Step height and flatness measuring method based on laser interference method

Abstract

The invention discloses a step height and flatness measuring method based on a laser interference method, which comprises the following steps of: determining that a calibrated step is put into a laser interference measuring device, moving a reflector distance to obtain an interference image, and processing the interference image to obtain a step surface phase distribution diagram. Determining the position of a calculation point according to a step boundary, calculating a step measurement result, optimizing device parameters according to the step measurement result and step calibration value deviation to obtain optimal device parameters, and constructing a step device parameter library; and according to the step parameters of the to-be-measured step, matching the optimal device parameters in the step device parameter library to obtain reference device parameters, adjusting the laser interference measurement device, and measuring the to-be-measured step by using the adjusted laser interference measurement device to obtain the step height and the step flatness. The method can timely and accurately measure the height and flatness of the step, and has important significance for promoting the development of a high-precision measurement technology in the field of micro-nano manufacturing.

Description

Technical Field

[0001] The present invention relates to the field of laser measurement, and particularly to a method for measuring step height and flatness based on laser interferometry. Background Art

[0002] With the rapid development of modern precision manufacturing and nanotechnology, high-precision measurement of the step height and flatness of micro-scale structures has become a key link in fields such as semiconductor manufacturing, micro-electromechanical system processing, and optical element production. Accurately obtaining the step height and flatness parameters not only directly affects the product performance and quality, but also is an important technical support for promoting the innovation of micro-nano processing technology and ensuring the assembly accuracy of precision equipment.

[0003] Currently, traditional laser interference step measurement techniques mainly rely on single-wavelength interference and fixed parameter settings, and have the following limitations: First, the single measurement efficiency is low, and only a single step height can be obtained. For multi-step measurement, the optical path needs to be repeatedly adjusted, which is time-consuming and has poor consistency; second, parameter adjustment depends on experience. Key parameters such as refractive index and the deflection angle of the stage need to be calibrated by manual trial and error, which is prone to introducing subjective errors; at the same time, the environmental adaptability is insufficient. When factors such as temperature drift and vibration cause refractive index drift, the system stability drops significantly; finally, there is a lack of intelligent matching. When facing complex step structures, the optimal measurement conditions cannot be quickly adapted, which restricts the batch detection efficiency. Based on the above background, the present invention proposes a method for measuring step height and flatness based on laser interferometry. By introducing a calibration step into the measurement system, constructing a parameter constraint range for refractive index and deflection angle, and combining interference image phase analysis and parameter optimization strategies, the adaptive calibration of the parameters of the measurement device is realized, a step parameter-device parameter mapping library is constructed, and the historical optimal configuration is intelligently matched based on the rough measurement parameters to achieve "one-key" high-precision measurement. This not only significantly improves the measurement accuracy and efficiency, effectively solves the measurement deviation problem caused by system parameter errors in traditional laser interference measurement, but also has important significance for promoting the development of high-precision measurement technology in the field of micro-nano manufacturing. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for measuring step height and flatness based on laser interferometry.

[0005] To achieve the above object, the present invention is implemented according to the following technical solution: The present invention includes the following steps: Place the calibration step into the laser interference measurement device, determine the refractive index range of the interference lens according to the beam intensity distribution deviation of the incident light on the interference lens, and determine the stage deflection angle range according to the interference fringe parameters; the incident light includes a reference light and a measurement light; Adjust the distance of the mirror of the laser interferometric measuring device to obtain an interference image, process the interference image to obtain a step surface phase distribution map, determine the position of the calculation point according to the step boundary, and calculate the step measurement result according to the position of the calculation point and the step surface phase distribution map; the step measurement result includes the step measurement height and the step measurement flatness; Optimize the device parameters within the refractive index range and the stage deflection angle range according to the deviation between the step measurement result and the step calibration value to obtain the optimal device parameters; the step calibration value includes the step calibration height and the step calibration flatness; Form a set of step device parameters with the step parameters and the optimal device parameters, and obtain a step device parameter library by acquiring multiple sets of step device parameters of the calibrated steps; the step parameters include the rough measurement height, rough measurement length, rough measurement width and the number of steps of the step; Match the optimal device parameters in the step device parameter library according to the step parameters of the step to be measured to obtain the reference device parameters, and adjust the laser interferometric measuring device. Measure the step to be measured with the adjusted laser interferometric measuring device to obtain the step height and the step flatness.

[0006] Furthermore, the method for determining the refractive index range of the interference lens and the method for determining the stage deflection angle range include: Place the calibrated step into the laser interferometric measuring device, obtain the first reflected light and the first transmitted light by passing the incident light through the interference lens, and measure the beam intensities of the incident light, the first reflected light and the first transmitted light; the incident light includes the reference light and the measurement light; the first reflected light includes the first reference reflected light and the first measurement reflected light; the first transmitted light includes the first reference transmitted light and the first measurement transmitted light; Calculate the ratio of the absolute value of the difference between the intensity of the first reference reflected light and the intensity of the first reference transmitted light to the intensity of the reference light to obtain the reference light distribution deviation, calculate the ratio of the absolute value of the difference between the intensity of the first measurement reflected light and the intensity of the first measurement transmitted light to the intensity of the measurement light to obtain the measurement light distribution deviation, calculate the average value of the reference light distribution deviation and the measurement light distribution deviation to obtain the beam intensity distribution deviation, and select the refractive index of the interference lens corresponding to the beam intensity distribution deviation less than 0.2 as the refractive index range; Adjust the stage deflection angle to obtain interference fringes, and measure the interference fringe parameters; the stage deflection angle includes the x-axis deflection angle and the y-axis deflection angle; the interference fringes are formed by the coincidence of the second reflected light and the third reflected light at the interference lens; the second reflected light is formed by the first reflected light reflecting back along the original path through the step surface; the third reflected light is formed by the first transmitted light reflecting back along the original path through the mirror; the interference fringe parameters include the contrast, the spacing and the inclination; Adjust the stage deflection angle, and select the stage deflection angles for which the interference fringe parameters conform to the interference fringe parameter rules to form the stage deflection angle range.

[0007] Further, the method for calculating the step measurement result includes the following steps: Adjust the distance of the mirror of the laser interferometry device to obtain multiple interference images, and use the phase unwrapping algorithm to process the interference images to obtain the step surface phase distribution map; the distance of the mirror is controlled by a high-precision displacement stage; the interference images are collected by a high-definition camera on the imaging lens; the imaging lens is used to receive the interference fringes formed by the interference lens; The specific steps for obtaining the step surface phase distribution map include: denoising and distortion correction for each interference image, calculating the initial phase information in each interference image using the spatial carrier phase shift method, and calculating the phase distribution map of the interference fringes using the five-step phase unwrapping algorithm to obtain the step surface phase distribution map; the step surface phase distribution map includes multiple step surface interference regions and invalid regions; Determine the center points of each step surface according to the step boundaries, set the center points of each step surface as calculation points, calculate the height difference between adjacent calculation points according to the interference principle, the reference light wavelength, the measurement light wavelength, and the positions of adjacent calculation points, and define the height difference between adjacent calculation points as the corresponding step measurement height; Extract the data points of each step surface from the step surface phase distribution map, and use the least squares method to fit the ideal plane of each step surface to obtain the step measurement flatness.

[0008] Further, the method for obtaining the optimal parameters of the device includes: Determine the device optimization objective function according to the deviation between the step measurement result and the step calibration value: where is the device optimization objective function, is the set of device parameters, including the reference light wavelength , the measurement light wavelength , the refractive index of the interference lens , the x-axis deflection angle of the stage , the y-axis deflection angle of the stage , and the mirror distance , is the deviation weight, is the stability weight, is the number of step levels, , the th measured height and the calibrated height of the th step, and are the measured flatness and the calibrated flatness of the th step respectively, is the standard deviation of the height in multiple repeated measurements, is the standard deviation of the flatness in multiple repeated measurements; Determine the constraint conditions of the device optimization objective function according to the refractive index range, the stage deflection angle range, the performance of the laser emitter, and the optical path interference principle; Optimize the parameters of the laser interference measurement device according to the device optimization objective function and the corresponding constraint conditions. Use the improved whale optimization algorithm to search for the optimal parameters of the device. Divide the whale population into a main population and an auxiliary population, and perform a mixed chaotic mapping to generate the initial positions of the main and auxiliary populations: where is the value of the chaotic sequence after the th iteration in the chaotic mapping, is the value of the chaotic sequence after the th iteration, is the value of the chaotic sequence after the th iteration, is the maximum number of iterations; Calculate the value of the objective function and record the optimal position of the population at the th iteration, and enter the prey encirclement stage to update the particle position. The expression is: where is the updated position of the particles in the main and auxiliary particle swarms at the th iteration in the prey encirclement stage, is the random best position of the population, , are the vector coefficients, , are vectors randomly generated in [0,1], is a parameter that linearly decreases during the iteration, represents the distance vector between the whale and the optimal solution, is the random best position of the population, is a random number in [0,1], is the average best position of the population, is the contraction and expansion coefficient; Enter the bubble net predation stage, and use the contraction and encirclement mechanism and the spiral position update mechanism to update the particle position. The expression is: where is the updated position of the particles in the main and auxiliary particle swarms at the th iteration in the bubble net predation stage, is the distance between the first whale and the prey, is a constant of the logarithmic spiral shape, is a random number between [-1, 1]; Perform adaptive step size and hybrid perturbation on the auxiliary population, and update the position of the auxiliary population: where is the iteration of the position component update of the auxiliary population particle at the position, is the Lévy step size, is the Gaussian perturbation, is the standard deviation, is the maximum value of the position component, is the minimum value of the position component, is the step size coefficient, with an initial value of 0.1 and linearly increasing to 0.5 with the number of iterations, is the Lévy distribution function; Enter the prey search stage, and update the particle position using a dynamic strategy. The expression is: where is the position update of the particles in the main and auxiliary particle swarms at the iteration of the prey search stage, is a random whale in the current population; Update the ratio of the main and auxiliary populations every 10 generations. The expression is: where is the proportion of the main population, is the proportion of the auxiliary population; Repeat the above steps, and stop the iteration after multiple iterations until the objective function of the device optimization is minimized or the maximum number of iterations is reached, and output the optimal parameters of the device; the optimal parameters of the device include the incident light wavelength, the refractive index of the interference lens, the deflection angle of the stage, and the distance of the mirror; the incident light wavelength includes the reference light wavelength and the measurement light wavelength.

[0009] Furthermore, the method for obtaining the step height and step flatness includes: Perform Min-Max normalization on the step parameters of the measured step and all step parameter entries in the step device parameter library: wherein is the normalization result of the class parameter after Min - Max normalization, is the normalization result, is the minimum value of the corresponding parameter in the parameter library, is the maximum value of the corresponding parameter in the parameter library; According to the distribution characteristics of the data in the parameter library, the weights of different class parameters are dynamically adjusted, and the expression is: wherein is the dynamic correction weight of the class parameter, is the basic weight of the class parameter, is the standard deviation of the class parameter in the parameter library, and the parameter category set includes the rough - measured height 、the rough - measured length 、the rough - measured width and the order ; Calculate the Euclidean distance and cosine similarity between the step parameters of the measured step after Min - Max normalization and the step parameters in the step device parameter library respectively to obtain the comprehensive similarity: wherein is the comprehensive similarity, 、 are the similarity weights, is the normalization result of the class parameter of the step to be measured, is the normalization result of the class parameter of the step device parameter library, is the maximum possible distance between all entries in the parameter library and the step parameters of the step to be measured; Take the optimal parameter corresponding to the step parameter in the step device parameter library with the highest comprehensive similarity as the reference device parameter, set the laser interferometry device with the reference device parameter, and use the adjusted laser interferometry device to measure the step to be measured to obtain multiple interference images, and repeat the above operations to calculate the step height and step flatness.

[0010] Second aspect, a laser interference measurement device, comprising: a reference light emitter, a measurement light emitter, an optical fiber, a beam expander lens, an interference lens, a stage, a step gauge, a mirror, an imaging lens and a high-definition camera; the reference light emitter and the measurement light emitter are respectively used for emitting reference light and measurement light; the optical fiber connects the reference light emitter and the measurement light emitter, and projects the reference light and the measurement light onto the beam expander lens; the beam expander lens is used for performing chromatic aberration correction on the reference light and the measurement light and expanding them into parallel incident light; the interference lens forms an angle of 45° with the incident light, and is used for splitting the incident light into a first reflected light and a first transmitted light, and forming interference fringes through a second reflected light and a third reflected light; the stage is parallel to the incident light, and is used for adjusting the deflection angle and placing the step gauge; the step gauge is used for fixing steps to be measured with different specifications; the mirror is perpendicular to the incident light, and is used for returning the first transmitted light along the original path to form a third reflected light; the imaging lens is parallel to the incident light, and is used for receiving the interference fringes; the high-definition camera is used for collecting the interference fringes on the imaging lens to form an interference image; the step surface of the step to be measured is used for returning the first reflected light along the original path to form a third reflected light; the first reflected light and the second reflected light are perpendicular to the incident light, and their directions are opposite; the first transmitted light and the third reflected light are parallel to the incident light, and their directions are opposite.

[0011] The beneficial effects of the present invention are: The present invention is a method for measuring the step height and flatness based on the laser interference method. Compared with the prior art, the present invention has the following technical effects: Through steps of phase distribution diagram calculation, determination of the calculation point position, measurement result calculation, device parameter optimization and database parameter matching, the present invention can improve the data preprocessing ability and enhance the model adaptability in the measurement of step height and flatness, thereby improving the efficiency and accuracy of step height and flatness measurement. Optimizing the step height and flatness measurement technology can greatly save resources, improve work efficiency, realize the measurement of step height and flatness, provide strong support for the development of modern precision manufacturing and nanotechnology, and have important significance for promoting the development of high-precision measurement technology in the micro-nano manufacturing field. Description of the Drawings

[0012] Figure 1 is a step flow chart of a method for measuring the step height and flatness based on the laser interference method of the present invention; Figure 2 is a schematic diagram of a laser interference measurement device provided by the present invention; Figure 3 is an optical path schematic diagram of a laser interference measurement device provided by the present invention; In the figure: 1 - reference light emitter; 2 - measurement light emitter; 3 - optical fiber; 4 - beam expander lens; 5 - interference lens; 6 - stage; 7 - step gauge; 8 - mirror; 9 - imaging lens; 10 - high-definition camera; A - reference light; B - measurement light; C - incident light; D - first reflected light; E - first transmitted light; F - second reflected light; G - third reflected light; H - interference fringe. Detailed implementation mode

[0013] The present invention will be further described below through specific embodiments. The illustrative embodiments and explanations of this invention are used to explain the present invention, but do not limit the present invention.

[0014] A method for measuring step height and flatness based on laser interferometry of the present invention includes the following steps: As Figure 1 shown, in this embodiment, it includes the following steps: Put the calibrated step into the laser interference measurement device, determine the refractive index range of the interference lens according to the beam intensity distribution deviation of the incident light on the interference lens, and determine the stage deflection angle range according to the interference fringe parameters; the incident light includes reference light and measurement light; Adjust the distance of the mirror of the laser interference measurement device to obtain an interference image, process the interference image to obtain the step surface phase distribution map, determine the calculation point position according to the step boundary, and calculate the step measurement result according to the calculation point position and the step surface phase distribution map; the step measurement result includes the measured step height and the measured step flatness; Optimize the device parameters within the refractive index range and the stage deflection angle range according to the deviation between the step measurement result and the step calibration value to obtain the optimal device parameters; the step calibration value includes the calibrated step height and the calibrated step flatness; Form a set of step device parameters with the step parameters and the optimal device parameters, and obtain a step device parameter library by acquiring the step device parameters of multiple calibrated steps; the step parameters include the roughly measured step height, roughly measured length, roughly measured width, and number of steps; Match the optimal device parameters in the step device parameter library according to the step parameters of the step to be measured to obtain the reference device parameters and adjust the laser interference measurement device, and measure the step to be measured with the adjusted laser interference measurement device to obtain the step height and the step flatness.

[0015] In this embodiment, the method for determining the refractive index range of the interference lens and the method for determining the stage deflection angle range include: Place the calibration step into the laser interferometry device. Obtain the first reflected light and the first transmitted light by passing the incident light through the interference lens, and measure the beam intensities of the incident light, the first reflected light, and the first transmitted light. The incident light includes a reference light and a measurement light. The first reflected light includes a first reference reflected light and a first measurement reflected light. The first transmitted light includes a first reference transmitted light and a first measurement transmitted light. Calculate the ratio of the absolute value of the difference between the intensity of the first reference reflected light and the intensity of the first reference transmitted light to the intensity of the reference light to obtain the reference light distribution deviation. Calculate the ratio of the absolute value of the difference between the intensity of the first measurement reflected light and the intensity of the first measurement transmitted light to the intensity of the measurement light to obtain the measurement light distribution deviation. Calculate the average value of the reference light distribution deviation and the measurement light distribution deviation to obtain the beam intensity distribution deviation. Select the refractive index of the interference lens corresponding to a beam intensity distribution deviation less than 0.2 as the refractive index range. Adjust the deflection angle of the stage to obtain interference fringes and measure the interference fringe parameters. The deflection angle of the stage includes the x-axis deflection angle and the y-axis deflection angle. The interference fringes are formed by the coincidence of the second reflected light and the third reflected light at the interference lens. The second reflected light is formed by the first reflected light reflecting back along the original path through the step surface. The third reflected light is formed by the first transmitted light reflecting back along the original path through the mirror. The interference fringe parameters include contrast, spacing, and inclination. Adjust the deflection angle of the stage, and select the deflection angles of the stage for which the interference fringe parameters conform to the interference fringe parameter rules to form the deflection angle range of the stage. In the actual evaluation, obtain the calibrated 4-step height and flatness (unit: nm) of a certain factory: 100.1 / 0.2, 200.3 / 0.1, 300.2 / 0.1, 400.2 / 0.2. For this calibrated step, when the lens refractive index is 0.1, use the control variable method to set the reference light and the measurement light to the wavelengths (1000 nm, 2000 nm) at 1 / 4 and 3 / 4 of the emission band of the laser emitter, the light intensity is 100 lux, and only the reference light is emitted to measure the intensity of the first reference reflected light and the first reference transmitted light as 40 lux and 56 lux, corresponding to a reference light distribution deviation of 0.16. Only the measurement light is emitted to measure the intensity of the first measurement reflected light and the first measurement transmitted light as 51 lux and 45 lux, corresponding to a measurement light distribution deviation of 0.06 lux. Calculate the beam intensity distribution deviation as (0.16 + 0.06) / 2 = 0.11 < 0.2. Then the lens refractive index of 0.1 meets the measurement requirements for this calibrated step. Continuously adjust the lens refractive index to select the refractive index of the interference lens corresponding to a beam intensity distribution deviation less than 0.2 to determine the interference lens refractive index range as 0.1 - 0.2. The interference fringe parameter rules include that the interference fringe contrast is greater than 0.5, the interference fringe spacing is between [10, 100] (unit: pixel), and the interference fringe inclination is less than 5°. Select an interference lens with a refractive index of 0.1. At this time, the deflection angles of the x / y axes of the stage are 0.5° / 0.3°, and the corresponding interference fringe parameters are 0.6, 30 pixels, and 3°. This conforms to the interference fringe parameter rules. Continuously adjust the deflection angle of the stage to obtain a stage deflection angle range of 0.5 - 2.5° / 0.3 - 2.8°. Similarly, select an interference lens with a refractive index of 0.2 and adjust the stage deflection angle to obtain a stage deflection angle range of 0.8 - 2.7° / 0.5 - 2.5°. Take the intersection of the two deflection angle ranges to determine the adjusted stage deflection angle range of 0.8 - 2.5° / 0.5 - 2.5°.

[0016] In this embodiment, the method for calculating the step measurement result includes the following steps: Adjust the distance of the mirror of the laser interference measurement device to obtain multiple interference images. Use the phase unwrapping algorithm to process the interference images to obtain the phase distribution map of the step surface; the distance of the mirror is controlled by a high-precision displacement stage; the interference images are collected by a high-definition camera on the imaging lens; the imaging lens is used to receive the interference fringes formed by the interference lens; The specific steps for obtaining the phase distribution map of the step surface include: denoising and distortion correction for each interference image, using the spatial carrier phase shift method to calculate the initial phase information in each interference image, and using the five-step phase unwrapping algorithm to calculate the phase distribution map of the interference fringes to obtain the phase distribution map of the step surface; the phase distribution map of the step surface includes multiple step surface interference regions and invalid regions; Determine the center points of each step surface according to the step boundaries, set the center points of each step surface as calculation points, calculate the height difference between adjacent calculation points according to the interference principle, the reference light wavelength, the measurement light wavelength, and the positions of adjacent calculation points, and define the height difference between adjacent calculation points as the measured height of the corresponding step; Extract the data points of each step surface from the phase distribution map of the step surface, and use the least squares method to fit the ideal plane of each step surface to obtain the flatness of the step measurement; In actual evaluation, take the median value of the interference lens refractive index range of 0.15, the median value of the stage deflection angle of 1.65° / 1.5°, the reference light (1000 nm, 100 lux), and the measurement light (2000 nm, 100 lux) as the device parameters of the laser interference measurement device to calibrate the calibration step. Use a high-precision displacement stage to control and coarsely adjust the distance of the reflection lens from left to right step by step (1 mm / step) until interference fringes are generated and the interference images can be collected by a high-definition camera on the imaging lens. Then, finely adjust the distance of the reflection lens from left to right step by step (10 μm / step, 500 nm / step, 100 nm / step) to obtain multiple interference images, and use the phase unwrapping algorithm to process the interference images to obtain the phase distribution map of the step surface; According to the calibrated step boundaries, the center points of each step surface are determined as the centroid of the step surface, and the centroid of the step surface is set as the calculation point. The phase differences between adjacent calculation points are calculated based on the reference light wavelength, the measurement light wavelength, and the positions of adjacent calculation points, which are 0.628π, 1.256π, 1.884π, and 2.512π. According to the interference principle, the heights of each step are calculated as 100.3, 200.4, 299.8, and 400.1 nm respectively. The data points of each step surface are extracted from the step surface phase distribution map, and the least squares method is used to fit the ideal plane of each step surface to obtain the step measurement flatness of 0.22, 0.19, 0.15, and 0.24 nm.

[0017] In this embodiment, the method for obtaining the optimal parameters of the device includes: Determine the device optimization objective function according to the step measurement results and the deviation between the step calibration values: Where is the device optimization objective function, is the set of device parameters, including the reference light wavelength , the measurement light wavelength , the refractive index of the interference lens , the deflection angle of the x-axis of the stage , the deflection angle of the y-axis of the stage , and the distance of the mirror , is the deviation weight, is the stability weight, is the number of step levels, , are respectively the measured height and the calibrated height of the th step, , are respectively the measured flatness and the calibrated flatness of the th step, is the standard deviation of the height of multiple repeated measurements, is the standard deviation of the flatness of multiple repeated measurements; Determine the constraint conditions of the device optimization objective function according to the refractive index range, the stage deflection angle range, the performance of the laser emitter, and the optical path interference principle; Optimize the parameters of the laser interference measurement device according to the device optimization objective function and the corresponding constraint conditions. Use the improved whale optimization algorithm to search for the optimal parameters of the device. Divide the whale population into a main population and an auxiliary population, and perform a mixed chaotic mapping to generate the initial positions of the main and auxiliary populations: Where is the The chaotic sequence value after the th iteration is the chaotic sequence value after the th iteration, and the th iteration is the chaotic sequence value after the th iteration; Calculate the objective function value and record the population optimal position at the th iteration , and enter the prey encirclement stage to update the particle position. The expression is: where is the updated position of the particles in the main and auxiliary particle swarms at the th iteration in the prey encirclement stage, is the population random best position, , are vector coefficients, , are vectors randomly generated in [0, 1], is a parameter that linearly decreases during the iteration process, represents the distance vector between the whale and the optimal solution, is the population random best position, is a random number in [0, 1], is the population average best position, is the contraction and expansion coefficient; Enter the bubble net predation stage, and use the contraction encirclement mechanism and the spiral position update mechanism to update the particle position. The expression is: where is the updated position of the particles in the main and auxiliary particle swarms at the th iteration in the bubble net predation stage, is the th distance between the whale and the prey, is the constant of the logarithmic spiral shape, is a random number between [-1, 1]; Perform adaptive step size and mixed perturbation on the auxiliary population to update the position of the auxiliary population: where is the th iteration of the auxiliary population particle at Position component update, is the Lévy step size, is the Gaussian perturbation, is the standard deviation, is the maximum value of the position component, is the minimum value of the position component, is the step size coefficient, with an initial value of 0.1 and linearly increasing to 0.5 with the number of iterations, is the Lévy distribution function; Enter the prey search stage, and update the particle position using a dynamic strategy. The expression is: where is the updated position of the particle in the main and auxiliary particle swarms at the th iteration in the prey search stage, is a random whale in the current population; Update the main and auxiliary population ratios every 10 generations. The expression is: where is the proportion of the main population, is the proportion of the auxiliary population; Repeat the above steps and iterate multiple times until the device optimization objective function is minimized or the maximum number of iterations is reached, and then stop the iteration and output the optimal parameters of the device; the optimal parameters of the device include the incident light wavelength, the refractive index of the interference lens, the deflection angle of the stage, and the distance of the mirror; the incident light wavelength includes the reference light wavelength and the measurement light wavelength; In the actual evaluation, the constraint conditions of the device optimization objective function include: the optimized refractive index belongs to the refractive index range, the optimized deflection angle belongs to the stage deflection angle range, the reference light wavelength and the measurement light wavelength are within the emission band of the laser transmitter, and the distance of the mirror should ensure that the phase difference is at least greater than a certain proportion of the phase change (2π) corresponding to one wavelength; Take the deviation weight and the stability weight , the height standard deviation and the flatness standard deviation of multiple repeated measurements are (0.5, 0.6, 0.4, 0.5) and (0.02, 0.03, 0.02, 0.03) respectively, and the device optimization objective function is taken as 1.344545 according to the measurement results and calibration values of the calibration step; The improved whale optimization algorithm is used to search for the optimal parameters of the device, where the contraction and expansion coefficient , the constant of the logarithmic spiral shape , the maximum number of iterations . Taking the median value of the interference lens refractive index range as 0.15, the median value of the stage deflection angle as 1.65° / 1.5°, the reference light (1000nm, 100lux), the measurement light (2000nm, 100lux), and the mirror distance of 100 - 250mm corresponding to the particle position as the optimal position of the initial population , iterate repeatedly. When iterating to the 14th, 15th, and 16th times, the optimization objective function of the device takes 1.258, 1.251, and 1.29 respectively, and take the optimal position of the population at the 15th iteration The device parameters corresponding to the particles are the optimal parameters of the device: the refractive index of the interference lens is 1.47, the stage deflection angle is 1.25° / 0.75°, the mirror distance is 150 - 300mm, the reference light (736nm, 100lux), and the measurement light (1545nm, 100lux); The step parameters (400nm, 5mm, 3mm, 4) of the calibration step and the corresponding optimal device parameters are combined into a set of step device parameters, and multiple sets of step device parameters of the calibration step are obtained to form a step device parameter library.

[0018] In this embodiment, the method for obtaining the step height and step flatness includes: Min - Max standardize the step parameters of the measured step and all step parameter entries in the step device parameter library: Where is the standardized result of type parameters after Min - Max standardization, is the minimum value of the corresponding parameter in the parameter library, is the maximum value of the corresponding parameter in the parameter library; According to the distribution characteristics of the data in the parameter library, dynamically adjust the weights of different types of parameters. The expression is: Where is the dynamically corrected weight of type parameters, is the basic weight of type parameters, is the standard deviation of type parameters in the parameter library, and the parameter category set includes the rough measurement height And the order ; Calculate the Euclidean distance and cosine similarity between the step parameters of the measured step after Min-Max normalization and the step parameters in the step device parameter library respectively to obtain the comprehensive similarity: Where is the comprehensive similarity, , are the similarity weights, is the step to be measured the standardized result of the class parameters, is the step device parameter library the standardized result of the class parameters, is the maximum possible distance between all entries in the parameter library and the step parameters of the step to be measured; Take the optimal parameters corresponding to the step parameters in the step device parameter library with the highest comprehensive similarity as the reference device parameters, set the laser interferometer measurement device with the reference device parameters, and use the adjusted laser interferometer measurement device to measure the step to be measured to obtain multiple interference images, and repeat the above operations to calculate the step height and step flatness; In the actual evaluation, obtain the step parameters of the step to be measured (380nm, 4.5mm, 3mm, 4), the minimum and maximum values of the step parameters in the step device parameter library are 200nm / 2μm, 3mm / 10mm, 1mm / 5mm, 2 / 10 respectively. Min-Max normalize the step parameters of the measured step and all step parameter entries in the step device parameter library to obtain the standardized step parameters (1 / 10, 3 / 14, 1 / 2, 3 / 8); Dynamically adjust the weights of different class parameters according to the step parameter base weights (0.4, 0.15, 0.15, 0.3) and the standard deviation of the step parameters in the parameter library to obtain the dynamically corrected weights (0.45, 0.11, 0.12, 0.32). The maximum possible distance between all entries in the parameter library and the step parameters of the step to be measured. Calculate the Euclidean distance and cosine similarity between the step parameters of the measured step after Min-Max normalization and the step parameters in the step device parameter library respectively to obtain the comprehensive similarity. Take the optimal parameters corresponding to the step parameters in the step device parameter library with the highest comprehensive similarity of 0.88 as the reference device parameters: the refractive index of the interference lens is 1.36, the deflection angle of the stage is 1.10° / 0.9°, the distance of the mirror is 125 - 325mm, the reference light (1200nm, 100lux), the measurement light (1730nm, 100lux); The laser interferometer is set with reference device parameters. The adjusted laser interferometer is used to measure the step to be measured to obtain multiple interference images. By repeating the above operations, the step height and step flatness are calculated as (unit: nm): 95.05 / 0.15, 190.1 / 0.1, 285.2 / 0.15, 380.25 / 0.05.

[0019] As Figures 2 to 3 shown, in this embodiment, a cable based on fiber optic technology includes: a reference light emitter 1, a measurement light emitter 2, an optical fiber 3, a beam expander lens 4, an interference lens 5, a stage 6, a step gauge 7, a mirror 8, an imaging lens 9, and a high-definition camera 10; the reference light emitter 1 and the measurement light emitter 2 are respectively used to emit reference light A and measurement light B; the optical fiber 3 connects the reference light emitter 1 and the measurement light emitter 2, and projects the reference light A and the measurement light B onto the beam expander lens 4; the beam expander lens 4 is used to correct the chromatic aberration of the reference light A and the measurement light B and expand them into parallel incident light C; the interference lens 5 forms a 45° angle with the incident light C, and is used to split the incident light C into a first reflected light D and a first transmitted light E, and form an interference fringe H through a second reflected light F and a third reflected light G; the stage 6 is parallel to the incident light C, and is used to adjust the deflection angle and place the step gauge 7; the step gauge 7 is used to fix steps to be measured with different specifications; the mirror 8 is perpendicular to the incident light C, and is used to return the first transmitted light E along the original path to form the third reflected light G; the imaging lens 9 is parallel to the incident light C, and is used to receive the interference fringe H; the high-definition camera is used to collect the interference fringe H on the imaging lens 9 to form an interference image; the step surface of the step to be measured is used to return the first reflected light D along the original path to form the third reflected light F; the first reflected light D and the second reflected light F are perpendicular to the incident light C, and their directions are opposite; the first transmitted light E and the third reflected light G are parallel to the incident light C, and their directions are opposite.

[0020] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for measuring step height and flatness based on laser interferometry, characterized in that, Including the following steps: S1. Place the calibration step into the laser interferometric measuring device. Determine the refractive index range of the interference lens according to the beam intensity distribution deviation of the incident light on the interference lens, and determine the range of the deflection angle of the stage according to the interference fringe parameters. The incident light includes a reference light and a measurement light. S2. Adjust the distance of the mirror of the laser interferometric measuring device to obtain an interference image, process the interference image to obtain a step surface phase distribution map, determine the position of the calculation point according to the step boundary, and calculate the step measurement result according to the position of the calculation point and the step surface phase distribution map. The step measurement result includes the measured height of the step and the flatness of the step measurement plane. S3. Optimize the device parameters within the refractive index range and the range of the deflection angle of the stage according to the deviation between the step measurement result and the step calibration value to obtain the optimal device parameters. The step calibration value includes the calibrated height of the step and the flatness of the step calibration. S4. Combine the step parameters and the optimal device parameters into a set of step device parameters, and obtain a step device parameter library by acquiring multiple sets of step device parameters of the calibration steps. The step parameters include the roughly measured height, roughly measured length, roughly measured width, and number of steps of the step. S5. Match the optimal device parameters in the step device parameter library according to the step parameters of the step to be measured to obtain the reference device parameters, and adjust the laser interferometric measuring device. Measure the step to be measured with the adjusted laser interferometric measuring device to obtain the step height and the flatness of the step.

2. The step height and flatness measurement method based on the laser interference method according to claim 1, characterized in that, The method for determining the refractive index range of the interference lens and the range of the deflection angle of the stage includes: Place the calibration step into the laser interferometric measuring device, obtain a first reflected light and a first transmitted light by passing the incident light through the interference lens, and measure the beam intensities of the incident light, the first reflected light, and the first transmitted light. The incident light includes a reference light and a measurement light. The first reflected light includes a first reference reflected light and a first measurement reflected light. The first transmitted light includes a first reference transmitted light and a first measurement transmitted light. Calculate the ratio of the absolute value of the difference between the intensity of the first reference reflected light and the intensity of the first reference transmitted light to the intensity of the reference light to obtain the reference light distribution deviation, calculate the ratio of the absolute value of the difference between the intensity of the first measurement reflected light and the intensity of the first measurement transmitted light to the intensity of the measurement light to obtain the measurement light distribution deviation, calculate the average value of the reference light distribution deviation and the measurement light distribution deviation to obtain the beam intensity distribution deviation, and select the refractive index of the interference lens corresponding to the beam intensity distribution deviation less than 0.2 as the refractive index range. Adjust the deflection angle of the stage to obtain interference fringes, and measure the interference fringe parameters. The deflection angle of the stage includes the x-axis deflection angle and the y-axis deflection angle. The interference fringes are formed by the coincidence of a second reflected light and a third reflected light at the interference lens. The second reflected light is formed by the first reflected light reflecting back along the original path through the step surface. The third reflected light is formed by the first transmitted light reflecting back along the original path through the mirror. The interference fringe parameters include contrast, spacing, and inclination. Adjust the deflection angle of the stage, and select the deflection angles of the stage that meet the interference fringe parameter rules for the interference fringe parameters to form the range of the deflection angle of the stage.

3. The method for measuring the step height and flatness based on the laser interference method according to claim 1, wherein The method for calculating the step measurement result includes the following steps: Adjust the distance of the mirror of the laser interferometric measuring device to obtain multiple interference images, and use the phase unwrapping algorithm to process the interference images to obtain the phase distribution map of the stepped surface; the distance of the mirror is controlled by a high-precision displacement stage; the interference images are collected by a high-definition camera on the imaging lens; the imaging lens is used to receive the interference fringes formed by the interference lens; The specific steps for obtaining the phase distribution map of the stepped surface include: denoising and distortion correction for each interference image, calculating the initial phase information in each interference image using the spatial carrier phase-shifting method, and calculating the phase distribution map of the interference fringes using the five-step phase unwrapping algorithm to obtain the phase distribution map of the stepped surface; the phase distribution map of the stepped surface includes multiple stepped surface interference regions and invalid regions; Determine the center points of each stepped surface according to the stepped boundaries, set the center points of each stepped surface as calculation points, and calculate the height difference between adjacent calculation points according to the interference principle, the wavelength of the reference light, the wavelength of the measuring light, and the positions of adjacent calculation points, and define the height difference between adjacent calculation points as the measured height of the corresponding step; Extract the data points of each stepped surface from the phase distribution map of the stepped surface, and use the least squares method to fit the ideal plane of each stepped surface to obtain the flatness of the stepped measurement.

4. The method for measuring step height and flatness based on the laser interference method according to claim 3, characterized in that, The method for obtaining the optimal parameters of the device includes: Determine the device optimization objective function according to the deviation between the stepped measurement result and the stepped calibration value: where is the device optimization objective function, is the set of device parameters, including the reference light wavelength , the measurement light wavelength , the refractive index of the interference lens , the deflection angle of the stage in the x-axis direction , the deflection angle of the stage in the y-axis direction and the distance of the mirror, , is the deviation weight, is the stability weight, is the number of stage levels, , are respectively the measured height and the calibrated height of the -th stage, , are respectively the measured flatness and the calibrated flatness of the -th stage, is the standard deviation of the height in multiple repeated measurements, is the standard deviation of the flatness in multiple repeated measurements; Determine the constraint conditions of the device optimization objective function according to the refractive index range, the deflection angle range of the stage, the performance of the laser emitter, and the optical path interference principle; Optimize the parameters of the laser interferometric measuring device according to the device optimization objective function and the corresponding constraint conditions, and use the improved whale optimization algorithm to search for the optimal parameters of the device. Divide the whale population into a main population and an auxiliary population, and perform a hybrid chaotic mapping to generate the initial positions of the main and auxiliary populations: Among them is the value of the chaotic sequence after the -th iteration in the chaotic mapping, is the value of the chaotic sequence after the -th iteration, is the value of the chaotic sequence after the -th iteration, is the maximum number of iterations; Calculate the objective function value and record the population optimal position at the th iteration , and enter the prey surrounding stage to update the particle position. The expression is as follows: Among them is the position update of particles in the main and auxiliary particle swarms at the -th iteration during the prey surrounding stage, is the randomly best position of the population, , are vector coefficients, , are vectors randomly generated in [0, 1], is a parameter that linearly decreases during the iteration process, represents the distance vector between the whale and the optimal solution, is the randomly best position of the population, is a random number in [0, 1], is the average best position of the population, is the contraction-expansion coefficient; Enter the bubble net predation stage, and update the particle positions using the shrinking encircling mechanism and the spiral position update mechanism. The expression is: Among them is the position update of particles in the main and auxiliary particle swarms at the th iteration during the bubble-net hunting stage, is the distance between the th whale and the prey, is a constant for the shape of the logarithmic spiral, is a random number between [-1, 1]; Perform adaptive step size and hybrid perturbation on the auxiliary population to update the positions of the auxiliary population: Among them is the th iteration, which is the update of the position component of the particles in the auxiliary population at position component update, is the Lévy step size, is the Gaussian perturbation, is the standard deviation, is the maximum value of the position component, is the minimum value of the position component, is the step size coefficient, with an initial value of 0.1 and linearly increasing to 0.5 with the number of iterations, is the Lévy distribution function; Enter the prey search stage, and update the particle positions using a dynamic strategy. The expression is: Among them is the updated position of the particles in the main and auxiliary particle swarms at the th iteration during the prey search phase, is a random whale in the current population; Update the ratio of the main and auxiliary populations every 10 generations. The expression is: wherein is the proportion of the main population, is the proportion of the auxiliary population; Repeat the above steps, and stop the iteration after multiple iterations until the device optimization objective function is minimized or the maximum number of iterations is reached, and output the optimal parameters of the device; the optimal parameters of the device include the incident light wavelength, the refractive index of the interference lens, the deflection angle of the stage, and the distance of the mirror; the incident light wavelength includes the reference light wavelength and the measuring light wavelength.

5. The method for measuring the step height and flatness based on the laser interference method according to claim 3, wherein, The method for obtaining the stepped height and the flatness of the stepped surface includes: Perform Min-Max normalization on the stepped parameters of the measured step and all the stepped parameter entries in the stepped device parameter library: Among them is the class parameter after Min-Max normalization, is the minimum value of the corresponding parameter in the parameter library, is the maximum value of the corresponding parameter in the parameter library; Dynamically adjust the weights of different types of parameters according to the distribution characteristics of the data in the parameter library. The expression is: wherein is the dynamic correction weight of the class parameter, is the base weight of the class parameter, is the standard deviation of the class parameter in the parameter library, and the parameter category set includes the roughly measured height , the roughly measured length , the roughly measured width and the order ; Calculate the Euclidean distance and cosine similarity between the stepped parameters of the measured step after Min-Max normalization and the stepped parameters in the stepped device parameter library respectively to obtain the comprehensive similarity: wherein is the comprehensive similarity degree, , is the similarity weight, is the standardized result of the parameters of the step to be measured for the class of parameters, is the standardized result of the parameters of the step device parameter library for the class of parameters, is the maximum possible distance between all entries in the parameter library and the step parameters of the step to be measured; Take the optimal parameters corresponding to the step parameters in the step device parameter library with the highest comprehensive similarity as the reference device parameters. Set the laser interference measurement device using the reference device parameters. Use the adjusted laser interference measurement device to measure the step to be measured and obtain multiple interference images. Repeat the above operations to calculate the step height and step flatness.

6. A laser interferometry device for performing the method according to any one of claims 1-5, characterized in that, Including: A reference light emitter, a measurement light emitter, an optical fiber, a beam expander lens, an interference lens, a stage, a step gauge, a mirror, an imaging lens, and a high-definition camera; The reference light emitter and the measurement light emitter are respectively used to emit reference light and measurement light; the optical fiber connects the reference light emitter and the measurement light emitter and projects the reference light and the measurement light onto the beam expander lens; the beam expander lens is used to perform chromatic aberration correction on the reference light and the measurement light and expand them into parallel incident light; the interference lens forms a 45° angle with the incident light and is used to split the incident light into a first reflected light and a first transmitted light, and form interference fringes through a second reflected light and a third reflected light; the stage is parallel to the incident light and is used to adjust the deflection angle and place the step gauge; the step gauge is used to fix steps to be measured with different specifications; the mirror is perpendicular to the incident light and is used to return the first transmitted light along the original path to form a third reflected light; the imaging lens is parallel to the incident light and is used to receive the interference fringes; the high-definition camera is used to collect the interference fringes on the imaging lens to form an interference image; the step surface of the step to be measured is used to return the first reflected light along the original path to form a third reflected light; the first reflected light and the second reflected light are perpendicular to the incident light and have opposite directions; the first transmitted light and the third reflected light are parallel to the incident light and have opposite directions.

Images