Synchronous phase shift measurement system and method based on polarized light interference spectrum

Abstract

The present application belongs to the field of three-dimensional measurement of sample surface topography, and relates to a synchronous phase shift measurement system and method based on polarized light interference spectrum. The system comprises a light source module, a measurement interference module, a spectrum interference module, an image detection module and a computer control analysis module. A Linnik type microscopic interference structure is used as the measurement interference unit. The sample and the system optical axis are adjusted to be perpendicular by adjusting the object table. The computer collects interference images, and interference signals of four polarization angles are extracted respectively. The phase information is calculated by using a four-step phase shift method. The sample surface topography, the surface topography and the thickness information of the film sample are obtained through the relationship between the phase and the wave number. The system combines spatial phase shift and linear spectrum, greatly improves the measurement efficiency and anti-interference ability, and can be applied to the measurement of micro-nano semiconductor silicon wafers, precision optical devices and other samples.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of three-dimensional measurement of sample surface topography and surface topography and thickness of thin film sample, and particularly relates to a synchronous phase shift measurement system and method based on polarized light interference spectrum. BACKGROUND

[0002] The high demand of the market for ultra-precision devices such as semiconductor silicon wafers, mobile phone lenses, and precision optical devices puts higher requirements on the processing and detection methods of ultra-precision devices. The measurement parameters of ultra-precision devices mainly include micro-nano level length, width, height, surface roughness, thickness and other parameters. The present application focuses on micro-nano structure samples, and measures the surface topography of the sample and the surface topography and thickness of the thin film sample.

[0003] The measurement of the surface topography of micro-nano structure samples mainly includes non-contact measurement and contact measurement. Contact measurement such as contact probe profilometer, the probe contacts the measured sample surface during the measurement process, which can cause damage to the measured sample surface, and the size of the probe limits the measurable sample topography. Non-contact measurement such as scanning electron microscope, which uses an electron beam instead of a probe, does not damage the sample, but this method requires high experimental conditions and long measurement time. The present application uses non-contact measurement, and measures the surface topography of micro-nano structure samples and the surface topography and thickness of thin film samples based on synchronous phase shift measurement of polarized light interference.

[0004] When measuring the surface topography of micro-nano structures, the phase can be calculated by introducing a phase difference using a phase shifting algorithm. The phase shifting algorithm can be divided into time phase shifting method and space phase shifting method. The time phase shifting method introduces a known phase difference at different time points, records the interference images with the phase difference, calculates the phase from the interference images, and then calculates the surface topography of the sample. The time phase shifting method is measured at different time points, which is easily affected by the external environment. The space phase shifting method introduces a phase difference in space at the same time, collects multiple interference images with a fixed phase difference by one-time exposure, calculates the phase from the interference images, and then calculates the surface topography of the sample. Compared with the time phase shifting, the space phase shifting can realize the synchronization in time, avoid the error introduced by environmental vibration and other factors, and realize the measurement of dynamic samples. The measurement range of the system using the space phase shifting in the prior art is usually nanometer level, for example, in 2011, Cheng Weilin of Huazhong University of Science and Technology published Polarization Phase Shifting Microscopic Interference Superfine Surface Topography Measurement Research, which proposed a polarization phase shifting microscopic interference measurement method combining polarization phase shifting technology and Michelson interference microscope. According to the function relationship between the phase distribution and the height of the measured surface, the maximum height of the vertical step of the system is 316.4nm. When measuring some samples that need to be measured to micron level, it cannot be realized. The traditional white light interference spectrum measurement technology is point measurement, and the coverage range is small and the measurement efficiency is low. The phase extraction algorithm in the traditional white light interference spectrum measurement technology is Fourier transform method and time phase shifting method. The Fourier transform method has the problem of frequency spectrum leakage, and the accuracy of phase extraction depends largely on the selection of frequency domain window. At the same time, the Fourier transform method is not ideal for the processing of non-stationary signals. The time phase shifting method is sensitive to noise in the environment and is greatly affected by the environment. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a synchronous phase shifting measurement system and method based on polarization light interference spectrum, which combines space phase shifting method and line spectrum to greatly improve the measurement efficiency and anti-interference ability.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0007] The first aspect of the present application is to provide a measurement system for measuring the surface topography of a sample based on polarization light interference spectrum synchronous phase shifting, which comprises a light source module, a measurement interference module, a spectrum interference module, an image detection module and a computer control analysis module.

[0008] The light source module comprises a white light source, a lens, a diaphragm and a polarizer. The light emitted from the light source passes through the lens and then becomes linearly polarized light through the polarizer.

[0009] A measurement interference module comprises a polarization beam splitter, a first quarter-wave plate, a second quarter-wave plate, a third quarter-wave plate, a reference mirror, linearly polarized light is incident to the polarization beam splitter and is divided into reference light P light and measurement light S light with perpendicular vibration directions, the reference light P light is incident to the reference mirror after being changed into circularly polarized light by the first quarter-wave plate with the fast axis being placed at 45° to the x axis, is reflected, and is changed into reference light S light again by the first quarter-wave plate; the measurement light S light is incident to a sample after being changed into circularly polarized light by the second quarter-wave plate with the fast axis being placed at 45° to the x axis, is reflected, and is changed into measurement light P light again by the second quarter-wave plate, and the reference light S light and the measurement light P light are changed into two circularly polarized lights with opposite rotation directions after passing through the polarization beam splitter and the third quarter-wave plate with the fast axis being placed at 45° to the x axis;

[0010] A spectral interference module and an image detection module comprise a tube lens, a beam splitter, a linear spectrum module, a polarization camera and a CCD camera, two circularly polarized lights are transmitted through the tube lens, are transmitted through the beam splitter, are imaged on the CCD camera, and are reflected by the beam splitter, pass through the linear spectrum module and are imaged on the polarization camera;

[0011] A computer control analysis module is used for adjusting camera parameters, image acquisition and processing interference signals, and calculating surface topography information through phase information.

[0012] The second aspect of the present application is to provide a measurement method for synchronously phase-shifting measurement of micro-nano structure sample surface topography based on polarized light interference, comprising the following steps:

[0013] 1) placing the sample on the object table and moving to the required measurement area;

[0014] 2) adjusting the distance between the sample and the measurement objective lens until the sample is clearly imaged on the image acquired by the CCD camera;

[0015] 3) adjusting the tilt angle of the sample and the distance from the measurement objective lens until the interference fringes with good contrast appear on the image acquired by the polarization camera;

[0016] 4) acquiring the interference image by using the polarization camera and performing data processing;

[0017] 5) processing the interference image by using the four-step phase shift method to extract the phase information;

[0018] 6) calculating the surface topography information through the phase information.

[0019] Step 1) comprises:

[0020] (1.1) turning on the white light source and connecting the signal output end of the camera to the computer.

[0021] (1.2) Place the sample on the stage and move the area to be measured to the bright spot.

[0022] Step 2) includes:

[0023] (2.1) Adjust the Z displacement stage to move the sample up and down.

[0024] (2.2) The computer collects images from the camera in real time until the sample surface can be clearly imaged.

[0025] Step 3) includes:

[0026] (3.1) Adjust the tilt adjustment stage until interference fringes appear on the image collected by the polarization camera, at which point the sample and the light path are essentially perpendicular.

[0027] (3.2) Further adjust the Z displacement stage and the tilt adjustment stage until a small number of interference fringes with good contrast appear on the image collected by the polarization camera.

[0028] Step 4) includes:

[0029] (4.1) Adjust the camera parameters.

[0030] (4.2) Collect interference images from the polarization camera and extract images for four polarization angles respectively.

[0031] Step 5) According to the Jones matrix of the polarization light and the optical devices of the system, the interference images I for four polarization angles satisfy the formula:

[0032]

[0033]

[0034] I x , I y are the intensities of the measurement light and the reference light respectively. Φ represents the phase difference between the reference light and the measurement light, and α is the angle of the micro-polarizer. In the unit cell of the polarization camera, α is set to 0°, 45°, 90° and 135°, so four different phase shift interference images are generated simultaneously in one measurement.

[0035] The four-step phase shift method satisfies the formula:

[0036]

[0037] Step 6) includes:

[0038] (6.1) The relationship between each pixel and wavelength is obtained by spectral calibration before measuring the sample. The light source of spectral calibration uses a high-brightness continuous spectrum light source and an Acousto-Optic Tunable Filter (AOTF), which can quickly change the wavelength of its output light by adjusting the frequency of the electrical signal.

[0039] (6.2) When measuring the surface topography of the sample, the relationship between the absolute distance and the wave number is carried in the phase. The absolute distance can be calculated by the slope of the phase and the wave number, and the formula satisfies:

[0040]

[0041] Wherein

[0042]

[0043] (6.3) When measuring the thin film sample, the phase contains the relationship between the absolute distance of the thin film surface, the thickness of the thin film and the wave number. The phase Φ calculated by the four-step phase shift method contains two parts, one part is the phase generated by the reflection of the thin film sample surface, and the other part is the phase generated by the structure of the thin film. The formula satisfies:

[0044] Φ = Φ sur (h, k) + Φ film (d, k)

[0045] Wherein Φ sur (h, k) represents the linear phase generated by the reflection of the thin film sample surface, and Φ film (d, k) represents the phase generated by the structure of the thin film.

[0046] (6.3.1) The phase Φ film (d, k) generated by the structure of the thin film contains two parts, one part is the linear phase generated by the thickness of the film structure, and the other part is the nonlinear phase generated by the multiple reflections inside the film structure. The formula satisfies:

[0047]

[0048] Wherein d' is the initial estimate of the thickness of the thin film, is the nonlinear phase generated by the multiple reflections inside the film structure.

[0049] (6.3.2) The initial estimate of the thickness of the thin film d' is calculated by using the combination of Fourier transform and thickness initial estimate search method, and the formula satisfies:

[0050]

[0051] Wherein, λ min and n(λ minrespectively represent the minimum wavelength in the measured wavelength range and its corresponding refractive index, and max and n(λ max ) respectively represent the maximum wavelength in the measured wavelength range and its corresponding refractive index.

[0052] The evaluation function of the film thickness initial value search is the square sum of the difference between the actual measured value and the theoretical value of the nonlinear phase, a suitable initial value search step is set, and the position with the minimum evaluation function is selected as the initial value of the film thickness.

[0053] (6.3.3) After obtaining the initial value of the film thickness, the nonlinear fitting of the film phase is carried out, the L-M algorithm is used for nonlinear optimization fitting, and the evaluation function is the square sum of the difference between the actual measured value and the theoretical value of the nonlinear phase. Search for different thicknesses d, so that the evaluation function is minimum, and the evaluation function is expressed as:

[0054]

[0055] wherein, is the actual measured value of the nonlinear phase of the film structure, is the theoretical value of the nonlinear phase of the film structure.

[0056] (6.3.4) After obtaining the thickness of the film sample, the phase Φ film (d, k) generated by the film structure can be obtained by calculation, and then the phase generated by the surface reflection of the film sample is obtained, which satisfies the formula:

[0057] Φ sur (h, k) = Φ - Φ film (d, k)

[0058] (6.3.5) The phase generated by the surface reflection of the film sample carries the linear relationship of absolute distance and wave number, and the absolute distance can be calculated through the slope of the phase and the wave number, so that the film surface topography information is obtained, and the formula satisfies:

[0059]

[0060] The polarization interference spectrum-based synchronous phase shift measurement system and method of the application uses a Linnik type microscopic interference structure as a measurement interference unit. The sample and the system optical axis are perpendicular by adjusting the objective table; the interference image is collected by a computer, and interference signals at four polarization angles are extracted respectively; the phase information is calculated by using a four-step phase shift method; and the surface topography information of the sample and the surface topography and thickness of the film sample are obtained through the relationship between the phase and the wave number.

[0061] 1. Compared with the prior art, the technical features and effects of the present application are: the system combines spatial phase shift and line spectrum, realizes expansion of the measurement range, and can be applied to measurement of micro-nano semiconductor silicon wafers, precision optical devices and other samples.

[0062] 2. Compared with the traditional white light spectrum interference measurement, the system can realize line measurement without scanning device, has higher measurement accuracy and higher measurement efficiency, is suitable for measurement of complex topography, and is widely applied.

[0063] 3. The present application introduces spatial synchronous phase shift, reduces errors introduced by environmental vibration and other factors, realizes measurement of dynamic samples, has short measurement time, and is less affected by external environment.

[0064] 4. The measurement process of the present application is simple and easy to operate. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 is a system diagram of the synchronous phase shift measurement system based on polarized light interference spectrum of the present application;

[0066] Figure 2 is a flowchart of sample surface topography extraction in the measurement process of the present application;

[0067] Figure 3 is a flowchart of parameter extraction of film thickness and surface topography of the present application;

[0068] In the drawings:

[0069] 101 is a light source module, 102 is a light source, 103 is a lens, 104 is a diaphragm, and 105 is a polarizer;

[0070] 201 is a measurement interference module, 202 is a polarization beam splitter prism, 203 is a first quarter wave plate, 204 is a reference objective lens, 205 is a reference mirror, 206 is a horizontal displacement table, 207 is a second quarter wave plate, 208 is a measurement objective lens, 209 is a Z-direction displacement table, 210 is an inclination adjustment table, and 211 is a third quarter wave plate;

[0071] 301 is a spectrum interference module, 302 is a tube lens, 303 is a beam splitter prism, 304 is a line spectrum module, and 305 is a polarization camera;

[0072] 401 is an image detection module, and 402 is a CCD camera;

[0073] 501 is a computer control analysis module; DETAILED DESCRIPTION

[0074] The synchronous phase shift measurement system and method based on polarized light interference spectrum of the present application will be described in detail below in combination with examples and drawings.

[0075] As Figure 1 shown, the present application is based on the polarization interference spectrum synchronous phase shift measurement system, the system contains light source module 101, measurement interference module 201, spectral interference module 301, image detection module 401, computer control analysis module 501.

[0076] The light source module 101 contains light source 102, lens 103, diaphragm 104, polarizer 105. The light from the light source 102 passes through the lens 103, and the stray light is filtered out through the diaphragm 104, and becomes linearly polarized light through the polarizer 105.

[0077] The measurement interference module 201 contains polarization beam splitter prism 202, first quarter wave plate 203, reference objective 204, reference mirror 205, horizontal displacement table 206, second quarter wave plate 207, measurement objective 208, Z displacement table 209, tilt adjustment table 210, third quarter wave plate 211. Linearly polarized light is incident on the polarization beam splitter prism and is divided into reference light P light and measurement light S light with perpendicular vibration directions. The reference light P light is incident on the reference mirror 205 after being changed into circularly polarized light by the first quarter wave plate 203 placed at 45° with the x-axis, and is reflected again, and is changed into reference light S light by the first quarter wave plate 203. The measurement light S light is incident on the sample after being changed into circularly polarized light by the second quarter wave plate 207 placed at 45° with the x-axis, and is reflected again, and is changed into measurement light P light by the second quarter wave plate 207. The reference light S light and the measurement light P light pass through the polarization beam splitter prism 202 and are changed into two circularly polarized lights with opposite rotation directions by the third quarter wave plate 211 placed at 45° with the x-axis.

[0078] The spectral interference module 301 and the image detection module 401 contain tube lens 302, beam splitter prism 303, line spectrum module 304, polarization camera 305 and CCD camera 402. Two circularly polarized lights pass through the tube lens 302, one part is transmitted through the beam splitter prism 303 and is imaged on the CCD camera 402, and the other part is reflected by the beam splitter prism 303 and is imaged on the polarization camera 305 through the line spectrum module 304.

[0079] The computer control analysis module 501 contains camera parameter adjustment, image acquisition, and interference signal processing.

[0080] The present application is a kind of based on the measurement method of polarization interference synchronous phase shift measurement micro-nano structure sample surface topography and film sample surface topography and thickness, comprising the following steps:

[0081] (1.1) turn on the white light source, connect the signal output end of the polarization camera and the CCD camera to the computer, and the camera can normally collect images.

[0082] (1.2) Place the sample on the stage, move the sample, and move the area to be measured to the bright spot.

[0083] (2.1) Adjust the Z displacement table in the stage to move the sample vertically up and down.

[0084] (2.2) The computer collects images from the CCD camera and the polarization camera in real time until the sample surface can be clearly imaged.

[0085] (3.1) Adjust the tilt adjustment table until interference fringes appear on the image collected by the polarization camera, at which point the sample and the optical path are essentially perpendicular.

[0086] (3.2) Further adjust the Z displacement table and the tilt adjustment table until a small number of interference fringes with good contrast appear on the image collected by the polarization camera.

[0087] (4.1) Adjust the exposure time of the polarization camera so that the interference image is neither overexposed nor underexposed.

[0088] (4.2) Collect the interference image: The original interference image collected by the polarization camera contains four polarization angles. Process the image to extract the images of the four polarization angles respectively.

[0089] (5) According to the Jones matrix of the polarized light and the optical devices of the system, the light intensity of the interference image of the four polarization angles can be calculated, which satisfies the formula:

[0090]

[0091] I x 、I y are the light intensities of the measurement light and the reference light respectively. Φ represents the phase difference between the reference light and the measurement light, and α is the angle of the micro-polarizer. In the unit cell of the polarization camera, α is set to 0°, 45°, 90° and 135°, so four different phase shift interference images are generated simultaneously in one measurement.

[0092] The four-step phase shift method satisfies the formula:

[0093]

[0094] (6.1) The relationship between each pixel and wavelength is obtained by spectral calibration before measuring the sample. The spectral line image of monochromatic light is obtained: the spectral calibration light source uses a high-brightness continuous spectrum light source and an Acousto-Optic Tunable Filter (AOTF), which can quickly change the wavelength of the output light by adjusting the frequency of the electrical signal, and record the image of each wavelength of light in the polarization camera, while using a spectrometer to record the wavelength of the output light, and by changing the frequency of the electrical signal of the AOTF, the spectral line information of the imaging of different wavelengths of light in the polarization camera is collected; the effective area of the calibration spectral line image is extracted: binary is used to make the pixel value at the spectral line 1 and the other part 0; the centroid position of each column is calculated: the centroid position of each column is calculated for the binary processed spectral line image; the relationship between the pixel and the wave number is determined: according to the known centroid position and the relationship between the wave number, the relationship between the pixel and the wave number is twice fitted at the same column, i.e., the same spatial position, to obtain a pixel-wave number quadratic expression, and this step is repeated to twice fit the centroid position and the wave number value of each column.

[0095] (6.2) When measuring the surface topography of the sample, the absolute distance and the relationship between the wave number are carried in the phase, and the absolute distance can be calculated through the slope of the phase and the wave number, and the formula satisfies:

[0096]

[0097] wherein

[0098]

[0099] (6.3) When measuring a thin film sample, the absolute distance of the thin film surface, the thickness of the thin film and the relationship between the wave number are carried in the phase, and the phase Φ calculated by the four-step phase shift method contains two parts, one part is the phase generated by the reflection of the thin film sample surface, and the other part is the phase generated by the thin film structure, and the formula satisfies:

[0100] Φ = Φ sur (h, k) + Φ film (d, k)

[0101] wherein Φ sur (h, k) represents the linear phase generated by the reflection of the thin film sample surface, and Φ film (d, k) represents the phase generated by the thin film structure.

[0102] (6.3.1) The phase Φ film (d, k) generated by the thin film structure contains two parts, one part is the linear phase generated by the film thickness of the thin film structure, and the other part is the nonlinear phase generated by the multiple reflections inside the thin film structure, and the formula satisfies:

[0103]

[0104] where d' is the initial estimate of the film thickness, is the nonlinear phase caused by multiple reflections inside the film structure.

[0105] (6.3.2) Calculate the initial estimate of the film thickness d' using the Fourier transform combined with the film thickness initial estimate search method, the formula satisfies:

[0106]

[0107] where λ min and n(λ min ) represent the minimum wavelength and its corresponding refractive index in the measurement wavelength range, respectively, and λ max and n(λ max ) represent the maximum wavelength and its corresponding refractive index in the measurement wavelength range, respectively.

[0108] The evaluation function of the film thickness initial value search is the sum of the squares of the difference between the actual measured value and the theoretical value of the nonlinear phase. Set the appropriate initial value search step, and select the position with the minimum evaluation function as the initial value of the film thickness.

[0109] (6.3.3) After obtaining the initial value of the film thickness, perform nonlinear fitting of the film phase. Use the L-M algorithm for nonlinear optimization fitting, and the evaluation function is the sum of the squares of the difference between the actual measured value and the theoretical value of the nonlinear phase. Search for different thicknesses d to make the evaluation function minimum, and the evaluation function is expressed as:

[0110]

[0111] where, is the actual measured value of the nonlinear phase of the film structure, is the theoretical value of the nonlinear phase of the film structure.

[0112] (6.3.4) After obtaining the thickness of the film sample, the phase Φ film (d, k) generated by the film structure can be calculated, and then the phase generated by the reflection of the film sample surface is obtained, which satisfies the formula:

[0113] Φ sur (h, k) = Φ - Φ film (d, k)

[0114] (6.3.5) The phase carries the linear relationship of absolute distance and wave number, and the absolute distance can be calculated through the slope of the phase and the wave number, so as to obtain the film surface topography information, which satisfies the formula:

[0115]

[0116] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all belong to the protection scope of the present application.

Claims

1. A synchronous phase shift measurement system based on polarized light interferometry, characterized in that, include: The light source module includes a white light source, a lens, an aperture, and a polarizer. Light emitted from the white light source is converted into linearly polarized light after passing through the lens, aperture, and polarizer in sequence. The measurement interferometry module includes a polarizing beam splitter, a first quarter-wave plate, a second quarter-wave plate, a third quarter-wave plate, and a reference mirror. Linearly polarized light incident on the polarizing beam splitter is split into a reference beam (P-beam) and a measurement beam (S-beam) with mutually perpendicular vibration directions. The reference beam (P-beam) becomes circularly polarized after passing through the first quarter-wave plate, which is placed at a 45° angle between its fast axis and the x-axis. After being reflected by the reference mirror, it passes through the first quarter-wave plate again to become the reference beam (S-beam). The measurement beam (S-beam) becomes circularly polarized after passing through the second quarter-wave plate, which is placed at a 45° angle between its fast axis and the x-axis. After being reflected by the sample, it passes through the second quarter-wave plate again to become the measurement beam (P-beam). The reference beam (S-beam) and the measurement beam (P-beam) pass through the polarizing beam splitter and then through the third quarter-wave plate, which is placed at a 45° angle between its fast axis and the x-axis, to become two circularly polarized beams with opposite rotation directions. The spectral interferometry module and image detection module include a tube mirror, a beam splitter prism, a line spectrum module, a polarization camera, and a CCD camera. Two circularly polarized beams pass through the tube mirror, with one part transmitted through the beam splitter prism and imaged on the CCD camera, and the other part reflected through the beam splitter prism and imaged on the polarization camera through the line spectrum module. The computer-controlled analysis module acquires interference images, extracts interference signals at four polarization angles, calculates phase information using a four-step phase-shifting method, and calculates the absolute distance based on the relationship between phase and wavenumber to obtain the surface morphology information of the sample.

2. The synchronous phase shift measurement system based on polarized light interferometry spectrum according to claim 1, characterized in that, The sample is placed on a stage, which consists of a Z-axis displacement stage for vertically moving the sample and a tilt adjustment stage for adjusting the tilt angle of the sample.

3. The synchronous phase shift measurement system based on polarized light interferometry spectrum according to claim 2, characterized in that, The reference mirror is mounted on a horizontal displacement stage.

4. The synchronous phase shift measurement system based on polarized light interferometry spectrum according to claim 3, characterized in that, A reference objective is placed in the optical path between the first quarter-wave plate and the reference mirror, and a measuring objective is placed in the optical path between the second quarter-wave plate and the stage.

5. The measurement method of the synchronous phase shift measurement system based on polarized light interferometry according to claim 4, characterized in that, Includes the following steps: 1) Place the sample on the stage and move it to the required measurement area; 2) Adjust the distance between the sample and the measuring objective lens until the sample is clearly imaged on the image acquired by the CCD camera; 3) Adjust the tilt angle of the sample and the distance from the measuring objective lens until good contrast interference fringes appear on the image acquired by the polarization camera; 4) Acquire interference images using a polarization camera and perform data processing; 5) Use the four-step phase-shifting method to process the interferometric image and extract phase information; 6) When measuring the surface morphology of a sample, the surface morphology information is calculated using phase information; when measuring a thin film sample, the film thickness is calculated using phase information.

6. The measurement method according to claim 5, characterized in that, Step 4) Extract images from four polarization angles using a polarization camera.

7. The measurement method according to claim 5, characterized in that, Step 6) The method for calculating the film thickness using phase information is as follows: the extracted phase information is fitted with the wavenumber once to obtain the linear phase, and the nonlinear phase is obtained by subtracting the linear phase from the extracted phase information. The initial estimate of the thin film and the theoretical nonlinear phase are calculated. After obtaining the initial estimate of the thin film, the sum of the squares of the differences between the actual measured value and the theoretical value of the nonlinear phase is used as the evaluation function, and the LM algorithm is used to fit the film thickness.

8. The measurement method according to claim 7, characterized in that, The initial estimate of the film thickness d' is calculated using a combination of Fourier transform and initial film thickness estimation search methods, and the formula satisfies: Where, λ min and n(λ) min ) represent the minimum wavelength and its corresponding refractive index within the measurement band, respectively, λ max and n(λ) max () represent the maximum wavelength and its corresponding refractive index within the measurement band, respectively; The evaluation function for the initial film thickness search is the sum of the squares of the differences between the actual measured value and the theoretical value of the nonlinear phase. By setting an appropriate initial search step size, the position where the evaluation function is minimized is selected as the initial value of the film thickness.

9. The measurement method according to claim 8, characterized in that, After obtaining the thickness of the thin film sample, the phase generated by the thin film structure can be calculated. The linear phase obtained by subtracting the phase generated by the thin film structure from the extracted phase information is the phase generated by the reflection of the thin film sample surface. The surface morphology information of the thin film can be calculated by using the phase information generated by the reflection of the thin film sample surface.

Images