A multi-channel system for detecting patternless wafer defects

Abstract

The application discloses a kind of no-pattern wafer defect multi-channel detection systems, including optical fiber bundle, collimating lens, first slit diaphragm, polarizing beam splitter, first barrel lens, first dichroic mirror, second dichroic mirror, DIC prism, first objective lens, wafer, second slit diaphragm, relay lens, first linear array camera, second objective lens, mirror, polarizer, second barrel lens, second linear array camera, nanosecond laser, shaper, third dichroic mirror, third barrel lens, first TDI camera, fourth barrel lens, second TDI camera, fourth dichroic mirror, fifth barrel lens, third TDI camera, sixth barrel lens and fourth TDI camera.Through these elements, wafer surface, subsurface and internal stress defect detection can be achieved, and simultaneous detection of wafer surface defects and wafer subsurface defects, wafer internal stress defects and wafer subsurface defects can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of wafer inspection, specifically relating to a multi-channel inspection system for patternless wafer defects. Background Technology

[0002] A DIC prism is a differential interference prism, which can be a Wollaston prism or a Nomarsky prism. It is usually composed of two birefringent wedges. When polarized light is incident on a DIC prism, it will be split into two linearly polarized rays with perpendicularly intersecting polarization planes.

[0003] A polarizing beam splitter is an optical element that has polarization and analysis functions. It can transmit P-beams and reflect S-beams.

[0004] TDI cameras, also known as time-delay integration cameras, greatly enhance the signal-to-noise ratio of the collected images by taking multiple exposures of the same target and integrating the exposures over time.

[0005] Wafer defect inspection refers to the technology of detecting internal growth defects, subsurface defects, and surface defects on the wafer surface and recording their location and quantity. Wafer defect inspection can detect problems early and is therefore widely used in various stages of chip manufacturing, such as wafer fabrication and patterned wafer lithography. Wafer defect inspection is increasingly being automated, and with the improvement of manufacturing processes, wafer defect inspection equipment needs to detect smaller defect sizes and places higher demands on the inspection speed.

[0006] Patternless wafers refer to smooth wafers whose surfaces have not undergone etching and are free of patterns. The requirements for inspecting patternless wafers are high speed and high sensitivity. Conventional methods for inspecting patternless wafers include dark-field and bright-field methods, as well as fluorescence methods such as photoluminescence.

[0007] There are many types of defects in patternless wafers, which can be broadly classified into surface defects such as scratches, grains, and dirt; subsurface defects such as stacking faults and dislocations; and internal defects such as stress defects and bubbles.

[0008] Currently, both bare wafer manufacturers and lithography manufacturers need to pay attention to these defects. However, there is no equipment on the market that can detect all of these defects. Manufacturers need to purchase multiple sets of equipment to complete the wafer inspection task, which increases the procurement cost and inspection time cost. Therefore, there is an urgent need for a set of equipment that can simultaneously detect surface, subsurface and internal defects, and preferably be able to detect multiple types of defects at high speed. Summary of the Invention

[0009] In view of the above, the purpose of this invention is to provide a patternless wafer defect multi-channel detection system that can detect a variety of wafer defects, and is low in cost and has good imaging effect.

[0010] To achieve the above-mentioned objectives, an embodiment provides a patternless wafer defect multi-channel detection system. When used for wafer surface defect detection, it includes an optical fiber bundle, a collimating lens, a first slit stop, a polarizing beam splitter, a first tube mirror, a first dichroic mirror, a second dichroic mirror, a DIC prism, a first objective lens, a second slit stop, a repeater mirror, and a first linear array camera. The first slit stop is located at the focal point of the first tube mirror. The optical axis of the DIC prism is at 45° to the polarization direction of the incident light. The polarizing beam splitter's polarization direction and analysis direction are both at 45° to the optical axis of the DIC prism.

[0011] The continuous light emitted from the fiber bundle is collimated by a collimating lens and selectively transmitted through a first slit aperture before illuminating a polarizing beam splitter. The polarizing beam splitter splits the incident light into a first p-ray and a first s-ray with different polarization characteristics. The first s-ray is reflected by the polarizing beam splitter to a first tube mirror, collimated by the first tube mirror, and then transmitted through a first dichroic mirror and a second dichroic mirror before illuminating a DIC prism. The DIC prism splits the incident light into two separate beams, o-ray and e-ray, with the intersection plane of the o-ray and e-ray coinciding with the back focal plane of the first objective lens. The o-ray and e-ray converge on the wafer surface after passing through the first objective lens. The wafer surface reflects the o-ray and e-ray and collects them again by the first objective lens, then they are recombined by the DIC prism. A beam of light, after being converged, passes sequentially through a second dichroic mirror and a first dichroic mirror before reaching a first tube mirror. The first tube mirror focuses the information-carrying beam onto a polarizing beam splitter. The beam is first polarized by the polarizing beam splitter and reflected as a second s-ray. Then, it passes through a DIC prism and is analyzed by the polarizing beam splitter, thus creating the conditions for differential interference imaging. The polarizing beam splitter also transmits a second p-ray, which is converged by a second slit stop. The first slit stop, the second slit stop, and the upper surface of the wafer are conjugate to each other, creating the conditions for linear confocal imaging. The second slit stop filters out stray light from the upper and lower surfaces of the wafer, improving the imaging contrast. The light rays passing through the second slit stop are imaged by a relay mirror and then converged to a first linear array camera.

[0012] Preferably, when used for detecting internal stress defects in wafers, the system further includes a second objective lens, a reflector, an analyzer, a second telescope, and a second linear array camera.

[0013] The continuous light emitted from the fiber bundle is collimated by a collimating lens and selectively transmitted through a first slit aperture before illuminating a polarizing beam splitter. The polarizing beam splitter splits the incident light into a first p-ray and a first s-ray with different polarization characteristics. The first s-ray is reflected by the polarizing beam splitter to a first tube lens, collimated by the first tube lens, and then passed through a first dichroic mirror and a second dichroic mirror before directly entering the first objective lens. The first objective lens converges the light onto the lower surface of the wafer. Stress defects inside the wafer alter the polarization characteristics of the first s-ray, carrying information about the wafer's internal stress. The beam containing this stress information is received by the second objective lens, collimated into parallel light, and then reflected by a mirror to an analyzer. The polarization direction of the analyzer is perpendicular to the polarization direction of the first s-ray polarized by the polarizing beam splitter. Therefore, only the beam containing the wafer's internal stress information can pass through the analyzer and be received by the second tube lens. After being converged by the second tube lens, it is received by the second linear array camera.

[0014] The polarizing beam splitter, the first objective lens, the second objective lens, and the analyzer constitute the conditions for transmission stress observation.

[0015] Preferably, when used for wafer subsurface defect detection, the system further includes a nanosecond laser, a shaper, a third dichroic mirror, a third cylindrical mirror, a first TDI camera, a fourth cylindrical mirror, a second TDI camera, a fourth dichroic mirror, a fifth cylindrical mirror, a third TDI camera, a sixth cylindrical mirror, and a fourth TDI camera.

[0016] A nanosecond laser emits nanosecond pulses, which are shaped into patterned spots by a shaper and then irradiate the upper surface of a wafer. Part of the light irradiating the wafer's surface is absorbed, and part is reflected. When subsurface defects on the wafer absorb the light energy, they are excited to emit fluorescence of different wavelengths. This fluorescence is received and collimated by a first objective lens and then input to a second dichroic mirror.

[0017] The second dichroic mirror is a long-pass dichroic mirror. The short-wavelength fluorescence reflected by the second dichroic mirror enters the short-wavelength fluorescence imaging channel. In the short-wavelength fluorescence imaging channel, the reflected fluorescence passes through the third dichroic mirror for further subdivision of the fluorescence wavelength. The even shorter-wavelength fluorescence transmitted through the third dichroic mirror is received by the fourth tube mirror and converged to the second TDI camera. The fluorescence reflected by the third dichroic mirror is reflected to the third tube mirror and converged to the first TDI camera.

[0018] The long-wavelength fluorescence transmitted through the second dichroic mirror is received by the first dichroic mirror. The first dichroic mirror uses another long-pass dichroic mirror. The fluorescence reflected by the first dichroic mirror enters the long-wavelength fluorescence imaging channel. In the long-wavelength fluorescence imaging channel, the reflected fluorescence passes through the fourth dichroic mirror for further fluorescence wavelength subdivision. The longer-wavelength fluorescence transmitted through the fourth dichroic mirror is received by the fifth tube mirror and converged to the third TDI camera. The fluorescence reflected by the fourth dichroic mirror is reflected to the sixth tube mirror and converged to the fourth TDI camera.

[0019] Among them, the four RGI cameras, namely the first TDI camera 123, the second TDI camera 125, the third TDI camera 128, and the fourth TDI camera 130, have the same line frequency, and the output light frequency of the nanosecond laser 119 is an integer multiple of the line frequency of the first TDI camera 123.

[0020] Preferably, a first bandpass filter is inserted between the third tube mirror and the third dichroic mirror to further extract fluorescence;

[0021] A second bandpass filter is inserted between the fourth tube mirror and the third dichroic mirror to further extract fluorescence.

[0022] Preferably, a third bandpass filter is inserted between the third tube mirror and the fourth dichroic mirror to further extract fluorescence;

[0023] A fourth bandpass filter is inserted between the fifth tube mirror and the fourth dichroic mirror to further extract fluorescence.

[0024] Preferably, when performing wafer subsurface defect detection, the output light frequency of the nanosecond laser is an integer multiple of the line frequency of the TDI camera;

[0025] The exposure triggering of the first, second, third, and fourth TDI cameras all needs to be synchronized with the triggering and holding time of the nanosecond laser.

[0026] Preferably, when performing wafer subsurface defect detection, a fifth bandpass filter is inserted between the fourth tube mirror and the third dichroic mirror, so that the third dichroic mirror, the fifth bandpass filter, the fourth tube mirror, and the second TDI camera form a dark field imaging channel for dark field imaging.

[0027] Preferably, a linear scanning method is used for wafer defect detection.

[0028] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0029] The patternless wafer defect multi-channel detection system provided by this invention can detect defects on the wafer surface, subsurface and internal stress, and can simultaneously detect wafer surface defects and wafer subsurface defects, as well as wafer stress defects and wafer subsurface defects. Moreover, the system has low cost and good imaging effect. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the structure of the patternless wafer defect multi-channel detection system provided in the embodiment;

[0032] Figure 2 This is a schematic diagram illustrating the positional relationship between the polarization direction of the polarizing beam splitter and the crystal axis direction of the DIC prism during wafer surface defect detection, as provided in the embodiment.

[0033] Figure 3 This is a schematic diagram illustrating the positional relationship between the polarization direction of the polarizing beam splitter and the polarization direction of the analyzer during wafer internal stress defect detection, as provided in the embodiment.

[0034] Figure 4 This is a schematic diagram of the excitation light generated by the beam excitation of the wafer during wafer subsurface defect detection provided in the embodiment;

[0035] Figure 5 This is a schematic diagram of the scanning method of the patternless wafer defect multi-channel detection system provided in the embodiment during detection;

[0036] Figure 6 This is a schematic diagram of the scanning path provided in the embodiment;

[0037] Figure 7 This is a surface triangular defect image taken in Example 1;

[0038] Figure 8 This is an image of an internal triangular defect captured in Example 3;

[0039] Figure 9 The image is a photoluminescence image acquired using the unified scheme provided in the embodiment. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of this invention.

[0041] First, the terminology used in the embodiments of this invention will be explained:

[0042] Point confocal imaging refers to a technique where the object-side point field of view is received by the imaging system, stray light is filtered out through a pinhole, and then imaged onto the image detector by a relay optical system. Point confocal imaging can significantly improve the imaging resolution of the system.

[0043] Linear confocal imaging refers to a technique where the object-side linear field of view is received by the imaging system, stray light is filtered out by a slit, and then imaged onto the image detector by a relay optical system. Compared to point confocal imaging, linear confocal imaging technology can significantly improve the imaging rate.

[0044] Photoluminescence imaging (PLI) refers to the phenomenon where excitation light shines on a sample, causing fluorescence to be generated on the sample surface and inside the sample. The wavelength of the fluorescence light is usually different from that of the excitation light.

[0045] Differential interference contrast imaging technology refers to the technique of using differential interference contrast (DIC) prisms and a series of polarization and imaging elements to achieve differential interference contrast imaging, which can present a relief-like effect.

[0046] like Figure 1 As shown, the multi-channel detection system for patternless wafer defects provided in this embodiment includes an optical fiber bundle 101, a collimating lens 102, a first slit stop 103, a polarizing beam splitter 104, a first tube mirror 105, a first dichroic mirror 106, a second dichroic mirror 107, a DIC prism 108, a first objective lens 109, a wafer 110, a second slit stop 111, a repeater 112, a first linear array camera 113, a second objective lens 114, a reflector 115, an analyzer 116, a second tube mirror 117, a second linear array camera 118, a nanosecond laser 119, a shaper 120, a third dichroic mirror 121, a third tube mirror 122, a first TDI camera 123, a fourth tube mirror 124, a second TDI camera 125, a fourth dichroic mirror 126, a fifth tube mirror 127, a third TDI camera 128, a sixth tube mirror 129, and a fourth TDI camera 130. These components enable the detection of defects on the wafer surface, subsurface, and internal stress, and allow for the simultaneous detection of surface and subsurface defects, as well as internal stress defects and subsurface defects. The specific detection process for different defects on a wafer is described below.

[0047] Example 1

[0048] When performing wafer surface defect detection, differential interference imaging is used. Fiber bundle 101 emits continuous light with a certain divergence angle and a wavelength of 546 nm. This continuous light is collimated by collimating lens 102 and then blocked by first slit aperture 103, allowing only a small portion of the light in the middle to pass through. Therefore, starting from first slit aperture 103, it is similar to emitting a beam with a certain divergence angle, which is split into two beams with different polarization characteristics by polarizing beam splitter 104: a first p-beam and a first s-beam. The polarization directions of the first p-beam and the first s-beam are perpendicular to each other. The first p-beam passes through polarizing beam splitter 104, while the first s-beam is reflected by polarizing beam splitter 104. The reflected first s-beam passes through first tube mirror 105. Since first slit aperture 103 is located at the focal point of tube mirror 105, the s-beam is collimated by tube mirror 105 and then passes through first dichroic mirror 106. First dichroic mirror 106 allows light with a wavelength of 546 nm to pass through. Other properties are described in subsequent system descriptions. The light beam passing through the first dichroic mirror 106 then passes through the second dichroic mirror 107, which transmits light at a wavelength of 546 nm. Other properties are described later in the system description. The light beam passing through the second dichroic mirror 107 then passes through the DIC prism 108. The DIC prism 108 is designed to be insertable and removable; it is inserted into the system during surface defect detection. The optical axis of the DIC prism 108 is at 45° to the polarization direction of the incident s-ray. The polarized light passing through the DIC prism 108 is split into two separate polarized beams, o-ray and e-ray, and a specific optical path difference can be introduced between the o-ray and e-ray depending on the lateral position of the DIC prism 108. The o-ray and e-ray intersect at a certain position, called the interference plane of the DIC prism 108, which coincides with the back focal plane of the first objective lens 109. The o-ray and e-ray converge on the upper surface of the wafer 110 after passing through the first objective lens 109.

[0049] The unevenness of the wafer surface introduces a phase difference between the o-ray and e-ray. The o-ray and e-ray are reflected from the upper surface of wafer 110 and collected again by the first objective lens 109. They are then recombined into a single beam by the DIC prism 108. The converged beam then passes sequentially through the second dichroic mirror 107 and the first dichroic mirror 106 before reaching the first tube lens 105. The first tube lens 105 converges the information-carrying beam and then splits it into two beams with different polarization characteristics: a second p-ray and a second s-ray. Only the second p-ray can pass through the polarizing beam splitter 104. At this point, the beam is first polarized by the polarizing beam splitter 104, reflecting the second s-ray. It then passes through the DIC prism 108 and is analyzed by the polarizing beam splitter 104, thus creating the conditions for differential interference imaging. Figure 2As shown, the polarizing direction and the analyzing direction of the polarizing beam splitter 104 are both at 45° to the optical axis of the DIC prism 108. The second p-light passing through the polarizing beam splitter 104 converges at the position of the second slit stop 111. In the system structure, the first slit stop 103, the second slit stop 111, and the upper surface of the wafer 110 are conjugate to each other, constituting the conditions for linear confocal imaging. Therefore, the second slit stop 111 filters out stray light from the upper and lower surfaces of the wafer 110, improving the imaging contrast. The light passing through the second slit stop 111 is imaged by the relay mirror 112 and finally converges onto the first linear scan camera 113.

[0050] In the embodiments, the DIC prism can be a Wollaston prism or a Nomarsky prism.

[0051] Example 1 also provides a surface triangular defect photographed at an exposure time of 20 microseconds, such as Figure 7 As shown.

[0052] Example 2

[0053] When detecting internal stress defects in a wafer, polarization imaging is used. The fiber bundle 101 emits continuous light with a certain divergence angle and a wavelength of 546nm. After being collimated by the collimating lens 102, the continuous light is blocked by the first slit aperture 103, and only a small portion of the light in the middle can pass through the first slit aperture 103. Therefore, starting from the first slit stop 103, it is similar to emitting a beam with a certain divergence angle. After passing through the polarizing beam splitter 104, it is split into two beams with different polarization characteristics: a first p-beam and a first s-beam. The polarization directions of the first p-beam and the first s-beam are perpendicular to each other. The first p-beam passes through the polarizing beam splitter 104, while the first s-beam is reflected by the polarizing beam splitter 104. The reflected first s-beam passes through the first tube mirror 105. Since the first slit stop 103 is located at the focal point of the first tube mirror 105, the first s-beam is collimated by the first tube mirror 105 and then passes through the first dichroic mirror 106. The first dichroic mirror 106 transmits light with a wavelength of 546 nm. Other properties will be introduced later in the system description. The beam passing through the first dichroic mirror 106 then passes through the second dichroic mirror 107, which also transmits light with a wavelength of 546 nm. Other properties will be introduced later in the system description. Unlike surface defect detection, in internal stress defect detection, the DIC prism 108 is removed. Therefore, the light beam passing through the second dichroic mirror 107 bypasses the DIC prism 108 and directly enters the first objective lens 109, where it is focused onto the lower surface of the wafer 110. The first s-beam beam passes through the wafer 110. If there are stress defects inside the wafer, the polarization characteristics of the first s-beam will change, revealing internal stress information. This information is then received by the second objective lens 114, collimated into parallel light, and reflected by the mirror 115, reaching the analyzer 116. The polarization direction of the analyzer 116 is perpendicular to the polarization direction of the first s-beam polarized by the polarizing beam splitter 104. Figure 3 As shown. Therefore, only the beam containing information about the internal stress of the wafer can pass through the analyzer 116 and be received by the second telescope 117. The second telescope 117 converges the beam, which is then received by the second linear array camera 118. The polarizing beam splitter 104, the first objective lens 109, the second objective lens 114, and the analyzer 116 constitute the conditions for transmission stress observation.

[0054] Using the polarization imaging method described in Example 2 to detect internal stress defects can improve the accuracy of wafer internal stress detection.

[0055] Example 3

[0056] When inspecting subsurface defects on a wafer, a photoluminescence imaging method is used. A nanosecond laser 119 emits 355nm nanosecond pulsed laser light, which is coupled via optical fiber to a shaper 120. The shaper 120 shapes the nanosecond pulsed laser light into a patterned spot and illuminates the upper surface of the wafer 110. The patterned spot is a long, uniformly energetic strip-shaped spot with an illumination angle of 60 degrees to the optical axis, with the optimal Brewster angle on the wafer. Part of the patterned spot is absorbed by the wafer, while the rest is reflected from the wafer surface and does not enter the system. When the subsurface defects absorb the illumination energy, they excite fluorescence of different wavelengths. The wavelength of the fluorescence varies depending on the specific crystal defect. Figure 4 The wavelength diagram of SiC wafers under 365nm excitation light is shown. The fluorescence wavelength under 355nm excitation light is similar. Most defect wavelengths are below 530nm and above 600nm.

[0057] After receiving the excited fluorescence, the first objective lens 109 collimates the fluorescence beam. When using the wafer surface defect detection function, the beam passes through the DIC prism 108. However, when using the wafer internal stress detection function, the DIC prism 108 is removed, and the beam does not pass through it. Because fluorescence does not have polarization characteristics, the presence or absence of the DIC prism 108 will not affect the fluorescence beam. Subsequently, the fluorescence beam passes through the second dichroic mirror 107, which is a long-pass dichroic mirror that reflects fluorescence with wavelengths less than 530 nm. Therefore, fluorescence with wavelengths less than 530 nm is reflected into the short-wavelength fluorescence imaging channel. In this short-wavelength fluorescence imaging channel, the reflected fluorescence beam passes through the third dichroic mirror 121 to further subdivide the fluorescence wavelength, including 460 nm, 480 nm, and 500 nm fluorescence. The third dichroic mirror 121 reflects the fluorescence to the third tube lens, and then the third tube lens 122 converges the image onto the first TDI camera 123. Preferably, a first bandpass filter of a specific wavelength can be inserted between the third tube lens 122 and the third dichroic mirror 121 to further extract fluorescence. Additionally, short-wavelength fluorescence, such as that at 385 nm and 420 nm, passes through the third dichroic mirror 121 and is then converged by the fourth tube lens 124 to be imaged onto the second TDI camera 125. Preferably, a second bandpass filter of a specific wavelength can be inserted between the fourth tube lens 124 and the third dichroic mirror 121 to further extract fluorescence.

[0058] The light beam passing through the second dichroic mirror 107 contains near-infrared light above 600nm and 620nm. This light beam is received by the first dichroic mirror 106, a long-pass dichroic mirror designed to reflect near-infrared light above 600nm and 700nm, while transmitting the 546nm working wavelength for surface defect detection. Therefore, fluorescence with wavelengths greater than 600nm is reflected into a long-wavelength fluorescence imaging channel. In this channel, the fluorescence reflected by the first dichroic mirror 106 is further subdivided by the fourth dichroic mirror 126. The fourth dichroic mirror 126 transmits 660nm fluorescence to the fifth tube lens 127, which then converges the image onto the third TDI camera 128. Preferably, a third bandpass filter of a specific wavelength can be inserted between the fifth tube lens 127 and the fourth dichroic mirror 126 to further extract the fluorescence. The fourth dichroic mirror 126 reflects light with wavelengths above 620 nm, which is received by the sixth tube mirror 129 and then converged by the sixth tube mirror 129 onto the fourth TDI camera 130. Preferably, a fourth bandpass filter of a specific wavelength can be inserted between the sixth tube mirror 129 and the fourth dichroic mirror 126 to further extract the fluorescence.

[0059] When performing wafer subsurface defect detection, the line frequencies of the four RGI cameras—first TDI camera 123, second TDI camera 125, third TDI camera 128, and fourth TDI camera 130—must be equal, and the output light frequency of the nanosecond laser 119 must be an integer multiple of the line frequency of the first TDI camera 123. For example, if the line frequency of the TDI camera is 80 kHz, the output light frequency of the nanosecond laser 119 must also be 80 kHz, or 160 kHz, etc. An output light frequency of 160 kHz means that two fluorescence excitations occur within the exposure time of one TDI camera, which helps to improve signal strength and increase the signal-to-noise ratio. Furthermore, the exposure triggering of the first TDI camera 123, second TDI camera 125, third TDI camera 128, and fourth TDI camera 130 must be synchronized with the triggering and holding time of the nanosecond laser 119.

[0060] Example 1 also provides an internal triangular defect photographed at an exposure time of 20 microseconds, such as... Figure 8 As shown.

[0061] To compare the performance of the detection method provided in Example 3, a photoluminescence image of a triangular defect acquired using a conventional method of illumination with a mercury-xenon lamp and reception by a high-performance electron multiplier camera (EMCCD) is also provided. Figure 9 As shown, the exposure time is 200 microseconds. Analysis Figure 9The black area indicates the location of the defect. It is evident that the new solution, embodiment 3, significantly improves the signal-to-noise ratio of the acquired image while shortening the exposure time and increasing the product inspection rate.

[0062] Compared to the traditional method of using continuous light, such as mercury-xenon lamps, for illumination and high-performance electron multiplier cameras (EMCCDs) for reception, this embodiment combines a nanosecond laser and a TDI camera with synchronous triggering. The nanosecond laser can excite stronger fluorescence, while the TDI camera can enhance the image signal-to-noise ratio. This reduces the requirements for the receiving camera, significantly reducing costs without compromising detection speed and performance, while also ensuring high image contrast and signal-to-noise ratio.

[0063] In addition, when performing wafer subsurface defect inspection, the second TDI camera 125 can be used as a receiver for dark-field imaging. It is only necessary to insert a 355nm fifth bandpass filter between the fourth tube mirror 124 and the third dichroic mirror 121. In this way, the third dichroic mirror 121, the fifth bandpass filter, the fourth tube mirror 124 and the second TDI camera 125 form a dark-field imaging channel. As is well known, dark-field imaging channel detection can improve the sensitivity of defect detection.

[0064] When using the photoluminescence imaging method described in Example 3 to detect wafer subsurface defects, a nanosecond laser is used to generate high-energy pulsed light, and a linear TDI camera is used to receive fluorescence imaging. Compared with the method of using continuous light illumination and EMCCD reception, this method can significantly reduce device costs and obtain images with a high signal-to-noise ratio.

[0065] The patternless wafer defect multi-channel detection system provided in the above embodiments uses line scanning detection method when performing the three defect detection methods in embodiments 1-3. Figure 5 As shown, the displacement stage and wafer clamping device 201 fix the wafer 110 and can drive the wafer 110 to perform linear scanning along the horizontal X and Y directions. The wafer clamping device 201 has a hollow center to allow light to be received by the second objective lens 114 without obstruction during the detection of internal stress defects on the wafer. At the same time, the wafer clamping device needs to avoid interference with the second objective lens 114 during the detection process.

[0066] Scan path as follows Figure 6 As shown, the linear illumination area covers the imaging area of ​​the line scan camera. The displacement stage moves along one line, scanning the next line after one line is completed. The movement of the displacement stage triggers multiple camera exposures; for example, a 10-micrometer movement will result in one exposure. Since the object-side field of view of the line scan camera is exactly 10 micrometers, continuous scanning will form a long image. The system will stitch together the multiple scanned images, and the algorithm will identify defects based on the image and mark them on the defect map according to the displacement stage position information.

[0067] When the patternless wafer defect multi-channel detection system provided in this embodiment is used for inspection, the wafer surface defect detection function can be used simultaneously with the wafer subsurface defect detection function, and the wafer internal stress defect detection function can also be used simultaneously with the wafer subsurface defect detection function, which greatly improves the inspection efficiency. Simultaneously, the wafer subsurface defect detection function can use multiple TDI cameras to scan the characteristic wavelengths of crystal defects of interest, which is beneficial for rapid defect identification and comparison. The data acquired from multiple channels is helpful for further comparison and identification by subsequent algorithms, providing corresponding theoretical support for production or research.

[0068] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-channel inspection system for patternless wafer defects, characterized in that, When used for wafer surface defect detection, the system includes an optical fiber bundle, a collimating lens, a first slit stop, a polarizing beam splitter, a first tube mirror, a first dichroic mirror, a second dichroic mirror, a DIC prism, a first objective lens, a second slit stop, a relay mirror, and a first linear array camera. The first slit stop is located at the focal point of the first tube mirror. The optical axis of the DIC prism is at 45° to the polarization direction of the incident light. The polarizing beam splitter's polarization and analysis directions are both at 45° to the optical axis of the DIC prism. The continuous light emitted from the fiber bundle is collimated by a collimating lens and selectively transmitted through a first slit aperture before illuminating a polarizing beam splitter. The polarizing beam splitter splits the incident light into a first p-ray and a first s-ray with different polarization characteristics. The first s-ray is reflected by the polarizing beam splitter to a first tube mirror, collimated by the first tube mirror, and then transmitted through a first dichroic mirror and a second dichroic mirror before illuminating a DIC prism. The DIC prism splits the incident light into two separate beams, o-ray and e-ray, with the intersection plane of the o-ray and e-ray coinciding with the back focal plane of the first objective lens. The o-ray and e-ray converge on the wafer surface after passing through the first objective lens. The wafer surface reflects the o-ray and e-ray and collects them again by the first objective lens, then they are recombined by the DIC prism. A beam of light, after being converged, passes sequentially through a second dichroic mirror and a first dichroic mirror before reaching a first tube mirror. The first tube mirror focuses the information-carrying beam onto a polarizing beam splitter. The beam is first polarized by the polarizing beam splitter and reflected as a second s-ray. Then, it passes through a DIC prism and is analyzed by the polarizing beam splitter, thus creating the conditions for differential interference imaging. The polarizing beam splitter also transmits a second p-ray, which is converged by a second slit stop. The first slit stop, the second slit stop, and the upper surface of the wafer are conjugate to each other, creating the conditions for linear confocal imaging. The second slit stop filters out stray light from the upper and lower surfaces of the wafer, improving the imaging contrast. The light rays passing through the second slit stop are imaged by a relay mirror and then converged to a first linear array camera.

2. The patternless wafer defect multi-channel detection system according to claim 1, characterized in that, When used for detecting internal stress defects in wafers, the system further includes a second objective lens, a reflector, an analyzer, a second telescope, and a second linear array camera. The continuous light emitted from the fiber bundle is collimated by a collimating lens and selectively transmitted through a first slit aperture before illuminating a polarizing beam splitter. The polarizing beam splitter splits the incident light into a first p-ray and a first s-ray with different polarization characteristics. The first s-ray is reflected by the polarizing beam splitter to a first tube lens, collimated by the first tube lens, and then passed through a first dichroic mirror and a second dichroic mirror before directly entering the first objective lens. The first objective lens converges the light onto the lower surface of the wafer. Stress defects inside the wafer alter the polarization characteristics of the first s-ray, carrying information about the wafer's internal stress. The beam containing this stress information is received by the second objective lens, collimated into parallel light, and then reflected by a mirror to an analyzer. The polarization direction of the analyzer is perpendicular to the polarization direction of the first s-ray polarized by the polarizing beam splitter. Therefore, only the beam containing the wafer's internal stress information can pass through the analyzer and be received by the second tube lens. After being converged by the second tube lens, it is received by the second linear array camera. The polarizing beam splitter, the first objective lens, the second objective lens, and the analyzer constitute the conditions for transmission stress observation.

3. The patternless wafer defect multi-channel detection system according to claim 1 or 2, characterized in that, When used for wafer subsurface defect detection, the system further includes a nanosecond laser, a shaper, a third dichroic mirror, a third cylindrical mirror, a first TDI camera, a fourth cylindrical mirror, a second TDI camera, a fourth dichroic mirror, a fifth cylindrical mirror, a third TDI camera, a sixth cylindrical mirror, and a fourth TDI camera. A nanosecond laser emits nanosecond pulses, which are shaped into patterned spots by a shaper and then irradiate the upper surface of a wafer. Part of the light irradiating the wafer's surface is absorbed, and part is reflected. When subsurface defects on the wafer absorb the light energy, they are excited to emit fluorescence of different wavelengths. This fluorescence is received and collimated by a first objective lens and then input to a second dichroic mirror. The second dichroic mirror is a long-pass dichroic mirror. The short-wavelength fluorescence reflected by the second dichroic mirror enters the short-wavelength fluorescence imaging channel. In the short-wavelength fluorescence imaging channel, the reflected fluorescence passes through the third dichroic mirror for further subdivision of the fluorescence wavelength. The even shorter-wavelength fluorescence transmitted through the third dichroic mirror is received by the fourth tube mirror and converged to the second TDI camera. The fluorescence reflected by the third dichroic mirror is reflected to the third tube mirror and converged to the first TDI camera. The long-wavelength fluorescence transmitted through the second dichroic mirror is received by the first dichroic mirror. The first dichroic mirror uses another long-pass dichroic mirror. The fluorescence reflected by the first dichroic mirror enters the long-wavelength fluorescence imaging channel. In the long-wavelength fluorescence imaging channel, the reflected fluorescence passes through the fourth dichroic mirror for further fluorescence wavelength subdivision. The longer-wavelength fluorescence transmitted through the fourth dichroic mirror is received by the fifth tube mirror and converged to the third TDI camera. The fluorescence reflected by the fourth dichroic mirror is reflected to the sixth tube mirror and converged to the fourth TDI camera. Among them, the four RGI cameras, namely the first TDI camera 123, the second TDI camera 125, the third TDI camera 128, and the fourth TDI camera 130, have the same line frequency, and the output light frequency of the nanosecond laser 119 is an integer multiple of the line frequency of the first TDI camera 123.

4. The patternless wafer defect multi-channel detection system according to claim 3, characterized in that, A first bandpass filter is inserted between the third tube mirror and the third dichroic mirror to further extract fluorescence; A second bandpass filter is inserted between the fourth tube mirror and the third dichroic mirror to further extract fluorescence.

5. The patternless wafer defect multi-channel detection system according to claim 3, characterized in that, A third bandpass filter is inserted between the third tube mirror and the fourth dichroic mirror to further extract fluorescence; A fourth bandpass filter is inserted between the fifth tube mirror and the fourth dichroic mirror to further extract fluorescence.

6. The patternless wafer defect multi-channel detection system according to claim 3, characterized in that, When performing wafer subsurface defect detection, the output light frequency of the nanosecond laser is an integer multiple of the line frequency of the TDI camera; The exposure triggering of the first, second, third, and fourth TDI cameras all needs to be synchronized with the triggering and holding time of the nanosecond laser.

7. The patternless wafer defect multi-channel detection system according to claim 3, characterized in that, When performing wafer subsurface defect detection, a fifth bandpass filter is inserted between the fourth tube mirror and the third dichroic mirror. This forms a dark field imaging channel with the third dichroic mirror, the fifth bandpass filter, the fourth tube mirror, and the second TDI camera for dark field imaging.

8. The patternless wafer defect multi-channel detection system according to claim 1, 2, or 3, characterized in that, Wafer defect detection is performed using a linear scanning method.

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