Ellipsometer based on micro-nano deformable structure

Abstract

According to the ellipsometer based on the micro-nano deformable structure provided by the invention, the ellipsometer can be reduced to a sub-pixel level by the metasurface based on the micro-nano deformable structure, and when a large amount of the micro-nano deformable structure is integrated in the space, parameters of a measured surface of a whole measured material can be obtained in an imaging form; the limitation that a traditional ellipsometer can only perform single-point measurement is broken through; namely, two-dimensional measurement can be carried out in an imaging mode, the defect of single-point measurement of a traditional ellipsometer is overcome, the on-chip size of the ellipsometer is greatly reduced, and the size of the ellipsometer is reduced to the single-pixel level; the micro ellipsometer can be combined with different optical lens groups to detect the optical property and uniformity of the whole film in an imaging manner, and the defect of single-point detection of a traditional micro ellipsometer is overcome; according to the total variation-based full Stokes polarization vector reconstruction model, constraint is applied to iteration internal data, so that an operation result is more stable and is easy to converge.

Description

Technical Field

[0001] The invention belongs to the technical field of micro-scientific instruments, and in particular relates to an ellipsometer based on a micro-nano deformable structure. Background Art

[0002] In micro-nano processing technology, accurate measurement of the thickness of nano-scale films and their optical constants is of great significance to ensure the quality and efficiency of finished products. Instruments such as white light interferometers, scanning electron microscopes, and atomic force microscopes can measure film thickness with high precision, but their measurement speed is relatively slow, the system complexity is high, and the measurement may require direct contact with the sample being measured. Ellipsometers are an alternative method for high-precision, non-destructive measurement of film thickness and its optical constants, and have been widely used in semiconductor metrology and process monitoring.

[0003] Traditional ellipsometers require the mechanical rotation of a compensator or analyzer to modulate the polarization state, which may result in a large instrument size and sensitivity to mechanical vibration noise, and require a cascade of polarization modulation and detection systems. Recently, metasurfaces that can manipulate the amplitude, phase, polarization, and other aspects of light on a subwavelength scale may provide possibilities for miniature ellipsometers. On the one hand, polarization-sensitive metalens arrays and metasurface-based polarization gratings have been used to construct single-shot full-Stokes polarization detection and imaging systems. On the other hand, computational reconstructors based on metasurfaces have also received attention. Therefore, the use of metasurfaces based on micro-nano deformable structures can not only reduce the ellipsometer to the sub-pixel level, but also perform two-dimensional measurements in the form of imaging, breaking through the defects of single-point measurements of traditional ellipsometers. Summary of the invention

[0004] In order to solve the above problems, the present invention provides an ellipsometer based on a micro-nano deformable structure, which greatly reduces the on-chip size of the ellipsometer and reduces its volume to a single pixel level.

[0005] An ellipsometer based on a micro-nano deformable structure includes an ellipsometer chip 101 composed of multiple micro-nano deformable structures, a photoelectric sensor 102, a dynamic control circuit 103, a host computer 104, an imaging lens group 106 and a light source 107; wherein each pixel on the photoelectric sensor 102 corresponds to n 2 micro-nano deformable structures, wherein n is a multiple of the pixel side length relative to the period of the micro-nano deformable structure; the dynamic control circuit 103 is used to control the bias voltage of each micro-nano deformable structure on the ellipsometric chip 101, wherein different bias voltages correspond to different spectral responses of each micro-nano deformable structure;

[0006] The linearly polarized light emitted by the light source 107 is incident on the sample to be tested 105; the linearly polarized light is transmitted from the sample to be tested 105 or reflected from the sample to be tested 105 and then incident on the imaging lens group 106 as elliptically polarized light; the imaging lens group 106 collimates the elliptically polarized light, and the collimated polarized light is incident on the ellipsoid chip 101; the collimated polarized light is coupled with different spectral responses corresponding to the ellipsoid chip 101 under different bias voltages to obtain different coupled polarized lights; the different coupled polarized lights are sequentially incident on the photoelectric sensor 102 for imaging; the host computer 104 obtains the amplitude ratio Ψ and the phase difference Δ of the elliptically polarized light according to the imaging results of the photoelectric sensor 102.

[0007] Furthermore, the method for the host computer 104 to obtain the amplitude ratio Ψ and the phase difference Δ of the elliptically polarized light according to each imaging result of the photoelectric sensor 102 is specifically as follows:

[0008]

[0009] Where s = [s0, s1, s2, s3] T is the full Stokes polarization vector of the elliptically polarized light, s0 is the intensity of the elliptically polarized light, s1 is the intensity difference between the horizontal linear polarization component and the vertical linear polarization component of the elliptically polarized light, s2 is the intensity difference between the 45° linear polarization component and the 135° linear polarization component of the elliptically polarized light, and s3 is the intensity difference between the right-handed circular polarization component and the left-handed circular polarization component of the elliptically polarized light.

[0010] Furthermore, the full Stokes polarization vector of elliptically polarized light s=[s0,s1,s2,s3] T The calculation method is:

[0011] The energy function is constructed as follows:

[0012]

[0013] Among them, μ is the set regularization parameter; t represents the number of iterations; S t is the full Stokes polarization vector obtained at the tth iteration; S t-1 is the full Stokes polarization vector obtained at the t-1th iteration; I out is an N×1 column vector, N is the number of bias voltages, then I outEach element of represents the light intensity of the coupled polarized light collected by the photoelectric sensor 102 at the ellipsoid chip 101 under different bias voltages; M0 is an N×4 matrix, and the elements of each row of M0 are the first row elements of the Mueller matrix corresponding to the ellipsoid chip 101 under different bias voltages, wherein the first element of the first row in the Mueller matrix represents the proportional relationship between the total intensity of the collimated polarized light and the total intensity of the coupled polarized light; the second element of the first row represents the ratio of the difference between the intensity of the horizontal polarization component and the vertical polarization component in the coupled polarized light to the intensity of the horizontal polarization component in the collimated polarized light when the collimated polarized light is horizontally polarized light; the third element of the first row represents the ratio of the difference between the intensity of the horizontal polarization component and the 45° polarization component in the coupled polarized light to the intensity of the horizontal polarization component of the collimated polarized light when the collimated polarized light is horizontally polarized light; the fourth element of the first row represents the ratio of the difference between the intensity of the horizontal polarization component and the left-handed circular polarization component in the coupled polarized light to the intensity of the horizontal polarization component of the collimated polarized light when the collimated polarized light is horizontally polarized light;

[0014] S 0 = 0 as the initial value, and use the gradient descent method or augmented Lagrangian method to iteratively solve the energy function. When S between two adjacent iterations t and S t-1 When the difference between them is less than the set threshold, S t As the final full Stokes polarization vector S.

[0015] Furthermore, the method for obtaining the first row element of the Mueller matrix corresponding to the ellipsometric chip 101 under any bias voltage is as follows:

[0016] The intensities of the 0° linear polarization component, 45° linear polarization component, 90° linear polarization component and left-handed circular polarization component of the coupled polarized light output by the ellipsoid chip 101 under the current bias voltage are obtained through polarization detection technology, and the first row elements of the Mueller matrix are calculated according to the intensities of the 0° linear polarization component, 45° linear polarization component, 90° linear polarization component and left-handed circular polarization component.

[0017] Further, any micro-nano deformable structure includes a top layer, a support layer and a base layer;

[0018] Among them, the top layer is a gold film containing a hollow two-dimensional pattern, and the gold film and the base layer serve as the positive electrode and negative electrode of the loaded voltage respectively.

[0019] Furthermore, the support layer is a silicon dioxide, aluminum oxide, aluminum nitride or polyethylene support column.

[0020] Furthermore, the material of the base layer is a semiconductor material of silicon, indium tin oxide or silicon carbide.

[0021] Furthermore, the hollow two-dimensional pattern is four hollow arcs, wherein every two hollow arcs form a group, and the two groups of hollow arcs are centrally symmetrical, and a metamaterial shrapnel that can produce different deformations under different loading voltages is formed between the two arcs belonging to the same group.

[0022] Further, the photoelectric sensor 102 is a CMOS photoelectric sensor, a CCD photoelectric sensor, an organic semiconductor photoelectric sensor or a quantum colloidal dot photoelectric sensor.

[0023] Furthermore, an ellipsometer based on a micro-nano deformable structure also includes a post-processing module;

[0024] The post-processing module is used to calculate the thickness, refractive index or surface roughness of the sample 105 to be tested according to the amplitude ratio Ψ and the phase difference Δ of the elliptically polarized light.

[0025] Beneficial effects:

[0026] The present invention provides an ellipsometer based on a micro-nano deformable structure. The super surface based on the micro-nano deformable structure can not only reduce the ellipsometer to a sub-pixel level, but also when the micro-nano deformable structure is integrated in space in large quantities, the parameters of the measured surface of the entire measured material can be obtained in the form of imaging, breaking through the limitation that the traditional ellipsometer can only perform single-point measurement; that is, the present invention can perform two-dimensional measurement in the form of imaging, breaking through the defect of single-point measurement of the traditional ellipsometer, greatly reducing the on-chip size of the ellipsometer, and reducing its volume to the single-pixel level; the present invention can be combined with different optical lens groups to detect the optical properties and uniformity of the entire film in the form of imaging, breaking through the disadvantages of single-point detection of traditional micro-ellipsometers; the present invention is based on a full-Stokes polarization vector reconstruction model of total variation, and by imposing constraints on data within iterations, the calculation results are more stable and easy to converge. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the basic structure of a micro-ellipsometer based on a micro-nano deformable structure provided by the present invention.

[0028] Figure 2 This is a front view of the micro-nano deformable structure used in the present invention.

[0029] Figure 3 A top view of the micro-nano deformable structure used in the present invention.

[0030] Figure 4 This is a left view of the micro-nano deformable structure used in the present invention.

[0031] Figure 5 Schematic diagram of the double-layer membrane sample in the simulation experiment. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0033] like Figure 1 As shown, an ellipsometer based on a micro-nano deformable structure includes an ellipsometer chip 101 composed of multiple micro-nano deformable structures, a photoelectric sensor 102, a dynamic control circuit 103, a host computer 104, an imaging lens group 106, a light source 107 and a post-processing module; wherein each pixel on the photoelectric sensor 102 corresponds to n 2 A micro-nano deformable structure is provided, wherein n is a multiple of the pixel side length relative to the period of the micro-nano deformable structure. For example, in the present invention, the period of a single micro-nano deformable structure is one-n of the pixel size of the photodetector. When n=1 is used as the characteristic width of the micro-nano deformable structure, the period of the micro-nano deformable structure is 2.4 microns. The dynamic control circuit 103 is used to control the bias voltage of each micro-nano deformable structure on the ellipsometric chip 101. When the bias voltage is different, the spectral response corresponding to each micro-nano deformable structure is different.

[0034] like Figure 2 As shown, any micro-nano deformable structure includes a top layer, a support layer and a base layer; wherein the top layer is a gold film containing a hollow two-dimensional pattern, and the topological characteristic thickness of the metal film is 30-90nm; Figure 5 As shown, the gold film and the substrate layer are used as the positive electrode and the negative electrode for loading voltage, respectively. The support layer is silicon dioxide, aluminum oxide, aluminum nitride or polyethylene support column, such as Figure 4 As shown, the support layer is a deformation space reserved after etching, and its topological feature is that the thickness is 300-1000nm. The material of the base layer is a semiconductor material of silicon, indium tin oxide or silicon carbide, and its topological structure is characterized by a thickness of 300-1000nm. Figure 3 As shown, the hollow two-dimensional pattern is four hollow arcs, wherein every two hollow arcs form a group, and the two groups of hollow arcs are centrally symmetrical, and a metamaterial shrapnel that can produce different deformations under different loading voltages is formed between the two arcs belonging to the same group.

[0035] The linear polarized light emitted by the light source 107 is incident on the sample to be tested 105; the linear polarized light is transmitted or reflected from the sample to be tested 105 as elliptically polarized light and then incident on the imaging lens group 106; the imaging lens group 106 collimates the elliptically polarized light, and the collimated polarized light is incident on the elliptically polarized chip 101; the collimated polarized light is coupled with different spectral responses corresponding to the elliptically polarized chip 101 under different bias voltages to obtain different coupled polarized lights; different coupled polarized lights are sequentially incident on the photoelectric sensor 102 for imaging; the host computer 104 obtains the amplitude ratio Ψ and phase difference Δ of the elliptically polarized light according to each imaging result of the photoelectric sensor 102. The post-processing module is used to calculate the thickness, refractive index or surface roughness of the sample to be tested 105 according to the amplitude ratio Ψ and phase difference Δ of the elliptically polarized light.

[0036] Optionally, the photoelectric sensor 102 is a CMOS photoelectric sensor, a CCD photoelectric sensor, an organic semiconductor photoelectric sensor or a quantum colloidal dot photoelectric sensor. The dynamic control circuit is used to connect the top metal film of the micro-nano deformable structure with the substrate, and apply a bias voltage to realize the dynamic deformation of the micro-nano deformable structure; the dynamic control circuit can be directly controlled by the host computer S104, or it can be controlled by a separate data computing device. In the present invention, a single-chip microcomputer can also be used as a control element of the dynamic control circuit 103. The host computer 104 is a high-performance computing device, such as a processing unit such as an MCU, a CPU, an FPGA, and an NPU, which is used to read the energy collected from the photoelectric sensor and carry a full Stokes polarization reconstruction model based on total variation for reconstructing the full Stokes vector.

[0037] Specifically, the method for the host computer 104 to obtain the amplitude ratio Ψ and the phase difference Δ of the elliptically polarized light according to each imaging result of the photoelectric sensor 102 is as follows:

[0038]

[0039] Where s = [s0, s1, s2, s3] T is the full Stokes polarization vector of the elliptically polarized light, s0 is the intensity of the elliptically polarized light, s1 is the intensity difference between the horizontal linear polarization component and the vertical linear polarization component of the elliptically polarized light, s2 is the intensity difference between the 45° linear polarization component and the 135° linear polarization component of the elliptically polarized light, and s3 is the intensity difference between the right-handed circular polarization component and the left-handed circular polarization component of the elliptically polarized light.

[0040] Furthermore, the full Stokes polarization vector of elliptically polarized light s=[s0,s1,s2,s3] T The calculation method is:

[0041] The energy function is constructed as follows:

[0042]

[0043] Among them, μ is the set regularization parameter; t represents the number of iterations; S t is the full Stokes polarization vector obtained at the tth iteration; S t-1 is the full Stokes polarization vector obtained at the t-1th iteration; I out is an N×1 column vector, N is the number of bias voltages, then I out Each element of represents the light intensity of the coupled polarized light collected by the photoelectric sensor 102 at the ellipsoid chip 101 under different bias voltages; M0 is an N×4 matrix, and the elements of each row of M0 are the first row elements of the Mueller matrix corresponding to the ellipsoid chip 101 under different bias voltages, wherein the first element of the first row in the Mueller matrix represents the proportional relationship between the total intensity of the collimated polarized light and the total intensity of the coupled polarized light; the second element of the first row represents the ratio of the difference between the intensity of the horizontal polarization component and the vertical polarization component in the coupled polarized light to the intensity of the horizontal polarization component in the collimated polarized light when the collimated polarized light is horizontally polarized light; the third element of the first row represents the ratio of the difference between the intensity of the horizontal polarization component and the 45° polarization component in the coupled polarized light to the intensity of the horizontal polarization component of the collimated polarized light when the collimated polarized light is horizontally polarized light; the fourth element of the first row represents the ratio of the difference between the intensity of the horizontal polarization component and the left-handed circular polarization component in the coupled polarized light to the intensity of the horizontal polarization component of the collimated polarized light when the collimated polarized light is horizontally polarized light;

[0044] S 0 = 0 as the initial value, and use the gradient descent method or augmented Lagrangian method to iteratively solve the energy function. When S between two adjacent iterations t and S t-1 When the difference between them is less than the set threshold, S t As the final full Stokes polarization vector S.

[0045] It should be noted that the method for obtaining the first row element of the Mueller matrix corresponding to the ellipsometric chip 101 under any bias voltage is:

[0046] The intensities of the 0° linear polarization component, 45° linear polarization component, 90° linear polarization component and left-handed circular polarization component of the coupled polarized light output by the ellipsoid chip 101 under the current bias voltage are obtained through polarization detection technology, and the first row elements of the Mueller matrix are calculated according to the intensities of the 0° linear polarization component, 45° linear polarization component, 90° linear polarization component and left-handed circular polarization component.

[0047] It should be noted that the micro-ellipsometer provided by the present invention includes two stages: calibration and testing. In the calibration stage, the polarization detection technology is used to detect the intensity of 0° linear polarization, 45° linear polarization, 90° linear polarization and left-handed circular polarization under different bias voltages, which is used to build the Mueller matrix M0. In the testing stage, after placing the sample, the full Stokes vector of the sample is obtained by solving the energy function, and then the ellipsometric parameters of the sample are calculated: the amplitude ratio Ψ and the phase difference Δ.

[0048] In particular, the present invention uses Figure 3 The two-layer membrane structure shown verifies the performance of the ellipsometer based on the micro-nano deformable structure proposed in the present invention. Specifically, Figure 5 301 represents a silicon dioxide film, with a refractive index of 1.47 and a thickness of 100 nm, 302 represents an aluminum film, whose dielectric constant is described by the Drude model and whose thickness is 1000 nm, and an argon ion laser (488 nm) and a helium-neon laser (632.8 nm) are used as light sources. The experimental results are shown in Table 1.

[0049] Table 1 Evaluation of full Stokes polarization vector results

[0050]

[0051] It can be seen from Table 1 that the micro-nano deformable micro-ellipsometer provided by the present invention can obtain the full Stokes polarization vector more accurately, providing high-quality data support for further estimating the thickness and optical properties of the material. Therefore, it can be shown that the micro-ellipsometer provided by the present invention can obtain similar effects to the traditional ellipsometer at a size of 2.4 microns; and when the micro-nano deformable structure is integrated in large quantities in space, the parameters of the measured surface of the entire measured material can be obtained in the form of imaging, breaking through the limitation that the traditional ellipsometer can only measure a single point.

[0052] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may certainly make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. An ellipsometer based on a micro-nano deformable structure, characterized in that: The invention comprises an ellipsoid chip (101) composed of a plurality of micro-nano deformable structures, a photoelectric sensor (102), a dynamic control circuit (103), a host computer (104), an imaging lens group (106) and a light source (107); wherein each pixel point on the photoelectric sensor (102) corresponds to n 2 micro-nano deformable structures, wherein n is a multiple of the pixel side length relative to the period of the micro-nano deformable structure; a dynamic control circuit (103) is used to control the bias voltage of each micro-nano deformable structure on the ellipsometric chip (101), wherein different bias voltages correspond to different spectral responses of each micro-nano deformable structure; Linearly polarized light emitted by a light source (107) is incident on a sample to be tested (105); the linearly polarized light is transmitted from or reflected from the sample to be tested (105) and then incident on an imaging lens group (106) as elliptically polarized light; the imaging lens group (106) collimates the elliptically polarized light, and the collimated polarized light is incident on an elliptically polarized chip (101); the collimated polarized light is coupled with different spectral responses corresponding to the elliptically polarized chip (101) under different bias voltages to obtain different coupled polarized lights; the different coupled polarized lights are sequentially incident on a photoelectric sensor (102) for imaging; and a host computer (104) obtains an amplitude ratio Ψ and a phase difference Δ of the elliptically polarized light according to each imaging result of the photoelectric sensor (102).

2. An ellipsometer based on a micro-nano deformable structure as claimed in claim 1, characterized in that: The method for the host computer (104) to obtain the amplitude ratio Ψ and the phase difference Δ of the elliptically polarized light according to each imaging result of the photoelectric sensor (102) is specifically as follows: Where s = [s0, s1, s2, s3] T is the full Stokes polarization vector of the elliptically polarized light, s0 is the intensity of the elliptically polarized light, s1 is the intensity difference between the horizontal linear polarization component and the vertical linear polarization component of the elliptically polarized light, s2 is the intensity difference between the 45° linear polarization component and the 135° linear polarization component of the elliptically polarized light, and s3 is the intensity difference between the right-handed circular polarization component and the left-handed circular polarization component of the elliptically polarized light.

3. An ellipsometer based on a micro-nano deformable structure as claimed in claim 2, characterized in that: The full Stokes polarization vector of elliptically polarized light s=[s0,s1,s2,s3] T The calculation method is: The energy function is constructed as follows: Among them, μ is the set regularization parameter; t represents the number of iterations; S t is the full Stokes polarization vector obtained at the tth iteration; S t-1 is the full Stokes polarization vector obtained at the t-1th iteration; I out is an N×1 column vector, N is the number of bias voltages, then I out Each element of represents the light intensity of the coupled polarized light collected by the photoelectric sensor (102) at the ellipsoid chip (101) under different bias voltages; M0 is an N×4 matrix, and the elements of each row of M0 are the first row elements of the Mueller matrix corresponding to the ellipsoid chip (101) under different bias voltages, wherein the first element of the first row in the Mueller matrix represents the proportional relationship between the total intensity of the collimated polarized light and the total intensity of the coupled polarized light; the second element of the first row represents the ratio of the difference between the intensity of the horizontal polarization component and the vertical polarization component in the coupled polarized light to the intensity of the horizontal polarization component in the collimated polarized light when the collimated polarized light is horizontally polarized light; the third element of the first row represents the ratio of the difference between the intensity of the horizontal polarization component and the 45° polarization component in the coupled polarized light to the intensity of the horizontal polarization component of the collimated polarized light when the collimated polarized light is horizontally polarized light; the fourth element of the first row represents the ratio of the difference between the intensity of the horizontal polarization component and the left-handed circular polarization component in the coupled polarized light to the intensity of the horizontal polarization component of the collimated polarized light when the collimated polarized light is horizontally polarized light; S 0 = 0 as the initial value, and use the gradient descent method or augmented Lagrangian method to iteratively solve the energy function. When S between two adjacent iterations t and S t-1 When the difference between them is less than the set threshold, S t As the final full Stokes polarization vector S.

4. The ellipsometer based on micro-nano deformable structure as claimed in claim 3, characterized in that: A method for obtaining the first row element of the Mueller matrix corresponding to the ellipsometric chip (101) under any bias voltage is as follows: The intensity of the 0° linear polarization component, the 45° linear polarization component, the 90° linear polarization component and the left-hand circular polarization component of the coupled polarized light output by the ellipsoid chip (101) under the current bias voltage is obtained by polarization detection technology, and the first row element of the Mueller matrix is ​​calculated according to the intensity of the 0° linear polarization component, the 45° linear polarization component, the 90° linear polarization component and the left-hand circular polarization component.

5. The ellipsometer based on micro-nano deformable structure according to claim 1, characterized in that: Any micro-nano deformable structure includes a top layer, a support layer and a base layer; Among them, the top layer is a gold film containing a hollow two-dimensional pattern, and the gold film and the base layer serve as the positive electrode and negative electrode of the loaded voltage respectively.

6. The ellipsometer based on micro-nano deformable structure as claimed in claim 5, characterized in that: The support layer is a silicon dioxide, aluminum oxide, aluminum nitride or polyethylene support column.

7. The ellipsometer based on micro-nano deformable structure as claimed in claim 5, characterized in that: The material of the base layer is a semiconductor material such as silicon, indium tin oxide or silicon carbide.

8. The ellipsometer based on micro-nano deformable structure as claimed in claim 5, characterized in that: The hollow two-dimensional pattern is four hollow arcs, wherein every two hollow arcs form a group, and the two groups of hollow arcs are centrally symmetrical, and a metamaterial shrapnel that can produce different deformations under different loading voltages is formed between the two arcs belonging to the same group.

9. The ellipsometer based on micro-nano deformable structure according to claim 1, characterized in that: The photoelectric sensor (102) is a CMOS photoelectric sensor, a CCD photoelectric sensor, an organic semiconductor photoelectric sensor or a quantum colloidal dot photoelectric sensor.

10. The ellipsometer based on micro-nano deformable structure according to claim 1, characterized in that: Also includes post-processing modules; The post-processing module is used to calculate the thickness, refractive index or surface roughness of the sample (105) to be tested according to the amplitude ratio Ψ and the phase difference Δ of the elliptically polarized light.

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