Optical detection system

Abstract

Disclosed in the present disclosure is an optical detection system. The optical detection system comprises: an illumination assembly, which is configured to emit detection light; a bearing platform, which is configured to place thereon a workpiece to be tested, wherein the detection light irradiates said workpiece to form signal light comprising a surface defect of said workpiece; an optical imaging assembly, which is configured to collect the signal light, so as to form a detection signal for testing said workpiece; and an optical device, which is located between the optical imaging assembly and the bearing platform and configured to block a first distribution region of a spatial distribution of diffracted light from a background pattern in said workpiece, so as to reduce diffracted light related to a surface pattern of said workpiece from entering an objective lens.

Description

Optical inspection system

[0001] This application claims priority to Chinese Patent Application No. 202511698582.X, filed on November 18, 2025, entitled "Optical Inspection System", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of optical inspection, and more particularly to an optical inspection system. Background Technology

[0003] Surface defects in workpieces include particulate contamination, scratches, and residues. These defects not only affect the performance of the products manufactured from the workpieces but can also lead to product failure and even reduce the yield of the entire production line. Therefore, accurate and reliable defect detection technology has become a key link in ensuring product quality and production efficiency.

[0004] Optical inspection has become the mainstream method in the field of workpiece defect detection due to its advantages of non-contact, high speed, and large-area detection. Dark-field inspection technology is a mainstream optical inspection method that can achieve highly sensitive defect detection by acquiring the scattered light signal from the surface of the workpiece. Summary of the Invention

[0005] In a first aspect, this disclosure provides an optical inspection system comprising: an illumination assembly for emitting inspection light; a support platform for placing a workpiece to be inspected; the inspection light irradiating the workpiece to form signal light including surface defects of the workpiece; an optical imaging assembly for acquiring the signal light to form a detection signal for detecting the workpiece; and an optical device located between the optical imaging assembly and the support platform, the optical device being used to block a first distribution area of ​​the spatial distribution of background pattern diffraction light in the workpiece to reduce the entry of surface pattern-related diffraction light of the workpiece into the objective lens.

[0006] Optionally, the optical device can reflect the detection light; the detection light emitted by the illumination component is reflected by the optical device and then incident on the workpiece to be detected to form the signal light.

[0007] Optionally, the incident position of the detection light on the optical device is located at the target position of the optical device; the size of the optical device is positively correlated with the distance between the target position and the workpiece to be detected; the target position is the intersection of the surface of the optical device facing the workpiece to be detected and the optical axis of the optical imaging component.

[0008] Optionally, a three-dimensional Cartesian coordinate system is set as a reference, with three coordinate axes that are mutually perpendicular, the positive directions of which are sequentially a first direction, a second direction, and a third direction; the supporting platform is parallel to a first intersecting plane of the first and second directions; the optical device includes a rectangular reflector; the reflecting surface of the optical device for reflecting the detection light has a first angle with the third direction, the value of which is within the range of... °; the first side of the optical device has a second angle with the first direction, and the range of the first angle is . °; the detection light emitted by the illumination component has a third angle with the second direction, and the range of the third angle is _____. °; the detection light reflected by the optical device forms a fourth angle with the third direction, and the range of the fourth angle is _____. .

[0009] Optionally, the detection light is incident on the target position parallel to the second direction; the reflecting surface of the optical device is at a 45° angle to the second direction. 。 An angle is formed such that the reflected detection light is incident perpendicularly on the workpiece to be detected; wherein, in the third direction, the rectangular reflector blocks the first distribution area of ​​the spatial distribution of the background pattern diffracted light.

[0010] Optionally, the optical imaging assembly includes an objective lens, and the optical device is located between the objective lens and the workpiece to be inspected. The length of the first side of the optical device is positively correlated with the distance from the target position to the workpiece to be inspected and is also positively correlated with the numerical aperture of the objective lens. The length of the second side of the optical device is positively correlated with the distance between the target position and the workpiece to be inspected.

[0011] Optionally, the incident angle of the detection light emitted by the illumination component onto the workpiece to be detected is less than 90 degrees; the optical device is a reflective device or a light-absorbing device; the optical detection system further includes an optical trap, and the optical trap and the illumination component are respectively located on opposite sides of the optical axis of the optical imaging component.

[0012] Optionally, the optical device is rectangular, with a length of l and a width of w; the distance between the target position of the optical device and the workpiece to be inspected is d; the numerical aperture of the objective lens is r; the distance between the incident position of the detection light on the workpiece to be inspected and the target position of the optical device is d; the target position is the intersection of the surface of the optical device facing the workpiece to be inspected and the optical axis of the optical imaging component; the optical device forms a light-blocking region with a zenith angle of θ on the workpiece to be inspected, where θ is a constant related to the first distribution region of the diffracted light spatial distribution of the background pattern;

[0013] ;

[0014] .

[0015] Optionally, the thickness of the optical device is h; .

[0016] Optionally, the first distribution region of the spatial distribution of the background pattern diffracted light occupies 60% to 85% of the diffracted light intensity within the numerical aperture range of the objective lens. Attached Figure Description

[0017] Figure 1 is a schematic diagram of the structure of the optical detection system provided in an embodiment of this disclosure;

[0018] Figure 2 shows the distribution of diffraction light intensity of the workpiece under vertical illumination in the hemispherical space;

[0019] Figure 3 is a schematic diagram of the dimensions and structure of the optical device provided in the embodiment of this disclosure;

[0020] Figure 4 is a side view of the optical device shown in Figure 3 in the YZ plane of the optical system;

[0021] Figure 5 is a side view of the optical device shown in Figure 3 in the XZ plane of the optical system;

[0022] Figure 6 is a schematic diagram of the required occlusion area corresponding to different diffraction patterns provided in the embodiments of this disclosure.

[0023] Figure 7 is another structural schematic diagram of the optical detection system provided in an embodiment of this disclosure;

[0024] The annotations in the attached figures are explained as follows:

[0025] The components include: lighting assembly 100, support platform 101, workpiece to be inspected 102, optical imaging assembly 103, objective lens 104, detector 105, optical device 106, lighting source 107, light modulation assembly 108, background light 109, defect scattered light 110, first distribution area 111, incident detection light 112, reflected detection light 113, optical device blocking area 114, light trap 115, filter assembly 116, reflective film 1061, tube lens 117, beam expander module 118, shaping module 119, numerical aperture r, first direction X, second direction Y, third direction Z, length l, width w, thickness h, target position A, height d, and zenith angle θ. Detailed Implementation

[0026] To more clearly illustrate the technical solutions in the embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] The embodiments of this disclosure will now be clearly and completely described with reference to the accompanying drawings. Those skilled in the art will recognize that, with technological advancements and the emergence of new scenarios, the technical solutions provided in this disclosure are equally applicable to similar technical problems.

[0028] In related technologies, when the workpiece to be inspected is a wafer with a surface pattern, the surface pattern of the wafer can affect the detection accuracy and precision by acting as a background pattern during surface defect detection. In wafer inspection systems based on optical technology, optimized illumination design and suppression of the contribution of background patterns to the image jointly affect defect detection performance. The inventors have found that in related technical solutions, coaxial illumination methods generally have good defect detection capabilities, but the illumination light direction deflection device is generally a semi-transparent mirror or beam splitter embedded in the microscope objective. This design produces unavoidable negative effects, such as degrading image contrast, introducing additional aberrations, and changing the preset polarization state. In addition, images acquired by coaxial illumination methods inevitably contain bright background patterns, and when the grayscale difference between the defect and the background is not significant, the defect will be difficult to detect reliably.

[0029] In patterned wafer defect detection, patterned wafers are primarily periodically distributed, and the diffracted light exhibits multi-level characteristics in the frequency domain; while defects are uniformly non-periodic, and the scattered light exhibits anisotropic continuous distribution. The spatial frequency domain distribution patterns of the two differ, and Fourier spatial frequency filtering can be applied based on this difference to reduce the influence of pattern diffracted light. In signal acquisition, related technologies use a spatial filter near the pupil plane of the imaging optical path system to filter the diffracted light from the background pattern before detection. The inventors discovered that when detecting patterned wafer surface defects, the intensity of the diffracted light generated by the background pattern is much greater than the intensity of the scattered light generated by the defect (i.e., the signal light from the surface defect of the workpiece being inspected). In typical applications, the intensity ratio of the diffracted light generated by the background pattern to the scattered light from the defect is at least 10. 4 The magnitude of the background pattern diffracted light entering the imaging optical path composed of optical lenses is significant. Even with anti-reflection coatings on the lens surfaces, Fresnel reflections occur on the front and back surfaces of each lens. The imaging optical path includes an objective lens; the stray light generated by residual reflections from the optical surfaces of the optimized imaging objective lens is approximately two-thousandths of the incident light. These stray lights have different spatial frequency distributions than the background diffracted light. Therefore, Fourier spatial frequency filtering in the optical path cannot effectively filter out the residual Fresnel reflection stray light generated by the background pattern diffracted light entering the imaging optical path. This results in the stray light being non-negligible compared to the scattered light signal from small-sized defects, potentially forming ghost images or flares with intensity close to the defect signal, leading to false positives or false negatives in defect detection.

[0030] Furthermore, the inventors discovered that the wafer surface patterns of advanced process chips are mainly periodic structures. Since the typical feature size of the periodic structure is much smaller than the product of the illumination light wave and the working distance of the microscope objective, the diffraction of the surface pattern on the plane between the wafer under test and the objective approximately satisfies the far-field diffraction condition. That is, the diffraction distribution on this plane is a stable spatial spectrum related to the wafer surface pattern.

[0031] Based on this characteristic, embodiments of this disclosure provide a novel optical detection system, comprising:

[0032] Illumination component 100, the illumination component is used to emit detection light;

[0033] The support platform 101 is used to place the workpiece 102 to be inspected; the workpiece 102 to be inspected can generate signal light including surface defects of the workpiece 102 based on the detection light.

[0034] The optical imaging assembly 103 includes an objective lens 104, a filter assembly 116, a tube lens 117, and a detector 105. The objective lens 104 collects signal light, which is then filtered by the filter assembly 116 to filter out some of the background pattern diffracted light, forming a detection signal. This signal is then imaged within the detector 105 via the tube lens 117. The tube lens 117 consists of one or more lenses and works in conjunction with the objective lens to image the signal light from the surface defect onto the detector. The filter assembly 116 includes a spatial filter, which is positioned on the pupil plane or its conjugate plane.

[0035] In the embodiments of this disclosure, the spatial filter can be formed by multiple adjustable-spacing strip masks, can be a mask including a spatial light modulator (SLM), can be a wedge-shaped light-blocking structure disposed at one end of a light-blocking structure, can be a wedge-shaped light-blocking structure disposed at both ends of a light-blocking structure, can be a circular light-blocking structure disposed at any position of the light-blocking structure, can be a cross-shaped light-blocking structure, can be a strip-shaped light-blocking structure, can be a light-blocking structure including several strips forming a grid, or can be a light-blocking structure including a combination of strips and circles. All spatial filter embodiments described in this disclosure can be manufactured in any manner and using any materials known in the art. Although this disclosure describes several embodiments of spatial filters, these examples are not intended to limit the scope of the invention.

[0036] Alternatively, periodic sawtooth patterns in the spatial filter can be used to improve its performance.

[0037] Optical device 106 is located between objective lens 104 and support platform 101. Optical device 106 is used to block the first distribution area of ​​diffracted light of background pattern, that is, to block the spatial distribution area of ​​strong diffracted light of background pattern in workpiece 102 to be inspected, so as to reduce the diffracted light related to surface pattern entering objective lens 104. The diffracted light related to surface pattern of workpiece 102 to be inspected is defined as background light generated by diffraction effect of surface pattern.

[0038] The optical inspection system provided in this disclosure includes an optical device disposed between the objective lens and the support platform to filter out diffracted light (i.e., background light) generated by the surface pattern of the workpiece to be inspected. This optical device can achieve vertical coaxial illumination and filter out most of the diffracted light from the surface pattern of the workpiece to be inspected. Since the diffracted light generated by the surface pattern of the workpiece to be inspected is filtered out before entering the optical imaging assembly, Fresnel reflections generated by the front and rear surfaces of each optical lens in the imaging optical path are suppressed, especially the residual Fresnel reflections caused by the surface of the lens inside the objective lens are suppressed. This significantly reduces the influence of residual Fresnel reflections on the defect detection results, reduces the image contrast degradation and additional aberrations caused by the built-in illumination deflection device in the objective lens, suppresses the influence of diffracted light generated by the surface pattern of the workpiece to be inspected on the inspection image, improves the signal-to-noise ratio of the image, and improves the accuracy of the inspection results.

[0039] It should be noted that the embodiments of this disclosure take a wafer as an example to illustrate the workpiece to be inspected. In actual use, the optical inspection system is not limited to the surface defect detection of wafers. It can also be used for the surface defect detection of other workpieces with surface patterns, such as displays, optoelectronic chips, Micro-Electro-Mechanical System (MEMS) devices, and power semiconductor devices. The embodiments of this disclosure do not limit the type of workpiece to be inspected.

[0040] To make the above-mentioned objects, features and advantages of this disclosure more apparent and understandable, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Referring to Figures 1 and 2, Figure 1 is a schematic diagram of an optical inspection system provided in an embodiment of this disclosure, and Figure 2 is a distribution diagram of the diffracted light intensity of the workpiece under vertical illumination in a hemispherical space. In Figure 2, r represents the numerical aperture of the objective lens 104. The optical inspection system includes:

[0042] Illumination component 100, which is used to emit detection light;

[0043] The support platform 101 is used to place the workpiece 102 to be inspected; the detection light shines on the workpiece 102 to be inspected, forming signal light including the surface defects of the workpiece 102 to be inspected.

[0044] The optical imaging component 103 includes an objective lens 104 and a detector 105. The detector 105 collects signal light through the objective lens 104 to form a detection signal.

[0045] Optical device 106 is located between objective lens 104 and support platform 101. Optical device 106 is used to block the first distribution area 111 of the spatial distribution of background pattern diffracted light of the workpiece 102 to be inspected, so as to reduce the diffracted light related to the surface pattern of the workpiece 102 entering the objective lens 104. The diffracted light related to the surface pattern of the workpiece 102 is the background light generated by the diffraction effect of the surface pattern of the workpiece 102 on light. The first distribution area 111 of the spatial distribution of background pattern diffracted light corresponds to the area of ​​the surface of the workpiece 102 to be inspected that is blocked by optical device 106.

[0046] In Figure 1, the vertical dotted line AA represents the normal direction (i.e., perpendicular to the wafer surface) of the light spot incident point on the surface of the workpiece 102 to be inspected. In other embodiments of the optical inspection system described below, the normal direction of the light spot incident point on the surface of the workpiece 102 to be inspected is also represented by a vertical dotted line.

[0047] Optionally, the illumination assembly 100 includes an illumination source 107 and a light modulation assembly 108. The illumination source 107 emits initial illumination light, and the light modulation assembly 108 is used to expand and focus the initial illumination light to output the detection light required for the inspection of the workpiece 102. According to some embodiments, the illumination source can be a continuous light source, such as an arc lamp, a laser-enhanced plasma source, or a continuous-wave CW laser. According to other embodiments, the illumination source can be a pulsed light source, such as a mode-locked laser, a Q-switched laser, or a Q-switched laser-pumped plasma source. The illumination assembly 100 is used to send a beam of light of a preset wavelength to the workpiece to be inspected at a preset angle. The preset wavelength can be a wavelength used in the field of wafer inspection technology. The illumination source 107 can be any of a red laser, a blue laser, an ultraviolet light source, a deep ultraviolet (DUV) light source, a vacuum ultraviolet (VUV) light source, an extreme ultraviolet (EUV) light source, an LED light source, etc. The embodiments of this disclosure do not specifically limit the type of illumination source 107.

[0048] The optical inspection system provided in this embodiment includes an optical device 106 disposed between the objective lens 104 and the support platform 101 to filter out diffracted light (i.e., background light 109) generated by the surface pattern of the workpiece 102 to be inspected. The defect-scattered light 110 of the workpiece 102 to be inspected can be collected by the objective lens 104 to form a detection signal. The optical device 106 can achieve vertical coaxial illumination and filter out most of the diffracted light from the surface pattern of the workpiece 102 to be inspected. Since the diffracted light generated by the surface pattern of the workpiece 102 to be inspected is filtered out before entering the optical imaging assembly 103, the residual Fresnel reflection light caused by the inner lens surface of the objective lens 104 is also suppressed, significantly reducing the influence of residual Fresnel reflection light on the defect detection result. This can reduce the image contrast degradation and additional aberrations caused by the built-in illumination deflection device in the objective lens 104, suppress the influence of diffracted light generated by the surface pattern of the workpiece 102 to be inspected on the detection signal, improve the signal-to-noise ratio of the image, and improve the accuracy of the detection result.

[0049] In the optical detection system provided in this embodiment, the light modulation component 108 includes a beam expander module 118 and a shaping module 119. The beam expander module 118 can enlarge the beam spot diameter to meet the requirements of the subsequent shaping module 119. The beam expander module can be a beam expander lens group, which may include one or more beam expander optical elements, such as spherical lens groups, cylindrical lens groups, deformable prism groups, etc. They are combined to collimate the incident light after divergence, increase the size of the incident beam spot, and make the output beam reach a predetermined size, thereby meeting the incident conditions of the subsequent optical shaping module.

[0050] The shaping module 119 is used to shape the incident beam into a light spot with a specified shape distribution, and to converge it onto the sample plane. In this scheme, the light spot output by the shaping module 119 is a rectangular Gaussian flat-top light spot. The shaping module 119 can be a shaping element, comprising one or more transmission optical elements, such as diffractive optical elements (DOEs), freeform mirrors, microlens arrays, cylindrical mirrors, etc. These elements modulate parameters such as transmission direction, additional phase, and transmittance at various positions of the incident light, achieving single-degree-of-freedom linewidth compression in the narrow-side direction and uniform light in the long-side direction to obtain the target light spot. The light spot output by the shaping module 119 is emitted from the illumination component 100 in the form of detection light.

[0051] Objective lens 104 is used to receive the scattered light beam from workpiece 102 and image the scattered light beam onto detector 105.

[0052] Detector 105 is used to form a detection signal based on the scattered beam from objective lens 104, so as to detect defects in workpiece 102 according to the detection signal. Detector 105 includes, but is limited to, charge-coupled device (CCD) detectors, time-delay integration (TDI) detectors, photomultiplier tubes (PMTs), avalanche photodiodes (APDs), etc.

[0053] Optionally, in this embodiment, the size, shape, and setting of the first distribution region 111 of the spatial distribution of background pattern diffraction light need to comprehensively consider the distribution of background pattern diffraction light and the distribution of defect scattered light, selecting a region where the distribution of background pattern diffraction light is concentrated while the distribution of defect scattered light is not concentrated. In the detection of patterned wafer defects, the background pattern of the wafer is mainly divided into periodic distribution, and the diffraction light exhibits multi-level characteristics; while the defect is a single non-periodic distribution, and the scattered light exhibits anisotropic continuous distribution. The difference in the spatial frequency domain distribution rules of the two is the basis for the effective implementation of this disclosure. The actual wafer surface under inspection has a variety of background patterns, corresponding to a variety of background pattern diffraction light distributions. The spatial distribution of background pattern diffraction light can be obtained through experimental measurement or simulation analysis. The experimental measurement method is as follows: configure a measurement system and detect the signal collected at or near the pupil plane of the measurement system; without placing a filter component in front of the objective lens, insert the measurement system into the detection optical path, and generate an optical path branch to the measurement system through the beam splitter of the measurement system to collect the signal light of the background pattern, and observe it using an image detector on the pupil plane. The simulation analysis method is as follows: A simulation model is established based on the wafer pattern and measurement system settings such as illumination wavelength and direction. Numerical simulation is performed using electromagnetic simulation methods such as the finite-difference time-domain method and the finite element method to obtain the background diffracted light. In this embodiment, the first distribution region 111 of the spatial distribution of the background pattern diffracted light needs to comprehensively consider the distribution of diffracted light from each background pattern and the scattered light from each defect. A region where the background pattern diffracted light distribution is concentrated while the defect scattered light is not is selected, ensuring that the intensity of the diffracted light distributed in this region accounts for 60% to 85% of the diffracted light intensity within the numerical aperture range of the collecting objective lens. The specific percentage needs to be determined by comprehensively considering the spatial distribution patterns of the background pattern diffracted light and the defect scattered light. Although the first distribution region 111 is rectangular in Figure 2, this shape is merely illustrative. The shape of the first distribution region 111 in this disclosure can be other shapes, such as circles or ellipses. The first distribution region 111 is set according to the above light intensity ratio of 60%-85%, and is not limited to a specific shape.

[0054] In some embodiments of this disclosure, as shown in FIG1, the optical device 106 is capable of reflecting detection light; the detection light emitted from the illumination assembly 100 is reflected by the optical device 106 and then perpendicular or nearly perpendicular to the light source. The light is incident on the workpiece 102 and scattered by the workpiece 102 to form signal light. In this method, the optical device 106 serves to deflect the detection light in front of the objective lens 104 and filter out background light. Moreover, the optical device 106 is located between the objective lens 104 and the workpiece 102. The optical device 106 does not affect the imaging quality of the optical imaging assembly 103, and can also provide the workpiece 102 with perpendicular incident detection light parallel to the optical axis of the optical imaging assembly 103 by deflecting the detection light, thereby achieving vertical coaxial illumination. This can achieve large-area uniform illumination, reduce background noise, and improve detection efficiency and detection sensitivity.

[0055] Optionally, the optical device 106 includes a substrate and a reflective film 1061 located on the surface of the substrate. The reflective film 1061 can be a metal aluminum film or other high-reflectivity coating.

[0056] Referring to Figures 3-5, Figure 3 is a schematic diagram of the structure of the optical device provided in the embodiment of this disclosure, Figure 4 is a side view of the optical device shown in Figure 3 in the YZ plane of the optical system, and Figure 5 is a side view of the optical device shown in Figure 3 in the XZ plane of the optical system. The dashed arrows in Figures 4 and 5 indicate the transmission path of the detection light. A three-dimensional Cartesian coordinate system is set as a reference, with three mutually perpendicular coordinate axes. The positive directions of these three coordinate axes are, in order, the first direction X, the second direction Y, and the third direction Z. The XY plane is parallel or approximately parallel to the surface of the wafer, the Z direction is perpendicular or approximately perpendicular to the surface of the wafer, and the YZ plane is parallel or approximately parallel to the incident direction of the detection light incident on the optical device.

[0057] Based on other embodiments, in the configuration shown in Figures 3-5, the incident position of the incident detection light 112 on the optical device 106 is located at the target position A of the optical device 106, and the distance between the target position A and the workpiece 102 to be detected is d. The size of the optical device 106 is positively correlated with d; the larger the size of the optical device 106, the larger the distance d. The target position A is the intersection of the surface of the optical device 106 facing the wafer and the optical axis of the objective lens.

[0058] The line connecting the target position A and the incident position of the detection light on the workpiece 102 is parallel or approximately parallel to the third direction Z, i.e., the length of the line is d or approximately d. Optionally, the target position A coincides with or approximately coincides with the geometric center of the surface of the optical device 106 facing the wafer.

[0059] Optionally, the detection light is incident on the target position A of the optical device 106, and a reflected detection light 113 is formed at the target position A. The reflected detection light 113 can be incident perpendicularly or approximately perpendicularly on the workpiece 102 to be detected.

[0060] The greater the distance d between the optical device 106 and the workpiece 102 to be inspected, the more necessary it is to use a larger optical device 106 to block the background light 109 generated by the diffraction of the surface pattern of the workpiece to be inspected. This will better block the background light 109 from entering the objective lens 104, thereby effectively reducing the interference of the background light 109 on the inspection results and improving the accuracy and reliability of the inspection results.

[0061] The support platform 101 is parallel or approximately parallel to a first intersecting plane (i.e., the XY plane) of the first direction X and the second direction Y. The edge of the surface of the optical device 106 near the wafer forms a second angle with the first direction X, the value of which is within the range of... °, that is, the edge of the surface of the optical device 106 near the wafer is parallel to or approximately parallel to the first direction X.

[0062] Optical device 106 includes a rectangular reflector. The reflecting surface of optical device 106 that reflects the incident detection light has a first angle with the first intersecting plane, the value of which is within the range of... That is, the optical device 106 is at a 45° angle relative to the first intersecting plane. 。 ° or approximately 45 。 The light source is tilted at a certain angle, and the detection light emitted from the lighting component 100 forms a third angle with the second direction Y. The range of the third angle is... °, meaning the detection light is incident on the wafer-facing surface of the optical device 106 in a transmission direction parallel to or approximately parallel to the second direction Y, such that the detection light reflected by the optical device has a fourth angle with the third direction Z, the value of which is within the range of °. That is, the detection light is incident on the workpiece 102 to be detected perpendicularly or approximately perpendicularly.

[0063] In some embodiments of this disclosure, as shown in Figures 2-5, the optical device 106 includes a rectangular reflector; the side (e.g., the long side) of the rectangular reflector near the wafer surface is parallel to or approximately parallel to the first direction X; detection light is incident on the target position A of the rectangular reflector along the second direction Y; the first direction X and the second direction Y are perpendicular and both parallel to the plane of the support platform 101; the reflecting surface of the optical device 106 has a perpendicularity with the second direction Y. The angle is such that the reflected detection light is incident on the workpiece 102 near or perpendicularly; optionally, the reflecting surface of the optical device 106 has a 45° angle with the second direction Y. 。 An angle is formed such that the reflected detection light is perpendicularly incident on the workpiece 102 to be inspected; wherein, in the third direction Z, the rectangular reflector blocks the first distribution area 111 of the diffracted light spatial distribution of the background pattern, and the third direction Z is perpendicular to the plane where the support platform 101 is located. The third direction Z is parallel to the optical axis of the optical imaging component 103.

[0064] It should be noted that, in the embodiments of this disclosure, when two objects are described as parallel, it means that there can be a first included angle between them, and the first included angle can be equal to... The angle between them, when the angle is 0 。 When the two are perfectly parallel, the angle between them is not equal to 0. 。 At that time, the two are approximately parallel;

[0065] It should also be noted that, in the embodiments of this disclosure, when two objects are described as perpendicular, it means that there can be a second included angle between them, which can be... The angle between them, when the angle is 90° 。 When the two are perfectly perpendicular, the angle between them is not equal to 90°. 。 At that time, the two are approximately perpendicular.

[0066] Optionally, the optical element 106 is at a 45° angle. 。 By tilting the device at an angle, the reflected detection light 113 generated by the detection light incident parallel to the surface of the wafer is perpendicularly incident on the workpiece 102 to be inspected, thereby forming a vertical illumination design coaxial with the optical imaging component 103.

[0067] In some embodiments of this disclosure, the optical inspection system further includes an adjustment device, which is not shown in the accompanying drawings. An optical element 106 is mounted on the adjustment device, which is used to adjust the tilt angle of the optical element 106 relative to the workpiece 102 to be inspected and / or the distance between the optical element 106 and the workpiece 102. This facilitates more accurate adjustment of the tilt angle and height d of the optical element 106 relative to the workpiece 102 within the system, thereby facilitating the attitude adjustment of the optical element 106 and enabling more accurate detection of surface defects on the workpiece 102. The adjustment device may be a device with an adjustable pitch and one-dimensional adjustment mechanism, equipped with a clamp.

[0068] As shown in Figures 3-5, the length of the rectangular reflector is set to l (i.e., the length of the longer side parallel to the first direction X is l), and the width is w (i.e., it is at a 45° angle to the second direction Y). 。 The length of the shorter side of the included angle is w).

[0069] As described above, let the numerical aperture of objective lens 104 be r; let the length of the rectangular reflector be l and the width be w. Then l is positively correlated with d, and l is positively correlated with r, and w is positively correlated with d.

[0070] When l is positively correlated with d, and l is positively correlated with r, and w is positively correlated with d, in the third direction Z, the first distribution area 111 formed by the orthogonal projection area of ​​the optical device 106 on the workpiece 102 to be inspected can effectively block the background light 109, so as to better block the background light 109 from entering the objective lens 104 through the optical device 106, thereby effectively reducing the interference of the background light 109 on the detection results and improving the accuracy and reliability of the detection results.

[0071] In this embodiment of the present disclosure, the length l and width w of the rectangular reflective device can be determined together with the numerical aperture r of the objective lens and the surface pattern of the workpiece 102 to be inspected.

[0072] To determine the length *l* and width *w*, the distribution of far-field diffracted light on the workpiece 102 to be inspected can be determined first. Figure 2 shows the distribution of diffracted light intensity in a hemispherical space under vertical illumination conditions for a typical wafer with a logic array circuit pattern. The spatial solid angle range corresponding to the rectangular region (the first distribution region 111 of the background pattern diffracted light spatial distribution) in Figure 2 includes most of the energy of the diffracted light field of the wafer surface pattern. In order to filter out the influence of the wafer background pattern on the detection signal acquired by the optical detection system, the diffracted light in this rectangular region needs to be blocked. As described above, the rectangular region covers the area with high diffracted energy, and the energy peak in this region can be greater than -14 dB.

[0073] Secondly, the placement position of the optical device 106 in front of the objective lens 104, as well as its exact length l and width w, need to be determined based on the telescoping distance of the objective lens 104 relative to the workpiece to be inspected and its numerical aperture. Figures 4 and 5 show a schematic diagram illustrating the principle of the size calculation for the optical device 106. In the plane containing the second direction Y and the third direction Z, the rectangular reflective device forms an optical device blocking area 114 with a zenith angle θ. Here, θ is a constant related to the first distribution area 111 of the diffracted light spatial distribution of the background pattern. For a workpiece 102 with a defined surface pattern, its suitable zenith angle θ can be a definite constant. Due to the complexity of surface patterns in practical applications, this constant is generally obtained through experimental testing. This embodiment does not limit the specific value of the zenith angle θ. The zenith angle θ is the angle relative to the normal of the incident point of the light spot on the surface of the workpiece to be inspected.

[0074] In this embodiment of the disclosure, the tilt angle of the optical device 106 in the YZ plane is set to 45°. 。 °, based on simple triangular geometric relationships, the length l and width w of the rectangular reflector can be calculated and determined based on the following formulas (1) and (2), respectively.

[0075] (1).

[0076] (2).

[0077] Wherein, the numerical aperture r of objective lens 104 is a dimensionless parameter. It should be noted that in the angle-related conditions of this disclosure, when the angle deviation is within... When within the range, formulas (1) and (2) in this disclosure are equally applicable.

[0078] If the zenith angle θ of the workpiece 102 to be tested is 20° 。 (Corresponding to a radian value of 0.3491), if d=3.5mm and r=0.7, based on formulas (1) and (2), we can determine that l=6.88mm and w=2.64mm. At this time, the value of l in the optical detection system is not less than 6.88mm, which can effectively cover the area corresponding to the numerical aperture r of the objective lens 104. Only when the value of w is not less than 2.64mm can it cover the first distribution area 111 of the diffraction light spatial distribution of the background pattern within the zenith angle θ.

[0079] Based on the above formula (2), it can be seen that when the optical device 106 is a rectangular reflective device, if the distance d is a fixed constant, its width w is related to the zenith angle θ. The value of the zenith angle θ depends on the surface pattern of the workpiece 102 to be tested. Different surface patterns will produce different diffraction patterns. According to the spatial distribution of the diffraction pattern, the optical device 106 with the corresponding width w can be flexibly prepared to block the main diffraction energy region, thereby filtering out most of the noise caused by the background light 109.

[0080] Optionally, the optical element 106 is mounted on an adjustment device. The adjustment device includes multiple mounting positions for mounting optical elements 106 of different widths w. The adjustment device is rotatable so that the optical element 106 with the appropriate width is positioned between the workpiece 102 to be inspected and the objective lens 104. In this way, an optical element 106 with an appropriate width can be selected to perform defect detection on the workpiece 102 according to the surface pattern of the workpiece 102 to be inspected, making the optical inspection system suitable for inspecting workpieces 102 with various surface patterns.

[0081] Optionally, the optical inspection system of this disclosure includes multiple optical devices 106 with different widths. The multiple optical devices 106 are detachably mounted on the adjustment device. An optical device 106 with an appropriate width can be selected and mounted on the adjustment device according to the surface pattern of the workpiece 102 to be inspected. Similarly, an optical device 106 with an appropriate width can be selected to perform defect detection on the workpiece 102 to be inspected according to the surface pattern of the workpiece 102 to be inspected. This makes the optical inspection system suitable for inspecting workpieces 102 with a variety of different surface patterns.

[0082] In some embodiments of this disclosure, based on other embodiments, the thickness of the optical device 106 is set to h. On the one hand, setting This can reduce the problem of poor mechanical strength caused by insufficient thickness of optical device 106, which easily leads to thermal deformation and thermal damage. On the other hand, setting This can prevent the problem of strong edge effects caused by excessive thickness of the optical device 106 interfering with the detection results.

[0083] In this embodiment, the optical device 106 is not limited to a rectangular reflective device; it can also be an elliptical or other graphic structure with superior mechanical strength. The optical device 106 can be configured as a regular or irregular geometric structure as required. The optical device 106 can be any geometric structure including a target rectangular region with length l and width w, so that the vertical projection of the optical device 106 on the support platform 101 can completely block the first distribution area 111 of the diffracted light space of the background pattern, thereby blocking the background light 109 generated by the surface pattern from entering the objective lens 104. This embodiment does not limit the graphic structure of the optical device 106.

[0084] Referring to Figure 6, Figure 6 is a schematic diagram of the required shielding areas corresponding to different diffraction patterns of different workpieces to be inspected according to embodiments of this disclosure. Figure 6 takes a wafer as an example, where the surface pattern of the wafer is its surface circuit pattern. Figure 6 shows the background diffraction patterns of wafers with three different surface circuit patterns. Based on Figure 6, it can be seen that when the surface circuit patterns of the wafer to be inspected are different, the resulting background diffraction patterns are different. Corresponding to different sizes of background pattern diffraction light space, the first distribution area 111 requires optical devices 106 of different widths.

[0085] In the above embodiments, an example is given of a vertical illumination design where the optical device 106 reflects detection light, and the reflected detection light forms a vertical illumination pattern coaxial with the optical imaging assembly 103. In other embodiments, as shown in FIG7, an inclined illumination design may also be used.

[0086] Referring to Figure 7, which is another structural schematic diagram of the optical inspection system provided in this embodiment, the optical inspection system shown in Figure 7 realizes dark field defect detection of the workpiece 102 to be inspected through an inclined illumination optical path based on the above-described embodiments.

[0087] As shown in Figure 7, the detection light emitted from the illumination component 100 is obliquely incident on the workpiece 102 to be inspected. The optical inspection system also includes an optical trap 115, which is located on both sides of the optical axis of the optical imaging component 103, along with the illumination component 100. The optical trap 115 can be used to absorb reflected light to prevent it from freely reflecting within the system and forming stray light, thereby reducing the impact of stray light on the detection results and preventing harm to the human eye.

[0088] The method can be the same as that shown in Figures 3-5. In the method shown in Figure 7, the optical device 106 is also rectangular. Since this method does not require the optical device 106 to change the transmission direction of the detection light, the optical device 106 can be a reflective device or a light-absorbing device, as long as it can block the background signal from entering the objective lens 104.

[0089] Whether it is the vertical illumination method shown in Figures 3-5 or the oblique illumination method shown in Figure 7, in this embodiment, the optical device 106 can be rectangular. As mentioned above, the length of the optical device 106 is set to l, and the width to w; the distance between the target position A of the optical device 106 and the workpiece 102 to be detected is d; the numerical aperture of the objective lens 104 is r; and the distance between the incident position of the detection light on the workpiece 102 to be detected and the target position A of the optical device 106 is d. The length L and the width w are calculated in the same way, and can be calculated using the above formulas (1) and (2). The various embodiments in the specification of this disclosure are described in a progressive, parallel, or progressive and parallel manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. The embodiments provided in this disclosure can be combined with each other without contradiction.

[0090] By employing the above technical solution, the optical inspection system provided in this application includes an optical device that can block background light between the optical imaging component and the support platform. This allows for direct blocking of background light during the imaging process of the workpiece, reducing interference from background light on the inspection results and improving the signal-to-noise ratio of the defect signal relative to the background signal, thus enhancing inspection accuracy. Since the diffracted light generated by the surface pattern of the workpiece is filtered out before entering the optical imaging component, residual Fresnel reflection caused by the surface of the lens inside the objective lens is also suppressed, significantly reducing the impact of residual Fresnel reflection on the defect detection results. Compared to the traditional design of embedding an illumination deflector in the objective lens, utilizing the reflection deflection effect of an external optical device can improve image contrast and reduce additional aberrations caused by the built-in deflector, further improving the accuracy of the inspection results. Furthermore, the optical device also offers advantages such as low cost, flexible design, and ease of application.

[0091] It should be noted that, in the description of this disclosure, the accompanying drawings and embodiments are illustrative rather than restrictive. The same reference numerals identify the same structures throughout the embodiments. Additionally, for ease of understanding and description, the thicknesses of some layers, films, panels, regions, etc., may be exaggerated in the drawings. It is also understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element may be directly on the other element or there may be intermediate elements. Furthermore, "on" means positioning an element on or below another element, but does not inherently mean positioning it above another element according to the direction of gravity.

[0092] The terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this disclosure and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally at the same time.

[0093] It should also be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.

[0094] The above description of the disclosed embodiments enables those skilled in the art to make or use this disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An optical inspection system, comprising: An illumination assembly for emitting detection light; The support platform is used to place the workpiece to be inspected; The detection light shines onto the workpiece to be inspected, forming signal light that includes surface defects of the workpiece to be inspected; An optical imaging component that acquires the signal light to form a detection signal for detecting the workpiece to be detected; An optical device is located between the optical imaging assembly and the support platform. The optical device is used to block a first distribution area of ​​the spatial distribution of background pattern diffraction light in the workpiece to be inspected, so as to reduce the diffraction light related to the surface pattern of the workpiece to be inspected from entering the objective lens.

2. The optical detection system according to claim 1, wherein, The optical device is capable of reflecting the detection light; The detection light emitted by the illumination component is reflected by the optical device and then incident on the workpiece to be detected to form the signal light.

3. The optical detection system according to claim 2, wherein, The incident position of the detection light on the optical device is located at the target position of the optical device; The size of the optical device is positively correlated with the distance between the target position and the workpiece to be inspected; The target location is the intersection of the surface of the optical device facing the workpiece to be inspected and the optical axis of the optical imaging component.

4. The optical detection system according to claim 3, wherein, The three-dimensional Cartesian coordinate system used as a reference is set to have three coordinate axes that are perpendicular to each other. The positive directions of these three coordinate axes are the first direction, the second direction, and the third direction, respectively. The support platform is parallel to the first intersecting plane of the first direction and the second direction; The optical device includes a rectangular reflector; the reflective surface of the optical device for reflecting the detection light has a first angle with the third direction, the value of the first angle being within the range of The first side of the optical device has a second angle with the first direction, and the range of the first angle is [missing value]. ； The detection light emitted by the illumination component forms a third angle with the second direction, and the range of the third angle is [missing value]. °； The detection light reflected by the optical device forms a fourth angle with the third direction, and the range of the fourth angle is: 。 5. The optical detection system according to claim 4, wherein, The detection light is incident on the target position parallel to the second direction; The reflecting surface of the optical device is at a 45° angle to the second direction. 。 An angle is formed such that the reflected detection light is incident perpendicularly on the workpiece to be detected; In the third direction, the rectangular reflective device blocks the first distribution area of ​​the spatial distribution of the diffracted light of the background pattern.

6. The optical detection system according to claim 4, wherein, The optical imaging assembly includes an objective lens, and the optical device is located between the objective lens and the workpiece to be inspected. The length of the first side of the optical device is positively correlated with the distance from the target position to the workpiece to be inspected and is also positively correlated with the numerical aperture of the objective lens. The length of the second side of the optical device is positively correlated with the distance between the target position and the workpiece to be inspected.

7. The optical detection system according to claim 1, wherein, The detection light emitted by the illumination component is incident on the workpiece under test at an angle of less than 90 degrees; the optical device is a reflective device or a light-absorbing device. The optical detection system also includes an optical trap, which is located on both sides of the optical axis of the optical imaging component, along with the illumination component.

8. The optical inspection system according to any one of claims 1-7, wherein, The optical device is rectangular, with a length of l and a width of w; the distance between the target position of the optical device and the workpiece to be inspected is d. The numerical aperture of the objective lens is r; the distance between the incident position of the detection light on the workpiece to be detected and the target position of the optical device is d; the target position is the intersection of the surface of the optical device facing the workpiece to be detected and the optical axis of the optical imaging assembly. The optical device forms a light-blocking region with a zenith angle of θ for the workpiece to be inspected, where θ is a constant related to the first distribution region of the spatial distribution of the diffracted light of the background pattern; ； 。 9. The optical detection system according to claim 1, wherein, The thickness of the optical device is h; 。 10. The optical inspection system according to any one of claims 1-9, wherein, The first distribution region of the spatial distribution of the diffracted light of the background pattern occupies 60% to 85% of the diffracted light intensity within the numerical aperture range of the objective lens.

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