CN101231238A - A method and device for adjusting light intensity in ellipsometry - Google Patents

Abstract

The present invention relates to a device for light intensity adjustment in an ellipsometer, comprising a linear polarizer 12, a hollow polarizer rotating table 13 for fixing the linear polarizer 12, a Data collector 43, a control box 41 and an electronic computer 42; The linear polarizer 12 is placed on the incident optical axis of the ellipsometer, in front of the linear polarizer 14, and has an azimuth angle with the linear polarizer 14 Difference θ (0°≤θ≤90°). When adjusting the light intensity, the computer 42 sends instructions to the control box 41, and the control box 41 drives the polarizer rotating table 13 to drive the linear polarizer 12 to rotate around the incident optical axis, thereby changing the linear polarizer 12 and the linear polarizer 14. The included angle θ of the azimuth angle. When making measurements, always keep θ constant. The invention provides continuous adjustment of the light intensity in a large range, and has a simple structure.

Description

A method and device for adjusting light intensity in ellipsometry

technical field

The invention relates to a method and a device for adjusting the light intensity of a detection beam, in particular to a method and a device for adjusting the light intensity of a detection beam in an ellipsometer.

Background technique

Ellipsometry is one of the important methods for the characterization of nano-thin films. It uses the change of the polarization state of light waves before and after reflection from the surface to detect the information of the sample, such as refractive index, thickness, surface roughness, etc. This technology has two significant advantages: (1) It is non-disturbed and non-destructive to the sample, so it can be measured in real time, in vitro or even in vivo; (2) It can reach the measurement sensitivity at the atomic level. Therefore, since the method was established in the 19th century, especially with the development of microelectronics technology and automation technology in the mid-1960s, the method has been widely used in the fields of microelectronics industry, surface materials and biomedicine. Reference [1]: R.M.A.Azzam and N.M.Bashara, Ellipsometry and Polarized Light, 1st edition, Amsterdam: North-Holland publishing company, 1977, and reference [2]: Harland G.Tompkins and Eugene A.Irene, Handbook of ell ipsometry, NewYork: William Andrew Inc.. 2005.

There are many methods of ellipsometry. Usually, the ellipsometric parameters (ψ and Δ) of the sample are obtained by the ellipsometer, and then the characteristic parameters of the sample, such as the thickness of the film layer, are obtained by using the data fitting method through the physical model established for the sample. , Refractive index, etc. The most basic method for obtaining ellipsometric parameters by ellipsometry instruments is Null Ellipsometry. The more commonly used methods include the method of rotating polarizing devices, such as RPE (Rotating Polarizer Ellipsometry) of rotating polarizer, rotating analyzer RAE (RotatingAnalyzer Ellipsometry) of the device, RCE (Rotating CompensatorEllipsometry) of the rotary compensator, in addition to the phase modulation method PME (Phase Modulation Ellipsometry) and so on. Matching light intensity and detector response is a fundamental issue in measurements.

This is because the electrical signal output by the detector is related to the wavelength of the probe light, the intensity of the light source, the incident angle, the setting of the system polarizer, the absorption coefficient of each optical device in the system, and the spectral response of the detector. Therefore, solving this problem becomes One of the fundamental issues in instrument design and use. For example, when different samples are measured under the same system settings, due to the difference in layered samples, the light intensity reaching the detector will be too low and the signal-to-noise ratio will decrease, or the light intensity will exceed the detector’s limit due to too high light intensity. The range is saturated. Or for the same sample, when the incident angle or spectrum changes, the detected light intensity will be too low or too high due to the optical response of the system to the sample, the energy spectral distribution of the light source, or the spectral response of the detector. . Therefore, according to the measurement situation of the sample by the ellipsometry system, in order to make the measurement result in the best signal-to-noise ratio, the light intensity of the system detection beam must be adjusted during the measurement process.

Commonly used methods to solve this problem are: (1) In the ellipsometric device, the intensity of the incoming light is adjusted by adjusting the intensity of the outgoing light of the light source, such as using the diaphragm of the entrance or exit of the monochromator in the spectroscopic ellipsometer (2) Add a filter with variable transmission coefficient in the incident light path; (3) Adjust the electronic gain of the photodetector, and the output signal can be changed by gain adjustment, but this method usually cannot improve the signal. noise ratio. Therefore, the existing methods have disadvantages such as small adjustment range and difficulty in precise continuous adjustment.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects such as small adjustment range, difficulty in accurate continuous adjustment, and inability to improve the signal-to-noise ratio of the image; thereby providing a polarization device on the original ellipsometer, by changing the linearity The angle θ of the azimuth angle of the polarizer is used to obtain continuous and large-scale light intensity adjustment, that is, a device and a method for continuously adjusting light intensity in a wide range.

The purpose of the present invention is achieved like this:

The light intensity adjustment device used in ellipsometry provided by the present invention includes:

An incident rotating arm 1, the incident rotating arm 1 can be rotated around the central axis for changing the angle between the incident optical axis and the sample 20;

A sample rotary table 2 and an outgoing rotary arm 3, the end of the incident rotary arm 1 overlaps with the front end of the outgoing rotary arm 3, the sample rotary table 2 is placed on it and the three are connected by the axis of the sample rotary table 2, the sample 20 is installed on the sample rotating table 2, the sample is perpendicular to the incident surface, and its surface passes through the central axis;

A monochromatic light generating device 10 capable of wavelength scanning and quasi-monochromatic light output, the output beam is used to illuminate the sample to be tested;

A collimating lens 11, used to collimate and expand the light generated by the monochromatic light generating device 10;

A linear polarizer 12 for converting the probe beam into linearly polarized light with a controllable polarization direction, the linear polarizer 12 is installed on the optical path of the extended probe light generated by the monochromatic light generating device 10 and the collimator lens 11 ;

A reflective plane sample 20, the sample 20 is a flat reflective planar block or thin film material, used for the sample to receive the illumination from the collimated, quasi-monochromatic polarized light wave generated by the incident part, and the illumination of the light wave Polarization state modulation;

A linear analyzer 31 for modulating the polarization state of the reflected light of the sample 20, the linear analyzer is installed on the outgoing optical axis;

An image sensor 34 is used to receive the real image formed by the imaging objective lens of the sample and convert it into an electrical signal;

A data collector 43 is electrically connected with the photodetector 34 and the electronic computer 42, and is used to receive the electrical signal obtained by the photodetector 34 and convert it into a digital signal that the electronic computer 42 can process;

An electronic computer 42, electrically connected with the data collector 43 and the control box 41, is used to receive the signal of the data collector 43, process and analyze it, and send motion commands to the control box 41 according to the analysis results, and simultaneously receive signals from the control box. 41 motion position feedback signal;

A control box 41 is electrically connected with the electronic computer 42 and the moving parts, and is used to receive motion commands from the electronic computer 42, receive status feedback from various devices, feed back signals to the electronic computer 2 for processing, and drive the moving parts sports;

It is characterized in that it also includes a linear polarizer 12 fixed in the polarizer rotating table 13 through mechanical connection, the linear polarizer 12 is installed concentrically on the optical axis of the incident rotating arm 1, and placed on the Before the linear polarizer 14, it is used to convert the detection light wave into linearly polarized light; the motor on the polarizer rotating table 13 is electrically connected with the control box 41 and driven by it, which can drive the linear polarizer 12 to rotate 360°, thereby changing The difference θ between the azimuth angles of the linear polarizer 12 and the linear polarizer 14 is 0°≦θ≦90°.

In the above technical scheme, the linear polarizer 12 is a polarizing device that can convert any light wave into linearly polarized light, for example: dichroic linear polarizer, Glan-Thomson polarizer (Glan-Thompson polarizer) device) or Glan-Taylor polarizer (Glan-Taylor polarizer), etc.

In the above-mentioned technical solution, a phase compensator 16 and a compensator rotating table 17 are also included, the phase compensator 16 is installed on the described compensator rotating table 17, and the described phase compensator 16 is arranged on the incident rotating arm 1 After the linear polarizer 12 on the optical path, the motor in the compensator rotary table 17 is electrically connected to the control box 41, and the electronic computer 42 is electrically connected to the control box 41 to send motion commands to it and receive information from the control box 41. feedback information.

In the above technical solution, an imaging objective lens 33 is also included, and the imaging objective lens 33 and the image sensor 34 are coaxially installed on the outgoing rotating arm 3 in turn, and its optical axis coincides with the outgoing optical axis.

In above-mentioned technical scheme, described polarizer rotating table 13 is the precision transmission device driven by motor, for example the rotating table of worm gear-worm structure; The motor on this rotating table is electrically connected with the motor driver in drive control box 41, The computer 42 sends instructions to the motor control card in the drive control box 41, and then the motor control card transmits the signal to the motor driver to drive the driver to rotate, thereby changing the azimuth angle of the linear polarizer 12; through the position feedback device, the device can be The motion state of the motor is fed back to the motor control card in the drive control box 41, and the electronic computer 42 is notified of the motion state of the current moving device through the communication between the drive control box 41 and the electronic computer 42.

The working principle of the device of the present invention is: in the ellipsometry device, the light wave sent by the monochromatic light generator 10 first enters the collimating lens 11, and then places the polarizer fixed in the polarizer rotating table 13 before the linear polarizer 14. Linear polarizer 12 . The detection beam enters the photodetector 34 after passing through the linear polarizer 14 , the sample 20 , the linear analyzer 31 and other components. The signal of the photodetector 34 is converted into a data format that the electronic computer 42 can process by the data collector 43 . Then, according to the analysis of this data or a series of data, determine whether the light intensity entering the ellipsometry device is within the dynamic range of the detector (modify here!), and judge whether to need or need to linear polarizer 12 accordingly How much is the difference θ between the azimuth angle of the linear polarizer and the linear polarizer 14 to adjust. If it needs to be adjusted, the computer 42 sends an instruction to the control box 41, and the control box 41 drives the polarizer rotating table 13 to rotate, thereby changing the difference θ of the azimuth angles between the linear polarizer 12 and the linear polarizer 14 until the requirement is reached. until. Theoretically, the light intensity entering the linear polarizer 14 after adjustment is

I＝KI ₀ cos ² θ

Where K (0<K<1) is the transmittance, and I ₀ is the light intensity value incident on the linear polarizer 12 . It can be seen that the value of I can be continuously adjusted between 0 and KI ₀ . In fact, due to the defect of the device, when θ = 90°, I cannot reach zero, for example, for Glan-Taylor polarizers, it can usually reach 10 ^-5 KI ₀ , in this case, the adjustment range can reach 10 ⁵ times.

The method for adjusting light intensity using the light intensity adjusting device used in ellipsometry provided by the present invention comprises the following steps:

a) first set the azimuth of the linear polarizer 14, the motion step of the linear analyzer 31 and the number of sampling points;

b) read the azimuth Px of the current linear polarizer 12 and the azimuth P of the linear polarizer 14, and calculate the difference θ=Px-P between the two;

c) Use the current setting of the system to measure the sample 20, keep θ constant during the measurement, obtain one or a series of detection values I1, I2, ... by the photodetector 34, and convert them to the electronic computer 42 through the data collector 43 ;

d) Utilize the electronic computer 42 to analyze the measured value, obtain the maximum value Imax of the detected value, then compare Imax with the minimum value Tmin and the maximum value Tmax of the detection range of the photodetector 34, and determine that the linear polarizer 12 needs to be Execute step (d) to what extent the difference θ between the azimuth angle Px and the azimuth angle P of the linear polarizer 14 is adjusted;

e) The electronic computer 42 sends instructions to the control box 41, and the control box 41 drives the polarizer rotating table 13 to drive the linear polarizer 12 to rotate around the incident optical axis, thereby changing the clamping angle between the linear polarizer 12 and the linear polarizer 14. angle θ;

f) Execute steps (a)~(c) until the requirements are met.

The advantages of the present invention are:

The light intensity adjustment device used in ellipsometry provided by the present invention is simple in structure, by arranging a linear polarizer 12 in the ellipsometry device, by changing the included angle of the azimuth angle between the linear polarizer 12 and the linear polarizer 14 θ, to obtain a continuous wide range of light intensity adjustment, making the adjustment method flexible and convenient.

Description of drawings

Fig. 1 is the schematic diagram of the spectroscopic ellipsometer that the present invention is used for rotating polarizer

Fig. 2 is the schematic diagram of the ellipsometry device used for the rotating polarizer of the present invention

Fig. 3 is the schematic diagram of the ellipsometric imaging measuring device used for the rotary compensator of the present invention

Graphic mark

monochromatic light generator 10 collimator lens 11 linear polarizer 12

Polarizer Rotary Stage 13 Linear Polarizer 14 Polarizer Rotary Stage 15

Phase Compensator 16 Compensator Rotary Stage 17 Sample 20

Linear analyzer 31 Analyzer rotary table 32 Imaging objective lens 33

photodetector 34 control box 41 electronic computer 42

Data Collector 43

Detailed ways

The device and adjustment method of the present invention will be described in detail below through examples.

Referring to FIG. 1 , a method and device for adjusting light intensity in ellipsometry with a polarizer-sample-rotating analyzer structure are made, and a method for adjusting light intensity is performed on the spectroscopic ellipsometer.

The basic structure of the ellipsometer is as follows: a monochromatic light generator 10, a collimating lens 11, and a linear polarizer 14 are sequentially installed on the incident rotating arm 1, and the detection light enters the reflecting rotating arm 3 after being reflected by the sample 20, and the reflecting rotating arm 3, a linear analyzer 31 and a photodetector 34 fixed in the analyzer rotating table 32 are sequentially installed. In order to control the rotation of the linear analyzer 31 around the reflected optical axis, the motor in the analyzer rotating table 32 is electrically connected to the control box 41 to receive its drive. The electronic computer 42 is electrically connected with the control box 41 , sends motion commands to it, and receives feedback information from the control box 41 . On the other hand, the signal received by the photodetector 34 is transferred to the electronic computer 42 through the conversion of the data collector 43 . The improvement of the present invention is that a linear polarizer 12 is coaxially installed between the collimating lens 11 and the linear polarizer 14, and the linear polarizer 12 is fixed in a hollow polarizer rotating table 13, which can surround the incident optical axis Perform a 360° rotation. The polarizer turntable 13 is a motor-driven precision worm gear-worm structure turntable, the motor in the polarizer turntable 13 is electrically connected to the control box 41, receives the instruction sent by the electronic computer 42 and is driven by the electric power sent by the control box 41. The position signal of the polarizer rotating stage 13 is also fed back to the electronic computer 42 through the control box 41 .

During measurement, first set the azimuth angle of the linear polarizer 14, the motion step of the linear analyzer 31, and the number of sampling points. For example, the motion step is set to 45°, and the corresponding sampling points are 8. The electronic computer 42 sends a motion command to the control box 41, driven by the control box 41, the analyzer rotating table 32 moves a step distance, and then the photodetector 34 performs a data collection, which is converted into The data format that the electronic computer 42 can receive enters the electronic computer 42 for data storage and processing, and then performs the next cycle until all sampling points are completed. In this way, a series of data I1, I2, . . . , I8 are sequentially obtained, and the maximum value is recorded as Imax. If Imax is within the response range of the photodetector 34, the ellipsometric parameter values ψ and Δ of the sample can be obtained by Fourier analysis. However, if Imax exceeds the response range of the photodetector 34, invalid data in this set of data cannot be used as a data source for calculation. In this case, it is necessary to adjust the light intensity entering the linear polarizer 14 .

Let the angle between the azimuth angles of the linear polarizer 12 and the linear polarizer 14 be θ. This improved system compares the response range of the photodetector 34 with the series data I1, I2, . For example, whether Imax exceeds the response range, is too high or too low, or although Imax is within the response range, it is far below the upper limit of the response range, resulting in a low signal-to-noise ratio. Under these circumstances, the electronic computer 42 analyzes the degree to which θ should be adjusted, such as θ=60°, and then sends an instruction to the control box 41, and the control box 41 drives the polarizer rotating table 13 to drive the linear polarizer 12. rotate. Since the azimuth angle of the linear oscillator 14 does not change, the angle θ is changed by changing the azimuth angle of the linear polarizer 12, so the light intensity entering the linear polarizer becomes

I＝KI ₀ cos ² θ＝0.5KI ₀

I ₀ is the light intensity value incident on the linear polarizer 12 . It can be seen that the value of I can be continuously adjusted between 0 and KI ₀ . In fact, due to the defect of the device, when θ = 90°, I cannot reach zero, for example, for Glan-Taylor polarizers, it can usually reach 10 ^-5 KI ₀ , in this case, the adjustment range can reach 10 ⁵ times.

After the adjustment, the spectroscopic ellipsometer is used to measure again to evaluate whether the obtained series of data meet the requirements. If so, the Fourier analysis method can be used to obtain the ellipsometric parameters ψ and Δ. If not satisfied, you can continue to adjust θ.

Example 2

Referring to FIG. 2 , it is an example of adjusting light intensity on a spectroscopic ellipsometer with a rotating polarizer-sample-analyzer structure by using the present invention.

The basic structure of the spectroscopic ellipsometer is similar to that in FIG. 1 , the difference is that the device for rotating sampling is not the linear analyzer 31 but the linear polarizer 14 . On the incident rotating arm 1, a monochromatic light generator 10, a collimating lens 11, and a linear polarizer 14 fixed in the polarizer rotating table 15 are sequentially installed. The detection light enters the reflecting rotating arm 3 after being reflected by the sample 20, and is reflected A linear analyzer 31 and a photodetector 34 are sequentially installed on the rotating arm 3 . In order to control the rotation of the linear polarizer 12 around the incident optical axis, the motor in the polarizer rotating table 13 is electrically connected to the control box 41 to receive its drive. The electronic computer 42 is electrically connected with the control box 41 , sends motion commands to it, and receives feedback information from the control box 41 . On the other hand, the signal received by the photodetector 34 is transferred to the electronic computer 42 through the conversion of the data collector 43 .

During measurement, the azimuth angle of the linear polarizer 31 , the motion step of the linear polarizer 14 and the number of sampling points are firstly set. The electronic computer 42 sends a motion command to the control box 41, driven by the control box 41, the polarizer rotating table 15 moves a step, and then the photodetector 34 performs a data collection, and is converted into The data format that the electronic computer 42 can receive enters the electronic computer 42 for data storage and processing, and then performs the next cycle until all sampling points are completed. At each sampling point, a series of data I1, I2, . . . are sequentially obtained, and the maximum value is recorded as Imax. If Imax is within the response range of the photodetector 34, the ellipsometric parameter values ψ and Δ of the sample can be obtained by Fourier analysis. However, if Imax exceeds the response range of the photodetector 34, the invalid data in this set of data cannot be used as a data source for calculation. In this case, the light intensity entering the linear polarizer 14 needs to be adjusted.

According to the method and device proposed by the present invention, a linear polarizer 12 is coaxially installed between the collimating lens 11 and the linear polarizer 14, and the linear polarizer 12 is fixed in a hollow polarizer rotating table 13, which can surround the incident The optical axis rotates 360°. The polarizer turntable 13 is a motor-driven precision worm gear-worm structure turntable, the motor in the polarizer turntable 13 is electrically connected to the control box 41, receives the instruction sent by the electronic computer 42 and is driven by the electric power sent by the control box 41. The position signal of the polarizer rotating stage 13 is also fed back to the electronic computer 42 through the control box 41 .

During the measurement, the linear polarizer 12 rotates synchronously with the rotating linear polarizer 14, and the difference between the two azimuth angles is always kept as θ during sampling. This improved system compares the series of data I1, I2, . For example, whether Imax exceeds the response range, is too high or too low, or although Imax is within the response range, it is far below the upper limit of the response range, resulting in a low signal-to-noise ratio. Under these circumstances, the electronic computer 42 analyzes to what extent the linear polarizer 12 and the linear polarizer 14 are adjusted to what extent the azimuth angle difference θ is adjusted, and then sends an instruction to the control box 41, and the control box 41 drives the polarizer The rotary table 13 drives the linear polarizer 12 to rotate. The difference between the azimuth angle of the linear oscillator 14 and the azimuth angle of the linear polarizer 12 is θ, therefore, the light intensity entering the linear polarizer 14 becomes

I＝KI ₀ cos ² θ

Where K (0<θ<1) is the transmittance, and I ₀ is the light intensity value incident on the linear polarizer 12 . It can be seen that the value of I can be continuously adjusted between 0 and KI ₀ . In fact, due to the defect of the device, when θ = 90°, I cannot reach zero, for example, for Glan-Taylor polarizers, it can usually reach 10 ^-5 KI ₀ , in this case, the adjustment range can reach 10 ⁵ times.

After the adjustment, the spectroscopic ellipsometer is used to measure again to evaluate whether the obtained series of data meet the requirements. If so, the Fourier analysis method can be used to obtain the ellipsometric parameters ψ and Δ. If not satisfied, you can continue to adjust θ.

Example 3

Another preferred example of the present invention is shown in accompanying drawing 3, and this is the example that utilizes the present invention to carry out light intensity adjustment on the spectroscopic ellipsometry imager of a polarizer-rotary compensator-sample-analyzer structure .

The basic structure of the ellipsometer is as follows: a monochromatic light generator 10, a collimator lens 11, a linear polarizer 14 and a phase compensator 16 fixed in a compensator rotating table 17 are sequentially installed on the incident rotating arm 1, and the detection beam After being reflected by the sample 20, it enters the reflection rotating arm 3, on which a linear analyzer 31, an imaging lens 33, a photodetector 34 that can be used for area array imaging, a polarizer 31, an imaging objective lens 33 and an image sensor are sequentially installed 34 are coaxially installed on the outgoing rotating arm 3 in turn, and its optical axis coincides with the outgoing optical axis. In order to control the rotation of the phase compensator 16 around the incident optical axis, the motor in the compensator rotating table 17 is electrically connected to the control box 41 to receive its drive. The installation of the image sensor 34 ensures that its image sensitive surface coincides with the real image formed by the sample 20 through the imaging objective lens 33 . The analyzer rotating table 32 can rotate 360°. The outgoing rotating arm 3 can rotate around the central axis. Both the analyzer rotating table 32 and the exiting rotating arm 3 are transmission devices of a conventional worm gear-worm structure driven by a stepping motor, and the stepping motor on it is electrically connected with the motor driver in the drive control box 41 . The computer 42 sends an instruction to the stepper motor control card in the drive control box 41, and then the stepper motor control card transmits the signal to the motor driver to drive the driver to rotate, thereby changing the position of the analyzer 31 or the outgoing optical axis relative to the sample. angle. The motion state of the device can be fed back to the motor control card in the drive control box 41 through the position feedback device, and the computer 42 is notified of the motion state of the current motion device through the communication between the drive control box 41 and the computer 42 .

During measurement, the azimuth angle of the linear polarizer 14, the azimuth angle of the linear analyzer 31, the motion step of the compensator rotary table 17, and the number of sampling points are firstly set. The electronic computer 42 sends a movement command to the control box 41. Driven by the control box 41, the compensator rotary table 17 moves a step away, and then the data is collected by the photodetector 34, which is transformed into an electronic computer by the data collector 43. The image data format that can be received by 42 enters the electronic computer 42 for data storage and processing, and then performs the next cycle until all the sampling points are completed. At each sampling point, for the measured sample area, a series of data I1, I2, . If Imax is within the response range of the photodetector 34, the ellipsometric parameter values ψ and Δ of the sample can be obtained by Fourier analysis. However, if Imax exceeds the response range of the photodetector 34, the invalid data in this set of data cannot be used as a data source for calculation. Therefore, in this case, the light intensity entering the linear polarizer 14 needs to be adjusted.

According to the method and device proposed by the present invention, a linear polarizer 12 is coaxially installed between the collimating lens 11 and the linear polarizer 14, and the linear polarizer 12 is fixed in a hollow polarizer rotating table 13, which can surround the incident The optical axis rotates 360°. The polarizer turntable 13 is a motor-driven precision worm gear-worm structure turntable, the motor in the polarizer turntable 13 is electrically connected to the control box 41, receives the instruction sent by the electronic computer 42 and is driven by the electric power sent by the control box 41. The position signal of the polarizer rotating stage 13 is also fed back to the electronic computer 42 through the control box 41 .

Let the angle between the azimuth angles of the linear polarizer 12 and the linear polarizer 14 be θ. This improved system compares the series of data I1, I2, . For example, whether Imax exceeds the response range, is too high or too low, or although Imax is within the response range, it is far below the upper limit of the response range, resulting in a low signal-to-noise ratio. Under these circumstances, the electronic computer 42 analyzes to what extent θ should be adjusted, and then sends an instruction to the control box 41, and the control box 41 drives the polarizer rotating stage 13 to drive the linear polarizer 12 to rotate. Since the azimuth angle of the linear oscillator 14 does not change, the angle θ is changed by changing the azimuth angle of the linear polarizer 12, so the light intensity entering the linear polarizer becomes

I＝KI ₀ cos ² θ

Where K (0<θ<1) is the transmittance, and I ₀ is the light intensity value incident on the linear polarizer 12 . It can be seen that the value of I can be continuously adjusted between 0 and KI ₀ . In fact, due to the defect of the device, when θ = 90°, I cannot reach zero, for example, for Glan-Taylor polarizers, it can usually reach 10 ^-5 KI ₀ , in this case, the adjustment range can reach 10 ⁵ times.

After the adjustment, the spectroscopic ellipsograph is used to measure again to evaluate whether the obtained series of data meet the requirements. If so, the Fourier analysis method can be used to obtain the ellipsometric parameters ψ and Δ. If not satisfied, you can continue to adjust θ.

Claims (6)

1. A device for adjusting light intensity in an ellipsometer, comprising: an incident rotating arm (1), the incident rotating arm (1) can be rotated around the central axis, and is used to change the angle between the incident optical axis and the sample (20); A sample rotation table (2) and an exit rotation arm (3), the end of the entrance rotation arm (1) overlaps with the front end of the exit rotation arm (3), the sample rotation table (2) is placed on it and rotates through the sample The axis of the stage (2) connects the three, the sample (20) is installed on the sample rotating stage (2), the sample is perpendicular to the incident surface, and its surface passes through the central axis; A monochromatic light generating device (10) for quasi-monochromatic light output capable of wavelength scanning, the output beam is used to illuminate the sample to be tested; A collimating lens (11), used for collimating and expanding the light generated by the monochromatic light generating device (10); A linear polarizer (12) used to transform the probe beam into linearly polarized light with controllable polarization direction, the linear polarizer (12) is installed on the monochromatic light generating device (10) and the collimating lens (11) The optical path of the extended probe light generated; A reflective planar sample (20), the sample (20) is a flat reflective planar block or film material, used for the sample to receive the illumination from the collimated, quasi-monochromatic polarized light waves generated by the incident part, and modulating the polarization state of the light wave; A linear analyzer (31) for modulating the polarization state of the reflected light of the sample (20), the linear analyzer being installed on the outgoing optical axis; An image sensor (34) is used to receive the real image formed by the imaging objective lens of the sample and convert it into an electrical signal; A data collector (43), electrically connected with the photodetector (34) and the electronic computer (42), is used to receive the electric signal that the photodetector (34) obtains, converts it into the electronic signal that the electronic computer (42) can handle Digital signal; An electronic computer (42), is electrically connected with the data collector (43) and the control box (410), and is used to receive the signal of the data collector (43), and it is processed and analyzed, and the control box (41) is controlled according to the result of the analysis. Send a motion command and receive a motion position feedback signal from the control box (41) at the same time; A control box (41), electrically connected with the electronic computer (42) and the moving parts, used to receive motion commands from the electronic computer (42), receive status feedback from various devices, and feed back signals to the electronic computer (42) Processing in and driving moving parts to move; it is characterized in that, It also includes a linear polarizer (12) fixed in the polarizer rotation stage (13), the linear polarizer (12) is installed concentrically on the optical axis of the incident rotation arm (1), and placed on the Before the linear polarizer (14), it is used to convert the detection light wave into linearly polarized light; the motor on the polarizer rotating table (13) is electrically connected with the control box (41) and is driven by it, which can drive the linear polarizer (12 ) is rotated 360° to change the difference θ of the azimuth angle between the linear polarizer (12) and the linear polarizer (14), and the difference of the azimuth angle is 0°≤θ≤90°. 2. The device for light intensity adjustment in ellipsometry according to claim 1, characterized in that: it also includes a phase compensator (16) and a compensator rotary table (17), and the phase compensator (16) is installed On the described compensator turntable (17), the described phase compensator (16) is arranged behind the optical path of the linear polarizer (12) on the incident rotating arm (1), and the described compensator turntable ( The motor in 17) is electrically connected with the control box (41), and the electronic computer (42) is electrically connected with the control box (41), sends motion commands to it, and receives feedback information from the control box (41). 3. The device for adjusting light intensity in ellipsometry according to claim 1 or 2, characterized in that: it also includes an imaging objective lens (33), and the imaging objective lens (33) and the image sensor (34) are coaxial sequentially Installed on the outgoing rotating arm (3), its optical axis coincides with the outgoing optical axis. 4. The device for adjusting light intensity in ellipsometry according to claim 1, characterized in that: said linear polarizer (12) is a polarization device that converts any light wave into linearly polarized light, including a dichroic Chromatic linear polarizers, Glan-Thomson or Glan-Taylor polarizers. 5. The device for light intensity adjustment in ellipsometry according to claim 1, characterized in that: the polarizer rotating table (13) is a precision transmission device driven by a motor, and the motor and drive on it The motor driver in the control box (41) is electrically connected to drive the linear polarizer (12) to rotate 360° around the optical axis of the incident rotating arm (1). 6. A method for adjusting light intensity by applying the device according to claim 1, characterized in that: comprising the steps of: a) First set the azimuth angle of the linear polarizer (14), the motion step of the linear analyzer (31), the number of sampling points, and the step distance Step for adjusting θ; b) read the azimuth Px of the current linear polarizer (12) and the azimuth P of the linear polarizer (14), and calculate the difference θ=Px-P between the two; c) Use the current setting of the system to measure the sample (20), keep θ constant during the measurement, obtain one or a series of detection values I1, I2, ... by the photodetector (34), and pass through the data collector (43 ) is converted to an electronic computer (42); d) Utilize the electronic computer (42) to analyze the measured value to obtain the maximum value Imax of the detection value, then compare Imax with the minimum value Tmin and the maximum value Tmax of the dynamic range of the photodetector 34, and if it is in it, then terminate ; If it is less than Tmin, then adjust θ to a decreasing direction, if greater than Tmax, then adjust θ to a larger direction, and perform step d); e) The electronic computer (42) sends instructions to the control box (41), and the control box (41) drives the polarizer rotating table (13) to drive the linear polarizer (12) to rotate around the incident optical axis, and the direction of rotation is according to step d ), the step distance is Step, and the included angle θ of the azimuth angle of the linear polarizer (12) and the linear polarizer (14) is changed; f) Execute steps (a)~(c) until the requirements are met.

Images