Illuminating device and dark field detection system and method

Abstract

The invention provides a lighting device and a dark field detection system and method, and the method comprises the steps: carrying out the pre-detection of the distribution positions of bright defects and dark defects on the surface of a to-be-detected wafer based on a wide-view-field imaging device, and obtaining a defect distribution map of the to-be-detected wafer; classifying the brightness degree of each defect in the defect distribution map, and obtaining light source brightness level distribution corresponding to each position of the wafer to be detected; in the dark field detection device, a light source is provided for a to-be-detected area of a to-be-detected wafer based on linear illumination light, each to-be-detected area on the to-be-detected wafer is scanned, the intensity of a detection light signal is regulated and controlled according to the brightness level of the corresponding light source, and the adjusted detection light signal is collected so as to realize dark field detection. During dark field detection, the detection sensitivity consistency of different pixel positions is good, the light source intensity utilization rate is high, and the image acquisition dynamic range is large.

Description

Technical Field

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

[0002] Semiconductor defect detection uses optical microscopy to image the wafer surface, combined with image analysis and calculation, to detect scratches, stains, cracks or other irregular appearance defects produced in the semiconductor production process as early as possible, so as to eliminate the causes of the defects; and by discarding defective samples, defective grains are prevented from being processed further, affecting yield and productivity.

[0003] Bright field illumination imaging and dark field illumination imaging are two commonly used imaging techniques. Dark field illumination refers to the illumination beam being projected onto the sample surface at a very large incident angle, and the mirror-reflected light is reflected at a very large angle, so that it cannot enter the objective lens for imaging. The image acquisition grayscale is completely black. If there are defect features on the surface, part of the diffusely reflected light at the defect features enters the objective lens for imaging. These defect features appear as bright images against the dark field of view, which significantly improves the signal-to-noise ratio of feature defect imaging. Dark field imaging has better detection effects in defect detection applications.

[0004] Since dark field illumination mainly detects scattered light, a large amount of reflected light is lost, and the oblique incidence method will elongate the light spot and cause problems such as uneven illumination. Therefore, the intensity and uniformity of the dark field detection illumination light determine the quality of defect detection. Existing lighting devices generally have problems such as low illumination brightness, low light utilization, and poor illumination uniformity.

[0005] In order to increase the detection speed, semiconductor defect detection equipment generally uses linear array cameras to scan images, and completes the scanning of the entire wafer surface image at one time under specific light intensity conditions and specific scanning frequencies. Due to the different characteristics of defects on the wafer, some defects with strong scattering signals will cause the image to be saturated, and some defects with weak scattering signals will cause the image to have a very small grayscale, which may not be detected.

[0006] Therefore, how to take into account scattered signals of different intensities and improve the dynamic range of dark field detection has become one of the urgent problems to be solved by technical personnel in this field.

[0007] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present invention and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology section of the present invention. Summary of the invention

[0008] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide an illumination device, a dark field detection system and a method for solving the problem that dark field detection in the prior art cannot take into account scattered signals of different intensities and has a small dynamic range.

[0009] To achieve the above objectives and other related objectives, the present invention provides a dark field detection method, which at least includes:

[0010] 1) Preliminary detection of the distribution positions of bright defects and dark defects on the surface of the wafer to be tested is performed based on a wide-field imaging device to obtain a defect distribution map of the wafer to be tested;

[0011] 2) classifying the brightness and darkness of each defect in the defect distribution map, and obtaining the brightness and darkness level distribution of the light source corresponding to each position of the wafer to be tested based on the classification result;

[0012] 3) In the dark field detection device, a light source is provided for the test area of ​​the wafer to be tested based on line illumination light with uniform energy distribution, each test area on the wafer to be tested is scanned, and the intensity of the detection light signal is adjusted according to the brightness level of the light source corresponding to the position of the test area on the wafer to be tested, and the adjusted detection light signal is collected to realize dark field detection.

[0013] Optionally, in step 1), the wide-field imaging device captures images of the wafer to be tested for no more than 5 times; when the number of times the images are captured is greater than or equal to 2 times, images of various parts of the wafer to be tested are acquired by translating or rotating the wafer to be tested based on the same set of wide-field imaging devices, and the captured images of various parts are spliced ​​to obtain a defect distribution map of the entire wafer to be tested.

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

[0015] More optionally, in step 3), the line illumination light is obtained by using a line flat-top spot shaping light path of a double cylindrical microlens array, and the focal length of the second-stage cylindrical microlens array is adjusted to adjust the length of the line illumination light;

[0016] The focal length of the second-stage cylindrical microlens array is negatively correlated with the length of the linear illumination light.

[0017] In order to achieve the above-mentioned object and other related objects, the present invention further provides a lighting device, which at least comprises:

[0018] Preliminary homogenization of the optical path and line flat-top spot shaping of the optical path;

[0019] The preliminary homogenization optical path provides incident light and performs preliminary homogenization on the incident light to reduce the coherence of the incident light;

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

[0021] Optionally, the preliminary homogenized light path includes: a light source, a first lens, a diffuser, and a second lens;

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

[0023] The first lens is disposed at the output end of the light source and is used to converge the incident light;

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

[0025] The second lens is arranged on the optical path behind the diffuser and is used for collimating the light beam after preliminary homogenization.

[0026] Optionally, the line flat-top spot shaping optical path includes: 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 the incident surface, and the flat surface serves as the exit surface and is arranged 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 arranged at the exit end of the second cylindrical microlens array for converging the light beam.

[0028] More optionally, the lighting device further comprises a reflector, wherein the reflector is arranged between the preliminary homogenization light path and the line flat-top spot shaping light path, and is used for adjusting the propagation direction of the light beam.

[0029] In order to achieve the above-mentioned object and other related objects, the present invention 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 of the above lighting devices, where N is 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 tested, the wafer motion scanning path, and the imaging pixel position, and obtains the light source brightness and darkness level distribution corresponding to each position of the wafer to be tested based on the defect distribution map of the wafer to be tested, thereby controlling the motion platform, the DMD digital micro-mirror, and the line scan camera;

[0032] The motion platform is used to carry the wafer to be tested and drive the wafer to be tested to move;

[0033] Each lighting device is arranged on the upper side of the motion platform, and is used to provide a large-angle linear lighting light with uniform energy distribution to the test area on the test wafer; when N is greater than or equal to 2, each lighting device is distributed in a ring shape with the test area as the center;

[0034] The objective lens is arranged directly above the area to be measured, and is used to amplify the scattered light signal of the area to be measured;

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

[0036] The DMD digital micro-mirror adjusts the intensity of the detection light signal based on the brightness level of the light source corresponding to the position of the area to be measured.

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

[0038] The fourth lens is arranged on the optical path behind the objective lens and is used to converge the light beam;

[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 reflected light output end of the total internal reflection prism and is used for converging the light beam.

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

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

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

[0044] The imaging lens group is arranged above the wafer to be tested, and is used to reduce the scattered light signal on the surface of the wafer to be tested or transmit it to the wide field array camera at the same magnification;

[0045] The wide field array camera is used to collect images of the wafer to be tested to obtain a defect detection map of the wafer to be tested.

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

[0047] 1. The lighting device, dark field detection system and method of the present invention have high uniformity of illumination light source; compared with the traditional oblique incident illumination method after converging with a Gaussian lens, the present invention uses a two-layer uniform light path of a diffuser and a microlens array, so the illumination light has high uniformity, and the detection sensitivity consistency of different pixel positions is good during dark field detection.

[0048] 2. The lighting device, dark field detection system and method of the present invention have a high light source intensity utilization rate; the lighting light source is shaped into a linear lighting mode to match the scanning area of ​​the line scanning camera (under different objective lenses, the field of view of the line scanning camera is different, and the required lighting area size is different). Different lighting spot sizes can be flexibly adjusted and switched according to the size of the objective lens, effectively avoiding the waste of light source energy.

[0049] 3. The lighting device, dark field detection system and method of the present invention have a large dynamic range for image acquisition. By adjusting the reflected light intensity at the pixel level, defects with large differences in scattering signals can be detected simultaneously with bright defects and dark defects, replacing multiple cameras and multiple detections to achieve high dynamic range detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Shown is a schematic structural diagram of the lighting device of the present invention.

[0051] Figure 2 Shown is a schematic structural diagram of the dark field detection system of the present invention.

[0052] Figure 3 Shown is a schematic structural diagram of the pre-detection device of the present invention.

[0053] Figure 4 Shown is a schematic flow chart of the dark field detection method of the present invention.

[0054] Figure 5 Shown is a schematic diagram of a method for obtaining a defect distribution map of a wafer to be tested according to the present invention.

[0055] Figure 6 Shown is a schematic diagram of another method for obtaining a defect distribution map of a wafer to be tested according to the present invention.

[0056] Figure 7 It is a schematic diagram showing the mapping between the DMD digital micro-mirror and the line scan camera of the present invention.

[0057] Figure 8 It is a schematic diagram showing the second row of the wafer to be tested having bright defects and dark defects according to the present invention.

[0058] Fig. 9 Shown is a schematic diagram of scanning based on bright defects and dark defects according to the present invention.

[0059] Component number description

[0060] 1Dark field detection system

[0061] 11 Sports Platform

[0062] 12 lighting fixtures

[0063] 121 Preliminary homogenization of the optical path

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

[0065] 12a Light source

[0066] 12b First lens

[0067] 12c diffuser

[0068] 12d second lens

[0069] 12e First cylindrical microlens array

[0070] 12f Second cylindrical microlens array

[0071] 12g third lens

[0072] 12h reflector

[0073] 13 Objective lens

[0074] 14Optical element module

[0075] 141 Fourth lens

[0076] 142 Total Internal Reflection Prism

[0077] 143 Fifth lens

[0078] 15DMD digital micro mirror

[0079] 16 linescan camera

[0080] 17 Host computer

[0081] 18 Pre-detection device

[0082] 181 Wide field dark field illumination source

[0083] 182 imaging lens group

[0084] 183 wide field array camera

[0085] 18a Sixth lens

[0086] 18b seventh lens DETAILED DESCRIPTION

[0087] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0088] See also Figures 1 to 9 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0089] like Figure 1 As shown, the present invention provides an illumination device 12 , including a preliminary homogenization light path 121 and a line flat-top light spot shaping light path 122 .

[0090] Specifically, the preliminary homogenization optical path 121 provides incident light and performs preliminary homogenization on the incident light to reduce the coherence of the incident light. As an example, the preliminary homogenization optical path 121 includes a light source 12a, a first lens 12b, a diffuser 12c and a second lens 12d. The light source 12a is used to provide incident light, and the incident light is a parallel light beam. The first lens 12b is arranged at the output end of the light source 12a, and is used to converge the parallel incident light. The diffuser 12c is arranged on the focal plane of the first lens 12b, and performs preliminary homogenization on the converged light beam. The second lens 12d is arranged on the optical path behind the diffuser 12c, and is used to collimate the preliminary homogenized light beam. 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 homogenized optical path 121, and converts the parallel light beam output by the preliminary homogenized optical path into a flat-top line illumination light. As an example, the line flat-top spot shaping optical path 122 is implemented by 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 plane surface that are relatively arranged, wherein the convex surface serves as an incident surface and the plane surface serves as an exit surface, and the parallel light beam output by the preliminary homogenized optical path 121 is vertically incident on the incident surface of the first cylindrical microlens array 12e. The second cylindrical microlens array 12f also has a convex surface and a plane surface that are relatively arranged, wherein the plane surface serves as an incident surface and is arranged opposite to the plane of the first cylindrical microlens array 12e, and the convex surface serves as an exit surface. After the light beam is focused by each sub-unit of the microlens of the first cylindrical microlens array 12e, it is divided into a large number of fine light beams, which are rearranged to form a focus arranged in a linear array. The light emitted from this focus can be approximated as a beam cluster array corresponding to the cylindrical microlens array, which is incident on the second cylindrical microlens array 12f again. Due to the reduction in coherence, the generation of sharp edges between the small light spots imaged by the sub-units 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 beam so that the multiple small light beams emitted from the second cylindrical microlens array 12f are superimposed on each other to form a linear 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 of the present invention, the lighting device 12 also includes a reflector 12h, which is arranged between the preliminary homogenization optical path 121 and the line flat-top light spot shaping optical path 122, and is used to adjust the propagation direction of the light beam so that the line illumination light is incident on the surface of the wafer to be measured at a large angle, and the spatial layout position can be combined with the actual mechanical design; or multiple reflectors can be used for reflection to achieve the final effect, and the flexibility of the optical path adjustment can be improved through multiple reflections. The reflector 12h is an optional component, and when the incident angle is appropriate, the reflector is not needed to adjust the direction of the optical path.

[0093] The lighting device 12 of the present invention is used to provide linear lighting light (top light) with uniform energy distribution, and has the advantages of high uniformity and good consistency of detection sensitivity at different pixel positions during wide field of view detection.

[0094] like Figure 2 As shown, the present invention also provides a dark field detection system 1, which includes:

[0095] A motion platform 11, N lighting devices 12 of the present invention, an objective lens 13, an optical element module 14, a DMD digital micro-mirror 15, a line scan camera 16 and a host 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 to be tested and drive the wafer to be tested to move.

[0097] Specifically, in this embodiment, the motion platform 11 can translate in three directions: X-axis, Y-axis, and Z-axis, so as to achieve 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, which is not limited to this embodiment.

[0098] like Figure 2 As shown, each lighting device 12 is arranged on the upper side of the moving platform 11 to provide a large-angle linear illumination light with uniform energy distribution to the test area on the test wafer; when N is greater than or equal to 2, each lighting device 12 is distributed in a ring with the test area as the center.

[0099] Specifically, the lighting device 12 is incident on the surface of the wafer to be tested at a large angle and reflected at a large angle. The reflected light does not enter the objective lens 13, and only the scattered light caused by the defect can enter the objective lens 13. The lighting device 12 provides dark field illumination that can match the scanning of the line scan camera 16, and provides line illumination light for the area to be tested on the wafer to be tested; N can be set to a natural number greater than or equal to 2. At this time, the line illumination light provided by each lighting device 12 is superimposed on the area to be tested to improve the insufficient illumination brightness. Please refer to the above for the lighting device 12, which will not be described in detail here.

[0100] like Figure 2 As shown, the objective lens 13 is arranged just above the area to be measured, and is used to amplify the scattered light signal of the area to be measured.

[0101] Specifically, the objective lens 13 determines the resolution and imaging clarity of the microscope, and its main function is to amplify the scattered light for the first time. According to needs, the objective lens 13 can be configured as a high-power objective lens or a low-power objective lens. The high-power objective lens usually has a higher magnification, and the low-power objective lens has a relatively low magnification.

[0102] Specifically, in the present invention, for scenes where different magnification objective lenses are used to collect images, different line illumination spot sizes can be configured to achieve effective use of the light source and avoid energy waste in different objective lens scenes; a large line illumination spot is suitable for wide field imaging of a low-magnification objective lens, and a small line illumination spot is suitable for narrow field imaging of a high-magnification objective lens. 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 detection light signal output by the objective lens 13 into the DMD digital micro-mirror 15 , and also converges the light signal reflected by the DMD digital micro-mirror 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 arranged on the optical path behind the objective lens 13, and is used to converge the light beam. The total internal reflection prism 142 is arranged between the fourth lens 141 and the DMD digital micro-reflector 15; the total internal reflection prism 142 is composed of two triangular prisms, and the light beam converged by the fourth lens 141 is incident on the DMD digital micro-reflector 15 in the original direction, and the light beam reflected by the DMD digital micro-reflector 15 is totally reflected in the total internal reflection prism 142, thereby changing the propagation direction of the light; the total reflection process can effectively reduce the loss of light and improve the efficiency of light energy use. The fifth lens 143 is arranged at the reflected light output end of the total internal reflection prism 142, and is used to converge the light beam.

[0105] In actual use, any optical element structure that can converge the detection light signal into the DMD digital micro-mirror and converge the light signal reflected by the DMD digital micro-mirror into the line scan camera is applicable to the present invention.

[0106] like Figure 2 As shown, the DMD digital micro-mirror 15 adjusts the intensity of the detection light signal based on the brightness level of the light source corresponding to the position of the area to be detected.

[0107] Specifically, the DMD digital micro-mirror 15 is a micro-electromechanical system with electronic input and optical output. It is composed of many small aluminum reflective mirrors (high-speed digital optical reflective switch arrays), each of which is called a pixel. Each mirror can deflect ±12° around the diagonal, that is, the micro-mirror of the DMD digital micro-mirror 15 has three states: +12°, 0°, and -12°; by controlling the rotation and time domain response of each micro-mirror distributed in space, the spatial and temporal response distribution of the grayscale of the incident light can be achieved, thereby realizing programmable imaging of the spatial position over time. In the present invention, the DMD digital micro-mirror 15 performs pixel-level regulation on the intensity of the detection light based on the light source brightness level distribution and scanning strategy.

[0108] Further, when the DMD digital micro-mirror 15 is set to on, the scattered signal of the wafer to be tested is imaged on the surface of the DMD digital micro-mirror 15 through the objective lens 13 and the optical element module 14. The location of each area to be tested corresponds to a light source brightness level. The DMD digital micro-mirror 15 implements light intensity control (of the detection light) based on the light source brightness level. The regulated reflected light 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-lens 15 is set to 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, when the DMD digital micro-mirror 15 is turned on, it can be fed back to the host computer 17 to inform the line scan camera 16 that the scanning result has been regulated and taken effect, thereby realizing real-time regulation of the strength of the detection light signal based on the distribution position of bright defects and dark defects, thereby improving the dynamic range of dark field detection.

[0109] like Figure 2 As shown, the line scan camera 16 collects image information.

[0110] Specifically, there is a mapping relationship between the pixel positions of the DMD digital microlens 15 and the line scan camera 16, which is achieved through calibration; each exposure records a pixel line, which is accumulated in combination with the motion trajectory to form a complete two-dimensional image.

[0111] like Figure 2 As shown, the host computer 17 establishes a mapping relationship between the distribution positions of bright defects and dark defects on the surface of the wafer to be tested and the wafer movement scanning path and imaging pixel positions, and obtains the light source brightness and darkness level distribution corresponding to each position of the wafer to be tested based on the defect distribution map of the wafer to be tested, and then controls the motion platform 11, DMD digital micro-mirror 15 and line scan camera 16.

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

[0113] As an example, the defect distribution map is obtained based on the pre-detection device 18, such as Figure 3 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 field array camera 183, which are used to realize the function of macroscopic imaging. The wide-field dark-field illumination light source 181 is arranged on the upper side of the motion platform 11 (in another example, the motion platform for obtaining the defect distribution map can also be set separately), providing a large-angle dark-field detection illumination for the entire wafer to be tested. The imaging lens group 182 is arranged above the wafer to be tested, and is used to reduce or transmit the scattered light signal on the surface of the wafer to be tested to the wide-field field array camera 183 at the same magnification; in this example, the imaging lens group 182 includes a sixth lens 18a and a seventh lens 18b arranged in sequence on the optical path, and the imaging focal lengths of the sixth lens 18a and the seventh lens 18b are inconsistent or consistent, which is convenient for realizing rapid pre-detection of the wafer to be tested, and the magnification can be adjusted according to the imaging ratio of the two lenses. The wide-field array camera 183 is used to collect images of the wafer to be tested. It can realize the imaging of the entire wafer to be tested or the imaging of most areas of the wafer to be tested in a single time. Based on a small number of imaging times, a global dark-field imaging of the wafer to be tested can be given, thereby obtaining a defect detection map of the wafer to be tested.

[0114] The present invention achieves uniform line lighting effect (avoiding unnecessary light energy waste in the case of circular lighting spot) by passing the illumination light source through a preliminary homogenization light path composed of a diffuser and a line flat-top light spot shaping light path composed of a microlens array; realizes effective use of illumination energy and high-brightness and high-uniformity dark field illumination by superimposing multi-path illumination and adjusting the focal length of the second-surface microlenses on both sides; quickly evaluates the distribution of bright defects and dark defects through a pre-detection device, and then calculates the scanning path of the scanning camera based on the distribution position, so as to form a one-to-one mapping relationship between the positions of the bright defects and dark defects and the scanning path of the motion stage and the pixel position of the line scanning camera; and combines this mapping relationship with the DMD digital micro-mirror encoding to realize real-time regulation of the light intensity during bright defect and dark defect detection, realize low-flux detection at the bright defect detection position and pixel area, and realize high-flux detection at the dark defect detection position and pixel area, thereby achieving the effect of high dynamic range detection.

[0115] like Figure 4 As shown, the present invention further provides a dark field detection method. In this embodiment, the dark field detection method is implemented based on the dark field detection system 1 of the present invention. In actual use, any hardware circuit structure that can implement this method is applicable. The dark field detection method includes:

[0116] 1) A wide-field imaging device is used to pre-detect the distribution positions of bright and dark defects on the surface of the wafer to be tested, and a defect distribution map of the wafer to be tested is obtained.

[0117] Specifically, the number of times that the wide-field imaging device (in the present embodiment, the pre-detection device 18 is used) captures images of the wafer to be tested is no more than 5 times. When the number of times the image is captured is greater than or equal to 2 times, the captured images are spliced ​​to obtain a defect distribution map of the entire wafer to be tested; further, based on the same set of wide-field imaging devices, images of various parts of the wafer to be tested are obtained by translating or rotating the wafer to be tested. As an example, a defect distribution map of the entire wafer to be tested is obtained through one image capture. As another example, a defect distribution map of the entire wafer to be tested is obtained through four image captures; as Figure 5 As shown, each acquisition acquires an image of 1 / 4 of the wafer to be tested, and the entire image is obtained through four translations, and then a complete defect distribution map is obtained through splicing. As another example, the defect distribution map of the entire wafer to be tested is obtained through two image acquisitions; Figure 6 As shown, each acquisition acquires an image of 3 / 4 of the wafer to be tested, and the entire image is obtained by two rotations, and then a complete defect distribution map is obtained by splicing.

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

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

[0120] Specifically, each defect on the defect distribution map has a corresponding position and brightness level, and the brightness levels are classified by analysis to obtain the corresponding light source brightness level distribution, that is, each position (area) of the wafer to be tested has a corresponding light source brightness level.

[0121] 3) In the dark field detection device, a light source is provided for the test area of ​​the wafer to be tested based on a line illumination light with uniform energy distribution, each test area on the wafer to be tested is scanned, and the strength of the detection light signal is adjusted according to the brightness level of the light source corresponding to the position of the test area on the wafer to be tested, and the adjusted detection light signal is collected to realize dark field detection.

[0122] Specifically, Figure 7As shown, the calibration of the spatial position of the DMD digital micro-mirror 15 and the corresponding relationship of the line scan camera 16 is pre-implemented. The length (size) of the line illumination light is set based on the field of view of the dark field detection device to be suitable for the scenes of the low-power objective lens and the high-power objective lens respectively; in this example, the line illumination light is obtained by using the line flat-top spot shaping optical path 122 of the double cylindrical micro-lens array, and the focal length of the second-stage cylindrical micro-lens array (12f) is adjusted to adjust the length of the line illumination light; wherein, the focal length of the second-stage cylindrical micro-lens array (12f) is negatively correlated with the length of the line illumination light.

[0123] Specifically, Figure 2 As shown, the dark field line illumination light source provided by the illumination device 12 is irradiated on the motion platform 11 with the wafer to be tested; based on the scanning parameter settings such as the scanning wafer area and the scanning objective lens, combined with the light source brightness level distribution at different positions obtained by the host computer 17 according to the defect distribution map of the wafer to be tested, the DMD digital micro-mirror 15 reflection light intensity control strategy can be given in the scanning strategy for 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 corresponding light source brightness). Figure 8 As shown, as an example, there are two defects on the wafer to be tested, one bright defect and one dark defect. When detecting these two defects, it is necessary to adjust the detection light signal of the bright defect to be weaker and the detection light signal of the dark defect to be stronger; therefore, when the motion platform 11 moves to the second column Step2 for scanning, when scanning the pixel positions where the bright defect and the dark defect are located along the scanning motion direction, the light intensity reflected by the corresponding DMD digital micro-mirror 15 is adjusted, as shown in FIG. Fig. 9 shown.

[0124] Furthermore, when the DMD digital micro-mirror 15 is turned on, the line scan camera 16 detects the regulated detection signal; when the DMD digital micro-mirror 15 is turned off, the detected signal cannot enter the line scan camera 16. Thus, the function of real-time regulation of the detection light signal strength based on the distribution position of bright defects and dark defects is realized, and the dynamic range of dark field detection is improved.

[0125] In summary, the present invention provides an illumination device, a dark field detection system and method, including: pre-detecting the distribution positions of bright defects and dark defects on the surface of a wafer to be tested based on a wide field of view imaging device to obtain a defect distribution map of the wafer to be tested; classifying the brightness and darkness of each defect in the defect distribution map, and obtaining the distribution of light source brightness and darkness levels corresponding to each position of the wafer to be tested based on the classification result; in a dark field detection device, providing a light source for the test area of ​​the wafer to be tested based on a line illumination light with uniform energy distribution, scanning each test area on the wafer to be tested, and adjusting the intensity of the detection light signal according to the light source brightness and darkness level corresponding to the position of the test area on the wafer to be tested, collecting the adjusted detection light signal, so as to realize dark field detection. The illumination device, dark field detection system and method of the present invention have good consistency in detection sensitivity of different pixel positions during dark field detection, high utilization rate of light source intensity, and large dynamic range of image acquisition; the defects with large differences in scattered signals are adjusted by adjusting the pixel-level reflected light intensity to achieve the purpose of simultaneously detecting bright defects and dark defects. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0126] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A dark field detection method, characterized in that: The dark field detection method at least comprises: 1) Preliminary detection of the distribution positions of bright defects and dark defects on the surface of the wafer to be tested is performed based on a wide-field imaging device to obtain a defect distribution map of the wafer to be tested; 2) classifying the brightness and darkness of each defect in the defect distribution map, and obtaining the brightness and darkness level distribution of the light source corresponding to each position of the wafer to be tested based on the classification result; 3) In the dark field detection device, a light source is provided for the test area of ​​the wafer to be tested based on line illumination light with uniform energy distribution, each test area on the wafer to be tested is scanned, and the intensity of the detection light signal is adjusted according to the brightness level of the light source corresponding to the position of the test area on the wafer to be tested, and the adjusted detection light signal is collected to realize dark field detection.

2. The dark field detection method according to claim 1, characterized in that: In step 1), the wide-field imaging device captures images of the wafer to be tested for no more than 5 times; when the number of times the images are captured is greater than or equal to 2 times, images of various parts of the wafer to be tested are acquired by translating or rotating the wafer to be tested based on the same set of wide-field imaging devices, and the images of the various parts captured are spliced ​​to obtain a defect distribution map of the entire wafer to be tested.

3. The dark field detection method according to claim 1, characterized in that: In step 3), the length of the linear illumination light is set based on the field of view size of the dark field detection device.

4. The dark field detection method according to claim 3, characterized in that: In step 3), the line illumination light is obtained by shaping the line top light spot of the double cylindrical microlens array, and the focal length of the second cylindrical microlens array is adjusted to adjust the length of the line illumination light; The focal length of the second-stage cylindrical microlens array is negatively correlated with the length of the linear illumination light.

5. A lighting device, characterized in that: The lighting device at least comprises: Preliminary homogenization of the optical path and line flat-top spot shaping of the optical path; The preliminary homogenization optical path provides incident light and performs preliminary homogenization on the incident light to reduce the coherence of the incident light; The line flat-top light spot shaping optical path is arranged at the output end of the preliminary homogenization optical path, and converts the parallel light beam output by the preliminary homogenization optical path into a flat-top line illumination light.

6. The lighting device according to claim 5, characterized in that: The preliminary homogenized light path includes: a light source, a first lens, a diffuser and a second lens; The light source is used to provide the incident light, and the incident light is a parallel light beam; The first lens is disposed at the output end of the light source and is used to converge the incident light; The diffusion sheet is arranged on the focal plane of the first lens to preliminarily homogenize the converged light beam; The second lens is arranged on the optical path behind the diffuser and is used for collimating the light beam after preliminary homogenization.

7. The lighting device according to claim 5, characterized in that: The line flat-top spot shaping optical path comprises: a first cylindrical microlens array, a second cylindrical microlens array and a third lens; The convex surface of the first cylindrical microlens array is used as the incident surface, the flat surface is used as the exit surface and is arranged opposite to the flat surface of the second cylindrical microlens array; the flat surface of the second cylindrical microlens array is used as the incident surface, and the convex surface is used as the exit surface; The third lens is arranged at the exit end of the second cylindrical microlens array and is used for converging the light beam.

8. The lighting device according to any one of claims 5 to 7, characterized in that: The lighting device further comprises a reflector, which is arranged between the preliminary homogenization light path and the line flat-top light spot shaping light path and is used for adjusting the propagation direction of the light beam.

9. A dark field detection system, characterized in that: The dark field detection system at least comprises: A host computer, a motion platform, an objective lens, an optical element module, a DMD digital micro-mirror, a line scan camera, and N lighting devices according to any one of claims 5 to 8, wherein N is a natural number greater than or equal to 1; 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 tested, the wafer motion scanning path, and the imaging pixel position, and obtains the light source brightness and darkness level distribution corresponding to each position of the wafer to be tested based on the defect distribution map of the wafer to be tested, thereby controlling the motion platform, the DMD digital micro-mirror, and the line scan camera; The motion platform is used to carry the wafer to be tested and drive the wafer to be tested to move; Each lighting device is arranged on the upper side of the motion platform, and is used to provide a large-angle linear lighting light with uniform energy distribution to the test area on the test wafer; when N is greater than or equal to 2, each lighting device is distributed in a ring shape with the test area as the center; The objective lens is arranged directly above the area to be measured, and is used to amplify the scattered light signal of the area to be measured; The optical element module converges the detection light signal output by the objective lens into the DMD digital micro-mirror, and also converges the light signal reflected by the DMD digital micro-mirror into the line scan camera; The DMD digital micro-mirror adjusts the intensity of the detection light signal based on the brightness level of the light source corresponding to the position of the area to be measured.

10. The dark field detection system according to claim 9, characterized in that: The optical element module includes a fourth lens, a total internal reflection prism and a fifth lens; The fourth lens is arranged on the optical path behind the objective lens and is used to converge the light beam; The total internal reflection prism is arranged between the fourth lens and the DMD digital micro-mirror; The fifth lens is arranged at the reflected light output end of the total internal reflection prism and is used for converging the light beam.

11. The dark field detection system according to claim 9, characterized in that: The dark field detection system also includes a pre-detection device, which is used to obtain a defect distribution map of the wafer to be tested.

12. The dark field detection system according to claim 11, characterized in that: The pre-detection device includes a wide-field dark-field illumination light source, an imaging lens group, and a wide-field array camera; The wide-field dark-field illumination light source is disposed above the side of the motion platform to provide a light source for the wafer to be tested; The imaging lens group is arranged above the wafer to be tested, and is used to reduce the scattered light signal on the surface of the wafer to be tested or transmit it to the wide field array camera at the same magnification; The wide field array camera is used to collect images of the wafer to be tested to obtain a defect detection map of the wafer to be tested.

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