An imaging ellipsometer measurement system and system parameter calibration method

Abstract

The application discloses an imaging ellipsometer measuring system and a system parameter calibration method, and belongs to the field of optical instrument measurement, and comprises a sample table used for placing a sample, an incident light generation module used for generating parallel incident light in a working wavelength range, a polarization module used for modulating the polarization state of the incident light, a first converging lens used for focusing the polarized incident light on the sample to generate reflected light, a second converging lens used for converting the reflected light into parallel light, a detection polarization module used for modulating the polarization state of the parallel light, a light beam adjustment module used for converting the polarized parallel light into a first exit light beam and a second exit light beam, and an image information detection module used for imaging the sample after the first exit light beam is adjusted into monochromatic light. The application can accelerate the speed of imaging ellipsometer system parameter calibration, enable the imaging ellipsometer to have the ability of high transverse resolution and the ability of fast calibration at the same time, and thus improve the overall measurement speed of the imaging ellipsometer.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical instrument measurement, and more particularly relates to an imaging ellipsometer measurement system and a system parameter calibration method. BACKGROUND

[0002] In recent years, with the rapid development of the semiconductor and chip industry, nanometer manufacturing technology is constantly improving, and the surface structure of micro-nano materials is becoming increasingly complex. Moreover, the topography size and other parameters of the surface of micro-nano products are important indicators of production line yield. Therefore, it is of great significance to non-destructively, low-cost, quickly and accurately measure the surface geometric structure parameters of semiconductor chips and other micro-nano products.

[0003] The traditional measurement method of nanometer structure geometric parameters is mainly scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The above measurement methods have very high measurement resolution, but they have disadvantages in measuring semiconductor chip products. For example, atomic force microscopy (AFM) is a surface probe contact measurement, which will damage the sample during the measurement process, and it is a scanning measurement with low efficiency. Although scanning electron microscopy and transmission electron microscopy are non-contact measurements, they will also damage the sample during the measurement process. In comparison, the non-contact measurement method using spectral polarization information has the characteristics of being fast, accurate and efficient, and has a natural advantage in the field of semiconductor chips.

[0004] Ellipsometer is an instrument for measuring nanometer structure geometric parameters using spectral polarization information, which has the advantages of simple modulation, high measurement accuracy and non-destructive measurement. The measurement results are usually represented by Mueller matrix. The measurement accuracy of ellipsometer depends on the system parameters such as the azimuth angle of polarizer, the azimuth angle of phase retarder and the phase retardation. In order to ensure the measurement accuracy, the polarization needs to be calibrated before the actual measurement of ellipsometer. Ellipsometer can be divided into spectral ellipsometer and imaging ellipsometer. Spectral ellipsometer uses a spectrometer as a spectral signal detector, which can obtain all spectral signals in the working spectral range at a time. Therefore, spectral ellipsometer has the characteristics of fast measurement and calibration. However, the lateral resolution of spectral ellipsometer depends on the size of the illumination spot, and the geometric size of the illumination spot is limited, generally with a minimum diameter of 160 microns. This leads to the highest lateral resolution of spectral ellipsometer being 160 microns, which is generally suitable for measuring samples with uniform surface. When the sample has a micro-area with a geometric size smaller than 160 microns, it is difficult to measure by spectral ellipsometer.

[0005] Imaging ellipsometer combines the visual measurement capability of optical microscope into ellipsometry, and has higher lateral resolution because the lateral resolution of optical microscope can reach sub-micron level and the lateral resolution of ordinary ellipsometer can reach micron level. Therefore, the imaging ellipsometer is suitable for measuring not only uniform surface samples, but also micro area samples with geometric size less than 160 microns. However, the spectral information detector of the imaging ellipsometer, such as CCD or CMOS industrial camera, can only obtain the light intensity information corresponding to a single wavelength in a single measurement. Therefore, the system parameter calibration method needs to obtain the light intensity information in all wavelengths in the working wavelength range and calculate the system parameters. Although the system parameter calibration speed is fast at a single wavelength and can reach millisecond level, the system parameter calibration time is long because each wavelength needs to be traversed in the whole working wavelength range. Moreover, the light intensity signal acquisition time increases linearly with the number of traversed wavelengths. In the case of wide working wavelength range, the light intensity information acquisition time can reach several minutes or even tens of minutes, which seriously reduces the system parameter calibration speed. Therefore, although the imaging ellipsometer has the characteristic of high lateral resolution, the system parameter calibration time is long and the instrument measurement speed is slow due to the limitation of the light intensity information acquisition method by traversing wavelengths. Therefore, the imaging ellipsometer is not suitable for measuring in a wide spectral range. SUMMARY

[0006] In view of the defects of the prior art and the demand for improvement, the present application provides an imaging ellipsometer measurement system and a system parameter calibration method, which aims to accelerate the system parameter calibration speed of the imaging ellipsometer, so that the imaging ellipsometer has the ability of high lateral resolution and fast calibration at the same time, thereby improving the overall measurement speed of the imaging ellipsometer.

[0007] To achieve the above-mentioned purpose, according to one aspect of the present application, an imaging ellipsometer is provided, comprising:

[0008] a sample stage for placing a sample;

[0009] an incident light generation module, a polarizing module and a first converging lens arranged in sequence on one side of the sample stage along the light path; the incident light generation module is used for generating parallel incident light in a working wavelength range; the polarizing module is used for modulating the polarization state of the incident light to obtain polarized incident light; and the first converging lens is used for focusing the polarized incident light on the sample placed on the sample stage to generate reflected light;

[0010] and a second converging lens, a polarized light detection module, a light beam adjustment module and an image information detection module arranged in sequence on the other side of the sample table along the light path of the reflected light; the second converging lens is used for converting the reflected light into parallel light; the polarized light detection module is used for modulating the polarization state of the parallel light to obtain polarized parallel light; the light beam adjustment module is used for dividing the polarized parallel light in space or time to obtain a first exit light beam and a second exit light beam; the image information detection module is used for imaging the sample after adjusting the first exit light beam into monochromatic light to obtain a two-dimensional image of the sample.

[0011] The second exit light beam is used as the input of the spectrum detection module in a system parameter calibration process.

[0012] Further, the image information detection module comprises a filter unit, a barrel lens and a detection unit.

[0013] The filter unit is used for adjusting the first exit light beam into monochromatic light.

[0014] The barrel lens is used for converging the monochromatic light to the detection unit.

[0015] The detection unit is used for imaging the sample according to the received monochromatic light to obtain a two-dimensional image and light intensity information of the sample.

[0016] Further, the barrel lens is an achromatic barrel lens.

[0017] Further, the filter unit comprises a filter wheel and filters with different center wavelengths installed on the filter wheel.

[0018] Further, the first converging lens and the second converging lens are micro-spot converging lenses.

[0019] Further, the incident light generation module comprises a light source, an incident light fiber adapter and an incident light collimator arranged in sequence.

[0020] The light source is used for emitting non-polarized light in a working wavelength range.

[0021] The incident light fiber adapter is used for adapting the non-polarized light to the incident light collimator.

[0022] The incident light collimator is used for collimating the non-polarized light into parallel incident light.

[0023] Further, the incident light collimator comprises a light beam collimating lens and a first circular diaphragm arranged in sequence along the light path.

[0024] Further, the polarization modulation of the polarizing module and the polarized light detection module is a double-rotating phase retarder modulation, a single-rotating phase retarder modulation, a photoelastic modulator modulation or a coherent modulator modulation.

[0025] Further, the polarizing module comprises a first polarizer and a first phase retarder arranged in sequence along the light path.

[0026] The detection module comprises a second phase retarder and a second polarizer arranged in sequence along the light path.

[0027] According to another aspect of the present application, there is provided a system parameter calibration system of the imaging ellipsometer, comprising the imaging ellipsometer and a spectrum detection module.

[0028] The spectrum detection module is arranged on the propagation path of the second emergent light beam and is used to obtain the spectrum information of the second emergent light beam.

[0029] Further, the spectrum detection module comprises an emergent light concentrator, an emergent light fiber adapter and a spectrum instrument.

[0030] The emergent light concentrator is used to concentrate the second emergent light beam to the emergent light adapter.

[0031] The emergent light fiber adapter is used to adapt the concentrated second emergent light beam to the spectrum instrument.

[0032] The spectrum instrument is used to obtain the spectrum information of the second emergent light beam.

[0033] Further, the emergent light concentrator comprises a second circular diaphragm and a third converging lens arranged in sequence along the light path.

[0034] According to another aspect of the present application, there is provided a system parameter calibration method based on the system parameter calibration system, comprising:

[0035] A preprocessing step: a standard sample with known Mueller matrix is placed on the sample stage, and the incident light generation module emits parallel incident light in the working wavelength range;

[0036] A spectrum detection step: the spectrum information of the standard sample is obtained by the spectrum detection module, and the light intensity value of each wavelength in the working wavelength range is extracted from the spectrum information and recorded as a first light intensity value;

[0037] A spectrum fitting step: a fitting curve of each system parameter changing with wavelength is solved according to the first light intensity value, and is recorded as a first fitting curve; the system parameter is the device parameter affecting polarization in the polarizing module and the detection module;

[0038] An imaging detection step: two-dimensional images of the standard sample under N different wavelengths in the working wavelength range are obtained by the image information detection module, and the light intensity value under different wavelengths is calculated according to the two-dimensional images and recorded as a second light intensity value; N is a positive integer;

[0039] The calibration step: according to the second light intensity value, the discrete values of each system parameter at N different wavelengths are solved, and a fitting curve of each system parameter changing with wavelength is fitted, which is recorded as a second fitting curve, and the calibration of the imaging ellipsometer is completed; the second fitting curve has the same change trend as the first fitting curve.

[0040] According to another aspect of the present application, a micro-nano product surface measurement method based on the above imaging ellipsometer is provided, comprising:

[0041] The micro-nano product to be measured is placed on the sample table, and the image information detection module is adjusted so that the wavelength of the monochromatic light filtered is the target working wavelength, and the system parameters at the target working wavelength are determined according to the second fitting curve; the second fitting curve is calibrated by the above calibration method provided by the present application;

[0042] After the incident light generation module emits parallel incident light in the working wavelength range, the two-dimensional image of the micro-nano product to be measured at the target working wavelength is obtained through the image information detection module;

[0043] The light intensity information at the target working wavelength is calculated according to the two-dimensional image;

[0044] The Mueller matrix of the micro-nano product to be measured is calculated according to the system parameters at the target working wavelength and the light intensity information.

[0045] Overall, the above technical solutions conceived by the present application can achieve the following beneficial effects:

[0046] (1) The imaging ellipsometer provided by the present application will produce an additional light beam, i.e. a second exit light beam, during the imaging process. This light beam will be input into the spectral image information detection module during the calibration process of the ellipsometer, so that the fitting curve of the system parameters can be obtained through a single spectral measurement. Since this fitting curve carries the change trend of the system parameters with wavelength, with the aid of this fitting parameter, the system parameter fitting curve in the entire working wavelength range can be calibrated by only using the image information detection module to traverse a specific discrete wavelength, effectively reducing the time required for wavelength traversal, effectively improving the efficiency of system parameter calibration under the condition of ensuring high lateral resolution, and thus effectively improving the measurement speed of the imaging ellipsometer.

[0047] (2) The imaging ellipsometer provided by the present application has high lateral resolution capability, which can realize the measurement of both uniform samples and samples with micro-distributed samples. The imaging ellipsometer provided by the present application also has the capability of rapid parameter calibration, and the system parameter calibration can be quickly completed in a wide spectral range. Therefore, the present application has a wide range of applications and strong practicality.

[0048] (3) The imaging ellipsometer provided by the application has a cylindrical lens in the image information detection module, which is a achromatic cylindrical lens, can reduce chromatic aberration in the working wavelength range during imaging, effectively improves the imaging quality, and further improves the measurement accuracy, and can effectively reduce the adjustment range of the cylindrical lens, the detector and other devices during imaging.

[0049] (4) The imaging ellipsometer provided by the application has a filter unit, which includes a filter wheel and filter pieces with different central wavelengths installed on the filter wheel, so that the filter pieces with different central wavelengths can be conveniently switched by rotating the filter wheel.

[0050] (5) The imaging ellipsometer provided by the application has two converging lenses, i.e. a first converging lens and a second converging lens, which are micro-spot converging lenses. Since the spot size obtained by the micro-spot converging lens is small (usually 160 microns), the diameter of the converging lens can be set to a larger value under the premise of not interfering with the sample stage, so as to further improve the resolution of the system. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 The imaging ellipsometer structure block diagram provided by the embodiment of the application is shown in the figure;

[0052] Figure 2 The specific structure schematic diagram of the imaging ellipsometer provided by the embodiment of the application is shown in the figure;

[0053] Figure 3 The measured M O S2 sample two-dimensional picture;

[0054] Figure 4 The calibration system structure block diagram of the imaging ellipsometer provided by the embodiment of the application is shown in the figure;

[0055] Figure 5 The specific structure schematic diagram of the calibration system of the imaging ellipsometer provided by the embodiment of the application is shown in the figure;

[0056] Figure 6 The calibration method flow chart provided by the embodiment of the application is shown in the figure;

[0057] Figure 7 The calibration result schematic diagram provided by the embodiment of the application is shown in the figure;

[0058] In all the figures, the same reference signs are used to represent the same elements or structures, wherein:

[0059] 1- light source, 3- incident fiber adapter, 4- incident light collimator; 4-1- beam collimating lens, 4-2- first circular diaphragm;

[0060] 5-polarization module, 5-1-first polarizer, 5-2-first phase retarder;

[0061] 6-first converging lens, 7-second converging lens;

[0062] 8-analyzer module, 8-1-second phase retarder, 8-2-second polarizer;

[0063] 9-beam adjustment module;

[0064] 10-exit light converging device, 10-1-second circular diaphragm, 10-2-third converging lens;

[0065] 11-exit light fiber adapter, 12-spectrometer;

[0066] 13-filter unit, 14-barrel lens, 15-detection unit;

[0067] 2-optical fiber, 16-data line. DETAILED DESCRIPTION

[0068] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0069] In the present application, the terms "first", "second", etc. (if any) in the present application and the drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence.

[0070] In order to solve the technical problems of long system parameter calibration time and low measurement efficiency of the existing imaging ellipsometer, the present application provides an imaging ellipsometer measurement system and a system parameter calibration method, and the overall idea is to improve the structure of the imaging ellipsometer, so that it can be combined with the spectral detection module during calibration, so as to use the system parameter fitting curve obtained by spectral measurement calibration to assist the system calibration of the imaging ellipsometer, and only traverse specific discrete wavelengths, so as to calibrate the complete system parameter fitting curve in the target wavelength range, avoid wavelength traversal in the full spectral range, effectively improve the efficiency of system parameter calibration under the condition of ensuring high lateral resolution, and thus improve the overall measurement speed of the imaging ellipsometer.

[0071] The following is an embodiment.

[0072] Embodiment 1:

[0073] An imaging ellipsometer, as shown in Figure 1 , comprising:

[0074] a sample stage for placing a sample;

[0075] an incident light generating module, a polarizing module 5 and a first converging lens 6 arranged in sequence along the light path on one side of the sample stage; the incident light generating module is used for generating parallel incident light in a working wavelength range; the polarizing module 5 is used for modulating the polarization state of the incident light to obtain polarized incident light; and the first converging lens 6 is used for focusing the polarized incident light on the sample placed on the sample stage to generate reflected light;

[0076] and a second converging lens 7, a polarized light detecting module 8, a light beam adjusting module 9 and an image information detecting module arranged in sequence along the light path of the reflected light on the other side of the sample stage; the second converging lens 7 is used for converting the reflected light into parallel light; the polarized light detecting module 8 is used for modulating the polarization state of the parallel light to obtain polarized parallel light; the light beam adjusting module 9 is used for dividing the polarized parallel light in space or time to obtain a first exit light beam and a second exit light beam; and the image information detecting module is used for imaging the sample after adjusting the first exit light beam into monochromatic light to obtain a two-dimensional image of the sample;

[0077] In the system parameter calibration process, the second exit light beam is used as the input of the spectrum detecting module.

[0078] The imaging ellipsometer provided in the embodiment can perform imaging measurement on the sample placed on the sample stage, and finally calculate the Mueller matrix of the sample.

[0079] In the embodiment, the image information detecting module and the second converging lens 7 cooperate to complete imaging, as shown in Figure 2 The image information detecting module specifically includes a filter unit 13, a barrel lens 14 and a detecting unit 15.

[0080] The filter unit 13 is used for adjusting the first exit light beam into monochromatic light, and the wavelength of the monochromatic light can be flexibly adjusted according to actual imaging requirements; the filter unit 13 can be realized by any way that does not affect imaging and polarization; in order to facilitate the adjustment of the wavelength of the monochromatic light, as a preferred embodiment, the filter unit 13 includes a filter wheel and filter pieces with different center wavelengths installed on the filter wheel; in actual measurement, rotating the filter wheel can switch the filter pieces with different center wavelengths.

[0081] A cylindrical lens 14 is configured to converge the monochromatic light to the detection unit 15; as a preferred embodiment, the cylindrical lens 14 in the embodiment is a achromatic cylindrical lens, so that the chromatic aberration in the working wavelength range can be reduced, and the imaging quality is improved; in the imaging process, the focal shift caused by the light refraction cannot be eliminated, so the position of the image plane changes with the wavelength during the imaging of light beams with different wavelengths; the position of the image plane can be adjusted according to the wavelength change, and the achromatic cylindrical lens or the CCD detector can be adjusted; in the embodiment, the cylindrical lens is an achromatic cylindrical lens, and the chromatic aberration is effectively eliminated, so that the adjustment range of the cylindrical lens, the detector and other devices in the imaging process can be effectively reduced.

[0082] The detection unit 15 is configured to image the sample according to the received monochromatic light, and obtain a two-dimensional image and light intensity information of the sample; in the embodiment, the detection unit 15 is a CCD detector, and the sample picture taken by the CCD detector contains light intensity information of each region of the sample; in the actual measurement, the light intensity information of different pixel positions of the picture taken by the CCD detector can be selected to obtain the information of a specific region.

[0083] In the actual measurement, in order to improve the imaging resolution, the diameters of the first converging lens 6 and the second converging lens 7 can be increased to obtain a larger numerical aperture NA, but at the same time, the two converging lenses need to avoid interference with the sample table; preferably, in the embodiment, the first converging lens 6 and the second converging lens 7 are micro-spot converging lenses; the light beam converged by the micro-spot lens can form a spot with a diameter of 160 microns on the sample; since the spot size is small, the diameter of the converging lens can be set to a larger value without interfering with the sample table, so as to further improve the resolution of the system. Figure 3 As shown in the figure, the embodiment is used in the M O S2 is an example of a spot formed on a sample.

[0084] In the embodiment, the polarization module 5 and the detection module 8 can be used to modulate the polarization state of the light beam; through polarization state modulation, the light beam is modulated into elliptical polarized light which changes with time; the polarization modulation method and device of the polarization module 5 and the detection module 8 are not limited; specifically, the polarization modulation of the polarization module 5 and the detection module 8 can be double-rotating phase retarder modulation, single-rotating phase retarder modulation, photoelastic modulator modulation, coherent modulator modulation, etc.; the modulation principles adopted by the polarization module 5 and the detection module 8 need to be consistent; the specific device composition, thin film transmission matrix system model of the polarization module 5 and the detection module 8, and the system parameters to be calibrated in the parameter calibration process can be determined according to the corresponding polarization modulation principle.

[0085] Optionally, in the embodiment, the polarization modulation principle adopted by the polarizing module 5 and the analyzing module 8 is specifically a double-rotating phase retarder modulation principle, and specifically, as shown in Figure 2 In the embodiment, the polarizing module 5 includes a first polarizer 5-1 and a first phase retarder 5-2 arranged in sequence along the light path; correspondingly, the analyzing module 8 includes a second phase retarder 8-1 and a second polarizer 8-2 arranged in sequence along the light path.

[0086] Based on the polarizing module and the analyzing module shown in Figure 2 In the embodiment, the thin film transmission matrix system model is as follows:

[0087] S out = M A R(A')R(-C2)M C2 (δ2)R(C2)

[0088] × M S R(-C1)M C1 (δ1)R(C1)R(-P')M P R(P')S in

[0089] Wherein, S out is the exit light Stokes vector, M A represents the second polarizer Mueller matrix, A' represents the second polarizer azimuth angle, R(*) represents the Mueller rotation matrix when the rotation angle is “*”, M C2 represents the second phase retarder Mueller matrix, C2 represents the second phase retarder azimuth angle, δ2 represents the phase retardation thereof, M C1 represents the first phase retarder Mueller matrix, C1 represents the first phase retarder azimuth angle, δ1 represents the phase retardation thereof, M P represents the first polarizer Mueller matrix, P' represents the first polarizer azimuth angle, S in is the incident light Stokes vector; M S represents the Mueller matrix of the sample.

[0090] In the system parameter calibration process of the imaging ellipsometer provided in the embodiment, the system parameters to be calibrated include: the first polarizer azimuth angle P', the second polarizer azimuth angle A', the first phase retarder azimuth angle C1, the second phase retarder azimuth angle C2, the phase retardation δ1 of the first phase retarder, and the phase retardation δ2 of the second phase retarder.

[0091] As shown in Figure 2 In the embodiment, the incident light generating module includes a light source 1, an incident light fiber adapter 3, and an incident light collimator 4 arranged in sequence;

[0092] Light source 1 is used to emit unpolarized light within the working wavelength range; light source 1 is connected to incident fiber optic adapter 3 via optical fiber 2.

[0093] The incident fiber optic adapter 3 is used to transfer unpolarized light to the incident light collimator 4;

[0094] An incident light collimator 4 is used to collimate unpolarized light into parallel incident light. Optionally, in this embodiment, the incident light collimator 4 specifically includes a beam collimating lens 4-1 and a first circular aperture 4-2 arranged sequentially along the optical path. The beam collimating lens 4-1 is used to collimate the unpolarized light into parallel incident light, and the first circular aperture 4-2 is used to adjust the pupil diameter of the incident light.

[0095] In this embodiment, through the adjustment of the beam adjustment module, the polarized parallel light output from the analyzer module can be divided into a first outgoing beam and a second outgoing beam. The first outgoing beam is input to the image information detection module to complete the imaging measurement. The second outgoing beam does not play a role in the actual measurement process, but during the calibration process, it serves as the input to the spectral detection module to complete the spectral measurement of the sample, thereby assisting in the parameter calibration of the imaging ellipsometer. Optionally, in this embodiment, the beam adjustment module is specifically a beam splitter, which divides the polarized parallel light output from the analyzer module into a first outgoing beam and a second outgoing beam by spatially splitting the polarized parallel light. In other embodiments of the present invention, a reflector (e.g., a metal reflector) can also be used as the beam adjustment module. The propagation path of the parallel polarized light is adjusted by the reflector to achieve temporal division, obtaining a first outgoing beam and a second outgoing beam. Even when the light intensity is insufficient, an effective first outgoing beam and a second outgoing beam can still be obtained.

[0096] This embodiment improves the structure of the imaging ellipsometer. During the imaging process, it generates an additional beam, namely a second outgoing beam. By setting a spectral detection module in the propagation path of the second outgoing beam, it can form a spectral ellipsometer with the structure in the imaging ellipsometer. Thus, the fitting curve of the system parameters can be obtained through a single spectral measurement. Since the fitting curve carries the trend of the system parameters with wavelength, with the help of the fitting parameters, the system parameter fitting curve of the entire working wavelength range can be calibrated by using only the image information detection module to traverse specific discrete wavelengths. This effectively reduces the time required to traverse the wavelengths and improves the efficiency of system parameter calibration while ensuring high lateral resolution, thereby effectively improving the measurement speed of the imaging ellipsometer.

[0097] like Figure 2 As shown, the imaging ellipsometer provided in this embodiment is a vertical variable angle mechanism that can change the incident angle of the beam according to the measurement requirements. The sample stage is placed horizontally to meet the measurement requirements of different samples, such as liquid samples.

[0098] Optionally, in the embodiment, the working wavelength range is 380-1100 nm. The phase retarders in the polarizing module and the analyzing module are rotated at a speed ratio of 1:5 or 3:5, so that 16 Mueller matrix elements can be obtained through one measurement. The focal length ratio of the achromatic lens to the second converging lens 7 is 10:1, the focal length of the second converging lens 7 is 20 mm, and the focal length of the achromatic lens is 200 mm. According to the magnification relationship, the imaging magnification in the embodiment is 10 times; under 10 times magnification, the spot diameter of the object plane is 160 microns, and the spot diameter on the CCD image plane is 1.6 (mm); the light sensing size of the CCD detector image plane is 4.76*6.32 mm, and under 10 times magnification, the pattern details of the micro-area sample can be more conveniently observed, and the CCD detector pixels can be fully utilized.

[0099] Embodiment 2:

[0100] A system parameter calibration system of an imaging ellipsometer, in the embodiment, the imaging ellipsometer is the imaging ellipsometer provided in Embodiment 1; as shown in Figure 4 、 Figure 5 , the calibration system provided in the embodiment includes: the imaging ellipsometer and a spectrum detection module; the spectrum detection module is arranged on the propagation path of the second emergent light beam, and is used to obtain the spectrum information of the second emergent light beam.

[0101] As shown in Figure 5 , in the embodiment, the spectrum detection module specifically includes: an emergent light converging device 10, an emergent light fiber adapter 11, and a spectrum instrument 12;

[0102] The emergent light converging device 10 is used to converge the second emergent light beam to the emergent light adapter;

[0103] The emergent light fiber adapter 11 is used to adapt the second emergent light beam after convergence to the spectrum instrument;

[0104] The spectrum instrument 12 is used to obtain the spectrum information of the second emergent light beam;

[0105] Optionally, as shown in Figure 5 , in the embodiment, the emergent light converging device 10 includes a second circular diaphragm 10-1 and a third converging lens 10-2 arranged in sequence along the light path, wherein the second circular diaphragm 10-1 is used to adjust the pupil diameter.

[0106] The calibration system provided in the embodiment, together with the polarizing module and the analyzing module in the imaging ellipsometer, forms a spectral ellipsometer, and can complete the spectral measurement work. In other words, the calibration system provided in the embodiment includes the imaging ellipsometer and the spectral ellipsometer, and the spectral ellipsometer reuses the polarization structure in the imaging ellipsometer. Therefore, the calibration system provided in the embodiment can realize the spectral measurement of the sample and the imaging measurement of the sample.

[0107] The spectral measurement process is as follows:

[0108] The non-polarized light beam emitted by the light source 1 enters the incident fiber adapter 3 through the optical fiber 2, and then the divergent light enters the beam collimating lens 4-1 to collimate the divergent light. The collimated light passes through the first circular aperture 4-2 to adjust the pupil diameter, passes through the first polarizer 5-1 and the first phase retarder 5-2 to modulate the polarization state of the light beam, passes through the first micro-spot lens 6 to converge the polarized light on the sample to form an illumination area, and the reflected light enters the second micro-spot lens 7, the second phase retarder 8-1, and the second polarizer 8-2 to modulate the polarization state of the light beam. The light beam is divided into two beams, i.e., the first exit light beam and the second exit light beam, by the beam splitter. The second exit light beam propagates along the original propagation direction, and the first exit light beam is perpendicular to the original propagation direction. The light beam propagating along the original propagation direction enters the second circular aperture 10-1 to adjust the entrance pupil diameter, passes through the third converging lens 10-2, and converges to the exit fiber adapter 11. Then, the light spectrum information is acquired by the spectrometer 12, and then the data line 16 is connected to the computer for data processing.

[0109] The rotation speed of the first phase retarder 5-2 and the second phase retarder 8-1 is controlled by the hollow shaft motor, and the angle of the light beam irradiating the sample is controlled by the variable-angle mechanical structure. The first circular aperture 4-2 and the second circular aperture adjust the pupil diameter, so that the parallel light beam before the spectral converging lens can meet the pupil diameter requirement. The spectrometer 12 can simultaneously acquire the light intensity data of the wavelengths of 380-1100 nm.

[0110] Similar to the above embodiment 1, in the embodiment, the imaging process is as follows:

[0111] The unpolarized light beam emitted by light source 1 enters the incident fiber optic adapter 3 through optical fiber 2. Then, the diverging light enters the beam collimating lens 4-1 to collimate the diverging light. After passing through the first circular aperture 4-2 to adjust the pupil diameter, it passes through the first polarizer 5-1 and the first phase delayer 5-2 to modulate the polarization state of the beam. After passing through the first micro-spot lens 6, the polarized light is focused onto the sample to form an illumination area. The reflected light enters the second micro-spot lens 7, the second phase delayer 8-1, and the second polarizer 8-2 to modulate the polarization state of the beam. After passing through the beam splitter, the beam is split into two beams, one along the original propagation direction and the other perpendicular to the original propagation direction. The beam perpendicular to the original propagation direction enters the filter 13 to convert the polychromatic light into monochromatic light of a specific wavelength. The achromatic tube lens 14 focuses the parallel monochromatic light onto the CCD detector 15 to image the two-dimensional pattern of the sample and acquire light intensity information. The information acquired by the CCD detector is connected to the computer via the data cable 16 for data processing.

[0112] Optionally, in this embodiment, the focal length ratio of the third converging lens to the second converging lens is 3:1. Since the focal length of the second converging lens is 20mm, the focal length of the third converging lens is 60mm. The smaller focal length allows the overall structure of the third converging lens and the spectrometer to be more compact.

[0113] The calibration system provided in this embodiment has certain differences in optical path propagation between spectral measurement and imaging measurement. Therefore, the two calibration results will have certain deviations in actual measurement. However, experimental analysis shows that since the spectral ellipsometer reuses the polarization structure in the imaging ellipsometer, the polarization process is the same. The system parameters calibrated by the spectral ellipsometer and the imaging ellipsometer have the same trend of change with wavelength. Furthermore, the introduction of the spectral detection module has no impact on the internal structure of the imaging ellipsometer. Therefore, after calibrating the relevant system parameters through spectral measurement, the calibration result can assist in calibrating the system parameters in the imaging ellipsometer.

[0114] In this embodiment, when performing spectral measurements, the light source is a tungsten lamp, and the light intensity meets the test requirements. When performing imaging measurements, since the camera shutter time is set according to the spectrometer measurement settings, the exposure time may be relatively short, resulting in insufficient light intensity collected by the CCD detector. Therefore, a higher intensity light source, such as a deuterium lamp, can be selected for imaging measurements. A cubic prism beam splitter is selected, which can split the polarized parallel light into two beams with a light intensity of 50%, which enter the spectral detection module and the image information detection module respectively.

[0115] As described in Example 1 above, when the light intensity is insufficient, the beam splitter can be replaced with a metal mirror. That is, after the spectral measurement process is completed, the metal mirror is installed and the imaging test is performed.

[0116] The calibration system provided by the embodiment can also be used as an ellipsometer, can realize spectral measurement and imaging visual measurement, improves the applicability of the instrument, can be used in multiple modes, and reduces the use cost of the instrument.

[0117] Embodiment 3

[0118] The system parameter calibration method of the system parameter calibration system based on the above embodiment 2 comprises the following steps as shown in the figure: Figure 6

[0119] The preprocessing step is to place the standard sample with a known Mueller matrix on the sample table and make the incident light generation module emit parallel incident light in the working wavelength range.

[0120] The spectral detection step is to obtain the spectral information of the standard sample through the spectral detection module, extract the light intensity value of each wavelength in the working wavelength range from the spectral information, and mark it as the first light intensity value.

[0121] The spectral fitting step is to solve the fitting curve of each system parameter changing with the wavelength according to the first light intensity value, and mark it as the first fitting curve. The system parameter is the device parameter affecting polarization in the polarizing module 5 and the polarizing module 8.

[0122] The imaging detection step is to obtain the two-dimensional image of the standard sample under N different wavelengths in the working wavelength range through the image information detection module, and calculate the light intensity value under different wavelengths according to the two-dimensional image, and mark it as the second light intensity value. N is a positive integer.

[0123] The calibration step is to solve the discrete value of each system parameter under N different wavelengths according to the second light intensity value, and to solve the fitting curve of each system parameter changing with the wavelength, and mark it as the second fitting curve, to complete the calibration of the imaging ellipsometer. The second fitting curve has the same change trend as the first fitting curve. Since the change trend of the first fitting curve obtained by spectral fitting is the same as the trend of the discrete value of each system parameter changing with the wavelength solved by the second light intensity value, the system parameter discrete value obtained by the imaging detection system is fitted by using the first fitting curve, so that the system parameter fitting curve of the imaging ellipsometer in the entire working wavelength range is obtained.

[0124] Optionally, in the embodiment, the selected standard sample is a standard SiO2 sample, and the incident beam angle is set to the Brewster angle in the spectral measurement and imaging measurement process.

[0125] In the measurement process, the collected light intensity I (t) The light intensity can be expressed by the Fourier series as follows:

[0126]

[0127] ​Where I0 represents the light source exit light intensity value, ω represents the first second phase retarder rotation angular velocity greatest common divisor, φ 2n represents the difference value of the initial azimuth angle of the first phase retarder and the second phase retarder;

[0128] Since the polarizing module and the analyzing module both adopt the double-rotation phase retarder modulation principle, the thin film transmission matrix system model is as follows:

[0129] S out = M A R(A')R(-C2)M C2 (δ2)R(C2)

[0130] × M S R(-C1)M C1 (δ1)R(C1)R(-P')M P R(P')S in

[0131] Where S out is the exit light Stokes vector, I(t) is the S out at different times; M A represents the second polarizer Mueller matrix, A' represents the azimuth angle of the second polarizer, R(*) represents the Mueller rotation matrix when the rotation angle is “*”, M C2 represents the second phase retarder Mueller matrix, C2 represents the azimuth angle of the second phase retarder, δ2 represents the phase retardation thereof, M C1 represents the first phase retarder Mueller matrix, C1 represents the azimuth angle of the first phase retarder, δ1 represents the phase retardation thereof, M P represents the first polarizer Mueller matrix, P' represents the azimuth angle of the first polarizer; S in is the incident light Stokes vector, which can be expressed as S in = [I in , 0, 0, 0] T , I in is the incident light intensity, and the superscript “T” represents the matrix transpose; M S represents the Mueller matrix of the sample.

[0132] The first polarizer M P and the second polarizer M A have the same Mueller matrix expression, both of which are:

[0133]

[0134] The Mueller rotation matrix R(*) expression is:

[0135]

[0136] The first phase retarder MC1 With the second phase delay M C2 The Mueller matrix is ​​in the form of:

[0137]

[0138] The Mueller matrix expression for the sample is:

[0139]

[0140] Since the Mueller matrix of the standard SiO2 sample is known, the system parameters, namely A', P', C1, C2, δ1, and δ2, can be solved by using the above Fourier series representation of light intensity and the system thin film transport matrix model. Optionally, in this embodiment, the Levenberg-Marquardt gradient descent algorithm is used in the solution process. The gradient descent algorithm requires a good initial value to iterate. Therefore, in the solution, a set of system parameter values ​​is first calculated using a wavelength light intensity value as the initial value for iteration, and then iterative solution is performed. Finally, the system parameters corresponding to different wavelengths are solved, and the fitting curves of each system parameter changing with wavelength can be obtained.

[0141] In the process of spectral measurement, a single measurement can obtain the fitting curve for each wavelength across the entire spectrum, such as... Figure 7 As shown by the solid line in the image.

[0142] Since only a single measurement during imaging measurement can obtain light intensity information corresponding to a single wavelength, this embodiment utilizes the pattern information of a standard SiO2 sample at a specific wavelength obtained by the image information detection module to select the light intensity value at the target pixel position in the image. Similar to the method used by the spectral detection module to solve for system parameters, a set of system parameter values ​​at discrete wavelengths is then calculated. The changing trend carried by the system parameter fitting curve obtained by the spectral detection module is used to calibrate the system parameter values ​​calibrated by the image information detection module. The purpose of calibration is to ensure that the system parameters obtained by the imaging ellipsometer calibration and the system parameters obtained by the spectral ellipsometer calibration have the same changing trend. Figure 7 As shown, the system parameter spectral measurement results are represented by solid lines, while the imaging measurement results are represented by black dots. The polarizer azimuth angle values ​​for both spectral and imaging measurements are essentially the same, so the calibration results of the spectral ellipsometer for these two parameters can be used as the calibration results of the imaging ellipsometer. The phase retarder azimuth angles differ by a constant; therefore, the calibration results of the spectral ellipsometer for these two parameters can be correspondingly increased by a constant to serve as the calibration results of the imaging ellipsometer. The phase retardation values ​​exhibit the same trend and have a very small difference; therefore, it is only necessary to fit the system parameter values ​​measured by the imaging measurement method to the system parameter fitting curve measured by the spectral measurement method to obtain the accurate system parameter fitting curve of the imaging ellipsometer within its operating band.

[0143] It should be noted that when the polarization modulation principle used by the ellipsometer changes, the corresponding determination of the film transmission model and the specific system parameters to be calibrated can be made, and the specific calibration process is the same as the above process.

[0144] Based on the calibration method, in the embodiment, the imaging ellipsometer only uses the image information detection module to traverse a specific N discrete wavelengths, so as to calibrate the system parameter fitting curve in the entire working wavelength range, effectively reducing the time required for traversing the wavelength, effectively improving the efficiency of system parameter calibration under the condition of ensuring high lateral resolution, thereby effectively improving the measurement speed of the imaging ellipsometer.

[0145] Embodiment 4:

[0146] A micro-nano product surface measurement method based on the imaging ellipsometer provided in the above embodiment 1, comprising:

[0147] Place the micro-nano product to be measured on the sample table, and adjust the image information detection module so that the wavelength of the monochromatic light filtered is the target working wavelength, and determine the system parameters under the target working wavelength according to the second fitting curve; the second fitting curve is calibrated by the calibration method provided in the above embodiment 3;

[0148] After the incident light generation module emits parallel incident light in the working wavelength range, the two-dimensional image of the micro-nano product to be measured under the target working wavelength is obtained through the image information detection module;

[0149] According to the two-dimensional image, the light intensity information under the target working wavelength is calculated;

[0150] According to the system parameters under the target working wavelength and the light intensity information, the Mueller matrix of the micro-nano product to be measured is calculated.

[0151] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A system parameter calibration method based on a system parameter calibration system, characterized in that, The system parameter calibration system includes: an imaging ellipsometer and a spectral detection module; The imaging ellipsometer includes: Sample stage, used to place samples; An incident light generation module, a polarizing module, and a first converging lens are arranged sequentially along the optical path on one side of the sample stage. The incident light generation module is used to generate parallel incident light within the working wavelength range. The polarizing module is used to modulate the polarization state of the incident light to obtain polarized incident light. The first converging lens is used to focus the polarized incident light onto the sample placed on the sample stage to generate reflected light. The sample stage includes a second converging lens, a polarization analyzer, a beam adjustment module, and an image information detection module, all arranged sequentially along the optical path of the reflected light. The second converging lens converts the reflected light into parallel light. The polarization analyzer modulates the polarization state of the parallel light to obtain polarized parallel light. The beam adjustment module spatially or temporally divides the polarized parallel light to obtain a first outgoing beam and a second outgoing beam. The image information detection module adjusts the first outgoing beam to monochromatic light and then images the sample to obtain a two-dimensional image of the sample. The spectral detection module is disposed in the propagation optical path of the second emitted beam and is used to acquire the spectral information of the second emitted beam. The system parameter calibration method includes: Preprocessing steps: Place a standard sample with a known Mueller matrix on the sample stage, and make the incident light generation module emit parallel incident light within the working wavelength range; Spectral detection steps: Obtain the spectral information of the standard sample through the spectral detection module, extract the light intensity value of each wavelength within the working wavelength range from the spectral information, and record it as the first light intensity value; Spectral fitting steps: Based on the first light intensity value, calculate the fitting curves of each system parameter as a function of wavelength, and denot them as the first fitting curve; the system parameters are the device parameters affecting polarization in the polarization-inducing module and the polarization-detecting module; Imaging detection step: The image information detection module acquires the image within the working wavelength range. N Two-dimensional images of the standard sample at different wavelengths are obtained, and the light intensity values ​​at different wavelengths are calculated based on the two-dimensional images and recorded as the second light intensity value. N It is a positive integer; Calibration steps: Solve based on the second light intensity value N The discrete values ​​of each system parameter at different wavelengths are obtained, and a fitting curve of each system parameter changing with wavelength is plotted and denoted as the second fitting curve, thus completing the calibration of the imaging ellipsometer; the second fitting curve has the same trend of change as the first fitting curve. The second emitted beam serves as the input to the spectral detection module during system parameter calibration. The polarization module includes a first polarizer and a first phase retarder arranged sequentially along the optical path. The polarization analyzer module includes a second phase retarder and a second polarizer arranged sequentially along the optical path. The system parameters include the azimuth angle of the second polarizer. Azimuth angle of the first polarizer azimuth angle of the first phase delayer azimuth angle of the second phase delayer The phase delay of the azimuth angle of the first phase delayer The phase delay of the second phase delayer azimuth angle .

2. The system parameter calibration method as described in claim 1, characterized in that, The image information detection module includes: a filtering unit, a telescope, and a detection unit; The filtering unit is used to adjust the first emitted beam into monochromatic light; The tube mirror is used to focus the monochromatic light onto the detection unit; The detection unit is used to image the sample based on the received monochromatic light to obtain a two-dimensional image and light intensity information of the sample.

3. The system parameter calibration method as described in claim 2, characterized in that, The tube lens is an achromatic tube lens.

4. The system parameter calibration method as described in claim 2, characterized in that, The filtering unit includes: a filter wheel, and filter plates with different center wavelengths mounted on the filter wheel.

5. The system parameter calibration method according to any one of claims 1 to 4, characterized in that, Both the first converging lens and the second converging lens are micro-spot converging lenses.

6. The system parameter calibration method according to any one of claims 1 to 4, characterized in that, The polarization modulation used by the polarization initiation module and the polarization detection module is either dual-rotation phase delay modulator modulation, single-rotation phase delay modulator modulation, photoelastic modulator modulation, or coherent modulator modulation.

7. A method for measuring the surface of micro / nano products based on an imaging ellipsometer, characterized in that, The imaging ellipsometer includes: Sample stage, used to place samples; An incident light generation module, a polarizing module, and a first converging lens are arranged sequentially along the optical path on one side of the sample stage. The incident light generation module is used to generate parallel incident light within the working wavelength range. The polarizing module is used to modulate the polarization state of the incident light to obtain polarized incident light. The first converging lens is used to focus the polarized incident light onto the sample placed on the sample stage to generate reflected light. The sample stage includes a second converging lens, a polarization analyzer, a beam adjustment module, and an image information detection module, all arranged sequentially along the optical path of the reflected light. The second converging lens converts the reflected light into parallel light. The polarization analyzer modulates the polarization state of the parallel light to obtain polarized parallel light. The beam adjustment module spatially or temporally divides the polarized parallel light to obtain a first outgoing beam and a second outgoing beam. The image information detection module adjusts the first outgoing beam to monochromatic light and then images the sample to obtain a two-dimensional image of the sample. The surface measurement method for micro / nano products includes: The micro / nano product to be tested is placed on the sample stage, and the image information detection module is adjusted so that the wavelength of the monochromatic light filtered by it is the target working wavelength. The system parameters at the target working wavelength are determined according to the second fitting curve. The second fitting curve is obtained by calibration using the calibration method described in claim 1. After the incident light generation module emits parallel incident light within the working wavelength range, the image information detection module obtains a two-dimensional image of the micro / nano product under test at the target working wavelength. Calculate the light intensity information at the target operating wavelength based on the two-dimensional image; Calculate the Mueller matrix of the micro / nano product under test based on the system parameters and light intensity information at the target operating wavelength; The second emitted beam serves as the input to the spectral detection module during system parameter calibration. The polarization module includes a first polarizer and a first phase retarder arranged sequentially along the optical path. The polarization analyzer module includes a second phase retarder and a second polarizer arranged sequentially along the optical path. The system parameters include the azimuth angle of the second polarizer. Azimuth angle of the first polarizer azimuth angle of the first phase delayer azimuth angle of the second phase delayer The phase delay of the azimuth angle of the first phase delayer The phase delay of the second phase delayer azimuth angle .

8. The method for measuring the surface of micro / nano products as described in claim 7, characterized in that, The image information detection module includes: a filtering unit, a telescope, and a detection unit; The filtering unit is used to adjust the first emitted beam into monochromatic light; The tube mirror is used to focus the monochromatic light onto the detection unit; The detection unit is used to image the sample based on the received monochromatic light to obtain a two-dimensional image and light intensity information of the sample.

9. The method for measuring the surface of micro / nano products as described in claim 8, characterized in that, The tube lens is an achromatic tube lens.

10. The method for measuring the surface of micro / nano products as described in claim 8, characterized in that, The filtering unit includes: a filter wheel, and filter plates with different center wavelengths mounted on the filter wheel.

11. The method for measuring the surface of micro / nano products as described in any one of claims 7 to 10, characterized in that, Both the first converging lens and the second converging lens are micro-spot converging lenses.

12. The method for measuring the surface of micro / nano products as described in any one of claims 7 to 10, characterized in that, The polarization modulation used by the polarization initiation module and the polarization detection module is either dual-rotation phase delay modulator modulation, single-rotation phase delay modulator modulation, photoelastic modulator modulation, or coherent modulator modulation.

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