Filter structure, optical detection system, and optical detection method

Abstract

A filter structure, an optical detection system, and an optical detection method, which are used for improving the accuracy of acquiring a defect signal from an object to be inspected. The filter structure comprises: a first filter structure configured to filter main diffraction signals of structural units periodically arranged in an object to be inspected; and a second filter structure configured to filter secondary diffraction spots of the structural units periodically arranged in said object. The first filter structure comprises at least one filter structure that has a closed periphery, and when said object has structural units arranged therein, a light-blocking structure connected to any two ends of the filter structure is further provided in the closed filter structure. The second filter structure comprises a plurality of parallel light-blocking members, wherein the projection of the light-blocking members on the plane where the secondary diffraction spots are located is not less than the diameter of the secondary diffraction spots.

Description

Filtering structure, optical detection system and optical detection method

[0001] The present application claims priority to the Chinese patent application No. 202510124380.8, filed on January 26, 2025, and entitled "Filtering structure, optical detection system and optical detection method", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of semiconductor detection, and in particular to a filtering structure, an optical detection system and an optical detection method. BACKGROUND

[0003] Optical imaging detection is the main technology relied on by the semiconductor industry for process defect detection. With the continuous development of technology, the semiconductor industry process has shrunk from microns to nanometers, and more complex patterns require more sophisticated defect detection technology.

[0004] In the imaging detection system, the laser beam is irradiated on the feature region of the object to be detected and / or the rough surface of the object to be detected at a certain angle. The scattered light of the feature region frequency domain information, and / or the scattered light on the rough surface of the object to be detected is collected by the objective lens system. The parallel coherent light with the same incident angle on the optical plane forms a spot, and then passes through the tube lens system to re-image on the sensing surface of the detector.

[0005] However, as the periodical structure unit in the object to be detected shrinks, the defect signal in the object to be detected is buried in the scattered light signal of the periodical structure unit and / or the rough surface of the object to be detected, thereby reducing the accuracy of extracting the defect signal in the object to be detected. SUMMARY

[0006] The embodiments of the present application provide a filtering structure, an optical detection system and an optical detection method, which are used to filter the primary diffraction signal and the secondary diffraction spot of the periodical structure in the object to be detected, so as to improve the accuracy of obtaining the defect signal in the object to be detected.

[0007] The first aspect of the embodiments of the present application provides a filtering structure, comprising:

[0008] The first filtering structure is used to filter the primary diffraction signal of the periodical structure unit in the object to be detected;

[0009] and the second filtering structure is used to filter the secondary diffraction spot of the periodical structure unit in the object to be detected; wherein:

[0010] The first filter structure comprises at least one filter structure with a closed outer periphery, and when a structure unit is arranged in the object to be detected, a light blocking structure is further arranged in the filter structure to connect any two ends of the filter structure.

[0011] The second filter structure comprises a plurality of light blocking members arranged in parallel, wherein a projection of the light blocking member on a plane of the secondary diffraction spot is not less than a diameter of the secondary diffraction spot.

[0012] Optionally, a spatial orientation of the light blocking structure connecting any two ends of the filter structure is adapted to a position and shape of a rough surface scattering spot of the object to be detected.

[0013] Optionally, the light blocking structure arranged in the closed filter structure and adapted to the position and shape of the rough surface scattering spot of the object to be detected comprises an arc-shaped light blocking structure arranged at one end of the light blocking structure, arc-shaped light blocking structures arranged at two ends of the light blocking structure, a polygonal light blocking structure arranged at any position of the light blocking structure, or a circular light blocking structure arranged at any position of the light blocking structure.

[0014] Optionally, the filter structure is arranged in an optical detection system, the first filter structure is a plurality of filter structures, the plurality of first filter structures are arranged on the same plane, and a distance between centers of two adjacent first filter structures is not less than a diameter of an optical pupil surface of the optical detection system.

[0015] Optionally, the plurality of first filter structures are driven by a driving mechanism, and when the object to be detected is switched, different first filter structures are driven by the driving mechanism to be arranged in substantial overlap with the optical pupil surface.

[0016] Optionally, an inner peripheral wall of the closed filter structure, an edge of the light blocking structure, and an edge of the light blocking structure are arranged as non-sharp edge structures.

[0017] Optionally, the filter structure is arranged in an optical detection system, if a diameter of a pupil surface in the optical detection system is D, and a width of the light blocking member is d, then a number N of the light blocking members is calculated according to the following formula:

[0018] 。

[0019] Optionally, the plurality of light blocking members are arranged in at least one plane, and each plane in the at least one plane is perpendicular to a propagation direction of the scattering light beam.

[0020] Optionally, the plurality of light blocking members are arranged in a plurality of planes, and the light blocking members in different planes are partially arranged in layers.

[0021] Optionally, the filter structure is arranged in the optical detection system, and intervals between two adjacent light blocking pieces in each plane are fixedly arranged. The plurality of light blocking pieces in each plane are driven by the same driving mechanism, so that the plurality of light blocking pieces in each plane are substantially overlapped with the light plane in the optical detection system to shield the diffraction light spots at corresponding positions of the light plane.

[0022] Optionally, each light blocking piece is driven by an independent driving mechanism, so that the corresponding light blocking piece is substantially overlapped with the light plane in the optical detection system by driving the plurality of independent driving mechanisms.

[0023] Optionally, the edge of the light blocking piece is arranged as a non-sharp edge structure.

[0024] Optionally, the surface of the first filter structure and / or the second filter structure is coated with an anti-reflection film to reduce the reflectivity of the first filter structure and / or the second filter structure.

[0025] Optionally, the light blocking piece includes a strip-shaped light blocking piece, a cylindrical light blocking piece, a sawtooth-shaped light blocking piece or a wave-shaped light blocking piece.

[0026] The second aspect of the embodiment of the present application provides an optical detection system, comprising:

[0027] a light source configured to emit a coherent light beam of a preset waveband at a preset angle to a to-be-detected object;

[0028] an objective lens configured to receive a scattered light beam of the to-be-detected object and focus parallel light beams or near-parallel light beams in the scattered light beam to a pupil plane;

[0029] a filter structure as provided in the first aspect of the embodiment of the present application, which is substantially overlapped with the light plane;

[0030] a tube lens system configured to image the to-be-detected object to a detector;

[0031] the detector is configured to detect defects in the to-be-detected object according to an image of the to-be-detected object.

[0032] Optionally, the optical detection system further comprises a switchable mirror, a pupil imaging tube lens and a pupil imaging detector.

[0033] The switchable mirror is configured to be switched in between the tube lens system and the detector to change a propagation direction of the scattered light beam so that the scattered light beam is incident on the pupil imaging tube lens, or the switchable mirror is configured to be switched in between the filter structure and the tube lens system to change the propagation direction of the scattered light beam so that the scattered light beam is incident on the pupil imaging tube lens.

[0034] The pupil imaging tube is used for imaging the light field to the pupil imaging detector.

[0035] The pupil imaging detector is used for observing the light field according to the image of the light field.

[0036] Optionally, the filter structure includes a first filter structure and a second filter structure, wherein the second filter structure includes a plurality of light blocking pieces arranged on a plurality of planes, one of the plurality of planes is arranged to overlap the pupil plane, and the other planes of the plurality of planes are arranged at 0.1 mm to 2 mm in front of the light field along the propagation direction of the scattered light beam.

[0037] Or, the other planes of the plurality of planes are arranged at 0.1 mm to 2 mm behind the light field along the propagation direction of the scattered light beam, and the first filter structure is arranged at 0.1 mm to 2 mm in front of the light field along the propagation direction of the scattered light beam.

[0038] Optionally, the filter structure includes a first filter structure and a second filter structure, wherein the second filter structure includes a plurality of strip-shaped light blocking pieces arranged in parallel, the width of the strip-shaped light blocking piece is related to the diameter of the secondary diffraction spot of the periodically arranged structure unit, the length of the strip-shaped light blocking piece is not less than the diameter of the pupil plane, and the number of the strip-shaped light blocking pieces is related to the diameter of the light field and the width of each strip-shaped light blocking piece.

[0039] Optionally, the optical detection system further includes a beam expansion and shaping module arranged between the light source and the object to be detected, wherein the beam expansion and shaping module includes a beam expansion mirror and a shaping element, and the shaping element includes a phase element with a two-dimensional structure.

[0040] The third aspect of the embodiment of the application provides an optical detection method applied to the optical detection system provided in the second aspect of the embodiment of the application, and the method comprises the following steps:

[0041] The image of the pupil plane is observed by using the pupil imaging detector to obtain the distribution state of the scattered signal in the light field.

[0042] The first filter structure is driven to filter two or the latter of the scattered signal of the rough surface of the object to be detected and the primary diffraction signal of the periodically arranged structure unit in the object to be detected in the scattered signal.

[0043] The second filter structure is driven to filter the secondary diffraction signal of the periodically arranged structure unit in the object to be detected in the scattered signal.

[0044] From the above technical solutions, the embodiments of the present application have the following advantages:

[0045] The filtering structure in the embodiments of the present application includes a first filtering structure and a second filtering structure, wherein the first filtering structure is used to filter the primary diffraction signal of the periodically arranged structure unit in the to-be-detected object, and the second filtering structure is used to filter the secondary diffraction spot of the periodically arranged structure unit in the to-be-detected object, so that when the defects in the to-be-detected object are detected, the primary diffraction signal of the periodically arranged structure unit in the to-be-detected object can be filtered through the first filtering structure, and the secondary diffraction spot of the periodically arranged structure unit in the to-be-detected object can be filtered through the second filtering structure, thereby improving the accuracy of obtaining the defect signal in the to-be-detected object. BRIEF DESCRIPTION OF DRAWINGS

[0046] FIG. 1 is a schematic diagram of the first filtering structure in the embodiments of the present application;

[0047] FIG. 2 is a schematic diagram of the first filtering structure provided with different light-blocking structures in the embodiments of the present application;

[0048] FIG. 3 is a schematic diagram of the second filtering structure in the embodiments of the present application;

[0049] FIG. 4 is a structural schematic diagram of the servo motor, the ball screw, the guide rail and the first filtering structure in the embodiments of the present application;

[0050] FIG. 5 is a schematic diagram of the first position and the second position in the optical surface in the embodiments of the present application;

[0051] FIG. 6 is a schematic diagram of the bar-shaped light-blocking piece partially stacked in the embodiments of the present application;

[0052] FIG. 7 is a structural schematic diagram of the servo motor, the ball screw, the guide rail and the second filtering structure in the embodiments of the present application;

[0053] FIG. 8 is a schematic diagram of one embodiment of the optical detection system in the embodiments of the present application;

[0054] FIG. 9 is a schematic diagram of one position of the first filtering structure and the second filtering structure in the embodiments of the present application;

[0055] FIG. 10 is a schematic diagram of another position relationship of the first filtering structure and the second filtering structure in the embodiments of the present application;

[0056] FIG. 11 is a schematic diagram of another embodiment of the optical detection system in the embodiments of the present application;

[0057] FIG. 12 is a schematic diagram of one embodiment of the optical detection method in the embodiments of the present application. DETAILED DESCRIPTION

[0058] The embodiment of the present application provides a filtering structure, an optical detection system and an optical detection method, which are used for filtering out the primary diffraction signal and the secondary diffraction spot of the periodic structure in the pupil plane of a to-be-detected object, so as to improve the accuracy of obtaining the defect signal in the to-be-detected object.

[0059] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work should belong to the protection scope of the present application.

[0060] The terms "first", "second", "third", "fourth" and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or a chronological sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0061] In an actual semiconductor detection scene, if a to-be-detected object has a periodic arrangement of structure units etched on the surface of the to-be-detected object, or the to-be-detected object has a rough surface, when the to-be-detected object is detected, the incident light beam is irradiated on the surface of the to-be-detected object, and a scattered light beam is formed on the surface of the to-be-detected object. The scattered light beam of the periodic arrangement of structure units will form a spot at the pupil plane of the objective lens system (i.e. the back focal plane of the objective lens), and the scattered light spot of the rough surface will also form a spot at the pupil plane of the objective lens system, so that the defect signal of the to-be-detected object is submerged in the scattered light spot signal.

[0062] Specifically, the rough surface of the to-be-detected object can be the rough surface of the to-be-detected object which is not etched, or the rough surface of the periodic structure unit etched on the to-be-detected object. The specific position of the rough surface in the to-be-detected object is not limited herein. The to-be-detected object in the embodiment of the present application can be a wafer, a mask, glass, etc. The type of the to-be-detected object is not limited herein.

[0063] For the convenience of understanding, the filtering structure in the embodiment of the present application is described as follows:

[0064] Specifically, the filtering structure in the embodiment of the present application is used for filtering the pupil surface in the optical detection system, and the filtering structure in the present application comprises a first filtering structure and / or a second filtering structure, wherein the first filtering structure is used for filtering out the primary diffraction signal of the periodically arranged structural unit in the to-be-detected object, and the second filtering structure is used for filtering out the secondary diffraction spot of the periodically arranged structural unit in the to-be-detected object.

[0065] As an optional embodiment, the periodically arranged structural unit can be a structural unit periodically arranged along the vertical direction and the horizontal direction, which can be a groove, a protrusion or the like, and the specific form of the structural unit is not limited here.

[0066] The first filtering structure and the second filtering structure will be described respectively as follows:

[0067] Specifically, the first filtering structure in the embodiment of the present application comprises at least one closed filtering structure, and when the to-be-detected object is provided with the structural unit, the closed filtering structure is further provided with a light-blocking structure connecting any two ends of the filtering structure, wherein the width of the light-blocking structure is related to the numerical aperture NA of the illumination light source, and the greater the numerical aperture NA of the illumination light source, the wider the width of the light-blocking structure, and vice versa. For the convenience of understanding, a schematic diagram of the first filtering structure is shown in FIG. 1.

[0068] In an actual detection scene, as long as the surface of the to-be-detected object is provided with the structural unit, a bright light line will be generated at the center of the pupil surface, that is, the primary diffraction signal generated by the structural unit, and in order to filter out the primary diffraction signal, the embodiment of the present application is further provided with the light-blocking structure connecting any two ends of the filtering structure in the closed filtering structure of the first filtering structure, so as to filter out the light generated by the structural unit on the surface of the to-be-detected object at the center of the pupil surface, and the width of the light is directly related to the numerical aperture NA of the illumination light source.

[0069] Optionally, the closed filtering structure in the embodiment of the present application can be a circular ring filtering structure, or a filtering structure with a square, rectangular or polygonal outer periphery, and the shape of the outer periphery of the filtering structure is not limited here.

[0070] Further, the second filtering structure in the embodiments of the present application includes a plurality of light blocking pieces arranged in parallel, wherein a projection of the light blocking piece on a plane where the secondary diffraction spot is located is not less than a diameter of the secondary diffraction spot, and the plurality of light blocking pieces are used to filter the secondary diffraction spot formed by the periodically arranged structure unit in the object to be detected at the optical facet of the optical detection system. It is easy to understand that the periodically arranged structure unit in the object to be detected generally forms a plurality of periodically arranged diffraction spots at the optical facet, and as long as the plurality of light blocking pieces can block the plurality of periodically arranged diffraction spots, the actual detection scene is that if the periodically arranged structure unit in the object to be detected is the structure unit periodically arranged along the vertical direction and the horizontal direction, the plurality of light blocking pieces can be the strip-shaped light blocking pieces arranged in parallel along the horizontal direction or the vertical direction at the optical facet, and if the periodically arranged structure unit in the object to be detected is the structure unit periodically arranged along the first direction, the plurality of light blocking pieces correspond to the light blocking pieces arranged in parallel along the first direction, wherein the first direction is a direction at an arbitrary angle with the horizontal direction. For the convenience of understanding, FIG. 2 shows a schematic diagram of the second filtering structure composed of the plurality of light blocking pieces.

[0071] Specifically, the light blocking piece in the embodiments of the present application can be a strip-shaped light blocking piece, a cylindrical light blocking piece, a sawtooth-shaped light blocking piece or a wave-shaped light blocking piece, as long as the projection of the light blocking piece on the plane where the diffraction spot is located can block the secondary diffraction spot, and the shape of the light blocking piece is not limited here.

[0072] Further, if the light blocking piece is a strip-shaped light blocking piece, the width of the strip-shaped light blocking piece is related to the diameter of the secondary diffraction spot of the periodically arranged structure unit, for example, the wider the diameter of the secondary diffraction spot, the wider the width of the strip-shaped light blocking piece. In actual application, the width of the strip-shaped light blocking piece is generally set to be slightly wider than the diameter of the secondary diffraction spot. In order to make the strip-shaped light blocking piece completely block the plurality of periodically arranged secondary diffraction spots, the length of the strip-shaped light blocking piece is generally set to be not less than the diameter of the optical facet in the optical detection system, and the number of the strip-shaped light blocking pieces is related to the diameter of the optical facet and the width of each strip-shaped light blocking piece.

[0073] Specifically, in the actual application scenario, the strip-shaped light blocking piece can also be set as a strip-shaped light blocking stick, as long as it can block the secondary diffraction spot, and the specific shape of the light blocking piece in the strip-shaped light blocking piece is not limited here.

[0074] As an optional embodiment, the number N of the light blocking pieces can be calculated according to the following formula:

[0075] , wherein D is the diameter of the optical facet in the optical detection system, and d is the width of each light blocking piece.

[0076] The number N of the light blocking pieces can be calculated according to the formula, thereby improving the convenience and accuracy of obtaining the number N of the light blocking pieces.

[0077] Further, the material of the light blocking piece in the embodiment of the application can be plastic, wood or composite material, and the material of the light blocking piece is not limited here.

[0078] The filtering structure in the embodiment of the application includes a first filtering structure and a second filtering structure, wherein the first filtering structure is used to filter the primary diffraction signal of the periodically arranged structure unit in the to-be-detected object, and the second filtering structure is used to filter the secondary diffraction spot of the periodically arranged structure unit in the to-be-detected object, so that when the defects in the to-be-detected object are detected, the primary diffraction signal of the periodically arranged structure unit in the to-be-detected object can be filtered through the first filtering structure, and the secondary diffraction spot of the periodically arranged structure unit in the to-be-detected object can be filtered through the second filtering structure, thereby improving the accuracy of obtaining the defect signal in the to-be-detected object.

[0079] As an optional embodiment, the first filtering structure can also filter the scattering spot of the rough surface of the to-be-detected object. In an actual detection scene, the position of the rough surface in the to-be-detected object is different, and accordingly the size and position of the spot formed at the light plane are also uncertain. In order to filter out the spot formed at the light plane by the rough surface, the spatial orientation of the light blocking structure connecting any two ends of the closed filtering structure in the first filtering structure of the embodiment of the application is adapted to the position and shape of the scattering spot of the rough surface of the to-be-detected object. The light blocking structure adapted to the shape of the scattering spot of the rough surface of the to-be-detected object refers to that the shape of the light blocking structure is adapted to the shape of the scattering spot of the rough surface of the to-be-detected object. In an actual detection scene, the shape of the light blocking structure adapted to the shape of the scattering spot of the rough surface of the to-be-detected object can be arc-shaped, circular, polygonal or arc-shaped, and the shape of the light blocking structure adapted to the shape of the scattering spot of the rough surface of the to-be-detected object is not limited here.

[0080] As an optional embodiment, when the to-be-detected object is etched with a structure unit, according to the shape and position of most of the rough surface of the to-be-detected object, the light blocking structure adapted to the position and shape of the scattering spot of the rough surface of the to-be-detected object in the first filtering structure is specifically set as follows in the embodiment of the application:

[0081] The arc-shaped light blocking structure arranged at one end of the light blocking structure, the arc-shaped light blocking structure arranged at both ends of the light blocking structure, or the circular light blocking structure arranged at any position of the light blocking structure are shown in the corresponding schematic diagrams of FIGS. 3A, 3B and 3C for easy understanding.

[0082] Because the light-blocking structure in the first filter structure is arranged in an arc shape, a polygonal shape or a circular shape to adapt to the position and shape of the rough surface scattering light spot of the to-be-detected object, most of the rough surface scattering light spots of the to-be-detected object can be filtered out, thereby improving the universality of the first filter structure and the accuracy of filtering the rough surface scattering light spots of the to-be-detected object.

[0083] As an optional embodiment, because the position and shape of the rough surface in each type of to-be-detected object are uncertain, in order to realize filtering of the rough surface scattering light spots of different types of to-be-detected objects, the embodiment of the present application can further provide a plurality of first filter structures, and the first filter structures are arranged in the same plane, and the distance between the centers of two adjacent first filter structures is not less than the diameter of the optical detection surface in the optical detection system, so that the plurality of first filter structures can be driven by the driving mechanism, and when the to-be-detected object is switched, different first filter structures can be driven by the driving mechanism to be arranged in substantial overlap with the optical detection surface.

[0084] The shapes of the plurality of first filter structures can be determined according to the types of to-be-detected objects. When three or four types of to-be-detected objects are included, three or four first filter structures can be correspondingly provided, and the three or four first filter structures are arranged in the same plane and driven by the driving mechanism, so that when the first type of to-be-detected object is detected, the first first filter structure is used for filtering, and when the second type or the third type of to-be-detected object is detected, the second or the third first filter structure is used for filtering, thereby improving the convenience of switching the first filter structure in different detection scenarios.

[0085] It should be noted that the embodiment of the present application assumes that one type of to-be-detected object corresponds to one structure of the first filter structure, but in actual detection scenarios, one to-be-detected object can correspond to multiple first filter structures, or multiple to-be-detected objects can correspond to the same first filter structure. The types of to-be-detected objects when switching different first filter structures are not specifically limited.

[0086] As a specific embodiment of the driving mechanism, the embodiment of the present application can use a servo motor to drive a ball screw to push the first filter structure to slide along the guide rail, thereby switching different first filter structures when detecting different types of to-be-detected objects. For the convenience of understanding, FIG. 4 shows a schematic diagram of a servo motor 401, a ball screw 402, a guide rail 403 and a first filter structure 404.

[0087] Specifically, in the process of switching the first filter structure, in order to avoid mutual interference between two adjacent first filter structures, the distance between the centers of the two adjacent first filter structures is not less than the diameter of the light disc, so that the two first filter structures do not filter the light spots in the light disc at the same time, thereby realizing the accuracy of filtering the scattered light spots of the rough surface of the to-be-detected object by each first filter structure.

[0088] As an optional embodiment, in order to avoid the sharp edges of the first filter structure, thereby causing diffraction of the scattered light beam at the edges of the first filter structure, the inner circumferential wall of the enclosed filter structure, the edge of the light blocking structure and the edge of the light blocking piece in the first filter structure are set as a non-sharp edge structure, such as a sawtooth shape or a wave shape, and the form of the non-sharp edge structure is not limited here.

[0089] Because the edge of the first filter structure is set as a non-sharp edge structure, the diffraction phenomenon caused by the inner circumferential wall of the enclosed filter structure, the edge of the light blocking structure and the edge of the light blocking piece in the first filter structure is reduced, and the accuracy of obtaining the defect signal of the to-be-detected object is further improved.

[0090] Next, the second filter structure in the above embodiment will be described in detail:

[0091] As an optional embodiment, the plurality of light blocking pieces in the second filter structure are arranged in one plane or a plurality of planes, and the one plane or the plurality of planes are perpendicular to the propagation direction of the scattered light beam.

[0092] Specifically, when the plurality of light blocking pieces are arranged in the same plane, the distance between two adjacent light blocking pieces is fixed, and the plurality of light blocking pieces in the plane are driven by the same driving structure, so that the plurality of light blocking pieces arranged in the same plane are driven to substantially overlap the light disc by the same driving mechanism, and this driving mode of driving the plurality of light blocking pieces by the same driving mechanism enables the plurality of light blocking pieces to be driven to the position of the light disc by one driving, thereby improving the convenience of filtering by the first filter structure.

[0093] It should be noted that when the plurality of light blocking pieces are arranged in the same plane and driven by the same driving mechanism, the distance between two adjacent light blocking pieces is fixed in advance, and the distance between the two adjacent light blocking pieces depends on the distance between the periodically arranged structure units in the to-be-detected object, so that this way of arranging the plurality of light blocking pieces in the same plane and driving them by the same driving structure can only detect defects in a fixed type of to-be-detected object.

[0094] To solve the above problems, the embodiments of the present application can also be configured to drive each of the plurality of light blocking pieces by an independent driving mechanism. In this way, the distance between two adjacent light blocking pieces can be changed by the independent driving mechanism, so as to adapt to different types of objects to be detected, thereby improving the convenience of detecting different types of objects to be detected.

[0095] Specifically, when the plurality of light blocking pieces are arranged in different planes, in order to realize that the light blocking pieces in different planes can completely block the secondary diffraction spots generated by the periodically arranged structure units in the light facet, a driving mechanism can be arranged for each of the plurality of light blocking pieces in each plane, so that the driving mechanism drives the plurality of light blocking pieces in the plane to the position overlapping the light facet, so as to block the secondary diffraction spots at the corresponding position in the light facet.

[0096] For the convenience of understanding, the following examples are given:

[0097] Suppose that there are N*N (N is a positive integer greater than or equal to 2) secondary diffraction spots in the light facet as shown in FIG. 5, for the convenience of description, it is assumed that N=6, then 3 light blocking pieces can be arranged in the first plane, and another 3 light blocking pieces can be arranged in the second plane, and a first driving mechanism can be arranged for the 3 light blocking pieces in the first plane, and a second driving mechanism can be arranged for the 3 light blocking pieces in the second plane, so that the first driving mechanism drives the 3 light blocking pieces in the first plane to the first position 501 in FIG. 5, and the second driving mechanism drives the 3 light blocking pieces in the second plane to the second position 502 in FIG. 5, so that the plurality of light blocking pieces can cover the 6*6 diffraction spots in the main light facet.

[0098] It should be noted that in order to show the first position 501 and the second position 502, in FIG. 5, the 3 light blocking pieces are shown in the same plane, but in the actual application scenario, the first plane and the second plane are two different planes.

[0099] Further, when the plurality of light blocking pieces are arranged in different planes, the light blocking pieces in different planes can also be partially arranged in layers, which is equivalent to widening the width of the light blocking piece, thereby improving the accuracy of the light blocking piece blocking a plurality of secondary diffraction spots. For the convenience of understanding, FIG. 6 shows a schematic diagram of the light blocking piece arranged in layers.

[0100] Further, in order to realize the detection of a plurality of different types of objects to be detected, the embodiments of the present application can also be configured to arrange a corresponding driving mechanism for each light blocking piece in different planes, so that the distance between two adjacent light blocking pieces can be changed by the independent driving mechanism, so as to adapt to different types of objects to be detected, thereby improving the convenience of detecting different types of objects to be detected.

[0101] As a specific embodiment, as shown in FIG. 7, the embodiment of the present application can drive each light-blocking piece 703 in the second filtering structure to slide along the guide rail 704 by the servo motor 701 driving the ball screw 702, so as to drive each light-blocking piece 703 in the second filtering structure to a corresponding position in the light caustic surface to shield the diffracted light spot at the corresponding position in the light caustic surface.

[0102] As an optional embodiment, in order to avoid the sharp edges of the second filtering structure causing the diffraction of the scattered light beam at the edges of the second filtering structure, the embodiment of the present application can also set the edges of the light-blocking piece in the second filtering structure as a non-sharp edge structure, such as a sawtooth state or a wave shape, and the form of the non-sharp edge structure is not limited here.

[0103] Because the embodiment of the present application can set the edges of the second filtering structure as a non-sharp edge structure, the diffraction phenomenon caused by the edges of the light-blocking piece in the second filtering structure is reduced, and the accuracy of obtaining the defect signal in the object to be detected is further improved.

[0104] As an optional embodiment, when the filtering structure includes the first filtering structure and the second filtering structure, because the embodiment of the present application requires that the first filtering structure and the second filtering structure are both arranged to overlap the light caustic surface, and the diameter of the secondary diffracted light spot generated by the periodically arranged structure unit is small, in order to realize accurate filtering of the secondary diffracted light spot generated by the periodically arranged structure unit, the embodiment of the present application sets the second filtering structure at the light caustic surface, and sets the first filtering structure at a first position of 0.1mm to 2mm in front of or behind the light caustic surface (such as setting the first filtering structure at ±1mm from the light caustic surface), so that the first filtering structure is as close as possible to the position of the light caustic surface to realize accurate filtering of the scattered light spot formed by the rough surface of the object to be detected and the primary diffracted signal (i.e. the primary diffracted light spot) generated by the periodic structure unit.

[0105] Further, when the second filtering structure is arranged in multiple planes, one plane of the multiple planes can be arranged at the pupil surface, and the other planes can be arranged at a second position of 0.1mm to 2mm in front of or behind the light caustic surface, so that the other planes are also as close as possible to the position of the light caustic surface to realize accurate filtering of the secondary diffracted light spot of the periodic structure unit of the object to be detected.

[0106] As an optional embodiment, in order to reduce the reflectivity of the first filtering structure and / or the second filtering structure to light, the embodiment of the present application can also coat the surface of the first filtering structure and / or the second filtering structure with an anti-reflective film to reduce the reflectivity of the first filtering structure and / or the second filtering structure.

[0107] Specifically, the surface of the first filter structure and / or the second filter structure can be blackened to reduce the reflectivity of the first filter structure and / or the second filter structure.

[0108] Specifically, when the object to be detected is a wafer, in the image wafer defect detection scenario, there are mainly two types of optical noise. The first type is the diffraction of the wafer background pattern to the incident light, including the primary diffraction order and the high-order diffraction order. Since the background image of the wafer is regularly distributed, the diffraction light of the background image is discretely distributed in the spatial frequency domain, and the discrete distribution rule is determined by the background image. The primary diffraction order is distributed in the main plane, has high intensity, and has one-dimensional characteristics, but the primary diffraction order of different background images is different and is concentrated in the central strip. The second type of optical noise is the scattered light caused by the rough substrate of the wafer. Since the roughness of the substrate fluctuates randomly, the scattered light is continuously distributed in the frequency domain.

[0109] Based on the distribution characteristics of the two types of optical noise, the embodiment of the present application can adopt a two-stage filter structure. The first filter structure is used to filter the two or the latter of the scattered signal containing the rough surface of the object to be detected and the primary diffraction signal of the periodically arranged structure unit. The second filter structure is used to suppress the high-order diffraction of the first type of optical noise, so as to better suppress the noise, improve the signal-to-noise ratio, and improve the detection accuracy.

[0110] Further, the first filter structure and the second filter structure in the embodiment of the present application can realize two-stage filtering in the same pupil surface, which improves the filtering effect of optical noise. In order to efficiently filter out the optical noise for the dark field defect detection of the pattern wafer, the embodiment of the present application can realize the filtering of the two types of noise in the same pupil surface, so as to not introduce optical errors such as aberration compared with the scheme of adding a relay optical device in the optical detection system to realize two pupil surfaces in the prior art, thereby ensuring the detection accuracy.

[0111] Next, the optical detection system in the embodiment of the present application will be described. Please refer to FIG. 8:

[0112] The optical detection system in the embodiment of the present application includes a light source 801, an objective lens 802, a filter structure 803, a tube lens system 804, and a detector 805.

[0113] Specifically, the light source 801 is used to send a light beam of a preset wave band to the object to be detected 806 at a preset angle. Here, the light source 801 can be a red laser, a blue laser, or an LED light source, etc. The type of the light source 801 is not limited here.

[0114] The objective lens 802 is used to receive the scattered light beam of the object to be detected and focus the scattered light beam to the pupil surface.

[0115] The optical facet is a back focal facet of the objective 802.

[0116] The filter structure 803 is arranged substantially overlapping the optical facet, and is used for filtering two or both of the scattering signal of the rough surface of the object to be detected and the primary diffraction signal of the periodically arranged structure unit in the object to be detected, and filtering the secondary diffraction spot of the periodically arranged structure unit in the object to be detected.

[0117] It should be noted that the filter structure 803 is similar to the description in the above embodiments, and can be referred to each other, and will not be repeated here.

[0118] The tube lens system 804 is used for imaging the object to be detected to the detector 805.

[0119] It should be noted that the objective 802 and the tube lens system 804 are similar to the description in the prior art, and will not be repeated here.

[0120] The detector 805 is used for detecting the defects in the object to be detected according to the image of the object to be detected.

[0121] Specifically, the detector 805 can be a photodiode, a photodetector or an avalanche photodetector, and the type of the detector 805 is not limited here.

[0122] In the optical detection system in the embodiments of the present application, the filter structure 803 includes a first filter structure and a second filter structure, wherein the first filter structure is used for filtering two or both of the scattering signal of the rough surface of the object to be detected and the primary diffraction signal of the periodically arranged structure unit in the object to be detected, and the second filter structure is used for filtering the secondary diffraction spot of the periodically arranged structure unit in the object to be detected, so that when the defects in the object to be detected are detected, the primary diffraction signal of the periodically arranged structure unit in the object to be detected can be filtered through the first filter structure, and the secondary diffraction spot of the periodically arranged structure unit in the object to be detected can be filtered through the second filter structure, thereby improving the accuracy of obtaining the defect signal in the object to be detected.

[0123] As an optional embodiment, based on the embodiment described in FIG. 8, because the edges of the first filter structure and the second filter structure in the filter structure 803 are set as non-sharp edge structures, the diffraction phenomenon caused by the scattering light beams on the first filter structure and the second filter structure is avoided, thereby improving the Poisson scattering resolution of the optical detection system, so that even in the case that the resolution of the detector 805 is less than the Poisson scattering resolution of the optical detection system, the defects in the object to be detected can also be detected.

[0124] The Poisson scattering resolution of the optical detection system is also referred to as a PSF (Point Spread Function) resolution accuracy, and is used to evaluate the imaging quality of the optical detection system. Because the edge of the non-sharp structure of the first filter structure and / or the second filter structure can suppress the diffraction phenomenon caused by the scattered light beam, so that the light energy in the imaging of the object to be detected is mainly concentrated in the center, so that even in the case that the resolution of the detector 805 is less than the Poisson scattering resolution of the optical detection system, the defects in the object to be detected can be detected.

[0125] As an optional embodiment based on the embodiment described in FIG. 8, in order to improve the observation of the light caustic, the application embodiment can also be provided with the cut-in mirror 807, the pupil imaging tube mirror 808 and the pupil imaging detector 809, so that when the cut-in mirror 807 is cut in between the tube mirror system 804 and the detector 805, the scattered light beam is reflected to the pupil imaging tube mirror 808, wherein the pupil imaging tube mirror 808 is used to image the light caustic to the pupil imaging detector 809, and the pupil imaging detector 809 is used to observe the light caustic according to the image of the light caustic.

[0126] Optionally, the cut-in mirror 807 can also be cut in between the filter structure 803 and the tube mirror system 804, so as to reflect the scattered light beam to the pupil imaging tube mirror 808, wherein the pupil imaging tube mirror 808 is used to image the light caustic to the pupil imaging detector 809, and the pupil imaging detector 809 is used to observe the light caustic according to the image of the light caustic.

[0127] In the application embodiment, in order to realize the observation of the filtering condition in the light caustic, the application embodiment can also image the light caustic to the pupil imaging detector 809, so that the imaging condition of the light caustic can be observed through the pupil imaging detector 809, thereby improving the convenience of observing the light caustic.

[0128] As an optional embodiment, when the filtering structure 803 comprises the first filtering structure 8031 and the second filtering structure 8032, if the plurality of light blocking pieces in the second filtering structure 8032 are arranged on the same plane, the second filtering structure 8032 is arranged at the pupil plane, and the first filtering structure 8031 is arranged at a position 0.1 mm to 2 mm in front of the pupil plane or a position 0.1 mm to 2 mm behind the pupil plane along the propagation direction of the scattered light beam, so that the first filtering structure 8031 is as close to the pupil plane as possible, so as to filter the primary diffraction signal of the periodically arranged structure unit in the to-be-detected object and / or the scattered light spot of the rough surface of the to-be-detected object through the first filtering structure 8031, and filter the secondary diffraction light spot of the periodically arranged structure unit in the to-be-detected object through the second filtering structure 8032. For the convenience of understanding, FIG. 9 shows a schematic diagram of the positions of the first filtering structure 8031 and the second filtering structure 8032.

[0129] As another optional embodiment, when the filtering structure 803 comprises the first filtering structure 8031 and the second filtering structure 8032, if the plurality of light blocking pieces in the second filtering structure 8032 are arranged on a plurality of planes, one of the plurality of planes can be arranged to overlap with the pupil plane, and the other planes of the plurality of planes can be arranged at a position 0.1 mm to 2 mm in front of the pupil plane along the propagation direction of the scattered light beam, and the first filtering structure can be arranged at a position 0.1 mm to 2 mm behind the pupil plane along the propagation direction of the scattered light beam.

[0130] Or, the other planes of the plurality of planes can be arranged at a position 0.1 mm to 2 mm behind the pupil plane along the propagation direction of the scattered light beam, and the first filtering structure can be arranged at a position 0.1 mm to 2 mm in front of the pupil plane along the propagation direction of the scattered light beam. For the convenience of understanding, FIG. 10 shows a schematic diagram of the positions of the first filtering structure 8031 and the second filtering structure 8032.

[0131] Because the diameter of the diffraction light spot generated by the periodically arranged structure unit in the to-be-detected object is small in the application embodiment, in order to realize accurate filtering of the diffraction light spot generated by the periodically arranged structure unit, the second filtering structure 8032 is arranged at the pupil plane, and the first filtering structure 8031 is as close to the pupil plane as possible, so as to realize accurate filtering of the secondary diffraction light spot generated by the periodically arranged structure unit in the to-be-detected object.

[0132] As an optional embodiment, in order to control the spot size of the incident light beam irradiated to the surface of the object to be detected, the embodiment of the present application can further set a beam expanding and shaping module 810 between the light source 801 and the object to be detected 806, wherein the beam expanding and shaping module 810 comprises a beam expander and a shaping element, wherein the beam expander is used to expand the light source to obtain a light spot of a preset size, and the shaping element is a phase element with a two-dimensional structure to achieve the shaping of the expanded light beam to control the numerical aperture NA of the incident light. For the convenience of understanding, FIG. 11 shows a schematic diagram of an optical detection system comprising the switchable mirror 807, the pupil imaging tube mirror 808, the pupil imaging detector 809 and the beam expanding and shaping module 810.

[0133] Next, based on the optical detection system in FIG. 11, the optical detection method of the optical detection system is described, please refer to FIG. 12:

[0134] 1201, observing the image of the pupil surface by the pupil imaging detector to obtain the distribution state of the scattering signal in the pupil surface;

[0135] The switchable mirror 807, the pupil imaging tube mirror 808 and the pupil imaging detector 809 in the embodiment of the present application are used to cooperate with each other to image the pupil surface to the pupil imaging detector 809, so that the image of the pupil surface can be observed by the pupil imaging detector 809.

[0136] In this way, the image of the pupil surface can be observed by the pupil imaging detector to obtain the distribution state of the scattering signal in the pupil surface, so the first filter structure suitable for the position and shape of the scattering signal of the rough surface of the object to be detected is selected, that is, the first filter structure suitable for the position and shape of the scattering signal of the rough surface of the object to be detected is selected from the first filter structures in FIG. 3.

[0137] 1202, driving the first filter structure to filter the scattering signal of the rough surface of the object to be detected and the main diffraction signal of the periodically arranged structure unit in the object to be detected in the scattering signal;

[0138] When the first filter structure suitable for the position and shape of the scattering signal of the rough surface of the object to be detected is determined, the first filter structure suitable for the position and shape of the scattering signal of the rough surface of the object to be detected can be driven to filter the scattering signal of the rough surface of the object to be detected and the main diffraction signal of the periodically arranged structure unit in the object to be detected. Specifically, when the first filter structure and the second filter structure exist at the same time, the first filter structure is arranged at a position 0.1mm to 2mm in front of or behind the pupil surface along the propagation direction of the scattering light beam, so as to filter the scattering signal of the rough surface of the object to be detected and the main diffraction signal of the periodically arranged structure unit in the object to be detected.

[0139] 1203、drive the second filter structure to filter the secondary diffraction signal of the structural unit in the object to be detected in the scattering signal.

[0140] When the secondary diffraction signal (secondary diffraction spot) generated by the structural unit in the object to be detected still exists in the light surface, the second filter structure is driven to filter the secondary diffraction signal of the structural unit in the object to be detected in the scattering signal, so as to improve the accuracy of filtering the scattering signal in the light surface.

[0141] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A filter structure, characterized by, The application relates to a filter structure for optical detection system. The filter structure comprises: a first filter structure for filtering the primary diffraction signal of the periodically arranged structure unit in the object to be detected; and a second filter structure for filtering the secondary diffraction spot of the periodically arranged structure unit in the object to be detected; wherein: the first filter structure comprises at least one closed filter structure, and when the object to be detected is provided with the structure unit, the closed filter structure is further provided with a light-blocking structure connecting any two ends of the filter structure; 2. The filter structure of claim 1, wherein, the second filter structure comprises a plurality of light-blocking pieces arranged in parallel, wherein the projection of the light-blocking piece on the plane of the secondary diffraction spot is not less than the diameter of the secondary diffraction spot.

3. The filter structure of claim 2, wherein, The spatial orientation of the light-blocking structure connecting any two ends of the filter structure is adapted to the position and shape of the rough surface scattering spot of the object to be detected.

4. The filter structure of claim 1, wherein, The light-blocking structure provided in the closed filter structure and adapted to the position and shape of the rough surface scattering spot of the object to be detected comprises an arc-shaped light-blocking structure provided at one end of the light-blocking structure, arc-shaped light-blocking structures provided at both ends of the light-blocking structure, a polygonal light-blocking structure provided at any position of the light-blocking structure or a circular light-blocking structure provided at any position of the light-blocking structure.

5. The filter structure of claim 4, wherein, The filter structure is arranged in an optical detection system, the first filter structure is multiple, the multiple first filter structures are arranged on the same plane, and the distance between the centers of two adjacent first filter structures is not less than the diameter of the optical detection system.

6. The filtering structure of claim 1, wherein, The multiple first filter structures are driven by a driving mechanism, and when the object to be detected is switched, different first filter structures are driven by the driving mechanism and arranged in substantial overlap with the optical detection system.

7. The filtering structure of claim 1, wherein, The inner wall of the closed filter structure, the edge of the light-blocking structure and the edge of the light-blocking piece are arranged as non-sharp edge structures. 。 8. The filtering structure of claim 1, wherein, The filter structure is arranged in an optical detection system, if the diameter of the pupil surface in the optical detection system is D and the width of the light-blocking piece is d, the number N of the light-blocking pieces is calculated according to the following formula:

9. The filter structure of claim 8, wherein, The multiple light-blocking pieces are arranged in at least one plane, and each plane in the at least one plane is perpendicular to the propagation direction of the scattering beam.

10. The filter structure of claim 8, wherein, The multiple light-blocking pieces are arranged in multiple planes, and the light-blocking pieces in different planes are partially arranged in layers.

11. The filtering structure of claim 1, wherein, The filter structure is arranged in an optical detection system, the interval between two adjacent light-blocking pieces in each plane is fixedly arranged, and the multiple light-blocking pieces in each plane are driven by the same driving mechanism, so that the multiple light-blocking pieces in each plane are arranged in substantial overlap with the optical detection system, thereby shielding the diffraction spot at the corresponding position of the optical detection system.

12. The filtering structure of claim 1, wherein, The filter structure is arranged in an optical detection system, each light-blocking piece is driven by an independent driving mechanism, so that the corresponding light-blocking pieces are driven by multiple independent driving mechanisms and arranged in substantial overlap with the optical detection system. The edge of the light-blocking piece is arranged as a non-sharp edge structure.

13. The filtering structure of claim 1, wherein, A surface of the first filter structure and / or the second filter structure is coated with an anti-reflective film to reduce a reflectivity of the first filter structure and / or the second filter structure.

14. The filtering structure of claim 1, wherein, The light-blocking member includes a strip-shaped light-blocking member, a cylindrical light-blocking member, a sawtooth-shaped light-blocking member, or a wave-shaped light-blocking member.

15. An optical detection system, characterized in that The method comprises: a light source configured to emit a coherent light beam of a preset waveband at a preset angle towards a to-be-detected object; an objective lens configured to receive a scattered light beam of the to-be-detected object and focus parallel light beams or near-parallel light beams in the scattered light beam to a pupil plane; a filter structure as claimed in any one of claims 1 to 14, which is arranged substantially overlapping the pupil plane; a tube lens system configured to image the to-be-detected object to a detector; the detector configured to detect defects in the to-be-detected object according to an image of the to-be-detected object.

16. The system of claim 15, wherein, The optical detection system further comprises a switchable mirror, a pupil imaging tube lens, and a pupil imaging detector; The switchable mirror is configured to be switched in between the tube lens system and the detector to change a propagation direction of the scattered light beam so that the scattered light beam is incident on the pupil imaging tube lens, or the switchable mirror is configured to be switched in between the filter structure and the tube lens system to change the propagation direction of the scattered light beam so that the scattered light beam is incident on the pupil imaging tube lens. The pupil imaging tube lens is configured to image the pupil plane to the pupil imaging detector. The pupil imaging detector is configured to observe the pupil plane according to an image of the pupil plane.

17. The system of claim 15, wherein, The filter structure comprises a first filter structure and a second filter structure, wherein the second filter structure comprises a plurality of light-blocking members arranged on a plurality of planes, one of the plurality of planes is arranged overlapping the pupil plane, and the other planes are arranged at a distance of 0.1 mm to 2 mm in front of the pupil plane along a propagation direction of the scattered light beam, and the first filter structure is arranged at a distance of 0.1 mm to 2 mm behind the pupil plane along the propagation direction of the scattered light beam. Alternatively, the other planes are arranged at a distance of 0.1 mm to 2 mm behind the pupil plane along the propagation direction of the scattered light beam, and the first filter structure is arranged at a distance of 0.1 mm to 2 mm in front of the pupil plane along the propagation direction of the scattered light beam.

18. The system of claim 15, wherein, The filter structure comprises a first filter structure and a second filter structure, wherein the second filter structure comprises a plurality of strip-shaped light-blocking members arranged in parallel, a width of the strip-shaped light-blocking member is associated with a diameter of a secondary diffraction spot of a periodically arranged structure unit, a length of the strip-shaped light-blocking member is not less than a diameter of the pupil plane, and a number of the strip-shaped light-blocking members is associated with the diameter of the pupil plane and the width of each strip-shaped light-blocking member.

19. The system of claim 15, wherein, The optical detection system further comprises an expansion and shaping module arranged between the light source and the to-be-detected object, wherein the expansion and shaping module comprises an expansion mirror and a shaping element, and the shaping element comprises a phase element with a two-dimensional structure.

20. An optical detection method, characterized by, The method is applied to the optical detection system as claimed in any one of claims 15 to 19, and the method comprises: The distribution state of the scattering signal in the pupil surface is obtained by observing the image of the pupil surface by using a pupil imaging detector; The first filter structure is driven to filter the scattering signal of the rough surface of the object to be detected and the primary diffraction signal of the periodically arranged structure unit in the object to be detected in the scattering signal. The second filter structure is driven to filter the secondary diffraction signal of the periodically arranged structure unit in the object to be detected in the scattering signal.

Images