Automatic focusing method and device, equipment, storage medium and program product

Abstract

The invention discloses an automatic focusing method and device, equipment, a storage medium and a program product, and relates to the technical field of optical interference measurement, and the automatic focusing method comprises the steps: obtaining interference signals generated by the interference of a first light beam and a second light beam at preset time intervals, calculating the defocusing amount of the imaging microscope objective based on the interference signal set and the wavefront phase difference, and carrying out the automatic focusing of the imaging microscope objective based on the defocusing amount and the depth of field of the imaging microscope objective; according to the invention, errors caused by different objective lenses are eliminated by calculating the wavefront phase difference in advance, so that the precision of automatic focusing can be improved, and the microscope objective of which the parameter specification is lower than that of the imaging microscope objective can be used as the reference microscope objective, so that the cost of automatic focusing is reduced. Therefore, the automatic focusing cost can be reduced, and the automatic focusing precision can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of optical interference measurement, and in particular, to an autofocus method, apparatus, device, storage medium, and program product. Background Art

[0002] During the wafer inspection process, the depth of field of a high-resolution objective lens is very small, and the warping and jitter of the wafer during scanning will cause defocus, affecting the measurement accuracy. Therefore, real-time focusing is required for wafer inspection.

[0003] Currently, the common focusing method usually requires using two identical objective lenses to make the optical paths of the interference arms symmetrical for focusing. However, high-resolution objective lenses are expensive, and using two identical high-resolution objective lenses will increase the cost, and there will still be differences between the identical high-resolution objective lenses, making the optical paths not completely symmetrical, resulting in a decrease in focusing accuracy. That is, the current focusing method has the problems of high cost and insufficient focusing accuracy. Summary of the Invention The main purpose of the present application is to provide an autofocus method, apparatus, device, storage medium, and program product, aiming to solve the technical problem that the current focusing method has high cost and insufficient focusing accuracy.

[0004] To achieve the above object, the present application proposes an autofocus method applied to an autofocus device, and the method includes: At each preset time period, obtain an interference signal generated by the interference of a first light beam and a second light beam to obtain a corresponding set of interference signals, where the first light beam is a light beam incident on a reference microscope objective lens, the second light beam is a light beam incident on an imaging microscope objective lens, and the reference microscope objective lens has completed focusing and its parameter specifications are lower than those of the imaging microscope objective lens; Based on the set of interference signals and the wavefront phase difference, calculate the defocus amount of the imaging microscope objective lens, where the wavefront phase difference is pre-calculated based on the wavefront of the reference microscope objective lens and the wavefront of the imaging microscope objective lens; Based on the defocus amount and the depth of field of the imaging microscope objective lens, perform autofocus on the imaging microscope objective lens.

[0005] In one embodiment, the set of interference signals includes a plurality of phase-shifted interference signals with different phase shift amounts, and the step of calculating the defocus amount of the imaging microscope objective lens based on the set of interference signals and the wavefront phase difference includes: Based on the wavefront phase difference, perform phase compensation on the phase-shifted interference signals to calculate a compensated interference signal that eliminates the wavefront phase difference; Based on different numbers of adjacent compensated interference signals, calculate the defocus amount of the imaging microscope objective lens.

[0006] In one embodiment, before the step of obtaining the interference signal generated by the interference of the first light beam and the second light beam at each preset time interval, the method further includes: Obtaining a first distance between each point on the reference microscope objective lens and the optical axis of the first light beam when the first light beam passes through the reference microscope objective lens, and obtaining a first angle of each point on the reference microscope objective lens relative to the origin of the light beam; Obtaining a second distance between each point on the imaging microscope objective lens and the optical axis of the second light beam when the second light beam passes through the imaging microscope objective lens, and obtaining a second angle of each point on the imaging microscope objective lens relative to the origin of the second light beam; Calculating a wavefront phase difference between the imaging microscope objective lens and the reference microscope objective lens based on the first distance, the first angle, the second distance, and the second angle.

[0007] In one embodiment, the step of calculating the wavefront phase difference between the imaging microscope objective lens and the reference microscope objective lens based on the first distance, the first angle, the second distance, and the second angle includes: Calculating a reference objective lens wavefront of the reference microscope objective lens based on the first distance and the first angle; Calculating an imaging objective lens wavefront of the imaging microscope objective lens based on the second distance and the second angle; Calculating a wavefront optical path difference between the imaging microscope objective lens and the reference microscope objective lens based on the imaging objective lens wavefront and the reference objective lens wavefront; Calculating a wavefront phase difference between the imaging microscope objective lens and the reference microscope objective lens based on the wavefront optical path difference.

[0008] In one embodiment, the step of automatically focusing the imaging microscope objective lens based on the defocus amount and the depth of field of the imaging microscope objective lens includes: Determining whether the defocus amount is within the range of the depth of field; If it is not within the range of the depth of field, determining a displacement amount of the corresponding stage based on the defocus amount; Moving the corresponding stage based on the displacement amount to complete the automatic focusing of the microscope objective lens.

[0009] In addition, to achieve the above object, the present application further provides an automatic focusing device, and the automatic focusing device includes: A signal acquisition module, which is used to acquire the interference signal generated by the interference of the first light beam and the second light beam at preset time intervals, so as to obtain a corresponding interference signal set, where the first light beam is the light beam incident on the reference microscope objective lens, the second light beam is the light beam incident on the imaging microscope objective lens, and the reference microscope objective lens has been focused and its parameter specifications are lower than those of the imaging microscope objective lens; A defocus amount calculation module, which is used to calculate the defocus amount of the imaging microscope objective lens based on the interference signal set and the wavefront phase difference, where the wavefront phase difference is pre-calculated based on the wavefront of the reference microscope objective lens and the wavefront of the imaging microscope objective lens; An autofocus module, which is used to perform autofocus on the imaging microscope objective lens based on the defocus amount and the depth of field of the imaging microscope objective lens.

[0010] In addition, to achieve the above object, the present application also proposes an autofocus device, which includes: A light source, which is used to form a first light beam incident on the reference microscope objective lens and a second light beam incident on the imaging microscope objective lens; An interference unit, which is used to generate an interference signal based on the first light beam and the second light beam; A detection unit, which is used to acquire the interference signal at preset time intervals to obtain a corresponding interference signal set, and send the interference signal set to the processing and control unit; A processing and control unit, which is used to receive the interference signal set sent by the detection unit, calculate the defocus amount of the imaging microscope objective lens based on the interference signal set and the pre-calculated wavefront phase difference, and perform autofocus on the imaging microscope objective lens based on the defocus amount and the depth of field of the imaging microscope objective lens.

[0011] In a possible implementation manner of the present application, the autofocus device further includes: A feedback execution mechanism, which is used to receive the displacement amount sent by the processing and control unit, and move the corresponding stage displacement table based on the displacement amount to complete the autofocus of the imaging microscope objective lens; The processing and control unit is further used to: judge whether the defocus amount is within the range of the depth of field. If it is not within the range of the depth of field, then determine the displacement amount of the corresponding stage displacement table based on the defocus amount, and send the displacement amount to the feedback execution mechanism.

[0012] In addition, to achieve the above object, the present application also proposes a storage medium, which is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the autofocus method described above are implemented.

[0013] In addition, to achieve the above object, the present application also provides a computer program product, which includes a computer program that, when executed by a processor, implements the steps of the autofocus method described above.

[0014] One or more technical solutions proposed by the present application have at least the following technical effects: In the present application, at preset time intervals, an interference signal generated by the interference of a first light beam and a second light beam is acquired, and a corresponding interference signal set is obtained. Based on the interference signal set and the wavefront phase difference, the defocus amount of the imaging microscope objective is calculated, and based on the defocus amount and the depth of field of the imaging microscope objective, autofocus is performed on the imaging microscope objective.

[0015] Since the present application first calculates the wavefront phase difference based on the wavefronts of the reference microscope objective and the imaging microscope objective, and additionally calculates the defocus amount based on the wavefront phase difference, errors caused by different objectives can be eliminated when calculating the defocus amount. Thus, based on the already focused reference microscope objective, the defocus amount of the imaging microscope objective can be accurately calculated, improving the accuracy of autofocus. And because the present application eliminates the errors caused by different objectives through the above method, when performing autofocus, it is not necessary to use two expensive identical high-resolution objectives. Instead, a microscope objective with parameter specifications lower than those of the imaging microscope objective can be used as the reference microscope objective to reduce the cost of autofocus. Therefore, the present application can reduce the cost of autofocus and improve the accuracy of autofocus. Description of the Drawings

[0016] The drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0017] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a schematic flowchart provided for the first embodiment of the autofocus method of the present application; Figure 2 It is a schematic diagram of the first scenario provided for the first embodiment of the autofocus method of the present application; Figure 3 It is a schematic diagram of the second scenario provided for the first embodiment of the autofocus method of the present application; Figure 4 It is a schematic flowchart provided for the second embodiment of the autofocus method of the present application; Figure 5It is a schematic diagram of the module structure of the autofocus device according to the embodiment of the present application.

[0019] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. Specific embodiments

[0020] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0021] In order to better understand the technical solutions of the present application, the following will be described in detail with reference to the accompanying drawings of the specification and specific embodiments.

[0022] It should be noted that the execution subject of this embodiment can be a computing service device with data processing, network communication and program running functions, such as a tablet computer, a personal computer, a mobile phone, etc., or an electronic device, an autofocus device, etc. that can implement the above functions. The following takes the autofocus device as an example to illustrate this embodiment and the following embodiments.

[0023] During the wafer inspection process, the depth of field of the high-resolution objective lens is very small, and the wafer warping and wafer jitter during scanning will cause defocus, affecting the measurement accuracy. Therefore, real-time focusing is required. In the aspect of microscopic inspection, the linnik form is commonly used. The linnik microscopic focusing (Linnik, the proposer of linnik microscopic inspection) usually requires the optical paths of the two interference arms to be symmetric. However, in a high-resolution bright-field imaging system, the bright-field large NA (Numerical Aperture) imaging objective lens is expensive and it is difficult to use the linnik focusing method. Moreover, there are still differences between the same high-resolution objective lenses, which makes the optical paths used for focusing not completely symmetric, resulting in a decrease in focusing accuracy.

[0024] Based on this, the embodiment of the present application provides an autofocus method, which is applied to an autofocus device, referring to Figure 1 , Figure 1 It is a schematic flowchart of the first embodiment of the autofocus method of the present application.

[0025] In this embodiment, the autofocus method includes steps S10 to S30: Step S10, at every preset time period, obtain the interference signal generated by the interference of the first light beam and the second light beam, and obtain the corresponding interference signal set, wherein the first light beam is the light beam incident on the reference microscopic objective lens, the second light beam is the light beam incident on the imaging microscopic objective lens, and the reference microscopic objective lens has completed focusing and its parameter specifications are lower than those of the imaging microscopic objective lens; It should be noted that the first beam and the second beam are obtained by splitting a parallel beam using a beam splitter prism. The interference signal is an interference image generated by the interference of the first beam and the second beam, which contains phase information and can be used to reflect the defocus state of the microscope objective. The interference signal set is a set of interference image data collected at multiple time points and / or positions, which can be used for subsequent phase demodulation and defocus amount calculation.

[0026] The reference microscope objective is the reference arm of the interference system in this embodiment, and the imaging microscope objective is the measurement arm of the interference system in this embodiment. The parameter specifications include parameters such as the NA, magnification, and focal length of the microscope objective. The price of a microscope objective with low parameter specifications is lower than that of a microscope objective with high parameter specifications.

[0027] It can be understood that the interference phenomenon is the phenomenon that when two or more coherent light beams meet, corresponding interference signals are generated. The light intensity at the interference point is:

[0028] where I is the light intensity at the interference point, I r is the light intensity of the first beam (i.e., the reference beam), and I m is the light intensity of the second beam (i.e., the measurement beam), is the phase difference between the reference beam and the measurement beam. In the case of using a broadband light source, the spectral distribution of the broadband light source is:

[0029] where B(v) is a function describing the relationship between the wavelength and light intensity of the broadband light source, v is the frequency, and v c is the central frequency of the light source, is the half-width of the light source spectrum. The function of the coherent intensity of light changing with distance is:

[0030] where g( ) is the coherent intensity envelope function, is the height of the objective lens from the focus, is the distance between the wafer and the focal plane of the objective lens, is the coherent length of the light source, The specific calculation formula is , is the central wavelength of the light source. The relationship between the relative optical path difference between the reference arm and the measurement arm and the interference light intensity can be referred to Figure 2 .

[0031] According to the above formula, it can be known that the coherence intensity of light is related to the phase difference between two beams of light. For the two beams of light passing through the phase objective lens, their coherence intensity is related to the distance of the objective lens from the focal point. That is, the distance between the objective lens and the focal point can be determined by the phase difference between the two beams of light. Therefore, in this embodiment, it is necessary to obtain the interference signal generated by the interference of the first beam and the second beam at preset time intervals to obtain the corresponding interference signal set, so as to determine the defocus amount of the corresponding microscope objective lens for focusing.

[0032] In one embodiment, the process of forming the first beam and the second beam, and obtaining the interference signal is carried out on an autofocus device. The settings of the autofocus device can refer to Figure 3 , and the autofocus device includes a light source, an interference unit and a detection unit. The process of beam formation and interference includes: The light source is provided with a broadband light source, a collimator and a diaphragm. The broadband light source emits low-coherence light. The low-coherence light first passes through the collimator to become a parallel beam, and then the parallel beam passes through the diaphragm to become a parallel beam with a preset spot size and is incident on the beam splitter prism in the interference unit. The interference unit is provided with an imaging microscope objective lens, a reference microscope objective lens and a beam splitter prism. The parallel beam is first split into a first beam and a second beam by the beam splitter prism. Among them, the beam splitter prism has a preset splitting ratio, which is 50:50 in this embodiment. There is an object to be imaged in front of the imaging microscope objective lens. The object to be imaged is the object that needs to be imaged on the object stage. In this embodiment, the object to be imaged is a wafer. There is a reflector in front of the reference microscope objective lens. The first beam converges on the reflector after passing through the reference objective lens. The reflector reflects the converged first beam, so that the first beam passes through the reference objective lens again and returns to the beam splitter prism. The second beam converges on the object to be imaged after passing through the imaging objective lens. The object to be imaged reflects the converged second beam, so that the second beam passes through the imaging objective lens again and returns to the beam splitter prism. The first beam and the second beam are incident on the tube lens in the detection unit after passing through the beam splitter prism. The detection unit is provided with a tube lens and a camera. The detection surface of the camera is located at the focal point of the tube lens. After the first beam and the second beam are incident on the tube lens, the tube lens shortens the optical paths of the first beam and the second beam, so that the first beam and the second beam interfere at the focal point of the tube lens to generate an interference signal. The camera obtains the interference signal at preset time intervals and transmits the corresponding interference signal set to the processing and control unit. Among them, the interference signal obtained by the camera is an optical signal, and before transmitting the interference signal, the optical signal will be gain-amplified and converted into a corresponding electrical signal.

[0033] Step S20: Calculate the defocus amount of the imaging microscope objective based on the set of interference signals and the wavefront phase difference, where the wavefront phase difference is pre-calculated based on the wavefront of the reference microscope objective and the wavefront of the imaging microscope objective; It should be noted that the wavefront is the equiphase surface of each point during the propagation of the light beam, and the wavefront phase difference is the difference in phase between different wavefronts of different light beams. In this embodiment, it is the phase distribution difference caused by the objective parameter differences between the reference arm and the measurement arm. The defocus amount is the distance deviation between the focus of the imaging microscope objective and the object to be imaged.

[0034] It can be understood that the traditional Linnik-type interference autofocus method usually uses two identical large-aperture high-resolution microscope objectives to ensure high-quality interference fringes for accurate focusing. However, due to the high cost of large-aperture high-resolution microscope objectives, it is difficult to apply them in the Linnik-type interference autofocus method. And different microscope objectives will result in different optical paths passing through the microscope objectives, so it is impossible to use the phase difference of the interference signals for focusing. Therefore, the two identical microscope objectives in the above method cannot be directly replaced with different microscope objectives.

[0035] Furthermore, there are still some differences between identical microscope objectives due to manufacturing processes and other reasons, making the optical paths passing through the two microscope objectives not completely symmetrical. Therefore, there will still be errors when using the Linnik method for focusing, resulting in a decrease in focusing accuracy.

[0036] Therefore, in this embodiment, before calculating the defocus amount of the imaging microscope objective, the wavefront phase difference between the reference microscope objective and the imaging microscope objective is first calculated. By introducing the wavefront phase difference, the phase error caused by objective asymmetry is effectively eliminated, thereby improving the accuracy of defocus amount calculation and further enhancing the accuracy of focusing. And since the error caused by different objectives is eliminated, this embodiment can use an objective with parameter specifications lower than those of the imaging microscope objective as the reference objective, effectively reducing the focusing cost while improving the focusing accuracy.

[0037] Furthermore, the usual measurement method uses a monochromatic light source for focusing. The monochromatic light source has a long coherence length, so that even if there is a large optical path difference between the two light beams, clear interference fringes can be generated, thus no obvious envelope feature can be produced, and focusing can only be performed within a small range. In this embodiment, by using a broadband light source with a wide spectral range and a short coherence length, a clear interference envelope can be generated during interference, so that precise focusing can be performed within a larger range, improving the focusing range.

[0038] In a feasible embodiment, the set of interference signals includes a plurality of phase-shifted interference signals with different amounts of phase shift. The specific implementation of calculating the defocus amount of the imaging microscope objective based on the set of interference signals and the wavefront phase difference may also be: Based on the wavefront phase difference, perform phase compensation on the phase-shifted interference signals, calculate and obtain compensated interference signals with the wavefront phase difference eliminated, and calculate the defocus amount of the imaging microscope objective based on different numbers of adjacent compensated interference signals.

[0039] It should be noted that the phase-shifted interference signals are obtained when the focusing operation instruction is received, and the stage moves rapidly and continuously along the direction parallel to the light beam based on a preset displacement setting.

[0040] It should also be noted that phase compensation is an operation of correcting the phase-shifted interference signals according to the calculated wavefront phase difference to eliminate the error caused by the asymmetry of the objective lens. Through phase compensation, compensated interference signals can be obtained, and the interference light intensity of the compensated interference signals is:

[0041] where I r is the light intensity of the first light beam, I m is the light intensity of the second light beam, is the calculated wavefront phase difference, is the length of the point on the objective lens from the optical axis passing through the objective lens, with a range of [0, R], where R is the radius of the objective lens mirror surface, is the angle of the point on the objective lens relative to the origin of the light beam on the objective lens mirror surface, with a range of [0, 2 , that is, the angular range of the circle formed by the objective lens mirror surface.

[0042] It can be understood that after the wavefront phase difference is calculated, the calculated wavefront phase difference needs to be used to eliminate the error. The error is due to the different optical paths of the light beams caused by different objective lenses, which is reflected as the phase difference of different light beams. Therefore, in the process of resolving the interference signals in this embodiment, phase compensation is performed based on the calculated wavefront phase difference, so that the defocus amount obtained by resolution is the defocus amount with the wavefront phase difference eliminated.

[0043] The calculation of the defocus amount can use the Fourier transform method or the phase-shifting interference method. The phase-shifting interference method can be the three-frame method, the four-frame method, or the five-frame method. In this embodiment, the three-frame method is used as an example.

[0044] Take three adjacent interference signals as a resolution unit, and the light intensities of the adjacent interference signals are:

[0045]

[0046]

[0047] wherein, is the phase difference of the phase shift between adjacent interference signals, and the phase difference between the first light beam and the second light beam can be calculated through three adjacent interference signals as:

[0048] And since the phase difference refers to the difference in the relative positions of two coherent light waves at a certain moment, and the reference microscope objective is an objective lens in the focused state, therefore, the calculated phase difference can obtain the defocus amount, and thus the focusing can be performed according to the defocus amount.

[0049] Step S30, automatically focus the imaging microscope objective based on the defocus amount and the depth of field of the imaging microscope objective.

[0050] It should be noted that the defocus amount is the distance deviation between the focus of the imaging microscope objective and the object to be imaged, and the depth of field is the maximum range that the object plane is allowed to deviate from the ideal focal plane on the premise of keeping the image clear.

[0051] It can be understood that in this embodiment, the error caused by different objective lenses is eliminated by pre-calculating the wavefront phase difference when calculating the defocus amount. Therefore, focusing by using the calculated defocus amount can effectively improve the focusing accuracy.

[0052] In a feasible implementation manner, the specific implementation manner of automatically focusing the imaging microscope objective based on the defocus amount and the depth of field of the imaging microscope objective may also be: Judge whether the defocus amount is within the range of the depth of field. If it is not within the range of the depth of field, then determine the displacement amount of the corresponding stage based on the defocus amount, and move the corresponding stage based on the displacement amount to complete the automatic focusing of the microscope objective.

[0053] It should be noted that the depth of field range is a distance interval that extends half of the depth of field above and below the ideal focal plane as the center, and the stage is an actuator for precisely moving the position of the object to be imaged in the vertical direction (Z-axis).

[0054] It can be understood that if the defocus amount is within the depth of field, it means that the object to be imaged is still clear, and no focusing is required at this time. If the defocus amount is not within the depth of field, it is necessary to move the stage to perform focusing so that the object to be imaged is in a clear state in the imaging microscope objective. In this embodiment, by first judging whether the defocus amount is within the depth of field before focusing, the stage is only activated for adjustment when the defocus amount exceeds the depth of field range, avoiding frequent focusing and improving the stability and response efficiency of the focusing system.

[0055] In one embodiment, the calculation of the defocus amount, the judgment of whether to perform focusing, and the operation process of focusing are carried out on an autofocus device, and the autofocus device further includes a processing and control unit and a feedback execution mechanism. The specific processing processes of defocus amount calculation, focusing judgment, and focusing operation include: The processing and control unit is provided with a host computer, which receives the interference signal sent by the camera, calculates the focal position of the imaging objective lens based on the interference signal, calculates the defocus amount between the focal position and the position of the object to be observed, judges whether focusing is required based on the defocus amount and the depth of field range of the imaging microscope objective. If so, calculates the corresponding displacement amount based on the defocus amount, and sends the corresponding displacement amount to the feedback execution mechanism to complete the focusing; The feedback execution mechanism is provided with a stage, and the feedback execution mechanism receives the displacement amount sent by the host computer and displaces the stage based on the displacement amount to complete the autofocus of the imaging microscope objective.

[0056] In summary, in this embodiment, at each preset time interval, an interference signal generated by the interference of the first beam and the second beam is acquired, and a corresponding interference signal set is obtained. Based on the interference signal set and the wavefront phase difference, the defocus amount of the imaging microscope objective is calculated, and based on the defocus amount and the depth of field of the imaging microscope objective, the imaging microscope objective is automatically focused.

[0057] Since in this embodiment, the wavefront phase difference is first calculated based on the wavefronts of the reference microscope objective and the imaging microscope objective, and the defocus amount is additionally calculated based on the wavefront phase difference, the error caused by different objectives can be eliminated when calculating the defocus amount. Thus, based on the already focused reference microscope objective, the defocus amount of the imaging microscope objective can be accurately calculated, improving the accuracy of autofocus. And because in this embodiment, the error caused by different objectives is eliminated by the above method, when performing focusing, it is not necessary to use two expensive identical high-resolution objectives. Instead, a microscope objective with parameter specifications lower than those of the imaging microscope objective can be used as the reference microscope objective to reduce the cost of autofocus. Therefore, this embodiment can reduce the cost of autofocus and improve the accuracy of autofocus.

[0058] Based on the first embodiment of the present application, in the second embodiment of the present application, the same or similar content as that in the above-mentioned first embodiment can be referred to the above introduction and will not be repeated hereinafter. On this basis, please refer to Figure 4 , before step S10, the autofocus method further includes steps S01 to S03: Step S01, obtain the first distance between each point on the reference microscope objective lens and the optical axis of the first light beam when the first light beam passes through the reference microscope objective lens, and obtain the first angle of each point on the reference microscope objective lens relative to the origin of the light beam; It should be noted that the optical axis is the central propagation path of the focusing system in this embodiment, the first distance is a set of distances between each point in the reference microscope objective lens and the optical axis, and the first angle is a set of angles of each point in the reference microscope objective lens relative to the origin of the light beam on the mirror surface.

[0059] It can be understood that in this embodiment, since the imaging microscope objective lens and the reference microscope objective lens are different objective lenses, there will be a large wavefront aberration, and it is necessary to compensate the wavefront aberration to eliminate the error caused by the wavefront aberration. Therefore, in this embodiment, the first distance and the first angle of each point on the surface of the objective lens are sampled to perform subsequent wavefront calculation, and the position information of each sampling point is quantified by the first distance and the first angle, so as to improve the accuracy of subsequent wavefront fitting calculation.

[0060] Step S02, obtain the second distance between each point on the imaging microscope objective lens and the optical axis of the second light beam when the second light beam passes through the imaging microscope objective lens, and obtain the second angle of each point on the imaging microscope objective lens relative to the origin of the second light beam; It should be noted that the second distance is a set of distances between each point in the imaging microscope objective lens and the optical axis, and the second angle is a set of angles of each point in the imaging microscope objective lens relative to the origin of the light beam on the mirror surface.

[0061] Step S03, calculate the wavefront phase difference between the imaging microscope objective lens and the reference microscope objective lens based on the first distance, the first angle, the second distance, and the second angle.

[0062] It should be noted that the wavefront phase difference in this embodiment is calculated before focusing, and the wavefront phase difference has nothing to do with the light source used in the focusing process, the moving frequency of the stage, and the acquisition frequency of the interference signal, and is only related to the imaging microscope objective lens and the reference microscope objective lens.

[0063] It is understandable that the wavefront phase difference is the phase difference caused by the different specification parameters of the reference microscope objective and the imaging microscope objective. Therefore, it is only related to the reference microscope objective and the imaging microscope objective themselves. And if we want to calculate the wavefront phase difference, we need to sample the information of each point on the reference microscope objective and the imaging microscope objective. Therefore, in this embodiment, we first obtain the first distance, the first angle, the second distance, and the second angle, and then calculate the corresponding wavefront phase difference.

[0064] In a feasible implementation manner, the specific implementation manner of calculating the wavefront phase difference between the imaging microscope objective and the reference microscope objective based on the first distance, the first angle, the second distance, and the second angle may also be: Based on the first distance and the first angle, calculate the reference objective wavefront of the reference microscope objective. Based on the second distance and the second angle, calculate the imaging objective wavefront of the imaging microscope objective. Based on the imaging objective wavefront and the reference objective wavefront, calculate the wavefront optical path difference between the imaging microscope objective and the reference microscope objective. Based on the wavefront optical path difference, calculate the wavefront phase difference between the imaging microscope objective and the reference microscope objective.

[0065] It should be noted that the wavefront optical path difference refers to the actual distance difference between two points on their propagation paths. The wavefront is the geometric position set of waves with the same phase at a specific time point. In this embodiment, the wavefront is represented by a seventh-order thirty-six-term Zernike polynomial. The seventh-order thirty-six-term Zernike polynomial is a set of orthogonal polynomials defined on the unit circle. By defining the order and the number of terms, a specific type of description of the wavefront can be made. The description expression is:

[0066] Among them, ) is the fitted wave surface, is the length of the point on the objective lens from the optical axis passing through the objective lens, and the range is [0, R], where R is the radius of the objective lens surface, is the angle of the point on the objective lens relative to the origin of the light beam on the objective lens surface, and the range is [0, 2 , which is the angle range of the circle formed by the objective lens surface, is the coefficient of each term of the polynomial, s is the combination of different orders and numbers of terms of the polynomial. Specifically, the specific part of the entire Zernike polynomial can be divided into three parts:

[0067] Among them, is a radial polynomial, n represents the total order, and m represents the angular frequency. The wavefronts of the reference microscope objective and the imaging microscope objective can be calculated separately. and the wavefront of the imaging microscope objective , and the wavefront optical path difference between the two wavefronts after passing through the reflection beam splitter prism is:

[0068] The wavefront phase difference can be calculated as:

[0069] It can be understood that in this embodiment, two objective lenses with different parameter specifications are used. Therefore, the wavefronts of the first beam and the second beam after passing through the reference objective lens and the microscope objective lens are not simple plane waves, but complex wavefronts. And since in this embodiment, each point on the reference microscope objective and the imaging microscope objective has been sampled in advance, and the corresponding first distance, first angle, second distance, and second angle have been calculated. Therefore, in this embodiment, the wavefronts of the reference microscope objective and the imaging microscope objective can be accurately calculated, and then the wavefront phase difference can be calculated to eliminate the focusing error caused by different objective lenses and improve the accuracy of focusing.

[0070] In summary, in this embodiment, when obtaining the first beam passing through the reference microscope objective, the first distance between each point on the reference microscope objective and the optical axis of the first beam is obtained, and the first angle of each point on the reference microscope objective relative to the origin of the beam is obtained. When obtaining the second beam passing through the imaging microscope objective, the second distance between each point on the imaging microscope objective and the optical axis of the second beam is obtained, and the second angle of each point on the imaging microscope objective relative to the origin of the second beam is obtained. Based on the first distance, the first angle, the second distance, and the second angle, the wavefront phase difference between the imaging microscope objective and the reference microscope objective is calculated.

[0071] When using two objective lenses with different parameter specifications, the wavefronts of the first beam and the second beam after passing through the reference objective lens and the microscope objective lens are not simple plane waves, but complex wavefronts. Therefore, in this embodiment, the wavefront phase difference is calculated to eliminate the corresponding focusing error through the wavefront phase difference. And since the generated wavefront phase difference is only related to the objective lens itself, in this embodiment, each point on the mirror surface of the objective lens is sampled and quantitatively calculated, so that the wavefront can be accurately calculated through the calculated first distance, first angle, second distance, and second angle, and then the wavefront phase difference can be accurately calculated, so as to eliminate the focusing error through the calculated wavefront phase difference and improve the focusing accuracy.

[0072] It should be noted that the above examples are only for understanding the present application and do not constitute a limitation on the autofocus method of the present application. Based on this technical concept, more forms of simple transformations are within the protection scope of the present application.

[0073] The present application also provides an autofocus device, which includes: A light source for forming a first light beam directed at a reference microscope objective and a second light beam directed at an imaging microscope objective; An interference unit for generating an interference signal based on the first light beam and the second light beam; A detection unit for obtaining the interference signal at preset time intervals to obtain a corresponding set of interference signals, and sending the set of interference signals to a processing and control unit; A processing and control unit for receiving the set of interference signals sent by the detection unit, calculating the defocus amount of the imaging microscope objective based on the set of interference signals and a pre-calculated wavefront phase difference, and performing autofocus on the imaging microscope objective based on the defocus amount and the depth of field of the imaging microscope objective.

[0074] In a possible implementation manner of the present application, the autofocus device further includes: A feedback execution mechanism for receiving the displacement amount sent by the processing and control unit, and moving the corresponding stage based on the displacement amount to complete autofocus on the imaging microscope objective; The processing and control unit is further configured to: determine whether the defocus amount is within the range of the depth of field, and if not, determine the displacement amount of the corresponding stage based on the defocus amount, and send the displacement amount to the feedback execution mechanism.

[0075] The present application also provides an autofocus device. Please refer to Figure 5 , the autofocus device includes: A signal acquisition module 10 for obtaining, at preset time intervals, an interference signal generated by the interference of a first light beam and a second light beam to obtain a corresponding set of interference signals, where the first light beam is a light beam directed at a reference microscope objective, the second light beam is a light beam directed at an imaging microscope objective, and the reference microscope objective has been focused and its parameter specifications are lower than those of the imaging microscope objective; A defocus amount calculation module 20 for calculating the defocus amount of the imaging microscope objective based on the set of interference signals and a wavefront phase difference, where the wavefront phase difference is pre-calculated based on the wavefront of the reference microscope objective and the wavefront of the imaging microscope objective; An autofocus module 30 for performing autofocus on the imaging microscope objective based on the defocus amount and the depth of field of the imaging microscope objective.

[0076] In one embodiment, the defocus amount calculation module further includes: A compensation signal calculation sub-module, configured to perform phase compensation on the phase-shifted interference signal based on the wavefront phase difference, and calculate a compensated interference signal that eliminates the wavefront phase difference; A defocus amount calculation sub-module, configured to calculate the defocus amount of the imaging microscope objective based on different numbers of adjacent compensated interference signals.

[0077] In one embodiment, the autofocus device further includes: A first acquisition module, which acquires the first distance between each point on the reference microscope objective and the optical axis of the first light beam when the first light beam passes through the reference microscope objective, and acquires the first angle of each point on the reference microscope objective relative to the origin of the light beam; A second acquisition module, which acquires the second distance between each point on the imaging microscope objective and the optical axis of the second light beam when the second light beam passes through the imaging microscope objective, and acquires the second angle of each point on the imaging microscope objective relative to the origin of the second light beam; A phase difference calculation module, which calculates the wavefront phase difference between the imaging microscope objective and the reference microscope objective based on the first distance, the first angle, the second distance, and the second angle.

[0078] In one embodiment, the phase difference calculation module further includes: A first wavefront calculation sub-module, configured to calculate the reference objective wavefront of the reference microscope objective based on the first distance and the first angle; A second wavefront calculation sub-module, configured to calculate the imaging objective wavefront of the imaging microscope objective based on the second distance and the second angle; An optical path difference calculation sub-module, configured to calculate the wavefront optical path difference between the imaging microscope objective and the reference microscope objective based on the imaging objective wavefront and the reference objective wavefront; A phase difference calculation sub-module, configured to calculate the wavefront phase difference between the imaging microscope objective and the reference microscope objective based on the wavefront optical path difference.

[0079] In one embodiment, the autofocus module further includes: A range judgment sub-module, configured to judge whether the defocus amount is within the depth of field range; A displacement amount calculation sub-module, configured to, if it is not within the depth of field range, determine the displacement amount of the corresponding stage based on the defocus amount; An autofocus sub-module, configured to move the corresponding stage based on the displacement amount to complete the autofocus of the microscope objective.

[0080] The autofocus device provided by this application adopts the autofocus method in the above-mentioned embodiment, and can solve the technical problem that the current focusing method has high cost and insufficient focusing accuracy. Compared with the prior art, the beneficial effects of the autofocus device provided by this application are the same as those of the autofocus method provided by the above-mentioned embodiment, and other technical features in the autofocus device are the same as the features disclosed in the method of the above-mentioned embodiment, which will not be elaborated here.

[0081] This application provides a computer-readable storage medium with computer-readable program instructions (i.e., computer programs) stored thereon, and the computer-readable program instructions are used to execute the autofocus method in the above-mentioned embodiment.

[0082] The computer-readable storage medium provided by this application can be, for example, a USB flash drive, but is not limited to electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to: electrical connections with one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM) or flash memory, optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the above. In this embodiment, the computer-readable storage medium can be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, device, or device. The program code contained on the computer-readable storage medium can be transmitted by any appropriate medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination of the above.

[0083] The above computer-readable storage medium can be included in the autofocus device; it can also exist separately without being assembled into the autofocus device.

[0084] The above computer-readable storage medium carries one or more programs, and when the one or more programs are executed by the autofocus device, the autofocus device is caused to: execute the above autofocus method.

[0085] Computer program code for performing the operations of this application can be written in one or more programming languages or combinations thereof. The above-mentioned programming languages include object-oriented programming languages such as Java, Smalltalk, C++, and also include conventional procedural programming languages such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, executed as an independent software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN: Local Area Network) or a wide area network (WAN: Wide Area Network), or it can be connected to an external computer (for example, by using an Internet service provider to connect through the Internet).

[0086] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of the systems, methods, and computer program products according to the various embodiments of this application. In this regard, each block in the flowchart or block diagram may represent a module, a program segment, or a part of the code, and this module, program segment, or part of the code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than that marked in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, as well as the combination of blocks in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system for performing the specified functions or operations, or can be implemented by a combination of dedicated hardware and computer instructions.

[0087] The modules described in the embodiments of this application can be implemented in software or in hardware. Among them, the name of the module does not constitute a limitation to the unit itself in some cases.

[0088] The readable storage medium provided by this application is a computer-readable storage medium, and the computer-readable storage medium stores computer-readable program instructions (i.e., computer programs) for performing the above-mentioned autofocus method, which can solve the technical problem that the current focusing method has a high cost and insufficient focusing accuracy. Compared with the prior art, the beneficial effects of the computer-readable storage medium provided by this application are the same as those of the autofocus method provided by the above embodiments, and will not be elaborated here.

[0089] The present application also provides a computer program product, including a computer program which, when executed by a processor, implements the steps of the autofocus method as described above.

[0090] The computer program product provided by the present application can solve the technical problem that the existing autofocus method has high cost and insufficient autofocus accuracy. Compared with the prior art, the beneficial effects of the computer program product provided by the present application are the same as those of the autofocus method provided by the above embodiments, and will not be elaborated here.

[0091] The user-related data involved in the present application (for example, user attribute data, user behavior data, user geographical location, etc., and the data types here should be adaptively modified according to the content of the solution) are all obtained after obtaining the permission or consent of the user; that is to say, when the present application is applied to specific products or technologies, user permission is required to obtain and process relevant data, and the processing of relevant data needs to comply with relevant laws, regulations and regulatory standards in relevant countries and regions.

[0092] The above are only some embodiments of the present application, and thus do not limit the patent scope of the present application. Any equivalent structural transformation made by using the specification and drawings of the present application under the technical concept of the present application, or directly / indirectly applied to other related technical fields, is included in the patent protection scope of the present application.

Claims

1. An autofocus device, characterized in that, The autofocus device includes: a light source for forming a first light beam directed at a reference microscope objective and a second light beam directed at an imaging microscope objective; an interference unit for generating an interference signal based on the first light beam and the second light beam; a detection unit for acquiring the interference signal at preset time intervals to obtain a corresponding set of interference signals, and sending the set of interference signals to a processing and control unit; a processing and control unit for receiving the set of interference signals sent by the detection unit, calculating the defocus amount of the imaging microscope objective based on the set of interference signals and a pre-calculated wavefront phase difference, and performing autofocus on the imaging microscope objective based on the defocus amount and the depth of field of the imaging microscope objective.

2. The autofocus device according to claim 1, wherein The autofocus device further includes: a feedback actuator for receiving the displacement amount sent by the processing and control unit and moving a corresponding stage for specimen displacement based on the displacement amount to complete autofocus on the imaging microscope objective; The processing and control unit is further configured to: determine whether the defocus amount is within the range of the depth of field, and if not, determine the displacement amount of the corresponding stage for specimen displacement based on the defocus amount and send the displacement amount to the feedback actuator.

3. An autofocus method, characterized in that, Applied to an autofocus device, the method includes: acquiring at preset time intervals an interference signal generated by interference between a first light beam and a second light beam to obtain a corresponding set of interference signals, where the first light beam is a light beam directed at a reference microscope objective, the second light beam is a light beam directed at an imaging microscope objective, and the reference microscope objective has been focused and its parameter specifications are lower than those of the imaging microscope objective; calculating the defocus amount of the imaging microscope objective based on the set of interference signals and a wavefront phase difference, where the wavefront phase difference is pre-calculated based on the wavefront of the reference microscope objective and the wavefront of the imaging microscope objective; performing autofocus on the imaging microscope objective based on the defocus amount and the depth of field of the imaging microscope objective.

4. The method according to claim 3, wherein The set of interference signals includes a plurality of phase-shifted interference signals with different phase shift amounts, and the step of calculating the defocus amount of the imaging microscope objective based on the set of interference signals and the wavefront phase difference includes: performing phase compensation on the phase-shifted interference signals based on the wavefront phase difference to calculate a compensated interference signal with the wavefront phase difference eliminated; calculating the defocus amount of the imaging microscope objective based on different numbers of adjacent compensated interference signals.

5. The method according to claim 3, wherein Before the step of acquiring at preset time intervals an interference signal generated by interference between a first light beam and a second light beam, the method further includes: acquiring a first distance between each point on the reference microscope objective and the optical axis of the first light beam when the first light beam passes through the reference microscope objective, and acquiring a first angle of each point on the reference microscope objective relative to the origin of the light beam; acquiring a second distance between each point on the imaging microscope objective and the optical axis of the second light beam when the second light beam passes through the imaging microscope objective, and acquiring a second angle of each point on the imaging microscope objective relative to the origin of the second light beam; Calculate the wavefront phase difference between the imaging microscope objective and the reference microscope objective based on the first distance, the first angle, the second distance, and the second angle.

6. The method according to claim 5, wherein The step of calculating the wavefront phase difference between the imaging microscope objective and the reference microscope objective based on the first distance, the first angle, the second distance, and the second angle includes: Calculate the reference objective wavefront of the reference microscope objective based on the first distance and the first angle; Calculate the imaging objective wavefront of the imaging microscope objective based on the second distance and the second angle; Calculate the wavefront optical path difference between the imaging microscope objective and the reference microscope objective based on the imaging objective wavefront and the reference objective wavefront; Calculate the wavefront phase difference between the imaging microscope objective and the reference microscope objective based on the wavefront optical path difference.

7. The method according to claim 3, characterized in that, The step of automatically focusing the imaging microscope objective based on the defocus amount and the depth of field of the imaging microscope objective includes: Determine whether the defocus amount is within the range of the depth of field; If it is not within the range of the depth of field, determine the displacement amount of the corresponding stage based on the defocus amount; Move the corresponding stage based on the displacement amount to complete the automatic focusing of the microscope objective.

8. An autofocus device, characterized in that, The device includes: A signal acquisition module, configured to acquire an interference signal generated by the interference of a first light beam and a second light beam at preset time intervals, to obtain a corresponding set of interference signals, where the first light beam is a light beam incident on the reference microscope objective, the second light beam is a light beam incident on the imaging microscope objective, and the reference microscope objective has been focused and its parameter specifications are lower than those of the imaging microscope objective; A defocus amount calculation module, configured to calculate the defocus amount of the imaging microscope objective based on the set of interference signals and the wavefront phase difference, where the wavefront phase difference is pre-calculated based on the wavefront of the reference microscope objective and the wavefront of the imaging microscope objective; An automatic focusing module, configured to automatically focus the imaging microscope objective based on the defocus amount and the depth of field of the imaging microscope objective.

9. A storage medium, characterized in that, The storage medium is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the automatic focusing method according to any one of claims 3 to 7 are implemented.

10. A computer program product, characterized in that, The computer program product includes a computer program. When the computer program is executed by a processor, the steps of the automatic focusing method according to any one of claims 3 to 7 are implemented.

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