Optical collection device and optical detection apparatus

Abstract

An embodiment of the present application provides an optical collection device and an optical detection device. The optical collection device comprises an optical collection assembly configured to collect detected light generated by a surface of an object to be detected. The detected light comprises first scattered light and second scattered light. The first scattered light is generated by roughness of the surface of the object to be detected, and the second scattered light is generated by defects of the surface of the object to be detected. The optical collection assembly comprises a polarization modulation assembly configured to modulate a polarization state of the detected light to increase a difference between the first scattered light and the second scattered light in the polarization state. By setting the polarization modulation assembly, an active and deterministic intervention is made on the physical state (i.e. the polarization state) of the light, so that the difference in the polarization state between the signal and the noise is intentionally amplified, which provides a better initial condition for the separation of different types of scattered light and improves the signal-to-noise ratio. Moreover, it is beneficial to simplify the optical path structure and reduce the manufacturing cost.

Description

Technical Field

[0001] This application relates to the field of wafer inspection technology, and in particular, to an optical collection device and an optical inspection equipment. Background Technology

[0002] As semiconductor process nodes shrink, higher demands are placed on inspection technologies. Optical inspection equipment can quickly and accurately detect and identify various defects and anomalies that occur during the manufacturing process without contacting or damaging the wafer, thus meeting the challenges of advanced processes.

[0003] Optical inspection, based on different detection principles, can include bright-field inspection and dark-field inspection. Bright-field inspection, a more intuitive method, is typically used after image processing. It involves incident light perpendicularly or nearly perpendicularly onto the surface of the object to be inspected (such as a wafer), and then collecting the reflected light through an objective lens. This method not only provides clear images with high contrast but also allows for precise measurement of size and location. Dark-field inspection, a primary method for inspecting unpatterned surfaces or in the early stages of a process layer, physically separates the illumination and collection light paths, allowing the objective lens to collect scattered light from defects. Because the wafer is in an extremely dark background inspection environment, background interference signals are effectively suppressed, resulting in a high signal-to-noise ratio and the ability to detect defects much smaller than the wavelength of the detection light.

[0004] However, dark field testing is extremely sensitive to scattered light from defects (such as tiny particles) on the wafer surface, and the inherent micro-roughness of the surface (even after precision polishing) produces diffuse background scattered light, which often causes tiny defect signals to be submerged, seriously affecting the accuracy of the test. Summary of the Invention

[0005] In view of this, this application provides an optical collection device and an optical inspection equipment, which aim to solve to some extent the problem of reduced detection accuracy caused by the submersion of defect signals in dark field inspection.

[0006] In a first aspect, one embodiment of this application provides an optical collection device for dark field detection, comprising an optical collection component for collecting light to be detected generated by the surface of an object to be detected. The light to be detected includes a first type of scattered light and a second type of scattered light. The first type of scattered light is generated by the roughness of the surface of the object to be detected, and the second type of scattered light is generated by defects on the surface of the object to be detected. The optical collection component includes a polarization modulation component configured to modulate the polarization state of the light to be detected to increase the difference in polarization state between the first type of scattered light and the second type of scattered light.

[0007] Secondly, one embodiment of this application provides an optical inspection device for wafer inspection, which includes the aforementioned optical collection device and polarization detection component. The polarization detection component is located behind the optical path of the optical collection device. The polarization detection component includes a polarization beam splitting module, which is used to separate a first type of scattered light and a second type of scattered light in the light to be inspected. The first type of scattered light is generated by the roughness of the surface of the object to be inspected, and the second type of scattered light is generated by the defects on the surface of the object to be inspected.

[0008] By incorporating a polarization modulation component within the optical collection assembly, the physical state (i.e., polarization state) of light is actively and deterministically intervened. This intentionally amplifies the difference in polarization states between the signal and noise, providing better initial conditions for the subsequent separation of different types of scattered light, thereby improving the system's signal-to-noise ratio. Furthermore, since the polarization states of the noise or target signal are pre-unified, there is no need to subsequently install complex polarization components, thus simplifying the optical path structure and reducing manufacturing costs. Attached Figure Description

[0009] It should be understood that the following figures only show some embodiments of this application and should not be regarded as a limitation on the scope.

[0010] It should be understood that the same or similar reference numerals are used in the accompanying drawings to denote the same or similar elements.

[0011] It should be understood that the accompanying drawings are only schematic, and the dimensions and scales of the elements in the drawings are not necessarily precise.

[0012] Figure 1 This is one of the structural schematic diagrams of an optical collection device provided in an embodiment of this application.

[0013] Figure 2 This is a second schematic diagram of the structure of an optical detection device provided in one embodiment of this application.

[0014] Figure 3 This is the third schematic diagram of the structure of an optical detection device provided in an embodiment of this application.

[0015] Figure 4 for Figure 3 A simulation diagram of the angular compression ratio of the objective lens assembly in the provided optical collection device.

[0016] Figure 5 This is a simulation diagram illustrating the reflectivity of an optical thin film provided in an embodiment of this application and the phase difference between P-polarized and S-polarized light at different incident angles.

[0017] Figure 6 for Figure 3 A schematic diagram of the polarization distribution of the first type of scattered light collected at the entrance pupil of the objective lens assembly.

[0018] Figure 7 for Figure 3 A schematic diagram of the polarization distribution of the first type of scattered light collected at the exit pupil of the optical collecting device.

[0019] Figure 8 This is the fourth schematic diagram of the structure of an optical detection device provided in an embodiment of this application.

[0020] Figure 9 for Figure 8 A schematic diagram of the polarization distribution of the first type of scattered light collected at the entrance pupil of the objective lens assembly.

[0021] Figure 10 for Figure 8 A schematic diagram of the polarization distribution of the first type of scattered light collected at the exit pupil of the optical collecting device.

[0022] Figure 11 Based on Figure 8 A schematic diagram of wavefront simulation after the aberration correction component of the provided optical collection device.

[0023] Figure 12 The fifth schematic diagram of the structure of an optical inspection device provided in an embodiment of this application.

[0024] Figure 13 This is a schematic diagram of the polarization directions corresponding to different scattering angles on the central cross section of the wafer surface collected by the objective lens assembly provided in an embodiment of this application.

[0025] Figure 14 for Figure 12 A schematic diagram of the polarization state of the first type of scattered light collected by the objective lens assembly in the provided optical inspection device.

[0026] Figure 15 for Figure 12 A schematic diagram of the polarization state of the first type of scattered light after passing through the optical collection device in the provided optical detection equipment.

[0027] Figure label: Optical collection device 100, Optical collection assembly 10, polarization modulation assembly 11, objective lens assembly 12, aberration correction assembly 13. Mirror assembly 111, mirror 1111, optical thin film 1112, Polarization detection component 200, Sub-aperture beam splitter module 220, polarization beam splitter module 210, polarization beam splitter element 211, detector 212. The light to be detected is S0, the first type of scattered light is S1, and the second type of scattered light is S2. 300 optical inspection equipment. Detailed Implementation

[0028] The embodiments of this application are described below with reference to the accompanying drawings. It should be understood that there are various ways to implement this application, and it should not be construed as being limited to the embodiments described herein. The embodiments described herein are only for a more thorough and clear understanding of this application.

[0029] Application Overview: In semiconductor manufacturing, process nodes have reached the nanoscale, and even the smallest defects can cause chip malfunction. Therefore, inspection during production is deeply embedded in every critical step of the process. For example, in wafer inspection, detecting defects on the surface of a wafer without patterns can not only provide data to guide the optimization of the production process, but also prevent failures in subsequent processes such as photolithography, reduce manufacturing costs, and improve the yield of the final product.

[0030] Currently, the mainstream wafer surface defect detection equipment internationally is mainly based on the dark field detection principle, which generally obtains information about wafer surface defects by detecting scattered light. Since the intensity of scattered light is generally weak, in order to achieve high-sensitivity detection of tiny defects (such as particles) on the wafer surface, optical inspection systems typically include a collection end and a detection end.

[0031] Specifically, the collection end uses an objective lens with a large numerical aperture to collect scattered light from a wide angular range on the wafer surface and transmits the collected light energy to the detection end. In the optical path of the detection end, by configuring and switching different polarization elements (such as analyzers and waveplates), the collected scattered light with different polarization states is analyzed, thereby separating the signal scattered light generated by defects from the noise scattered light (i.e., "haze") generated by surface roughness. Since this optical detection system can directly use optical elements to filter the polarization state of light, it can theoretically distinguish between the two types of scattered signals.

[0032] However, when this optical detection system is applied to highly demanding detection scenarios (such as detecting nanoscale particles), the detection results are not ideal. Analysis revealed that the collection end typically employs a large-angle collection (i.e., high NA) to improve signal collection efficiency. This results in the collected scattered light exhibiting a continuously varying and diverse polarization state distribution. The detection end requires an exceptionally complex design to effectively distinguish between noise-scattered light (i.e., background noise) and signal-scattered light generated by defects. This not only increases the optical complexity and assembly difficulty of the system but also limits the potential for improving the signal-to-noise ratio and the detection accuracy due to the inherent angle dependence and insertion loss of the polarization elements.

[0033] Further analysis by the inventors revealed that the performance of polarization elements (such as waveplates and polarizing beam splitters) in the detection end is closely related to the incident angle of light. The collection end directly transmits beams with wide angular distribution and different polarization states to the detection end, causing the optical performance of the polarization elements to no longer remain constant at the interface of the entire beam. This results in spatial non-uniformity in their performance, which restricts the efficiency of polarization separation of the optical collection device, thereby limiting the potential for improving the signal-to-noise ratio and meeting the requirements for high-sensitivity detection.

[0034] To overcome the above contradictions, embodiments of this application propose an optical collection device and an optical detection device. By introducing an active polarization modulation component into the optical path of the optical collection device, the polarization state of different types of scattered light (including first type scattered light generated by the roughness of the surface of the object to be detected and second type scattered light generated by defects on the surface of the object to be detected) is modulated. This increases the difference in polarization state between the first type scattered light and the second type scattered light, which helps to reduce the complexity requirements of the detection end and improves the separability of defect signals and haze noise signals in polarization state.

[0035] Terminology definition: In this application, some key terms need to be defined in order to make the description clearer.

[0036] Type I scattered light: Light scattering signal caused by the microscopic roughness of the surface of the object to be tested, also known as "haze," which is the main background noise in dark-field detection. This scattered light is mainly based on non-directional background scattered light caused by the microscopic roughness of the surface of the object to be tested. Its physical essence is scattered light generated by small perturbations of the boundary conditions of the surface electric field. The intensity and polarization state of this scattered light are the key factors restricting the sensitivity and signal-to-noise ratio of defect detection.

[0037] Type II scattered light: Scattered light signals caused by discrete defects or contaminant particles on the surface of the object to be detected. This scattered light is generated based on the interaction between the incident light and the discrete object, and its polarization state change mode is significantly different from that of Type I scattered light. It is the target signal that needs to be extracted and enhanced in dark-field detection.

[0038] Polarization modulation component: any device or element capable of actively changing or modulating the polarization state of incident light to increase the difference in polarization state between the first type of scattered light and the second type of scattered light, thereby facilitating separation at the detection end. Examples include, but are not limited to, mirrors with specific film designs to introduce phase delay, waveplates capable of providing specific phase delay, electrically controlled polarization modulation devices such as liquid crystals, or combinations thereof.

[0039] Mirror assembly: A combination structure comprising a mirror and its surface functional coating, as a specific form of polarization modulation. Examples include, but are not limited to, off-axis mirrors coated with specific optical thin films, plane mirrors coated with specific optical thin films, or combinations thereof.

[0040] Optical collection components: These enable the collection and conduction of scattered light. Examples include, but are not limited to, lens groups consisting of one or more lenses, mirrors, or combinations thereof, configured to have a specific numerical aperture to receive scattered light within a specific angular range and guide the collected light to the detection end.

[0041] Equivalent fast axis: Used to describe the reference direction by which an optical element (such as an optical thin film) introduces a phase delay effect on incident light. It characterizes the reference direction by which the optical thin film modulates the polarization state of incident linearly polarized light at a specific incident angle. Its direction is determined by the film structure on the surface of the mirror.

[0042] Polarization modulation component: Any optical element or combination of elements that actively alters the polarization state of light waves passing through it. In this application, addressing the problem of insufficient difference in polarization states between scattered light generated by surface roughness and scattered light generated by defects, an additional and controllable change is applied to the polarization state of at least one type of scattered light, artificially amplifying the difference in polarization states between the two. Examples include, but are not limited to, coated mirrors, waveplates, liquid crystal polarization modulators, or combinations thereof, with specific phase delay characteristics.

[0043] Objective lens assembly: An optical element or lens group positioned at the front end of the optical collecting assembly, used to directly receive and preliminarily process scattered light from the surface of the object to be tested. In the specific context of this application, it is not only configured for light collection but also for purposeful modulation of the propagation angle and polarization state of the scattered light. For example, including but not limited to lenses or lens groups designed to nonlinearly compress the angle of light rays, such that large-angle scattered light is compressed to a greater extent than small-angle scattered light.

[0044] Aberration correction components: Optical elements or lens groups located behind the polarization modulation component's optical path, used to correct wavefront distortion introduced by the preceding optical elements (such as objective lenses or mirrors with special surface shapes in optical collection devices), ensuring that the modulated beam is emitted to the detection end in a high-quality state (e.g., close to a plane wave), guaranteeing the accuracy of subsequent detection. Examples include, but are not limited to, aberration correction components composed of multiple lenses, whose focal length and surface shape are designed to compensate for specific aberrations, such as spherical aberration and coma.

[0045] Local radius of curvature of a surface: a parameter describing the degree of curvature of the geometry of a mirror surface within a small region.

[0046] Angle modulation function: Characterizes the ability of an objective lens to transform the angle of light rays. In this application, the objective lens assembly maps the angle of scattered light from the surface of the object under test to the angle of its outgoing light ray (or the angle incident on subsequent elements) through a mathematical relationship or physical transformation. For example, including but not limited to, the angle modulation function exhibits a nonlinear angle compression relationship, meaning that the output angle changes nonlinearly with the input angle, and for larger original scattering angles, the compression ratio is higher.

[0047] Phase delay: The relative phase difference between two orthogonally polarized components of a light wave when it passes through an optical element or is reflected from an interface. This phase delay is a direct physical quantity that alters the polarization state of light. Examples include, but are not limited to, the half-wave plate effect used to rotate the polarization direction of linearly polarized light by approximately 90 degrees.

[0048] Nonlinear angle compression: An angle transformation method in which the output angle and input angle have a nonlinear relationship, resulting in a compression ratio that is greater at a large input angle than at a small input angle. Examples include, but are not limited to, objective lens assemblies that compress large-angle scattered light from a wafer surface into a relatively smaller and more concentrated angular range to suit the optimal operating angle range of subsequent polarization modulation elements.

[0049] Sub-aperture beam splitting module: An optical component that separates sub-beams from different fields of view or different angular ranges into different detection channels based on the spatial position of different regions on the cross-section (i.e., "aperture") of the beam, thereby achieving signal separation in the angular dimension. For example, including but not limited to using beam splitters that partially transmit and partially reflect light to separate the light from the central and edge regions of the beam into different detection channels.

[0050] The specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the embodiments described herein and illustrated are non-limiting examples, and any modifications or substitutions based on the core concept of this application should be considered to fall within the protection scope of this application.

[0051] Exemplary optical collection device: refer to Figure 1 The optical collection device 100 provided in the embodiments of this application is mainly used for dark field detection, which detects by collecting scattered light from defects on the surface of the object to be detected (such as wafer W). However, the scattered light collected by the optical collection device 100 includes not only the scattered light generated from defects (i.e., second type scattered light S2, i.e., target signal), but also the background scattered light generated by the inherent micro-roughness of the wafer surface (even after precision polishing) (i.e., first type scattered light S1, also known as "haze", i.e. noise signal).

[0052] Because the mechanisms by which first-type and second-type scattered light are generated differ, the changes they cause to the polarization state of the incident light also differ. Specifically, first-type scattered light S1, generated by a rough surface, mainly originates from minute perturbations in the boundary conditions of the electric field. For a very smooth surface, this weak scattering largely maintains a certain polarization state. Second-type scattered light S2, generated by discrete particles or defects, mainly originates from the interaction between particles or defects of different sizes and the wavelength that causes the scattering. For example, when the size of the particles or defects is much smaller than the wavelength, the second-type scattered light can be Rayleigh scattering; when the size of the particles or defects is comparable to the wavelength, the second-type scattered light can be Mie scattering. The generation process of second-type scattered light strongly alters the propagation direction and polarization state of the light, and the distribution of the propagation direction and polarization state of the scattered light is complex and related to the characteristics of the defects.

[0053] By comparison, it can be seen that the first type of scattered light and the second type of scattered light have a significant difference in polarization state. By setting the optical collection component 10 in the optical collection device to amplify the difference between different polarization states, the first type of scattered light and the second type of scattered light can be separated, which helps to reduce noise signals and improve the signal-to-noise ratio of detection. A higher signal-to-noise ratio helps to improve the accuracy of detection.

[0054] refer to Figure 1 The optical collection device 100 may include an optical collection component 10 for collecting the light S0 to be detected (including first type scattered light S1 and second type scattered light S2) generated on the surface of the wafer W. The optical collection component 10 may include a polarization modulation component 11, configured to modulate the polarization state of either the first type scattered light S1 or the second type scattered light S2 to increase the difference in polarization state between them. This larger difference makes it easier for subsequent optical elements to distinguish between the first type scattered light S1 and the second type scattered light S2, thereby providing the possibility of improving the signal-to-noise ratio of the detection signal.

[0055] By incorporating a polarization modulation component within the optical collection assembly, the physical state (i.e., polarization state) of light is actively and deterministically intervened. This intentionally amplifies the difference in polarization states between the signal and noise, providing better initial conditions for the subsequent separation of different types of scattered light, thereby improving the system's signal-to-noise ratio. Furthermore, since the polarization states of the noise or target signal are pre-unified, there is no need to subsequently install complex polarization components, thus simplifying the optical path structure and reducing manufacturing costs.

[0056] For example, the difference in polarization states between the first type of scattered light S1 and the second type of scattered light S2 can be increased by modulating the polarization state of the first type of scattered light S1. Similarly, the difference in polarization states between the first type of scattered light S1 and the second type of scattered light S2 can be increased by modulating the polarization state of the second type of scattered light S2. Modulation methods can include various implementations, such as using polarizers, rotating analyzers, or zone filtering.

[0057] refer to Figure 2 The polarization modulation component 11 may include a mirror component 111, which may include a mirror 1111 and an optical thin film 1112 disposed on the surface of the mirror 1111. The optical thin film 1112 is configured to introduce a phase delay to the incident first type scattered light S1 and second type scattered light S2 within a specific angle range, so that the phase values ​​of the first type scattered light and the second type scattered light emitted after passing through the optical thin film 1112 are controlled within a preset range to modulate the polarization state of the light to be detected. The direction of the equivalent fast axis of the optical thin film 1112 changes with the change of the light to be detected S0.

[0058] It should be noted that, on the one hand, the optical thin film is used to introduce a controllable phase delay into the incident light within a specific angular range, so that the phase difference between the two orthogonal polarization components of the outgoing light after reflection by the optical thin film is controlled within a preset range. Different phase difference values ​​make the polarization state of the outgoing light uncertain, while phase difference values ​​within the preset range make the polarization state of the outgoing light somewhat deterministic. By introducing phase delay, the polarization state of the scattered light is modulated. On the other hand, due to different incident light angles, the direction of the equivalent fast axis of the optical thin film 1112 changes with the change of the light to be detected S0, allowing the optical thin film to rotate the polarization direction of the incident linearly polarized light by a fixed angle (the rotation angle is determined by the angle between the equivalent fast axis and the incident polarization direction) within a continuous range of incident angles, rather than at a single angle.

[0059] It can be understood that the equivalent fast axis is equivalent to the reference direction of the phase delay. The optical thin film in this application has an adaptively adjusted equivalent fast axis, which is equivalent to introducing a phase delay that varies with the incident angle, thus providing the possibility for unifying the polarization direction of a certain type of scattered light.

[0060] In this way, the correlation between the direction of the equivalent fast axis and the incident angle (i.e., following a specific functional relationship) allows the phase delay introduced by the optical thin film for scattered light to be stably controlled within a preset range. This helps to achieve the same or nearly the same phase modulation for incident light over a wide angle, ensuring that the polarization direction of a certain type of scattered light output is consistent. For example, it is possible to obtain first-type scattered light signals with consistent polarization directions.

[0061] Optionally, the preset range includes greater than or equal to 0 and less than or equal to π. In this way, by introducing a non-zero phase delay to increase the polarization difference between the two types of scattered light, better initial conditions are provided for the subsequent separation of different types of scattered light.

[0062] For example, the preset range can be approximately π / 4 (i.e., a 45-degree phase difference) or π / 3 (i.e., a 60-degree phase difference).

[0063] Preferably, the preset range can be less than or equal to 0.9π and greater than or equal to π to achieve a polarization conversion effect close to that of a half-wave plate. This means that when linearly polarized light irradiates the optical thin film at an incident angle within a specific angular range, the polarization state of the reflected light will rotate by nearly 90 degrees.

[0064] By integrating the characteristics of stable half-wave delay and dynamically adjustable equivalent fast axis on the same optical thin film 1112, the optical thin film 1112 can be regarded as a polarization converter whose parameters can be dynamically optimized according to input conditions. This allows the scattered light, after being reflected by the mirror assembly 111, to be modulated into a roughly uniform polarization direction, such as the first type of scattered light (i.e., haze signal), whose polarization state originally changes with the angle.

[0065] Of course, the preset range can be any angle greater than 0 and less than π. For example, you can choose 0.5π, and the polarization state of the reflected light will rotate by nearly 45 degrees. There is no specific limitation here.

[0066] Different phase modulations of optical thin films can be achieved by selecting different combinations of coating materials, through the design of material refractive index, thickness, and layered structure. For example, an optical thin film may contain about 80 alternating layers of magnesium fluoride, silicon dioxide, hafnium oxide, aluminum oxide, etc., with a total physical thickness on the order of several micrometers. Through optimization algorithms, the phase difference is made to be π at an incident angle of 45 degrees, and the phase difference deviates from π by less than 0.1π in the range of 35 degrees to 55 degrees.

[0067] It should be noted that optical thin films can include multilayer dielectric films, formed by alternating deposition of materials with high and low refractive indices. For example, high refractive index materials used in the deep ultraviolet band include hafnium oxide and aluminum oxide, while low refractive index materials include magnesium fluoride and silicon dioxide. Optical thin films may have tens to hundreds of layers. Through specific thickness distribution designs (such as using irregular or graded refractive index film systems), the reflected phase difference for S-polarized and P-polarized light at the designed center wavelength is stabilized near π within the target angle range (e.g., 30° ± 20°). For instance, an optical thin film can contain approximately 80 alternating layers of HfO2 and MgF2, with a total physical thickness on the order of several micrometers. Through optimization algorithms, the phase difference is made to be π at an incident angle of 45 degrees, and the phase difference deviates from π by less than 0.1π within the range of 35° to 55°.

[0068] The surface shape of the reflector assembly 111 can be varied according to the layout of the optical path and performance requirements. In one example, referencing... Figure 2 The mirror assembly 111 may include an axisymmetric off-axis mirror (see [reference]). Figure 3 and Figure 8 For example, the surface shape of the reflector can be parabolic, ellipsoidal, hyperboloid, etc., which helps to reduce processing and assembly costs. Moreover, using an off-axis reflector allows the incident light and reflected light to be spatially staggered, which is conducive to achieving an unobstructed light path, thereby improving light energy utilization and ensuring that all collected scattered light can participate in polarization modulation.

[0069] In one example, reference Figure 12 The reflector assembly 111 may include a planar reflector, which helps to significantly reduce the difficulty of processing and the cost of assembly and adjustment.

[0070] refer to Figures 1 to 3 The optical collection assembly 10 may further include an objective lens assembly 12, which is used to receive the light to be detected S0 and guide it to the mirror assembly 111. The objective lens assembly 12 may be disposed at the front end of the optical collection assembly 10 for collecting first-type and second-type scattered light at different angles on the surface of the wafer W.

[0071] It should be understood that the objective lens assembly 12 in this application is not used for collimation or high-quality imaging, but is configured to modulate the angle of the light to be detected S0 so that the exit angles of the modulated first type of scattered light S1 and the second type of scattered light S2 meet the range of the incident angle of the mirror assembly 111, so as to meet the requirements of the optical thin film for the angle of the incident light, thereby providing a premise for subsequent phase delay.

[0072] Initial adjustment of the angle of the light to be detected using the objective lens assembly 12 improves the interaction between the scattered light and the optical thin film. Of course, the optical thin film does not have specific requirements regarding the incident angle, as long as phase delay and polarization state separation are achieved. Furthermore, different angle requirements can be flexibly designed according to different needs.

[0073] It should be noted that the surface shape of the reflector 1111 can be configured to match the angle modulation function of the objective lens assembly 12, so that the incident angles of the modulated first type scattered light S1 and the second type scattered light S2 meet a specific angular range. This not only helps to ensure that the collected scattered light can be accurately connected with the subsequent polarization modulation assembly 11, but also helps to optimize the beam quality. In other words, the design of the reflector surface shape matches the angular transformation characteristics of the objective lens assembly, and this matching helps to ensure that the outgoing light with a specific angle-spatial position mapping relationship after passing through the objective lens assembly can illuminate the corresponding position on the reflector surface at the expected incident angle for subsequent phase modulation.

[0074] In one example, reference Figure 2 , Figure 3 and Figure 8 The local radius of curvature of the surface of the reflector 1111 is matched with the angle modulation function of the objective lens assembly 12 so that the incident angles of the modulated first type of scattered light and the second type of scattered light meet a specific angle range, which helps to ensure that the polarization direction of a certain type of scattered light remains consistent after modulation within a specific angle range.

[0075] Specifically, the angle modulation function of the objective lens assembly 12 can be configured to perform nonlinear angle compression on the first type of scattered light S1 and the second type of scattered light S2. The compression ratio for the larger angle of the light to be detected is greater than the compression ratio for the smaller angle, so that the scattered light emitted from the surface of the object to be detected (such as wafer W) at different angles is incident on the surface of the optical thin film of the mirror assembly 111 within a relatively concentrated angular range. This nonlinear angle compression ensures that all scattered light incident at all angles collected by the objective lens assembly 12 falls within the effective specific angular range of the optical thin film 1112, thereby ensuring that all collected scattered light is modulated, increasing the intensity of the second type of scattered light, and thus improving the accuracy of the detection.

[0076] It can be understood that the nonlinear angle compression here is to compress the light to be detected with a large angle range into scattered light with a smaller angle range. Under the premise that it does not affect the polarization state, phase, amplitude, etc. of the scattered light, it only changes the direction of its transmission without affecting the polarization state characteristics of the first type of scattered light, thus increasing the possibility of subsequent phase modulation.

[0077] For example, refer to Figure 4 The nonlinear angle compression in this application can adopt an edge compression enhancement design, which has stronger compression for large-angle light rays, while the angle change ratio of small-angle light rays in the center is smaller as the angle increases.

[0078] refer to Figure 2The objective lens assembly 12 may include one, two or more lens groups formed by several lenses, and there is no specific limitation, as long as it can converge light and form a clear image.

[0079] Continue to refer to Figures 1 to 3 The optical collection device 100 may also include an aberration correction component 13, which may be disposed behind the optical path of the polarization modulation component 11 (i.e., the objective lens component 12 and the mirror component 111) to correct the wavefront aberration of the modulated second type scattered light S2 and the first type scattered light S1, thereby helping to ensure that the subsequent beam has better quality (e.g., close to a plane wave) to facilitate subsequent accurate beam splitting and detection.

[0080] The aberration correction component 13 may include one or more lenses for correcting the wavefront aberrations carried by the second type of scattered light S2 and the first type of scattered light S1 after being modulated by the preceding optical path. After correction by the aberration correction component 13, the wavefront distortion of the outgoing beam is significantly reduced, such as... Figure 11 As shown, its wavefront error is controlled within a very small range, for example, the RMS value is less than 0.005 wavelengths, so that the scattered light enters the subsequent detection system as an approximately plane wave.

[0081] It should also be noted that the light to be detected is preferably linearly polarized light, thereby separating different types of polarized light according to different polarization characteristics. Furthermore, the embodiments of this application optimize the combination of the objective lens assembly 12 and the reflector assembly 111 to specifically modulate the polarization state of the haze signal or particle scattering signal generated by the roughness of the wafer surface itself, so as to convert them from different polarization directions to the same polarization direction. This effectively improves the ratio of defect signal to haze signal at the detection end, which is beneficial for achieving high-sensitivity detection, while also reducing the complexity of the polarization detection module.

[0082] Example 1: refer to Figures 3 to 7 The objective lens assembly 12 has a NA value of 0.965, corresponding to a maximum scattered light collection angle of 74°. The proportion of nonlinear modulation of the angle of the outgoing light scattered at various angles by the objective lens assembly 12 is shown in the figure. Figure 4 As shown, this effectively compresses large-angle scattered light into a smaller angular range. The objective lens assembly 12 provided in this embodiment may include a first lens, a second lens, a third lens, and a fourth lens arranged sequentially along the direction of light propagation. Each lens includes a front surface away from the mirror assembly 111 and a rear surface facing the mirror assembly 111. Table 1 provides relevant parameters of the objective lens assembly (including radius of curvature, thickness, and material). Of course, different combinations of objective lens assemblies are acceptable as long as they meet the required imaging requirements; no specific limitations are made here.

[0083] It should be noted that the thickness of each lens in Table 1 includes the distance between the apex of the front surface and the apex of the rear surface of the lens along the optical axis (i.e., 13.900 mm, 16.800 mm, 12.000 mm and 12.000 mm), as well as the center distance between adjacent lenses (i.e., 1.000 mm, 1.000 mm and 1.000 mm).

[0084] Table 1 Through the nonlinear compression of the objective lens assembly, all scattered light from the object side (0-74°) is directed to the surface of the optical thin film at an incident angle of approximately 25°-50°. Figure 5 As shown, the phase difference after passing through the optical thin film is all near π. The optical thin film has high reflectivity to make the amplitude (i.e., intensity) attenuation of S-polarized light and P-polarized light similar, thus outputting high-quality linearly polarized light. If the reflectivity of the two differs greatly, even if the phase difference is π, the degree of polarization of the output light will decrease. Furthermore, the polarization modulation effect of the mirror is as follows... Figure 6 and Figure 7 As shown, the polarization state of the first type of scattered light is modulated into a horizontal polarization state.

[0085] The aberration correction component 13 may include a first lens group and a second lens group arranged sequentially along the direction of light propagation. The first lens group may include four lenses arranged sequentially along the direction of light propagation, and the second lens group may include three lenses arranged sequentially along the direction of light propagation. The focal length ratio of the first lens group and the second lens group may be 4:1. This helps to correct the aberration of the light to be detected and also helps to reduce the pupil (i.e., the diameter of the beam cross section) to 25mm.

[0086] Table 2 shows the relevant parameters (including radius of curvature, thickness, and material) of the aberration correction component in this embodiment. Each lens in the first and second lens groups can include a front surface near the mirror assembly 111 and a rear surface away from the mirror assembly 111. Of course, the aberration correction component can also include other lens groups, as long as certain imaging requirements can be achieved; no specific limitation is made here.

[0087] It should be noted that the thickness of each lens in Table 2 includes the distance between the apex of the front surface and the apex of the rear surface along the optical axis (i.e., 5.749 mm, 15.551 mm, 5.082 mm, 11.739 mm, 9.429 mm, 4.671 mm and 12.731 mm), as well as the center distance between adjacent lenses (i.e., 10.713 mm, 0.937 mm, 8.059 mm, 69.366 mm, 3.292 mm and 10.227 mm).

[0088] Table 2 Example 2: refer to Figures 8 to 11 The difference between this embodiment and Embodiment 1 is that the NA value of the objective lens assembly 12 is 0.85, corresponding to a maximum scattered light collection angle of 58°. The polarization modulation effect of the reflector assembly 111 is as follows: Figure 9 and Figure 10 As shown, the polarization state of the first type of scattered light S1 is modulated into a horizontal polarization state.

[0089] The objective lens assembly 12 provided in this embodiment may include a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged sequentially along the direction of light propagation. Each lens includes a front surface away from the mirror assembly 111 and a rear surface facing the mirror assembly 111. Table 3 shows the relevant parameters of the objective lens assembly in this embodiment (including radius of curvature, thickness, and material). Of course, the objective lens assembly can also be implemented with other lens groups, as long as the required imaging requirements can be met; no specific limitation is made here.

[0090] It should be noted that the thickness of each lens in Table 3 includes the distance between the apex of the front surface and the apex of the rear surface along the optical axis (i.e., 10.828 mm, 10.291 mm, 18.449 mm, 19.536 mm, 19.890 mm and 22.410 mm), as well as the center distance between adjacent lenses (i.e. 0.867 mm, 1.010 mm, 3.525 mm, 6.736 mm and 0.749 mm).

[0091] Table 3 The two sets of lenses in the aberration correction assembly 13 are used to correct aberrations exiting from the large pupil. The corrected wavefront, such as... Figure 11 As shown. The aberration correction component 13 of this embodiment may include a first lens group and a second lens group arranged sequentially along the direction of light propagation, wherein the first lens group may include two lenses arranged sequentially along the direction of light propagation, and the second lens group may include two lenses arranged sequentially along the direction of light propagation.

[0092] Table 4 shows the relevant parameters (including radius of curvature, thickness, and material) of the aberration correction component in this embodiment. Each lens in the first and second lens groups can include a front surface near the mirror assembly 111 and a rear surface away from the mirror assembly 111. Of course, the aberration correction component can also include other lens groups, as long as certain imaging requirements can be achieved; no specific limitation is made here.

[0093] It should be noted that the thickness of each lens in Table 4 includes the distance between the apex of the front surface and the apex of the rear surface of the lens along the optical axis (i.e., 10.828 mm, 10.291 mm, 18.449 mm and 19.536 mm), as well as the center distance between adjacent lenses (i.e., 0.867 mm, 1.010 mm and 3.525 mm).

[0094] Table 4 Example 3: refer to Figures 12 to 15 The difference between this embodiment and Embodiment 1 is that the NA value of the objective lens assembly 12 is 0.9, corresponding to a maximum scattered light collection angle of 64.15°. The objective lens assembly 12 provided in this embodiment may include a first lens, a second lens, and a third lens arranged sequentially along the direction of light propagation. Each lens includes a front surface away from the mirror assembly 111 and a rear surface facing the mirror assembly 111. Table 5 shows the relevant parameters of the objective lens assembly in this embodiment (including radius of curvature, thickness, and material). Of course, the objective lens assembly can also be implemented with other lens groups, as long as the required imaging requirements are met; no specific limitations are made here.

[0095] Table 5 The reflector is a plane reflector, and the angle of the optical thin film designed with the central axis of symmetry modulates the scattering polarization state of the full pupil.

[0096] The polarization modulation effect of mirror 1111 is as follows Figure 14 and Figure 15 As shown, the polarization state of the first type of scattered light S1 is modulated to a near-horizontal state. Although it is not as completely corrected to a linear polarization state as in Example 1, it effectively reduces the difficulty of engineering and implementation.

[0097] The aberration correction component 13 of this embodiment may include a first lens group and a second lens group arranged sequentially along the direction of light propagation. The first lens group may include four lenses arranged sequentially along the direction of light propagation, and the second lens group may include three lenses arranged sequentially along the direction of light propagation. The focal length ratio of the first lens group and the second lens group may be 2:1. This helps to correct the aberrations of the light to be detected and also helps to compress the size of the beam (i.e., the diameter of the beam cross-section). Moreover, the aberration correction component 13 of this embodiment is designed with a real focal point position so that filtering processing can be performed at the focal point later.

[0098] Furthermore, aberration correction components can also be made using combinations of different numbers of lenses, as long as the detection requirements are met. For example, if high accuracy is required for detection, the aberration correction component can include a more complex lens group to improve accuracy. Of course, if high accuracy is not required for detection, the aberration correction component can include a simpler lens group; no specific limitations are made here.

[0099] Table 6 provides the relevant parameters (including radius of curvature, thickness, and material) of the aberration correction component in this embodiment. Each lens in the first and second lens groups may include a front surface near the mirror assembly 111 and a rear surface away from the mirror assembly 111. Of course, the aberration correction component may also include other lens groups, as long as certain imaging requirements can be achieved; no specific limitation is made here.

[0100] It should be noted that the thickness of each lens in Table 6 includes the distance between the apex of the front surface and the apex of the rear surface along the optical axis (i.e., 35.0009 mm, 35.000 mm, 5.082 mm, 11.739 mm, 9.429 mm, 8.000 mm, and 12.731 mm), as well as the center distance between adjacent lenses (i.e., 10.713 mm, 0.937 mm, 8.059 mm, 69.366 mm, 3.292 mm, and 10.227 mm).

[0101] Table 6 It should be noted that the technical features described in the above embodiments can be freely combined without contradicting each other. For example, the off-axis mirror scheme can be used with different objective lens designs, and the plane mirror scheme can be applied to systems with different numerical apertures. The specific number of lenses in the objective lens assembly, the specific materials and number of layers of the optical thin film, and the composition of the aberration correction components can all be varied and selected under the guidance of the core concept of this application.

[0102] It is understood that the objective lens assembly 12 may include four to six lenses. By reasonably allocating the optical power of each lens, using aspherical lenses, and optimizing the spacing between the lenses, a nonlinear mapping relationship can be achieved between the angle of the outgoing light and the incident angle of the scattered light. The lens materials can be optical materials suitable for the deep ultraviolet band, such as fused silica and calcium fluoride. The angle modulation function can be fitted by a polynomial, the details of which are not elaborated here.

[0103] Exemplary optical inspection equipment: refer to Figure 2 , Figure 3 , Figure 8 and Figure 12Based on the aforementioned optical collection device 100, one embodiment of this application provides an optical detection device 300, which may include the optical collection device 100 and a polarization detection component 200. The polarization detection component 200 may be located behind the optical path of the optical collection device 100. The polarization detection component 200 may include a polarization beam splitting module 210, which can be used to separate a first type of scattered light and a second type of scattered light in the light to be detected. The first type of scattered light S1 is generated by the roughness of the surface of the object to be detected, and the second type of scattered light S2 is generated by the defects of the surface of the object to be detected. The polarization beam splitting module 210 includes a polarization beam splitting element 211 and a corresponding detector 212.

[0104] In one example, the polarization detection assembly 200 may further include a sub-aperture beam splitter 220 (SABS), located in front of the polarization beam splitter 210. The SABS receives light after passing through the aberration correction assembly and separates wide / narrow channels. This can be achieved, for example, by designing different ratios between the aperture of the light-transmitting and reflecting mirrors. Alternatively, different annular regions (corresponding to different scattering angle ranges) can be used to separate the emitted light into different detection channels. Each channel is then equipped with a polarization beam splitter 210 to separate the second type of scattered light signal. The specific form of the sub-aperture beam splitter 220 can also be varied, for example, by using a combination of partial reflecting mirrors, diffractive optical elements, or microlens arrays with a beam splitter.

[0105] The optical inspection device 300 may further include a light source assembly for illuminating the surface of the wafer to generate second-type scattered light S2. For example, the light source assembly may be a laser to generate laser light that illuminates the surface of the wafer. Thus, the laser light is incident on the wafer surface at an oblique angle, generating light to be detected S0, which includes first-type and second-type scattered light. The light to be detected S0 is collected by the objective lens assembly, which compresses the scattered light at different angles at specific angles and guides it to the optical thin film of the mirror assembly. The polarization states of the compressed scattered light at different incident angles are modulated, wherein a certain type of scattered light is modulated to the same polarization state. The modulated light to be detected is reflected to an aberration correction assembly, which corrects the residual aberrations in the preceding optical path, enabling a plane wave to be emitted into the sub-aperture beam splitter 220 in the polarization detection assembly 200. This allows light rays at different scattered angles to be split into corresponding polarization detection channels, and then signal detection is performed in different detection channels by the polarization beam splitter 210.

[0106] In addition, each functional unit or module in the various embodiments of this application can be integrated into one processing unit or module, or each unit or module can exist physically separately, or two or more units or modules can be integrated into one unit or module.

[0107] It is understood that in this application, directional descriptions such as "upper," "lower," "inner," and "outer" are relative rather than absolute. These directional terms may be applicable when the optical collecting device provided in this application is positioned according to the posture and location shown in the accompanying drawings.

[0108] It should be understood that although terms such as "first" or "second" may be used in this application to describe various elements (such as first type of scattered light and second type of scattered light), these elements are not limited by these terms, which are only used to distinguish one element from another.

[0109] The basic principles of this application have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential features of each embodiment of this application. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the application to the necessity of employing the aforementioned specific details for implementation.

[0110] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this application to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

[0111] The components and devices described in this application are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the accompanying drawings. As those skilled in the art will recognize, these components and devices can be connected, arranged, and configured in any manner.

[0112] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An optical collection device for dark field detection, characterized in that, include: An optical collection component is used to collect light to be detected generated by the surface of an object to be detected. The light to be detected includes a first type of scattered light and a second type of scattered light. The first type of scattered light is generated by the roughness of the surface of the object to be detected, and the second type of scattered light is generated by defects on the surface of the object to be detected. The optical collection component includes a polarization modulation component, which is configured to modulate the polarization state of the light to be detected to increase the difference in polarization state between the first type of scattered light and the second type of scattered light.

2. The optical collection device according to claim 1, characterized in that, The polarization modulation assembly includes a mirror assembly, which includes a mirror and an optical thin film disposed on the surface of the mirror. The optical thin film is configured to modulate the polarization state of the light to be detected, and the direction of the equivalent fast axis of the optical thin film changes with the light to be detected. The optical film is also configured to introduce a phase delay to the incident first type of scattered light and the second type of scattered light within a specific angular range, so that the phase values ​​of the emitted first type of scattered light and the second type of scattered light after passing through the optical film are controlled within a preset range.

3. The optical collection device according to claim 2, characterized in that, The preset range includes values ​​greater than or equal to 0 and less than or equal to π.

4. The optical collection device according to claim 3, characterized in that, The preset range includes values ​​greater than or equal to 0.9π and less than or equal to π.

5. The optical collection device according to claim 2, characterized in that, The mirror assembly includes an axisymmetric off-axis mirror.

6. The optical collection device according to claim 2, characterized in that, The optical collection assembly includes an objective lens assembly, which is used to receive the light to be detected and guide it to the mirror assembly.

7. The optical collection device according to claim 6, characterized in that, The objective lens assembly is configured to modulate the angle of the light to be detected, such that the incident angles of the modulated first type of scattered light and the second type of scattered light satisfy a specific angle range and illuminate the mirror assembly.

8. The optical collection device according to claim 7, characterized in that, The surface shape of the reflector is configured to match the angle modulation function of the objective lens assembly, such that the incident angles of the modulated first type of scattered light and the second type of scattered light satisfy the specific angle range.

9. The optical collection device according to claim 7, characterized in that, The local radius of curvature of the surface of the reflector is matched with the angle modulation function of the objective lens assembly so that the incident angles of the modulated first type of scattered light and the second type of scattered light satisfy the specific angle range.

10. The optical collection device according to claim 8 or 9, characterized in that, The angle modulation function of the objective lens assembly is configured to perform nonlinear angle compression on the first type of scattered light and the second type of scattered light, wherein the compression ratio of the light to be detected at a larger angle is greater than the compression ratio of the light to be detected at a smaller angle.

11. The optical collection device according to claim 1, characterized in that, Both the first type of scattered light and the second type of scattered light are linearly polarized light.

12. The optical collection device according to claim 1, characterized in that, The optical collection device further includes an aberration correction component, which is disposed behind the optical path of the polarization modulation component and is used to correct the wavefront aberrations of the modulated second type of scattered light and the first type of scattered light.

13. The optical collection device according to any one of claims 1 to 10, characterized in that, The polarization modulation assembly sequentially includes an objective lens assembly and a mirror assembly. The mirror assembly includes a mirror and an optical thin film disposed on the surface of the mirror. The optical thin film is configured to modulate the polarization state of the incident light, and the direction of the equivalent fast axis of the optical thin film changes with the incident angle. Furthermore, the optical thin film is configured to introduce a phase delay into the incident light to be detected within a specific angular range, so that the phase values ​​of the first type of scattered light and the second type of scattered light emitted after passing through the optical thin film are controlled to be greater than or equal to 0.9π and less than or equal to π. The surface shape of the reflector is configured to match the angle modulation function of the objective lens assembly so that the incident angle of the modulated light to be detected satisfies the specific angle range. The angle modulation function of the objective lens assembly is further configured to perform nonlinear angle compression on the first type of scattered light and the second type of scattered light, wherein the compression ratio of the light to be detected at a larger angle is greater than the compression ratio of the light to be detected at a smaller angle.

14. An optical inspection device for wafer inspection, characterized in that, The optical inspection device includes an optical collection device and a polarization detection component as described in any one of claims 1 to 13. The polarization detection component is located behind the optical path of the optical collection device. The polarization detection component includes a polarization beam splitting module, which is used to separate a first type of scattered light and a second type of scattered light in the light to be inspected. The first type of scattered light is generated by the roughness of the surface of the object to be inspected, and the second type of scattered light is generated by the defects on the surface of the object to be inspected.

15. The optical inspection device according to claim 14, characterized in that, The optical inspection equipment also includes a light source assembly for illuminating the surface of the wafer to generate the second type of scattered light.

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