A filtering structure, an optical detection system and an optical detection method

Abstract

Embodiments of the present invention provide a filtering structure, an optical detection system, and an optical detection method for improving the accuracy of obtaining defect signals in an object to be detected. The filtering structure in the embodiments of the present invention includes: a first filtering structure for filtering the main diffraction signal of the periodically arranged structural units in the object to be detected; and a second filtering structure for filtering the secondary diffraction spots of the periodically arranged structural units in the object to be detected; the first filtering structure includes at least one filtering structure with a closed outer periphery, and when there are structural units in the object to be detected, a light-blocking structure connecting any two ends of the filtering structure is further arranged inside the closed filtering structure; the second filtering structure includes a plurality of light-blocking members arranged in parallel, wherein the projection of the light-blocking member on the plane where the secondary diffraction spot is located is not less than the diameter of the secondary diffraction spot.

Description

Technical Field

[0001] The present invention 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 Art

[0002] Optical imaging detection is the main technology relied on for process defect detection in the semiconductor industry. With the continuous development of the process, the semiconductor industry process has shrunk from the micron level to the nanometer scale, and more complex patterns require more refined defect detection technologies.

[0003] In an imaging detection system, a laser beam is irradiated on a characteristic region of an object to be detected and / or a rough surface of the object to be detected at a certain angle. The scattered light of the frequency domain information of the characteristic region and / or the scattered light on the rough surface of the object to be detected is collected by an objective lens system. Parallel coherent light with the same incident angle forms a light spot on the pupil plane, and then passes through a tube lens system to be re-imaged on the sensing surface of a detector.

[0004] However, with the reduction of the periodic structural units in the object to be detected, the defect signals in the object to be detected will be buried in the scattered light signals of the periodic structural units and / or the rough surface of the object to be detected, resulting in a low accuracy of extracting the defect signals in the object to be detected. Summary of the Invention

[0005] Embodiments of the present invention provide a filtering structure, an optical detection system, and an optical detection method for filtering out the main diffraction signal and secondary diffraction spots of the periodic structure in the object to be detected on the pupil plane, so as to improve the accuracy of obtaining the defect signals in the object to be detected.

[0006] A first aspect of an embodiment of the present application provides a filtering structure, including:

[0007] A first filtering structure for filtering the main diffraction signal of the periodically arranged structural units in the object to be detected;

[0008] And a second filtering structure for filtering the secondary diffraction spots of the periodically arranged structural units in the object to be detected; wherein:

[0009] The first filtering structure includes at least one filtering structure with a closed outer periphery. When there are structural units in the object to be detected, a light-blocking structure connecting any two ends of the filtering structure is further arranged inside the closed filtering structure;

[0010] The second filtering structure includes a plurality of light-blocking members arranged in parallel, wherein the projection of the light-blocking member on the plane where the secondary diffraction spot is located is not less than the diameter of the secondary diffraction spot.

[0011] Optionally, the spatial orientation of the light-blocking structure connecting any two ends of the filtering structure is adapted to the position and shape of the scattered light spot on the rough surface of the object to be detected.

[0012] Optionally, the light-blocking structure disposed in the closed filtering structure and adapted to the position and shape of the scattered light spot on the rough surface of the object to be detected includes: an arcuate light-blocking structure disposed at one end of the light-blocking structure, arcuate light-blocking structures disposed at both ends of the light-blocking structure, a polygonal light-blocking structure disposed at any position in the light-blocking structure, or a circular light-blocking structure disposed at any position in the light-blocking structure.

[0013] Optionally, the filtering structure is disposed in an optical detection system. There are multiple first filtering structures, and the multiple first filtering structures are disposed on the same plane, and the distance between the centers of adjacent two first filtering structures is not less than the diameter of the pupil plane of the optical detection system.

[0014] Optionally, the multiple first filtering structures are driven by a driving mechanism. When switching the object to be detected, different first filtering structures are driven by the driving mechanism to be substantially overlapped with the pupil plane.

[0015] Optionally, the inner peripheral wall of the closed filtering structure, the edge of the light-blocking structure, and the edge of the light-blocking structure are set as non-sharp edge structures.

[0016] Optionally, the filtering structure is disposed in an optical detection system. If the diameter of the pupil plane in the optical detection system is D and the width of the light-blocking member is d, then the number N of the light-blocking members is calculated according to the following formula: 。

[0017] Optionally, the multiple light-blocking members are disposed in at least one plane, and each plane in the at least one plane is perpendicular to the propagation direction of the scattered light beam.

[0018] Optionally, the multiple light-blocking members are disposed in multiple planes, and the light-blocking members in different planes are partially stacked.

[0019] Optionally, the filtering structure is disposed in an optical detection system. The interval between adjacent two light-blocking members in each plane is fixedly set, and the multiple light-blocking members in each plane are driven by the same driving mechanism so that the multiple light-blocking members in each plane are substantially overlapped with the pupil plane of the optical detection system to block the diffraction spots at the corresponding positions in the pupil plane.

[0020] Optionally, each light-blocking member is driven by an independent driving mechanism so that the corresponding light-blocking member is driven by multiple independent driving mechanisms to be substantially overlapped with the pupil plane of the optical detection system.

[0021] Optionally, the edge of the light-blocking member is configured as a non-sharp edge structure.

[0022] Optionally, an anti-reflection film is coated on the surface of the first filtering structure and / or the second filtering structure to reduce the reflectance of the first filtering structure and / or the second filtering structure.

[0023] Optionally, the light-blocking member includes a strip-shaped light-blocking member, a cylindrical light-blocking member, a serrated light-blocking member, or a wavy light-blocking member.

[0024] A second aspect of the embodiments of the present application provides an optical detection system, including:

[0025] A light source for emitting a coherent beam of a preset wavelength band to a to-be-detected object at a preset angle;

[0026] An objective lens for receiving the scattered beam of the to-be-detected object and focusing the parallel beam or near-parallel beam in the scattered beam onto the pupil plane;

[0027] A filtering structure as provided in the first aspect of the embodiments of the present application, which is disposed substantially overlapping with the pupil plane;

[0028] A tube lens system for imaging the to-be-detected object onto a detector;

[0029] The detector for detecting defects in the to-be-detected object according to the image of the to-be-detected object.

[0030] Optionally, the optical detection system further includes: a switchable mirror, a pupil imaging tube lens, and a pupil imaging detector;

[0031] Wherein, the switchable mirror is configured to cut into between the tube lens system and the detector to change the propagation direction of the scattered beam so that the scattered beam is incident on the pupil imaging tube lens; or, the switchable mirror is configured to cut into between the filtering structure and the tube lens system to change the propagation direction of the scattered beam so that the scattered beam is incident on the pupil imaging tube lens;

[0032] The pupil imaging tube lens is configured to image the pupil plane onto the pupil imaging detector;

[0033] The pupil imaging detector for observing the pupil plane according to the image of the pupil plane.

[0034] Optionally, the filtering structure includes a first filtering structure and a second filtering structure. Among them, the second filtering structure includes a plurality of light blocking members disposed on a plurality of planes. One of the plurality of planes overlaps with the pupil plane, and the other planes among the plurality of planes are disposed 0.1 mm to 2 mm in front of the pupil plane along the propagation direction of the scattered light beam. The first filtering structure is disposed 0.1 mm to 2 mm behind the pupil plane along the propagation direction of the scattered light beam;

[0035] Alternatively, the other planes among the plurality of planes are disposed 0.1 mm to 2 mm behind the pupil plane along the propagation direction of the scattered light beam, and the first filtering structure is disposed 0.1 mm to 2 mm in front of the pupil plane along the propagation direction of the scattered light beam.

[0036] Optionally, the filtering structure includes a first filtering structure and a second filtering structure. Among them, the second filtering structure includes a plurality of strip-shaped light blocking members arranged in parallel. The width of the strip-shaped light blocking member is related to the diameter of the secondary diffraction spot of the periodically arranged structural unit, the length of the strip-shaped light blocking member is not less than the diameter of the pupil plane, and the number of the strip-shaped light blocking members is related to the diameter of the pupil plane and the width of each strip-shaped light blocking member.

[0037] Optionally, the optical detection system further includes an expanding and shaping module disposed between the light source and the object to be detected. Among them, the expanding and shaping module includes an expander and a shaping element, and the shaping element includes a phase element having a two-dimensional structure.

[0038] A third aspect of the embodiments of the present application provides an optical detection method, which is applied to the optical detection system provided in the second aspect of the embodiments of the present application. The method includes:

[0039] Observing the image of the pupil plane by using a pupil imaging detector to obtain the distribution state of the scattered signal in the pupil plane;

[0040] Driving an adapted first filtering structure to filter both or the latter of the scattered signal of the rough surface of the object to be detected and the main diffraction signal of the periodically arranged structural unit in the object to be detected in the scattered signal;

[0041] Driving a second filtering structure to filter the secondary diffraction signal of the periodically arranged structural unit in the object to be detected in the scattered signal.

[0042] It can be seen from the above technical solutions that the embodiments of the present invention have the following advantages:

[0043] The filtering structure in the embodiments of the present application includes a first filtering structure and a second filtering structure. Among them, the first filtering structure is used to filter the main diffraction signal of the periodically arranged structural units in the object to be detected, and the second filtering structure is used to filter the secondary diffraction spots of the periodically arranged structural units in the object to be detected. Thus, when detecting the defects in the object to be detected, the main diffraction signal of the periodically arranged structural units in the object to be detected can be filtered by the first filtering structure, and the secondary diffraction spots of the periodically arranged structural units in the object to be detected can be filtered by the second filtering structure, thereby improving the accuracy of obtaining the defect signals in the object to be detected. Description of the Drawings

[0044] Figure 1 Schematic diagram of the first filtering structure in the embodiments of the present application;

[0045] Figure 2 Schematic diagram of the first filtering structure with different light-blocking structures in the embodiments of the present application;

[0046] Figure 3 Schematic diagram of the second filtering structure in the embodiments of the present application;

[0047] Figure 4 Schematic diagram of the servo motor, ball screw, guide rail and the first filtering structure in the embodiments of the present application;

[0048] Figure 5 Schematic diagram of the first position and the second position in the pupil plane in the embodiments of the present application;

[0049] Figure 6 Schematic diagram of the partially stacked strip-shaped light-blocking members in the embodiments of the present application;

[0050] Figure 7 Schematic diagram of the servo motor, ball screw, guide rail and the second filtering structure in the embodiments of the present application;

[0051] Figure 8 Schematic diagram of an embodiment of the optical detection system in the embodiments of the present application;

[0052] Figure 9 Schematic diagram of a position of the first filtering structure and the second filtering structure in the embodiments of the present application;

[0053] Figure 10 Schematic diagram of another positional relationship between the first filtering structure and the second filtering structure in the embodiments of the present application;

[0054] Figure 11 Schematic diagram of another embodiment of the optical detection system in the embodiments of the present application;

[0055] Figure 12This is a schematic diagram of an embodiment of the optical detection method in the embodiments of the present application. Detailed implementation manners

[0056] Embodiments of the present invention provide a filtering structure, an optical detection system, and an optical detection method for filtering the main diffraction signal and secondary diffraction spots of a periodic structure on the pupil plane of an object to be detected, so as to improve the accuracy of obtaining defect signals in the object to be detected.

[0057] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0058] The terms "first", "second", "third", "fourth", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments described here can be implemented in an order different from that shown or described here. In addition, the terms "comprising" and "having" 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 may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0059] In an actual semiconductor detection scenario, if the surface of the object to be detected is etched with periodically arranged structural units, or the object to be detected has a rough surface, when detecting the object to be detected, an incident light beam is irradiated on the surface of the object to be detected, and a scattered light beam will be formed on the surface of the object to be detected. Among them, the scattered light beam of the periodically arranged structural units will form a spot at the pupil plane of the objective lens system (i.e., the rear focal plane of the objective lens), and the scattered 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 object to be detected is submerged in the above-mentioned scattered spot signals.

[0060] Specifically, the rough surface of the object to be detected may be the rough surface of the unetched part of the object to be detected, or the rough surface of the periodic structural units at the etched part of the object to be detected. There is no limitation on the specific position of the rough surface in the object to be detected here. The object to be detected in the embodiments of the present application may be a wafer, a mask, glass, etc., and there is no specific limitation on the type of the object to be detected here.

[0061] For the convenience of understanding, the filtering structure in the embodiments of the present application will be described below:

[0062] Specifically, the filtering structure in the embodiments of the present application is used to filter the pupil plane in an optical detection system. The filtering structure in the present application includes a first filtering structure and / or a second filtering structure. Among them, the first filtering structure is used to filter the main diffraction signal of the periodically arranged structural units in the object to be detected, and the second filtering structure is used to filter the secondary diffraction spots of the periodically arranged structural units in the object to be detected.

[0063] As an optional embodiment, the periodically arranged structural units may be structural units periodically arranged in the vertical and horizontal directions. The structural units may be structures such as grooves and protrusions. The specific form of the structural units is not specifically limited herein.

[0064] The first filtering structure and the second filtering structure will be described separately below:

[0065] Specifically, the first filtering structure in the embodiments of the present application includes at least one filtering structure with a closed outer periphery. When a structural unit is provided in the object to be detected, a light-blocking structure connecting any two ends of the filtering structure is further provided inside the closed filtering structure. Among them, the width of the light-blocking structure is related to the numerical aperture NA of the illumination light source. When the numerical aperture NA of the illumination light source is larger, the width of the light-blocking structure is wider; conversely, the width of the light-blocking structure is narrower. For the convenience of understanding, Figure 1 a schematic diagram of the first filtering structure is given.

[0066] In an actual detection scenario, as long as a structural unit is provided on the surface of the object to be detected, a bright light will be generated at the center of the pupil plane, that is, the main diffraction signal generated by the structural unit. In order to filter the main diffraction signal, in the embodiments of the present application, a light-blocking structure connecting any two ends of the filtering structure is further provided inside the closed filtering structure of the first filtering structure to filter the light generated at the center of the pupil plane by the structural unit on the surface of the object to be detected, and the width of the light is directly related to the numerical aperture NA of the illumination light source.

[0067] Optionally, the closed filtering structure in the embodiments of the present application may be an annular filtering structure, or a filtering structure with a square, rectangular, or polygonal outer periphery. The outer shape of the filtering structure is not specifically limited herein.

[0068] Further, the second filtering structure in the embodiments of the present application includes a plurality of light blocking members arranged in parallel. Among them, the projection of the light blocking member on the plane where the secondary diffraction spot is located is not less than the diameter of the secondary diffraction spot. The plurality of light blocking members are used to filter the secondary diffraction spots formed by the incident light beam at the pupil plane of the structure units arranged in multiple periods in the optical detection system. It is easy to understand that the structure units arranged in periods in the object to be detected generally form a plurality of diffraction spots arranged in periods at the pupil plane. As long as the plurality of light blocking members can block the plurality of diffraction spots arranged in periods. In the actual detection scenario, if the structure units arranged in periods in the object to be detected are the structure units arranged in periods along the vertical direction and the horizontal direction, then the plurality of light blocking members can be strip-shaped light blocking members arranged in parallel along the horizontal direction or the vertical direction at the pupil plane. If the structure units arranged in periods in the object to be detected are the structure units arranged in periods along the first direction, then the plurality of light blocking members correspondingly are the light blocking members arranged in parallel along the first direction, where the first direction is a direction at an arbitrary angle to the horizontal direction. For the convenience of understanding, Figure 2 FIG. shows a schematic diagram of the second filtering structure composed of a plurality of light blocking members.

[0069] Specifically, the light blocking member in the embodiments of the present application can be a strip-shaped light blocking member, a cylindrical light blocking member, a serrated light blocking member or a wavy light blocking member. As long as the projection of the light blocking member on the plane where the diffraction spot is located can block the secondary diffraction spot, the shape of the light blocking member is not specifically limited here.

[0070] Further, if the light blocking member is a strip-shaped light blocking member, the width of the strip-shaped light blocking member is related to the diameter of the secondary diffraction spot of the structure unit arranged in periods. For example, the wider the diameter of the secondary diffraction spot, the wider the width of the strip-shaped light blocking member. In actual application, generally, the width of the strip-shaped light blocking member is set slightly wider than the diameter of the secondary diffraction spot. In order to enable the strip-shaped light blocking member to completely block the plurality of secondary diffraction spots arranged in periods, generally, the length of the strip-shaped light blocking member is not less than the diameter of the pupil plane in the optical detection system, and the number of the strip-shaped light blocking members is related to the diameter of the pupil plane and the width of each strip-shaped light blocking member.

[0071] Specifically, in the actual application scenario, the strip-shaped light blocking member can also be set as a strip-shaped light blocking stick, as long as it can block the secondary diffraction spot. The specific form of the light blocking member in the strip-shaped light blocking member is not specifically limited here.

[0072] As an optional embodiment, the number N of the light blocking members can be calculated according to the following formula: , where D is the diameter of the pupil plane in the optical detection system, and d is the width of each light blocking member.

[0073] In the embodiments of the present application, the number N of the light blocking members can be calculated according to the above formula, thereby improving the convenience and accuracy of obtaining the number N of the light blocking members.

[0074] Further, the material of the light shielding member in the embodiments of the present application may be plastic, wood, composite material, etc., and no specific limitation is imposed on the material of the light shielding member herein.

[0075] The filtering structure in the embodiments of the present application includes a first filtering structure and a second filtering structure. Among them, the first filtering structure is used to filter the main diffraction signal of the periodically arranged structural units in the object to be detected, and the second filtering structure is used to filter the secondary diffraction spots of the periodically arranged structural units in the object to be detected. Thus, when detecting the defects in the object to be detected, the main diffraction signal of the periodically arranged structural units in the object to be detected can be filtered by the first filtering structure, and the secondary diffraction spots of the periodically arranged structural units in the object to be detected can be filtered by the second filtering structure, thereby improving the accuracy of obtaining the defect signal in the object to be detected.

[0076] As an optional embodiment, the first filtering structure can also filter the scattered light spots on the rough surface of the object to be detected. In an actual detection scenario, if the position of the rough surface in the object to be detected is different, the size and position of the light spots formed on the pupil plane are also uncertain. In order to filter the light spots formed on the pupil plane by the rough surface, the spatial orientation of the light shielding structure connecting any two ends of the closed filtering structure in the first filtering structure of the embodiments of the present application adapts to the position and shape of the scattered light spots of the rough surface of the object to be detected. Among them, the light shielding structure adapted to the shape of the scattered light spots of the rough surface of the object to be detected refers to that the shape of the light shielding structure adapts to the form of the scattered light spots of the rough surface of the object to be detected. In an actual detection scenario, the shape of the light shielding structure adapted to the shape of the scattered light spots of the rough surface of the object to be detected may be bow-shaped, circular, polygonal, circular arc-shaped, etc., and no specific limitation is imposed on the shape of the light shielding structure adapted to the shape of the scattered light spots of the rough surface of the object to be detected herein.

[0077] As an optional embodiment, when the structural units are etched in the object to be detected, according to the shape and position of most of the rough surfaces in the object to be detected, the light shielding structure in the first filtering structure of the embodiments of the present application that adapts to the position and shape of the scattered light spots of the rough surface of the object to be detected is specifically set as:

[0078] A bow-shaped light shielding structure provided at one end of the light shielding structure, bow-shaped light shielding structures provided at both ends of the light shielding structure, or a circular light shielding structure provided at any position of the light shielding structure. For ease of understanding, Figure 3 Figures A, B, and C therein respectively give corresponding schematic diagrams.

[0079] Since the light-blocking structure adapted to the position and shape of the scattered light spots on the rough surface of the object to be detected in the first filter structure is set to be bow-shaped, polygonal, and circular, most of the scattered light spots on the rough surface of the object to be detected can be filtered out, thereby improving the versatility of the first filter structure and the accuracy of filtering the scattered light spots on the rough surface of the object to be detected.

[0080] As an optional embodiment, since the positions and shapes of the rough surfaces in each type of object to be detected are uncertain, and in order to filter the scattered light spots on the rough surfaces of different types of objects to be detected, the embodiments of the present application can also set multiple first filter structures, and arrange the first filter structures in the same plane, and set the distance between the centers of two adjacent first filter structures to be not less than the diameter of the pupil plane in the optical detection system, so that multiple first filter structures can be driven by a driving mechanism, and when switching the detection object, different first filter structures can be driven by the driving mechanism to be substantially overlapped with the pupil plane.

[0081] Among them, the forms of the multiple first filter structures can be determined according to the types of the objects to be detected. When there are three or four types of objects to be detected, three or four first filter structures can be correspondingly set, and the three or four filter structures are arranged in the same plane and driven by a driving mechanism. Thus, when detecting the first type of object to be detected, the first first filter structure is used for filtering, and when detecting the second type or the third type of object to be 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.

[0082] It should be noted here that the embodiments of the present application assume that one type of object to be detected corresponds to one structure of the first filter structure. However, in actual detection scenarios, it may also be that one object to be detected corresponds to multiple first filter structures, or multiple objects to be detected correspond to the same first filter structure. Here, no specific restrictions are imposed on the types of the objects to be detected when switching different first filter structures.

[0083] As a specific embodiment of the driving mechanism, the embodiments 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, so as to switch different first filter structures when detecting different types of objects to be detected. For the convenience of understanding, Figure 4 a schematic diagram of the servo motor 401, the ball screw 402, the guide rail 403, and the first filter structure 404 is given.

[0084] Specifically, during the process of switching the first filtering structure, in order to avoid mutual interference between two adjacent first filtering structures, embodiments of the present application can also set the distance between the centers of two adjacent first filtering structures to be not less than the diameter of the pupil plane, so that two first filtering structures do not simultaneously filter the light spot in the pupil plane, thereby realizing the accuracy of each first filtering structure in filtering the scattered light spot of the rough surface in the object to be detected.

[0085] As an alternative embodiment, in order to avoid the sharp edges of the first filtering structure, which may cause diffraction of the scattered light beam at the edges of the first filtering structure, embodiments of the present application can also set the inner peripheral wall of the closed filtering structure in the first filtering structure, the edges of the light blocking structure, and the edges of the light blocking member to non-sharp edge structures, such as being set in a serrated state or a wavy shape, etc. The specific form of the non-sharp edge structure is not specifically limited here.

[0086] Since embodiments of the present application can set the edges of the first filtering structure to non-sharp edge structures, the diffraction phenomenon caused by the scattered light beam at the inner peripheral wall of the closed filtering structure in the first filtering structure, the edges of the light blocking structure, and the edges of the light blocking member is reduced, and the accuracy of obtaining the defect signal in the object to be detected is further improved.

[0087] Next, the second filtering structure in the above embodiments will be described in detail:

[0088] As an alternative embodiment, multiple light blocking members in the second filtering structure are arranged in one plane or multiple planes, and the above one plane or multiple planes are perpendicular to the propagation direction of the scattered light beam.

[0089] Specifically, when multiple light blocking members are arranged in the same plane, the interval between two adjacent light blocking members can be set to be fixed, and multiple light blocking members in this plane are driven by the same driving structure, so that multiple light blocking members arranged in the same plane can be driven to be substantially overlapped with the pupil plane through the same driving mechanism. Moreover, this driving method of driving multiple light blocking members through the same driving mechanism enables multiple light blocking members to be driven to the position of the pupil plane through one driving, thereby improving the convenience of filtering using the first filtering structure.

[0090] It should be noted that when multiple light blocking members are arranged in the same plane and driven by the same driving mechanism, since the distance between two adjacent light blocking members needs to be fixed in advance, and the interval distance between two adjacent light blocking members depends on the distance between the periodically arranged structural units in the object to be detected, this method of arranging multiple light blocking members in the same plane and driving them by the same driving structure can only detect defects in fixed types of objects to be detected.

[0091] In view of the above problems, in the embodiments of the present application, each of the multiple light-shielding members can also be driven by an independent driving mechanism. In this way, through the respective independent driving structures, the distance between two adjacent light-shielding members can be changed, 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.

[0092] Specifically, when multiple light-shielding members are arranged in different planes, in order to ensure that the light-shielding members in different planes can completely block the secondary diffraction spots generated by the periodically arranged structural units in the pupil plane, a driving mechanism can be set for the multiple light-shielding members in each plane, so that the driving mechanism drives the multiple light-shielding members in that plane to a position overlapping with the pupil plane to block the secondary diffraction spots at the corresponding positions in the pupil plane.

[0093] For ease of understanding, the following is an example:

[0094] Suppose, as Figure 5 shown, there are (N is a positive integer greater than or equal to 2) secondary diffraction spots in the pupil plane. For ease of explanation, assume N = 6. Then, 3 light-shielding members can be arranged in the first plane, and the other 3 light-shielding members can be arranged in the second plane. A first driving mechanism is set for the 3 light-shielding members in the first plane, and a second driving mechanism is set for the 3 light-shielding members in the second plane, so that the first driving mechanism drives the 3 light-shielding members in the first plane to Figure 5 the first position 501 of Figure 5 , and the second driving mechanism drives the 3 light-shielding members in the second plane to the second position 502 of

[0095] so that the multiple light-shielding members can cover the diffraction spots in the main pupil plane.

[0095] It should be noted that, for the purpose of showing the first position 501 and the second position 502, in Figure 5 , the 3 light-shielding members are shown in the same plane, but in the actual application scenario, the first plane and the second plane are two different planes.

[0096] Furthermore, when multiple light-shielding members are arranged in different planes, the light-shielding members in different planes can also be partially overlapped. In this way, it is equivalent to widening the width of the light-shielding members, thereby improving the accuracy of the light-shielding members in blocking multiple secondary diffraction spots. For ease of understanding, Figure 6 a schematic diagram of the partially overlapped light-shielding members is given.

[0097] Further, in order to detect multiple different types of objects to be detected, embodiments of the present application may further set corresponding driving mechanisms for each light-shielding member in different planes, so that the distance between two adjacent light-shielding members can be changed through their respective independent driving structures, thereby adapting to different types of objects to be detected and improving the convenience of detecting different types of objects to be detected.

[0098] As a specific embodiment, as Figure 7 shown, embodiments of the present application may drive a ball screw 702 through a servo motor 701 to push each light-shielding member 703 in the second filtering structure to slide along a guide rail 704, so as to drive each light-shielding member 703 in the second filtering structure to a corresponding position in the pupil plane to block the diffraction spots at the corresponding positions in the pupil plane.

[0099] As an alternative embodiment, in order to avoid the sharp edges of the second filtering structure, which may cause diffraction of the scattered light beam at the edges of the second filtering structure, embodiments of the present application may also set the edges of the light-shielding members in the second filtering structure to non-sharp edge structures, such as serrated states or wavy shapes. The form of the non-sharp edge structure is not specifically limited here.

[0100] Since embodiments of the present application can set the edges of the second filtering structure to non-sharp edge structures, the diffraction phenomenon caused by the scattered light beam at the edges of the light-shielding members in the second filtering structure is reduced, and the accuracy of obtaining the defect signals in the object to be detected is further improved.

[0101] As an alternative embodiment, when the filtering structure includes a first filtering structure and a second filtering structure, since embodiments of the present application require that both the first filtering structure and the second filtering structure overlap with the pupil plane, and because the diameter of the secondary diffraction spots generated by the periodically arranged structural units is small, in order to achieve precise filtering of the secondary diffraction spots generated by the periodically arranged structural units, embodiments of the present application set the second filtering structure at the pupil plane and set the first filtering structure at a first position 0.1 mm to 2 mm in front of or behind the pupil plane (such as setting the first filtering structure at a distance of ±1 mm from the pupil plane), so that the first filtering structure is as close as possible to the position of the pupil plane to achieve precise filtering of the scattered spots formed by the rough surface of the object to be detected and the main diffraction signal (i.e., the main diffraction spot) generated by the periodic structural units.

[0102] Further, when the second filtering structure is disposed in multiple planes, one of the multiple planes can be disposed at the pupil plane, and the other planes can be disposed at a second position 0.1 mm to 2 mm in front of or behind the pupil plane, so that the other planes are also as close as possible to the position of the pupil plane, so as to achieve precise filtering of the secondary diffraction spots of the periodic structural units of the object to be detected.

[0103] As an optional embodiment, in order to reduce the reflectivity of the first filtering structure and / or the second filtering structure to light, an anti-reflection film can also be coated on the surface of the first filtering structure and / or the second filtering structure in the embodiments of the present application to reduce the reflectivity of the first filtering structure and / or the second filtering structure.

[0104] Specifically, the surface of the first filtering structure and / or the second filtering structure can be blackened to reduce the reflectivity of the first filtering structure and / or the second filtering structure.

[0105] Specifically, when the object to be detected is a wafer, in the scenario of image wafer defect detection, there are mainly two types of optical noises. The first type is the diffraction of incident light by the wafer background pattern, including the main diffraction secondary and higher-order diffraction orders. Since the background image of the wafer is regularly distributed, the diffracted light of the background image presents a discrete distribution in the spatial frequency domain, and its discrete distribution law is determined by the background image. Among them, the main diffraction secondary is distributed in the main plane, with high intensity and one-dimensional characteristics, but the main diffraction secondary distributions of different background images are different, but they are all concentrated in the central strip; the second type of optical noise is the scattered light caused by the rough substrate of the wafer. Because the roughness of the substrate has randomness, the scattered light presents a continuous distribution in the frequency domain.

[0106] Based on the distribution characteristics of these two types of optical noises, the embodiments of the present application can adopt a two-stage filtering structure. Among them, the first filtering structure is used to suppress both or the latter of the scattered signal containing the rough surface of the object to be detected and the main diffraction signal of the periodically arranged structural units for filtering, and the second filtering structure is used to suppress the higher-order diffraction in the first type of optical noise, so as to better suppress the noise, improve the signal-to-noise ratio, and improve the detection accuracy.

[0107] Further, the first filtering structure and the second filtering structure in the embodiments of the present application can achieve double filtering on the same pupil plane, which improves the filtering effect on optical noise. For the requirement of efficiently filtering optical noise for the detection of dark-field defects of patterned wafers, the embodiments of the present application can achieve the filtering of two types of noises on the same pupil plane. Therefore, compared with the scheme of adding a relay optical device in the optical detection system in the prior art to achieve two pupil planes, optical errors such as aberration will not be introduced, ensuring the detection accuracy.

[0108] Next, the optical detection system in the embodiments of the present application will be described below. Please refer toFigure 8 :

[0109] The optical detection system in the embodiment of the present application includes a light source 801, an objective lens 802, a filtering structure 803, a tube lens system 804, and a detector 805;

[0110] Specifically, the light source 801 is used to send a light beam in a preset 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, an LED light source, etc. The type of the light source 801 is not specifically limited here.

[0111] The objective lens 802 is used to receive the scattered light beam of the object to be detected and focus the scattered light beam onto the pupil plane;

[0112] Here, the pupil plane is the rear focal plane of the objective lens 802.

[0113] The filtering structure 803 is arranged to be substantially overlapped with the pupil plane, so as to filter both or the latter of the scattered signal of the rough surface of the object to be detected and the main diffraction signal of the periodically arranged structural units in the object to be detected, and filter the secondary diffraction spots of the periodically arranged structural units in the object to be detected;

[0114] It should be noted that the filtering structure 803 here is similar to that described in the above embodiment and can be referred to each other, and will not be elaborated here.

[0115] The tube lens system 804 is used to image the object to be detected onto the detector 805;

[0116] Among them, the objective lens 802 and the tube lens system 804 here are similar to those described in the prior art and will not be elaborated here either.

[0117] The detector 805 is used to detect the defects in the object to be detected according to the image of the object to be detected.

[0118] Specifically, the detector 805 can be a photodiode, a photodetector, an avalanche photodetector, etc. The type of the detector 805 is not specifically limited here.

[0119] In the embodiment of the present application, the optical detection system is used to detect defects in the object to be detected. During the detection process, the filtering structure 803 includes a first filtering structure and a second filtering structure. Among them, the first filtering structure is used to filter two or the latter of the scattering signals of the rough surface and the main diffraction signals of the periodically arranged structural units in the object to be detected, and the second filtering structure is used to filter the secondary diffraction spots of the periodically arranged structural units in the object to be detected. Therefore, when detecting the defects in the object to be detected, the main diffraction signals of the periodically arranged structural units in the object to be detected can be filtered by the first filtering structure, and the secondary diffraction spots of the periodically arranged structural units in the object to be detected can be filtered by the second filtering structure, thereby improving the accuracy of obtaining the defect signals in the object to be detected.

[0120] As an alternative embodiment, based on Figure 8 In the above embodiment, since the edges of the first filtering structure and the second filtering structure in the filtering structure 803 are set as non-sharp edge structures, the diffraction phenomenon caused by the first filtering structure and the second filtering structure to the scattered light beam is avoided, thereby improving the Poisson scattering resolution of the optical detection system. Even when 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 still be detected.

[0121] Among them, the Poisson scattering resolution of the optical detection system is also called the PSF (Point Spread Function) resolution accuracy, which is used to evaluate the imaging quality of the optical detection system. Since the non-sharp edges of the first filtering structure and / or the second filtering structure can suppress the diffraction phenomenon caused by the scattered light beam, the light energy in the imaging of the object to be detected is mainly concentrated in the center. Even when 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 still be detected.

[0122] As an alternative embodiment, based on Figure 8 In the above embodiment, in order to improve the observation of the pupil plane, the present application embodiment can also set an insertable mirror 807, a pupil imaging tube lens 808, and a pupil imaging detector 809, so that when the insertable mirror 807 is inserted between the tube lens system 804 and the detector 805, the scattered light beam is reflected to the pupil imaging tube lens 808. Among them, the pupil imaging tube lens 808 is used to image the pupil plane to the pupil imaging detector 809, and the pupil imaging detector 809 is used to observe the pupil plane according to the image of the pupil plane.

[0123] Optionally, the switchable mirror 807 can also be switched between the filter structure 803 and the tube lens system 804, so as to reflect the scattered light beam to the pupil imaging tube lens 808. The pupil imaging tube lens 808 is used to image the pupil plane to the pupil imaging detector 809, and the pupil imaging detector 809 is used to observe the pupil plane according to the image of the pupil plane.

[0124] In the embodiments of the present application, in order to observe the filtering situation in the pupil plane, the embodiments of the present application can also image the pupil plane to the pupil imaging detector 809, so that the imaging situation of the pupil plane can be observed through the pupil imaging detector 809, thereby improving the convenience of observing the pupil plane.

[0125] As an optional embodiment, when the filter structure 803 includes a first filter structure 8031 and a second filter structure 8032, if the multiple light blocking members in the second filter structure 8032 are arranged on the same plane, the second filter structure 8032 is arranged at the pupil plane, and along the propagation direction of the scattered light beam, the first filter structure 8031 is arranged 0.1 mm to 2 mm in front of the pupil plane, or the first filter structure 8031 is arranged 0.1 mm to 2 mm behind the pupil plane, so that the first filter structure 8031 is as close as possible to the pupil plane, so as to filter the main diffraction signal of the periodically arranged structural units in the object to be detected and / or the scattered light spots on the rough surface of the object to be detected through the first filter structure 8031, and filter the secondary diffraction spots of the periodically arranged structural units in the object to be detected through the second filter structure 8032. For the convenience of understanding, Figure 9 a schematic diagram of the positions of the first filter structure 8031 and the second filter structure 8032 is given.

[0126] As another optional embodiment, when the filter structure 803 includes a first filter structure 8031 and a second filter structure 8032, if the multiple light blocking members in the second filter structure 8032 are arranged on multiple planes, one of the multiple planes can be overlapped with the pupil plane, and the other planes of the multiple planes are arranged 0.1 mm to 2 mm in front of the pupil plane along the propagation direction of the scattered light beam, and the first filter structure is arranged 0.1 mm to 2 mm behind the pupil plane along the propagation direction of the scattered light beam;

[0127] Or, the other planes of the multiple planes are arranged 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 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, Figure 10 a schematic diagram of the positions of the first filter structure 8031 and the second filter structure 8032 is given.

[0128] In the application embodiment, since the diameter of the diffraction spot generated by the structure units arranged periodically for the object to be detected is small, in order to achieve precise filtering of the diffraction spots generated by the structure units arranged periodically, the second filtering structure 8032 is arranged at the pupil plane in the application embodiment, and the first filtering structure 8031 is made as close as possible to the pupil plane, thereby achieving precise filtering of the secondary diffraction spots generated by the periodic structure units in the object to be detected.

[0129] As an optional embodiment, in order to control the spot size of the incident light beam irradiating the surface of the object to be detected, the application embodiment may further provide an expanding and shaping module 810 between the light source 801 and the object to be detected 806. The expanding and shaping module 810 includes an expander and a shaping element. The expander is used to expand the light source to obtain a spot of a preset size, and the shaping element is a phase element with a two-dimensional structure to achieve shaping of the expanded light beam, so as to achieve the purpose of controlling the numerical aperture NA of the incident light. For ease of understanding, Figure 11 a schematic diagram of an optical detection system including a cut-in mirror 807, a pupil imaging tube lens 808, a pupil imaging detector 809, and an expanding and shaping module 810 is given.

[0130] Based on Figure 11 the optical detection system described above, the optical detection method of the optical detection system will be described. Please refer to Figure 12 :

[0131] 1201. Use the pupil imaging detector to observe the image of the pupil plane to obtain the distribution state of the scattering signal in the pupil plane;

[0132] In the application embodiment, the cut-in mirror 807, the pupil imaging tube lens 808, and the pupil imaging detector 809 are used to cooperate with each other to image the pupil plane to the pupil imaging detector 809, so that the image of the pupil plane can be observed through the pupil imaging detector 809.

[0133] In this way, it is possible to observe the image of the pupil plane through the pupil detector to obtain the distribution state of the scattering signal in the pupil plane. Therefore, according to the position and shape of the scattering signal on the rough surface of the object to be detected, a suitable first filtering structure is selected, that is, according to the position and shape of the scattering signal on the rough surface of the object to be detected, a suitable first filtering structure is selected from Figure 3 the first filtering structures.

[0134] 1202. Drive a suitable first filtering structure to filter both or the latter of the scattering signal of the rough surface of the object to be detected and the main diffraction signal of the periodically arranged structure units in the object to be detected in the scattering signal;

[0135] After determining the adapted first filtering structure 8031, the adapted first filtering structure 8031 can be driven to filter the scattering signals of the rough surface of the object to be detected and the main diffraction signals of the periodically arranged structural units in the object to be detected in the scattering signal. Specifically, when both the first filtering structure and the second filtering structure exist, the first filtering structure is arranged at a position 0.1 mm to 2 mm in front of or behind the pupil plane along the propagation direction of the scattering beam, so as to filter the scattering signals of the rough surface of the object to be detected and the main diffraction signals of the periodically arranged structural units in the object to be detected.

[0136] 1203. Drive the second filtering structure to filter the secondary diffraction signals of the structural units in the object to be detected in the scattering signal.

[0137] When there are still secondary diffraction signals (secondary diffraction spots) generated by the structural units in the object to be detected in the pupil plane, the second filtering structure is driven to filter the secondary diffraction signals of the structural units in the object to be detected in the scattering signal, thereby improving the accuracy of filtering the scattering signals in the pupil plane.

[0138] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A filtering structure, characterized in that: include: A first filtering structure is used to filter the main diffraction signal of the periodically arranged structural units in the object to be detected; and a second filtering structure, for filtering the secondary diffraction spots of the periodically arranged structural units in the object to be detected; wherein: The first filtering structure includes at least one filtering structure with a closed outer periphery. When a structural unit is provided in the object to be detected, a light-blocking structure connecting any two ends of the closed filtering structure is further provided in the closed filtering structure; the spatial orientation of the light-blocking structure connecting any two ends of the closed filtering structure is adapted to the position and shape of the scattered light spot on the rough surface of the object to be detected; The second filtering structure comprises a plurality of light blocking members arranged in parallel, wherein the projection of the light blocking members on the plane where the secondary diffraction light spot is located is not less than the diameter of the secondary diffraction light spot; If the plurality of light blocking members in the second filtering structure are arranged in the same plane, the second filtering structure is arranged at the pupil plane, and the first filtering structure is arranged 0.1 mm to 2 mm in front of the pupil plane along the propagation direction of the scattered light beam, or the first filtering structure is arranged 0.1 mm to 2 mm behind the pupil plane; If the second filtering structure includes a plurality of light blocking members arranged on a plurality of planes, one of the plurality of planes is arranged to overlap with the pupil plane, the other planes of the plurality of planes are arranged 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 is arranged 0.1 mm to 2 mm behind the pupil plane along the propagation direction of the scattered light beam; Or, the other planes among the plurality of planes are arranged at 0.1 mm to 2 mm behind the light beam surface along the propagation direction of the scattered light beam, and the first filtering structure is arranged at 0.1 mm to 2 mm in front of the light beam surface along the propagation direction of the scattered light beam; The filtering structure is arranged in the optical detection system, and each of the light blocking members is driven by an independent driving mechanism, so that the corresponding light blocking members are driven by a plurality of independent driving mechanisms to overlap with the light blocking surface in the optical detection system.

2. The filtering structure according to claim 1, characterized in that: The light-blocking structure arranged in the closed filtering structure and adapted to the position and shape of the scattered light spot on the rough surface of the object to be detected includes: an arched light-blocking structure arranged at one end of the light-blocking structure, an arched light-blocking structure arranged at both ends of the light-blocking structure, a polygonal light-blocking structure arranged at any position in the light-blocking structure, or a circular light-blocking structure arranged at any position in the light-blocking structure.

3. The filtering structure according to claim 1, characterized in that: The filtering structure is arranged in the optical detection system. There are multiple first filtering structures, which are arranged in the same plane, and the distance between the centers of two adjacent first filtering structures is not less than the diameter of the light beam surface of the optical detection system.

4. The filtering structure according to claim 3, characterized in that: The plurality of first filtering structures are driven by a driving mechanism.

5. The filtering structure according to claim 1, characterized in that: The inner peripheral wall of the closed filtering structure, the edge of the light blocking structure and the edge of the light blocking member are configured as non-sharp edge structures.

6. The filtering structure according to claim 1, characterized in that: The filtering structure is arranged in an optical detection system. If the diameter of the pupil plane in the optical detection system is D and the width of the light blocking member is d, the number N of the light blocking members is calculated according to the following formula: 。 7. The filtering structure according to claim 1, characterized in that: The plurality of light blocking members are arranged in at least one plane, and each of the at least one plane is perpendicular to a propagation direction of the scattered light beam.

8. The filtering structure according to claim 7, characterized in that: The plurality of light blocking members are arranged on a plurality of planes, and the light blocking members in different planes are partially stacked.

9. The filtering structure according to claim 1, characterized in that: The edge of the light blocking member is configured as a non-sharp edge structure.

10. The filtering structure according to claim 1, characterized in that: The surface of the first filter structure and / or the second filter structure is coated with an anti-reflective film to reduce the reflectivity of the first filter structure and / or the second filter structure.

11. The filtering structure according to claim 1, characterized in that: 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.

12. An optical detection system, characterized in that: The filter structure comprising any one of claims 1 to 11; A light source, used for emitting a coherent light beam of a preset wavelength band at a preset angle toward the object to be detected; An objective lens, used for receiving the scattered light beam of the object to be detected, and focusing a parallel light beam or a nearly parallel light beam in the scattered light beam to a pupil plane; A tube lens system, used for imaging the object to be detected onto a detector; The detector is used to detect defects in the object to be detected based on the image of the object to be detected.

13. The system according to claim 12, characterized in that The optical detection system also includes: a cut-in reflector, a pupil imaging tube lens, and a pupil imaging detector; The cuttable reflector is used to cut between the tube lens system and the detector to change the propagation direction of the scattered light beam so that the scattered light beam is incident on the pupil imaging tube lens; or the cuttable reflector is used to cut 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 used to image the light beam onto the pupil imaging detector; The pupil imaging detector is used to observe the pupil surface according to the image of the pupil surface.

14. The system according to claim 12, characterized in that The filtering structure includes a first filtering structure and a second filtering structure, wherein the second filtering structure includes a plurality of strip light blocking members arranged in parallel, the width of the strip light blocking members is related to the diameter of the secondary diffraction spots of the periodically arranged structural units, the length of the strip light blocking members is not less than the diameter of the pupil plane, and the number of the strip light blocking members is related to the diameter of the pupil plane and the width of each strip light blocking member.

15. The system according to claim 12, characterized in that The optical detection system further comprises a beam expansion and shaping module disposed between the light source and the object to be detected, wherein the beam expansion and shaping module comprises a beam expander and a shaping element, and the shaping element comprises a phase element having a two-dimensional structure.

16. An optical detection method, characterized in that: The optical detection system applied to any one of claims 12 to 15, the method comprising: Observing the image of the pupil surface by using a pupil imaging detector to obtain the distribution state of the scattered signal in the pupil surface; driving the adapted first filtering structure to filter both or the latter of the scattered signal of the rough surface of the object to be detected and the main diffraction signal of the periodically arranged structural units in the object to be detected; The second filtering structure is driven to filter the secondary diffraction signal of the periodically arranged structural units in the object to be detected in the scattering signal.

Images