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CN113739919A - Reflection type near-field optical polarization spectrometer - Google Patents

Reflection type near-field optical polarization spectrometer Download PDF

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CN113739919A
CN113739919A CN202010464915.3A CN202010464915A CN113739919A CN 113739919 A CN113739919 A CN 113739919A CN 202010464915 A CN202010464915 A CN 202010464915A CN 113739919 A CN113739919 A CN 113739919A
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CN113739919B (en
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刘涛
张凌云
王玥
陈楠
李磊
王博雨
冷兴龙
李楠
赵丽莉
景玉鹏
刘键
何萌
夏洋
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/447—Polarisation spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
    • G01B11/0641—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating with measurement of polarization
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    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/21—Polarisation-affecting properties
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    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/21—Polarisation-affecting properties
    • G01N21/211—Ellipsometry
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    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/21—Polarisation-affecting properties
    • G01N21/211—Ellipsometry
    • G01N2021/213—Spectrometric ellipsometry

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Abstract

一种反射式近场光学偏振光谱仪，包括：入射光发生模块、探针扫描显微模块和出射光检测模块，其中，探测光在入射光发生模块中经过整形和调制，发出不同偏振状态的探测光，入射光束聚焦至探针扫描显微模块的探针针尖上，探测光与探针针尖和样品表面构成的微纳空间结构相互作用，偏振状态发生变化，然后该光束的反射光/散射光由出射光检测模块收集后进行整形聚焦。本发明能够实现纳米级的超高横向空间分辨率，满足半导体关键器件对纳米级尺寸精确测量需求；可避免因使用透镜元件产生色差而造成的离焦问题；同时可通过保偏结构保证探测光经调制后的偏振态在经反射元件反射后到达探针时保持不变；并且具有与样品非接触、对样品无破坏性等优点。

Figure 202010464915

A reflective near-field optical polarization spectrometer, comprising: an incident light generating module, a probe scanning microscope module, and an outgoing light detection module, wherein the detection light is shaped and modulated in the incident light generation module to emit detections of different polarization states Light, the incident beam is focused on the probe tip of the probe scanning microscope module, the probe light interacts with the micro-nano space structure formed by the probe tip and the sample surface, the polarization state changes, and then the reflected light/scattered light of the beam After being collected by the outgoing light detection module, it is shaped and focused. The invention can realize ultra-high lateral spatial resolution of nanometer level, and meet the requirements for precise measurement of nanometer-level dimensions of key semiconductor devices; it can avoid the problem of defocusing caused by chromatic aberration caused by the use of lens elements; The modulated polarization state remains unchanged when it reaches the probe after being reflected by the reflective element; and it has the advantages of non-contact with the sample and no damage to the sample.

Figure 202010464915

Description

Reflection type near-field optical polarization spectrometer
Technical Field
The invention relates to the technical field of testing of spectral instruments, in particular to a reflection type near-field optical polarization spectrometer.
Background
With the development of semiconductor manufacturing processes, the critical dimension of semiconductor devices is continuously reduced, 5nm nodes are realized, and the requirements of the semiconductor manufacturing industry on the lateral spatial resolution of device dimension measurement are higher and higher. The measured parameter of the traditional polarization spectrometer is the average value of the light spots formed by the detection light on the surface of the measured sample. Although the longitudinal resolution of the traditional polarization spectrometer depends on the phase measurement sensitivity of the instrument and can generally realize angstrom level, the transverse resolution of the polarization spectrometer is limited by the size of a light spot, the diameter of the light spot size of the micro-light spot type polarization spectrometer is between 25 and 50 micrometers, the spatial resolution of the imaging type polarization spectrometer can mostly only reach 5 micrometer levels, even if the detection wavelength develops towards the deep ultraviolet band, because the polarization spectrum measurement requires a smaller numerical aperture, the transverse resolution of the traditional polarization spectrometer can realize ten times of diffraction limit at most, and the transverse spatial resolution below the micrometer levels is difficult to reach. For a sample to be measured with a fine structure, the averaged measurement may cause a large error, and the accuracy of the measurement result may be reduced. The near-field optical microscopy breaks through the limit of the traditional optical diffraction limit, can reach the ultrahigh resolution of one tenth of wavelength, and realizes the optical measurement and characterization of nanometer scale; the scattering type near-field probe scanning microscope can realize the transverse spatial resolution of 1-2 nm in a visible light wave band, and has the advantages of non-contact measurement and no damage to a sample.
When a light source in the polarization spectrometer uses a wide-spectrum light source, shaping and focusing of a detection light beam by using a lens element in the polarization spectrometer causes different focusing positions of light with different wavelengths due to chromatic aberration, and under the condition, the wide-spectrum light beam can cause inaccurate measurement results due to chromatic dispersion when being focused on a probe tip; even with achromatic lenses, it is difficult to have good results over the entire spectrum.
Disclosure of Invention
It is therefore an objective of the claimed invention to provide a reflective near-field optical polarization spectrometer, which is aimed at solving at least one of the above problems.
To achieve the above object, as an aspect of the present invention, there is provided a reflective near-field optical polarization spectrometer comprising: the device comprises an incident light generation module, a probe scanning microscopic module and an emergent light detection module, wherein the incident light generation module is used for shaping and modulating the detecting light to emit detecting light with different polarization states, the incident light beam is focused on a probe needle point of the probe scanning microscopic module, the detecting light interacts with a micro-nano space structure formed by the probe needle point and the surface of a sample, the polarization state changes, then reflected light/scattered light of the light beam is collected by the emergent light detection module and then shaped and focused, the change information generated by the polarization state in the interaction is obtained by demodulating the polarization state of the detecting light, and the information is subjected to inversion calculation, so that the optical constant and the related information of the thickness of the measured sample can be obtained.
Based on the technical scheme, the reflection type near-field optical polarization spectrometer disclosed by the invention at least has a part of the following beneficial effects compared with the prior art:
by adopting the reflective near-field optical polarization spectrometer, the ultrahigh transverse spatial resolution of a nanometer level can be realized, the requirement of a semiconductor key device on accurate measurement of the nanometer level dimension can be met, the problem that light with different wavelengths is different in focusing position due to chromatic aberration caused by using a lens element can be avoided, meanwhile, the polarization state of the detection light modulated by the polarization device and the compensation device can be kept unchanged when the detection light reaches the probe after being reflected by the reflecting element through the polarization maintaining structure, and the reflective near-field optical polarization spectrometer has the advantages of being non-contact with a sample, non-destructive to the sample and the like.
Drawings
FIG. 1 is a schematic diagram showing a reflective near-field optical polarization spectrometer according to a first embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating a reflective near-field optical polarization spectrometer according to a second embodiment of the present invention.
In the above figures, the reference numerals have the following meanings:
1. a light source; 2. a first curved reflective element; 3. a polarization generating device;
4. a first phase compensation device; 5. a second curved reflective element; 6. a probe scanning microscopic module;
7. a sample; 8. a third curved reflective element; 9. a second phase compensation device;
10. a polarization detection device; 11. a fourth curved reflective element; 12. a detection device;
13. an electric platform module; 14. a phase-locked amplifier; 15. a beam splitting element;
16. a planar reflective element.
Detailed Description
The invention discloses a reflection type near-field optical polarization spectrometer, which comprises: the device comprises an incident light generation module, a probe scanning microscopic module and an emergent light detection module. The incident light generation module comprises at least one light source, at least one polarization generation device and at least two curved surface reflection elements; the emergent light detection module comprises at least one detector, at least one polarization detection device and at least two curved surface reflecting elements. The incident light generation module emits detection light with different polarization states, the detection light is incident on a probe needle point of the probe scanning microscopic module, the detection light interacts with a micro-nano space structure formed by the probe needle point and the surface of a sample, the polarization state changes, then scattered light/transmitted light/reflected light of the light beam is collected by the emergent light detection module, change information generated by the polarization state in the interaction is obtained through demodulation of the polarization state of the emergent light, and information such as an optical constant, film thickness and the like of the sample to be detected can be obtained through inversion calculation of the information.
The reflective near-field optical polarization spectrometer of the invention utilizes the curved surface reflecting element to shape and focus the light beam and change the propagation direction of the light beam. The reflecting element can be coated to realize high reflectivity in a wider spectral band, the problem of chromatic aberration is avoided, and the problem that light with different wavelengths is different in focusing position due to chromatic aberration caused by the use of a lens element can be avoided. And a polarization maintaining structure is used for ensuring that the polarization state of the probe light modulated by the polarizing device and the compensating device is kept unchanged when the probe light reaches the probe after being reflected by the reflecting element. The near-field optical microscopy technology is combined with a polarization spectrometer, the 10 nm-level transverse spatial resolution can be realized, and the method has great significance for realizing the accurate measurement of the dimensions of semiconductor key devices.
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
The probe scanning microscope module generally comprises a light source (monochromatic or broad spectrum), a knock-mode atomic force microscope, a detection light collection module, a sample stage and a photoelectric detector. The core component of the probe scanning microscopic module is a probe, and when the material morphology is obtained, the local optical property (about 10 nm) with sub-wavelength resolution can be obtained by utilizing the electric field enhancement and the electric field local area generated by the 'lightning rod effect' of the probe tip. Unlike traditional optical detection, which only involves light and material in interaction, the probe in the probe scanning microscopic module has strong electromagnetic interaction with the material and affects the signal light focused on the probe. Thus, it is possible to provideA probe-sample coupling model must be constructed to reduce the near-field interaction, with the simplest model being a dipole model. In this model the probe polarisation induced by the incident optical electric field is replaced by a dipole, the tip dipole in turn inducing polarisation of the material, which in turn affects the susceptibility of the tip, and so on iteratively. Electric field E scattered by the tipsc＝σnf·Einc∝αeff·Einc，σnfIs the near field scattering coefficient, alphaeffIs to take into account the effective polarizability of the probe after interaction with the material, EincIs the incident electric field. When incident electric field EincPerpendicular to the sample surface, the effective polarizability is expressed as:
Figure RE-GDA0002561874930000041
when incident electric field EincParallel to the sample surface, the effective polarizability is expressed as:
Figure RE-GDA0002561874930000042
in both equations, r is the probe tip radius and d is the tip-sample spacing. Alpha is alphaeff⊥And alphaeff||The molecule in the expression (1) represents the polarizability of the probe, wherein
Figure RE-GDA0002561874930000043
Is an inherent property of the probe; the denominator is the interaction of the probe and the sample, wherein
Figure RE-GDA0002561874930000044
It is determined only by the dielectric coefficient of the material and represents the "near field reflection coefficient" of the sample to the probe dipole. The dielectric properties of the material can thus be deduced from the scattered electric field. Other models that describe near-field interactions such as monopole models and "lightning rod" models can also accurately reverse the dielectric constant of the material.
The reflectance of the sample can be expressed by jones matrix as:
Figure RE-GDA0002561874930000045
we refer to the state of polarization with the polarization direction parallel to the plane of incidence as p-polarization and the state of polarization with the polarization direction perpendicular to the plane of incidence as s-polarization. If the incident polarization state of the probe beam is p polarization and the polarization state of the emergent beam after the interaction with the probe is s polarization, the absolute reflectivity is rpsIt is shown that,
Figure RE-GDA0002561874930000046
the same principle is thatpp、rspAnd rss. The Jones matrix elements vary with the azimuth angle of the sample surface probe beam incident plane and the incident angle within the incident plane. Typically, the uniform film is composed of a non-birefringent material, and r is the angle of incidence at any azimuth angleps＝rsp＝0。
(1) Absolute reflectance measurements. Near-field optical polarization spectrometer capable of measuring r in sample Jones matrixpp、rps、rspAnd rss. To measure the reflectance of a sample, the following should be done:
a. measuring dark value I of spectrometerd；
b. Measuring the reflectivity of a reference sample, e.g. a bare silicon wafer, and obtaining a spectral value Ir；
c. Measuring the sample and obtaining a value I;
thus, the reflectance of the sample to be measured is:
Figure RE-GDA0002561874930000051
where R (ref) is the absolute reflectivity of the reference sample. R (ref) can be obtained from other measurements or calculated from characteristics of a reference sample, typically the reflectivity of bare silicon.
As shown in fig. 1, actual measurementThe time-measuring adjustment polarization generating device 2 and the polarization detecting device 6 respectively correspond to the polarization direction p corresponding to the polarization state in the sample incidence plane&p、p&s、s&p and s&s the absolute reflectance of the sample in four cases, i.e. rpp、rps、rspAnd rss. When r isps＝rspWhen r is 0, only the polarization generating device 2 or the polarization detecting device 6 is required to obtain r by measurementppAnd rss。
(2) Elliptical polarization measurement method: as shown in FIG. 1, the near-field optical polarization spectrometer of the present invention is equivalent to an ellipsometer with a structure of a polarization generating device 2-a sample 4-a polarization detecting device 6 (PSA). The polarization detection device 6 can be fixed by rotating the polarization generation device 2, or the polarization detection device 6 fixes the polarization generation device 2, or the polarization generation device 2 and the polarization detection device 6 rotate according to a certain frequency ratio, Fourier coefficients are obtained by calculation, and then a measurement sample is calculated by comparison with a numerical simulation result and numerical regression. The principle formula illustrated, below, is only briefly described in the case of a rotating polarization detection device 6 (RAE):
Lout＝AR(A)JsR(-P)PLin，
namely:
Figure RE-GDA0002561874930000052
it can be derived that:
EA＝(ρpp+ρpstanP)cos(A)+(ρsp+tanP)sinA，
detected light intensity:
I＝|EA|2＝I0(1+αcos2A+βsin2A)。
wherein alpha and beta are Fourier coefficients of the light intensity I, and experimental values can be obtained through calculation. Corresponding to the expression as
Figure RE-GDA0002561874930000061
Figure RE-GDA0002561874930000062
When r isps＝rsp0, i.e. pps＝ρspWhen 0, the calculation formula of the common isotropic film sample can be obtained:
Figure RE-GDA0002561874930000063
Figure RE-GDA0002561874930000064
wherein tan ψ is rpp、rssAmplitude of the ratio, Δ being rpp、rssThe phase difference of the ratio.
By means of an elliptical polarization measurement method, spectral lines of alpha and beta Fourier coefficients can be calculated, and the spectral lines contain elements rho after being normalized with a Jones matrixpp、ρps、ρspAre directly related. By calculating spectral lines and curve regression fits through mathematical models, the optical constants of the sample material, the film thickness, and/or the Critical Dimension (CD) or three-dimensional topography of the sample used to analyze the periodic structure can be calculated.
In general, the spot size focused on the probe tip is about 100 μm2And the probe tip has a size of 10-30 nm. Near field focusing efficiency of ηN＝PN/PIIn which P isIIs the incident light power, PNIs the power converted into the local field at the probe tip, and is reported to indicate eta, respectivelyNThe values of (a) are only 0.0003 and 0.000001. Therefore, most of the scattered light is background signal from the probe arm and the sample surface, so subtracting the background to extract the near-field signal is the key to the application of the probe scanning microscopy module. A lock-in amplifier is an amplifier that can extract a signal at a known carrier frequency from an extreme noise environment. Operation dependence of lock-in amplifierIn the orthogonality of the sine functions, when a frequency is f1Multiplication of a function by another frequency unequal to f1Has a frequency of f2The result of their integration over time over the period of the two functions is 0. And if f1And f2Equal and in phase, the magnitude of the integral of the product of the two functions is equal to half of their amplitude product.
The probe scanning microscopic module adopting the knocking mode can generate a modulation signal with stable frequency in a frequency range of 10k Hz-50k Hz in a resonant mode, the modulation signal is used as a reference signal and input into the phase-locked amplifier, and the detection device converts the collected detection light into an input signal and inputs the input signal into the phase-locked amplifier. The lock-in amplifier multiplies the input signal by the reference signal and then integrates over a specified time period (typically a few milliseconds to a few seconds) to produce a dc signal, while other signal components at frequencies different from the reference signal will decay to 0. This is because the phase-locked amplifier can also be used as a phase-sensitive detector because the output phase signal is attenuated at the same position as the frequency of the reference signal due to the orthogonality of the sine function and the cosine function of the same frequency.
For an input signal Uin(t), the output signal of the dc can be calculated for an analog lock-in amplifier as:
Figure RE-GDA0002561874930000071
wherein the phase position
Figure RE-GDA0002561874930000072
Is a phase factor that can be adjusted by the lock-in amplifier and is typically set to 0. If the averaging time is long enough, many times larger than the period of the signal, all unwanted noise is suppressed and the output becomes:
Figure RE-GDA0002561874930000073
in the formula VsigIs the input amplitude of the signal at the reference frequency and theta is the signal difference between the reference signal and the input signal.
Many applications of lock-in amplifiers only require amplitude considerations and not phase considerations, such as single phase lock-in amplifiers, which typically require manual adjustment so that the phase difference becomes 0. A more powerful dual-phase lock-in amplifier comprises another multiplier and an integrator, and phase signals of two channels have a phase difference of 90 degrees. The lock-in amplifier has two outputs, i.e. the in-phase component X ═ Vsigcos θ and quadrature component Y ═ Vsigsin θ. At the same time, the amplitude and phase information of the input signal can be calculated:
Figure RE-GDA0002561874930000074
Figure RE-GDA0002561874930000075
next, a near-field optical polarization spectrometer according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
First embodiment
A reflective near-field optical polarization spectrometer according to a first embodiment of the present invention is shown in fig. 1. As shown in fig. 1, the reflective near-field optical polarization spectrometer includes an incident light generation module (a light source 1, a first curved surface reflection element 2, a polarization generation device 3, a first phase compensation device 4, and a second curved surface reflection element 5), a probe scanning microscopy module 6, a sample 7, and an emergent light detection module (a third curved surface reflection element 8, a second phase compensation device 9, a polarization detection device 10, a fourth curved surface reflection element 11, and a detection device 12). The polarization generating device 3, the first phase compensating device 4, the second phase compensating device 9 and the polarization detecting device 10 are used or not according to actual needs, and structural forms such as PSA (polarization generating device 3-sample 7-polarization detecting device 10), PSCA (polarization generating device 3-sample 7-second phase compensating device 9-polarization detecting device 10), PCSA (polarization generating device 3-first phase compensating device 4-sample 7-polarization detecting device 10), PCSCA (polarization generating device 3-first phase compensating device 4-sample 7-second phase compensating device 9-polarization detecting device 10) and the like can be formed; the polarization generating device 3, the first phase compensating device 4, the second phase compensating device 9 and the polarization detecting device 10 can also determine whether to rotate according to actual needs, and the structure forms of R.P. (rotating the polarization generating device 3), R.A. (rotating the polarization detecting device 10), R.C. (rotating the first phase compensating device 4 or the second phase compensating device 9), multi-device rotation according to a certain frequency ratio and the like are formed.
The light source 1 is arranged at the focal position of the first curved surface reflecting element 2, and light beams emitted by the light source 1 are emitted as parallel light beams after being incident on the first curved surface reflecting element 2. The parallel light beams are modulated into detection light with different polarization states by a polarization generating device 3 and a first phase compensation device 4, the detection light is focused on a probe tip of a probe scanning microscopic module 6 through a second curved surface reflecting element 5, the probe tip and a sample 7 to be detected form a micro-nano space structure, the detection light interacts with the micro-nano space structure, the polarization state changes, then light beams scattered to a certain direction by a probe are collected by a third curved surface reflecting element 8 and are emitted into parallel light beams, and the parallel light beams are demodulated by a second phase compensation device 9 and a polarization detection device 10 and then are focused on a detection device 12 through a fourth curved surface reflecting element 11.
The electric platform module 13 can adjust X, Y, Z, Theta for carrying the sample 7, and can control the movement of the electric platform module 13 through the program instruction to realize X, Y, Theta-direction two-dimensional scanning, thereby acquiring the related information of the whole measured sample surface.
The probe tip vibrates up and down at a certain modulation frequency, the vibration signal is used as a reference signal and input into the lock-in amplifier 14, the detection device 12 collects a detection light signal and converts the detection light signal into an input signal and inputs into the lock-in amplifier 14, the lock-in amplifier 14 demodulates the vibration frequency of the probe tip to obtain the change information generated by the polarization state in the interaction, and then the information is subjected to inversion calculation to obtain the information such as the optical constant, the film thickness and the like of the detected sample 7.
The first curved surface reflecting element 2 and the second curved surface reflecting element 5 have the same reflecting material and coating structure, and meet the conditions that the incident angle of the main beam is the same and is between 10 degrees and 45 degrees and two incident planes are perpendicular to each other, so that the polarization state of the detection light modulated by the polarization generating device 3 and the first phase compensation device 4 can be kept unchanged when the detection light reaches the probe after being reflected by the reflecting elements. Similarly to the third curved reflective element 8 and the fourth curved reflective element 11. Specific principle description reference may be made to the patent "li national light, liu billo, adig keni europe, maje, seas, oblique incidence broadband polarization spectrometer and optical measurement system [ P ] CN102297721A,2011-12-28 ].
The spectrum of the light source 1 may be in the vacuum ultraviolet to terahertz range. The light source 1 may be a broad spectrum light source such as a xenon lamp, a deuterium lamp, a tungsten lamp, a halogen lamp, a mercury lamp, a composite broadband light source including a deuterium lamp and a tungsten lamp, a composite broadband light source including a tungsten lamp and a halogen lamp, a composite broadband light source including a mercury lamp and a xenon lamp, a composite broadband light source including a deuterium tungsten halogen, or the like; or a single-wavelength light source with adjustable wavelength, such as a helium-neon laser, a carbon dioxide laser, a solid laser, a semiconductor laser, a fiber laser and the like.
The light beam is emitted by the incident light generation module and hits on the probe tip of the probe scanning microscopic module 6, and the included angle between the incident light beam and the probe is larger than 30 degrees and smaller than 90 degrees. The emergent light detection module can collect scattered light or reflected light emitted after passing through the probe tip, the collected emergent angle can be in the range of 0-180 degrees, and the azimuth angle can be in the range of 0-360 degrees.
The polarization generating device 3 and the polarization detecting device 10 comprise at least one polarizing element, which may be a thin film polarizer, a granthon prism polarizer, a rochon prism polarizer, a grantaylor prism polarizer, or a grantre laser polarizer, etc.
The first phase compensation device 4 and the second phase compensation device 9 comprise at least one phase compensation element which may be a half wave plate, a quarter wave plate, a soliry-babinet compensator, a photoelastic modulator, an automatic phase retarder, etc.
The first curved surface reflecting element 2, the second curved surface reflecting element 5, the third curved surface reflecting element 8 and the fourth curved surface reflecting element 11 can be off-axis paraboloid reflecting elements or toroidal reflecting elements and the like.
The detector 12 may be a Charge Coupled Device (CCD), a deep ultraviolet photodiode, an indium gallium arsenic photodiode, a mercury cadmium telluride infrared detector, a quadrant photodiode, a photodiode array (PDA) spectrometer, or the like.
The reflection near-field optical polarization spectrometer may further include at least one diaphragm, located between the polarization generating device 3 and the polarization detecting device 10, for preventing e light generated after passing through the polarization generating device 3 from being incident to the surface of the sample or preventing reflected light thereof from being incident to the polarization detecting device 10 after being reflected.
The reflection type near-field optical polarization spectrometer can further comprise an analysis unit, and the analysis unit is used for calculating information such as optical constants, film thickness and anisotropic characteristics of a measured sample.
Second embodiment
A reflective near-field optical polarization spectrometer according to a second embodiment of the present invention is shown in fig. 2. As shown in fig. 2, the reflective near-field optical polarization spectrometer includes an incident light generation module (a light source 1, a first curved surface reflection element 2, a polarization generation device 3, a first phase compensation device 4, and a second curved surface reflection element 5), a probe scanning microscopy module 6, a sample 7, and an emergent light detection module (a second curved surface reflection element 5, a beam splitting element 15, a plane reflection element 16, a second phase compensation device 9, a polarization detection device 10, a fourth curved surface reflection element 11, and a detection device 12). The polarization generating device 3, the first phase compensating device 4, the second phase compensating device 9 and the polarization detecting device 10 are used or not according to actual needs, and structural forms such as PSA (polarization generating device 3-sample 7-polarization detecting device 10), PSCA (polarization generating device 3-sample 7-second phase compensating device 9-polarization detecting device 10), PCSA (polarization generating device 3-first phase compensating device 4-sample 7-polarization detecting device 10), PCSCA (polarization generating device 3-first phase compensating device 4-sample 7-second phase compensating device 9-polarization detecting device 10) and the like can be formed; the polarization generating device 3, the first phase compensating device 4, the second phase compensating device 9 and the polarization detecting device 10 can also determine whether to rotate according to actual needs, and the structure forms of R.P. (rotating the polarization generating device 3), R.A. (rotating the polarization detecting device 10), R.C. (rotating the first phase compensating device 4 or the second phase compensating device 9), multi-device rotation according to a certain frequency ratio and the like are formed.
The light source 1 is arranged at the focal position of the first curved surface reflecting element 2, and light beams emitted by the light source 1 are emitted as parallel light beams after being incident on the first curved surface reflecting element 2. The parallel light beams are modulated into detection light with different polarization states by the polarization generating device 3 and the first phase compensation device 4, the detection light penetrates through the beam splitting element 15, and is focused onto a probe needle point of the probe scanning microscopic module 6 by the second curved surface reflection element 5, the detection light interacts with a micro-nano space structure formed by the probe needle point and a detected sample 7, the polarization state changes, then light beams returning along the original incident direction after being scattered by the probe are collected by the second curved surface reflection element 5 and are emitted into parallel light beams, the parallel light beams are reflected by the beam splitting element 15 and are reflected by the plane reflection element 16, and the parallel light beams are focused onto the detection device 12 by the fourth curved surface reflection element 11 after being demodulated by the second phase compensation device 9 and the polarization detection device 10.
The electric platform module 13 can adjust X, Y, Z, Theta for carrying the sample 7, and can control the movement of the electric platform module 13 through the program instruction to realize X, Y, Theta-direction two-dimensional scanning, thereby acquiring the related information of the whole measured sample surface.
The probe tip vibrates up and down at a certain modulation frequency, the vibration signal is used as a reference signal and input into the lock-in amplifier 14, the detection device 12 collects a detection light signal and converts the detection light signal into an input signal and inputs into the lock-in amplifier 14, the lock-in amplifier 14 demodulates the vibration frequency of the probe tip to obtain the change information generated by the polarization state in the interaction, and then the information is subjected to inversion calculation to obtain the information such as the optical constant, the film thickness and the like of the detected sample 7.
The same as the first embodiment, the first curved surface reflective element 2 and the second curved surface reflective element 5 have the same reflective material and coating structure, and satisfy the condition that the incident angle of the main beam is the same and is between 10 ° and 45 ° and the two incident planes are perpendicular to each other, which can ensure that the polarization state of the probe light modulated by the polarization generating device 3 and the first phase compensating device 4 remains unchanged when the probe light reaches the probe after being reflected by the reflective element. Similarly to the second curved reflective element 5, the beam splitting element 15, the reflective element 16 and the fourth curved reflective element 11. Specific principle description reference may be made to the patents "li national light, liu billo, adig keni europe, ma iron, severe seas, oblique incidence broadband polarization spectrometer and optical measurement system [ P ] CN102297721A,2011-12-28 ].
The spectrum of the light source 1 may be in the vacuum ultraviolet to terahertz range. The light source 1 may be a broad spectrum light source such as a xenon lamp, a deuterium lamp, a tungsten lamp, a halogen lamp, a mercury lamp, a composite broadband light source including a deuterium lamp and a tungsten lamp, a composite broadband light source including a tungsten lamp and a halogen lamp, a composite broadband light source including a mercury lamp and a xenon lamp, a composite broadband light source including a deuterium tungsten halogen, or the like; or a single-wavelength light source with adjustable wavelength, such as a helium-neon laser, a carbon dioxide laser, a solid laser, a semiconductor laser, a fiber laser and the like.
The light beam is emitted by the incident light generation module and hits on the probe tip of the probe scanning microscopic module 6, and the included angle between the incident light beam and the probe is larger than 30 degrees and smaller than 90 degrees.
The polarization generating device 3 and the polarization detecting device 10 comprise at least one polarizing element, which may be a thin film polarizer, a granthon prism polarizer, a rochon prism polarizer, a grantaylor prism polarizer, or a grantre laser polarizer, etc.
The first phase compensation device 4 and the second phase compensation device 9 comprise at least one phase compensation element which may be a half wave plate, a quarter wave plate, a soliry-babinet compensator, a photoelastic modulator, an automatic phase retarder, etc.
The first curved surface reflecting element 2, the second curved surface reflecting element 5 and the fourth curved surface reflecting element 11 can be off-axis paraboloid reflecting elements or toroidal reflecting elements, etc.
The beam splitting element 15 may be a plate beam splitter, a cube beam splitter, a pellicle beam splitter, or the like.
The detector 12 may be a Charge Coupled Device (CCD), a deep ultraviolet photodiode, an indium gallium arsenic photodiode, a mercury cadmium telluride infrared detector, a quadrant photodiode, a photodiode array (PDA) spectrometer, or the like.
The near-field optical polarization spectrometer may further include at least one diaphragm, located between the polarization generating device 3 and the polarization detecting device 10, for preventing e light generated after passing through the polarization generating device 3 from being incident on the surface of the sample or reflected light thereof from being incident on the polarization detecting device 10.
The near-field optical polarization spectrometer can further comprise an analysis unit, and the analysis unit is used for calculating information such as optical constants, film thickness and anisotropic characteristics of a measured sample.
The invention combines the polarization spectrometer technology with the near-field optical microscopy technology, utilizes the curved surface reflecting element, invents a reflective near-field optical polarization spectrometer, can break through the optical diffraction limit limiting the resolution ratio of the traditional polarization spectrometer, realizes the non-contact and nondestructive accurate measurement of the nanometer scale of semiconductor key devices, avoids the problem that light with different wavelengths is out of focus due to chromatic aberration caused by using a lens element, and ensures that the polarization state of the detection light modulated by the polarization device and the compensating device is kept unchanged when the detection light reaches the probe after being reflected by the reflecting element through the polarization maintaining structure.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A reflective near-field optical polarization spectrometer, comprising: the device comprises an incident light generation module, a probe scanning microscopic module and an emergent light detection module, wherein the incident light generation module is used for shaping and modulating the detecting light to emit detecting light with different polarization states, the incident light beam is focused on a probe needle point of the probe scanning microscopic module, the detecting light interacts with a micro-nano space structure formed by the probe needle point and the surface of a sample, the polarization state changes, then reflected light/scattered light of the light beam is collected by the emergent light detection module and then shaped and focused, the change information generated by the polarization state in the interaction is obtained by demodulating the polarization state of the detecting light, and the information is subjected to inversion calculation, so that the optical constant and the related information of the thickness of the measured sample can be obtained.
2. The reflective near-field optical polarization spectrometer of claim 1, wherein the incident light generating module comprises at least one light source, at least one polarization generator, at least two curved reflective elements, and further comprising at least one phase compensator;
the emergent light detection module comprises at least one detector, at least one polarization detector, at least two curved surface reflecting elements and at least one phase compensator;
the two curved surface reflecting elements have the same reflecting material and coating structure and meet the conditions that the incident angle of the main light beam is the same and is between 10 degrees and 45 degrees and the two incident planes are perpendicular to each other, so that the polarization characteristic of the detection light is ensured to be unchanged.
3. The reflective near-field optical polarization spectrometer of claim 1, further comprising at least one planar reflective element, at least one beam splitting element, at least one lock-in amplifier, and further comprising at least one adjustable load-bearing platform module for bearing a sample under test; the beam splitting element is a flat plate beam splitter, a cube beam splitter or a film beam splitter.
4. The reflective near-field optical polarization spectrometer of claim 1, further comprising at least one stop, located between the polarization generating device in the incident light generating module and the polarization detecting device in the outgoing light detecting module, for preventing e light generated after passing through the polarization generating device in the incident light generating module from being incident on the surface of the sample or reflected light thereof from being incident on the polarization detecting device in the outgoing light detecting module.
5. The reflective near-field optical polarization spectrometer of claim 1, further comprising an analysis unit for calculating optical constants, film thickness and anisotropy characteristic information of the sample under test.
6. The reflective near-field optical polarization spectrometer of claim 1, wherein the incident light beam and the probe have an angle of more than 30 ° and less than 90 °, the emergent light collected by the emergent light detection module has an emergent angle in the range of 0-180 ° and an azimuth angle in the range of 0-360 °.
7. The reflective near-field optical polarization spectrometer of claim 2, wherein the light source has a spectrum in the vacuum ultraviolet to terahertz range, and the light source is a broad-spectrum light source comprising a xenon lamp, a deuterium lamp, a tungsten lamp, a halogen lamp, a mercury lamp, a composite broadband light source comprising a deuterium lamp and a tungsten lamp, a composite broadband light source comprising a tungsten lamp and a halogen lamp, a composite broadband light source comprising a mercury lamp and a xenon lamp, or a composite broadband light source comprising deuterium tungsten halogen; the light source can also be a single-wavelength light source or a single-wavelength light source with adjustable wavelength, and comprises a helium-neon laser, a carbon dioxide laser, a solid laser, a semiconductor laser and a fiber laser.
8. The reflective near-field optical polarization spectrometer of claim 2, wherein the polarization generator and the polarization detector are thin film polarizers, grand Thompson prism polarizers, Rochon prism polarizers, Glan Taylor prism polarizers, or Glan laser polarizers;
the phase compensator is a half wave plate, a quarter wave plate, a Sorrier-Babinet compensator, a photoelastic modulator or an automatic phase retarder.
9. The reflective near-field optical polarization spectrometer of claim 2, wherein the curved reflective elements are off-axis parabolic reflective elements and toroidal reflective elements.
10. The reflective near-field optical polarization spectrometer of claim 2, wherein the detector is a charge coupled device, a deep ultraviolet photodiode, an indium gallium arsenic photodiode, a mercury cadmium telluride infrared detector, a quadrant photodiode, or a photodiode array spectrometer.
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