Illumination device, dark field detection system and method

Abstract

The application provides a kind of lighting device, dark field detection system and method, comprising: based on wide field of view imaging device, the distribution position of bright defect and dark defect on the surface of wafer to be measured is pre-detected, and the defect distribution map of wafer to be measured is obtained;The light and dark degree of each defect in the defect distribution map is classified, and the light source light and dark level distribution corresponding to each position of wafer to be measured is obtained;In dark field detection device, based on line illumination light, the light source for the to-be-tested region of wafer to be measured is provided, each to-be-tested region on wafer to be measured is scanned, and the intensity of detection light signal is adjusted according to the light and dark level corresponding to light source, and the adjusted detection light signal is collected, to realize dark field detection.The application has good consistency in detection sensitivity of different pixel positions during dark field detection, high utilization rate of light source intensity, and large image acquisition dynamic range.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor defect detection, in particular to an illumination device, a dark field detection system and method. BACKGROUND

[0002] Semiconductor defect detection is to use optical microscopic imaging to perform microscopic imaging on the wafer surface, and combine image analysis and calculation to find scratches, stains, cracks or other irregularity defects on the surface of the wafer, so as to facilitate the exclusion of defect causes, and prevent the defect dies from being processed, thereby affecting the yield and productivity.

[0003] Bright field illumination imaging and dark field illumination imaging are two commonly used imaging technologies, wherein the dark field illumination refers to that the illumination light beam is projected to the sample surface at a large incident angle, and the specular reflection light is reflected at a large angle and cannot enter the objective lens to form an image. The gray scale of the image collected is all black, and the defect features on the surface exist. A part of the diffused light at the defect features enters the objective lens to form an image. These defect features are bright in the dark field, which obviously improves the signal-to-noise ratio of the defect feature imaging, and the dark field imaging has better detection effect in defect detection application.

[0004] Since the dark field illumination is mainly to detect scattered light, a large amount of reflected light is lost, and the oblique incidence mode will cause the light spot to be elongated and cause uneven illumination. Therefore, the intensity and uniformity of the dark field detection illumination light determine the quality of the defect detection, and the existing illumination device generally has problems of low illumination brightness, low light utilization rate, poor illumination uniformity and the like.

[0005] In order to improve the detection speed, the semiconductor defect detection equipment generally uses a line array camera to scan the image. Under certain light intensity conditions and certain scanning frequency, the scanning of the whole wafer surface image is completed at one time. Since the defect features on the wafer are different, some defects with strong scattering signals will cause the image to be saturated, and some defects with weak scattering signals will cause the image gray scale to be very small, which cannot be detected.

[0006] Therefore, how to consider different intensity of scattering signals and improve the dynamic range of dark field detection has become one of the problems to be solved by the person skilled in the art.

[0007] It should be noted that the above introduction to the technical background is only to facilitate the clear and complete description of the technical scheme of the present application, and to facilitate the understanding of the person skilled in the art. The above technical scheme cannot be considered as known by the person skilled in the art only because it is described in the background section of the present application. SUMMARY

[0008] In view of the above-mentioned defects of the prior art, the purpose of the present application is to provide a lighting device, a dark field detection system and a method for solving the problem that the dark field detection in the prior art cannot take into account different intensity of scattered signals and has a small dynamic range.

[0009] To achieve the above-mentioned purpose and other related purposes, the present application provides a dark field detection method, which at least comprises:

[0010] 1) a wide-field imaging device is used to pre-detect the distribution positions of bright defects and dark defects on the surface of a wafer to be measured, so as to obtain a defect distribution map of the wafer to be measured;

[0011] 2) the bright-dark degree of each defect in the defect distribution map is classified, and a light-dark level distribution corresponding to each position of the wafer to be measured is obtained based on the classification result;

[0012] 3) in a dark field detection device, a line illumination light with uniform energy distribution is used to provide light sources for the measured regions of the wafer to be measured, each measured region on the wafer to be measured is scanned, and the strength of a detection light signal is adjusted according to the light-dark level of the light source corresponding to the position of the measured region on the wafer to be measured, and the adjusted detection light signal is collected to realize dark field detection.

[0013] Optionally, the number of times of collecting images of the wafer to be measured by the wide-field imaging device in step 1) is not more than 5 times; when the number of times of collecting images is greater than or equal to 2 times, the images of each part of the wafer to be measured are obtained by translating or rotating the wafer to be measured based on the same set of wide-field imaging devices, and the defect distribution map of the entire wafer to be measured is obtained by splicing the collected part pictures.

[0014] Optionally, the length of the line illumination light is set based on the field of view of the dark field detection device in step 3).

[0015] More optionally, the line illumination light is obtained by using a double-cylindrical microlens array line flat-top spot shaping light path, and the focal length of a second-stage cylindrical microlens array is adjusted to realize the adjustment of the length of the line illumination light.

[0016] The focal length of the second-stage cylindrical microlens array is negatively related to the length of the line illumination light.

[0017] To achieve the above-mentioned purpose and other related purposes, the present application further provides a lighting device, which at least comprises:

[0018] a preliminary homogenization light path and a line flat-top spot shaping light path;

[0019] The preliminary homogenization light path provides incident light and preliminarily homogenizes the incident light to reduce the coherence of the incident light.

[0020] The line flat-top light spot shaping light path is arranged at the output end of the preliminary homogenization light path, and converts the parallel light beam output by the preliminary homization light path into a line illumination light with a flat top.

[0021] Optionally, the preliminary homogenization light path comprises a light source, a first lens, a diffusion sheet and a second lens.

[0022] The light source is configured to provide the incident light, and the incident light is a parallel light beam.

[0023] The first lens is arranged at the output end of the light source and is configured to converge the incident light.

[0024] The diffusion sheet is arranged on the focal plane of the first lens and is configured to preliminarily homogenize the converged light beam.

[0025] The second lens is arranged on the light path after the diffusion sheet and is configured to collimate the light beam after the preliminary homogenization.

[0026] Optionally, the line flat-top light spot shaping light path comprises a first cylindrical microlens array, a second cylindrical microlens array and a third lens.

[0027] The convex surface of the first cylindrical microlens array serves as an incident surface, and the plane serves as an exit surface and is arranged opposite to the plane of the second cylindrical microlens array; the plane of the second cylindrical microlens array serves as an incident surface, and the convex surface serves as an exit surface; and the third lens is arranged at the exit end of the second cylindrical microlens array and is configured to converge the light beam.

[0028] More optionally, the illumination device further comprises a reflector arranged between the preliminary homogenization light path and the line flat-top light spot shaping light path and configured to adjust the propagation direction of the light beam.

[0029] To achieve the above object and other related objects, the present application further provides a dark field detection system, which at least comprises:

[0030] a host computer, a motion platform, an objective lens, an optical element module, a DMD digital micro-mirror, a line scan camera and N illumination devices described above, N being a natural number greater than or equal to 1.

[0031] The host computer establishes a mapping relationship between the distribution positions of bright defects and dark defects on the surface of the wafer to be measured and the wafer motion scanning path and the imaging pixel position, obtains the light source bright-dark level distribution corresponding to each position of the wafer to be measured based on the defect distribution map of the wafer to be measured, and then controls the motion platform, the DMD digital micro-mirror and the line scan camera.

[0032] The motion platform is configured to carry and move the wafer to be measured.

[0033] Each of the illumination devices is arranged above the side of the motion platform, for providing large-angle line illumination light with uniform energy distribution for the to-be-tested region on the to-be-tested wafer; when N is greater than or equal to 2, each of the illumination devices is arranged in a ring around the to-be-tested region;

[0034] The objective lens is arranged directly above the to-be-tested region, for amplifying the scattered light signal of the to-be-tested region;

[0035] The optical element module converges the probe light signal output by the objective lens into the DMD digital micro-mirror, and converges the light signal reflected by the DMD digital micro-mirror into the line scanning camera;

[0036] The DMD digital micro-mirror controls the intensity of the probe light signal based on the light-dark level of the light source corresponding to the position of the to-be-tested region.

[0037] Optionally, the optical element module comprises a fourth lens, a total internal reflection prism and a fifth lens;

[0038] The fourth lens is arranged on the light path behind the objective lens, for converging light beams;

[0039] The total internal reflection prism is arranged between the fourth lens and the DMD digital micro-mirror;

[0040] The fifth lens is arranged at the light output end of the total internal reflection prism, for converging light beams.

[0041] Optionally, the dark field detection system further comprises a pre-detection device, which is used to obtain a defect distribution map of the to-be-tested wafer.

[0042] Optionally, the pre-detection device comprises a wide-field dark field illumination light source, an imaging lens group and a wide-field area array camera;

[0043] The wide-field dark field illumination light source is arranged above the side of the motion platform, for providing a light source for the to-be-tested wafer;

[0044] The imaging lens group is arranged above the to-be-tested wafer, for reducing or equal-magnification transmission of the scattered light signal on the surface of the to-be-tested wafer into the wide-field area array camera;

[0045] The wide-field area array camera is used to collect an image of the to-be-tested wafer, so as to obtain a defect detection map of the to-be-tested wafer.

[0046] As described above, the illumination device, the dark field detection system and the method of the present application have the following beneficial effects:

[0047] 1. The illumination device, dark field detection system and method of the present application have high uniformity of the illumination light source; compared with the traditional way of converging and obliquely incident illumination by a Gauss lens, the present application uses two layers of homogenization light paths of diffusion sheet and microlens array, and has high uniformity of the illumination light and good consistency of the detection sensitivity of different pixel positions in dark field detection.

[0048] 2. The illumination device, dark field detection system and method of the present application have high utilization rate of the light source intensity; the illumination light source is shaped into a line illumination mode, which is matched with the scanning area of the line scan camera (the required illumination area size is different under different objectives, and the field of view size of the line scan camera is different, so the flexible adjustment and switching of different illumination spot sizes can be realized according to the objective size, and the waste of light source energy is effectively avoided.

[0049] 3. The illumination device, dark field detection system and method of the present application have large image acquisition dynamic range; the defects with large scattering signal difference are controlled by pixel-level reflected light intensity, so that the bright defects and dark defects are detected at the same time, and the high dynamic range detection is realized by replacing multiple cameras and multiple detections. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 The structure schematic diagram of the illumination device of the present application is shown.

[0051] Figure 2 The structure schematic diagram of the dark field detection system of the present application is shown.

[0052] Figure 3 The structure schematic diagram of the pre-detection device of the present application is shown.

[0053] Figure 4 The flowchart of the dark field detection method of the present application is shown.

[0054] Figure 5 The schematic diagram of one method for obtaining the defect distribution map of the wafer to be detected of the present application is shown.

[0055] Figure 6 The schematic diagram of another method for obtaining the defect distribution map of the wafer to be detected of the present application is shown.

[0056] Figure 7 The mapping schematic diagram of the DMD digital micro mirror and the line scan camera of the present application is shown.

[0057] Figure 8 The schematic diagram of the wafer to be detected with the second column having bright defects and dark defects of the present application is shown.

[0058] Figure 9 The schematic diagram of scanning based on the bright defects and the dark defects of the present application is shown.

[0059] ELEMENT NUMBER EXPLANATION

[0060] 1 dark field detection system

[0061] 11 motion platform

[0062] 12 illumination device

[0063] 121 preliminary homogenization light path

[0064] 122 line flat-top spot shaping light path

[0065] 12a light source

[0066] 12b first lens

[0067] 12c diffusion sheet

[0068] 12d second lens

[0069] 12e first cylindrical microlens array

[0070] 12f second cylindrical microlens array

[0071] 12g third lens

[0072] 12h mirror

[0073] 13 objective lens

[0074] 14 optical element module

[0075] 141 fourth lens

[0076] 142 total internal reflection prism

[0077] 143 fifth lens

[0078] 15 DMD digital micro-mirror

[0079] 16 line-scan camera

[0080] 17 host computer

[0081] 18 pre-detection device

[0082] 181 wide-field dark-field illumination light source

[0083] 182 imaging lens group

[0084] 183 wide-field area array camera

[0085] 18a sixth lens

[0086] 18b seventh lens DETAILED DESCRIPTION

[0087] Following, the present application is described in details by the specific examples. Other advantages and effects of the present application can be easily understood by those skilled in the art from the description. The present application can also be implemented or applied by other different specific embodiments, and the details in the description can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0088] Please refer to Figures 1-9 . It is noted that the figures provided in the embodiments only schematically illustrate the basic concept of the present application, and thus the figures only show the components related to the present application, but not the number, shape and size of the components in actual implementation. The shape, number and ratio of the components in actual implementation can be arbitrarily changed, and the layout of the components can be more complicated.

[0089] As shown in Figure 1 , the present application provides a lighting device 12, which includes a primary homogenization light path 121 and a line-flat-top light spot shaping light path 122.

[0090] Specifically, the primary homogenization light path 121 provides incident light and performs primary homogenization on the incident light to reduce the coherence of the incident light. As an example, the primary homogenization light path 121 includes a light source 12a, a first lens 12b, a diffusion sheet 12c and a second lens 12d. The light source 12a is configured to provide incident light, and the incident light is a parallel light beam. The first lens 12b is disposed at the output end of the light source 12a and configured to converge the parallel incident light. The diffusion sheet 12c is disposed on the focal plane of the first lens 12b and configured to perform primary homogenization on the converged light beam. The second lens 12d is disposed on the light path after the diffusion sheet 12c and configured to collimate the light beam after the primary homogenization. In this example, the first lens 12b and the second lens 12d are focusing lenses with the same parameters.

[0091] Specifically, the line flat-top spot shaping optical path 122 is arranged at the output end of the preliminary homogenization optical path 121, and converts the parallel light beams output by the preliminary homogenization optical path into line illumination light with a flat top. As an example, the line flat-top spot shaping optical path 122 is implemented by using a double-cylindrical microlens array, including a first cylindrical microlens array 12e, a second cylindrical microlens array 12f, and a third lens 12g. The first cylindrical microlens array 12e has a convex surface and a flat surface arranged oppositely, wherein the convex surface serves as an incident surface, and the flat surface serves as an exit surface. The parallel light beams output by the preliminary homogenization optical path 121 are vertically incident to the incident surface of the first cylindrical microlens array 12e. The second cylindrical microlens array 12f also has a convex surface and a flat surface arranged oppositely, wherein the flat surface serves as an incident surface and is arranged opposite to the flat surface of the first cylindrical microlens array 12e, and the convex surface serves as an exit surface. After each subunit of the microlenses of the first cylindrical microlens array 12e focuses the light beams, the light beams are split into a large number of fine light beams, and are rearranged to form a focal point arranged in a line array. The light emitted by the focal point can be approximately a light beam cluster array corresponding to the cylindrical microlens array, and is incident to the second cylindrical microlens array 12f again. Due to the reduction of coherence, the sharp edges between the small light spots of the subunit imaging on the receiving surface of the cylindrical microlens array can be greatly reduced. The third lens 12g is arranged at the exit end of the second cylindrical microlens array 12f, and is used to converge the light beams, so that the multiple small light beams emitted from the second cylindrical microlens array 12f are superimposed on each other to become a line illumination light spot with uniform energy distribution. In this example, the third lens 12g is a Fourier lens, which plays an integrating role.

[0092] As another implementation manner of the present application, the illumination device 12 further includes a reflector 12h arranged between the preliminary homogenization optical path 121 and the line flat-top spot shaping optical path 122, which is used to adjust the propagation direction of the light beams, so that the line illumination light is incident to the surface of the wafer to be measured at a large angle. The actual mechanical design space layout position can be combined. A plurality of reflectors are used to achieve the final effect, and the flexibility of the optical path adjustment is improved through multiple reflections. The reflector 12h is an optional element, and when the incident angle is appropriate, the reflector is not needed to adjust the direction of the optical path.

[0093] The illumination device 12 of the present application is used to provide line illumination light (flat-top light) with uniform energy distribution, and has the advantages of high uniformity, good consistency of detection sensitivity of different pixel positions in wide field detection, and the like.

[0094] As shown in Figure 2 The present application further provides a dark field detection system 1, which comprises:

[0095] The motion platform 11, the N illumination devices 12 of the present application, the objective lens 13, the optical element module 14, the DMD digital micro reflector 15, the line scanning camera 16, and the upper computer 17; N is a natural number greater than or equal to 1.

[0096] like Figure 2 As shown, the motion platform 11 is used to carry the wafer under test and drive the wafer under test to move.

[0097] Specifically, in this embodiment, the motion platform 11 can translate in three directions: X-axis, Y-axis, and Z-axis, thereby achieving movement in three-dimensional space. In actual use, the motion platform 11 can at least move horizontally within the plane where the wafer to be tested is located, and is not limited to this embodiment.

[0098] like Figure 2 As shown, each illumination device 12 is located above the side of the motion platform 11 to provide a large-angle, uniformly distributed line illumination light for the test area on the wafer under test; when N is greater than or equal to 2, each illumination device 12 is distributed in a ring around the test area.

[0099] Specifically, the illumination device 12 incident on the surface of the wafer under test at a large angle and reflected out at a large angle. The reflected light does not enter the objective lens 13; only the scattered light caused by defects can enter the objective lens 13. The illumination device 12 provides dark-field illumination that can be matched to the scanning of the line scan camera 16, providing line illumination light for the area under test on the wafer. N can be set to a natural number greater than or equal to 2. In this case, the line illumination light provided by each illumination device 12 is superimposed on the area under test to improve the insufficient illumination brightness. The illumination device 12 is described above and will not be repeated here.

[0100] like Figure 2 As shown, objective lens 13 is positioned directly above the area to be measured to amplify the scattered light signal from the area to be measured.

[0101] Specifically, objective lens 13 determines the microscope resolution and image clarity, and its main function is to amplify the scattered light for the first time. As needed, objective lens 13 can be configured as a high-power objective lens or a low-power objective lens. High-power objectives usually have a higher magnification, while low-power objectives have a lower magnification.

[0102] Specifically, in this invention, different line illumination spot sizes can be configured for scenarios where images are acquired using objectives of different magnifications, in order to achieve effective utilization of the light source and avoid energy waste under different objective scenarios; a large line illumination spot is suitable for wide field-of-view imaging with low-magnification objectives, while a small line illumination spot is suitable for narrow field-of-view imaging with high-magnification objectives. In this embodiment, the desired line illumination spot size is obtained by changing the focal length of the second cylindrical microlens array 12f; wherein, the larger the focal length of the second cylindrical microlens array 12f, the smaller the spot length.

[0103] like Figure 2As shown, the optical element module 14 converges the probe light signal output by the objective lens 13 into the DMD digital micromirror 15, and also converges the light signal reflected by the DMD digital micromirror 15 into the line scan camera 16.

[0104] Specifically, in this embodiment, the optical element module 14 includes a fourth lens 141, a total internal reflection prism 142, and a fifth lens 143. The fourth lens 141 is positioned in the optical path behind the objective lens 13 and is used to converge the light beam. The total internal reflection prism 142 is positioned between the fourth lens 141 and the DMD digital micromirror 15; the total internal reflection prism 142 is composed of two triangular prisms. The light beam converged by the fourth lens 141 is incident into the DMD digital micromirror 15 in its original direction. The light beam reflected by the DMD digital micromirror 15 undergoes total internal reflection in the total internal reflection prism 142, thereby changing the direction of light propagation. The total internal reflection process effectively reduces light loss and improves the efficiency of light energy utilization. The fifth lens 143 is positioned at the reflected light output end of the total internal reflection prism 142 and is used to converge the light beam.

[0105] In practical applications, any optical element structure that can converge the probe light signal into the DMD digital micromirror and converge the light signal reflected by the DMD digital micromirror into the line scan camera is applicable to this invention.

[0106] like Figure 2 As shown, the DMD digital micromirror 15 adjusts the intensity of the probe light signal based on the brightness level of the light source corresponding to the position of the area to be measured.

[0107] Specifically, the DMD digital micromirror 15 is a microelectromechanical system (MEMS) with electronic input and optical output. It consists of many small aluminum mirrors (high-speed digital optical reflection switch arrays), each mirror being called a pixel. Each mirror can deflect ±12° around its diagonal, meaning the micromirrors of the DMD digital micromirror 15 have three states: +12°, 0°, and -12°. By controlling the rotation and temporal response of each spatially distributed micromirror, the spatial and temporal response distribution of the incident light's grayscale can be achieved, thereby realizing programmable imaging of the spatial position over time. In this invention, the DMD digital micromirror 15 performs pixel-level control of the probe light intensity based on the light source brightness distribution and scanning strategy.

[0108] Further, when the DMD digital micro-mirror 15 is set to be on, the scattering signal of the wafer to be measured is imaged on the surface of the DMD digital micro-mirror 15 through the objective lens 13 and the optical element module 14, and each position of the region to be measured corresponds to a light source light-dark level. The DMD digital micro-mirror 15 realizes light intensity control (of the probe light) based on the light source light-dark level. The reflected light after regulation enters the total internal reflection prism 142 again, undergoes total internal reflection, and then enters the fifth lens 143 to be detected by the line-scan camera 16. When the DMD digital micro-mirror 15 is set to be off, the light signal is not regulated by the DMD digital micro-mirror 15, and the detected light signal cannot enter the line-scan camera 16. That is, only the light signal regulated by the DMD digital micro-mirror 15 can enter the line-scan camera 16 to be detected; a photoelectric feedback system can be formed, for example, the DMD digital micro-mirror 15 is on, which can feedback to the upper computer 17, and inform that the scanning result of the line-scan camera 16 is regulated and takes effect, so as to realize real-time regulation of the intensity of the probe light signal based on the distribution positions of the bright defects and the dark defects, and improve the dynamic range of the dark field detection.

[0109] As shown in FIG. 1, the line-scan camera 16 collects image information. Figure 2

[0110] Specifically, the DMD digital micro-mirror 15 and the pixel position of the line-scan camera 16 have a mapping relationship, which is realized by calibration; each exposure records a pixel line, and the complete two-dimensional image is formed by combining the motion trajectory.

[0111] As shown in FIG. 1, the line-scan camera 16 collects image information. Figure 3 As shown in FIG. 1, the line-scan camera 16 collects image information.

[0112] Specifically, the upper computer 17 is connected with the motion platform 11, the DMD digital micro-mirror 15 and the line-scan camera 16, obtains the defect distribution map of the wafer to be measured, and the defect distribution map contains the position information and the light-dark degree information of each defect. The upper computer 17 analyzes the light-dark degree (light-dark ratio) of each defect, divides the intervals according to the light-dark values, and sets the corresponding light source light-dark levels for each interval. At the same time, the upper computer 17 establishes the mapping relationship between the distribution positions of the bright defects and the dark defects on the surface of the wafer to be measured and the imaging pixel position and the wafer motion scanning path; that is, the motion platform 11 drives the wafer to be measured to move to determine the region to be measured. At this time, the DMD digital micro-mirror 14 generates a corresponding light intensity regulation strategy, and the image collected by the line-scan camera 15 has a corresponding relationship with the position of the region to be measured on the wafer to be measured.

[0113] ​As an example, the defect distribution map is acquired based on the pre-detection device 18, as shown in Figure 4 As shown, the pre-detection device 18 includes a wide-field dark-field illumination light source 181, an imaging lens group 182, and a wide-field array camera 183, which are used to realize the function of macro imaging. The wide-field dark-field illumination light source 181 is arranged above the side of the motion platform 11 (in another example, the motion platform for acquiring the defect distribution map can also be additionally arranged), which provides a large-angle dark-field detection illumination for the whole wafer to be detected. The imaging lens group 182 is arranged above the wafer to be detected, which is used to transmit the scattered light signal on the surface of the wafer to be detected to the wide-field array camera 183 at a reduced or equal magnification; in this example, the imaging lens group 182 includes a sixth lens 18a and a seventh lens 18b arranged in the optical path in sequence, and the imaging focal lengths of the sixth lens 18a and the seventh lens 18b are inconsistent or consistent, which facilitates fast pre-detection of the wafer to be detected, and the size of the magnification can be adjusted according to the imaging ratio of the two lenses. The wide-field array camera 183 is used to collect the image of the wafer to be detected, which can realize single-shot full-wafer imaging or most-area imaging of the wafer to be detected, and on the basis of a small number of images, the global dark-field imaging of the wafer to be detected can be given, and then the defect detection map of the wafer to be detected can be obtained.

[0114] The illumination light source is passed through a preliminary homogenization light path composed of a diffusion sheet and a line flat-top spot shaping light path composed of a microlens array to achieve uniform line illumination (avoiding unnecessary waste of light energy in the case of circular illumination spot); through the superposition of multiple illumination and the adjustment of the focal length of the second microlens on both sides, the effective utilization of illumination energy is realized, and high-brightness and high-uniformity dark-field illumination is realized; the distribution of bright defects and dark defects is rapidly evaluated through the pre-detection device, then the scanning path of the scanning camera is calculated based on the distribution position, and a one-to-one mapping relationship between the positions of bright defects and dark defects and the scanning path of the motion stage and the pixel position of the line scanning camera is formed, which is combined with the DMD digital micro-mirror coding, so that the real-time acceptance intensity is regulated during the detection of bright defects and dark defects, the low-flow detection is realized in the bright defect detection position and the pixel area, and the high-flow detection is realized in the dark defect detection position and the pixel area, thereby achieving the effect of high dynamic range detection.

[0115] As shown in Figure 5 The present application also provides a dark-field detection method, which is realized based on the dark-field detection system 1 in the embodiment; in actual use, any hardware circuit structure capable of realizing the method is suitable. The dark-field detection method comprises:

[0116] 1) The bright defect and dark defect distribution positions on the surface of the wafer to be detected are pre-detected based on the wide-field imaging device, and the defect distribution map of the wafer to be detected is obtained.

[0117] Specifically, the imaging device with wide field of view (in this embodiment, the pre-detection device 18) collects images of the wafer to be detected no more than 5 times. When the number of image collection is greater than or equal to 2 times, the collected images are spliced to obtain the defect distribution map of the entire wafer to be detected; further, based on the same set of imaging devices with wide field of view, the images of each part of the wafer to be detected are obtained by translating or rotating the wafer to be detected. As an example, the defect distribution map of the entire wafer to be detected is obtained by one-time image collection. As another example, the defect distribution map of the entire wafer to be detected is obtained by four-time image collection; as shown in Figure 6 , each time the image of 1 / 4 of the wafer to be detected is collected, the entire image is obtained by four-time translation, and the complete defect distribution map is obtained by splicing. Figure 7 As another example, the defect distribution map of the entire wafer to be detected is obtained by two-time image collection; as shown in , each time the image of 3 / 4 of the wafer to be detected is collected, the entire image is obtained by two-time rotation, and the complete defect distribution map is obtained by splicing.

[0118] It should be noted that the pre-detection is a wide field of view dark field detection, which can only obtain rough image information (defect position and brightness).

[0119] 2) Classify the brightness of each defect in the defect distribution map, and obtain the light source brightness level distribution corresponding to each position of the wafer to be detected based on the classification result. As an example, the higher the brightness of the defect, the lower the light intensity of the corresponding light source, and the lower the light intensity controlled by the DMD.

[0120] Specifically, each defect on the defect distribution map has a corresponding position and brightness, and the corresponding light source brightness level distribution is obtained by classifying the brightness, that is, each position (region) of the wafer to be detected has a corresponding light source brightness level.

[0121] 3) In the dark field detection device, the line illumination light with uniform energy distribution is used as the light source for the detected region of the wafer to be detected, each detected region on the wafer to be detected is scanned, and the strength of the detection light signal is adjusted according to the light source brightness level corresponding to the position of the detected region on the wafer to be detected, and the adjusted detection light signal is collected to realize dark field detection.

[0122] Figure 2As shown, the spatial position of the DMD digital micromirror 15 and its correspondence with the line scan camera 16 are pre-calibrated. The length (size) of the line illumination light is set based on the field of view of the dark field detection device to suit both low-magnification and high-magnification objectives. In this example, the line illumination light is obtained by using the line flat-top spot shaping optical path 122 of the dual cylindrical microlens array. The focal length of the second-stage cylindrical microlens array (12f) is adjusted to adjust the length of the line illumination light. The focal length of the second-stage cylindrical microlens array (12f) is negatively correlated with the length of the line illumination light.

[0123] Specifically, such as Figure 8 As shown, the dark-field line illumination source provided by the illumination device 12 illuminates the motion platform 11 carrying the wafer under test. Based on the scanning parameters such as the scanning wafer area and scanning objective lens, and combined with the brightness distribution of the light source at different positions obtained by the host computer 17 from the defect distribution map of the wafer under test, the scanning strategy can provide a control strategy for the intensity of the reflected light from the DMD digital micromirror 15 at each scanning position of the motion platform 11 (with the corresponding pixel position of the line scan camera 16). (That is, the higher the brightness of the defect at the corresponding position, the lower the brightness of the corresponding light source.) Figure 9 As shown, as an example, the wafer under test has two defects, one bright and one dark. During detection, the detection light signal for the bright defect needs to be weakened, while the detection light signal for the dark defect needs to be strengthened. Therefore, when the motion platform 11 moves to the second column (Step 2) for scanning, when the pixel positions of the bright and dark defects are scanned along the scanning direction, the light intensity reflected by the corresponding DMD digital micromirror 15 is adjusted, such as... ​ As shown.

[0124] Furthermore, when the DMD digital micromirror 15 is on, the line scan camera 16 detects the modulated detection signal; when the DMD digital micromirror 15 is off, the detected signal cannot enter the line scan camera 16. This achieves the function of real-time adjustment of the intensity of the detection light signal based on the distribution position of bright and dark defects, improving the dynamic range of dark field detection.

[0125] In summary, the present application provides a kind of lighting device, dark field detection system and method, comprising: based on the imaging device of wide field of view, the distribution position of bright defect and dark defect on the surface of wafer to be measured is pre-detected, and the defect distribution map of wafer to be measured is obtained;The light and dark degree of each defect in the defect distribution map is classified, and the light and dark grade distribution corresponding to each position of wafer to be measured is obtained based on the classification result;In dark field detection device, based on the line illumination light of energy distribution uniformity, the light source of the measured region of wafer to be measured is provided, each measured region on wafer to be measured is scanned, and the intensity of detection light signal is adjusted according to the light and dark grade of light source corresponding to the position of measured region on wafer to be measured, and the adjusted detection light signal is collected, to realize dark field detection.The lighting device, dark field detection system and method of the present application have good consistency of detection sensitivity at different pixel positions, high utilization rate of light source intensity and large dynamic range of image acquisition during dark field detection;The defects with large scattering signal difference are controlled by pixel-level reflected light intensity, so that the purpose of simultaneously detecting bright defects and dark defects is achieved.Therefore, the present application effectively overcomes the shortcomings of the prior art and has high industrial utilization value.

[0126] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical idea disclosed by the present application should be covered by the claims of the present application.

Claims

1. A dark field detection system, characterized in that, The dark field detection system includes at least: The system includes a host computer, a motion platform, an objective lens, an optical component module, a DMD digital micromirror, a line scan camera, and N illumination devices, where N is a natural number greater than or equal to 1. The host computer establishes a mapping relationship between the distribution locations of bright and dark defects on the surface of the wafer under test and the wafer motion scanning path and imaging pixel positions. Based on the defect distribution map of the wafer under test, it obtains the light source brightness and darkness level distribution corresponding to each position of the wafer under test, and then controls the motion platform, the DMD digital micromirror and the line scan camera. The motion platform is used to carry the wafer under test and move the wafer under test. Each illumination device is positioned above and to the side of the motion platform to provide uniformly distributed line illumination light with a large angle to the test area on the wafer under test. When N is greater than or equal to 2, the illumination devices are arranged in a ring around the test area. Each illumination device includes a preliminary homogenization optical path and a line flat-top spot shaping optical path. The preliminary homogenization optical path provides incident light and performs preliminary homogenization on the incident light to reduce its coherence. The line flat-top spot shaping optical path is located at the output end of the preliminary homogenization optical path and converts the parallel beam output by the preliminary homogenization optical path into a flat-top line illumination light. The objective lens is positioned directly above the area to be measured and is used to amplify the scattered light signal from the area to be measured. The optical element module converges the probe light signal output from the objective lens into the DMD digital micromirror, and also converges the light signal reflected by the DMD digital micromirror into the line scan camera; The DMD digital micromirror adjusts the intensity of the probe light signal based on the brightness level of the light source corresponding to the position of the area to be measured.

2. The dark field detection system according to claim 1, characterized in that: The preliminary homogenization optical path includes: a light source, a first lens, a diffuser, and a second lens; The light source is used to provide the incident light, which is a parallel beam. The first lens is disposed at the output end of the light source and is used to converge the incident light; The diffuser is disposed on the focal plane of the first lens to initially homogenize the converging light beam; The second lens is disposed in the optical path behind the diffuser to collimate the light beam after preliminary homogenization.

3. The dark field detection system according to claim 1, characterized in that: The line flat-top spot shaping optical path includes: a first cylindrical microlens array, a second cylindrical microlens array, and a third lens; The convex surface of the first cylindrical microlens array serves as the incident surface, and the flat surface serves as the exit surface, and is positioned opposite to the flat surface of the second cylindrical microlens array; the flat surface of the second cylindrical microlens array serves as the incident surface, and the convex surface serves as the exit surface. The third lens is disposed at the exit end of the second cylindrical microlens array and is used to converge the light beam.

4. The dark field detection system according to any one of claims 1-3, characterized in that: The lighting device also includes a reflector, which is disposed between the preliminary homogenization optical path and the line-top spot shaping optical path to adjust the beam propagation direction.

5. The dark field detection system according to claim 1, characterized in that: The optical element module includes a fourth lens, a total internal reflection prism, and a fifth lens; The fourth lens is disposed in the optical path behind the objective lens and is used to converge the light beam; The total internal reflection prism is disposed between the fourth lens and the DMD digital micromirror; The fifth lens is disposed at the reflected light output end of the total internal reflection prism and is used to converge the light beam.

6. The dark field detection system according to claim 1, characterized in that: The dark field detection system also includes a pre-detection device, which is used to acquire the defect distribution map of the wafer under test.

7. The dark field detection system according to claim 6, characterized in that: The pre-detection device includes a wide field-of-view dark field illumination source, an imaging lens group, and a wide field-of-view array camera; The wide field-of-view dark field illumination source is positioned above and to the side of the motion platform to provide a light source for the wafer under test; The imaging lens group is positioned above the wafer under test and is used to reduce or transmit the scattered light signal from the surface of the wafer under test to the wide-view field array camera at the same magnification. The wide-view field-array camera is used to acquire images of the wafer under test to obtain a defect detection map of the wafer under test.

8. A dark field detection method, implemented based on the dark field detection system as described in any one of claims 1-7, characterized in that, The dark field detection method includes at least the following: 1) The wide field-of-view imaging device performs pre-detection of the distribution positions of bright and dark defects on the surface of the wafer under test by dark field detection, and obtains the defect distribution map of the wafer under test. 2) Classify the brightness of each defect in the defect distribution map, and obtain the light source brightness level distribution corresponding to each position of the wafer under test based on the classification results; 3) In the dark field detection device, a light source is provided for the test area of ​​the wafer under test based on the uniformly distributed line illumination light. The test area on the wafer under test is scanned, and the intensity of the probe light signal is adjusted according to the brightness level of the light source corresponding to the position of the test area on the wafer under test. The adjusted probe light signal is collected to realize dark field detection.

9. The dark field detection method according to claim 8, characterized in that: In step 1), the wide field-of-view imaging device acquires images of the wafer under test no more than 5 times; when the number of image acquisitions is greater than or equal to 2, the same wide field-of-view imaging device acquires images of each part of the wafer under test by translating or rotating the wafer under test, and stitches together the acquired images of each part to obtain the defect distribution map of the entire wafer under test.

10. The dark field detection method according to claim 8, characterized in that: In step 3), the length of the line illumination light is set based on the field of view size of the dark field detection device.

11. The dark field detection method according to claim 10, characterized in that: In step 3), the linear illumination light is obtained by shaping the optical path with a flat-top spot using a dual cylindrical microlens array. The focal length of the second-stage cylindrical microlens array is adjusted to adjust the length of the linear illumination light. The focal length of the second-order cylindrical microlens array is negatively correlated with the length of the linear illumination light.

Images