Focusing method and focusing system

Abstract

The invention provides a focusing method and a focusing system, the focusing method is applied to the focusing system, a characteristic interference spectrum corresponding to a to-be-measured target is obtained, the characteristic interference spectrum comprises a plurality of reference interference spectrums, and different reference interference spectrums correspond to different defocusing amounts of a to-be-measured sample deviating from a front focal plane of a measurement objective lens. The reference interference spectrum is used for identifying the spectral intensity corresponding to each wavelength; when the to-be-detected sample is configured in the light path, a first interference spectrum is collected through a spectrum collection device, and the first interference spectrum is used for identifying the spectral intensity corresponding to each wavelength; based on the matching degree of the feature interference spectrum and the first interference spectrum, determining the target defocusing amount of the to-be-detected sample; and adjusting the distance between the to-be-measured sample and the measuring objective lens based on the target defocusing amount, so that the to-be-measured sample is located at the front focal plane of the measuring objective lens. According to the invention, rapid and high-precision focusing can be realized, the time consumption of single focusing is greatly shortened, and the focusing efficiency is improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor detection, and in particular to a focusing method and a focusing system. Background Art

[0002] In optical measurement equipment, microscopic imaging is usually used to optically image the sample to be measured. The sample to be measured is, for example, a wafer. This requires that the sample to be measured be at the front focal plane of the objective lens in order to obtain a clear imaging result. In image-based overlay measurement equipment, in order to ensure high-precision focusing, Linnik interferometry is usually used to detect the relative distance between the sample to be measured and the objective lens in real time. In related technologies, when focusing on the mark to be measured on the sample to be measured, the distance between the mark to be measured and the objective lens needs to be gradually adjusted for each mark to be measured. Single focusing takes a long time, and fast focusing cannot be achieved. Summary of the Invention

[0003] In view of this, the purpose of this application is to provide a focusing method and focusing system that can achieve fast and high-precision focusing, greatly shorten the time consumed by a single focusing, and improve focusing efficiency. The specific scheme is as follows:

[0004] On the one hand, the present application provides a focusing method, which is applied to a focusing system, wherein the focusing system includes a light source, a beam splitter, a reference objective lens, a reference reflector, a measurement objective lens, and a spectrum acquisition device; a sample to be measured is used to be arranged on the light-emitting side of the measurement objective lens, and the sample to be measured has a target to be measured;

[0005] The beam splitter is used to split the light emitted by the light source into a reference beam propagating toward the optical path where the reference objective lens is located, and a measuring beam propagating toward the optical path where the measuring objective lens is located; the spectrum acquisition device is used to acquire an interference spectrum formed between the reference beam reflected by the reference reflector and the measuring beam reflected by the target to be measured; the method includes:

[0006] Acquire a characteristic interference spectrum corresponding to the target to be measured, wherein the characteristic interference spectrum includes a plurality of reference interference spectra, wherein different reference interference spectra correspond to different defocus amounts of the sample to be measured from the front focal plane of the measuring objective lens, and the reference interference spectrum is used to identify the spectral intensity corresponding to each wavelength;

[0007] When the sample to be tested is arranged in the optical path, a first interference spectrum is collected by the spectrum collection device, where the first interference spectrum is used to identify the spectral intensity corresponding to each wavelength;

[0008] determining a target defocus amount of the sample to be tested based on a matching degree between the characteristic interference spectrum and the first interference spectrum;

[0009] The distance between the sample to be measured and the measuring objective lens is adjusted based on the target defocus amount, so that the sample to be measured is located at the front focal plane of the measuring objective lens.

[0010] Optionally, before obtaining the characteristic interference spectrum corresponding to the target to be measured, the method further includes:

[0011] Determining a reference target that satisfies target similarity conditions with the target to be measured; the reference target is located on a reference sample;

[0012] When the reference sample is arranged in the optical path, adjusting the defocus amount of the reference sample from the front focal plane of the measuring objective lens, and collecting, by the spectrum collection device, a reference interference spectrum formed between the reference beam reflected by the reference reflector and the measuring beam reflected by the reference target at each defocus amount;

[0013] The plurality of reference interference spectra are used as the characteristic interference spectra corresponding to the target to be measured.

[0014] Optionally, the target similarity condition is that the degree of similarity between the marking patterns of the target to be measured and the reference target is greater than a preset degree of similarity, and / or the difference between the depth of the target to be measured in the sample to be measured and the depth of the reference target in the reference sample is less than a preset difference.

[0015] Optionally, determining a target defocus amount of the sample to be tested based on a matching degree between the characteristic interference spectrum and the first interference spectrum includes:

[0016] calculating a matching score between each of the reference interference spectra in the characteristic interference spectrum and the first interference spectrum;

[0017] The defocus amount corresponding to the reference interference spectrum with the highest matching score is used as the target defocus amount of the sample to be tested.

[0018] Optionally, when the first interference spectrum includes a plurality of first interference spectra, determining the target defocus amount of the sample to be tested based on the matching degree between the characteristic interference spectrum and the first interference spectrum includes:

[0019] determining a target interference spectrum based on a plurality of said first interference spectra;

[0020] The target defocus amount of the sample to be tested is determined based on the matching degree between the characteristic interference spectrum and the target interference spectrum.

[0021] Optionally, before determining the target defocus amount of the sample to be tested based on the matching degree between the characteristic interference spectrum and the first interference spectrum, the method further includes:

[0022] Adjusting the distance between the measuring objective lens and the sample to be measured, and collecting a second interference spectrum through the spectrum collection device, wherein the second interference spectrum is used to identify the spectral intensity corresponding to each wavelength;

[0023] The determining a target defocus amount of the sample to be tested based on a matching degree between the characteristic interference spectrum and the first interference spectrum includes:

[0024] The target defocus amount corresponding to the sample to be measured is determined based on a first matching degree between the characteristic interference spectrum and the first interference spectrum, and a second matching degree between the characteristic interference spectrum and the second interference spectrum.

[0025] Optionally, determining the target defocus amount corresponding to the sample to be tested based on a first matching degree between the characteristic interference spectrum and the first interference spectrum, and a second matching degree between the characteristic interference spectrum and the second interference spectrum, includes:

[0026] determining a maximum matching degree from the first matching degree and the second matching degree;

[0027] The defocus amount of the reference interference spectrum corresponding to the maximum matching degree is used as the target defocus amount corresponding to the sample to be tested.

[0028] On the other hand, an embodiment of the present application further provides a focusing system, comprising a light source, a beam splitter, a reference objective lens, a reference reflector, a measurement objective lens, and a spectrum acquisition device; the reference reflector is disposed on the light-emitting side of the reference objective lens, a sample to be measured is disposed on the light-emitting side of the measurement objective lens, and the sample to be measured has a target to be measured;

[0029] The beam splitter is used to split the light emitted by the light source into a reference beam propagating toward the optical path where the reference objective lens is located, and a measuring beam propagating toward the optical path where the measuring objective lens is located, and is used to combine the reference beam reflected by the reference reflector and the measuring beam reflected by the target to be measured;

[0030] The spectrum acquisition device is used to acquire an interference spectrum formed between the reference light beam reflected by the reference reflector and the measurement light beam reflected by the target to be measured.

[0031] Optionally, the spectrum collection device is a spectrometer, or the spectrum collection device includes a dispersion element and a photodetector array located on the light-emitting side of the dispersion element.

[0032] Optionally, the focusing system further includes an optical fiber, one end of which is connected to the spectrum acquisition device, and the other end of which is used to collect the reference beam reflected by the reference reflector and the measurement beam reflected by the target to be measured.

[0033] The embodiment of the present application provides a focusing method and a focusing system, the focusing method is applied to the focusing system, the focusing system includes a light source, a beam splitter, a reference objective lens, a reference reflector, a measuring objective lens and a spectrum acquisition device; the sample to be measured is used to be arranged on the light-emitting side of the measuring objective lens, and the sample to be measured has a target to be measured; the beam splitter is used to split the light emitted by the light source into a reference beam propagating toward the optical path where the reference objective lens is located, and a measuring beam propagating toward the optical path where the measuring objective lens is located, and the spectrum acquisition device is used to collect the interference spectrum formed between the reference beam reflected by the reference reflector and the measuring beam reflected by the target to be measured; the method includes: obtaining the sample to be measured A characteristic interference spectrum corresponding to the target, the characteristic interference spectrum includes multiple reference interference spectra, different reference interference spectra correspond to different defocus amounts of the sample to be tested from the front focal plane of the measuring objective lens, and the reference interference spectrum is used to identify the spectral intensity corresponding to each wavelength; when the sample to be tested is configured in the optical path, a first interference spectrum is collected by a spectrum collection device, and the first interference spectrum is used to identify the spectral intensity corresponding to each wavelength; based on the matching degree of the characteristic interference spectrum and the first interference spectrum, the target defocus amount of the sample to be tested is determined; based on the target defocus amount, the distance between the sample to be tested and the measuring objective lens is adjusted so that the sample to be tested is located at the front focal plane of the measuring objective lens.

[0034] In an embodiment of the present application, by obtaining in advance the reference interference spectra corresponding to the sample to be measured and the measuring objective lens at different distances, that is, by vertically scanning the Linnik interference optical path in advance, each time the target to be measured is focused, it is only necessary to obtain the first interference spectrum corresponding to the target to be measured and the measuring objective lens at the current distance. By comparing the interference spectra, the defocus amount corresponding to the target to be measured at the current position can be quickly determined. In this way, by adjusting the distance between the sample to be measured and the measuring objective lens based on the defocus amount, fast and high-precision focusing can be achieved, which greatly shortens the time consumed in a single focusing and improves the focusing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 A schematic diagram of a focusing system provided by an embodiment of the present application is shown;

[0037] Figure 2 A schematic diagram of another focusing system provided by an embodiment of the present application is shown;

[0038] Figure 3A schematic diagram of a focusing method according to an embodiment of the present application is shown;

[0039] Figure 4 A schematic diagram of a characteristic interference spectrum provided by an embodiment of the present application is shown;

[0040] Figure 5 A schematic diagram of a first interference spectrum provided in an embodiment of the present application is shown;

[0041] Figure 6 A schematic diagram of a matching score provided in an embodiment of the present application is shown.

[0042] Reference numerals

[0043] Light source 101 , beam splitter 102 , reference objective lens 103 , reference reflector 104 , measurement objective lens 105 , spectrum acquisition device 106 , sample to be measured 107 , dispersion element 108 , photodetector array 109 . DETAILED DESCRIPTION

[0044] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below with reference to the accompanying drawings.

[0045] In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0046] For ease of understanding, a focusing method and a focusing system provided in an embodiment of the present application are described in detail below with reference to the accompanying drawings.

[0047] refer to Figure 1 FIG2 is a schematic diagram of a focusing system provided in an embodiment of the present application, wherein the focusing system includes a light source 101, a beam splitter 102, a reference objective lens 103, a reference reflector 104, a measurement objective lens 105, and a spectrum acquisition device 106. The optical path in the focusing system is a Linnik optical path.

[0048] Beam splitter 102 is used to split the light emitted by light source 101 into a reference beam that propagates along the optical path of reference objective lens 103 and a measuring beam that propagates along the optical path of measurement objective lens 105. In other words, the light emitted by light source 101 is split into two beams by beam splitter 102: one is the reference beam that is incident on reference objective lens 103, and the other is the measuring beam that is incident on measurement objective lens 105.

[0049] A reference reflector 104 is disposed on the light-exiting side of the reference objective lens 103. The reference beam is incident on the reference reflector 104 and reflected by the reference reflector 104, passing through the reference objective lens 103 and the beam splitter 102 again. A sample 107 is disposed on the light-exiting side of the measurement objective lens 105. The sample 107 is a sample to be inspected, such as a wafer. Before inspecting the sample 107, the sample 107 must be positioned at the front focal plane of the measurement objective lens 105. This application focuses on how to quickly and accurately position the sample 107 at the front focal plane of the measurement objective lens 105 to achieve rapid focusing. The subsequent process of inspecting the sample 107 will not be further elaborated.

[0050] A target to be measured is provided on the sample 107. The shape of the target to be measured is not limited herein and may be, for example, a cross, square, or circle. Focusing on the sample 107 primarily refers to focusing on each target to be measured on the sample 107. As an example, the target to be measured may be an overlay mark having two layers of marks, which are used to measure the alignment accuracy between the two layers of patterns on the sample 107.

[0051] The beam splitter 102 is also used to combine the reference light beam reflected by the reference reflector 104 and the measurement light beam reflected by the target to be measured. That is, the reference light beam reflected by the reference reflector 104 will enter the beam splitter 102 again, and the measurement light beam reflected by the target to be measured on the sample to be measured 107 will also enter the beam splitter 102 again. The beam splitter 102 is used to combine these two beams of light into one beam of light.

[0052] Spectrum acquisition device 106 is used to collect the interference spectrum formed between the reference beam reflected by reference reflector 104 and the measurement beam reflected by the target. Specifically, the light beams combined by beam splitter 102 enter spectrum acquisition device 106, whereupon spectrum acquisition device 106 can collect the interference spectrum formed by the interference between the reference beam and the measurement beam. By comparing the interference spectra, the target can be quickly focused.

[0053] In a possible implementation, the spectrum collection device 106 is a spectrometer, or the spectrum collection device 106 includes a dispersion element 108 and a photodetector array 109 located on the light-emitting side of the dispersion element 108 .

[0054] In other words, a spectrometer can be used as the spectrum acquisition device 106 to acquire interference spectra, facilitating the acquisition of interference spectra. Furthermore, since the spectrometer's internal components are integrated, the spectrometer can be easily moved when adjusting the position of the spectrum acquisition device 106. Furthermore, the spectrometer's low cost can reduce the overall cost of the focusing system. Furthermore, the system composed of the spectrometer is less complex, making adjustments easier for technicians.

[0055] In addition, the interference spectrum can also be collected using the dispersion element 108 and the photodetector array 109. The dispersion element 108 is, for example, a prism, a grating, etc. The photodetector array 109 is an array structure composed of multiple photoelectric detectors (PDs). After the light emitted from the beam splitter 102 passes through the dispersion element 108, the light of different wavelengths is separated and then enters the photodetector array 109, so that the photodetector array 109 can distinguish signals of different wavelengths. The photodetector array 109 can collect the interference spectrum.

[0056] Thus, when the dispersion element 108 and the photodetector array 109 are used as the spectrum acquisition device 106, the sampling rate of the photodetector is much greater than that of the spectrometer, which further shortens the data acquisition time and enables faster acquisition of the interference spectrum, thereby improving the focusing speed. Furthermore, the number of photodetectors in the photodetector array 109 can be freely set based on demand, enabling customization. If a sufficiently fast focusing speed is required, the focusing speed can be increased by increasing the number of photodetectors; if a slower focusing speed is required, the number of photodetectors can be reduced. Furthermore, the number of photodetectors can be increased or decreased at any time during the focusing process based on actual needs, enhancing the flexibility of the focusing system.

[0057] refer to Figure 2 FIG. 1 is a schematic diagram of another focusing system provided by an embodiment of the present application. The light emitted from the beam splitter 102 passes through the dispersion element 108 and enters the photodetector array 109 to collect the interference spectrum. In addition, if a spectrometer is used as the spectrum collection device 106, then Figure 2 The photodetector array 109 is moved out of the optical path, and the position of the dispersion element 108 is replaced by a spectrometer.

[0058] In one possible implementation, spatial light can be directly used to be incident on the spectrum collection device 106 , that is, the light emitted from the beam splitter 102 directly enters the spectrum collection device 106 without adding other components, and the complexity of the focusing system is relatively low.

[0059] In order to achieve miniaturization of the optical path in the focusing system, in one possible implementation, the focusing system may also include an optical fiber, one end of which is connected to the spectrum acquisition device 106, and the other end of the optical fiber is used to collect the reference beam reflected by the reference reflector 104 and the measurement beam reflected by the target to be measured.

[0060] That is, the reference beam reflected by the reference reflector 104 and the measurement beam reflected by the target are combined by the beam splitter 102 and then enter the optical fiber. The optical fiber is connected to the spectrum collection device 106, so that the light beam can enter the spectrum collection device 106 through the optical fiber. In this way, the spectrum collection device 106 does not need to be fixed in the optical path. The spectrum collection device 106 can be set at any position and the interference spectrum can be collected through the optical fiber. For example, the spectrum collection device 106 can be further away from the optical path, thereby reducing the space occupied by the optical path of the focusing system and making the optical path more compact.

[0061] refer to Figure 3 As shown, it is a flow chart of a focusing method provided in an embodiment of the present application, which is applied to the aforementioned focusing system, wherein the focusing system includes a light source 101, a beam splitter 102, a reference objective lens 103, a reference reflector 104, a measuring objective lens 105 and a spectrum acquisition device 106; a sample to be measured 107 is used to be arranged on the light-emitting side of the measuring objective lens 105, and the sample to be measured 107 has a target to be measured; the beam splitter 102 is used to split the light emitted by the light source 101 into a reference beam propagating toward the optical path where the reference objective lens 103 is located, and a measuring beam propagating toward the optical path where the measuring objective lens 105 is located, and the spectrum acquisition device 106 is used to collect the reference beam reflected by the reference reflector 104 and the interference spectrum formed between the measuring beam reflected by the target to be measured. The method may include the following steps.

[0062] S101, obtaining a characteristic interference spectrum corresponding to the target to be measured.

[0063] Specifically, a characteristic interference spectrum corresponding to the target to be measured may be obtained. The characteristic interference spectrum is an interference spectrum formed by interference between the measurement beam reflected by the target to be measured and the reference beam reflected by the reference reflector 104 .

[0064] The characteristic interference spectrum can include multiple reference interference spectra, each corresponding to a different defocus of the sample 107 from the front focal plane of the measurement objective lens 105. That is, a reference interference spectrum will be generated for each instance of the characteristic interference spectrum. For example, when the defocus of the sample 107 from the measurement objective lens 105 is f1, one reference interference spectrum will be generated, while when the defocus is f2, another reference interference spectrum will be generated. The reference interference spectra are subsequently used as a reference for comparison of the interference spectra.

[0065] The reference interference spectrum is used to identify the spectral intensity corresponding to each wavelength. That is, in the reference interference spectrum, the horizontal axis can represent the wavelength and the vertical axis can represent the spectral intensity. The reference interference spectrum can reflect the spectral intensity at each wavelength.

[0066] refer to Figure 4 Figure 1 is a schematic diagram of a characteristic interference spectrum provided by an embodiment of the present application. The horizontal axis represents the defocus, the vertical axis represents the wavelength, and the grayscale represents the spectral intensity. When the defocus is 0, it means that the target to be measured is exactly located at the front focal plane of the measurement objective lens 105.

[0067] Next, the acquisition process of the characteristic interference spectrum is described.

[0068] In a possible implementation, before S101 of acquiring a characteristic interference spectrum corresponding to the target to be measured, the method may further include S201 to S203.

[0069] S201, determining a reference target that meets target similarity conditions with the target to be measured.

[0070] The reference target is located on the reference sample. The reference sample and the sample to be measured 107 can be the same sample or different samples, as long as the reference target and the target to be measured meet the target similarity condition. Because the reference target and the target to be measured are sufficiently similar, the reference interferometer spectrum obtained by vertically scanning the reference target can also be considered the reference interferometer spectrum corresponding to the target to be measured.

[0071] In actual applications, the reference sample can be the same sample as the sample to be tested 107. In this case, the reference target and the target to be tested are different marks on the same sample to be tested 107. For example, the reference target is the mark located in area A on the sample to be tested 107, and the target to be tested is the mark located in area B on the sample to be tested 107. The two marks meet the target similarity condition.

[0072] Of course, the reference sample can also be a different sample from the sample to be tested 107. For example, the reference sample is wafer 1 and the sample to be tested 107 is wafer 2. The two wafers are the same, so the reference target and the target to be tested also meet the target similarity condition.

[0073] In one possible implementation, the target similarity condition may be that the degree of similarity between the marking patterns of the target to be measured and the reference target is greater than a preset degree of similarity, and / or that the difference between the depth of the target to be measured in the sample to be measured 107 and the depth of the reference target in the reference sample is less than a preset difference.

[0074] In other words, the target similarity condition can be based on a similarity condition for the marking patterns. If the degree of similarity between the marking patterns of the target to be measured and the reference target is high, greater than a preset similarity, then the target to be measured and the reference target meet the target similarity condition. As an example, the reference target and the target to be measured that meet the target similarity condition can be exactly the same, for example, both having a cross pattern. In another example, the reference target and the target to be measured that meet the target similarity condition can also be substantially identical, for example, the reference target has a rounded square pattern, while the target to be measured has a right-angled square pattern.

[0075] In addition, the target similarity condition can also be a similarity condition based on the mark depth. If the depth of the target to be measured in the sample to be measured 107 is not much different from the depth of the reference target in the reference sample, and is less than the preset difference, it means that the target to be measured and the reference target meet the target similarity condition.

[0076] For example, if the target to be measured is overlay mark I and the reference target is overlay mark II, then if overlay mark I is located in layers 1 and 2 of the sample to be measured 107, and overlay mark II is located in layers 1 and 2 of the reference sample, and the film thicknesses of the reference sample and the sample to be measured 107 are the same, then the two marks are considered to meet the target similarity condition. If overlay mark II is located in layers 2 and 3 of the reference sample, then the two marks are considered to not meet the target similarity condition, and the reference interferometer spectrum corresponding to overlay mark II cannot be used as the reference interferometer spectrum corresponding to overlay mark I for subsequent comparison.

[0077] In this way, by setting the target to be measured and the reference target to meet at least one of the conditions of similar marking patterns and similar marking depths, the marking consistency of the target to be measured and the reference target is improved, thereby improving the accuracy of the reference interference spectrum corresponding to the target to be measured.

[0078] S202, when the reference sample is arranged in the optical path, the defocus amount of the reference sample from the front focal plane of the measuring objective lens 105 is adjusted, and at each defocus amount, the spectrum acquisition device 106 collects the reference interference spectrum formed between the reference light beam reflected by the reference reflector 104 and the measuring light beam reflected by the reference target.

[0079] That is to say, a reference interference spectrum formed by a reference target on a reference sample can be collected. Specifically, the reference sample can be placed on the light-emitting side of the measuring objective lens 105. When the sample to be measured 107 deviates from the front focal plane of the measuring objective lens 105 by a certain defocus amount, that is, when the sample to be measured 107 is at a certain distance from the measuring objective lens 105, the reference interference spectrum corresponding to the defocus amount is collected by an interference collection device, and the defocus amount is continuously changed to obtain multiple reference interference spectra.

[0080] In short, the Linnik interferometer optical path can be scanned vertically, and the distance between the reference sample and the measuring objective lens 105 can be continuously adjusted to change the defocus amount of the reference sample from the front focal plane of the measuring objective lens 105, so that the spectrum acquisition device 106 can acquire reference interference spectra at various defocus amounts. By synthesizing multiple reference interference spectra, the following can be obtained: Figure 4 Characteristic interference spectrum shown.

[0081] S203 , using the multiple reference interference spectra as characteristic interference spectra corresponding to the target to be measured.

[0082] Since the reference target on the reference sample and the target to be measured on the sample to be measured 107 meet the target similarity condition, it means that the reference interference spectrum corresponding to the reference target is sufficiently similar to the reference interference spectrum corresponding to the target to be measured. The reference interference spectrum corresponding to the reference target can be used as the reference interference spectrum corresponding to the target to be measured, thereby obtaining the characteristic interference spectrum.

[0083] In this way, by obtaining the reference interference spectra corresponding to each defocus amount in a vertical scanning manner, a plurality of reference interference spectra can be obtained quickly and accurately, which are used as a basis for subsequent interference spectrum comparison.

[0084] S102 , when the sample to be tested 107 is arranged in the optical path, a first interference spectrum is collected by the spectrum collection device 106 .

[0085] When focusing on the sample to be measured 107, the sample to be measured 107 can be located in the optical path, specifically on the light-emitting side of the measuring objective lens 105. Interference occurs between the measuring beam reflected back by the target to be measured on the sample to be measured 107 and the reference beam reflected back by the reference reflector 104, and a first interference spectrum is obtained by collecting it through the spectrum collection device 106.

[0086] The first interference spectrum is used to identify the spectral intensity corresponding to each wavelength, that is, the spectral intensity corresponding to each wavelength can be reflected in the first interference spectrum. Figure 5 , which is a schematic diagram of a first interference spectrum provided in an embodiment of the present application, wherein the horizontal axis is the wavelength and the vertical axis is the spectrum intensity.

[0087] S103 , determining a target defocus amount of the sample to be tested 107 based on a matching degree between the characteristic interference spectrum and the first interference spectrum.

[0088] Because the defocus amount of the sample 107 under test from the measurement objective lens 105 is unknown—that is, it is unknown whether the sample 107 under test is located at the front focal plane of the measurement objective lens 105—it is necessary to compare the first interference spectrum acquired at the current position of the sample 107 under test with the characteristic interference spectrum corresponding to the target under test. The characteristic interference spectrum already reflects the reference interference spectrum corresponding to each defocus amount. Therefore, by comparing the first interference spectrum with each reference interference spectrum, the target defocus amount of the sample 107 under test can be determined. The target defocus amount is the defocus amount corresponding to the reference interference spectrum that is consistent with the first interference spectrum.

[0089] S104 , adjusting the distance between the sample to be measured 107 and the measuring objective lens 105 based on the target defocus amount, so that the sample to be measured 107 is located at the front focal plane of the measuring objective lens 105 .

[0090] After determining the target defocus amount of the sample to be tested 107 from the measuring objective lens 105, the distance between the sample to be tested 107 and the measuring objective lens 105 can be adjusted along the optical axis based on the target defocus amount. For example, the sample to be tested 107 can be moved or the measuring objective lens 105 can be moved so that the sample to be tested 107 is located at the front focal plane of the measuring objective lens 105 to achieve rapid focusing.

[0091] In an embodiment of the present application, by obtaining reference interference spectra corresponding to different distances between the sample to be tested 107 and the measuring objective lens 105 in advance, that is, by pre-scanning the Linnik interferometer optical path vertically, each time the target to be tested is focused, it is only necessary to obtain the first interference spectrum corresponding to the target to be tested and the measuring objective lens 105 at the current distance. By comparing the interference spectra, the defocus amount corresponding to the target to be tested at the current position can be quickly determined. Compared to the vertical scanning process required when focusing each target to be tested, the present application does not need to adjust the distance between the sample to be tested 107 and the measuring objective lens 105 multiple times. It is only necessary to collect the first interference spectrum at the current position and compare the first interference spectrum with multiple reference interference spectra collected in advance to obtain the defocus amount. In this way, adjusting the distance between the sample to be tested 107 and the measuring objective lens 105 based on the defocus amount can achieve fast and high-precision focusing, greatly shortening the time consumed by a single focusing, and improving focusing efficiency.

[0092] In practical applications, when a single test sample 107 has multiple similar markers to be tested, using the method provided in this application to focus on each marker to be tested, only the first marker to be tested needs to be vertically scanned to obtain a characteristic interference spectrum. The remaining markers to be tested can then use this characteristic interference spectrum for spectral comparison, eliminating the need to waste time performing vertical scanning. This significantly improves the focusing efficiency for multiple markers to be tested. Furthermore, for the same type of test sample 107, this characteristic interference spectrum can be reused, eliminating the need to determine a characteristic interference spectrum for each test sample 107, thereby improving the focusing efficiency for batches of test samples 107.

[0093] In a possible implementation, S103 determines a target defocus amount of the sample to be tested 107 based on a matching degree between the characteristic interference spectrum and the first interference spectrum, including S1031 - S1032 .

[0094] S1031 , calculating a matching score between each reference interference spectrum in the characteristic interference spectrum and the first interference spectrum.

[0095] Specifically, since the characteristic interference spectrum includes multiple reference interference spectra, and both the reference interference spectra and the first interference spectrum reflect the correspondence between wavelength and spectral intensity, the matching score between each reference interference spectrum and the first interference spectrum can be calculated. The matching score is used to measure the degree of match between the reference interference spectrum and the first interference spectrum. The higher the matching score, the greater the degree of match and the more similar the two are. In this way, the matching score of the reference interference spectrum corresponding to each defocus value can be obtained.

[0096] As an example, refer to Figure 6 As shown, this is a schematic diagram of a matching score provided in an embodiment of the present application. The horizontal axis is the defocus amount, and the vertical axis is the matching score. There is a corresponding matching score at each defocus amount, and the defocus amount corresponding to a higher matching score is approximately in the range of -500nm to 500nm.

[0097] In addition, the numerical range of the matching score is not limited here, for example, 0-1. When the matching score is 1, it means that the first interference spectrum is most matched with the reference interference spectrum.

[0098] S1032 , taking the defocus amount corresponding to the reference interference spectrum with the highest matching score as the target defocus amount of the sample to be tested 107 .

[0099] Specifically, for the reference interference spectrum with the highest matching score, the degree of match between the reference interference spectrum and the first interference spectrum is the greatest, so the defocus amount corresponding to the reference interference spectrum can be used as the target defocus amount of the sample to be measured 107. As an example, the defocus amount corresponding to the reference interference spectrum with the highest matching score is 20 nm, indicating that the sample to be measured 107 deviates from the front focal plane of the measurement objective lens 105 by 20 nm at its current position.

[0100] In order to improve the signal-to-noise ratio of spectral acquisition and improve focusing accuracy, in a possible implementation, when the first interference spectrum includes multiple, S103 determines the target defocus amount of the sample to be tested 107 based on the matching degree between the characteristic interference spectrum and the first interference spectrum, which can specifically include S1033-S1034.

[0101] S1033 : Determine a target interference spectrum based on the multiple first interference spectra.

[0102] That is, when the sample to be tested 107 is placed in the optical path, multiple first interference spectra can be acquired by the spectrum acquisition device 106. That is, multiple first interference spectra can be acquired at the same position. For example, five first interference spectra can be acquired five times. The multiple first interference spectra are processed to obtain a target interference spectrum. For example, they can be averaged. This can reduce noise in the target interference spectrum and improve the signal-to-noise ratio of the target interference spectrum. In other words, the target interference spectrum can more accurately reflect the interference spectrum obtained when the sample to be tested 107 is at the current position.

[0103] S1034 , determining a target defocus amount of the sample to be tested 107 based on the matching degree between the characteristic interference spectrum and the target interference spectrum.

[0104] Specifically, the matching degree between the target interference spectrum and each reference interference spectrum may be calculated, thereby obtaining the target defocus amount of the sample to be tested 107 .

[0105] In this way, since the target interference spectrum is more accurate, accurate matching can be achieved, and the target defocus value obtained is also more accurate, achieving accurate focusing. In short, by acquiring multiple first interference spectra at a single location, the signal-to-noise ratio of the spectrum acquisition can be improved, thereby improving focusing accuracy.

[0106] In order to further improve the focusing accuracy, in one possible implementation, before S103 determines the target defocus amount of the sample to be tested 107 based on the matching degree of the characteristic interference spectrum and the first interference spectrum, the method may further include S105, adjusting the distance between the measuring objective lens 105 and the sample to be tested 107, and collecting a second interference spectrum through the spectrum acquisition device 106, the second interference spectrum being used to identify the spectral intensity corresponding to each wavelength; then S103 determines the target defocus amount of the sample to be tested 107 based on the matching degree of the characteristic interference spectrum and the first interference spectrum, and may include S1035, determining the target defocus amount corresponding to the sample to be tested 107 based on the first matching degree of the characteristic interference spectrum and the first interference spectrum, and the second matching degree of the characteristic interference spectrum and the second interference spectrum.

[0107] Specifically, not only can the first interference spectrum be acquired at the current position of the sample 107 under test, but the distance between the sample 107 under test and the measuring objective lens 105 can also be adjusted to acquire a second interference spectrum at other positions. The other positions can be one or more, and thus the second interference spectrum can be one or more. In other words, the first interference spectrum and the second interference spectrum are multiple interference spectra acquired at different positions.

[0108] Furthermore, when performing interference spectrum matching, not only the first matching degree between the first interference spectrum and each reference interference spectrum can be calculated, but also the matching degree between the second interference spectrum and each reference interference spectrum can be calculated. Based on multiple matching degrees, the target defocus amount corresponding to the sample to be tested 107 can be obtained.

[0109] In this way, multiple interference spectra are collected at multiple positions, and each interference spectrum is matched and compared with the characteristic interference spectrum, so that more spectral information can be integrated for matching, exchanging time for accuracy, and further improving the focusing accuracy.

[0110] In one possible implementation, S1035 determines the target defocus amount corresponding to the sample to be tested 107 based on a first matching degree between the characteristic interference spectrum and the first interference spectrum, and a second matching degree between the characteristic interference spectrum and the second interference spectrum, and may include determining a maximum matching degree from the first matching degree and the second matching degree; and using the defocus amount of the interference spectrum corresponding to the maximum matching degree as the target defocus amount corresponding to the sample to be tested 107.

[0111] Specifically, when comparing multiple interference spectra with the characteristic interference spectrum and obtaining a first matching degree and a second matching degree, the maximum matching degree can be determined from the first matching degree and the second matching degree. The reference interference spectrum corresponding to the maximum matching degree is most similar to the collected interference spectrum, so the defocus amount of the interference spectrum corresponding to the maximum matching degree can be used as the target defocus amount corresponding to the sample 107 to be tested.

[0112] As an example, if the maximum matching score (first matching degree) obtained by matching the first interference spectrum with multiple reference interference spectra is 0.8, and the maximum matching score (second matching degree) obtained by matching the second interference spectrum with multiple reference interference spectra is 1, the defocus amount corresponding to 1 point can be used as the target defocus amount, so that the sample to be measured 107 is located at the front focal plane of the measurement objective lens 105. In this way, determining the target defocus amount based on the maximum matching degree can further improve focusing accuracy.

[0113] The various embodiments in this specification are described in a progressive manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences from the other embodiments. In particular, the device embodiments are generally similar to the method embodiments, so the description is relatively simple. For relevant parts, refer to the description of the method embodiments.

[0114] The above is only a preferred embodiment of the present application. Although the present application has been disclosed as a preferred embodiment, it is not intended to limit the present application. Any technician familiar with the art can use the above-disclosed methods and technical contents to make many possible changes and modifications to the technical solution of the present application without departing from the scope of the technical solution of the present application, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application are still within the scope of protection of the technical solution of the present application.

Claims

1. A focusing method, characterized in that: Applied to a focusing system, the focusing system includes a light source, a beam splitter, a reference objective lens, a reference reflector, a measuring objective lens and a spectrum acquisition device; the sample to be measured is used to be arranged on the light-emitting side of the measuring objective lens, and the sample to be measured has a target to be measured; The beam splitter is used to split the light emitted by the light source into a reference beam propagating toward the optical path where the reference objective lens is located, and a measuring beam propagating toward the optical path where the measuring objective lens is located; the spectrum acquisition device is used to acquire an interference spectrum formed between the reference beam reflected by the reference reflector and the measuring beam reflected by the target to be measured; the method includes: Acquire a characteristic interference spectrum corresponding to the target to be measured, wherein the characteristic interference spectrum includes a plurality of reference interference spectra, wherein different reference interference spectra correspond to different defocus amounts of the sample to be measured from the front focal plane of the measuring objective lens, and the reference interference spectrum is used to identify the spectral intensity corresponding to each wavelength; When the sample to be tested is arranged in the optical path, a first interference spectrum is collected by the spectrum collection device, where the first interference spectrum is used to identify the spectral intensity corresponding to each wavelength; determining a target defocus amount of the sample to be tested based on a matching degree between the characteristic interference spectrum and the first interference spectrum; The distance between the sample to be measured and the measuring objective lens is adjusted based on the target defocus amount, so that the sample to be measured is located at the front focal plane of the measuring objective lens.

2. The method according to claim 1, characterized in that Before obtaining the characteristic interference spectrum corresponding to the target to be measured, the method further includes: Determining a reference target that satisfies target similarity conditions with the target to be measured; the reference target is located on a reference sample; When the reference sample is arranged in the optical path, adjusting the defocus amount of the reference sample from the front focal plane of the measuring objective lens, and collecting, by the spectrum collection device, a reference interference spectrum formed between the reference beam reflected by the reference reflector and the measuring beam reflected by the reference target at each defocus amount; The plurality of reference interference spectra are used as the characteristic interference spectra corresponding to the target to be measured.

3. The method according to claim 2, characterized in that The target similarity condition is that the similarity between the marking patterns of the target to be measured and the reference target is greater than a preset similarity, and / or the difference between the depth of the target to be measured in the sample to be measured and the depth of the reference target in the reference sample is less than a preset difference.

4. The method according to claim 1, wherein The determining a target defocus amount of the sample to be tested based on a matching degree between the characteristic interference spectrum and the first interference spectrum includes: calculating a matching score between each of the reference interference spectra in the characteristic interference spectrum and the first interference spectrum; The defocus amount corresponding to the reference interference spectrum with the highest matching score is used as the target defocus amount of the sample to be tested.

5. The method according to claim 1, characterized in that When the first interference spectrum includes a plurality of first interference spectra, determining the target defocus amount of the sample to be tested based on the matching degree between the characteristic interference spectrum and the first interference spectrum includes: determining a target interference spectrum based on a plurality of said first interference spectra; The target defocus amount of the sample to be tested is determined based on the matching degree between the characteristic interference spectrum and the target interference spectrum.

6. The method according to claim 1, wherein Before determining the target defocus amount of the sample to be tested based on the matching degree between the characteristic interference spectrum and the first interference spectrum, the method further includes: Adjusting the distance between the measuring objective lens and the sample to be measured, and collecting a second interference spectrum by the spectrum collection device, wherein the second interference spectrum is used to identify the spectral intensity corresponding to each wavelength; The determining a target defocus amount of the sample to be tested based on a matching degree between the characteristic interference spectrum and the first interference spectrum includes: The target defocus amount corresponding to the sample to be measured is determined based on a first matching degree between the characteristic interference spectrum and the first interference spectrum, and a second matching degree between the characteristic interference spectrum and the second interference spectrum.

7. The method according to claim 6, characterized in that The determining the target defocus amount corresponding to the sample to be tested based on a first matching degree between the characteristic interference spectrum and the first interference spectrum, and a second matching degree between the characteristic interference spectrum and the second interference spectrum, includes: determining a maximum matching degree from the first matching degree and the second matching degree; The defocus amount of the reference interference spectrum corresponding to the maximum matching degree is used as the target defocus amount corresponding to the sample to be tested.

8. A focusing system, characterized in that: The focusing system includes a light source, a beam splitter, a reference objective lens, a reference reflector, a measuring objective lens, and a spectrum acquisition device; the reference reflector is arranged on the light-emitting side of the reference objective lens, the sample to be measured is arranged on the light-emitting side of the measuring objective lens, and the sample to be measured has a target to be measured; The beam splitter is used to split the light emitted by the light source into a reference beam propagating toward the optical path where the reference objective lens is located, and a measuring beam propagating toward the optical path where the measuring objective lens is located, and is used to combine the reference beam reflected by the reference reflector and the measuring beam reflected by the target to be measured; The spectrum acquisition device is used to acquire an interference spectrum formed between the reference light beam reflected by the reference reflector and the measurement light beam reflected by the target to be measured.

9. The focusing system according to claim 8, wherein: The spectrum collection device is a spectrometer, or the spectrum collection device includes a dispersion element and a photodetector array located on the light-emitting side of the dispersion element.

10. The focusing system according to claim 8, wherein: The focusing system further includes an optical fiber, one end of which is connected to the spectrum acquisition device, and the other end of which is used to collect the reference beam reflected by the reference reflector and the measurement beam reflected by the target to be measured.

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