An interferometric measurement method and apparatus for large warp wafers

Abstract

This invention relates to an interferometric measurement method and apparatus for large warp wafers, belonging to the field of optical detection and semiconductor measurement technology. The detection light is polarized and birefringently split to form P-beams and S-beams, which are then further divided into P-reference beams, S-silicon beams, S-reference beams, and P-silicon beams, respectively. By adjusting the spatial orientation of the reference mirror and the wafer under test, and using an aperture for spatial filtering, the P-reference beam and S-silicon beam are allowed to enter the subsequent optical path, while the S-reference beam and P-silicon beam are blocked. The S-silicon beam forms a measurement wavefront carrying information about the surface shape of the wafer under test. The P-reference beam is modulated by a deformable mirror to form a modulated reference wavefront similar to the measurement wavefront. The two form a resolvable interference fringe pattern at the camera. A wavefront sensor measures the surface shape information of the deformable mirror, and a calculation system obtains the surface shape information of the wafer under test based on the deformable mirror surface shape information and the relative surface shape change. This invention can reduce the interference fringe density in the detection of large warp wafers, reduce splicing measurement errors, and improve detection efficiency and accuracy.

Description

Technical Field

[0001] This invention relates to the fields of optical inspection and semiconductor measurement technology, and in particular to an interferometric measurement method and apparatus for detecting the surface morphology of wafers with large warpage. Background Technology

[0002] Wafers are the fundamental carriers in semiconductor manufacturing, and their flatness directly affects the stability and processing accuracy of front-end processes such as photolithography, thin film deposition, etching, and material handling. Large wafers, in particular, are prone to overall bending or localized warping after processes such as polishing, oxidation, annealing, and chemical vapor deposition due to thermal stress, film stress, or the release of internal material stress. For wafers with significant bending or warping, if their surface morphology parameters cannot be accurately measured, it can lead to problems such as focusing errors, pattern transfer deviations, unstable equipment adhesion, or wafer jamming in subsequent processes. Therefore, it is usually necessary to inspect the wafer surface morphology during the manufacturing process.

[0003] In existing technologies, interferometry is commonly used to obtain the height distribution between the wafer surface and a reference plane for wafer surface morphology inspection, and then parameters such as wafer curvature and warpage are calculated based on this. This type of method has advantages such as non-contact and high precision, and has been widely used in the field of wafer flatness inspection. Typically, an interferometry system uses the interference between the reference wavefront returned by a reference mirror and the measurement wavefront returned by the wafer under test, and analyzes the wafer surface shape based on the resulting interference fringes. However, in the inspection of wafers with large warpage, the reference wavefront returned by the reference mirror is usually approximately a plane wave, while the measurement wavefront returned by a wafer with large warpage may exhibit an approximately spherical wave or other non-plane wave state due to the overall curvature or local warpage of the wafer. When the difference between the two wavefronts is large, the interference fringes become significantly denser, especially in the wafer edge region, where high-density fringes are easily formed, even exceeding the resolution of camera pixels, resulting in the inability to effectively resolve phase information, and thus making it difficult to obtain complete and accurate wafer surface shape information.

[0004] To address the challenge of directly measuring large-warped wafers, existing methods typically employ a segmented measurement and subsequent stitching reconstruction approach. This involves measuring different local areas of the wafer separately and then stitching the results together to obtain the overall wafer surface morphology. However, this method increases the number of measurements, leading to decreased detection efficiency. Furthermore, the wafer's support state, orientation, and stress conditions may change during the measurement of different areas, introducing additional measurement errors and affecting the accuracy of the overall morphology reconstruction. In addition, in actual interferometric measurement optical paths, the reference and measurement return beams usually do not exist on a single path. If multiple return beams simultaneously enter the subsequent imaging path, it can cause chaotic superposition of interference fringes, further reducing fringe discernibility.

[0005] Therefore, how to ensure that the reference wavefront involved in the interference maintains a small wavefront difference with the measurement wavefront returned by the wafer under test during the detection of large warp wafers, and how to limit the non-target backlight from entering the imaging path through a reasonable optical path structure, so as to obtain a resolvable interference fringe pattern and achieve a one-time, high-stability measurement of the surface shape of large warp wafers, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to address the problems of existing interferometry techniques for detecting large warp wafers, where the significant difference between the planar reference wavefront and the non-planar measurement wavefront returned from the wafer under test leads to overly dense interference fringes and difficulty in phase resolution. Furthermore, existing splicing measurement methods suffer from low efficiency and error accumulation. This invention provides an interferometry method and apparatus for large warp wafers. By using a deformable mirror to modulate the reference wavefront to a modulated reference wavefront similar to the measurement wavefront of the wafer under test, and by combining this with an aperture to selectively filter the returned light, a resolvable interference fringe pattern can be obtained. This improves the efficiency, accuracy, and stability of large warp wafer surface shape detection.

[0007] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: An interferometric measurement method for a large warp wafer, comprising: S1. A detection light is emitted from a laser, and the detection light enters a birefringent crystal after passing through a first quarter-wave plate to form orthogonally polarized P-light and S-light; S2. The P-beam and S-beam are passed through a microscope objective, a first beam splitter, and a first collimating lens to form parallel light with opposite angles relative to the optical axis of the first collimating lens, and P-reference light, S-silicon light, S-reference light, and P-silicon light are formed. S3. Adjust the spatial orientation of the reference mirror and / or the wafer under test so that the P-reference light and the S-silicon light pass through the aperture and the S-reference light and the P-silicon light are deviated from the aperture and blocked. S4. The silicon light is returned through the second collimating lens, polarizing beam splitter, second quarter-wave plate and plane mirror, and then enters the camera through the third quarter-wave plate and imaging mirror to form a measurement wavefront carrying the surface shape information of the wafer being measured. S5. The P-reference light is incident on the deformable mirror through the second collimating mirror, the polarizing beam splitter, the fourth quarter-wave plate, and the second beam splitter, and the surface shape of the deformable mirror is adjusted to modulate the planar reference wavefront formed by the P-reference light into a modulated reference wavefront that matches the measured wavefront. S6. The modulated reference wavefront reflected by the deformable mirror is split by the second beam splitter. One path enters the wavefront sensor to obtain the surface shape information V1 of the deformable mirror, and the other path enters the camera and interferes with the measured wavefront to obtain an interference fringe pattern. S7. The relative surface shape change ΔV of the wafer under test relative to the deformable mirror is obtained by analyzing the interference fringe pattern, and the surface shape information Vsilicon of the wafer under test is calculated by the calculation system based on the surface shape information V1 and the relative surface shape change ΔV. The deformable mirror is used to reduce the wavefront difference between the two interference beams entering the camera, so that the camera can obtain a resolvable interference fringe pattern.

[0008] Optionally, in step S1, the detection light is converted from polarized light to circularly polarized light after passing through the first quarter-wave plate, and the circularly polarized light is converted into P-beam and S-beam that are parallel to each other and located on opposite sides of the optical axis after passing through the birefringent crystal.

[0009] Optionally, in step S2, after the P-beam and S-beam are collimated by the first collimating lens, they respectively form parallel beams with opposite angles relative to the optical axis of the first collimating lens; In step S3, by adjusting the tilt angle of the reference mirror, the P-reference light is made to return along the principal optical axis of the first collimating mirror; by adjusting the placement orientation of the wafer under test, the S-silicon light is made to return along the principal optical axis of the first collimating mirror.

[0010] Optionally, the S-parameter light is blocked because its return direction deviates from the aperture of the aperture, and the P-silicon light is blocked because its return direction deviates from the aperture of the aperture, so that the light beam passing through the aperture includes only the P-parameter light and the S-silicon light.

[0011] Optionally, in step S4, the S-silicon light is reflected after entering the polarizing beam splitter, converted into circularly polarized light by the second quarter-wave plate, reflected by the plane mirror and returned along the original path, and converted into P-silicon light after passing through the second quarter-wave plate again. The P-silicon light passes through the polarizing beam splitter and is converted into circularly polarized light by the third quarter-wave plate before entering the imaging mirror and camera.

[0012] Optionally, in step S5, the deformable mirror is a liquid lens. The liquid lens drives the liquid to squeeze towards or back from the center of the diaphragm, causing the reflecting surface of the deformable mirror to change between convex, concave, and planar states, thereby modulating the planar reference wavefront.

[0013] Optionally, the calculation system calculates the surface shape information of the wafer under test according to the following relationship:

[0014] in, For the surface shape information of the wafer being tested, The surface shape information of the deformable mirror measured by the wavefront sensor. The relative surface shape change of the tested wafer relative to the deformable mirror is obtained from the analysis of the interference fringe pattern.

[0015] To achieve the above-mentioned technical objectives, the present invention also adopts the following technical solution: An interferometric measurement apparatus for a large warp wafer, comprising: A laser, used to output detection light; A quarter-wave plate and a birefringent crystal are arranged sequentially along the outgoing optical path of the detection light to convert and separate the detection light into orthogonally polarized P-light and S-light; The microscope objective, the first beam splitter, and the first collimating lens are used to form the P-ray and S-ray into parallel rays with opposite angles relative to the optical axis of the first collimating lens; The reference mirror and the wafer carrier under test are used to form P-reference light, S-reference light, and S-silicon light and P-silicon light, respectively; An aperture is positioned on the return path to allow the P-reference light and the S-silicon light to pass through, while blocking the S-reference light and the P-silicon light. The second collimating lens and the polarizing beam splitter are disposed on the optical path after the aperture; The first reflection branch includes a second quarter-wave plate and a plane mirror, used to receive the S-silicon light and form a measurement beam carrying information about the surface shape of the wafer under test; The second reflection branch includes a fourth quarter-wave plate, a second beam splitter, and a deformable mirror, for receiving the P-reference light and modulating the planar reference wavefront formed by the P-reference light into a modulated reference beam that matches the measurement beam through the deformable mirror; The imaging branch, including a third quarter-wave plate, an imaging mirror, and a camera, is used to receive the measurement beam and the modulated reference beam and form an interference fringe pattern. A wavefront sensor is used to measure the surface shape information V1 of the deformable mirror; The computing system, connected to the wavefront sensor and the camera, is used to analyze the relative surface shape change ΔV based on the interference fringe pattern, and to calculate the surface shape information Vsilicon of the wafer under test based on the surface shape information V1 and the relative surface shape change ΔV. The deformable mirror is configured to modulate the surface shape of the planar reference wavefront corresponding to the P-reference beam, so that a resolvable interference fringe is formed between the modulated reference beam entering the camera and the measurement beam.

[0016] Optionally, at least one of the reference mirror and the wafer under test carrier is connected to an attitude adjustment mechanism. The attitude adjustment mechanism is used to adjust the spatial attitude of the reference mirror and / or the wafer under test, so that the P-reference light and the S-silicon light return along the light transmission direction of the aperture, and so that the S-reference light and the P-silicon light deviate from the light transmission direction of the aperture.

[0017] Optionally, the deformable mirror is a liquid lens, which includes a deformable diaphragm and a driving mechanism for driving liquid to act on the deformable diaphragm. The driving mechanism is used to change the convex or concave state of the deformable diaphragm to change the reflected wavefront of the deformable mirror. The wavefront sensor is used to measure the radius and / or surface shape changes of the deformable mirror in real time and transmit the measurement results to the computing system.

[0018] The main advantages of this invention compared to existing technologies are as follows: This invention involves directing the reference wavefront returned by the reference mirror into a deformable mirror, and using the deformable mirror to modulate the planar reference wavefront into a modulated reference wavefront that is similar to the measurement wavefront of the wafer under test. This reduces the wavefront difference between the modulated reference wavefront and the measurement wavefront carrying the surface shape information of the wafer under test, thereby avoiding the problem of excessively dense fringes when the planar reference wavefront directly interferes with the approximately spherical wavefront returned by the large warp wafer. This allows the camera to obtain a resolvable interference fringe pattern, solving the problem in the prior art that large warp wafers are difficult to directly resolve interference fringes.

[0019] This invention selectively filters backlights using an aperture, allowing P-parameter light and S-silicon light to enter the subsequent optical path while blocking non-target backlights such as S-parameter light and P-silicon light from entering the imaging path. This reduces interference and aliasing caused by the superposition of multiple backlights, and improves the determinism and stability of the interference beam entering the camera.

[0020] This invention measures the surface shape information of a deformable mirror using a wavefront sensor and analyzes the relative surface shape change of the wafer under test relative to the deformable mirror using an interference fringe pattern obtained by a camera. Then, a calculation system calculates the surface shape information of the wafer under test based on the surface shape information of the deformable mirror and the relative surface shape change. This provides a clear data source and calculation basis for the surface shape restoration process of large warp wafers, improving the completeness and accuracy of the detection results.

[0021] This invention eliminates the need for multi-angle, multi-region splicing measurements on large-warped wafers. It can obtain wafer surface shape information based on the interference result between the reference wavefront modulated by the deformable mirror and the measurement wavefront of the wafer under test, thereby reducing the number of measurements, improving detection efficiency, and reducing splicing errors caused by multiple adjustments to wafer orientation, different support states, and the influence of gravity.

[0022] This invention, through the coordination of polarization beam splitting, polarization state conversion, reflection branch, and imaging branch, enables the measurement beam carrying the surface shape information of the wafer under test and the modulation reference beam carrying the surface shape information of the deformed mirror to enter the same imaging path and form stable interference. This is beneficial to improving the contrast, continuity, and resolvability of interference fringes, thereby enhancing the stability of large warp wafer surface morphology detection. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the steps of the interferometric measurement method for large warp wafers of the present invention. Figure 2 A schematic diagram illustrating the basic principle of fringe formation in existing interferometry of large-warped silicon wafers. Figure 3 This is a schematic diagram of the optical path of the interferometric measurement method and apparatus for large warp wafers of the present invention. Detailed Implementation

[0024] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the following embodiments are used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions or conventional modifications made by those skilled in the art to the type of optical element, mounting method, driving method, or data processing method without departing from the technical concept of the present invention should all fall within the scope of protection of the present invention.

[0025] This embodiment provides an interferometric measurement method and apparatus for a large warpage wafer. The large warpage wafer can be a silicon wafer or crystal wafer processed during semiconductor manufacturing, including polishing, oxidation, annealing, and chemical vapor deposition. Its surface undergoes overall bending or localized warping due to thermal stress, film stress, or the release of internal material stress. For ease of explanation, the wafer under test 8 is used as the object of measurement in the following description; the wafer under test 8 can also be understood as the wafer to be measured.

[0026] like Figure 2 As shown, Figure 2This describes the fringe variation patterns when different wavefronts interfere in existing interferometry. Typically, when two plane waves or two beams with similar wavefront morphologies interfere, the resulting interference fringes are sparse, and their width can be effectively resolved by the camera. The morphology information of the measured surface can then be obtained through phase resolution. When a plane wave interferes with a spherical wave or near-spherical wave, the interference fringes usually exhibit a ring-like or near-ring-like distribution, with relatively sparse fringes in the central region and denser fringes closer to the edges. The smaller the radius of the spherical wave, i.e., the greater the wavefront curvature, the denser the fringes. For highly warped wafers, the reflected wavefront usually deviates from a plane wave and is affected by the overall wafer curvature or local warping, exhibiting a near-spherical wave or other non-plane wave state. Therefore, if the plane reference wavefront returned by the plane reference mirror is still directly interfered with the measurement wavefront returned by the highly warped silicon wafer, extremely dense fringes are easily formed in the edge region, even exceeding the camera's pixel resolution, making the interference fringes unresolved and thus unable to accurately obtain the silicon wafer surface morphology information.

[0027] Based on the above problems, the basic idea of ​​this invention is as follows: First, the P-reference light and S-silicon light that need to participate in subsequent interferometric measurements are screened out through the optical path structure, while the S-reference light and P-silicon light that do not need to participate in the interference are blocked; then, the planar reference wavefront carried by the P-reference light enters the deformable mirror 19, and the deformable mirror 19 modulates the planar reference wavefront into a modulated reference wavefront that is close to the measurement wavefront of the wafer under test 8; then, the modulated reference wavefront interferes with the measurement wavefront carrying the surface shape information of the wafer under test 8 at the camera 16. Since the wavefront difference between the modulated reference wavefront and the measurement wavefront of the wafer under test 8 is smaller than the wavefront difference between the planar reference wavefront and the measurement wavefront of the large warp silicon wafer, a relatively sparse and resolvable interference fringe pattern can be formed. Further, the wavefront sensor 20 measures the surface shape information V1 of the deformable mirror 19, and the calculation system 21 analyzes the relative surface shape change ΔV of the wafer under test 8 relative to the deformable mirror 19 based on the interference fringe pattern obtained by the camera 16, and combines V1 and ΔV to obtain the surface shape information of the wafer under test 8.

[0028] like Figure 3 As shown, the large warp wafer interferometry apparatus of this embodiment includes a laser 1, a first quarter-wave plate 2, a birefringent crystal 3, a microscope objective 4, a first beam splitter 5, a first collimating mirror 6, a reference mirror 7, a wafer under test 8, an aperture 9, a second collimating mirror 10, a polarizing beam splitter prism 11, a second quarter-wave plate 12, a plane mirror 13, a third quarter-wave plate 14, an imaging mirror 15, a camera 16, a fourth quarter-wave plate 17, a second beam splitter 18, a deformable mirror 19, a wavefront sensor 20, and a computing system 21.

[0029] Laser 1 is used to emit detection light. The detection light can be a parallel, narrow beam that meets the requirements of interferometry, possessing stable coherence and intensity stability. A first quarter-wave plate 2 is disposed in the output optical path of laser 1 to convert the polarized light emitted by laser 1 into circularly polarized light. A birefringent crystal 3 is disposed in the subsequent optical path of the first quarter-wave plate 2 to separate the incident circularly polarized light into two parallel and orthogonally polarized linearly polarized beams, namely P-beams and S-beams. P-beams can be defined as polarized light vibrating parallel to the plane of the paper, and S-beams can be defined as polarized light vibrating perpendicular to the plane of the paper. P-beams and S-beams are located on opposite sides of the optical axis and maintain the same or substantially the same distance relative to the optical axis.

[0030] The microscope objective 4 is positioned in the post-stage optical path of the birefringent crystal 3 to form divergent beams from the P-beams and S-beams. The first beam splitter 5 and the first collimating lens 6 constitute part of the pre-stage Fizeau measurement optical path. Since the P-beams and S-beams are not located on the optical axis of the first collimating lens 6, after passing through the first beam splitter 5 and the first collimating lens 6, the P-beams and S-beams are collimated into two parallel beams with a certain angle to the optical axis of the first collimating lens 6, and the two parallel beams have opposite angles relative to the optical axis of the first collimating lens 6. This allows the formation of two detection beams with different incident directions, providing a basis for spatial screening of subsequent reference and measurement backlights.

[0031] Reference mirror 7 is positioned on one side of the outgoing light path of the first collimating mirror 6 to reflect the corresponding incident light and form a reference return beam. The wafer under test 8 is positioned at another detection location to reflect the corresponding incident light and form a measurement return beam. Reference mirror 7 can be a plane standard mirror to provide an initial plane reference wavefront. The wafer under test 8 is a large-warped silicon wafer, whose surface may have overall or local warping; therefore, the measurement wavefront formed by the reflection from the wafer under test 8 is typically an approximately spherical wave or other non-planar wave.

[0032] At least one of the reference mirror 7 and the wafer under test 8 may be equipped with an attitude adjustment mechanism. The attitude adjustment mechanism is used to adjust the tilt angle of the reference mirror 7 and / or the placement orientation of the wafer under test 8, so that a specific backlight returns along a preset direction. Specifically, by adjusting the angle between the reference mirror 7 and the principal optical axis, the P-light returned by the reference mirror 7 returns along the principal optical axis direction of the first collimating mirror 6; this beam is defined as the P-reference light. After passing through the first collimating mirror 6 and the first beam splitter 5, the P-reference light can pass through the aperture 9. By adjusting the angle of the wafer under test 8, the S-silicon light formed after the S-light is reflected by the wafer under test 8 returns along a direction parallel or substantially parallel to the principal optical axis; this S-silicon light, after passing through the first collimating mirror 6 and the first beam splitter 5, can also pass through the aperture 9.

[0033] Aperture 9 is positioned on the return path to spatially filter the returned light. Since the P-beam and S-beam have opposite angles relative to the optical axes of the first collimating mirror 6, the S-reference beam reflected by the reference mirror 7 cannot meet the light transmission conditions of aperture 9 in its return direction, and therefore cannot enter aperture 9. Similarly, the P-silicon beam returned from the wafer under test 8 also cannot enter aperture 9 because its return direction deviates from the aperture of aperture 9. Thus, by coordinating the orientation of the reference mirror 7, the orientation of the wafer under test 8, and the position of aperture 9, the beams passing through aperture 9 can be made to primarily consist of P-reference beams and S-silicon beams, while non-target returned light such as S-reference beams and P-silicon beams is blocked outside aperture 9. This arrangement reduces interference and aliasing caused by multiple returned beams entering subsequent optical paths, making the source of subsequent beams involved in interference clearer.

[0034] The second collimating lens 10 is positioned after the aperture stop 9 to collimate the P-parameter light and S-silicon light passing through the aperture stop 9, ensuring they enter the polarization beam splitter prism 11 in a state suitable for subsequent polarization beam splitting and reflection branch processing. The polarization beam splitter prism 11 splits the P-parameter light and S-silicon light according to their polarization states, causing them to enter different reflection branches and then return to the same imaging path after returning from their respective reflection branches.

[0035] In this process, S-silicon light is reflected after entering the polarizing beam splitter 11, and then passes through the second quarter-wave plate 12. After passing through the second quarter-wave plate 12, the S-silicon light is converted into circularly polarized light. This circularly polarized light is reflected by the plane mirror 13 and returns along its original path, passing through the second quarter-wave plate 12 again, thus being converted into P-silicon light. The P-silicon light then passes through the polarizing beam splitter 11 and through the third quarter-wave plate 14, where it is converted into circularly polarized light carrying information about the surface shape of the wafer 8 under test. This light then enters the camera 16 through the imaging mirror 15. Because the wafer 8 under test has significant warpage, the measurement wavefront entering the camera 16 carries information about the surface shape of the wafer 8 under test and can exhibit a wavefront shape similar to a spherical wave or a non-planar wave.

[0036] The P-reference beam is directly transmitted after entering the polarizing beam splitter 11 and converted into circularly polarized light by the fourth quarter-wave plate 17. This circularly polarized light is then incident on the deformable mirror 19 via the second beam splitter 18. Since the P-reference beam originates from the reference mirror 7, it initially carries the plane wave information of the reference mirror 7. Therefore, before being modulated by the deformable mirror 19, its corresponding reference wavefront can be considered as a plane reference wavefront. After the plane reference wavefront illuminates the deformable mirror 19, the reflected wavefront of the deformable mirror 19 is made close to the measured wavefront of the wafer 8 by adjusting the surface shape of the deformable mirror 19. In other words, the deformable mirror 19 is used to modulate the plane reference wavefront formed by the P-reference beam into a modulated reference wavefront that matches or substantially matches the warp state of the surface of the wafer 8 under test, thereby reducing the wavefront difference between the modulated reference wavefront and the measured wavefront.

[0037] In one specific embodiment, the deformable mirror 19 can employ a liquid lens structure. This liquid lens can be driven by a voice coil motor or other driving mechanism to push liquid towards the center of the diaphragm, or to retract the liquid from the center of the diaphragm, thereby causing the diaphragm to bulge, concave, or remain flat. In this way, the reflecting surface of the deformable mirror 19 can vary between convex, concave, and flat states, enabling it to simulate or approximate the wavefront morphology corresponding to different degrees of warpage of the measured wafer 8. It should be understood that the deformable mirror 19 is not required to completely replicate the surface shape of the measured wafer 8, but rather to reduce the difference between the reference wavefront and the measured wavefront to a range within which the camera 16 can obtain resolvable interference fringes.

[0038] The modulated reference wavefront, reflected by deformable mirror 19, returns along its original path to the second beam splitter 18. The second beam splitter 18 splits the returned circularly polarized light into two parts: one part is reflected into wavefront sensor 20, and the other part is transmitted and passes through the fourth quarter-wave plate 17 again, where it is converted into S-parametric light. Wavefront sensor 20 is used to measure the modulated wavefront information reflected by deformable mirror 19, including but not limited to the radius, curvature, or surface shape change information of deformable mirror 19, and transmits this surface shape information to computing system 21. The S-parametric light formed by the transmitted part enters polarization beam splitter prism 11, is reflected, and then passes through the third quarter-wave plate 14 to be converted into circularly polarized light carrying the surface shape information of deformable mirror 19, and then enters camera 16 through imaging mirror 15.

[0039] At this point, the measurement wavefront carrying information about the surface shape of the tested wafer 8 and the modulated reference wavefront carrying information about the surface shape of the deformable mirror 19 both enter the camera 16 and interfere. Since the deformable mirror 19 has modulated the reference wavefront to a shape similar to the measurement wavefront of the tested wafer 8, the wavefront difference between them is significantly smaller than the wavefront difference between the planar reference wavefront and the measurement wavefront of the large-warp silicon wafer. Therefore, the interference fringes formed at the camera 16 will not exhibit an extremely dense state due to excessive wavefront difference, and a resolvable interference fringe pattern can be formed. This interference fringe pattern can be used to analyze the relative surface shape change ΔV of the tested wafer 8 relative to the surface shape of the deformable mirror 19.

[0040] The computing system 21 is connected to the camera 16 and the wavefront sensor 20. The camera 16 outputs an interference fringe pattern, and the computing system 21 analyzes the interference fringe pattern to obtain the relative surface shape change ΔV of the tested wafer 8 relative to the surface shape of the deformable mirror 19. The wavefront sensor 20 measures the surface shape information V1 of the deformable mirror 19 and transmits this information to the computing system 21. Based on the surface shape information V1 of the deformable mirror 19 and the relative surface shape change ΔV, the computing system 21 calculates the surface shape information Vsilicon of the tested wafer 8, the relationship of which can be expressed as:

[0041] in, This indicates the surface shape information of wafer 8 under test. This represents the surface shape information of the deformable mirror 19 measured by the wavefront sensor 20. This represents the relative surface shape change of the tested wafer 8 relative to the deformable mirror 19, obtained by analyzing the interference fringe pattern acquired by camera 16. This method avoids the problem of excessively dense fringes when directly interfering with the large-warp silicon wafer wavefront using a planar reference wavefront, and allows for the reconstruction of the actual surface shape information of the tested wafer 8 based on resolvable interference fringes.

[0042] In one specific embodiment, the aperture of the first collimating lens 6 can be 100 mm, and the focal length can be 500 mm. The detection light emitted by the laser 1 is converted into circularly polarized light after passing through the first quarter-wave plate 2, and then forms two point light sources, namely a P-ray point light source and an S-ray point light source, after passing through the birefringent crystal 3 and the microscope objective 4. The separation distance between the two point light sources can be 2 mm, and they are located on both sides of the optical axis of the first collimating lens 6, about 1 mm away from the optical axis. The two point light sources can be located at the focal plane of the first collimating lens 6. After collimation by the first collimating lens 6, the angle between the parallel light formed by the P-ray and the S-ray and the optical axis of the first collimating lens 6 is about ±1 / 500, or about ±2 mrad. At this point, the tilt angles of the optical axes of the reference mirror 7 and the wafer under test 8 are adjusted to approximately ±1 mrad relative to the optical axis of the first collimating mirror 6. This allows the parallel light emitted from the first collimating mirror 6 to be reflected by the reference mirror 7 and the wafer under test 8, returning in a direction parallel or substantially parallel to the optical axis of the first collimating mirror 6 and converging at the aperture 9. Through this adjustment, the P-reference light and the S-silicon light can pass through the aperture 9, while the S-reference light and the P-silicon light are blocked because their return direction does not meet the light transmission conditions of the aperture 9. This ensures that the P-reference light and the S-silicon light passing through the center of the aperture 9 carry the surface shape information of the reference mirror 7 and the wafer under test 8, respectively.

[0043] like Figure 1 As shown, based on the above device structure, the large warp silicon wafer interferometry method of the present invention may include the following seven steps.

[0044] S1. The laser 1 emits a detection light, which passes through the first quarter-wave plate 2 and enters the birefringent crystal 3 to form orthogonally polarized P-light and S-light.

[0045] Specifically, laser 1 emits a parallel, narrow beam of light. This detection light, after passing through a first quarter-wave plate 2, is converted from linearly polarized light to circularly polarized light. The circularly polarized light, incident on a birefringent crystal 3, is separated into two parallel, orthogonally linearly polarized beams, namely, the P-beam and the S-beam. The P-beam and the S-beam are located on opposite sides of the optical axis, and the distances between the two beams relative to the optical axis can be equal or substantially equal. Through this step, the single detection beam is decomposed into two beams with different polarization states and different spatial positions, providing a foundation for the subsequent formation of the P-parameter beam and the S-silicon beam.

[0046] S2. The P-beam and S-beam are passed through the microscope objective 4, the first beam splitter 5 and the first collimating lens 6 to form two parallel beams with opposite angles relative to the optical axis of the first collimating lens 6, and respectively form the P-reference beam returned by the reference lens 7, the S-silicon beam returned by the wafer under test 8, the S-reference beam returned by the reference lens 7 and the P-silicon beam returned by the wafer under test 8.

[0047] Specifically, the P-beam and S-beam form a diverging beam after passing through the microscope objective 4. This diverging beam is then collimated into a parallel beam after passing through the first beam splitter 5 and the first collimating lens 6. Since the P-beam and S-beam are located on opposite sides of the optical axis of the first collimating lens 6, they form two parallel beams with opposite angles relative to the optical axis of the first collimating lens 6 after collimation. These two beams are incident on the reference mirror 7 and the wafer under test 8, respectively, forming multiple return paths. Specifically, these include: the P-reference beam returned by the reference mirror 7, the S-silicon beam returned by the wafer under test 8, the S-reference beam returned by the reference mirror 7, and the P-silicon beam returned by the wafer under test 8. The P-reference beam and S-silicon beam are the target return paths that need to be retained, while the S-reference beam and P-silicon beam are the non-target return paths that need to be blocked.

[0048] S3. Adjust the spatial orientation of the reference mirror 7 and / or the wafer under test 8 so that the P-reference light and the S-silicon light return along the preset light transmission direction and pass through the aperture 9, while the S-reference light and the P-silicon light deviate from the aperture 9 and are blocked.

[0049] Specifically, the angle between the reference mirror 7 and the principal optical axis is adjusted so that the P-reference light returned by the reference mirror 7 returns along the principal optical axis direction of the first collimating mirror 6 or a preset light transmission direction. After passing through the first collimating mirror 6 and the first beam splitter 5, the P-reference light can pass through the aperture 9. The placement orientation of the wafer 8 under test is further adjusted so that the S-silicon light formed after the S-light is reflected by the wafer 8 under test is parallel or substantially parallel to the principal optical axis after passing through the reference mirror 7, and can pass through the first collimating mirror 6 and the first beam splitter 5 before passing through the aperture 9.

[0050] Because the P-beam and S-beam have opposite exit angles, the S-beam returning from the reference mirror 7 cannot return along the light transmission direction of the aperture 9, and therefore cannot enter the aperture 9; similarly, the P-beam returning from the wafer under test 8 also cannot enter the aperture 9. Through the above attitude adjustment and aperture selection, the system can ensure that the beams passing through the center of the aperture 9 are mainly P-beam and S-beam, so that the P-beam carries the surface shape information of the reference mirror 7, and the S-beam carries the surface shape information of the wafer under test 8, thereby preventing non-target return light such as S-beam and P-beam from entering the subsequent polarization conversion and imaging path.

[0051] S4. The silicon light passing through the aperture 9 is returned by the second collimating lens 10, the polarizing beam splitter 11, the second quarter-wave plate 12 and the plane mirror 13, and then enters the camera 16 through the third quarter-wave plate 14 and the imaging mirror 15 to form a measurement wavefront carrying the surface shape information of the wafer being measured.

[0052] Specifically, the S-silicon light passing through aperture 9 is collimated by the second collimating lens 10 and then enters the polarizing beam splitter 11. After entering the polarizing beam splitter 11, the S-silicon light is reflected and converted into circularly polarized light by the second quarter-wave plate 12. The circularly polarized light is reflected by the plane mirror 13 and returns along its original path, passing again through the second quarter-wave plate 12 and being converted into P-silicon light. The P-silicon light passes through the polarizing beam splitter 11 and is converted into circularly polarized light by the third quarter-wave plate 14 before entering the camera 16 via the imaging mirror 15. Since this beam originates from the reflection of the wafer 8 under test, it carries the surface shape information of the wafer 8 and participates in subsequent interference as a measurement wavefront. For silicon wafers with large warpage, this measurement wavefront typically exhibits a wavefront shape similar to a spherical wave or a non-planar wave.

[0053] S5. The P-reference light passing through the aperture 9 is incident on the deformable mirror 19 through the second collimating mirror 10, the polarizing beam splitter 11, the fourth quarter-wave plate 17, and the second beam splitter 18. The surface shape of the deformable mirror 19 is adjusted so that the deformable mirror 19 modulates the planar reference wavefront formed by the P-reference light into a modulated reference wavefront that matches the measured wavefront.

[0054] Specifically, the P-reference light passing through aperture 9 is collimated by the second collimating lens 10 and then enters the polarizing beam splitter 11, passing through which it travels. The P-reference light is then converted into circularly polarized light by the fourth quarter-wave plate 17 and incident on the deformable mirror 19 via the second beam splitter 18. Since the P-reference light originates from the reference mirror 7 and carries the plane wave information of the reference mirror 7, it corresponds to a plane reference wavefront before incident on the deformable mirror 19. By adjusting the surface shape of the deformable mirror 19, the wavefront reflected by the deformable mirror 19 is transformed from a plane reference wavefront into a modulated reference wavefront similar to the measured wavefront of the wafer 8 under test. This modulation can be set according to the approximate warp direction and degree of warp of the wafer 8 under test, or by pre-measured rough topographic information, or by adjusting the deformable mirror 19 to a state where the camera 16 can obtain resolvable interference fringes.

[0055] In one specific embodiment, the deformable mirror 19 can be a liquid lens. The liquid lens can be driven by a voice coil motor to push liquid towards the center of the diaphragm, causing the diaphragm to bulge; alternatively, it can be driven in the opposite direction to push the liquid back from the center of the diaphragm, causing the diaphragm to concave or return to a planar state. By changing the shape of the diaphragm, the reflecting surface of the deformable mirror 19 can be adjusted from a planar state to a convex or concave state, thereby modulating the reference wavefront from a plane wave to a spherical wave or a non-planar wave similar to the reflected wavefront of the measured wafer 8. Because the wavefront difference between the modulated reference wavefront and the measured wavefront of the measured wafer 8 becomes smaller, subsequent interference between the two no longer produces overly dense fringes, but instead forms an interference fringe pattern that can be resolved by the camera 16.

[0056] S6. The modulated reference wavefront reflected by the deformable mirror 19 is split into a first beam and a second beam by the second beam splitter 18. The first beam enters the wavefront sensor 20 to obtain the surface shape information V1 of the deformable mirror 19. The second beam enters the camera 16 through the polarizing beam splitter 11, the third quarter-wave plate 14 and the imaging mirror 15, and interferes with the measured wavefront at the camera 16 to obtain an interference fringe pattern.

[0057] Specifically, the modulated reference wavefront reflected by deformable mirror 19 returns along its original path to the second beam splitter 18. The second beam splitter 18 divides the modulated reference wavefront into a first beam and a second beam. The first beam is guided to wavefront sensor 20. Wavefront sensor 20 performs wavefront detection on this beam to obtain surface shape information V1 corresponding to the wavefront reflected by deformable mirror 19. The surface shape information V1 may include the surface shape distribution, radius of curvature, wavefront height distribution, or other data that can characterize the wavefront morphology reflected by deformable mirror 19, and is transmitted to computing system 21.

[0058] The second beam, after passing through the second beam splitter 18, passes again through the fourth quarter-wave plate 17 and is converted into S-parameter light. The S-parameter light enters the polarizing beam splitter 11, is reflected, and then passes through the third quarter-wave plate 14 to be converted into circularly polarized light carrying surface shape information from the deformable mirror 19. It then enters the camera 16 through the imaging mirror 15. At this point, the measurement wavefront from the S-silicon light path and the modulation reference wavefront from the P-parameter light path interfere at the camera 16. Since the deformable mirror 19 has modulated the planar reference wavefront to a modulation reference wavefront similar to the measurement wavefront of the measured wafer 8, the interference fringe pattern is sparser than the fringes formed by direct interference between the planar reference wavefront and the measurement wavefront of the large-warp silicon wafer. The fringe width can be resolved by the camera 16, and therefore can be used for subsequent phase resolution and calculation of relative surface shape changes.

[0059] S7. The relative surface shape change ΔV of the tested wafer 8 relative to the deformable mirror 19 is obtained by analyzing the interference fringe pattern, and the surface shape information Vsilicon of the tested wafer 8 is calculated by the calculation system 21 based on the surface shape information V1 and the relative surface shape change ΔV.

[0060] Specifically, the interference fringe pattern acquired by camera 16 is sent to computing system 21. Computing system 21 can process the interference fringe pattern using existing phase analysis methods, such as phase-shifting interferometry, Fourier transform phase extraction, or other algorithms suitable for interference fringe processing, to obtain the relative surface shape change ΔV of the measured wafer 8 relative to the deformable mirror 19. Simultaneously, the surface shape information V1 of the deformable mirror 19 measured by wavefront sensor 20 is also transmitted to computing system 21. Computing system 21 calculates the surface shape information of the measured wafer 8 according to the following relationship:

[0061] in, For the surface shape information of wafer 8 under test, The surface shape information of the deformable mirror 19 measured by the wavefront sensor 20. This represents the relative surface shape change of the tested wafer 8 relative to the deformable mirror 19, obtained from the interference fringe pattern analysis. Using this calculation method, the system does not directly use a planar reference wavefront to obtain the complete surface shape of the large-warped silicon wafer. Instead, it first uses the deformable mirror 19 to provide a modulated reference wavefront similar to that of the tested wafer 8, enabling the camera 16 to obtain resolvable fringes. Then, the surface shape information of the tested wafer 8 is reconstructed through the superposition of V1 and ΔV. Therefore, the morphology inspection of the large-warped silicon wafer can be completed in one step, reducing or avoiding the measurement efficiency reduction and splicing error accumulation problems caused by traditional splicing inspection.

[0062] In the above embodiments, Figure 1 This is used to explain the principle that when an existing planar reference wavefront directly interferes with an approximately spherical wave on a highly warped silicon wafer, the fringes gradually become denser and the edges become difficult to resolve. Figure 2 To illustrate the specific optical path structure of this invention, the P-reference light and S-silicon light are filtered by the aperture 9. The planar reference wavefront corresponding to the P-reference light is modulated by the deformable mirror 19 into a modulated reference wavefront similar to the wavefront measured on the wafer 8 under test. The actual surface shape of the wafer 8 under test is then reconstructed by the wavefront sensor 20 and the computing system 21. This invention does not rely solely on back-end algorithms to remedy excessively dense fringes, but actively changes the reference wavefront morphology at the optical front end, resulting in a smaller wavefront difference between the two interference beams entering the camera 16. This reduces the interference fringe density at the source, improving the feasibility and stability of detecting the surface shape of large-warped silicon wafers.

[0063] In summary, this invention allows the reference wavefront returned by the reference mirror to enter a deformable mirror, and uses the deformable mirror to modulate the planar reference wavefront into a modulated reference wavefront that is close to the measurement wavefront of the wafer under test. This reduces the wavefront difference between the modulated reference wavefront and the measurement wavefront carrying the surface shape information of the wafer under test, thereby avoiding the problem of excessively dense fringes when the planar reference wavefront directly interferes with the approximately spherical wavefront returned by the large warp wafer. This enables the camera to obtain a resolvable interference fringe pattern, solving the problem in the prior art that large warp wafers are difficult to directly resolve interference fringes.

[0064] This invention selectively filters backlights using an aperture, allowing P-parameter light and S-silicon light to enter the subsequent optical path while blocking non-target backlights such as S-parameter light and P-silicon light from entering the imaging path. This reduces interference and aliasing caused by the superposition of multiple backlights, and improves the determinism and stability of the interference beam entering the camera.

[0065] This invention measures the surface shape information of a deformable mirror using a wavefront sensor and analyzes the relative surface shape change of the wafer under test relative to the deformable mirror using an interference fringe pattern obtained by a camera. Then, a calculation system calculates the surface shape information of the wafer under test based on the surface shape information of the deformable mirror and the relative surface shape change. This provides a clear data source and calculation basis for the surface shape restoration process of large warp wafers, improving the completeness and accuracy of the detection results.

[0066] This invention eliminates the need for multi-angle, multi-region splicing measurements on large-warped wafers. It can obtain wafer surface shape information based on the interference result between the reference wavefront modulated by the deformable mirror and the measurement wavefront of the wafer under test, thereby reducing the number of measurements, improving detection efficiency, and reducing splicing errors caused by multiple adjustments to wafer orientation, different support states, and the influence of gravity.

[0067] This invention, through the coordination of polarization beam splitting, polarization state conversion, reflection branch, and imaging branch, enables the measurement beam carrying the surface shape information of the wafer under test and the modulation reference beam carrying the surface shape information of the deformed mirror to enter the same imaging path and form stable interference. This is beneficial to improving the contrast, continuity, and resolvability of interference fringes, thereby enhancing the stability of large warp wafer surface morphology detection.

[0068] In the above embodiments, the reference mirror 7 can be a plane standard mirror; the deformable mirror 19 can be a liquid lens, a continuous surface deformable mirror, or other wavefront modulation device capable of changing the reflected wavefront; the wavefront sensor 20 can be a Hartmann wavefront sensor or other wavefront detection device capable of measuring the reflected wavefront of the deformable mirror 19; and the computing system 21 can be a computer, an industrial control computer, or other processing equipment with image processing and data calculation functions. All equivalent substitutions described above do not affect the basic technical concept of this invention.

Claims

1. An interferometric measurement method for a large warp wafer, characterized in that, include: S1. A detection light is emitted from a laser, and the detection light enters a birefringent crystal after passing through a first quarter-wave plate to form orthogonally polarized P-light and S-light; S2. The P-beam and S-beam are passed through a microscope objective, a first beam splitter, and a first collimating lens to form parallel light with opposite angles relative to the optical axis of the first collimating lens, and P-reference light, S-silicon light, S-reference light, and P-silicon light are formed. S3. Adjust the spatial orientation of the reference mirror and / or the wafer under test so that the P-reference light and the S-silicon light pass through the aperture and the S-reference light and the P-silicon light are deviated from the aperture and blocked. S4. The silicon light is returned through the second collimating lens, polarizing beam splitter, second quarter-wave plate and plane mirror, and then enters the camera through the third quarter-wave plate and imaging mirror to form a measurement wavefront carrying the surface shape information of the wafer being measured. S5. The P-reference light is incident on the deformable mirror through the second collimating mirror, the polarizing beam splitter, the fourth quarter-wave plate, and the second beam splitter, and the surface shape of the deformable mirror is adjusted to modulate the planar reference wavefront formed by the P-reference light into a modulated reference wavefront that matches the measured wavefront. S6. The modulated reference wavefront reflected by the deformable mirror is split by the second beam splitter. One path enters the wavefront sensor to obtain the surface shape information V1 of the deformable mirror, and the other path enters the camera and interferes with the measured wavefront to obtain an interference fringe pattern. S7. The relative surface shape change ΔV of the wafer under test relative to the deformable mirror is obtained by analyzing the interference fringe pattern, and the surface shape information Vsilicon of the wafer under test is calculated by the calculation system based on the surface shape information V1 and the relative surface shape change ΔV. The deformable mirror is used to reduce the wavefront difference between the two interference beams entering the camera, so that the camera can obtain a resolvable interference fringe pattern.

2. The interferometric measurement method for a large warped wafer according to claim 1, characterized in that, In step S1, the detection light is converted from polarized light to circularly polarized light after passing through the first quarter-wave plate, and the circularly polarized light is converted into P-light and S-light that are parallel to each other and located on opposite sides of the optical axis after passing through the birefringent crystal.

3. The interferometric measurement method for a large warped wafer according to claim 1, characterized in that, In step S2, after the P-beam and S-beam are collimated by the first collimating lens, they respectively form parallel beams with opposite angles relative to the optical axis of the first collimating lens; In step S3, by adjusting the tilt angle of the reference mirror, the P-reference light is made to return along the principal optical axis of the first collimating mirror; by adjusting the placement orientation of the wafer under test, the S-silicon light is made to return along the principal optical axis of the first collimating mirror.

4. The interferometric measurement method for a large warped wafer according to claim 1, characterized in that, The S-reference beam is blocked because its return direction deviates from the aperture of the aperture, and the P-silicon beam is blocked because its return direction deviates from the aperture of the aperture, so that the beam passing through the aperture consists only of the P-reference beam and the S-silicon beam.

5. The interferometric measurement method for a large warped wafer according to claim 1, characterized in that, In step S4, the S-silicon light enters the polarizing beam splitter and is reflected, then converted into circularly polarized light by the second quarter-wave plate, and after being reflected by the plane mirror, it returns along the original path. After passing through the second quarter-wave plate again, it is converted into P-silicon light. The P-silicon light passes through the polarizing beam splitter and is converted into circularly polarized light by the third quarter-wave plate before entering the imaging mirror and camera.

6. The interferometric measurement method for a large warped wafer according to claim 1, characterized in that, In step S5, the deformable mirror is a liquid lens. The liquid lens drives the liquid to squeeze towards the center of the diaphragm or back from the center of the diaphragm, so that the reflecting surface of the deformable mirror changes between convex, concave and planar states, thereby modulating the planar reference wavefront.

7. The interferometric measurement method for a large warped wafer according to claim 1, characterized in that, The calculation system calculates the surface shape information of the wafer under test according to the following relationship: ； in, For the surface shape information of the wafer being tested, The surface shape information of the deformable mirror measured by the wavefront sensor. The relative surface shape change of the tested wafer relative to the deformable mirror is obtained from the analysis of the interference fringe pattern.

8. An interferometric measurement device for a large warped wafer, characterized in that, include: A laser, used to output detection light; A quarter-wave plate and a birefringent crystal are arranged sequentially along the outgoing optical path of the detection light to convert and separate the detection light into orthogonally polarized P-light and S-light; The microscope objective, the first beam splitter, and the first collimating lens are used to form the P-ray and S-ray into parallel rays with opposite angles relative to the optical axis of the first collimating lens; The reference mirror and the wafer carrier under test are used to form P-reference light, S-reference light, and S-silicon light and P-silicon light, respectively; An aperture is positioned on the return path to allow the P-reference light and the S-silicon light to pass through, while blocking the S-reference light and the P-silicon light. The second collimating lens and the polarizing beam splitter are disposed on the optical path after the aperture; The first reflection branch includes a second quarter-wave plate and a plane mirror, used to receive the S-silicon light and form a measurement beam carrying information about the surface shape of the wafer under test; The second reflection branch includes a fourth quarter-wave plate, a second beam splitter, and a deformable mirror, for receiving the P-reference light and modulating the planar reference wavefront formed by the P-reference light into a modulated reference beam that matches the measurement beam through the deformable mirror; The imaging branch, including a third quarter-wave plate, an imaging mirror, and a camera, is used to receive the measurement beam and the modulated reference beam and form an interference fringe pattern. A wavefront sensor is used to measure the surface shape information V1 of the deformable mirror; The computing system, connected to the wavefront sensor and the camera, is used to analyze the relative surface shape change ΔV based on the interference fringe pattern, and to calculate the surface shape information Vsilicon of the wafer under test based on the surface shape information V1 and the relative surface shape change ΔV. The deformable mirror is configured to modulate the surface shape of the planar reference wavefront corresponding to the P-reference beam, so that a resolvable interference fringe is formed between the modulated reference beam entering the camera and the measurement beam.

9. The interferometric measurement apparatus for large warped wafers according to claim 8, characterized in that, At least one of the reference mirror and the wafer under test carrier is connected to an attitude adjustment mechanism. The attitude adjustment mechanism is used to adjust the spatial attitude of the reference mirror and / or the wafer under test, so that the P-reference light and the S-silicon light return along the light transmission direction of the aperture, and so that the S-reference light and the P-silicon light deviate from the light transmission direction of the aperture.

10. The interferometric measurement apparatus for a large warped wafer according to claim 8, characterized in that, The deformable mirror is a liquid lens, which includes a deformable diaphragm and a driving mechanism for driving liquid to act on the deformable diaphragm. The driving mechanism is used to change the convex and concave state of the deformable diaphragm to change the reflected wavefront of the deformable mirror. The wavefront sensor is used to measure the radius and / or surface shape changes of the deformable mirror in real time and transmit the measurement results to the computing system.

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