Ellipsometer based on micro-nano deformable structure

Abstract

The application provides an ellipsometer based on micro-nano deformable structures, the super surface based on the micro-nano deformable structures can not only reduce the ellipsometer to a sub-pixel level, but also can obtain the parameters of the measured surface of the whole measured material in the form of imaging when the micro-nano deformable structures are integrated in a large amount in space, thereby breaking the limitation that the traditional ellipsometer can only measure a single point; that is, the application can perform two-dimensional measurement in the form of imaging, break the defect of single-point measurement of the traditional ellipsometer, greatly reduce the on-chip size of the ellipsometer, and reduce the volume of the ellipsometer to a single-pixel level; the application can be combined with different optical lens groups to detect the optical properties and uniformity of the whole film in the form of imaging, thereby breaking the disadvantage of single-point detection of the traditional micro ellipsometer; and the application is based on a total variation full Stokes polarization vector reconstruction model, and the operation result is more stable and easy to converge by applying constraints on the data in iteration.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of micro scientific instruments, and particularly relates to an ellipsometer based on micro-nano deformable structures. BACKGROUND

[0002] In micro-nano processing technology, it is of great significance to accurately measure the thickness and optical constants of nanoscale thin films to ensure the quality and efficiency of finished products. White light interferometer, scanning electron microscope and atomic force microscope can be used to measure the thickness of thin films with high precision, but they have relatively slow measurement speed, high system complexity, and may need to be in direct contact with the measured sample. Ellipsometer is an alternative method for high-precision and non-destructive measurement of thin film thickness and optical constants, and has been widely used in semiconductor metrology and process monitoring.

[0003] Traditional ellipsometers need to modulate the polarization state by mechanical rotation of compensators or analyzers, which may result in 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 of light on a subwavelength scale extremely diversely may provide possibilities for micro-ellipsometers. On the one hand, polarization-sensitive superlens arrays and polarization gratings based on metasurfaces have been used to construct single full-Stokes polarization detection and imaging systems. On the other hand, metasurface-based computational reconstructor has also attracted attention. Therefore, using metasurfaces based on micro-nano deformable structures can not only reduce the size of the ellipsometer to sub-pixel level, but also break through the defect of single-point measurement of traditional ellipsometers in the form of imaging. SUMMARY

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

[0005] An ellipsometer based on micro-nano deformable structures includes an ellipsometer chip 101 composed of a plurality of micro-nano deformable structures, a photoelectric sensor 102, a dynamic control circuit 103, an upper 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; the dynamic control circuit 103 is used to control the bias voltage of each micro-nano deformable structure on the ellipsometer chip 101, wherein the bias voltage is different, and the spectral response of each micro-nano deformable structure is different;

[0006] The linearly polarized light emitted by the light source 107 is incident on the sample 105 to be measured; the linearly polarized light transmitted or reflected from the sample 105 to be measured is 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 ellipsometer chip 101; the collimated polarized light is coupled with different spectral responses of the ellipsometer chip 101 under different bias voltages to obtain different coupled polarized light; the different coupled polarized light is incident on the photosensor 102 in turn for imaging; and 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 photosensor 102.

[0007] Further, 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 the imaging results of the photosensor 102 is specifically as follows:

[0008]

[0009] wherein s=[s0,s1,s2,s3] T is the full Stokes polarization vector of the elliptically polarized light, s0 is the light 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 circular polarization component and the left circular polarization component of the elliptically polarized light.

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

[0011] The energy function is constructed as follows:

[0012]

[0013] wherein μ is a set regularization parameter; t represents the iteration number; S t is the full Stokes polarization vector obtained in the tth iteration; S t-1 is the full Stokes polarization vector obtained in the (t-1)th iteration; I out is an N×1 column vector, N is the number of bias voltages, and then I outEach element represents the light intensity of coupled polarized light collected by the ellipsoidal chip 101 of the photoelectric sensor 102 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 ellipsoidal chip 101 under different bias voltages. The first element of the first row of the Mueller matrix represents the proportional relationship between the total intensity of collimated polarized light and the total intensity of 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; 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 in the collimated polarized light when the collimated polarized light is horizontally polarized; 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 in the collimated polarized light when the collimated polarized light is horizontally polarized.

[0014] With S 0 Using 0 as the initial value, the energy function is solved iteratively using the gradient descent method or the augmented Lagrange method. When the S value between two adjacent iterations... t and S t-1 When the difference between them is less than a set threshold, S will be... t As the final all-Stokes polarization vector S.

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

[0016] The intensity of the 0° linear polarization component, 45° linear polarization component, 90° linear polarization component, and 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. The first row elements of the Mueller matrix are calculated based on the intensity of the 0° linear polarization component, 45° linear polarization component, 90° linear polarization component, and left-hand circular polarization component.

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

[0018] The top layer is a gold film containing a hollowed-out two-dimensional pattern, and the gold film and the base layer serve as the positive and negative electrodes for the applied voltage, respectively.

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

[0020] Furthermore, the substrate layer is made of semiconductor materials such as silicon, indium tin oxide, or silicon carbide.

[0021] Further, the hollowed-out two-dimensional pattern is four hollowed-out circular arcs, wherein every two hollowed-out circular arcs form a group, and two groups of hollowed-out circular arcs are centrally symmetric, and the two circular arcs in the same group form a metamaterial bullet capable of generating different deformations under different loading voltages.

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

[0023] Further, the ellipsometer based on the micro-nano deformable structure further comprises 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 measured according to the amplitude ratio Ψ and the phase difference Δ of the elliptical polarized light.

[0025] Beneficial effects:

[0026] The ellipsometer based on the micro-nano deformable structure can not only reduce the ellipsometer to a sub-pixel level, but also can obtain the parameters of the measured surface of the whole measured material in the form of imaging when the micro-nano deformable structure is integrated in a large amount in space, thereby breaking through the limitation of the traditional ellipsometer that can only measure a single point. That is, the ellipsometer based on the micro-nano deformable structure can perform two-dimensional measurement in the form of imaging and break through the defect of the traditional ellipsometer that can only measure a single point, thereby greatly reducing the on-chip size of the ellipsometer and reducing the volume of the ellipsometer to a single pixel level. The ellipsometer based on the micro-nano deformable structure can be combined with different optical lens groups to detect the optical properties and uniformity of the whole film in the form of imaging, thereby breaking through the disadvantage of the traditional micro-ellipsometer that can only detect a single point. The ellipsometer based on the micro-nano deformable structure is based on a total variation-based full Stokes polarization vector reconstruction model, and by applying a constraint to the data in the iteration, the operation result is more stable and easy to converge. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A basic structure diagram of the micro-ellipsometer based on the micro-nano deformable structure is provided.

[0028] Figure 2 A front view of the micro-nano deformable structure used by the ellipsometer based on the micro-nano deformable structure.

[0029] Figure 3 A top view of the micro-nano deformable structure used by the ellipsometer based on the micro-nano deformable structure.

[0030] Figure 4 A left view of the micro-nano deformable structure used by the ellipsometer based on the micro-nano deformable structure.

[0031] Figure 5 A schematic diagram of a double-layer film sample for a simulation experiment. DETAILED DESCRIPTION

[0032] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0033] like Figure 1 As shown, an ellipsometer based on micro / nano deformable structures 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 Each micro / nano deformable structure has a period of 2.4 micrometers. The n is a multiple of the pixel side length relative to the period of the micro / nano deformable structure. For example, in this invention, the period of a single micro / nano deformable structure is one-nth of the pixel size of the photodetector. When n = 1 is the characteristic width of the micro / nano deformable structure, the period is 2.4 micrometers. The dynamic control circuit 103 controls the bias voltage of each micro / nano deformable structure on the elliptic chip 101. Different bias voltages result in different spectral responses for each micro / nano deformable structure.

[0034] like Figure 2 As shown, any micro / nano deformable structure includes a top layer, a support layer, and a substrate layer; wherein, the top layer is a gold film containing a perforated two-dimensional pattern, and the thickness of the metal film has a topological characteristic of 30-90 nm; for example... Figure 5 As shown, the gold film and the substrate layer serve as the positive and negative electrodes for the applied voltage, respectively. The support layer is made of silicon dioxide, aluminum oxide, aluminum nitride, or polyethylene support pillars, such as... Figure 4 As shown, the support layer is the deformation space reserved after etching, and its topological characteristic is a thickness of 300-1000 nm. The substrate layer is made of semiconductor materials such as silicon, indium tin oxide, or silicon carbide, and its topological structure is characterized by a thickness of 300-1000 nm. Figure 3 As shown, the hollow two-dimensional pattern consists of four hollow arcs, with each pair of hollow arcs forming a group, and the two groups of hollow arcs being centrally symmetrical. Between the two arcs belonging to the same group, a metamaterial spring sheet that can produce different deformations under different loading voltages is formed.

[0035] Linearly polarized light emitted from light source 107 is incident on the sample 105 to be tested. The transmitted or reflected light from the sample 105 is then incident as elliptically polarized light onto the imaging lens group 106. The imaging lens group 106 collimates the elliptically polarized light, which is then incident on the elliptically polarized chip 101. The collimated polarized light is coupled with different spectral responses of the elliptically polarized chip 101 under different bias voltages to obtain different coupled polarized light. The different coupled polarized light is 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 based on the imaging results of the photoelectric sensor 102. The post-processing module is used to calculate the thickness, refractive index, or surface roughness of the sample 105 to be tested based on the amplitude ratio Ψ and phase difference Δ of the elliptically polarized light.

[0036] Optionally, the photoelectric sensor 102 can be a CMOS photoelectric sensor, a CCD photoelectric sensor, an organic semiconductor photoelectric sensor, or a quantum colloidal dot photoelectric sensor. The dynamic control circuit connects the top metal film of the micro / nano deformable structure to the substrate and applies a bias voltage to achieve dynamic deformation of the micro / nano deformable structure. The dynamic control circuit can be directly controlled by the host computer S104 or by a separate data computing device. In this invention, a microcontroller can also be used as the control element of the dynamic control circuit 103. The host computer 104 is a high-performance computing device, such as a MCU, CPU, FPGA, NPU, or other processing unit, used to read the energy collected by the photoelectric sensor and to reconstruct the full Stokes vector using a total variation-based full Stokes polarization reconstruction model.

[0037] Specifically, the method by which the host computer 104 obtains the amplitude ratio Ψ and phase difference Δ of elliptically polarized light based on the imaging results of the photoelectric sensor 102 is as follows:

[0038]

[0039] Where s = [s0, s1, s2, s3] T Let s0 be the total Stokes polarization vector of elliptically polarized light, s1 be the intensity of elliptically polarized light, s2 be the intensity difference between the horizontal and vertical linear polarization components of elliptically polarized light, s3 be the intensity difference between the 45° and 135° linear polarization components of elliptically polarized light, and s4 be the intensity difference between the right-hand and left-hand circular polarization components of elliptically polarized light.

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

[0041] The energy function is constructed as follows:

[0042]

[0043] wherein μ is a set regularization parameter; t represents the iteration number; 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-1)th iteration; I out is an N x 1 column vector, N is the number of bias voltages, then I out each element of I represents the light intensity of the coupled polarized light collected by the photoelectric sensor 102 at the ellipsometric chip 101 under different bias voltages; M0 is an N x 4 matrix, the elements of each row of M0 are the first row elements of the Mueller matrix corresponding to the ellipsometric chip 101 under different bias voltages, wherein the first element of the first row of 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 horizontal polarization component and the vertical polarization component in the coupled polarized light and the horizontal polarization component in the collimated polarized light when the collimated polarized light is horizontal polarized light; the third element of the first row represents the ratio of the difference between the horizontal polarization component and the 45° polarization component in the coupled polarized light and the horizontal polarization component in the collimated polarized light when the collimated polarized light is horizontal polarized light; the fourth element of the first row represents the ratio of the difference between the horizontal polarization component and the left circular polarization component in the coupled polarized light and the horizontal polarization component in the collimated polarized light when the collimated polarized light is horizontal polarized light;

[0044] with S 0 =0 as the initial value, the gradient descent method or the augmented Lagrange method is used to iteratively solve the energy function, and when the difference between S t and S t-1 between two adjacent iterations is less than a set threshold value, S t is taken as the final full Stokes polarization vector S.

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

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

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

[0048] In particular, the present application uses Figure 3 The 2-layer film structure shown in the figure verifies the performance of the micro-ellipsometer based on the micro-nano deformable structure provided by the present application. Specifically, Figure 5 301 represents a silicon dioxide film with a refractive index of 1.47 and a thickness of 100 nm, and 302 represents an aluminum film with a dielectric constant described by a Drude model and a thickness of 1000 nm, with an argon ion laser (488 nm) and a helium-neon laser (632.8 nm) as light sources. The experimental results are shown in Table 1.

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

[0050]

[0051] As can be seen from Table 1, the micro-nano deformable micro-ellipsometer provided by the present application can more accurately obtain the full Stokes polarization vector, providing high-quality data support for further estimating the material thickness and optical properties. Therefore, it can be shown that the micro-ellipsometer provided by the present application can obtain similar effects to traditional ellipsometers under a size of 2.4 microns; and when the micro-nano deformable structure is integrated 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 of traditional ellipsometers that can only measure a single point.

[0052] Of course, the present application can have other various embodiments, and those skilled in the art can certainly make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes and modifications should all belong to the protection scope of the claims attached to the present application.

Claims

1. A micro- and nano-morphable structure based ellipsometer, characterized in that, The ellipsometric 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 structure, wherein, n The pixel side length is a multiple of the period of the micro-nano deformable structure; the dynamic control circuit (103) is used for controlling the bias voltage of each micro-nano deformable structure on the ellipsometric chip (101), wherein the bias voltage is different, and the spectral response of each micro-nano deformable structure is different; any one 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 gold film and the base layer are respectively used as the positive electrode and the negative electrode for loading voltage. The linearly polarized light emitted by the light source (107) is incident on the sample (105) to be measured; the transmitted light or reflected light from the sample (105) to be measured is 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 ellipsometer chip (101); the collimated polarized light is coupled with different spectral responses of the ellipsometer chip (101) under different bias voltages, and different coupled polarized light is obtained; the different coupled polarized light is sequentially incident on the photosensor (102) for imaging; and the host computer (104) obtains the amplitude ratio Ψ and the phase difference of the elliptically polarized light according to the imaging results of the photosensor (102) . The host computer (104) obtains an amplitude ratio Ψ and a phase difference of the elliptically polarized light from each imaging result of the photoelectric sensor (102) The method is specifically: wherein S is the full stokes vector of the elliptically polarized light, I is the intensity of the elliptically polarized light, is the intensity difference between the horizontal linear polarization component and the vertical linear polarization component of the elliptically polarized light, is the intensity difference between the 45° linear polarization component and the 135° linear polarization component of the elliptically polarized light, is the intensity difference between the right-handed circular polarization component and the left-handed circular polarization component of the elliptically polarized light; Full stokes vector of elliptically polarized light The method for calculating the full stokes vector of elliptically polarized light is: The energy function is constructed as follows: in, The first row element of the Mueller matrix corresponding to the ellipsometric chip (101) under any bias voltage is obtained by the following method: The regularization parameters are set; t Indicates the number of iterations; For the first t The full Stokes polarization vector obtained in the next iteration; For the first t The full Stokes polarization vector obtained in the -1st iteration; for N A column vector of size 1, N If the number of bias voltages is [number], then [then...] Each element represents the light intensity of coupled polarized light collected by the photoelectric sensor (102) at the ellipsoid chip (101) under different bias voltages; for N A 4×4 matrix Each row contains elements of the first row of the Mueller matrix corresponding to the ellipsoidized chip (101) under different bias voltages. The first element of the first row of the Mueller matrix represents the ratio 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. 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 in the collimated polarized light when the collimated polarized light is horizontally polarized. 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 in the collimated polarized light when the collimated polarized light is horizontally polarized. With S 0 =0 as an initial value, the gradient descent method or the augmented Lagrange method is used to iteratively solve the energy function, and when the difference between adjacent two iterations and is less than a set threshold value, the is taken as the final Stokes polarization vector S .

2. A micro- and nano-morphable structure based ellipsometer according to claim 1, wherein, The intensity of the 0° linear polarization component, the 45° linear polarization component, the 90° linear polarization component and the left-handed circular polarization component of the coupled polarized light output by the ellipsometric chip (101) under the current bias voltage is obtained by the 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-handed circular polarization component. The support layer is a silicon dioxide, aluminum oxide, aluminum nitride or polyethylene support column.

3. The micro / nano-morphable structure based ellipsometer of claim 1, wherein, The material of the base layer is a semiconductor material such as silicon, indium tin oxide or silicon carbide.

4. The micro / nano-morphable structure based ellipsometer of claim 1, wherein, 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 symmetric, and the two arcs in the same group form a metamaterial bullet that can produce different deformations under different loading voltages.

5. The micro / nano-morphable structure based ellipsometer of claim 1, wherein, The photoelectric sensor (102) is a CMOS photoelectric sensor, a CCD photoelectric sensor, an organic semiconductor photoelectric sensor or a quantum colloidal point photoelectric sensor.

6. The micro / nano-morphable structure based ellipsometer of claim 1, wherein, It also includes a post-processing module; 7. The micro / nano-morphable structure based ellipsometer of claim 1, wherein, ​ The post-processing module is configured to calculate the thickness, refractive index or surface roughness of the sample (105) according to the amplitude ratio Ψ and the phase difference δ of the elliptical polarized light calculate the thickness, refractive index or surface roughness of the sample (105).

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