurement is switched to a shorter wavelength for morphology measurement. Similarly, a shorter wavelength can be used preferentially for morphology measurement. The control unit controls the light source 100 to emit a second wavelength beam to obtain the warpage amount or range of the wafer 400 under test based on the interference fringe image acquired by the second detection. When the short-wave test results in warpage exceeding the limit, i.e., there is an area where the wafer morphology cannot be detected, the measurement is automatically switched to the first wavelength beam for morphology measurement, further improving measurement yield and testing accuracy.

[0100] Furthermore, in performing the above four measurement modes, it is not limited to using the first wavelength, the second wavelength, or the first wavelength followed by the second wavelength. New wavelengths can be added according to application needs. For example, in high-precision measurement mode, the first wavelength can be used to obtain the warp result, and then the light source can be switched to the second or third wavelength, or even more wavelengths, depending on the warp range. For example, the first wavelength could be infrared, the second visible, and the third ultraviolet. The smaller the wafer warp, the smaller the wavelength can be, thus selecting a suitable wavelength based on the degree of wafer warp. As another example, the wavelength can be selected according to testing requirements. The higher the testing accuracy requirement, the larger the wavelength can be used. The first wavelength can be used to obtain the warp result, and then N test areas can be divided according to the warp amount, ensuring that the warp amount of each test area is within the test range of the required wavelength beam.

[0101] It should be noted that when using the above four testing modes, the selection of wavelength should also take into account the material and process characteristics of the wafer. For example, if the wafer material has a very low reflectivity for certain wavelengths, then the wavelength of light in that band cannot be used for testing.

[0102] Furthermore, the control unit can control the deflection of the wafer stage so that the wafer under test reaches a preset tilt angle, thereby ensuring that the warpage of the wafer under test 400 within the preset tilt angle falls within the wavelength testing range of the corresponding beam.

[0103] Specifically, in the high-yield measurement mode or the small warpage mode, the control unit drives the wafer stage to deflect so that the wafer under test reaches a preset tilt angle. The warpage of the wafer under test 400 within the preset tilt angle falls within the wavelength test range of the first wavelength or the second wavelength. Then, the first wavelength or the second wavelength beam is used for measurement. At this time, the tilt angle of the wafer under test is between 0 degrees and 2 degrees.

[0104] Specifically, in the high-precision measurement mode, the control unit drives the wafer stage to deflect so that the wafer under test reaches a preset tilt angle. After the warpage of the wafer under test 400 within the preset tilt angle falls within the first wavelength test range, it is measured using a beam of the first wavelength. Then, a beam of the second wavelength is used to measure the morphology of the corresponding test area.

[0105] Furthermore, in the high-precision measurement mode, there is another situation where, when the warpage exceeds the maximum range of a single test of the second wavelength, the control unit drives the wafer stage to deflect so that the test area of ​​the wafer under test reaches a preset tilt angle, thereby ensuring that the warpage of each test area is within the test range of the second wavelength beam, and the morphology of the corresponding test area is measured using the second wavelength beam.

[0106] Specifically, the wafer stage is driven to deflect so that the wafer under test reaches the tilt angle corresponding to the first test area, and the morphology is measured using a second wavelength beam; the wafer stage is driven to deflect so that the wafer under test reaches the tilt angle corresponding to the second test area, and the morphology is measured using a second wavelength beam; the wafer stage is driven to deflect so that the wafer under test reaches the tilt angle corresponding to the Nth test area, and the morphology is measured using a second wavelength beam, thereby realizing the zonal measurement of the wafer under test and effectively improving the detection accuracy.

[0107] For example, path planning is performed based on warpage during zonal measurement. First, N test areas are divided according to the warpage and labeled as 1, 2...N; then, the control unit drives the wafer stage to deflect so that the N test areas of the wafer under test reach a preset tilt angle, and the tilt angles corresponding to the N test areas are sequentially labeled as A1, A2...A... N The control unit tilts the first test area of ​​the wafer to a tilt angle of A1, and then uses the second wavelength to measure the morphology; the control unit tilts the second test area of ​​the wafer to a tilt angle of A2, and then uses the second wavelength to measure the morphology; all test areas are completed sequentially according to the path plan, thereby completing the overall measurement of the wafer under test.

[0108] Understandably, in practice, test paths can be planned according to requirements, and measurements can be taken in some test areas. For example, in N test areas, some areas can be tested using high-volume mode, while other areas can be measured using high-precision mode. When using high-precision mode for measurement, the second wavelength can be used directly, or the measurement can be performed according to the partitioned planned path. For specific measurement modes, please refer to the above description, which will not be repeated here.

[0109] It should be noted that traditional Fizeau interferometer systems often use perpendicular reflection to calculate the optical path difference between the silicon wafer surface and the reference mirror surface. To improve the vertical ranging accuracy and reduce errors, a smaller interferometric cavity length is required, which is theoretically the original optical path difference between the two beams. However, if the interferometric cavity distance is too small, the structural space is limited, making it inconvenient to place the wafer under test. Especially for the measurement of wafers with large warpage, it is necessary to coordinate with wafer tilt adjustment for regional measurement and then stitch the measurement results together. In this embodiment, the control unit controls the deflection of the wafer stage or stress-free clamping device, giving the wafer stage or stress-free clamping device more room to move, expanding the placement space of the wafer under test, and further increasing the warpage measurement range of the wafer under test. For wafers under test with the same amount of warpage, compared with tilt measurement by perpendicular incident interferometers such as Fizeau or Thyman Green, the placement space of the wafer under test is larger and the movement is more flexible, effectively reducing the number of times the wafer under test needs to be measured in sections for regional measurement and then stitched together, resulting in higher detection accuracy and efficiency.

[0110] In this embodiment, the measuring device further includes a second interference system 300, which has the same optical path structure as the first interference system 200 and is symmetrically arranged on both sides of the wafer 400 being measured.

[0111] It is understandable that when the optical paths on both sides of the wafer under test are measured simultaneously, the overall morphological characteristics of the wafer under test can be obtained based on the coordinate information calibrated by the optical system, including but not limited to parameters such as warpage, twist, flatness, thickness, edge roll-off, and nano-morphology.

[0112] It is understood that this embodiment uses a two-way reflection structure, and the wafer under test 400 can move in the horizontal direction along the line connecting the two reference mirrors, which removes the distance limitation between the wafer under test 400 and the reference mirrors, so that the stress-free clamping device or wafer stage has more room for movement, further expanding the placement space of the wafer under test 400, and further improving the detection accuracy and detection efficiency.

[0113] It is understood that the reference optical path and the optical path under test designed in this embodiment can have the same optical path length, or a specific initial optical path difference can be designed according to system requirements. Methods that can be used include, but are not limited to, using beam-splitting prisms or beam splitters of different thicknesses or materials, and adding phase delay elements such as phase plates to the optical path.

[0114] The method for measuring the morphology of large-size wafers provided in this application involves splitting a parallel beam emitted from a light source into a reference beam and a test beam. The reference beam is reflected by a reference mirror and then enters a beam combiner. The test beam is reflected by the surface of one side of the wafer 400 under test and then enters the beam combiner. The beam combiner combines the incident reference beam and the test beam and then converges them to a detector to generate an interference fringe image. The control unit controls the movement of the wafer 400 under test and / or the reference mirror to change the optical path difference between the wafer 400 under test and the reference mirror, thereby determining the wafer surface morphology and improving the testing yield and accuracy of large warpage wafers.

[0115] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A device for measuring the morphology of large-size, highly warped crystal wafers, characterized in that, include: A light source, which is used to emit a parallel light beam; The first interferometric system includes a beam splitter, a reference mirror, a beam combiner, and a detector. and The control unit is used to control the movement of the wafer under test and to control the wafer under test to tilt to a preset range of tilt angles, wherein the warpage of the wafer under test within the preset range of tilt angles falls within the wavelength testing range of the parallel beam emitted by the light source; wherein: The parallel beam emitted from the light source is split by the beam splitter to form a reference beam and a test beam; The reference light is reflected by the reference mirror and then enters the beam combiner; the test light is reflected by the surface of one side of the wafer under test and then enters the beam combiner. The beam combiner combines the incident reference light and the test light and then focuses them onto the detector, which generates an interference fringe image. The control unit controls the movement of the wafer under test and / or the reference mirror to change the optical path difference between the wafer under test and the reference mirror, and determines the wafer surface morphology based on the generated interference fringe image. The control unit controls the light source to emit a first wavelength beam to obtain the warpage amount of each sub-region of the wafer under test; divides the wafer into N test regions according to the warpage amount, and ensures that the warpage amount of each test region is within the test range of the second wavelength beam, where N is a natural number greater than or equal to 2; the control unit switches the light source to emit the second wavelength beam and sequentially performs morphology measurements on the N test regions.

2. The large-size, large-warpage wafer morphology measurement device as described in claim 1, characterized in that, The measuring device also includes a stress-free clamping device that holds the wafer under test vertically, and the control unit can control the movement of the stress-free clamping device to drive the wafer under test to translate and / or deflect.

3. The large-size, large-warpage wafer morphology measurement device as described in claim 1, characterized in that, The measuring device further includes a wafer stage on which the wafer to be measured is fixed. The control unit can control the wafer stage to move so as to drive the wafer to be measured to translate and / or deflect.

4. The large-size, large-warpage wafer morphology measurement device as described in claim 1, 2, or 3, characterized in that, The wafer under test and one of the reference mirrors move toward or away from the other.

5. The large-size, large-warpage wafer morphology measurement device as described in claim 4, characterized in that, The measuring device further includes a second interference system, which has the same optical path structure as the first interference system and is symmetrically arranged on both sides of the wafer under test.

6. The large-size, large-warpage wafer morphology measurement device as described in claim 5, characterized in that, The wafer under test is moved horizontally along the line connecting the two reference mirrors.

7. The large-size, large-warpage wafer morphology measurement device as described in claim 5, characterized in that, The light source is a single light source and is split into two laser beams by a beam splitter, which are respectively used as the incident light for the first interference system and the second interference system.

8. The large-size, large-warpage wafer morphology measurement device as described in claim 5, characterized in that, The light source consists of two light sources, which serve as the incident light for the first interference system and the second interference system, respectively.

9. The large-size, large-warpage wafer morphology measurement device as described in claim 1, characterized in that, The incident angle of the test light on the wafer under test is between 20° and 60°.

10. The large-size, large-warpage wafer morphology measurement device as described in claim 1, characterized in that, The control unit controls the wavelength of the parallel beam emitted by the light source to switch between a first wavelength and a second wavelength, wherein the first wavelength is greater than the second wavelength.

11. The large-size, large-warpage wafer morphology measurement device as described in claim 10, characterized in that, The first wavelength is the infrared wavelength, and the second wavelength is the visible or ultraviolet wavelength.

12. The large-size, large-warpage wafer morphology measurement device as described in claim 1, characterized in that, The warpage of the test area of ​​the wafer under test falls within the wavelength test range of the corresponding light beam within the preset tilt angle range.

13. The large-size, large-warpage wafer morphology measurement device as described in claim 3, characterized in that, The deflection angle of the wafer stage is determined based on the warpage measured by the first wavelength beam.

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