Laser interferometer, method of measuring thereof, optical detection system, and storage medium

Abstract

The application discloses a laser interferometer and a measurement method thereof, an optical detection system and a storage medium, and relates to the technical field of optical detection. In the laser interferometer, a first optical measurement element projects first measurement light to a measured grating according to a preset first incidence direction angle, and receives a first interference pattern formed by diffraction of the first measurement light by the measured grating; a second optical measurement element symmetrically arranged with the first optical measurement element projects second measurement light to the measured grating according to a second incidence direction angle symmetrical to the first incidence direction angle, and receives a second interference pattern formed by diffraction of the second measurement light by the measured grating; and an imaging acquisition module is used for determining a measurement result of the measured grating according to the first interference pattern and the second interference pattern, so that fast measurement of uniformity of a large-size grating period is realized without sacrificing measurement accuracy and non-destructiveness, and the detection requirement in industrial production is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical detection, in particular to a laser interferometer, a measurement method thereof, an optical detection system and a storage medium. BACKGROUND

[0002] With the deepening of the industrial application of micro-nano optical elements in the field of consumer AR (Augmented Reality, augmented reality) / XR (Extended Reality, extended reality) and other fields, users have higher requirements for the measurement accuracy, measurement efficiency and mass production applicability of the uniformity of the period of gratings and other micro-nano structures.

[0003] At present, the measurement of the period uniformity of gratings in the industry mainly relies on technical means such as optical microscopes, electron microscopes and atomic force microscopes. However, the above-mentioned measurement methods of the period uniformity of gratings all have significant technical defects. The optical microscope can only be used for qualitative observation and cannot realize quantitative measurement; the electron microscope is a destructive measurement method, which requires sample preparation and is easy to cause damage to the grating structure, affecting the measurement authenticity; the atomic force microscope can be used for quantitative measurement, but the speed is extremely slow and is only suitable for small field detection in the process development stage, that is, the above-mentioned measurement methods of the period uniformity of gratings are difficult to realize rapid, non-destructive and quantitative measurement of large-size (such as cm²) grating samples, and cannot meet the real-time monitoring and quality inspection requirements in the mass production process.

[0004] Therefore, under the premise of not sacrificing the measurement accuracy and non-destructiveness, how to realize the rapid measurement of the period uniformity of large-size gratings to adapt to the detection requirements in the industrial mass production is a technical problem to be solved at present. SUMMARY

[0005] The main purpose of the present application is to provide a laser interferometer, a measurement method thereof, an optical detection system and a storage medium, which aims to realize rapid measurement of the period uniformity of large-size gratings under the premise of not sacrificing the measurement accuracy and non-destructiveness, so as to adapt to the detection requirements in the industrial mass production.

[0006] To achieve the above-mentioned purpose, the present application provides a laser interferometer, which comprises:

[0007] a first optical measurement element, which is arranged to project first measurement light to a measured grating at a preset first incident direction angle, and receive a first interference pattern formed by diffraction of the first measurement light by the measured grating;

[0008] a second optical measurement element, the second optical measurement element is symmetrically arranged with the first optical measurement element, the second optical measurement element is arranged to project second measurement light to the measured grating at a second incident direction angle which is symmetric to the first incident direction angle, and receive a second interference pattern formed by diffraction of the second measurement light by the measured grating;

[0009] an imaging acquisition module, the imaging acquisition module is separately arranged at an imaging side of the first optical measurement element and an imaging side of the second optical measurement element, the imaging acquisition module is arranged to determine a measurement result of the measured grating according to the first interference pattern and the second interference pattern.

[0010] In an embodiment, the first optical measurement element and the second optical measurement element are the same optical measurement structure, the optical measurement structure is arranged at a grating period side of the measured grating.

[0011] The optical measurement structure comprises a laser light source, a reflecting optical element and a reference optical element, the reflecting optical element is arranged between the laser light source and the reference optical element, an imaging side of the reflecting optical element is arranged towards a side of the imaging acquisition module, and the reference optical element is arranged close to the grating period side.

[0012] In an embodiment, the first incident direction angle is a Littrow angle corresponding to a +1 diffraction order of the measured grating, and the second incident direction angle is a Littrow angle corresponding to a -1 diffraction order of the measured grating.

[0013] In an embodiment, the imaging acquisition module comprises:

[0014] a first image acquisition unit, the first image acquisition unit is arranged at an imaging side of the first optical measurement element, the first image acquisition unit is arranged to acquire the first interference pattern;

[0015] a second image acquisition unit, the second image acquisition unit is arranged at an imaging side of the second optical measurement element, the second image acquisition unit is arranged to acquire the second interference pattern;

[0016] a processing unit, the processing unit is electrically connected with the first image acquisition unit and the second image acquisition unit respectively, the processing unit is arranged to determine a measurement result of the measured grating according to the first interference pattern and the second interference pattern.

[0017] In addition, the present application also provides a measurement method of a laser interferometer, the measurement method of the laser interferometer is applied to the laser interferometer described above, and the measurement method of the laser interferometer comprises:

[0018] After the first optical measurement element projects the first measurement light to the measured grating according to the preset first incident direction angle, a first interference pattern formed by diffraction of the first measurement light by the measured grating is acquired;

[0019] After the second optical measurement element projects the second measurement light to the measured grating according to the second incident direction angle symmetrical to the first incident direction angle, a second interference pattern formed by diffraction of the second measurement light by the measured grating is acquired;

[0020] The measurement result of the measured grating is determined according to the first interference pattern and the second interference pattern.

[0021] In an embodiment, the step of determining the measurement result of the measured grating according to the first interference pattern and the second interference pattern comprises:

[0022] A two-dimensional image coordinate system is constructed with the image width of the first interference pattern and the second interference pattern as the horizontal axis and the image height of the first interference pattern and the second interference pattern as the vertical axis;

[0023] The first horizontal axis phase distribution function of the first interference pattern in the horizontal axis direction and the second horizontal axis phase distribution function of the second interference pattern in the horizontal axis direction are determined based on the two-dimensional image coordinate system;

[0024] The uniformity threshold of the measured grating is determined according to the first horizontal axis phase distribution function and the second horizontal axis phase distribution function, and the measurement result of the measured grating is determined according to the uniformity threshold.

[0025] In an embodiment, the step of determining the uniformity threshold of the measured grating according to the first horizontal axis phase distribution function and the second horizontal axis phase distribution function comprises:

[0026] The period error accumulation of the measured grating along the grating period arrangement direction is determined according to the first horizontal axis phase distribution function and the second horizontal axis phase distribution function;

[0027] All local period errors of the measured grating along the grating period arrangement direction are obtained by differentiating the period error accumulation, and the number of local period errors satisfying a preset error condition among all the local period errors is counted;

[0028] The uniformity threshold of the measured grating is obtained based on the number of local period errors satisfying the preset error condition and the total number of all the local period errors.

[0029] In an embodiment, the step of determining the measurement result of the measured grating according to the uniformity threshold comprises:

[0030] detecting whether the uniformity threshold exceeds a preset uniformity reference threshold;

[0031] if the uniformity threshold does not exceed the uniformity reference threshold, determining that the measurement result of the measured grating is that the measured grating is unqualified;

[0032] if the uniformity threshold exceeds the uniformity reference threshold, determining that the measurement result is that the measured grating is qualified

[0033] In addition, to achieve the above object, the present application also provides an optical detection system, which comprises the laser interferometer described above, or a memory, a processor and a computer program stored in the memory and executable on the processor, which implements the steps of the measurement method of the laser interferometer as described above when executed by the processor.

[0034] In addition, to achieve the above object, the present application also provides a computer storage medium, which stores a computer program, which implements the steps of the measurement method of the laser interferometer as described above when executed by a processor.

[0035] The laser interferometer provided by the present application realizes fast and quantitative measurement of the periodic uniformity of a large-size grating under the premise of not sacrificing measurement accuracy and non-destructiveness, and significantly improves the detection efficiency and applicability in the production process of the grating. Specifically, by symmetrically arranging the first optical measurement element and the second optical measurement element, the first incidence direction angle and the second incidence direction angle are symmetrically projected onto the measured grating to project the first measurement light and the second measurement light, respectively. Next, the first optical measurement element and the second optical measurement element respectively receive the first measurement light and the second measurement light diffracted by the measured grating to form a first interference pattern and a second interference pattern, effectively avoiding the problems of traditional optical microscopes, which can only be qualitatively observed and cannot realize quantitative measurement, and electron microscopes and atomic force microscopes, which are destructive, slow or have limited field of view. Subsequently, by arranging the imaging acquisition modules on the imaging side of the first optical measurement element and the imaging side of the second optical measurement element, the measurement result of the measured grating is determined according to the obtained first interference pattern and second interference pattern, thereby overcoming the defects of traditional measurement methods, such as low measurement efficiency and limited applicable size, caused by the inability to synchronously acquire multi-angle diffraction information and integrate processing, thereby realizing fast and quantitative measurement of large-size grating samples while maintaining non-destructiveness and high accuracy, significantly improving real-time monitoring and quality inspection capabilities in the production scene, and meeting the efficient detection needs in industrial applications. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The figure is a schematic diagram of the architecture of the laser interferometer of the present application.

[0037] Figure 2 Structure diagram of the laser interferometer involved in the present application;

[0038] Figure 3 Two-dimensional phase distribution map involved in the embodiment scheme of the present application;

[0039] Figure 4 Net phase difference distribution map involved in the embodiment scheme of the present application;

[0040] Figure 5 Local period error distribution map involved in the embodiment scheme of the present application;

[0041] Figure 6 Flowchart of the second embodiment involved in the measurement method of the laser interferometer of the present application;

[0042] Figure 7 Device structure diagram of the hardware running environment of the device involved in the present application.

[0043] Explanation of reference numerals:

[0044] 10, first optical measurement element; 20, second optical measurement element; 30, imaging acquisition module; 100, laser light source; 200, reflecting optical element; 300, reference optical element; 31, first image acquisition unit; 32, second image acquisition unit; 33, processing unit.

[0045] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0046] It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0047] In order to better understand the technical solutions of the present application, the following will be described in detail in combination with the drawings and specific embodiments.

[0048] Micro-nano optical elements, such as diffraction gratings, super lenses, etc., are being industrialized, and especially waveguide elements based on diffraction gratings have been applied to many consumer-grade AR (Augmented Reality) and XR (Extended Reality) products.

[0049] The measurement methods of micro-nano optical elements usually include OM (Optical Microscope), SEM (Scanning Electron Microscope), AFM (Atomic Force Microscope), etc. OM cannot quantitatively represent the characteristics of micro-nano elements, and is usually used in dark field mode to qualitatively observe the uniformity of processing; SEM is destructive, and needs to be sliced and sprayed with gold powder for sample preparation, and the photoresist structure will change under the bombardment of electrons, which makes it difficult to guarantee the measurement accuracy; the test speed of AFM is extremely slow, and it can only be used to develop process parameters. SEM and AFM are generally used to quantitatively measure micro-nano structures in a small field (um 2 level), and cannot measure macro areas (cm 2 level) through single imaging. Obviously, the above three conventional measurement methods are difficult to be used for mass production monitoring, and it is urgent to develop a non-destructive, fast and quantitative micro-nano element measurement method to meet the measurement needs of mass production.

[0050] Therefore, based on the technical defects of the above three micro-nano element measurement methods, the laser interferometer of the present application is proposed. The solution of the embodiment of the present application is: through the symmetrically arranged first optical measurement element and second optical measurement element, respectively, the first incidence direction angle and the second incidence direction angle are symmetrically projected to the measured grating first measurement light and second measurement light; next, through the first optical measurement element and the second optical measurement element, respectively, the first measurement light and the second measurement light diffracted by the measured grating form a first interference graph and a second interference graph, which effectively avoids the problems of traditional optical microscopes that can only be qualitatively observed and cannot be quantitatively measured, and the destructive, slow speed or limited field of view of electron microscopes and atomic force microscopes; then, through the imaging acquisition modules arranged on the imaging side of the first optical measurement element and the imaging side of the second optical measurement element, the measurement results of the measured grating are determined according to the obtained first interference graph and second interference graph, thereby overcoming the defects of traditional measurement methods that cannot synchronously obtain multi-angle diffraction information and perform integrated processing, resulting in low measurement efficiency and limited applicable scale, so as to realize fast and quantitative measurement of large-size grating samples while maintaining non-destructive and high precision, significantly improve the real-time monitoring and quality inspection capability in the mass production scene, and meet the efficient detection needs in industrial application.

[0051] Based on this, the embodiment of the present application provides a laser interferometer, referring Figure 1 , Figure 1 to the schematic diagram of the architecture of the laser interferometer of the present application. The laser interferometer comprises:

[0052] The first optical measurement element 10 is arranged to project first measurement light to the measured grating at a preset first incidence direction angle, and receive first-order diffracted light of the first measurement light returned along the same path after being diffracted by the measured grating.

[0053] In the embodiment, with reference to Figure 1 , the first optical measurement element 10 projects first measurement light to the measured grating at a preset first incidence direction angle, and receives first-order diffracted light of the first measurement light returned along the same path after being diffracted by the measured grating; then, the first-order diffracted light and first reference light inside the first optical measurement element 10 form a first interference pattern on the imaging side of the first optical measurement element 10. The phase information of the measured grating at a specific direction (usually Littrow angle) is quickly, non-contact and full-field collected.

[0054] It should be noted that the preset first incidence direction angle usually refers to the Littrow angle, i.e. a specific incidence angle satisfying the Littrow configuration. The angle of the first incidence direction angle can be determined based on the grating equation of the measured grating, and can also be customized according to application requirements, which is not limited in the present application; wherein the grating equation based on the measured grating is as follows:

[0055] … Equation (1)

[0056] Wherein, represents the nominal period of the measured grating; represents the first incidence direction angle; represents the diffraction angle;

[0057] is the diffraction order, =1; is the wavelength of the laser used by the laser interferometer.

[0058] Under the Littrow configuration, the first-order diffracted light returns along the original path, i.e. the diffraction angle is equal to the first incidence direction angle . Therefore, by substituting the condition , the simplified equation based on equation (1) is obtained , so that the first incidence direction angle can be accurately calculated.

[0059] The first interference pattern includes the period distribution information of the measured grating itself and the geometric contribution of the substrate surface.

[0060] A second optical measurement element 20 is symmetrically arranged with the first optical measurement element 10, and is arranged to project second measurement light to the measured grating at a second incident direction angle which is symmetric to the first incident direction angle, and to receive a second interference pattern formed by diffraction of the second measurement light by the measured grating.

[0061] In the embodiment, with reference to Figure 1 , the second optical measurement element 20 is strictly symmetric to the first optical measurement element 10 about the normal of the measured grating in the spatial light path arrangement, and projects second measurement light to the same measured grating at a second incident direction angle which is symmetric to the first incident direction angle, and receives corresponding first-order diffraction light which returns along the original path to form a second interference pattern.

[0062] It should be noted that the present application symmetrically arranges the second optical measurement element 20 with the first optical measurement element 10, so that the second measurement light and the first measurement light are incident on the same measured grating at angles of equal size and opposite direction, which lays a physical foundation for subsequent differential measurement to eliminate common-mode errors.

[0063] The second interference pattern also includes the period distribution information of the measured grating itself and the geometric contribution of the substrate surface profile.

[0064] An imaging acquisition module 30 is separately arranged on the imaging side of the first optical measurement element 10 and the imaging side of the second optical measurement element 20, and is arranged to determine the measurement result of the measured grating according to the first interference pattern and the second interference pattern.

[0065] In the embodiment, with reference to Figure 1, the imaging acquisition module 30 is arranged on the imaging side of the first optical measurement element 10 and the second optical measurement element 20, and is responsible for synchronously or according to a preset image acquisition sequence acquiring the first interference pattern and the second interference pattern; next, the first interference pattern and the second interference pattern are image-registered to ensure strict correspondence of the first interference pattern and the second interference pattern in spatial pixel positions, thereby laying a foundation for subsequent accurate differential calculation; after the image registration is completed, the corresponding first transverse-axis phase distribution function and the second transverse-axis phase distribution function are extracted from the first interference pattern and the second interference pattern by calling a phase demodulation algorithm arranged in the imaging acquisition module 30; next, the first transverse-axis phase distribution function and the second transverse-axis phase distribution function are processed by difference, so that common-mode errors introduced by the base surface of the measured grating can be automatically offset, and phase difference information purely reflecting the period distribution of the measured grating can be extracted; subsequently, by performing spatial differential operation on the phase difference information, a local period error two-dimensional distribution map in units of "nanometer / period" can be directly obtained; next, according to the local period error two-dimensional distribution map, the measurement result of the measured grating can be accurately obtained, and rapid and quantitative evaluation of the period uniformity of the large-size grating (centimeter level) in the full field of view is realized, thereby providing a direct basis for process monitoring and product quality grading.

[0066] It should be noted that the preset image acquisition sequence can be understood as being customized based on application requirements, and the image acquisition sequence can be to acquire the first interference pattern first and then acquire the second interference pattern, or to acquire the second interference pattern first and then acquire the first interference pattern, which is not limited in the present application.

[0067] Further, in some other possible embodiments, referring to Figure 2 , the first optical measurement element 10 and the second optical measurement element 20 are the same optical measurement structural member, and the optical measurement structural member is arranged on the grating period side of the measured grating; the optical measurement structural member includes a laser light source 100, a reflecting optical element 200 and a reference optical element 300, the reflecting optical element 200 is arranged between the laser light source 100 and the reference optical element 300, the imaging side of the reflecting optical element 200 is arranged towards one side of the imaging acquisition module 30, and the reference optical element 300 is arranged close to the grating period side.

[0068] In the embodiment, the position of the reflective optical element 200 is adjusted so that the measurement light provided by the laser light source 100 is incident at the Littrow angle and penetrates the reference optical element 300 to project to the side of the grating period of the measured grating, at this time, the reflected light formed by the measurement light on the reference optical element 300 is projected to the reflective optical element 200 as the reference light; next, the diffraction light formed by the measurement light via the measured grating returns to the reflective optical element 200 along the original path, and the diffraction light and the reference light interfere to form an interference phase map.

[0069] It should be noted that the laser light source 100 can be a gas laser or a solid-state single-frequency laser, which can provide a high-coherence laser beam for grating uniformity measurement.

[0070] The reference optical element 300 can be a reference mirror. The reflective optical element 200 can be a partial mirror, which can divide the measurement light into two light beams, one of which is reflected to the reflective optical element 200 as the reference light, and the other of which penetrates the partial mirror to the measured grating; in addition, the light beam ratio of the two light beams can be customized according to application requirements, for example, the light beam ratio can be 50:50.

[0071] When the optical measurement structure is the first optical measurement element 10, the measurement light is the first measurement light, the reference light is the first reference light, the diffraction light is the first diffraction light, and the interference phase map is the first interference map; when the optical measurement structure is the second optical measurement element 20, the measurement light is the second measurement light, the reference light is the second reference light, the diffraction light is the second diffraction light, and the interference phase map is the second interference map.

[0072] Further, in some possible embodiments, the first incidence direction angle is the Littrow angle corresponding to the +1 diffraction order of the measured grating, and the second incidence direction angle is the Littrow angle corresponding to the -1 diffraction order of the measured grating.

[0073] In the embodiment, the first incidence direction angle is the Littrow angle corresponding to the +1 diffraction order of the measured grating, and the second incidence direction angle is the Littrow angle corresponding to the -1 diffraction order of the measured grating. Specifically, the Littrow angles of ±1 diffraction order can be understood as two specific incidence angles of equal size but opposite direction, which are symmetrically distributed on the two sides of the grating normal as shown by the dashed line. Figure 2

[0074] ​Further, in some possible embodiments, the imaging acquisition module 30 comprises: a first image acquisition unit 31 arranged on the imaging side of the first optical measurement element 10, configured to acquire the first interference pattern; a second image acquisition unit 32 arranged on the imaging side of the second optical measurement element 20, configured to acquire the second interference pattern; and a processing unit 33 electrically connected to the first image acquisition unit 31 and the second image acquisition unit 32 respectively, configured to determine the measurement result of the measured grating according to the first interference pattern and the second interference pattern.

[0075] In the present embodiment, referring to Figure 2 , the first image acquisition unit 31 is arranged on the imaging side of the first optical measurement element 10, and the first image acquisition unit 31 is configured to acquire the first interference pattern formed by the interaction of the first measurement light and the measured grating; the second image acquisition unit 32 is symmetrically arranged on the imaging side of the second optical measurement element 20, and the second image acquisition unit 32 is configured to acquire the second interference pattern formed by the interaction of the second measurement light and the measured grating; then, the processing unit 33 is electrically connected to the first image acquisition unit 31 and the second image acquisition unit 32 respectively, and after receiving the first interference pattern and the second interference pattern sent by the first image acquisition unit 31 and the second image acquisition unit 32 respectively, the processing unit 33 performs image registration on the first interference pattern and the second interference pattern, so as to ensure the strict correspondence of the first interference pattern and the second interference pattern in the spatial pixel position, thereby laying a foundation for the subsequent accurate difference calculation; after completing the image registration, the processing unit 33 calls the phase demodulation algorithm arranged in the imaging acquisition module 30 to extract the corresponding first transverse axis phase distribution function and the second transverse axis phase distribution function from the first interference pattern and the second interference pattern respectively; then, the first transverse axis phase distribution function and the second transverse axis phase distribution function are processed by difference, so as to automatically offset the common-mode error introduced by the base surface of the measured grating, thereby extracting the phase difference information which purely reflects the period distribution of the measured grating; subsequently, by performing spatial differential operation on the phase difference information, the local period error two-dimensional distribution map in the unit of "nanometer / period" can be directly obtained; then, according to the local period error two-dimensional distribution map, the measurement result of the measured grating can be accurately obtained, so as to realize the rapid and quantitative evaluation of the period uniformity of the large-size grating (centimeter level) in the full field of view, and provide a direct basis for process monitoring and product quality grading.

[0076] It should be noted that the first image acquisition unit 31 and the second image acquisition unit 32 can be a camera, a camera, an image sensor, etc.

[0077] In specific embodiments, after the processing unit 33 receives the first interference pattern and the second interference pattern sent by the first image acquisition unit 31 and the second image acquisition unit 32 respectively, the processing unit 33 respectively performs phase demodulation on the first interference pattern and the second interference pattern to obtain Figure 3 a first two-dimensional phase distribution shown in (a) and Figure 3 a second two-dimensional phase distribution shown in (b); next, the first two-dimensional phase distribution and the second two-dimensional phase distribution are precisely image-registered to realize pixel-level spatial alignment; then, the registered first two-dimensional phase distribution and the registered second two-dimensional phase distribution are subtracted to obtain Figure 4 a net phase difference distribution shown in (c) which eliminates the common-mode error of the base surface type, the net phase difference distribution is used to represent the accumulated amount of period error of the actual grating relative to the ideal grating at any position in the two-dimensional plane, which provides a direct basis for further extracting local period uniformity; subsequently, the accumulated amount of period error is spatially differentiated along the grating line direction (i.e. the horizontal axis direction) of the measured grating to obtain Figure 5 a local period error distribution shown in (d) in units of “nanometer / period”, thereby realizing full-field and quantitative characterization of the period uniformity of the grating.

[0078] It should be noted that the phase information of the first two-dimensional phase distribution can be represented by a first horizontal axis phase distribution function; the phase information of the second two-dimensional phase distribution can be represented by a second horizontal axis phase distribution function; the local period error distribution includes a plurality of local period errors, and each local period error can be an error of the grating period corresponding to each horizontal axis coordinate relative to the ideal optical period.

[0079] In summary, the laser interferometer provided by the application realizes rapid and quantitative measurement of the uniformity of the period of a large-size grating without sacrificing measurement accuracy and non-destructiveness, and significantly improves the detection efficiency and applicability in the production process of the grating. Specifically, the first optical measurement element 10 and the second optical measurement element 20 are symmetrically arranged, and the first incidence direction angle and the second incidence direction angle are symmetrically arranged to project the first measurement light and the second measurement light to the measured grating; then, the first optical measurement element 10 and the second optical measurement element 20 receive the first measurement light and the second measurement light diffracted by the measured grating to form the first interference pattern and the second interference pattern, which effectively avoids the problems of the traditional optical microscope that can only be qualitatively observed and cannot realize quantitative measurement, and the problems of the electron microscope and the atomic force microscope that are destructive, slow or have limited field of view; then, the imaging acquisition module 30 arranged on the imaging side of the first optical measurement element 10 and the imaging side of the second optical measurement element 20 determines the measurement result of the measured grating according to the obtained first interference pattern and second interference pattern, thereby overcoming the defects of the traditional measurement method that cannot synchronously obtain multi-angle diffraction information and perform integrated processing, resulting in low measurement efficiency and limited applicable scale, thereby realizing rapid and quantitative measurement of a large-size grating sample while maintaining non-destructiveness and high accuracy, significantly improving the real-time monitoring and quality inspection capability in the production scene, and meeting the efficient detection requirements in industrial applications.

[0080] Further, based on the first embodiment of the application described above, referring to Figure 6 , the second embodiment of the measurement method of the laser interferometer applied by the application is proposed. It should be noted that the execution subject of the 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 a device, an optical detection system, etc. that can realize the above functions. The optical detection system integrated with the laser interferometer is taken as an example to describe the embodiment and the following embodiments.

[0081] The measurement method of the laser interferometer provided by the application includes steps S10 to S30.

[0082] Step S10: After the first optical measurement element 10 projects the first measurement light to the measured grating at the preset first incidence direction angle, a first interference pattern formed by the first measurement light diffracted by the measured grating is obtained.

[0083] In the embodiment, referring to Figure 1, the first optical measurement element 10 projects first measurement light to the measured grating at a preset first incidence direction angle, and receives first-order diffracted light of the first measurement light returned along the same path after being diffracted by the measured grating; then, the first-order diffracted light and first reference light inside the first optical measurement element 10 form a first interference pattern on the imaging side of the first optical measurement element 10. The phase information of the measured grating at a specific direction (usually Littrow angle) is quickly, non-contact and full-field collected.

[0084] It should be noted that the preset first incidence direction angle usually refers to the Littrow angle, that is, a specific incidence angle satisfying the Littrow configuration. The angle of the first incidence direction angle can be determined based on the grating equation of the measured grating, and can also be customized according to application requirements, which is not limited in the present application; wherein the grating equation based on the measured grating is as follows:

[0085] … Equation (1)

[0086] Wherein, represents the nominal period of the measured grating; represents the first incidence direction angle; represents the diffraction angle;

[0087] is the diffraction order, = 1; is the wavelength of the laser used by the laser interferometer.

[0088] Under the Littrow configuration, the first-order diffracted light returns along the original path, that is, the diffraction angle is equal to the first incidence direction angle . Therefore, by substituting the condition , the simplified equation based on equation (1) is obtained , so that the first incidence direction angle can be accurately calculated.

[0089] The first interference pattern includes the period distribution information of the measured grating itself and the geometric contribution of the base surface type.

[0090] Step S20: After the second optical measurement element 20 projects second measurement light to the measured grating at a second incidence direction angle symmetrical to the first incidence direction angle, a second interference pattern formed by diffracting the second measurement light by the measured grating is obtained.

[0091] In the present embodiment, reference is made to Figure 1The second optical measurement element 20 is strictly symmetrical with the first optical measurement element 10 about the normal of the measured grating on the spatial light path arrangement, the second optical measurement element 20 projects second measurement light to the same measured grating according to a second incident direction angle symmetrical with the first incident direction angle, and receives corresponding first-order diffracted light returned along the original path to form a second interference pattern.

[0092] It should be noted that the second optical measurement element 20 is symmetrically arranged with the first optical measurement element 10, so that the second measurement light and the first measurement light are incident on the same measured grating at equal size and opposite direction angles, which lays a physical foundation for subsequent differential measurement to eliminate common-mode errors.

[0093] The second interference pattern also includes the period distribution information of the measured grating itself and the geometric contribution of the substrate surface type.

[0094] Step S30: determining the measurement result of the measured grating according to the first interference pattern and the second interference pattern.

[0095] In the embodiment, the imaging and collecting module 30 is arranged on the light exit side of the first light path module and the second light path module, respectively, for synchronously receiving and collecting the first interference pattern formed by the first light path module and the second interference pattern formed by the second light path module, and performing grating uniformity measurement on the first interference pattern and the second interference pattern, so that the measurement result of the measured grating can be accurately obtained, and high-precision grating uniformity detection can be completed without moving the measured grating, which significantly improves the measurement efficiency of the grating uniformity.

[0096] In the embodiment, referring to Figure 1, the imaging acquisition module 30 is responsible for synchronously or according to a preset image acquisition sequence acquiring the first interference pattern and the second interference pattern; next, the first interference pattern and the second interference pattern are image registered, the strict correspondence of the first interference pattern and the second interference pattern on the spatial pixel position is ensured, thereby laying a foundation for subsequent accurate differential calculation; after the image registration is completed, the corresponding first transverse axis phase distribution function and the second transverse axis phase distribution function are respectively extracted from the first interference pattern and the second interference pattern by calling a phase demodulation algorithm arranged in the imaging acquisition module 30; next, the first transverse axis phase distribution function and the second transverse axis phase distribution function are processed by difference, thereby the common-mode error introduced by the base surface of the measured grating can be automatically offset, and the phase difference information purely reflecting the period distribution of the measured grating is extracted; subsequently, the local period error two-dimensional distribution graph in units of "nanometer / period" can be directly obtained by performing spatial differential operation on the phase difference information; next, the measurement result of the measured grating can be accurately obtained according to the local period error two-dimensional distribution graph, the rapid and quantitative evaluation of the period uniformity in the full field of view of the large-size grating (centimeter level) is realized, and a direct basis for process monitoring and product quality grading is provided.

[0097] It should be noted that the preset image acquisition sequence can be understood as being customized based on application requirements, and the image acquisition sequence can be acquiring the first interference pattern first and then acquiring the second interference pattern, or acquiring the second interference pattern first and then acquiring the first interference pattern, which is not limited in the present application.

[0098] Further, in other feasible embodiments, the step S30 of determining the measurement result of the measured grating according to the first interference pattern and the second interference pattern can further include steps S301 to S303.

[0099] The step S301: a two-dimensional image coordinate system is constructed with the image width of the first interference pattern and the second interference pattern as a transverse axis and with the image height of the first interference pattern and the second interference pattern as a longitudinal axis.

[0100] In the present embodiment, the two-dimensional image coordinate system is constructed with the image width of the first interference pattern and the second interference pattern as a transverse axis and with the image height of the first interference pattern and the second interference pattern as a longitudinal axis, thereby the unified two-dimensional image coordinate system can be constructed for the pixel-level spatial position registration of the first interference pattern and the second interference pattern.

[0101] The step S302: a first transverse axis phase distribution function of the first interference pattern in the transverse axis direction and a second transverse axis phase distribution function of the second interference pattern in the transverse axis direction are respectively determined based on the two-dimensional image coordinate system.

[0102] In this embodiment, in a two-dimensional image coordinate system, phase demodulation processing is performed on the first interferogram and the second interferogram respectively, and the phase distribution of the first interferogram and the second interferogram in the horizontal axis direction (usually corresponding to the grating line direction) is extracted, so that the first horizontal axis phase distribution function of the first interferogram and the second horizontal axis phase distribution function of the second interferogram can be accurately obtained.

[0103] It should be noted that the first horizontal axis phase distribution function can be the horizontal position coordinates of the grating extracted from the first interferogram. The changing phase distribution function, the second horizontal axis phase distribution function can be the lateral position coordinates of the grating extracted from the second interferogram. The changing phase distribution function.

[0104] Step S303: Determine the uniformity threshold of the grating under test based on the first horizontal axis phase distribution function and the second horizontal axis phase distribution function, and determine the measurement result of the grating under test based on the uniformity threshold.

[0105] In this embodiment, based on the first horizontal axis phase distribution function and the second horizontal axis phase distribution function, the cumulative periodic error of the grating under test along the grating scribe line direction (i.e., the horizontal axis direction) can be accurately calculated, thereby reflecting the overall distribution trend and accumulation degree of the grating periodic error. Next, by differentiating the cumulative periodic error, the horizontal position coordinates of each grating on the grating under test are obtained. The local periodic error is transformed from macroscopic cumulative quantity to microscopic local characteristics. Finally, by counting the number of local periodic errors that meet the preset error conditions among all local periodic errors and comparing it with the total number of all local periodic errors, the uniformity threshold that can quantify the overall uniformity level of the grating under test is finally calculated.

[0106] It should be noted that the preset error condition can be understood as the condition that the local periodic error is within a preset ideal error range, which can be represented by […]. ] indicates that, This represents the lower limit of the error corresponding to the ideal error range. This represents the upper limit of the error corresponding to the ideal error range, and as well as The value can be customized according to application requirements, and this application does not impose any restrictions here.

[0107] Furthermore, in some other feasible embodiments, the above step S303: determining the uniformity threshold of the grating under test based on the first horizontal axis phase distribution function and the second horizontal axis phase distribution function may also include steps S3031 to S3033.

[0108] Step S3031: Based on the first horizontal axis phase distribution function and the second horizontal axis phase distribution function, determine the cumulative periodic error of the grating under test arranged along the horizontal axis direction.

[0109] In this embodiment, the first horizontal axis phase distribution function is... Phase distribution function with the second horizontal axis After subtraction, it is compared with the nominal period of the grating being measured. By performing a product process, the cumulative periodic error of the actual grating relative to the ideal grating is obtained, which can reflect the distribution trend and accumulation degree of the grating periodic error as a whole.

[0110] Step S3032: Perform differentiation processing based on the cumulative periodic error to obtain all local periodic errors of the grating under test, and count the number of local periodic errors that meet the preset error conditions among all the local periodic errors.

[0111] In this embodiment, the cumulative periodic error is calculated. Regarding the lateral position coordinates of each grating The first derivative is used to obtain the coordinates of the transverse position of the grating under test in each grating. Local periodic error at the location This process transforms macroscopic cumulative quantities into microscopic local characteristics. Subsequently, it detects whether each local periodic error is within a preset ideal error range and counts the number of local periodic errors within this ideal error range, thus obtaining the number of local periodic errors that meet the preset error conditions.

[0112] It should be noted that local periodic errors The expression for the calculation algorithm is as follows:

[0113] ;

[0114] ;

[0115] in, Indicates the lateral position coordinates of the grating; This represents the cumulative periodic error of the actual grating relative to the ideal grating. Represents the phase distribution function of the first horizontal axis; This represents the phase distribution function along the second horizontal axis; Indicates the nominal period of the grating being measured; This represents the local periodic error, which can be understood as the lateral position coordinate of the grating under test. The error of the grating period at a given location relative to the ideal optical period.

[0116] Step S3033: obtaining the uniformity threshold of the measured grating based on the number of the local period errors satisfying the preset error condition and the total number of all the local period errors.

[0117] In the embodiment, the proportion data between the number of the local period errors satisfying the preset error condition and the total number of all the local period errors is calculated, and the percentage of the proportion data is taken as the uniformity threshold quantitatively representing the overall uniformity level of the measured grating. Finally, the uniformity threshold is compared with the preset uniformity reference threshold, so that the measurement result of whether the measured grating is qualified can be accurately obtained, the complex interference pattern information is converted into an objective and quantitative qualification determination, and the efficiency and reliability of the grating uniformity measurement are significantly improved.

[0118] Further, in some possible embodiments, the step S303 of determining the measurement result of the measured grating according to the uniformity threshold can further include steps A10 to A30.

[0119] Step A10: detecting whether the uniformity threshold exceeds a preset uniformity reference threshold.

[0120] In the embodiment, by automatically comparing the calculated uniformity threshold with the preset uniformity reference threshold, an objective and unified determination reference is established, the subjectivity and inconsistency introduced by the manual experience in interpreting the interference pattern in the traditional detection are completely eliminated, the measurement result has the standardized characteristics of repeatability and verifiability, and a reliable data decision basis is laid for subsequent automatic determination.

[0121] It should be noted that the preset uniformity reference threshold can be customized according to application requirements, and the present application does not make any limitation here.

[0122] Step A20: if the uniformity threshold does not exceed the uniformity reference threshold, determining that the measurement result of the measured grating is that the measured grating is unqualified.

[0123] In the embodiment, when it is detected that the uniformity threshold does not exceed the preset reference threshold, it is automatically determined that the measurement result of the measured grating is that the measured grating is unqualified, the fast and accurate screening of the substandard grating product is realized, the defective gratings are prevented from flowing into the subsequent process link, the real-time closed-loop quality interception mechanism is realized, the decision can be made without manual intervention, and the response speed and overall quality control efficiency of the detection process are significantly improved.

[0124] Step A30: if the uniformity threshold exceeds the uniformity reference threshold, determining that the measurement result is that the measured grating is qualified.

[0125] In the embodiment, if the uniformity threshold exceeds the preset uniformity reference threshold, it is automatically determined that the measurement result of the measured grating is qualified, thereby eliminating the uncertainty of human judgment and ensuring the accuracy of the grating uniformity measurement.

[0126] The application provides an optical detection system, comprising: at least one processor; and a memory connected with the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the laser interferometer in the above-mentioned embodiment one.

[0127] Reference will be made to the following description Figure 7 which shows a structural schematic diagram of the optical detection system suitable for implementing the embodiments of the application. Figure 7 The optical detection system shown is only an example and should not bring any limitation to the function and use range of the embodiments of the application.

[0128] As Figure 7 shown, the optical detection system can comprise a processing device 1001 (for example, a central processor, a graphics processor, etc.), which can perform various appropriate actions and processes according to programs stored in a read-only memory (ROM) 1002 or programs loaded from a storage device 1003 into a random access memory (RAM) 1004. In the RAM 1004, various programs and data required for the operation of the optical detection system are also stored. The processing device 1001, the ROM 1002, and the RAM 1004 are connected to each other through a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Generally, the following systems can be connected to the I / O interface 1006: an input device 1007 comprising, for example, a touch screen, a touchpad, a keyboard, a mouse, an image sensor, a microphone, an accelerometer, a gyroscope, etc.; an output device 1008 comprising, for example, a liquid crystal display (LCD), a speaker, a vibrator, etc.; the storage device 1003 comprising, for example, a magnetic tape, a hard disk, etc.; and a communication device 1009. The communication device 1009 can allow the optical detection system to communicate with other devices wirelessly or by wire to exchange data. Although the optical detection system with various devices is shown in the figure, it should be understood that it is not required to implement or have all the devices shown. More or fewer devices can be alternatively implemented or provided.

[0129] In particular, according to the embodiments disclosed in the present application, the process described above with reference to the flowchart can be implemented as a computer software program. For example, the embodiments disclosed in the present application include a computer program product comprising a computer program carried on a computer readable medium, the computer program containing program codes for executing the method shown in the flowchart. In such embodiments, the computer program can be downloaded and installed from a network through a communication device, or installed from the storage device 1003, or installed from the ROM 1002. When the computer program is executed by the processing device 1001, the above-mentioned functions defined in the method of the embodiments disclosed in the present application are executed.

[0130] The optical detection system provided by the present application adopts the measurement method of the laser interferometer in the above-mentioned embodiments, and can solve the technical problem of how to improve the measurement efficiency of grating uniformity without sacrificing measurement accuracy and non-destructiveness. Compared with the prior art, the optical detection system provided by the present application has the same beneficial effects as the laser interferometer provided by the above-mentioned embodiments, and other technical features in the optical detection system are the same as the features disclosed in the previous embodiment method, which will not be repeated here.

[0131] It should be understood that various parts of the present application can be realized by hardware, software, firmware or a combination thereof. In the description of the above-mentioned embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0132] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0133] The present application provides a medium having computer readable program instructions (i.e. computer program) stored thereon, the computer readable program instructions being used to execute the measurement method of the laser interferometer in the above-mentioned embodiments.

[0134] The computer storage medium provided in this application may be, for example, a USB flash drive, but is not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or any combination thereof. More specific examples of the medium 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 fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof. In this embodiment, the medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, system, or device. The program code contained on the medium may be transmitted using any suitable medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination thereof.

[0135] The aforementioned medium may be included in the optical inspection system, or it may exist independently without being assembled into the optical inspection system.

[0136] The aforementioned medium carries one or more programs, which, when executed by the optical detection system, cause the optical detection system to perform the following measurement operations of the laser interferometer:

[0137] After the first optical measuring element projects the first measuring light onto the grating under test at a preset first incident direction angle, a first interference pattern is obtained by diffracting the first measuring light through the grating under test.

[0138] After the second optical measuring element projects a second measuring light onto the grating under test at a second incident direction angle symmetrical to the first incident direction angle, a second interference pattern is obtained by diffracting the second measuring light through the grating under test.

[0139] The measurement results of the grating under test are determined based on the first interferogram and the second interferogram.

[0140] Computer program code for carrying out operations of the present application can be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code can execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection can be made to an external computer (for example, through the Internet using an Internet Service Provider).

[0141] The flow diagrams and the block diagrams in the drawings are illustrations of architectures, functionalities, and operations of possible implementations of systems, methods, and computer program products according to various embodiments of the present application. In this regard, each block in the flow diagrams or block diagrams can represent a module, a segment, or a portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks can occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks may

[0142] The modules involved in the embodiments of the present application can be implemented in the form of software or in the form of hardware. In some cases, the name of the module does not constitute a limitation on the module itself.

[0143] The computer storage medium provided by the present application stores computer readable program instructions (i.e. computer program) for executing the above laser interferometer. The technical problem of how to improve the measurement efficiency of grating uniformity can be solved without sacrificing the measurement accuracy and non-destructiveness. Compared with the prior art, the computer storage medium provided by the present application has the same beneficial effects as the laser interferometer provided by the above embodiments, which will not be described here.

[0144] The application further provides a computer program product comprising a computer program which, when executed by a processor, implements the steps of the measurement method of the laser interferometer as described above.

[0145] The computer program product provided by the application can solve the technical problem of how to improve the measurement efficiency of grating uniformity without sacrificing measurement accuracy and non-destructiveness. Compared with the prior art, the beneficial effects of the computer program product provided by the application are the same as those of the measurement method of the laser interferometer provided by the above-mentioned embodiments, and will not be repeated here.

[0146] The above is only some embodiments of the application, and does not limit the patent scope of the application. Any equivalent structural transformation made by using the content of the specification and drawings, or direct / indirect application in other related technical fields under the technical concept of the application is included in the patent protection scope of the application.

Claims

1. A laser interferometer, characterized in that, The laser interferometer includes: A first optical measuring element is configured to project a first measuring light onto the grating under test at a preset first incident angle, and to receive a first interference pattern formed by the diffraction of the first measuring light through the grating under test. The grating under test does not need to be moved. The first incident angle is determined based on the grating equation of the grating under test, and the expression of the grating equation is: , Indicates the nominal period of the grating being measured; Indicates the first incident direction angle; Indicates the diffraction angle; For diffraction orders, =1; The laser wavelength used in the laser interferometer; in the Littoral configuration, the first-order diffracted light returns along its original path to achieve the stated diffraction angle. With the first incident direction angle If they are equal in size, then the condition will be met. = Substituting the expression of the grating equation, the first incident direction angle is calculated; The second optical measuring element is symmetrically arranged with the first optical measuring element and is located on the grating period side of the grating under test. The second optical measuring element is configured to project a second measuring light onto the grating under test at a second incident direction angle symmetrical to the first incident direction angle, and to receive a second interference pattern formed by the diffraction of the second measuring light through the grating under test. An imaging acquisition module is provided, which is located on the imaging side of the first optical measuring element and the imaging side of the second optical measuring element. The imaging acquisition module is configured to determine the measurement result of the periodic uniformity of the grating under test based on the first interferogram and the second interferogram. The imaging acquisition module is configured to, after completing image registration of the first interferogram and the second interferogram, extract the corresponding first horizontal axis phase distribution function and second horizontal axis phase distribution function from the first interferogram and the second interferogram respectively using the phase demodulation algorithm in the imaging acquisition module. The first horizontal axis phase distribution function and the second horizontal axis phase distribution function are subtracted to cancel the common mode error introduced by the substrate surface shape of the grating under test, thereby obtaining the phase difference information of the periodic distribution of the grating under test. Based on the phase difference information, spatial differentiation is performed to obtain a two-dimensional distribution map of the local periodic error of the grating under test in nanometers / period. The measurement result of the periodic uniformity of the grating under test is determined based on the two-dimensional distribution map of the local periodic error.

2. The laser interferometer as described in claim 1, characterized in that, The first optical measuring element and the second optical measuring element are the same optical measuring structure, and the optical measuring structure is disposed on the grating period side of the grating under test; The optical measurement structure includes a laser source, a reflective optical element, and a reference optical element. The reflective optical element is disposed between the laser source and the reference optical element. The imaging side of the reflective optical element is disposed facing the imaging acquisition module, and the reference optical element is disposed close to the grating period side.

3. The laser interferometer as described in claim 1, characterized in that, The first incident direction angle is the Littoral angle of the +1 diffraction order of the grating under test, and the second incident direction angle is the Littoral angle of the -1 diffraction order of the grating under test.

4. The laser interferometer as described in claim 1, characterized in that, The imaging acquisition module includes: A first image acquisition unit is disposed on the imaging side of the first optical measurement element, and the first image acquisition unit is configured to acquire the first interferogram. The second image acquisition unit is disposed on the imaging side of the second optical measurement element, and the second image acquisition unit is configured to acquire the second interferogram; The processing unit is electrically connected to the first image acquisition unit and the second image acquisition unit, respectively, and is configured to determine the measurement result of the grating under test based on the first interferogram and the second interferogram.

5. A measurement method using a laser interferometer, characterized in that, The measurement method of the laser interferometer is applied to the laser interferometer according to any one of claims 1 to 4, and the measurement method of the laser interferometer includes: After the first optical measuring element projects a first measuring light onto the grating under test at a preset first incident direction angle, a first interferogram is acquired formed by the diffraction of the first measuring light through the grating under test. The grating under test does not need to be moved. The first incident direction angle is determined based on the grating equation of the grating under test, and the expression for the grating equation is: , Indicates the nominal period of the grating being measured; Indicates the first incident direction angle; Indicates the diffraction angle; For diffraction orders, =1; The laser wavelength used in the laser interferometer; in the Littoral configuration, the first-order diffracted light returns along its original path to achieve the stated diffraction angle. With the first incident direction angle If they are equal in size, then the condition will be met. = Substituting the expression of the grating equation, the first incident direction angle is calculated; After the second optical measuring element projects a second measuring light onto the grating under test at a second incident direction angle symmetrical to the first incident direction angle, a second interference pattern is obtained by diffracting the second measuring light through the grating under test; wherein, the second optical measuring element and the first optical measuring element are both disposed on the grating period side of the grating under test. The measurement result of the period uniformity of the grating under test is determined based on the first interferogram and the second interferogram. The step of determining the measurement result of the period uniformity of the grating under test based on the first interferogram and the second interferogram includes: After image registration of the first and second interferograms is completed, the phase demodulation algorithm in the imaging acquisition module extracts the corresponding first horizontal axis phase distribution function and second horizontal axis phase distribution function from the first and second interferograms, respectively. The difference between the first and second horizontal axis phase distribution functions is calculated to cancel the common-mode error introduced by the substrate surface shape of the grating under test, thereby obtaining the phase difference information of the periodic distribution of the grating under test. Based on the phase difference information, spatial differentiation is performed to obtain a two-dimensional distribution map of the local periodic error of the grating under test in nanometers / period. The measurement result of the periodic uniformity of the grating under test is determined based on the two-dimensional distribution map of the local periodic error.

6. The measurement method of the laser interferometer as described in claim 5, characterized in that, The step of determining the measurement result of the grating under test based on the first interferogram and the second interferogram includes: A two-dimensional image coordinate system is constructed with the image widths of the first and second interferograms as the horizontal axis and the image heights of the first and second interferograms as the vertical axis. Based on the two-dimensional image coordinate system, the first horizontal axis phase distribution function of the first interferogram in the horizontal axis direction and the second horizontal axis phase distribution function of the second interferogram in the horizontal axis direction are determined respectively. The uniformity threshold of the grating under test is determined based on the first horizontal axis phase distribution function and the second horizontal axis phase distribution function, and the measurement result of the grating under test is determined based on the uniformity threshold.

7. The measurement method of the laser interferometer as described in claim 6, characterized in that, The step of determining the uniformity threshold of the grating under test based on the first horizontal axis phase distribution function and the second horizontal axis phase distribution function includes: Based on the first horizontal axis phase distribution function and the second horizontal axis phase distribution function, the cumulative periodic error of the grating under test arranged along the horizontal axis direction is determined; Based on the cumulative periodic error, perform differential processing to obtain all local periodic errors of the grating under test, and count the number of local periodic errors that meet the preset error conditions among all the local periodic errors. The uniformity threshold of the grating under test is obtained based on the number of local periodic errors that meet the preset error conditions and the total number of all local periodic errors.

8. The measurement method of the laser interferometer as described in claim 6, characterized in that, The step of determining the measurement result of the grating under test based on the uniformity threshold includes: Detect whether the uniformity threshold exceeds a preset uniformity reference threshold; If the uniformity threshold does not exceed the uniformity reference threshold, then the measurement result of the grating under test is determined to be that the grating under test is unqualified. If the uniformity threshold exceeds the uniformity reference threshold, then the measurement result is determined to be a qualified grating.

9. An optical detection system, characterized in that, The optical detection system includes the laser interferometer as described in any one of claims 1 to 4; Alternatively, a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when executed by the processor, implements the steps of the measurement method of the laser interferometer as described in any one of claims 5 to 8.

10. A computer storage medium, characterized in that, The computer storage medium stores a computer program, which, when executed by a processor, implements the steps of the measurement method of the laser interferometer as described in any one of claims 5 to 8.

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