Focusing control method and system, detection equipment and storage medium

Abstract

The invention relates to the technical field of optical detection, in particular to a focusing control method and system, detection equipment and a storage medium. The focusing control is realized by acquiring the mass center coordinate difference between the light spot corresponding to the real-time detection light beam and the standard light spot / monitoring light spot, determining the defocusing amount of the light spot based on the mass center coordinate difference, determining the oblique incidence angle adjustment amount through the defocusing amount, and adjusting the oblique incidence angle based on the oblique incidence angle adjustment amount. Focusing can be rapidly and accurately achieved, and meanwhile the size and the shape of a light spot can be monitored.

Description

Technical Field

[0001] The present invention relates to the field of optical detection technology, and in particular to a focus control method, system, detection equipment and storage medium. Background Art

[0002] In integrated circuit manufacturing, wafers need to be inspected through optical inspection. The lighting module in the optical inspection equipment is usually developed based on the inspection needs and the overall machine architecture. The commonly used light source is laser, which needs to be shaped or propagated through optical devices to form a light spot.

[0003] The current existing technology is to emit oblique light to the wafer surface and then reflect it to the four-quadrant sensor by a mirror, and determine the defocus amount by detecting the differential calculation results of the energy occupied by the light spot in the four quadrants. The focusing detection optical path of this method cannot detect the shape and size of the light spot. In the current device for detecting wafer defects based on the principle of optical scattering, it is often necessary to detect the shape and size of the light spot while focusing. Therefore, only using a four-quadrant detector cannot meet the current need to simultaneously detect the spot size and focus. Summary of the invention

[0004] In view of this, in order to solve the above technical problems, an object of the present invention is to provide a focus control method, system, detection equipment and storage medium, which can realize the control of focus during the detection process.

[0005] In a first aspect, an embodiment of the present invention provides a focus control method, the method comprising: obtaining a real-time light spot after a detection beam passes through an optical element, and a characteristic position of the real-time light spot; the detection beam is an oblique incident beam; comparing the position difference between this characteristic position and a standard characteristic position, and obtaining a defocus amount based on the position difference; determining an incident angle adjustment amount of the detection beam based on the defocus amount and a preset incident angle-defocus relationship, and adjusting the angle of the incident light based on the incident angle adjustment amount.

[0006] In some specific implementations, the standard feature position is determined based on a current scanning stroke of the detection light beam.

[0007] In another embodiment, a focus control method is also provided, the method comprising: obtaining two characteristic positions corresponding to a first light spot and a second light spot after the detection light beam passes through an optical element; the first light spot is a light spot formed when the detection light beam is obliquely incident on the surface of the object to be measured after passing through the optical element, and the second light spot is a light spot formed when the detection light beam is vertically incident on the surface of the object to be measured; obtaining a position difference between the first light spot and the second light spot, and obtaining a defocus amount based on the position difference; determining an incident angle adjustment amount of the oblique incident light based on the defocus amount and a preset incident angle-defocus relationship, and adjusting the angle of the oblique incident light based on the oblique incident angle adjustment amount.

[0008] In some specific implementations, the characteristic position is the centroid coordinate of the light spot, and the position difference is the centroid coordinate difference.

[0009] In some specific implementations, the method further includes: correcting the defocus amount based on a correction parameter to obtain a target defocus amount; the correction parameter is obtained by performing a linear fitting method on multiple defocus amounts.

[0010] In some specific implementations, the defocus amount is obtained based on the position difference, incident parameters and imaging parameters, the incident parameters include the incident angle of the incident light, and the imaging parameters include a magnification parameter and a pixel size.

[0011] In some specific implementations, obtaining the centroid coordinates includes: extracting effective pixels based on the grayscale distribution of the light spot, determining an effective pixel range based on the distribution of effective pixels, and obtaining the centroid coordinates of the light spot based on the effective pixel range.

[0012] In a second aspect, a focus control system is provided, comprising: an optical element, wherein a detection light beam forms a spot image after passing through the optical element; a position difference calculation module, which determines the position difference of the light spot based on the spot image; and a processing module, which adjusts the incident angle of the detection light beam passing through the optical element based on the position difference.

[0013] In some specific implementations, the optical element includes an incident element and a receiving element, the detection light beam forms a light spot through the incident element, and the receiving element is used to receive reflected light of the light spot and form a light spot image.

[0014] In some specific implementations, the incident element includes at least one angle-adjustable reflector, and the incident angle of the detection light beam is adjusted by the reflector.

[0015] In some specific implementations, the receiving element includes an imaging lens and a sensor, and the imaging lens is configured with a magnification.

[0016] In some specific implementations, the incident element includes a first incident element and a second incident element, and at least one angle-adjustable reflector is provided in the first incident element, and the detection light beam forms oblique incident light to the surface of the object to be measured through the reflector; the detection light beam forms vertical incident light to the surface of the object to be measured through the second incident element.

[0017] In some specific implementations, the processing module includes a defocus calculation module and a query module, the defocus calculation module calculates the defocus based on the position difference, and the query module determines the incident angle adjustment amount of the detection light beam based on the defocus.

[0018] In some specific implementations, the processing module is configured with an incident angle-defocus relationship table, and the query module determines the incident angle adjustment amount of the detection light beam based on the incident angle-defocus relationship table.

[0019] According to a third aspect, a detection device is provided, comprising: a light source for generating a detection light beam; and a focus control system as described in any one of the above items.

[0020] In a fourth aspect, a computer-readable storage medium is provided, on which a program is stored, and the program can be executed by a processor to implement the focus control method as described in any one of the above items.

[0021] The embodiments of the present invention bring the following beneficial effects:

[0022] The embodiments of the present invention provide a focus control method, system, detection device and storage medium, which obtain the centroid coordinate difference between the light spot corresponding to the real-time detection beam and the standard light spot / monitoring light spot, determine the defocus amount of the light spot through the centroid coordinate difference, determine the oblique incident angle adjustment amount through the defocus amount, and adjust the oblique incident angle based on the oblique incident angle adjustment amount, thereby realizing focus control. It can focus quickly and accurately while monitoring the size and shape of the light spot.

[0023] Other features and advantages of the present disclosure will be set forth in the following description, or some features and advantages may be inferred or unambiguously determined from the description, or may be learned by implementing the above-mentioned technology of the present disclosure.

[0024] In order to make the above-mentioned objectives, features and advantages of the present disclosure more obvious and easy to understand, preferred embodiments are specifically cited below and described in detail with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] The methods, systems and / or programs in the accompanying drawings will be further described according to exemplary embodiments. These exemplary embodiments will be described in detail with reference to the drawings. These exemplary embodiments are non-limiting exemplary embodiments, wherein example numbers represent similar mechanisms in the various views of the accompanying drawings.

[0027] Figure 1 It is a schematic diagram of light spot deviation in the prior art;

[0028] Figure 2 A schematic diagram of the focus control system structure provided in Example 1;

[0029] Figure 3 A schematic diagram of the focus control method flow provided in Example 1;

[0030] Figure 4 A schematic diagram of the focus control system structure provided in Example 2;

[0031] Figure 5 A schematic flow chart of a focus control method provided in Embodiment 2;

[0032] Figure 6 A schematic diagram of the focus control system structure provided in Example 3;

[0033] Figure 7 A schematic diagram of the shaping result of the shaping component provided in Example 3;

[0034] Figure 8 A schematic diagram of a defocus amount-angle adjustment amount table provided in this embodiment;

[0035] Fig. 9 is a schematic diagram of focusing results in this embodiment;

[0036] Fig.10 A schematic diagram of the readable medium structure provided for this embodiment. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The device for detecting wafer defects based on the principle of optical scattering requires oblique illumination. In actual scenarios, the position of the light spot may deviate on the surface of the wafer to be tested due to the unevenness of the wafer or the tolerance and strain of the inclined light path.

[0039] In order to solve the above technical problems, it is necessary to adjust the height of the wafer to be tested to eliminate the deviation of the spot position during the actual detection process. Among them, an equidistant spiral scanning method is adopted for the detection of the wafer to be tested. The wafer to be tested is placed on a high-speed rotating table, and the wafer is driven to rotate by the high-speed rotation of the high-speed rotating table, thereby realizing the scanning of equidistant spiral lines. However, because the turntable speed of the rotating table set in this way is relatively high and the carrier has a large weight in general design to ensure the stability of the rotation, resulting in a large load on the carrier. Therefore, the speed of adjusting the wafer height cannot match the high-speed turntable, resulting in delayed adjustment and failure to achieve the effect of timely elimination of the spot deviation.

[0040] Therefore, based on this technical background, the present embodiment provides a focus control method, which eliminates the position deviation of the light spot by controlling the incident angle of the detection beam. Compared with the wafer height adjustment in the prior art, adjusting the incident angle of the detection beam is more accurate and controllable.

[0041] Wherein, for the present embodiment, "wafer" generally refers to a substrate formed of semiconductor or non-semiconductor materials. Examples include (but are not limited to) single crystal silicon, gallium arsenide, gallium nitride, and indium phosphide. Such substrates are typically found and / or processed in semiconductor manufacturing facilities. In some cases, a wafer may include only a substrate (i.e., a bare die). Alternatively, a wafer may include one or more layers of different materials formed on a substrate. One or more layers formed on a wafer may be "patterned" or "unpatterned". For example, a wafer may include multiple dies with repeatable pattern features.

[0042] In this embodiment, a detection device is first provided, which includes at least a light source and a focus control system, wherein the light source is used to generate a detection beam and may be a laser; the focus control system is used to perform focus control on the detection beam so that a light spot formed by the detection beam on the surface of the wafer to be tested has no deviation.

[0043] Among them, for the detection equipment in this embodiment, especially the light source, there are two configuration modes. The first configuration mode is to configure only one detection beam, and according to the wafer detection principle, for both bright field detection and dark field detection, at least one oblique incident detection beam is required, and the detector receives the reflected light or scattered light formed by the light spot. Therefore, the detection beam in the first configuration mode should be an oblique incident beam. The second configuration mode is to configure a normal incident beam, that is, a detection beam that is perpendicular to the wafer to be tested, on the basis of configuring an oblique incident beam.

[0044] Wherein, for the first configuration mode, the deviation of the light spot formed on the surface of the wafer to be tested should be the deviation between the current position of the light spot and the standard position.

[0045] In the second configuration, since normal incidence will not cause spot deviation due to wafer height changes, the spot deviation in the second configuration should be the deviation between the spot formed by the oblique incident detection beam and the spot formed by the normal incident detection beam. Figure 1 This is a schematic diagram of the light spot deviation caused by height change. Figure 1 It can be seen that when the height of the wafer to be measured is generated, the light spot formed by the oblique incident detection beam moves from position A to position B, while the light spot formed by the normal incident detection beam does not change.

[0046] Therefore, in this embodiment, in view of the above two different configurations of the detection light beams, two corresponding focus control systems are provided in this embodiment, which are described in detail based on the first embodiment and the second embodiment.

[0047] Embodiment 1

[0048] See also Figure 2 , a focus control system 20 including only an oblique incident detection beam is provided, wherein the system comprises:

[0049] The optical element 21 in this embodiment is used to allow the detection light beam to pass through, form a real-time light spot when incident on the surface of the wafer to be tested, and receive scattered light / reflected light generated by the real-time light spot to form a light spot image.

[0050] The position difference calculation module 22, in this embodiment, is used for determining the position difference of the light spot according to the light spot image.

[0051] The calculation of the position difference in this embodiment is performed based on the deviation of the characteristic position of the real-time light spot and the standard light spot.

[0052] The processing module 23 adjusts the incident angle of the detection light beam passing through the optical element based on the position difference.

[0053] The needle detection light beam is generated by a light source 10, namely a laser.

[0054] In this embodiment, the optical element 21 includes an incident element 211 and a receiving element 212, wherein the incident element is used to pass a detection light beam to make the detection light beam incident on the surface of the wafer to be tested to form a light spot. The receiving element is used to receive the scattered light / reflected light generated by the light spot and form a corresponding light spot image.

[0055] Specifically, the receiving element 212 includes an imaging lens 2121 and a sensor 2122 , wherein the imaging lens has a specific magnification M, and the sensor is preferably a TDI line sensor, wherein the TDI line sensor has a specific pixel size D, and 8um≦D / M≦20um.

[0056] In this embodiment, the characteristic position refers to the centroid coordinates of the light spots, and the corresponding position difference is the centroid coordinate difference between the two light spots.

[0057] Among them, the real-time spot is the spot formed and collected on the surface of the wafer to be tested during the scanning process of the detection beam, while the standard spot is not the spot collected during the current scanning process. This spot is under ideal conditions, that is, standard wafer height, no adjustment tolerance and strain factor. Because the standard spot does not have the above-mentioned factors that affect the deviation of the spot formation, the characteristic position corresponding to the standard spot is the standard characteristic position.

[0058] In this embodiment, the focus control is implemented by comparing the characteristic position of the real-time light spot with the characteristic position of the standard light spot, namely, the center of mass coordinates, to determine whether the real-time light spot has a deviation and the corresponding center of mass coordinate difference. The defocus amount can be determined according to the center of mass coordinate difference, wherein the defocus amount is used to indicate the specific defocus result of the detection light beam, and finally the focus is adjusted according to the defocus amount.

[0059] Among them, as can be seen from the background technology introduction part, the scanning mode of the detection light beam during detection is equidistant spiral line scanning. And in order to ensure that no detection points are missed during the scanning process, the scanning path is fixed and unique, and the scanning time is also a standard fixed time based on the scanning speed and the area of ​​the wafer to be measured. Therefore, for each time point, the position of the detection light beam on the wafer surface should be fixed, which also means that the characteristic position of the light spot at each time point should also be fixed. Therefore, the determination of the standard characteristic position of the standard light spot can be determined based on the preset scanning path, scanning time point and scanning speed.

[0060] Therefore, the focus control system in this embodiment pre-stores standard feature position information corresponding to each time node. During the actual focus control process, the standard feature position information is retrieved according to the current time node in the real-time scanning process of the detection light beam.

[0061] Please refer again to Figure 2 , point A is the standard spot position, point B is the real-time spot position, is the standard spot image, and is the real-time spot image.

[0062] It is worth noting that the time point in this embodiment is a time node within a scanning cycle, which is a relative time concept. In addition, the standard light spot and the real-time light spot are light spots with the same shape, and their size and shape are the same, which can be pre-configured. The size and shape of the real-time light spot are determined based on the configuration at the beginning of the scan. If the size and shape of the light spot are changed during the scanning process, the characteristic position of the standard light spot will be updated according to the changed size and shape.

[0063] Specifically, the centroid coordinates of the real-time spot are determined based on the grayscale distribution within the effective pixel range, as shown in the following formula: , where m and n are the upper and lower boundaries of the effective pixels of the spot image, i.e., the effective pixel range, f(x) is the grayscale value of the real-time spot image, and x is the x-direction coordinate of the effective pixel. Therefore, the determination of the centroid coordinates requires the determination of the effective pixel range of the real-time spot image.

[0064] In this embodiment, the effective pixel range is extracted according to the calculated threshold value. The threshold value is determined based on the pixel peak grayscale value in the real-time spot image and the radius of the spot. Specifically, the above process first obtains the Gaussian distribution state and the pixel peak grayscale value of the real-time spot image, and determines the real-time spot radius according to the Gaussian spot radius definition, and finally determines the effective pixel range m and n based on the product of the real-time spot radius and the pixel peak grayscale value.

[0065] The standard feature position can be directly retrieved according to the current scanning time point, and this process will not be described in detail.

[0066] In the above process, the centroid coordinates corresponding to the real-time spot image and the centroid coordinates corresponding to the standard spot can be determined, and based on the above two centroid coordinates, the centroid coordinate difference between the two can be obtained, and whether the current detection beam is in a defocused state is determined by whether there is a centroid coordinate difference. However, it is worth noting that the centroid coordinate difference is the position deviation between the centroids of the spot image, which cannot be used as a reference for directly controlling the focus of the detection beam, so it is necessary to convert the centroid coordinate difference of the image into a defocus amount, and adjust the focus by the defocus amount, so as to solve the defocus problem.

[0067] As for the conversion of the defocus amount and the focus adjustment based on the defocus amount, it is implemented based on the processing module in this embodiment.

[0068] The conversion of the defocus amount is implemented by a defocus amount calculation module configured in the processing module, wherein the defocus amount calculation module calculates the defocus amount based on the position difference determined above.

[0069] Specifically, the acquisition of the real-time spot image is implemented based on a receiving element, wherein the receiving element includes an imaging lens and a sensor, wherein the imaging lens has a specific magnification M, and the sensor preferably selects a TDI line sensor, wherein the TDI line sensor has a pixel D of a specific size.

[0070] It can be seen that the imaging result of the real-time spot image is correlated with the magnification and pixel size. The magnification is used to enlarge the real-time spot image to a corresponding size, and the pixel size determines the size of the target surface, i.e., the imaging surface. Therefore, when restoring the defocus amount, the real-time spot size must be restored first. And because the real-time spot is formed by an oblique incident detection beam, and the oblique incident detection beam has an angle with the surface of the wafer to be measured, it is necessary to restore the focal length change caused by the incident angle of the oblique incident detection beam.

[0071] Specifically, the calculation of the defocus amount in this embodiment is determined based on the following formula: , where is the centroid coordinate difference, represents the angle of the detection light beam, and in this embodiment, this angle is the angle between the detection light beam and the orthogonal direction of the wafer to be measured.

[0072] Through the above process, the process of calculating the defocus amount based on the centroid coordinate difference can be realized, and the defocus amount of the detection light beam can be preliminarily determined through the above process.

[0073] However, it is worth noting that in actual optical systems there are magnification errors or angle errors, which can cause deviations between theoretical values ​​and actual measured values. Therefore, the defocus value determined by the above process cannot be used directly, and needs to be corrected based on correction parameters to eliminate the influence of system errors and obtain the target defocus value that can be used directly.

[0074] Among them, the correction parameters in this embodiment are determined by linear fitting of multiple defocus amounts in a simulation environment or a debugging experimental environment. Specifically, based on a pre-constructed simulation environment or debugging test environment, a standard gauge block is placed on the surface of the wafer for calibration testing. The thickness of the standard gauge block is Hd, and Hd is 1um, 2um, ..., n, and changes incrementally at equal intervals of 1um to obtain the defocus test results. The test results Z corresponding to the interval changes in the above-mentioned defocus acquisition method are Z1, Z2, ..., Zn. Then, multiple defocus test results are linearly fitted, and then correction and calibration are performed according to the linear equation of the gauge block to obtain the correction parameter R.

[0075] In this embodiment, the acquisition of the correction parameter R is a process before detection. In the actual detection process, the initial defocus amount corresponding to the real-time light spot is obtained, and then the initial defocus amount is updated based on the correction parameter R to obtain the target defocus amount:.

[0076] The acquired target defocus amount is used to indicate the defocus state of the current real-time light spot. In order to achieve defocus compensation, it can be seen from the calculation formula of the target defocus amount that it can be achieved by adjusting the incident angle of the detection light beam, that is, by adjusting the angle to make the target defocus amount 0, the defocus compensation is completed.

[0077] In order to adjust this angle, please refer to Figure 2 In this embodiment, the incident element includes at least one angle-adjustable reflector 2111, which is arranged on the optical path of the detection beam. The incident angle of the detection beam relative to the wafer to be measured is achieved by adjusting the angle of the reflector.

[0078] The determination of the angle adjustment amount of the reflector is implemented in this embodiment through a query module, in which a defocus amount-angle adjustment amount form is configured. For details about this form, please refer to Figure 8 The calculated target defocus amount is queried in this form by the table lookup method to obtain the angle adjustment amount corresponding to the current target defocus amount, and the incident angle is adjusted based on the angle control command fed back to the angle of the reflector until the target defocus amount is 0, completing the focusing.

[0079] For the distribution of the light spot after focusing, please refer to Fig. 9 As shown, through Fig. 9 It can be seen that the real-time light spot B and the standard light spot A are overlapped by changing the angle of the reflector, that is, by adjusting the angle.

[0080] See also Figure 3 In view of the focus control system provided in the first embodiment, a focus control method is also provided. The control method is applied to the position difference calculation module and the processing module, and specifically includes the following steps:

[0081] Step S31: Obtain the real-time light spot after the detection light beam passes through the optical element, and the characteristic position of the real-time light spot.

[0082] Step S32: Compare the position difference between the characteristic position and the standard characteristic position, and obtain the defocus amount based on the position difference.

[0083] Step S33: Determine the incident angle adjustment amount of the detection light beam based on the defocus amount and a preset incident angle-defocus relationship, and adjust the angle of the incident light based on the incident angle adjustment amount.

[0084] In this embodiment, the detection beam is an oblique incident beam, and the standard feature position is determined based on the current scanning stroke of the detection beam. The feature position and the standard feature position correspond to the center of mass coordinates of the real-time light spot and the center of mass coordinates of the standard light spot, respectively, and the position difference is the center of mass coordinate difference.

[0085] Embodiment 2

[0086] With respect to the first embodiment, the light source of the second embodiment is different from that of the first embodiment. The second embodiment adopts two light sources to form the first detection beam and the second detection beam respectively, wherein the first detection beam is an oblique incident beam, and the second detection beam is a normal incident beam, wherein the first detection beam is the same as the detection beam in the first embodiment, and the second detection beam will not be defocused due to the height change of the wafer stage because of its normal incidence. Therefore, in this embodiment, with respect to the normal incident beam as the monitoring beam, unlike the first embodiment, in the second embodiment, there is no need to introduce a standard light spot, and the second detection beam is used as the standard detection beam, and the light spot formed is a standard light spot.

[0087] For details, see Figure 4 , in accordance with the second embodiment, a focus control system 40 is provided, including:

[0088] The optical element 41 is used to form a spot image after the detection light beam passes through the optical element.

[0089] The position difference calculation module 42 determines the position difference of the light spot based on the light spot image.

[0090] The processing module 43 adjusts the incident angle of the detection light beam passing through the optical element based on the position difference.

[0091] The optical element includes an incident element 411 and a receiving element 412, wherein the receiving element is the same as that in the first embodiment, including an imaging lens 4121 and a sensor 4122, wherein the imaging lens has a specific magnification M, and the sensor is preferably a TDI line sensor, wherein the TDI line sensor has a pixel D of a specific size, and 8um≦D / M≦20um.

[0092] The difference from the first embodiment is that the incident element in this embodiment includes a first incident element 411 and a second incident element 412, wherein at least one angle-adjustable reflector 4111 is arranged in the first incident element, and the detection light beam is angled through the first incident element to the surface of the wafer to be measured to form a first light spot, and the second incident element is used to pass the normal incident detection light beam to the surface of the wafer to be measured to form a second light spot.

[0093] In the absence of defocus, the first light spot and the second light spot should be in an overlapping relationship. However, in the defocus situation, the first light spot and the second light spot do not overlap due to the change in wafer height.

[0094] Please refer again Figure 3 ,about Figure 3 Point A and point B in are the real-time spot positions at two different wafer heights, and are the real-time spot images corresponding to the real-time spots at the above two different wafer heights.

[0095] Therefore, relative to the first embodiment, the second light spot is the standard light spot in the first embodiment.

[0096] Among them, the position difference calculation module is different from the embodiment one in that the position difference calculation module in the embodiment one is used to calculate the position difference between the real-time light spot and the standard light spot, while the position difference calculation module in this embodiment introduces the normally incident detection beam, and its second light spot will not be defocused due to the change in wafer height, so the position difference calculation module in this embodiment is used to calculate the position difference between the first light spot and the second light spot.

[0097] Among them, this position difference is also the centroid coordinate difference. The specific calculation first adopts the centroid coordinate calculation method of embodiment 1 to sequentially obtain the first centroid coordinate and the second centroid coordinate corresponding to the first light spot image corresponding to the first light spot and the second light spot image corresponding to the second light spot, and calculate the coordinate difference between the two as the position difference.

[0098] The processing module in this embodiment has the same configuration as the processing module in Embodiment 1, including a defocus calculation module and a query module, wherein the defocus calculation module is used to calculate the defocus based on the position difference, and the query module determines the incident angle adjustment amount of the detection light beam based on the defocus, and adjusts the angle of the reflector in the first incident element based on the adjustment amount until the defocus is 0.

[0099] Therefore, for the focus control system provided in the second embodiment, a normal incident detection beam is also generated when an oblique incident detection beam is generated. This normal incident detection beam is a monitoring beam that forms a second light spot on the surface of the wafer to be tested. The second light spot replaces the standard light spot in the first embodiment. Because the normal incident detection beam is generated in real time, the control cost is low and only the light source needs to be controlled, and there will be no defocus due to changes in the wafer height. Therefore, the second light spot solves the technical difficulty and control cost of the need to set the standard light spot in advance and the need to accurately determine the standard light spot in the first embodiment. Therefore, the second embodiment is a preferred embodiment among the embodiments of this application.

[0100] For the focus control system in the second embodiment, a focus control method is also configured, which is applied to the position difference calculation module and the processing module, see Figure 5 , this method includes the following steps:

[0101] Step S51: Acquire two characteristic positions corresponding to the first light spot and the second light spot after the detection light beam passes through the optical element.

[0102] Step S52: Obtain a position difference between the first light spot and the second light spot, and obtain a defocus amount based on the position difference.

[0103] Step S53: determining an incident angle adjustment amount of the oblique incident light based on the defocus amount and a preset incident angle-defocus relationship, and adjusting the angle of the oblique incident light based on the oblique incident angle adjustment amount.

[0104] In this embodiment, the first light spot is a light spot formed when the detection light beam passes through the optical element and is obliquely incident on the surface of the object to be measured, and the second light spot is a light spot formed when the detection light beam is vertically incident, that is, normally incident on the surface of the object to be measured.

[0105] In the embodiments of the present application, two focus control systems are provided for Embodiment 1 and Embodiment 2. The above two systems obtain the centroid coordinate difference between the light spot corresponding to the real-time detection beam and the standard light spot / monitoring light spot, determine the defocus amount of the light spot through the centroid coordinate difference, determine the oblique incident angle adjustment amount through the defocus amount, and adjust the oblique incident angle based on the oblique incident angle adjustment amount, thereby achieving focus control.

[0106] Compared with the prior art, the embodiments of the present application can quickly obtain factors that affect the focusing accuracy of the light spot and achieve precise control of the focus.

[0107] Embodiment 3

[0108] In order to further control the size of the light spot, another focus control system is proposed based on the first and second embodiments. In this system, a shaping component is arranged on the detection beam path to control the size of the light spot.

[0109] For details, see Figure 6 For the convenience of explanation, the focus control system 60 is configured with a shaping component based on the focus control system in the first embodiment, but this does not mean that the shaping component can only be configured in the focus control system of the structure shown in the first embodiment.

[0110] The shaping component 64 includes a beam expander 641, a first cylindrical lens 642 and a second cylindrical lens 643 which are sequentially arranged along the propagation path of the detection beam. The beam expander is used to expand and collimate the detection beam, and the first cylindrical lens and the second cylindrical lens are used to form a real-time light spot with a target size.

[0111] Among them, the first cylindrical lens and the second cylindrical lens are a lens combination with different optical focal lengths, and the optical focal lengths of the first cylindrical lens and the second cylindrical lens are between 0.0001 and 0.01, and the relative distance between the first cylindrical lens and the second cylindrical lens can be adjusted. By adjusting the relative distance between the first cylindrical lens and the second cylindrical lens, the size change of the real-time light spot, especially the size change of the long side of the real-time light spot, can be achieved.

[0112] For details, please refer to Figure 7, is the corresponding relationship between the relative distance change between the first cylindrical lens and the second cylindrical lens and the change in the real-time spot size. Wherein, the relative distance L between the first cylindrical lens and the second cylindrical lens varies in the range of 1-12 mm, and within the above variation range, the long side of the real-time spot varies in the range of 50-380 um.

[0113] The relative distance change between the first cylindrical lens and the second cylindrical lens is achieved by setting a moving motor 644 on the above two lenses or any one of the lenses, wherein the above two lenses are moved relatively or any one of the lenses is moved.

[0114] Any of the above-mentioned focus control systems provided by the present invention can be applied to a detection device or a dark field defect detection device or a bright field defect detection device. In other words, the detection device includes a light source and the above-mentioned focus control system. The light source is used to generate and emit a detection light beam, which is shaped by an optical element to form a light spot A on the surface of the wafer to be tested. An image acquisition module such as a TDI camera obtains a light spot image and a light intensity characterization quantity for defect detection, and a processing module such as this processor detects and analyzes the light spot image and the light intensity characterization quantity to obtain detection results such as whether there is a defect and the defect location. As for the monitoring and correction of the light spot A by the detection device, it has been explained in detail in the above-mentioned embodiment of the focus control system and will not be repeated here.

[0115] See also Fig.10 An embodiment of the present invention provides a readable medium 10, which stores computer-readable instructions 101. The computer-readable instructions 101 include instructions for executing any one of the focus control methods in the first and second embodiments.

[0116] The functions and technical effects of the readable medium 10 provided in the embodiment of the present invention can refer to the technical effects of the focus control method in the above-mentioned embodiment 1 and embodiment 2, and will not be repeated here.

[0117] It should be noted that in the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and / or methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units / modules is only a logical function division. There may be other division methods in actual implementation, such as multiple units or modules can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0118] The units / modules described as separate components may or may not be physically separated, and the components shown as units / modules may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units / modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0119] In addition, each functional unit / module in each embodiment of the present invention may be integrated into one processing unit / module, or each unit / module may exist physically separately, or two or more units / modules may be integrated into one unit / module. The above-mentioned integrated unit / module may be implemented in the form of hardware or in the form of hardware plus software functional units / modules.

[0120] The above-mentioned integrated unit / module implemented in the form of a software functional unit / module can be stored in a computer-readable storage medium. The above-mentioned software functional unit is stored in a storage medium, including a number of instructions for causing one or more processors of a computer device (which can be a personal computer, a server, or a network device, etc.) to perform some steps of the method described in each embodiment of the present invention.

[0121] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A focus control method, characterized in that: The method comprises: Acquire a real-time light spot after the detection light beam passes through the optical element, and a characteristic position of the real-time light spot; the detection light beam is an oblique incident light beam; comparing a position difference between a characteristic position and a standard characteristic position, and obtaining a defocus amount based on the position difference; The incident angle adjustment amount of the detection light beam is determined based on the defocus amount and a preset incident angle-defocus relationship, and the angle of the incident light is adjusted based on the incident angle adjustment amount.

2. The focus control method according to claim 1, characterized in that: The standard feature position is determined based on a current scanning stroke of the detection light beam.

3. A focus control method, characterized in that: The method comprises: Acquire two characteristic positions corresponding to a first light spot and a second light spot after the detection light beam passes through the optical element; the first light spot is a light spot formed when the detection light beam is obliquely incident on the surface of the object to be measured after passing through the optical element, and the second light spot is a light spot formed when the detection light beam is vertically incident on the surface of the object to be measured; Acquire a position difference between the first light spot and the second light spot, and obtain a defocus amount based on the position difference; An incident angle adjustment amount of the oblique incident light is determined based on the defocus amount and a preset incident angle-defocus relationship, and an angle of the oblique incident light is adjusted based on the oblique incident angle adjustment amount.

4. The focus control method according to claim 1 or 3, characterized in that: The characteristic position is the centroid coordinate of the light spot, and the position difference is the centroid coordinate difference.

5. The focus control method according to claim 1 or 3, characterized in that: The method further includes: correcting the defocus amount based on a correction parameter to obtain a target defocus amount; the correction parameter is obtained by performing a linear fitting method on multiple defocus amounts.

6. The focus control method according to claim 4, characterized in that: The defocus amount is obtained based on the position difference, incident parameters and imaging parameters, the incident parameters include the incident angle of the incident light, and the imaging parameters include a magnification parameter and a pixel size.

7. The focus control method according to claim 4, characterized in that: Acquiring the centroid coordinates includes: extracting effective pixels based on the grayscale distribution of the light spot, determining an effective pixel range based on the distribution of the effective pixels, and acquiring the centroid coordinates of the light spot based on the effective pixel range.

8. A focus control system, characterized in that: include: An optical element, through which a detection light beam forms a light spot image; A position difference calculation module, which determines the position difference of the light spot based on the light spot image; A processing module is configured to adjust an incident angle of the detection light beam passing through the optical element based on the position difference.

9. The focus control system according to claim 8, characterized in that: The optical element comprises an incident element and a receiving element. The detection light beam forms a light spot through the incident element. The receiving element is used to receive reflected light of the light spot and form a light spot image.

10. The focus control system according to claim 9, characterized in that: The incident element includes at least one reflector with adjustable angle, and the incident angle of the detection light beam is adjusted by the reflector.

11. The focus control system according to claim 9, characterized in that: The receiving element includes an imaging lens and a sensor, and the imaging lens is configured with a magnification.

12. The focus control system according to claim 9, characterized in that: The incident element includes a first incident element and a second incident element. At least one angle-adjustable reflector is arranged in the first incident element. The detection light beam forms oblique incident light to the surface of the object to be measured through the reflector; the detection light beam forms vertical incident light to the surface of the object to be measured through the second incident element.

13. The focus control system according to claim 8, characterized in that: The processing module includes a defocus amount calculation module and a query module, the defocus amount calculation module calculates the defocus amount based on the position difference, and the query module determines the incident angle adjustment amount of the detection light beam based on the defocus amount.

14. The focus control system according to claim 13, characterized in that: The processing module is provided with an incident angle-defocus relationship table, and the query module determines the incident angle adjustment amount of the detection light beam based on the incident angle-defocus relationship table.

15. A detection device, characterized in that: include: a light source for generating a detection light beam; A focus control system as claimed in any one of claims 8 to 14.

16. A computer-readable storage medium, characterized in that: The medium stores a program, and the program can be executed by a processor to implement the focus control method according to any one of claims 1 to 7.

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