阅读说明：本技术 基于传递函数的白光扫描干涉测量法高频形貌补偿方法 (High-frequency morphology compensation method of white light scanning interferometry based on transfer function ) 是由 闫英 李萍 周平 安奕同 马锦伟 于 2020-12-28 设计创作，主要内容包括：本发明公开了一种基于传递函数的白光扫描干涉测量法高频形貌补偿方法,包括如下步骤：计算白光扫描干涉仪形貌测量结果的傅里叶频谱；利用幅频曲线计算得到功率谱密度曲线；对功率谱密度曲线与传递函数的平方相除进行修正,以得到修正后的功率谱密度曲线；采用逆周期图法,复原形貌。本发明利用白光干涉仪传递函数,对白光干涉仪直接测得的形貌可直接补偿各频谱信息,模拟出具有部分高频信息的白光干涉仪测量形貌。本发明利用传递函数直接对测量出来的形貌进行补偿处理,无需改变测量仪器的软硬件,补偿方法简单有效；同时提高了白光扫描干涉测量超精密表面形貌的精度和准确性,尤其是形貌轮廓和形貌粗糙度,为超精密加工的测量奠定基础。(The invention discloses a high-frequency morphology compensation method of a white light scanning interferometry based on a transfer function, which comprises the following steps: calculating a Fourier spectrum of the appearance measurement result of the white light scanning interferometer; calculating by using the amplitude-frequency curve to obtain a power spectral density curve; correcting the power spectral density curve and the square division of the transfer function to obtain a corrected power spectral density curve; and restoring the morphology by adopting an inverse periodogram method. The invention utilizes the transfer function of the white light interferometer to directly compensate the spectrum information of the morphology directly measured by the white light interferometer, and simulates the measurement morphology of the white light interferometer with partial high-frequency information. The invention directly compensates the measured appearance by using the transfer function without changing the software and hardware of the measuring instrument, and the compensation method is simple and effective; meanwhile, the precision and accuracy of the ultra-precise surface topography of the white light scanning interferometry are improved, especially the topography profile and the topography roughness, and a foundation is laid for the ultra-precise processing measurement.)

1. A high-frequency morphology compensation method of a white light scanning interferometry based on a transfer function is characterized in that: the method comprises the following steps:

s1: directly measuring by using a white light scanning interferometer to obtain the appearance of the workpiece;

s2: calculating the Fourier spectrum of the morphology measurement result of the white light scanning interferometer by adopting a mathematical tool:

in the formula (f)_xIs the sampling frequency in the X direction, N is the number of sampling points in the X direction, and N is 1, 2, … …, N, X (f)_x) Is a Fourier spectrum, z (x)_n) Is x_nSurface height of position, wherein x_nIs the nth sampling point position in the x direction;

and obtaining amplitude-frequency curves S (f) respectively_x) Phase-frequency curveThe following were used:

S(f_x)＝|X(f_x)|

s3: calculating to obtain PSD (f) of power spectral density curve by using amplitude-frequency curve_x) The following were used:

wherein, Δ L ═ L/N is the sampling interval, and L is the sampling length;

s4: correcting the power spectral density curve of the measurement result of the white light scanning interferometer by dividing the square of the transfer function to obtain the corrected PSD_re(f_x) The following were used:

wherein TF is a transfer function;

s5: and (5) restoring the morphology by adopting an inverse periodogram method and combining the corrected power spectral density curve and the phase-frequency curve in the step S2.

2. The method for high-frequency shape compensation of white light scanning interferometry based on transfer function according to claim 1, wherein: the calculation method of the transfer function in step S4 is as follows:

assuming that the sample has isotropy in the same direction, extracting a power spectral density curve PSD from the morphology measured by a plurality of groups of white light scanning interferometers_CiWherein i is 1, 2, 3, … … and k, k is the number of the topography groups measured by the white light scanning interferometer, the same topography is measured by using an atomic force microscope, and a power spectral density curve PSD is extracted from the topography_AiRespectively extracting the average power spectral density curves measured by the two instrumentsAnd

wherein, PSD_CiPower spectral density curves extracted for the measurement appearance of the white light scanning interferometer at i different appearance positions in the same direction of the same measurement sample,obtaining the average power spectral density curve of the white light scanning interferometer; PSD_AiPower spectral density curves extracted for measuring the shapes of the atomic force microscope at different shape positions in the same direction i of the same measured sample,obtaining the average power spectral density curve of the atomic force microscope;

obtaining a transfer function expression according to the obtained average power spectral density curve of the white light scanning interferometer and the obtained average power spectral density curve of the atomic force microscope:

where TF is a transfer function.

3. The method for high-frequency shape compensation of white light scanning interferometry based on transfer function according to claim 2, wherein: the number k of the topography groups measured by the white light scanning interferometer is 20-30.

4. The method for high-frequency shape compensation of white light scanning interferometry based on transfer function according to claim 1, wherein: the specific steps of the inverse periodogram method in step S5 are as follows:

firstly, PSD_re(f_x) Converting the single-side power spectrum into a double-side power spectrum, wherein the formula is as follows:

secondly, obtaining an amplitude-frequency characteristic curve A of Fourier transform by using a bilateral power spectral density curve:

combining amplitude-frequency characteristic curve A and phase-frequency curveObtaining a modified Fourier spectrum Z (f)_x)：

Finally, Z (f)_x) Obtaining the corrected geometric morphology z (n) by performing inverse Fourier transform:

and (6) ending.

Technical Field

The invention relates to the field of white light scanning interferometry, in particular to a high-frequency morphology compensation method of a white light scanning interferometry based on a transfer function, which is used for realizing the morphology result compensation of the white light scanning interferometry and improving the measurement accuracy.

Background

The white light scanning interferometer determines the surface appearance by scanning and positioning interference fringes based on a white light interference principle, has the measurement precision as high as nanoscale or even sub-nanoscale, does not damage the surface of a workpiece, and is widely applied to the appearance measurement of ultra-precision machined surfaces. However, because the measurement principle of each measuring instrument is different, different instruments measure the same surface, and the accurate and uniform appearance is difficult to obtain. Instrumental comparisons with each other on the same or nearly the same substrates have been reported and valued.

In 1990, Hillamann et al suggested that the results measured optically deviate significantly from those of the needle-type instrument. Duparre and Jakobs investigated the effect of surface space wavelength on the roughness of various substrate surfaces. In their study, the atomic force microscopy measured surface roughness was about 5 times that of the white light scanning interferometer measurements for silicon wafers. The measuring instruments and techniques have different surface space wavelength band limitations and the measured roughness cannot be directly compared.

When the height of the measured object surface varies by far less than a quarter of a wavelength, the white light scanning interferometer measurement system is considered to be a linear system, having a low-pass filtering characteristic, with a transfer function size close to 1 in the low frequency domain, and gradually decreasing with increasing spatial frequency. The transfer function of the interferometer is influenced by the optical system, signal processing, software algorithm and the like of the interferometer, and is also influenced by the shape signal to be measured. It is difficult to calculate the influence of each part on the transfer function of the interferometer separately in the actual measurement compensation. Due to the influence of the interferometer itself and other factors, the transfer function response at some spatial frequencies is different from the calibrated transfer function, so that the correction of the power spectral density measurement value only by means of the transfer function curve given by the merchant is problematic.

In summary, the conventional white light scanning interferometer and other measuring instruments have different limitations on surface space wave bands due to different technical principles, and roughness measurement results cannot be directly compared, so that the measurement precision and accuracy comparison is limited.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a high-frequency morphology compensation method for a white light scanning interferometry based on a transfer function, which compensates the morphology by fitting a power spectral density curve, improves the measurement precision and accuracy of the white light scanning interferometry, and can directly compare the surface roughness value obtained by compensation with other instruments.

In order to achieve the purpose, the technical means adopted by the invention are as follows:

a high-frequency morphology compensation method of a white light scanning interferometry based on a transfer function comprises the following steps:

s1: and directly measuring by using a white light scanning interferometer to obtain the appearance of the workpiece.

S2: calculating the Fourier spectrum of the morphology measurement result of the white light scanning interferometer by adopting a mathematical tool:

in the formula (f)_xIs the sampling frequency in the X direction, N is the number of sampling points in the X direction, and N is 1, 2, … …, N, X (f)_x) Is a Fourier spectrum, z (x)_n) Is x_nSurface height of position, wherein x_nThe nth sample point position in the x direction.

And obtaining amplitude-frequency curves S (f) respectively_x) Phase-frequency curveThe following were used:

S(f_x)＝|X(f_x)|

s3: calculating to obtain PSD (f) of power spectral density curve by using amplitude-frequency curve_x) The following were used:

where, Δ L ═ L/N is the sampling interval, and L is the sampling length.

S4: correcting the power spectral density curve of the measurement result of the white light scanning interferometer by dividing the square of the transfer function to obtain the corrected PSD_re(f_x) The following were used:

where TF is a transfer function.

S5: and (5) restoring the morphology by adopting an inverse periodogram method and combining the corrected power spectral density curve and the phase-frequency curve in the step S2.

Further, the calculation method of the transfer function in step S4 is as follows:

assuming that the sample has isotropy in the same direction, extracting a power spectral density curve PSD from the morphology measured by a plurality of groups of white light scanning interferometers_CiWherein i is 1, 2, 3, … … and k, k is the number of the topography groups measured by the white light scanning interferometer, the same topography is measured by using an atomic force microscope, and a power spectral density curve PSD is extracted from the topography_AiRespectively extracting the average power spectral density curves measured by the two instrumentsAnd

wherein, PSD_CiPower spectral density curves extracted for the measurement appearance of the white light scanning interferometer at i different appearance positions in the same direction of the same measurement sample,obtaining the average power spectral density curve of the white light scanning interferometer; PSD_AiPower spectral density curves extracted for measuring the shapes of the atomic force microscope at different shape positions in the same direction i of the same measured sample,and obtaining the average power spectral density curve of the atomic force microscope.

Obtaining a transfer function expression according to the obtained average power spectral density curve of the white light scanning interferometer and the obtained average power spectral density curve of the atomic force microscope:

where TF is a transfer function.

Further, the number k of the topography sets measured by the white light scanning interferometer is 20-30.

Further, the specific steps of the inverse periodogram method in step S5 are as follows:

firstly, PSD_re(f_x) Converting the single-side power spectrum into a double-side power spectrum, wherein the formula is as follows:

secondly, obtaining an amplitude-frequency characteristic curve A of Fourier transform by using a bilateral power spectral density curve:

combining amplitude-frequency characteristic curve A and phase-frequency curveObtaining a modified Fourier spectrum Z (f)_x)：

Finally, Z (f)_x) Obtaining the corrected geometric morphology z (n) by performing inverse Fourier transform:

and (6) ending.

Compared with the prior art, the invention has the following advantages:

1. the invention utilizes the transfer function of the white light interferometer to directly compensate the spectrum information of the morphology directly measured by the white light interferometer, and simulates the measurement morphology of the white light interferometer with partial high-frequency information.

2. The method solves the power spectral density of the white light scanning interferometer and the atomic force microscope by using a periodogram method, and further obtains the surface transfer function by solving the average power spectral density and fitting and extracting the transfer function.

3. The invention directly compensates the measured appearance by using the transfer function without changing the software and hardware of the measuring instrument, and the compensation method is simple and effective; meanwhile, the precision and accuracy of the ultra-precise surface topography of the white light scanning interferometry are improved, especially the topography profile and the topography roughness, and a foundation is laid for the ultra-precise processing measurement.

Drawings

FIG. 1 is a flow chart of a method for compensating the topography of a white light scanning interferometry according to the present invention.

FIG. 2 shows the features before and after compensation of triangular waves of a simulated basic signal.

FIG. 3 shows the appearance of the simulated fundamental signal before and after cosine wave compensation.

FIG. 4 is a graph of the simulated random signal before and after compensation.

Fig. 5 shows the transfer function determined for the basic signal.

FIG. 6 is a three-dimensional topography of a 3000# ground silicon wafer measured by a white light scanning interferometer and an atomic force microscope.

FIG. 7 is a profile line topography of the extracted white light scanning interferometer.

FIG. 8 is a profile topographic map of example 1 before and after compensation in accordance with the present invention.

FIG. 9 is a contour power spectral density plot before and after compensation in example 1 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

Example 1

As shown in fig. 1, the high-frequency topography compensation method of white light scanning interferometry based on transfer function of the present invention specifically comprises the following steps: the initial appearance measured by the white light interferometer solves Fourier transform on the appearance to obtain a phase-frequency curve and an amplitude-frequency curve, solves a power spectral density curve PSD on the amplitude-frequency curve, obtains a corrected PSD by utilizing a transfer function, and obtains a compensation appearance by utilizing an inverse periodogram method by combining the corrected PSD and the phase-frequency curve.

The invention adopts software to carry out analog simulation and compensation in the measuring process, and the specific method is as follows:

s1: a triangular wave signal simulation morphology is given, a measurement process of a white light interferometer is simulated by combining mathematical software with a white light interference process, the central wavelength of a light source simulated by the software is 600nm, the numerical aperture is 0.55, the simulation morphology is shown as a solid line in figure 2, the amplitude is 20nm, and the period is 2 mu m of a triangular wave signal, the morphology measured and output by the white light interferometer obtained through simulation is shown as a dotted line in figure 2, a transfer function obtained by solving a power spectral density curve is shown as a solid line in figure 5, a compensation algorithm provided by the invention is obtained as shown as a dot-dash line in figure 2, and the morphologies before and after compensation of simulation measurement can be obtained by comparing the morphologies before and: the compensated triangular wave morphology (amplitude of 17.47nm) is closer to the given simulated morphology (amplitude of 20nm) than the CSI simulation measurement morphology (amplitude of 10.90nm) before compensation, and the result effectiveness of the simulation compensation for the triangular wave signal is shown.

S2: a sine wave signal simulation morphology is given, a measurement process of a white light interferometer is simulated by combining mathematical software with a white light interference process, the central wavelength of a light source simulated by the software is 600nm, the numerical aperture is 0.55, the simulation morphology is shown as a solid line in FIG. 3, the amplitude is 20nm, and the period is 2 μm, the morphology output by the white light interferometer obtained through simulation is shown as a dotted line in FIG. 3, a transfer function obtained by solving a power spectral density curve is shown as a dotted line in FIG. 5, a compensation algorithm provided by the invention is obtained as shown as a dotted line in FIG. 3, and the morphologies before and after compensation of simulation measurement can be obtained by comparing the morphologies before and after the compensation: the compensated sine wave profile (amplitude of 19.97nm) is closer to the given simulated profile (amplitude of 20nm) than the CSI simulation measurement profile (amplitude of 13.27nm) before compensation, which shows the effectiveness of the result of simulation compensation for sine wave signals.

S3: the method comprises the following steps of giving a random signal simulation morphology, simulating a measurement process of a white light interferometer by combining mathematical software with a white light interference process, wherein the central wavelength of a light source simulated by the software is 600nm, the numerical aperture is 0.55, the simulation morphology is random signals shown by a solid line in a figure 4, the morphology output by measurement of the white light interferometer obtained through simulation is shown by a dotted line in a figure 4, a transfer function obtained by solving a power spectral density curve is shown by a dash-dot line in a figure 5, a compensation algorithm provided by the invention is obtained and is shown by the dash-dot line in the figure 4, and the morphologies before and after compensation of simulation measurement can: the result effectiveness of simulation compensation for random wave signals is demonstrated in that the compensated random topography (profile arithmetic mean deviation Ra value of 3.22nm, profile root mean square deviation of 4.27nm) is closer to the given simulated topography (profile arithmetic mean deviation Ra value of 3.43nm, profile root mean square deviation of 4.10nm) than the CSI simulation measurement topography (profile arithmetic mean deviation Ra value of 1.76nm, profile root mean square deviation of 2.21nm) before compensation.

Example 2

The morphology of a 3000 ultra-precision ground silicon wafer is measured by a New view 9000 type white light scanning interferometer from ZYGO, as shown in fig. 6(a), k groups (k is 20) of two-dimensional profile curves with the length of 20 μm are randomly extracted from the direction perpendicular to the grinding track by using mathematical software, and a power spectral density curve PSD is extracted from the morphology by using the mathematical software_CiWherein i is 1, 2, 3, … …, k, and the profile of the same No. 3000 ground silicon wafer sample is measured by XE-200 atomic force microscope of Park Systems company, as shown in FIG. 6(b), k groups (k is 20) of two-dimensional profile curves with length of 20 μm are randomly extracted from the vertical grinding trace direction by using mathematical software, and a power spectral density curve PSD is extracted from the profile by using mathematical software_AiRespectively calculating the average power spectral density curves measured by the two instruments

As shown in fig. 9, it is analyzed that the power spectral density curve of the ZYGO profile measurement does not completely coincide with the power spectral density curve of the AFM profile measurement, and the ZYGO is much lower than the AFM power spectral density curve in the high frequency stage, which is in a significantly lower trend. This is due to the resolution limitation of the ZYGO white light scanning interferometer instrument, resulting in low pass characteristics, high frequency power loss. High frequency signal components on the real topography are filtered out and distort the measurement results.

In order to solve the problem of high-frequency power loss caused by instrument resolution limitation mentioned above of the white light scanning interferometer, the invention provides a high-frequency morphology compensation method of a white light scanning interferometry based on a transfer function, which comprises the following steps:

s1: measuring the shape of No. 3000 ground silicon wafer by using a white light interferometer;

s11: marking the contour line of the sample piece to be measured, and measuring the surface contour appearance of the sample by adopting a white light interferometer, as shown in FIG. 7;

s12: extracting the contour line to be detected from the direction perpendicular to the grinding track by using interferometer related software, and carrying out numerical processing to obtain the appearance contour as shown in the figure 8;

s2: fourier transformation is carried out on the morphology in the step S1 by adopting a mathematical tool to obtain an amplitude-frequency curve and a phase-frequency curve;

s3: generating a power spectral density curve of a measurement result of the white light scanning interferometer by adopting a mathematical tool;

s4: dividing the power spectral density curve by the square of the transfer function to obtain a corrected power spectral density curve as shown in fig. 9, combining the corrected power spectral density curve with a phase-frequency curve, and obtaining a reconstructed real morphology of the white light scanning interferometry as shown in fig. 9 by using an inverse periodogram method;

as shown in fig. 9, comparing the topography findings before and after compensation of the interferometer measurements: the surface roughness Ra value before profile compensation of the profile is 4.14nm, the surface roughness Ra value measured by using an AFM under the same profile is 9.28nm, the surface roughness Ra value of the profile obtained by using a compensation algorithm is 8.68nm, compared with the profile before compensation, the contact ratio of the compensated measured profile and an ideal profile (AFM) curve is higher, and the surface roughness value is closer to the measured result of the AFM. The comparison verifies the effectiveness of the morphology compensation method of the invention.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.