Wafer defect detection method based on phase information

Abstract

The application discloses a wafer defect detection method based on phase information and belongs to the technical field of wafer detection. The method is realized based on a wafer defect detection system of common-path interference structure. An illumination assembly in the system emits a light beam, the light beam passes through a wafer sample and a microscopic imaging assembly, and amplified wafer sample reflected light is obtained. A grating beam-splitting interference assembly diffracts and splits the reflected light and causes interference. A CMOS image sensor converts the interference light intensity signal into an electric signal and transmits the electric signal to a computer for image processing and defect identification. After interference images of a reference wafer and a wafer to be detected are acquired, the reconstructed results of different diffraction distances are calculated according to the recovered complex amplitude. Since a focusing evaluation function of defect information has higher sensitivity to diffraction distance change, the defect information can be distinguished from the background according to the statistical characteristics of the focusing evaluation function. The application has high detection precision, low calculation complexity, can suppress noise information and has important practical significance.

Description

Technical Field

[0001] This invention relates to the field of wafer inspection technology, and in particular to a wafer defect detection method based on phase information. Background Technology

[0002] With the deepening of global digital transformation, the rapid development and integration of information technology and the internet have promoted the comprehensive upgrading of various industries towards digitalization, networking, and intelligence. Against this backdrop, advanced technology industries such as smartphones, personal computers, IoT devices, and automotive electronics have experienced significant growth. This rapid development in these fields has placed higher demands on the performance of semiconductor chips, primarily including enhanced computing power, lower energy consumption, smaller size, and higher integration. As a key foundation for semiconductor manufacturing, the quality of wafers directly affects chip yield and production costs.

[0003] Common defects on bare wafer surfaces, such as particle contamination and scratches, can significantly impact subsequent processing steps. Particle defects may originate from environmental contamination during manufacturing, such as dust and chemical residues, while scratches may be introduced by equipment or caused by physical contact. Even nanoscale defects can severely affect the performance of integrated circuits or even cause them to fail.

[0004] In the field of wafer defect detection technology, optical inspection systems based on bright-field and dark-field illumination are currently the mainstream methods used in wafer defect inspection equipment on the market. Considering the physical properties of light, both bright-field and dark-field detection technologies identify defects by analyzing the amplitude information of light.

[0005] Compared to the amplitude information of light, phase information is more sensitive in the vertical direction. Phase-based optical systems utilize the wavelength of light as a measurement scale, enabling precise capture of even extremely minute morphological changes on the sample surface. Even very slight morphological changes can induce significant changes in interference fringes by proportionally adjusting the wavelength of light, thus achieving highly sensitive detection. Although phase-based optical detection technology has seen significant development in other fields, its application in the semiconductor industry is relatively limited.

[0006] Nativ et al. [Nativ A, Feldman H, Shaked NT. Wafer defect detection by apolarization-insensitive external differential interference contrast module[J]. Applied optics, 2018, 57(13): 3534-3538.] used a differential interference phase contrast system to detect defects in semiconductor wafers. Compared with bright field imaging, they obtained an enhancement of the defect signal relative to the surrounding wafer pattern. However, differential interference phase contrast technology provides a qualitative measurement relative to the phase change and cannot directly give quantitative data of the sample phase, so it has significant limitations.

[0007] Zhou et al. [Zhou R, Edwards C, Popescu G, et al. Diffraction phasemicroscopy for wafer inspection[C] / / IEEE Photonics Conference 2012. IEEE,2012: 644-645.] used acquired interferograms to calculate the wafer surface profile and highlighted wafer defect information by subtracting the difference results obtained from adjacent images. However, for certain types of noise, especially when the noise level varies over time or is related to the level of the data itself, the simple difference method cannot effectively reduce noise.

[0008] Therefore, in order to improve the accuracy and efficiency of wafer defect detection, it is necessary to design a wafer defect detection method based on phase information. Summary of the Invention

[0009] To address the issues of insufficient accuracy and efficiency in existing wafer defect detection technologies, the present invention aims to provide a wafer defect detection method based on phase information, thereby at least partially solving the aforementioned problems.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows:

[0011] In a first aspect, the present invention provides a wafer defect detection method based on phase information, the method comprising the following steps:

[0012] S1. Construct a wafer defect detection system based on a common optical path interference structure and adjust the focus correctly;

[0013] S2. The wafer defect detection system acquires interference images of a defect-free reference wafer and the wafer under test, respectively.

[0014] S3. The interference images of the reference wafer and the wafer under test are calculated using the digital holographic restoration algorithm to obtain the complex amplitude of the reference wafer and the complex amplitude of the wafer under test.

[0015] S4. Using the diffraction distance as a variable and setting its range and spacing, perform diffraction reconstruction on the complex amplitudes of the reference wafer and the wafer under test respectively to obtain two complex amplitude sequences, each containing n diffraction reconstruction results.

[0016] S5. Through formula Phase images are obtained by calculating the diffraction reconstruction results based on the same diffraction distance in two complex amplitude sequences. ;in, O i Indicates the first i The diffraction reconstruction results are obtained by reconstructing the complex amplitude of the wafer under test at various diffraction distances. R i Indicates the first i The diffraction reconstruction results are obtained by reconstructing the complex amplitude of the reference wafer at various diffraction distances. This indicates finding the complex conjugate, angle{} is the phase extraction function, and Wrap{} is the unwrapping function;

[0017] S6. Use the Laplace function as the focus evaluation function to calculate the pixel-level focus evaluation function value for the phase image and obtain n discrete values ​​of the focus evaluation function corresponding to each pixel.

[0018] S7. Calculate the standard deviation of the discrete values ​​of the n focus evaluation functions corresponding to each pixel, and generate an output image based on the standard deviation of all pixels. Obtain the defect information of the wafer under test based on the output image.

[0019] In some preferred embodiments, in step S1, the wafer defect detection system based on a common-path interference structure includes an illumination component, a wafer sample platform, a microscopic imaging component, a grating beam splitter interference component, a CMOS image sensor, and a computer; wherein, the illumination component is used to generate a uniformly distributed Gaussian beam; the wafer sample platform is used to support a reference wafer and a wafer under test; the microscopic imaging component and the grating beam splitter interference component constitute an interference microscopic imaging subsystem, which is used to perform microscopic imaging of the reflected light from the reference wafer and the wafer under test and generate interference; the CMOS image sensor is used to record the interference information generated by the interference microscopic imaging subsystem and form an interference image; and the computer is used to process the interference image.

[0020] In some preferred embodiments, the wafer defect detection system based on the common-path interference structure further includes a beam-expanding filter component for filtering and expanding the Gaussian beam.

[0021] In some preferred embodiments, in step S4, the diffraction reconstruction calculation process is implemented using the exact transfer function method based on angular spectrum theory.

[0022] In a second aspect, the present invention also provides an electronic device, including a memory storing executable program code and a processor coupled to the memory; wherein the processor calls the executable program code stored in the memory to execute the method described above.

[0023] Thirdly, the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the method described above.

[0024] The beneficial effects of the present invention using the above technical solution are as follows: The present invention utilizes the high sensitivity of light phase information in the vertical direction to convert the phase information of wafer defects into intensity information through interference and record it in the interference pattern, thereby effectively improving detection accuracy. The wafer defect detection method based on phase information provided by the present invention utilizes the higher sensitivity of the defect information's focusing evaluation function to diffraction distance changes, and distinguishes defect information from the background based on differential detection, thereby effectively suppressing interference from noise information. Attached Figure Description

[0025] Figure 1 This is a flowchart of the wafer defect detection method based on phase information according to the present invention.

[0026] Figure 2 This is a schematic diagram of the wafer defect detection system based on the common optical path interference structure in this invention.

[0027] Figure 3 This is an interference image of a wafer containing 200nm microsphere defects, as illustrated in an embodiment of the present invention.

[0028] Figure 4 This is an output image reflecting the calculation results of wafer defects in an embodiment of the present invention.

[0029] Figure 5 This is the phase result obtained by calculating the original complex amplitude in an embodiment of the present invention.

[0030] Figure 6 This is the defect detection result in an embodiment of the present invention.

[0031] Figure 7 This refers to the electronic device described in this embodiment of the invention.

[0032] The diagram is labeled as follows: 1-Illumination source; 2-Beam expander and filter assembly; 21-Aspherical lens; 22-Precision pinhole; 23-Planar-convex lens; 3-Wafer sample platform; 4-Wafer under test; 5-Microscopic imaging assembly; 51-Cemented doublet lens; 52-Microscopic objective lens; 53-Planar beam splitter; 54-Planar mirror; 55-Tube lens; 6-Grating beam splitter interference assembly; 61-Transmission grating; 62-Cemented doublet lens; 63-Spatial filter; 64-Cemented doublet lens; 7-CMOS image sensor; 8-Computer. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] Example 1

[0035] A wafer defect detection method based on phase information, such as Figure 1 As shown, the method includes seven steps, S1-S7.

[0036] S1. Construct a wafer defect detection system based on a common optical path interference structure and adjust the focus correctly.

[0037] like Figure 2 As shown, the wafer defect detection system based on the common-path interference structure includes an illumination component 1, a beam expander and filter component 2, a wafer sample platform 3, a microscopic imaging component 5, a grating beam splitter and interference component 6, a CMOS image sensor 7, and a computer 8.

[0038] The illumination component 1 is used to generate a uniformly distributed Gaussian beam, such as a laser diode module capable of emitting a wavelength of 455 nm.

[0039] The beam expander and filter assembly 2 is used to filter and expand the Gaussian beam emitted by the illumination assembly 1. The beam expander and filter assembly 2 includes an aspherical lens 21, a precision pinhole 22, and a plano-convex lens 23. The aspherical lens 21 and the plano-convex lens 23 constitute a Keplerian beam expander system for expanding the incident beam to reduce its divergence angle. The precision pinhole 22 is located at the back focal plane of the aspherical lens 21 and is used to filter out edge fringes around the Gaussian beam spot.

[0040] The wafer sample platform 3 is used to hold a defect-free reference wafer or a wafer under test 4, and to perform rotation, translation, and focusing operations. The wafer under test 4 is reflected after the laser beam is incident perpendicularly on its surface, and the reflected light carries information that can characterize the surface condition of the wafer under test.

[0041] The microscopic imaging component 5 and the grating beam splitting interference component 6 constitute an interference microscopic imaging subsystem. This interference microscopic imaging subsystem is used to perform microscopic imaging and generate interference on the reflected light from the reference wafer and the wafer under test.

[0042] Specifically, the microscopic imaging component 5 is used to image and magnify the reflected light from the wafer (reference wafer or wafer under test 4, hereinafter the same). The microscopic imaging component 5 includes a cemented doublet lens 51, a microscope objective lens 52, a flat beam splitter 53, a plane mirror 54, and a tube lens 55. First, the incident beam transmitted from the beam expander and filter component 2 is reflected by the cemented doublet lens 51 and the flat beam splitter 53, then focused on the front focal plane of the microscope objective lens 52. It is then transformed into parallel light by the microscope objective lens 52, and finally imaged and magnified after passing through the microscope objective lens 52, the flat beam splitter 53, the plane mirror 54, and the tube lens 55. The plane mirror 54 is used to fold the optical path and can be adjusted according to actual spatial requirements.

[0043] The grating beam splitter interference assembly 6 is used to achieve interference imaging of the reflected light from the wafer. The grating beam splitter interference assembly 6 includes a transmission grating 61, a cemented doublet lens 62, a spatial filter 63, and a cemented doublet lens 64. The cemented doublet lens 62 and the cemented doublet lens 64 form a 4f system, with the spatial filter 63 located in its Fourier plane, and the front focal plane of the cemented doublet lens 62 coinciding with the rear focal plane of the tube lens 55. The incident beam transmitted from the microscopic imaging assembly 5 undergoes multi-order diffraction after passing through the transmission grating 61. The +1st order diffracted light is focused at the small circular aperture of the spatial filter 63 after passing through the cemented doublet lens 62, retaining only the DC term, and then becomes parallel light through the cemented doublet lens 64, serving as the reference beam for interference. The 0th order light is focused at the large circular aperture of the spatial filter 63 after passing through the cemented doublet lens 62, retaining the object light information, and then serves as the object light wave for interference through the cemented doublet lens 64.

[0044] The CMOS image sensor 7 is used to record the interference information generated by the interferometric microscopy imaging subsystem and form an interference image. The CMOS image sensor 7 has a 2048×2048 rectangular pixel array, exhibiting high quantum efficiency and a 16-bit bit depth. The target surface of the CMOS image sensor 7 is located at the back focal plane of the cemented doublet lens 64, and the CMOS image sensor 7 is connected to the computer 8. The computer 8 controls its exposure time and other parameters, transmitting the acquired interference image to the computer 8 for processing.

[0045] Computer 8 then processes the interference image according to the other steps of the method of the present invention.

[0046] S2. Interference images of a defect-free reference wafer and the wafer under test are acquired using a wafer defect detection system.

[0047] First, a defect-free reference wafer is placed on the wafer sample platform 3, and the reference wafer is adjusted and properly focused. The interference image of the reference wafer is acquired using the CMOS image sensor 7. Then, the reference wafer is replaced with the wafer under test, and the interference image of the wafer under test is acquired, as shown below. Figure 3 As shown, it is a wafer interference image containing 200nm microsphere defects.

[0048] S3. The interference images of the reference wafer and the wafer under test are calculated using the digital holographic restoration algorithm to obtain the complex amplitude of the reference wafer and the complex amplitude of the wafer under test.

[0049] In this embodiment, Fourier transforms are performed on the interference images of the reference wafer and the wafer under test, respectively, and their Fourier spectra are obtained. Then, the +1 order terms in the spectrum are filtered out and shifted to the center of the spectrum, and then an inverse Fourier transform is performed to obtain the complex amplitude of the object light wave. This process can be described as follows:

[0050] Where IFT and FT represent the inverse Fourier transform and the Fourier transform, respectively. I To obtain the interference image, w This is a filter function that can filter out the +1 level portion and shift it to the center of the spectrum. A The obtained complex amplitude.

[0051] S4. Using the diffraction distance as a variable and setting its range and spacing, perform diffraction reconstruction on the complex amplitudes of the reference wafer and the wafer under test respectively to obtain two complex amplitude sequences, each containing n diffraction reconstruction results.

[0052] Here, n refers to the number of times the diffraction distance changes, and each time the diffraction distance changes, the complex amplitude of the reference wafer and the wafer under test is reconstructed by diffraction.

[0053] The diffraction reconstruction calculation process is implemented using the exact transfer function method based on angular spectrum theory.

[0054] S5. Through formula Phase images are obtained by calculating the diffraction reconstruction results based on the same diffraction distance in two complex amplitude sequences. ;in, O i Indicates the first i The diffraction reconstruction results are obtained by reconstructing the complex amplitude of the wafer under test at various diffraction distances. R i Indicates the first i The diffraction reconstruction results are obtained by reconstructing the complex amplitude of the reference wafer at various diffraction distances. This indicates finding the complex conjugate, angle{} is the phase extraction function, and Wrap{} is the unwrapping function.

[0055] S6. Use the Laplace function as the focus evaluation function to calculate the pixel-level focus evaluation function value for the phase image, and obtain n discrete values ​​of the focus evaluation function corresponding to each pixel.

[0056] S7. Calculate the standard deviation of the discrete values ​​of the n focus evaluation functions corresponding to each pixel, and generate an output image based on the standard deviation of all pixels. Obtain the defect information of the wafer under test based on the output image.

[0057] Since wafer 4 under test is near the optimal focusing position, the defects on it have a higher phase gradient compared to the wafer background. The focusing evaluation function value of the pixel corresponding to this defect varies significantly with the diffraction distance. Noise introduced by the detection system, such as false fringes, as well as secondary reflections from optical elements in the system and small dust or scratches on the surface of the elements, are far from the optimal focusing position, and the focusing evaluation function value of the corresponding pixel varies less with the diffraction distance.

[0058] Thus, the standard deviation is calculated for the n discrete values ​​of the focus evaluation function corresponding to each pixel, and the result is as follows: Figure 4 As shown, this is the output image reflecting the wafer defect calculation results. The image consists of defect areas represented by high-value pixels and defect-free areas represented by a smooth background, compared with the phase result obtained through the original complex amplitude calculation. Figure 5 In contrast, this image highlights defect information and suppresses interference from noise; reasonable threshold segmentation is used to... Figure 4 After processing, the following can be obtained: Figure 6 The defect detection results are shown.

[0059] In summary, the wafer defect detection method based on phase information provided by this invention can obtain the phase information of wafer defects through interference, thereby effectively improving the detection accuracy of wafer defects. Furthermore, the application of a differential denoising algorithm improves the signal-to-noise ratio of defect information in the output image compared to the phase information in the original complex amplitude, thus further enhancing detection accuracy and efficiency.

[0060] Example 2

[0061] An electronic device, such as Figure 7 As shown, it includes a memory storing executable program code and a processor coupled to the memory; wherein the processor calls the executable program code stored in the memory to execute the method steps disclosed in the above embodiments.

[0062] Example 3

[0063] A computer storage medium storing a computer program, wherein the computer program is executed by a processor to perform the method steps disclosed in the above embodiments.

[0064] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0065] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0066] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0067] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "front", "rear", etc., indicate the orientation or positional relationship based on the description of the structure of this invention shown in the accompanying drawings. They are only for the convenience of describing this invention 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. Therefore, they should not be construed as limitations on this invention.

[0068] The terms "first" and "second" in this technical solution are merely designations for corresponding structures that are identical or similar, or that perform similar functions. They do not represent an arrangement of the importance of these structures, nor do they imply any ranking, comparison of size, or other meaning.

[0069] Furthermore, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, a connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two structures. Those skilled in the art can understand the specific meaning of the above terms in this invention by considering the overall concept of the invention and the specific context of the solution.

[0070] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A wafer defect detection method based on phase information, characterized in that, The method includes the following steps: S1. Construct a wafer defect detection system based on a common optical path interference structure and adjust the focus correctly; S2. The wafer defect detection system acquires interference images of a defect-free reference wafer and the wafer under test, respectively. S3. The interference images of the reference wafer and the wafer under test are calculated using the digital holographic restoration algorithm to obtain the complex amplitude of the reference wafer and the complex amplitude of the wafer under test. S4. Using the diffraction distance as a variable and setting its range and spacing, calculate the diffraction reconstruction results at different distances for the complex amplitude of the reference wafer and the wafer under test, respectively, and obtain two complex amplitude sequences, each containing n diffraction reconstruction results. S5. Through formula Phase images are obtained by calculating the diffraction reconstruction results based on the same diffraction distance in two complex amplitude sequences. ;in, O i Indicates the first i The diffraction reconstruction results are obtained by reconstructing the complex amplitude of the wafer under test at various diffraction distances. R i Indicates the first i The diffraction reconstruction results are obtained by reconstructing the complex amplitude of the reference wafer at various diffraction distances. This indicates finding the complex conjugate, angle{} is the phase extraction function, and Wrap{} is the unwrapping function; S6. Use the Laplace function as the focus evaluation function to calculate the pixel-level focus evaluation function value for the phase image, and obtain n discrete values ​​of the focus evaluation function corresponding to each pixel in the phase image. S7. Calculate the standard deviation of the discrete values ​​of the n focus evaluation functions corresponding to each pixel, and generate an output image based on the standard deviation of all pixels. Obtain the defect information of the wafer under test based on the output image.

2. The method according to claim 1, characterized in that: In step S1, the wafer defect detection system based on the common-path interference structure includes an illumination component, a wafer sample platform, a microscopic imaging component, a grating beam splitter interference component, a CMOS image sensor, and a computer. The illumination component generates a uniformly distributed Gaussian beam. The wafer sample platform supports a reference wafer and the wafer under test. The microscopic imaging component and the grating beam splitter interference component constitute an interference microscopic imaging subsystem, which performs microscopic imaging of the reflected light from the reference wafer and the wafer under test to generate interference. The CMOS image sensor records the interference information generated by the interference microscopic imaging subsystem and forms an interference image. The computer processes the interference image.

3. The method according to claim 2, characterized in that: The wafer defect detection system based on the common-path interference structure also includes a beam-expanding filter component for filtering and expanding the Gaussian beam.

4. The method according to claim 1, characterized in that: In step S4, the diffraction reconstruction calculation process is implemented using the exact transfer function method based on angular spectrum theory.

5. An electronic device, characterized in that: The method includes a memory storing executable program code and a processor coupled to the memory; wherein the processor invokes the executable program code stored in the memory to perform the method as described in any one of claims 1-4.

6. A computer-readable storage medium storing a computer program, characterized in that: The computer program is executed by the processor to perform the method as described in any one of claims 1-4.

Images