Interference detection device focusing method, system and transfer function acquisition method thereof

Abstract

The present invention discloses a focusing method, system and transfer function acquisition method of an interference detection device, which relates to the field of optical systems and is used to solve the problem that the existing manual judgment of focus is prone to errors due to the influence of factors such as operator experience. The present invention places a test plate at multiple positions on the light-emitting side of the interference detection device and measures the measured surface shape, and uses a Gaussian model to construct a simulated degraded wavefront of the test plate at each position and obtains a simulated surface shape. By establishing an objective function that describes the difference between the simulated surface shape and the measured surface shape of the test plate at the at least two positions and solving the objective function, the optimal position of the test plate that minimizes the value of the objective function is obtained, so as to move the test plate to the optimal position and achieve focusing. Therefore, compared with the prior art, the present invention can improve focusing accuracy and reduce focusing errors by measuring the measured surface shape of the test plate and establishing a simulated surface shape and achieving focusing of the interference detection device through corresponding calculations.

Description

Technical Field

[0001] The present invention relates to the field of optical systems, and in particular to a focusing method and system for an interference detection device and a method for acquiring a transfer function thereof. Background Art

[0002] Precision optical components are crucial components of large scientific facilities, semiconductor device manufacturing equipment, and other critical equipment. Developments in related fields are driving higher demands on the surface accuracy of optical components at medium and high frequencies. This poses a significant challenge to optical manufacturing capabilities. As a means of measuring the surface accuracy of optical components, high-precision, wide-band surface measurement technology has become a key technology in urgent need of breakthroughs.

[0003] Interferometry is the most accurate known method for inspecting optical components, and the interferometer is the core instrument required for interferometry. To meet the demands of high-precision, wide-band inspection, it is necessary to evaluate the interferometer's frequency-domain response. The instrument transfer function (ITF) is a key metric for evaluating an interferometer's frequency-domain response. Accurately measuring the ITF enables precise evaluation of the interferometer's frequency-domain response, facilitating more accurate analysis of interferometer results in practical inspection tasks.

[0004] The ITF measurement process requires the use of test plates whose surfaces contain specific structural features. Common surface structures include single-step structures, periodic step structures, or periodic sinusoidal structures. The surface shape and surface structure of the test plates required for high-precision ITF measurement must also be high-precision.

[0005] A key factor affecting the accuracy of interferometer ITF testing is interferometer focusing error. When the interferometer is out of focus, the ITF will drop significantly. Therefore, determining whether the interferometer is properly focused is crucial. Current focusing methods involve adding an obstructing edge to the optical path, such as a sharp-edged baffle, and manually determining whether the image of the added obstructing edge on the detector is clear to determine if the focus is good. Alternatively, when the surface to be tested contains a step structure pattern, the sharpness of the step structure pattern in the captured image is used to determine focus. Manual focus judgment is prone to errors due to factors such as operator experience. Summary of the Invention

[0006] In view of this, an object of the present invention is to provide a focusing method and system for an interference detection device, which can improve focusing accuracy and reduce focusing error. The present invention also provides a transfer function acquisition method for an interference detection device.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A focusing method for an interference detection device, comprising:

[0009] Placing a test plate on the light-emitting side of an interference detection device, such that the test plate is located at at least two positions along the light field propagation direction of the test plate, and obtaining a measured surface shape of the test plate by detecting with the interference detection device when the test plate is located at any of the at least two positions, wherein the at least two positions include an initial position, and for any of the at least two positions, the distance of the any position relative to the initial position along the light field propagation direction of the test plate represents the position of the any position along the light field propagation direction of the test plate;

[0010] Constructing an ideal wavefront of the test plate, obtaining a simulated degraded wavefront of the test plate at any of the at least two positions, and obtaining a simulated surface shape of the test plate at any position based on phase information of the simulated degraded wavefront at any position, wherein the simulated degraded wavefront at any position is represented by the convolution of the ideal wavefront and a Gaussian model at any position, wherein the Gaussian model at any position describes the decomposition of the light field of the test plate into a plurality of microelements, and the complex amplitudes of the microelements when propagating to any position;

[0011] An objective function is established and solved to obtain the optimal position of the test plate along the light field propagation direction of the test plate that minimizes the value of the objective function, so as to move the test plate to the optimal position. The objective function describes the difference between the simulated surface shape and the measured surface shape of the test plate at the at least two positions.

[0012] In some embodiments, positioning the test plate at at least two positions along a propagation direction of a light field of the test plate, and obtaining a measured surface shape of the test plate by detecting with the interference detection device when the test plate is at any of the at least two positions includes:

[0013] The test plate is positioned at the initial position, and the measured surface shape of the test plate is obtained by detecting with the interference detection device;

[0014] The test plate is moved at least once along the propagation direction of the light field of the test plate. After each movement of the test plate, the moving distance is obtained, and the measured surface shape of the test plate is obtained by detection using the interference detection device.

[0015] In some embodiments, the simulated degraded wavefront at any position is expressed as:

[0016] ;

[0017] Wherein, o(x, y, z) represents the simulated degraded wavefront, u(x, y) represents the ideal wavefront, and g(x, y, z) represents the Gaussian model of the light field element of the test plate. An XYZ three-dimensional coordinate system is established with the Z axis parallel to the optical axis of the light propagating from the test plate to the interference detection device, the XY plane is perpendicular to the optical axis, and (x, y, z) represents the position coordinates.

[0018] In some embodiments, the Gaussian model of the light field element of the test plate is expressed as:

[0019] ;

[0020] Wherein, g(x, y, z) represents the Gaussian model of the light field element of the test plate, E(z) represents the light field amplitude, Φ E (x, y, z) represents the phase term related to the distribution in the direction perpendicular to the optical axis, Φ G (z) represents the Gouy phase term, Φ AC (z) represents the phase term related to the position along the optical axis, Φ0 represents the initial phase, j represents the imaginary unit, wherein the Z axis is parallel to the optical axis of the light propagating from the test plate to the interference detection device, an XYZ three-dimensional coordinate system is established, the XY plane is perpendicular to the optical axis, and (x, y, z) represents the position coordinates.

[0021] In some embodiments, the ideal wavefront is expressed as:

[0022] ;

[0023] Where A represents the amplitude of the ideal wavefront, Represents the phase of the ideal wavefront, k represents the wave vector and k=2π / λ, j represents the imaginary unit, wherein the Z axis is parallel to the optical axis of the light propagating from the test plate to the interference detection device, an XYZ three-dimensional coordinate system is established, the XY plane is perpendicular to the optical axis, and (x, y) represents the position coordinates in the XY plane.

[0024] In some embodiments, the objective function describes the sum of preset absolute values ​​of the test plate at the at least two positions, and the preset absolute value at any position represents the absolute value of the difference between the simulated surface shape and the measured surface shape at any position.

[0025] In some embodiments, establishing the objective function includes:

[0026] For the measured surface shape at any of the at least two positions, surface shape data of an area having the same pattern as the simulated surface shape at any position is selected from the measured surface shape at any position, and the objective function is established based on the difference between the simulated surface shape of the test plate at the at least two positions and the surface shape data selected from the corresponding measured surface shape.

[0027] In some embodiments, positioning the test plate at at least two positions along a propagation direction of the light field of the test plate comprises:

[0028] The test plate is moved along a guide rail so that the test plate is located at the at least two positions respectively, wherein the guide rail is arranged on the light-emitting side of the interference detection device and along the direction of the test light emitted by the interference detection device, and the test plate is arranged on the guide rail.

[0029] A focusing system for an interference detection device, comprising:

[0030] an acquisition device, configured to acquire a measured surface shape of the test plate detected by the interference detection device when the test plate is located at any of at least two positions on the light-exiting side of the interference detection device, and to acquire a position of any of the at least two positions along the propagation direction of the light field of the test plate, wherein the at least two positions include an initial position, and for any of the at least two positions, the position of the any position along the propagation direction of the light field of the test plate is represented by a distance relative to the initial position along the propagation direction of the light field of the test plate;

[0031] a simulation device for constructing an ideal wavefront of the test plate, obtaining a simulated degraded wavefront of the test plate at any of the at least two positions, and obtaining a simulated surface shape of the test plate at any position based on phase information of the simulated degraded wavefront at any position, wherein the simulated degraded wavefront at any position is represented by the convolution of the ideal wavefront and a Gaussian model at any position, wherein the Gaussian model at any position describes the decomposition of the light field of the test plate into a plurality of microelements, and the complex amplitudes of the microelements when propagating to any position;

[0032] A solving device is used to establish an objective function and solve the objective function to obtain the optimal position of the test plate along the light field propagation direction of the test plate that minimizes the value of the objective function, so as to move the test plate to the optimal position, wherein the objective function describes the difference between the simulated surface shape and the measured surface shape of the test plate at the at least two positions.

[0033] A method for obtaining a transfer function of an interference detection device, comprising:

[0034] According to any of the above methods for focusing an interference detection device, the test plate is moved to a focusing position of the interference detection device;

[0035] The interference detection device is enabled to obtain the measured surface shape of the test plate, and the instrument transfer function of the interference detection device is obtained according to the measured surface shape.

[0036] It can be seen from the above technical solution that the present invention provides a focusing method and system for an interference detection device, the method comprising: placing a test plate on the light-emitting side of the interference detection device, so that the test plate is respectively located at at least two positions along the light field propagation direction of the test plate, when the test plate is located at any of the at least two positions, obtaining the measured surface shape of the test plate by detecting with the interference detection device, wherein the at least two positions include an initial position, and for any of the at least two positions, the distance of any position along the light field propagation direction of the test plate relative to the initial position is used to represent the position of any position along the light field propagation direction of the test plate; constructing an ideal wavefront of the test plate, and obtaining the test plate. The method comprises the following steps: obtaining a simulated degraded wavefront of the test plate at any of the at least two positions, and obtaining a simulated surface shape of the test plate at any position based on the phase information of the simulated degraded wavefront at any position, wherein the simulated degraded wavefront at any position is represented by the convolution of the ideal wavefront and the Gaussian model at any position, and the Gaussian model at any position describes the decomposition of the light field of the test plate into multiple infinitesimals, and the complex amplitude of the infinitesimals when propagating to any position; establishing an objective function and solving the objective function, obtaining the optimal position of the test plate along the propagation direction of the light field of the test plate that minimizes the value of the objective function, and moving the test plate to the optimal position, wherein the objective function describes the difference between the simulated surface shape and the measured surface shape of the test plate at the at least two positions.

[0037] The beneficial effects of the present invention are that, by placing a test plate at multiple positions on the light-emitting side of an interference detection device and measuring the actual surface shape, and using a Gaussian model to construct a simulated degraded wavefront of the test plate at each position and obtain a simulated surface shape, an objective function is established to describe the difference between the simulated surface shape and the actual surface shape of the test plate at the at least two positions and the objective function is solved, the optimal position of the test plate that minimizes the value of the objective function is obtained, and the optimal position of the test plate is used as the focusing position of the interference detection device. Then, compared with the existing manual focus judgment, which is prone to errors due to factors such as operator experience, the focusing method and system of the interference detection device of the present invention can improve focusing accuracy and reduce focusing errors by measuring the actual surface shape of the test plate and establishing a simulated surface shape and realizing the focusing of the interference detection device through corresponding calculations.

[0038] The method for obtaining the transfer function of an interference detection device of the present invention has a relatively accurate transfer function of the interference detection device due to the relatively high focusing accuracy and relatively small focusing error of the interference detection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention 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 only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 A flowchart of a focusing method for an interference detection device provided in one embodiment;

[0041] Figure 2 A schematic diagram of the arrangement of an interference detection device and a test plate for a focusing method of an interference detection device according to an embodiment;

[0042] Figure 3 A flowchart of a method for focusing and obtaining a transfer function of an interference detection device provided by an embodiment is provided.

[0043] The reference numerals in the drawings of the specification include:

[0044] 1-test board in initial position, 2-test board after moving position, 3-guide rail, 4-standard component, 5-interference detection device, 6-optical component, 7-detector. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0046] For reference Figure 1 , Figure 1 This is a flow chart of a focusing method for an interference detection device provided in one embodiment. As shown in the figure, the focusing method for the interference detection device includes the following steps:

[0047] S11: The test plate is arranged on the light-emitting side of the interference detection device, so that the test plate is respectively located at at least two positions along the light field propagation direction of the test plate. When the test plate is located at any of the at least two positions, the measured surface shape of the test plate is obtained by detecting with the interference detection device, wherein the at least two positions include an initial position, and for any of the at least two positions, the distance of the any position relative to the initial position along the light field propagation direction of the test plate is used to represent the position of the any position along the light field propagation direction of the test plate.

[0048] The test board is arranged on the light-emitting side of the interference detection device, and the test board and the interference detection device are arranged opposite to each other.

[0049] The at least two positions are at least two positions along the test board with different light field propagation directions. When the test board is at any of the at least two positions, the interference detection device emits test light, which is reflected by the test board. The interference detection device captures the test light reflected back from the test board and obtains the measured surface shape of the test board based on the interference result measured by the interference detection device. For any of the at least two positions, the measured surface shape of the test board at that position can be obtained. The light field propagation direction of the test board is the direction in which the test light reflected back from the test board propagates toward the interference detection device.

[0050] S12: Construct an ideal wavefront of the test plate, obtain a simulated degraded wavefront of the test plate at any of the at least two positions, and obtain a simulated surface shape of the test plate at any position based on the phase information of the simulated degraded wavefront at any position, wherein the simulated degraded wavefront at any position is represented by the convolution of the ideal wavefront and the Gaussian model at any position, and the Gaussian model at any position describes the decomposition of the light field of the test plate into multiple infinitesimals, and the complex amplitude of the infinitesimals when propagating to any position.

[0051] In this method, the light field of the test board is decomposed into multiple microelements. Complex beam tracing can be used to describe the propagation of the light field for each microelement. The microelement can be called a Gaussian microelement.

[0052] This method uses a Gaussian model to quantitatively describe the wavefront degradation phenomenon in interferometric testing. The Gaussian model is used to describe the wavefront degradation of the test panel's light field. The Gaussian model decomposes the light field into multiple Gaussian elements and describes the propagation of each Gaussian element using complex beam tracing. The degraded wavefront caused by defocus in interferometric testing is described by convolution of the test panel's ideal wavefront and the Gaussian model, serving as the simulated degraded wavefront. The test panel's surface shape is incorporated into the phase information of the simulated degraded wavefront.

[0053] An ideal wavefront of the test plate is constructed based on the pattern of the test plate. When the test plate is at any of the at least two positions, a simulated degraded wavefront at that position is obtained based on the ideal wavefront and the Gaussian model at that position. Simulated degraded wavefronts are obtained for each of the at least two positions.

[0054] For any one of the at least two positions, the simulated surface shape of the test plate at the position can be obtained based on the phase information of the simulated degenerate wavefront of the test plate at the position.

[0055] S13: Establish an objective function and solve the objective function to obtain the optimal position of the test plate along the light field propagation direction of the test plate that minimizes the value of the objective function, so as to move the test plate to the optimal position, wherein the objective function describes the difference between the simulated surface shape and the measured surface shape of the test plate at the at least two positions.

[0056] An objective function is established, describing the difference between the simulated and measured surface shapes of the test board at the at least two positions. The objective function is solved to obtain the optimal position of the test board along the light field propagation direction of the test board that minimizes the objective function. The optimal position of the test board is considered to be the focus position of the interferometer detection device. The test board is then moved to the optimal position, thereby achieving focus on the interferometer detection device.

[0057] Since the distance of any position along the test panel's light field propagation direction relative to the initial position represents the position of any position along the test panel's light field propagation direction, obtaining the test panel's optimal position along the test panel's light field propagation direction means obtaining the distance of the test panel along the test panel's light field propagation direction relative to the initial position when the test panel is at that optimal position. Therefore, by moving the test panel a corresponding distance from its initial position, the test panel can be moved to its optimal position.

[0058] The focusing method of the interference detection device of the present embodiment is to place the test plate at multiple positions on the light-emitting side of the interference detection device and measure the actual surface shape, and use the Gaussian model to construct the simulated degraded wavefront of the test plate at each position and obtain the simulated surface shape, and to establish an objective function that describes the difference between the simulated surface shape and the measured surface shape of the test plate at the at least two positions and solve the objective function to obtain the optimal position of the test plate that minimizes the value of the objective function, and the optimal position of the test plate is used as the focusing position of the interference detection device. Therefore, compared with the existing manual focus judgment, which is prone to errors due to factors such as operator experience, the focusing method of the interference detection device of the present embodiment measures the actual surface shape of the test plate and establishes the simulated surface shape and realizes the focusing of the interference detection device through corresponding calculations, which can improve the focusing accuracy and reduce the focusing error.

[0059] In some embodiments, the test plate is positioned at at least two positions along the propagation direction of the light field of the test plate. When the test plate is positioned at any of the at least two positions, obtaining the measured surface shape of the test plate by detecting with the interference detection device may include the following steps:

[0060] S111: placing the test plate at the initial position, and obtaining the measured surface shape of the test plate by detecting with the interference detection device;

[0061] S112: moving the test plate at least once along the propagation direction of the light field of the test plate, acquiring the moving distance after each movement of the test plate, and obtaining the measured surface shape of the test plate through detection by the interference detection device.

[0062] The test board is set on the light-emitting side of the interference detection device. First, the test board is located at the initial position, and the measured surface shape of the test board is obtained by the interference detection device to obtain the measured surface shape of the test board when it is in the initial position.

[0063] The test plate is then moved along the direction of the test plate's light field propagation. After each movement, the distance moved is measured and detected using an interferometer to determine the actual surface shape of the test plate. The distance moved is the distance the test plate's position after the movement is relative to its initial position. Since the test plate is moved along the direction of the test plate's light field propagation, the distance moved is the distance the test plate's position after the movement is relative to its initial position along the direction of the test plate's light field propagation.

[0064] Since the test board and the interference detection device are arranged relative to each other, the test light reflected back by the test board propagates to the interference detection device, so the light field propagation direction of the test board is along the light propagation direction from the test board to the interference detection device. Therefore, moving the test board along the light propagation direction from the test board to the interference detection device is equivalent to moving the test board along the light field propagation direction of the test board. In some embodiments, positioning the test board at at least two positions along the light field propagation direction of the test board includes: moving the test board along a guide rail so that the test board is positioned at the at least two positions, wherein the guide rail is arranged on the light-emitting side of the interference detection device and along the direction of the test light emitted by the interference detection device, and the test board is arranged on the guide rail. This makes it convenient to move the test board.

[0065] For example, you can refer to Figure 2 , Figure 2 This is a schematic diagram of the arrangement of an interference detection device and a test board in a focusing method of an interference detection device according to an embodiment. As shown in the figure, a guide rail 3 is provided on the light-emitting side of the interference detection device 5 , and the test board is provided on the guide rail 3 . Figure 2 The figure shows the test board 1 at the initial position and the test board 2 after the movement. Position A is the initial position and position B is the position after the movement. Figure 2 The example above uses the movement of the test plate once. In actual applications, the test plate can be moved multiple times, and the distance moved relative to the initial position after each movement is recorded accordingly, as well as the surface shape data at the corresponding position detected by the interference detection device 5. In actual applications, the specific value of each movement distance can be determined based on the actual application.

[0066] For any position on the test panel, the distance from the initial position along the light field propagation direction of the test panel is used to represent the position of that position along the light field propagation direction of the test panel. For example, if the position of any position along the light field propagation direction of the test panel is represented by z, then if the initial position, i.e., position A, has z=0, and if position B moves a distance d1 to the left relative to position A, then position B's z=-d1. If position B moves a distance d1 to the right relative to position A, then position B's z=d1. In other examples, if position B moves a distance d1 to the left relative to position A, then position B's z=d1, and if position B moves a distance d1 to the right relative to position A, then position B's z=-d1.

[0067] In some embodiments, the simulated degenerate wavefront at any location is expressed as:

[0068] ; (1)

[0069] Wherein, o(x, y, z) represents the simulated degraded wavefront, u(x, y) represents the ideal wavefront, and g(x, y, z) represents the Gaussian model of the light field element of the test plate. An XYZ three-dimensional coordinate system is established with the Z axis parallel to the optical axis of the light propagating from the test plate to the interference detection device, the XY plane is perpendicular to the optical axis, and (x, y, z) represents the position coordinates.

[0070] In some embodiments, the Gaussian model of the light field element of the test plate is expressed as:

[0071] ; (2)

[0072] Among them, g(x,y,z) represents the Gaussian model of the light field element of the test board, E(z) represents the light field amplitude, Φ E (x, y, z) represents the phase term related to the distribution in the direction perpendicular to the optical axis, Φ G (z) represents the Gouy phase term, Φ AC (z) represents the phase term related to the position along the optical axis, Φ0 represents the initial phase, and j represents the imaginary unit. An XYZ three-dimensional coordinate system is established, with the Z axis parallel to the optical axis of light propagating from the test plate to the interferometer. The XY plane is perpendicular to the optical axis, and (x, y, z) represents the position coordinates. This Gaussian model is also called an elliptical Gaussian model.

[0073] In some embodiments, the ideal wavefront can be expressed as:

[0074] ; (3)

[0075] Where A represents the amplitude of the ideal wavefront, Represents the phase of the ideal wavefront, k represents the wave vector and k=2π / λ, λ represents the wavelength of light, j represents the imaginary unit, wherein the Z axis is parallel to the optical axis of the light propagating from the test plate to the interference detection device, an XYZ three-dimensional coordinate system is established, the XY plane is perpendicular to the optical axis, and (x, y) represents the position coordinates in the XY plane.

[0076] Similar to the point spread function in image processing, in this embodiment, the degraded wavefront caused by defocus in interferometric detection is described by the convolution of the ideal wavefront of the test surface and a Gaussian model. The surface shape of the test surface is contained in the phase portion of the degraded wavefront. The method of this embodiment adopts the phase difference method, which can be applied to phase restoration and characterize the optical system by introducing an image containing known errors. For example, for an incoherent optical imaging system, the phase difference method can solve the point spread function of the optical imaging system. Based on the point spread function, the errors contained in the measured image can be decoupled to obtain a clearer image.

[0077] In the established objective function, the position z of the test board along the direction of the test board's light field propagation is an unknown quantity. The objective function is solved to obtain the position that minimizes the objective function. When the objective function value is minimized, z at this time is considered to be the test board's optimal position along the direction of the test board's light field propagation, and is considered to be the actual defocus amount compared to the initial position from the focused position. When the objective function value is minimized, z = z0. Therefore, the test board is moved from its initial position z0 to the focused position.

[0078] When solving the objective function, z is changed to find the z that satisfies the minimum value of the objective function. Finding the z value that satisfies the minimum objective function can be regarded as an optimization problem. The z that satisfies the minimum objective function can be solved by a line search algorithm, or other one-dimensional optimization algorithms can be used to solve it.

[0079] In some embodiments, the objective function describes the sum of preset absolute values ​​of the test plate at the at least two positions, and the preset absolute value at any position represents the absolute value of the difference between the simulated surface shape and the measured surface shape at any position.

[0080] In some embodiments, establishing the objective function includes: for the measured surface shape at any of the at least two positions, selecting surface shape data of an area having the same pattern as the simulated surface shape at any of the at least two positions from the measured surface shape at any of the at least two positions, and establishing the objective function based on the difference between the simulated surface shape of the test plate at the at least two positions and the surface shape data selected from the corresponding measured surface shape.

[0081] When establishing a simulated degraded wavefront for a test plate, a specific area can be selected from the test plate, a simulated degraded wavefront established for that area, an ideal wavefront established based on the pattern of that area on the test plate, and further a simulated degraded wavefront established when the test plate is moved to any position. Furthermore, for the measured surface shape of the test plate at any position, surface shape data for the corresponding area is selected from the measured surface shape, that is, surface shape data for the area with the same pattern as the simulated surface shape is selected from the measured surface shape. Then, an objective function is established based on the difference between the simulated surface shape of the test plate at the at least two positions and the surface shape data selected from the corresponding measured surface shape.

[0082] In some embodiments, the interference detection device 5 includes: an optical component 6, which is used to allow the reference light from the standard element 4 and the test light reflected by the test board to pass through the optical component 6 and then be incident on the detector 7; the standard element 4, which is used to separate a reference light from the test light incident on the standard element 4, return the reference light to the detector 7, allow the remaining test light to be emitted to the test board, and allow the test light reflected by the test board to pass through the standard element 4 and then be incident on the optical component 6; the detector 7 is used to obtain the interference result of the reference light and the test light reflected by the test board. For example, reference can be made to Figure 2 As shown, the interference detection device 5 includes a detector 7, an optical component 6 and a standard element 4. The optical component 6 represents an equivalent optical path inside the interference detection device 5.

[0083] This embodiment further provides a focusing system for an interference detection device, comprising:

[0084] an acquisition device, configured to acquire a measured surface shape of the test plate detected by the interference detection device when the test plate is located at any of at least two positions on the light-exiting side of the interference detection device, and to acquire a position of any of the at least two positions along the propagation direction of the light field of the test plate, wherein the at least two positions include an initial position, and for any of the at least two positions, the position of the any position along the propagation direction of the light field of the test plate is represented by a distance relative to the initial position along the propagation direction of the light field of the test plate;

[0085] a simulation device for constructing an ideal wavefront of the test plate, obtaining a simulated degraded wavefront of the test plate at any of the at least two positions, and obtaining a simulated surface shape of the test plate at any position based on phase information of the simulated degraded wavefront at any position, wherein the simulated degraded wavefront at any position is represented by the convolution of the ideal wavefront and a Gaussian model at any position, wherein the Gaussian model at any position describes the decomposition of the light field of the test plate into a plurality of microelements, and the complex amplitudes of the microelements when propagating to any position;

[0086] A solving device is used to establish an objective function and solve the objective function to obtain the optimal position of the test plate along the light field propagation direction of the test plate that minimizes the value of the objective function, so as to move the test plate to the optimal position, wherein the objective function describes the difference between the simulated surface shape and the measured surface shape of the test plate at the at least two positions.

[0087] The focusing system of the interference detection device of this embodiment places a test plate at multiple positions on the light-emitting side of the interference detection device and measures the actual surface shape, and uses a Gaussian model to construct a simulated degraded wavefront of the test plate at each position and obtain a simulated surface shape. By establishing a target function that describes the difference between the simulated surface shape and the actual surface shape of the test plate at the at least two positions and solving the target function, the optimal position of the test plate that minimizes the value of the target function is obtained, and the optimal position of the test plate is used as the focusing position of the interference detection device. Therefore, compared with the existing manual focus judgment, which is prone to errors due to factors such as operator experience, the focusing system of the interference detection device of this embodiment measures the actual surface shape of the test plate and establishes a simulated surface shape and realizes the focusing of the interference detection device through corresponding calculations, which can improve focusing accuracy and reduce focusing errors.

[0088] This embodiment also provides a method for obtaining a transfer function of an interference detection device, comprising the following steps:

[0089] S21: moving the test plate to a focusing position of the interference detection device according to the focusing method of the interference detection device described in any one of the above embodiments;

[0090] S22: enabling the interference detection device to obtain the measured surface shape of the test plate, and obtaining the instrument transfer function of the interference detection device according to the measured surface shape.

[0091] In the method for obtaining the transfer function of the interference detection device of this embodiment, the transfer function of the interference detection device obtained is more accurate because the focusing accuracy of the interference detection device is higher and the focusing error is smaller.

[0092] For example, you can refer to Figure 3 , Figure 3 This is a flow chart of a method for focusing and obtaining a transfer function of an interference detection device provided in one embodiment. As shown in the figure, it mainly includes the following steps:

[0093] Step 1: Set up the optical path and adjust the test board so that the test light reflected by the test board can be received by detector 7 of interference detection device 5. Interference fringes are obtained by reading the signal received by detector 7. The test board is adjusted so that detector 7 receives the interference signal. After adjustment, the surface shape data of the test board at this time is obtained based on the interference signal, and the position of the test board at this time is recorded and set as the initial position.

[0094] Step 2: Move the test plate and record the position of the test plate after the movement and the surface shape data detected by the interference detection device 5. Recording the position of the test plate after the movement means recording the distance of the test plate relative to the initial position after the movement.

[0095] Step 3: Construct the objective function.

[0096] Step 4: Solve the objective function. Determine whether the objective function is at its minimum. If not, change the focus error estimate and then determine again whether the objective function is at its minimum. If so, obtain an accurate estimate of the focus error. The focus error estimate is the position of the test plate that was solved.

[0097] Step 5: Move the test panel based on the accurate estimate of the focus error obtained to eliminate the focus error.

[0098] Step 6: The interference detection device 5 detects and obtains the measured surface shape of the test plate, and obtains the instrument transfer function of the interference detection device 5 according to the measured surface shape.

[0099] The present invention generates a virtual idealized test plate geometry, simulates a surface shape containing defocus error using an elliptical Gaussian model, and compares this with the measured surface shape of the test plate at two different locations. The defocus value corresponding to the minimum deviation is recorded as the desired defocus value. The test plate is then moved based on the obtained defocus value to eliminate the defocus error. The instrument transfer function (ITF) measured after the test plate is re-moved represents the optimal operating state of the interferometry device.

[0100] The pattern structure of the test board used in the instrument transfer function (ITF) test is known, so the wavefront degradation process in the interference detection can be simulated. Based on this, the present invention proposes to use an elliptical Gaussian model to simulate the wavefront degradation result, calculate the error between it and the measured wavefront degradation surface result caused by the defocus of the interference detection device, and find the distance to the optimal focus position by minimizing the error between the simulated wavefront degradation result and the measured result. In order to solve the problem that a single surface shape detection result of the interference detection device cannot accurately determine the direction of the defocus amount within the linear response range, the present invention proposes to introduce additional surface shape test results with known relative defocus amounts to determine the positive and negative signs of the defocus amount. Finally, accurate focusing can also be achieved by compensating for the defocus amount by moving the detector. When the detector of the interference detection device can be controlled to achieve precise quantitative movement, the method can be automatically implemented using a computer. If the detector of the interference detection device cannot be controlled, the defocus amount can be compensated by moving the test board.

[0101] The above is a detailed introduction to the focusing method, system and transfer function acquisition method of the interference detection device provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the present invention.

Claims

1. A focusing method for an interference detection device, characterized in that: include: Placing a test plate on the light-emitting side of an interference detection device, such that the test plate is located at at least two positions along the light field propagation direction of the test plate, and obtaining a measured surface shape of the test plate by detecting with the interference detection device when the test plate is located at any of the at least two positions, wherein the at least two positions include an initial position, and for any of the at least two positions, the distance of the any position relative to the initial position along the light field propagation direction of the test plate represents the position of the any position along the light field propagation direction of the test plate; Constructing an ideal wavefront of the test plate, obtaining a simulated degraded wavefront of the test plate at any of the at least two positions, and obtaining a simulated surface shape of the test plate at any position based on phase information of the simulated degraded wavefront at any position, wherein the simulated degraded wavefront at any position is represented by the convolution of the ideal wavefront and a Gaussian model at any position, wherein the Gaussian model at any position describes the decomposition of the light field of the test plate into a plurality of microelements, and the complex amplitudes of the microelements when propagating to any position; An objective function is established and solved to obtain the optimal position of the test plate along the light field propagation direction of the test plate that minimizes the value of the objective function, so as to move the test plate to the optimal position. The objective function describes the difference between the simulated surface shape and the measured surface shape of the test plate at the at least two positions.

2. The focusing method of the interference detection device according to claim 1, characterized in that: Positioning the test plate at at least two positions along a propagation direction of a light field of the test plate, and obtaining a measured surface shape of the test plate by detecting with the interference detection device when the test plate is at any of the at least two positions, comprises: The test plate is positioned at the initial position, and the measured surface shape of the test plate is obtained by detecting with the interference detection device; The test plate is moved at least once along the propagation direction of the light field of the test plate. After each movement of the test plate, the moving distance is obtained, and the measured surface shape of the test plate is obtained by detection using the interference detection device.

3. The focusing method of the interference detection device according to claim 1, characterized in that: The simulated degenerate wavefront at any position is expressed as: ； Wherein, o(x, y, z) represents the simulated degraded wavefront, u(x, y) represents the ideal wavefront, and g(x, y, z) represents the Gaussian model of the light field element of the test plate. An XYZ three-dimensional coordinate system is established with the Z axis parallel to the optical axis of the light propagating from the test plate to the interference detection device, the XY plane is perpendicular to the optical axis, and (x, y, z) represents the position coordinates.

4. The focusing method of the interference detection device according to claim 1, characterized in that: The Gaussian model of the light field element of the test plate is expressed as: ； Wherein, g(x, y, z) represents the Gaussian model of the light field element of the test plate, E(z) represents the light field amplitude, Φ E (x, y, z) represents the phase term related to the distribution in the direction perpendicular to the optical axis, Φ G (z) represents the Gouy phase term, Φ AC (z) represents the phase term related to the position along the optical axis, Φ0 represents the initial phase, j represents the imaginary unit, wherein the Z axis is parallel to the optical axis of the light propagating from the test plate to the interference detection device, an XYZ three-dimensional coordinate system is established, the XY plane is perpendicular to the optical axis, and (x, y, z) represents the position coordinates.

5. The focusing method of the interference detection device according to claim 1, characterized in that: The ideal wavefront is expressed as: ； Where A represents the amplitude of the ideal wavefront, Represents the phase of the ideal wavefront, k represents the wave vector and k=2π / λ, j represents the imaginary unit, wherein the Z axis is parallel to the optical axis of the light propagating from the test plate to the interference detection device, an XYZ three-dimensional coordinate system is established, the XY plane is perpendicular to the optical axis, and (x, y) represents the position coordinates in the XY plane.

6. The focusing method of the interference detection device according to claim 1, characterized in that: The objective function describes the sum of preset absolute values ​​of the test plate at the at least two positions, and the preset absolute value at any position represents the absolute value of the difference between the simulated surface shape and the measured surface shape at any position.

7. The focusing method of the interference detection device according to claim 1, characterized in that: Establishing the objective function includes: For the measured surface shape at any of the at least two positions, surface shape data of an area having the same pattern as the simulated surface shape at any position is selected from the measured surface shape at any position, and the objective function is established based on the difference between the simulated surface shape of the test plate at the at least two positions and the surface shape data selected from the corresponding measured surface shape.

8. The focusing method of an interference detection device according to any one of claims 1 to 7, characterized in that: The step of positioning the test plate at at least two positions along a propagation direction of the light field of the test plate comprises: The test plate is moved along a guide rail so that the test plate is located at the at least two positions respectively, wherein the guide rail is arranged on the light-emitting side of the interference detection device and along the direction of the test light emitted by the interference detection device, and the test plate is arranged on the guide rail.

9. A focusing system for an interference detection device, characterized in that: include: an acquisition device, configured to acquire a measured surface shape of the test plate detected by the interference detection device when the test plate is located at any of at least two positions on the light-exiting side of the interference detection device, and to acquire a position of any of the at least two positions along the propagation direction of the light field of the test plate, wherein the at least two positions include an initial position, and for any of the at least two positions, the position of the any position along the propagation direction of the light field of the test plate is represented by a distance relative to the initial position along the propagation direction of the light field of the test plate; a simulation device for constructing an ideal wavefront of the test plate, obtaining a simulated degraded wavefront of the test plate at any of the at least two positions, and obtaining a simulated surface shape of the test plate at any position based on phase information of the simulated degraded wavefront at any position, wherein the simulated degraded wavefront at any position is represented by the convolution of the ideal wavefront and a Gaussian model at any position, wherein the Gaussian model at any position describes the decomposition of the light field of the test plate into a plurality of microelements, and the complex amplitudes of the microelements when propagating to any position; A solving device is used to establish an objective function and solve the objective function to obtain the optimal position of the test plate along the light field propagation direction of the test plate that minimizes the value of the objective function, so as to move the test plate to the optimal position, wherein the objective function describes the difference between the simulated surface shape and the measured surface shape of the test plate at the at least two positions.

10. A method for obtaining a transfer function of an interference detection device, characterized in that: include: The focusing method for an interference detection device according to any one of claims 1 to 8, wherein the test plate is moved to a focusing position of the interference detection device; The interference detection device is enabled to obtain the measured surface shape of the test plate, and the instrument transfer function of the interference detection device is obtained according to the measured surface shape.

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