RU2638092C1 - Ellipsometer - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: ellipsometer includes the radiation source, the polarizer arm and the analyzer arm, which are arranged along the optical axis. Moreover, the analyzer arm is made in the form of a non-polarizing beam splitter, dividing the beam of light rays that came from the test sample into two parts. Wherein, the beam of light rays reflected from the non-polarizing beam splitter is incident on the first polarizing beam splitter, dividing it into two linearly polarized light streams with orthogonal directions of the polarization plane, and the transmitted beam of light rays hits the compensator, which introduces a known phase shift between the orthogonal linearly polarized components of the light wave, then it is incident on the second polarizing beam splitter. Then, all four luminous fluxes are fed to the input of a four-channel spectrometer.

EFFECT: finding 16 components of the Mueller matrix and increasing the measurement speed in a wide spectral range.

8 cl, 3 dwg

Description

The invention relates to the field of research and analysis of materials, thin-film structures and surfaces using optical means and can be used to determine: optical constants, film thicknesses, parameters of the semiconductor band structure, composition of solid solutions, measures of roughness of interfaces and surfaces, porosity, optical parameters anisotropy, magnetic and depolarizing properties.

To assess the novelty and inventive step of the claimed technical solution, we consider a number of well-known technical means of a similar purpose.

Known spectral ellipsometer with parallel detection of light flux according to the patent US 6,384,916, which has no moving parts and operates in real time for in-situ monitoring of the surface properties of the thin film of the sample inside the chamber in which it is processed. The ellipsometer includes a broadband light source to create a collimated beam of light rays, which is transmitted through the polarizer and sent to the surface of the sample. In the process of reflection, the state of polarization of light changes in accordance with the internal structure of the sample. The light reflected from the sample is divided into 4 separate polarized beams of rays, each of which has its own spectral intensity dependence. Each of the 4 light fluxes is transmitted to one or more spectrometers, where their spectral dependences are recorded. The data obtained for all light fluxes are processed using real-time conversion algorithms.

The disadvantage of this analogue is that the arm of the ellipsometer polarizer does not allow illuminating the sample under study with light with different polarization states, which, in turn, will not allow to determine all 16 components of the sample Mueller matrix.

A known ellipsometer for the study of samples in a wide spectral range according to US 7,298,480, which contains a broadband light source, a polarization state generator (GSP), which includes a stationary linear polarizer and largely achromatic compensator mounted for rotation, a sample holder, a state detector polarization (DSP), which includes a stationary linear polarizer and largely achromatic compensator, mounted with the possibility of rotation, the main A detection system that measures the spectral dependence of the intensity of transmitted DSP light, optics for collimating the beams of rays transmitted by the GSP and DSP, as well as focusing the light on the sample and detector. The linear polarizer and achromatic compensator in the particleboard are identical to those that are part of the SHG, but are installed in the reverse order along the propagation of light.

The disadvantage of this analogue is that in the arm of the polarizer and the arm of the analyzer of the ellipsometer, not separation / switching of light fluxes is used, but the rotation of polarizing elements (linear polarizer, compensator), which will allow measurements of the components of the Mueller matrix of the test sample only with a limited speed, insufficient to solve real-time metrological control tasks.

A known spectral ellipsometer according to the patent of the Russian Federation 2247969, containing a radiation source sequentially located along the optical axis, collimating optics, a polarizer, an analyzer, a polychromator with a photographic recorder electrically connected to a control and signal processing unit, characterized in that both the polarizer and the analyzer are made in the form sequentially located on the optical axis of two identical prisms oriented towards each other, of which the first is dividing the light beam into two orthogonally polarized bathrooms, running in parallel, and the second connecting again into one, placed between them a shutter, mounted on an electric motor shaft, which is electrically connected to the control and signal processing unit, two optocouplers that are in electrical communication with the control and signal processing unit, the breakers of which are made in the shutter there are two circular paths of windows intersecting the first and second beams, respectively, while the windows in the circular paths are arranged periodically, with a shift in the outer and inner rings itelno other by 1/2 period and executed synchronously rotating in the same frequency obturator polarizer and analyzer with a duty ratio 1/4 and 1/2, respectively, and when measuring the azimuth of a polarizer is + 30 °, and the azimuth of the analyzer is -30 °.

In this analogue there are signs similar to those of the claimed technical solution. In particular, it implements the principle of separation of light fluxes in both shoulders of an ellipsometer and overlapping fluxes in the polarizer arm to change the polarization state of the light incident on the sample.

The disadvantage of this method, which we adopted as a prototype, as well as all other known methods, is the limited metrological capabilities, which make it impossible to determine all 16 components of the Mueller matrix, which gives the most comprehensive description of a linear optical system, the measurement of which allows you to effectively study, including , optical anisotropy, magnetic properties, depolarization of light by a sample.

The objective of the invention is to expand the metrological capabilities of the ellipsometer, to provide the ability to find all 16 components of the Mueller matrix, as well as to increase the measurement speed provided that they are carried out in a wide spectral range.

The essence of the claimed invention as a technical solution is expressed in the following set of essential features.

An ellipsometer including a radiation source sequentially located along the optical axis, a polarizer arm and an analyzer arm is characterized in that the analyzer arm is made in the form of a non-polarizing beam splitter (NS), dividing the beam of light rays coming from the sample into two parts, while the beam reflected from the beam splitter of light rays falls on the first polarizing beam splitter (PS), which divides it into two linearly polarized light flux with orthogonal directions of the plane of polarization radiation, and the transmitted NS beam of light rays enters the compensator, introducing a known phase shift between the orthogonal linearly polarized components of the light wave, after which it falls on the second PS, also dividing it into two linearly polarized light fluxes, then all four light fluxes are input four-channel spectrometer.

In addition, the first independent object of the claimed technical solution is characterized by the presence of a number of additional optional features, namely:

- a four-channel spectrometer contains lenses on each of the four light fluxes emerging from the PS, by which the light fluxes are focused on the entrance slits, after which one mirror on each light flux forms four collimated beams of rays and direct them to the diffraction grating, and the radiation expanded into the spectrum by other mirrors on each light flux focuses on the corresponding multichannel detectors;

- multichannel detectors can be made in the form of one-dimensional arrays of photodetector elements;

- multichannel detectors can be made in the form of one two-dimensional array of photodetector elements;

- multichannel detectors can be made in the form of several two-dimensional arrays of photodetector elements;

- PS can be made in the form of Wollaston prisms;

- the ellipsometer can be equipped with additional NS, PS, and a compensator placed relative to each other with the formation of additional light fluxes arriving at the inputs of two additional four-channel spectrometers, while the beam of light rays coming from the sample under investigation first of all enters the first additional NS, and the reflected from it, the beam of light rays by means of a second additional NS is divided into two beams, and one of them is converted by means of the corresponding PS and additional NS four light streams, two of which go to the inputs of the first additional four-channel spectrometer, and two others go to the inputs of the second additional four-channel spectrometer, while the second beam of light from the second additional NS is converted into four light by means of a compensator corresponding to the PS and additional NS flow, two of which go to the inputs of the first additional four-channel spectrometer, and two others go to the inputs of the second additional four-channel spectro Etra;

- in all the above-described variants of the ellipsometer, the polarizer arm can be made in the form of a combination of linear polarizers and NS placed relative to each other with the organization of four different optical channels sequentially directed to the test sample, while in the first optical channel of the polarizer arm the collimated beam of light rays passes sequentially the first linear polarizer and the first and second NS, after which it is sent to the sample under study, in the second optical channel they are collimated the light beam passes sequentially through the second linear polarizer, is reflected from the first NS passes through the second NS, and then sent to the sample under study, in the third optical channel the collimated beam of light rays passes through the third linear polarizer sequentially, passes through the third NS, is reflected from the second NS, and then sent on the test sample, in the fourth optical channel, the collimated beam of light rays passes sequentially through the fourth linear polarizer, compensator, sequentially property of reflecting the third and second NA, then sent to the sample, in addition, each of the four optical channels are provided with overlapping of its optical shutter arranged between a source of light rays and the NA of the first optical channel.

The set of essential features of the claimed technical solution ensures the achievement of a technical result, which consists in providing the following capabilities, unattainable when using all known analogues:

- the ability to send a light flux to the sample with four different polarization states, which makes it possible to measure all 16 components of the Mueller matrix of the sample under study;

- measurement of all four Stokes parameters of light reflected from a sample for many wavelengths from a wide spectral range, which is important for measurement accuracy and the ability to obtain physically significant quantities in general (optical constants, film thicknesses, semiconductor band structure parameters, composition of solid solutions, roughness measure interfaces and surfaces, porosity);

- a change in the polarization of the light incident on the sample under study is achieved by switching the light flux due to the operation of opening / closing optical shutters, the time of which can be reduced to units of milliseconds, which as a result allows to accelerate measurements by 2 orders of magnitude compared to existing analogues;

The invention is illustrated by drawings, where in FIG. 1 is an optical diagram of the arm of the analyzer of the claimed ellipsometer; FIG. 2 is a variant of an ellipsometer using additional 4-channel spectrometers in the analyzer arm; FIG. 3 is an optical diagram of the polarizer arm of the claimed ellipsometer.

The ellipsometer includes a radiation source, a polarizer arm and an analyzer arm sequentially located along the optical axis. The analyzer arm contains NS 1, the first PS 2, the compensator 3 and the second PS 4, a four-channel spectrometer 5, lenses 6, entrance slits 7, collimating mirrors 8, a diffraction grating 9, focusing mirrors 10 and multi-channel detectors 11.

The ellipsometer can be equipped with additional NS 12-13 and 17-20, PS 14 and 15, a compensator 16, and two additional four-channel spectrometers 21 and 22. In all embodiments of the claimed ellipsometer, the polarizer arm can be made in the form of a combination of linear polarizers 23-26 , NS 27-29, compensator 30, optical shutters 31-34.

The claimed ellipsometer works as follows.

Shoulder of the polarizer - forms a beam of light rays with a given state of polarization, spectral composition, geometric parameters (diameter, divergence) and direction. After reflection from the test sample at a given angle θ, the light enters the arm of the analyzer, in which the polarization state of the light reflected from the test solid structure is measured. Knowing how the polarization of light changed under reflection at a given angle of incidence allows us to obtain information about the sample under study: optical constants, film thicknesses, parameters of the semiconductor band structure, composition of solid solutions, measure of the roughness of interfaces and surface, porosity. Measurement of the polarized state of reflected light for various states of polarization of the incident light allows us to calculate the components of the Muller matrix, which gives the most comprehensive description of a linear optical system. The measurement of the components of the Mueller matrix allows one to efficiently study optical anisotropy, magnetic properties, and depolarization.

A beam of light rays arriving from the sample under investigation falls on NS 1, dividing it into two parts. The radiation reflected from the NS falls on PS 2, which divides it into two linearly polarized light fluxes with orthogonal directions of the electric vector. The transmitted NS 1 beam of rays is passed through a compensator 3, introducing a known phase shift between the orthogonal linearly polarized components of the light wave, and then falls on PS 4. For each of the four light fluxes emerging from the PS 2 and 4, the spectral dependence of the intensity is measured in spectrometer 5. By lenses 6, the radiation emerging from the prisms is focused on the entrance slits 7. The mirrors 8 form four collimated beams of rays and direct them to the diffraction grating 9. The mirrors 10 focus the spectrum expanded p radiation on multi-channel detectors 11, made in the form of one-dimensional, one two-dimensional or several two-dimensional arrays of photodetector elements. A single diffraction grating 9 is used for simultaneous decomposition into a radiation spectrum in the 4 channels of spectrometer 5. A separate section of the grating is used for each channel. Measurement of the spectral dependences of four radiation fluxes emitted from the PS 2 and 4 makes it possible to determine the spectral dependences of the 4 Stokes parameters of the light arriving from the sample under study. The working spectral range of such measurements will be determined, first of all, by the parameters of HC 1, compensator 3, diffraction grating 9, and multichannel detectors 11. The speed of measuring the state of polarization of light for all wavelengths from the working spectral range will be determined only by the accumulation and read time in multichannel detectors eleven.

The working spectral range of the analyzer arm can be significantly expanded using additional 4-channel spectrometers 21 and 22. In this embodiment, the light coming from the sample under investigation falls on an additional NS 12, dividing it into two parts, each of which, in turn, is still divided into two parts of NS 1 and 13. The radiation reflected from NS 1 falls on PS 2, which divides it into two linearly polarized light fluxes with orthogonal directions of the plane of polarization. The transmitted NS 1 radiation is passed through a compensator 3, introducing a known phase shift between the orthogonal linearly polarized components of the light wave, and then falls on PS 4. The four light fluxes emitted from the PS 2 and 4 are decomposed into the spectrum and detected in spectrometer 5. In turn, the transmitted NS 13 a beam of rays enters PS 14. The orthogonally polarized light fluxes emerging from it enter NS 17 and 18. A beam of rays reflected from NS 13 is passed through a compensator 16 and enters PS 15. Oscillations coming out of it are orthogonal izovannye light fluxes enter the NA 19, and 20. Left of the beam splitters 17-20 luminous fluxes are grouped and are inserted into the additional four-channel spectrometers 21 and 22 formed similarly to the spectrometer 5, which can be expanded in range and detected.

The simultaneous use of more than one 4-channel spectrometer provides the following advantages in the operation of the analyzer arm and ellipsometer:

- at the same time, the total polarization state of the light reflected from the sample is measured (all 4 Stokes parameters) in a wide spectral range;

- increases the sensitivity of the device due to the fact that a narrower spectral range of each individual spectrometer allows the use of a diffraction grating near the maximum spectral dependence of the intensity of the iris radiation;

- fundamentally there are no measurement errors associated with radiation from higher diffraction orders reaching the radiation detectors.

In the claimed embodiment, the arm of the polarizer using beam splitters 27-29 light with different states of polarization from four different optical channels is sequentially directed to the sample under study. In the first channel, the collimated beam of light rays sequentially passes through a linear polarizer 23, HC 27-28, after which it is sent to the test sample. In the 2nd channel, the collimated beam of light rays sequentially passes through a linear polarizer 24, is reflected from NS 27, passes NS 28, and then is sent to the sample under study. In the 3rd channel, the collimated beam of light rays sequentially passes through a linear polarizer 25, NS 29, is reflected from NS 28, and then sent to the test sample. In the 4th channel, the collimated beam of light rays sequentially passes through the linear polarizer 26, the compensator 30, is subsequently reflected from the NS 29 and 28, and then sent to the sample under study. For each of the 4 channels, the light input can be blocked by the corresponding optical shutter 31-34. Inside the channel, the gate can be located anywhere along the propagation of radiation between its source and the first NS in this channel. The change in the polarization state of the light incident on the sample is carried out by opening one of the channels and simultaneously closing the remaining 3 channels using optical shutters. Thus, the rate of change of the polarization state of the light incident on the sample is determined only by the speed of operation of the optical shutters 31-34.

Claims (9)

1. An ellipsometer comprising a radiation source sequentially located along the optical axis, a polarizer arm and an analyzer arm, characterized in that the analyzer arm is made in the form of a non-polarizing beam splitter, dividing the beam of light rays coming from the test sample into two parts, while the beam reflected from the non-polarizing beam splitter of light rays falls on the first polarizing beam splitter, which divides it into two linearly polarized light fluxes with orthogonal plane directions polarization, and the beam of light rays passing through a non-polarizing beam splitter hits the compensator, introducing a known phase shift between the orthogonal linearly polarized components of the light wave, after which it falls on the second polarizing beam splitter, then all four light fluxes are input to the four-channel spectrometer. 2. The ellipsometer according to claim 1, characterized in that the light flux emerging from the polarizing beam splitter through the lenses is focused on the entrance slits of the four-channel spectrometer, after which one mirror on each light flux forms four collimated beams of rays and direct them to the diffraction grating, and decomposed into spectrum radiation through other mirrors on each luminous flux is focused on the corresponding multichannel detectors. 3. The ellipsometer according to claim 2, characterized in that the multichannel detectors are made in the form of one-dimensional arrays of photodetector elements. 4. The ellipsometer according to claim 2, characterized in that the multichannel detectors are made in the form of one two-dimensional array of photodetector elements. 5. The ellipsometer according to claim 2, characterized in that the multichannel detectors are made in the form of several two-dimensional arrays of photodetector elements. 6. The ellipsometer according to claim 1, characterized in that the polarizing beam splitters can be made in the form of Wollaston prisms. 7. The ellipsometer according to claim 1, characterized in that it is equipped with additional non-polarizing beam splitters, polarizing beam splitters and a compensator located relative to each other with the formation of additional light fluxes arriving at the inputs of two additional four-channel spectrometers, while the light beam coming from the sample under study First of all, it falls on the first additional non-polarizing beam splitter, and the beam of light rays reflected from it by means of the second additional non-polarizing beam splitter the polarizing beam splitter is divided into two beams, and one of them is converted into four light fluxes using the corresponding polarizing beam splitter and additional non-polarizing beam splitters, two of which go to the inputs of the first additional four-channel spectrometer, and the other two to the inputs of the second additional four-channel spectrometer, while the second a beam of light rays from a second additional non-polarizing beam splitter through a compensator corresponding to the polarization guide non-polarizing beamsplitter and additional beamsplitters converted into four light fluxes, two of which are applied to the inputs of the first additional four-channel spectrometer, and the other two - the inputs of the second additional four-spectrometer 8. The ellipsometer according to any one of paragraphs. 1-7, characterized in that the polarizer arm is made in the form of a combination of linear polarizers and non-polarizing beam splitters, arranged relative to each other with the organization of four different optical channels, sequentially directed to the studied the sample, in this case, in the first optical channel of the polarizer arm, the collimated beam of light rays sequentially passes the first linear polarizer and the first and second non-polarizing beam splitters, after which it is sent to the sample under study, in the second optical channel the collimated beam of light rays sequentially passes the second linear polarizer, is reflected from the first a non-polarizing beam splitter, a second non-polarizing beam splitter passes, after which it is sent to the sample under study, in the third optical Ohm channel, the collimated beam of light rays passes through the third linear polarizer sequentially, the third non-polarizing beam splitter passes through, is reflected from the second non-polarizing beam splitter, and then it is directed to the sample under study, in the fourth optical channel the collimated beam of light rays passes through the fourth linear polarizer, the compensator, is successively reflected from the third and a second non-polarizing beam splitter, after which it is sent to the test sample, in addition, each and Of the four optical channels, it is equipped with an optical shutter overlapping it, located between the light source and the non-polarizing beam splitter of this optical channel.

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