CN103196658B - Method and device for measuring phase delay spectral characteristic of wave plate - Google Patents

Abstract

The invention discloses a method and a device for measuring a phase delay spectral characteristic of a wave plate, comprising a broadband light source; and continuously emergent light is received after passing through a multi-wavelength photoelectric detector through a collimator, a polarizer, two wave plates to be detected, a polarization analyzer and an optical splitter respectively, wherein the two wave plates to be detected are connected with a motor, data received by the multi-wavelength photoelectric detector are uploaded to a data acquisition card which transmits the data to a computer which is connected with the motor. The method disclosed by the invention can automatically measure the phase delay spectral characteristics of the two wave plates to be detected within a wide spectral range, not only can be used for measuring the phase delay spectral characteristics of two rotary wave plates in a rotating double-compensator type broad-spectrum ellipsometer so as to eliminate system errors caused by inaccurate calibration, but also can be used for directly calibrating the phase delay spectral characteristics of two unknown wave plates in practical production and research work, and besides, the measurement result is not influenced by the light source and the spectral characteristic of a detector.

Description

The measuring method of phase delay spectral characteristic of wave plate and device

Technical field

The invention belongs to polarization optics detection field, particularly a kind of measuring method of phase delay spectral characteristic of wave plate and device.

Background technology

Wave plate is commonly used for the transformation device of light signal polarization state in ellipsometry or optical measurement.The phase delay error of wave plate can have a huge impact measurement result.Therefore, making and using in the process of wave plate, the phase delay spectral characteristic accurately measuring wave plate is often needed.Such as in rotation double compensation device formula wide spectrum ellipsometer (PCSCA type ellipsometer), the precise calibration of two compensator C1, C2 retardations is the prerequisites realizing high-acruracy survey, and the operating wavelength range of two whirl compensators has material impact to complete machine characteristic.

As everyone knows, although whirl compensator C1 and C2 in PCSCA type ellipsometer is designed to broadband quarter wave plate, the broadband quarter wave plate of reality in considered bandwidth range, always not strict 90 ° of its phase-delay quantity, but have certain error range; For the zero-th order waveplates of magnesium fluoride compound, when spectral range is 200 ~ 1000nm, the phase-delay quantity just fluctuations within the scope of 60 ° ~ 130 ° of this wave plate.

In the Design and manufacturing process of PCSCA type ellipsometer, first the step of carrying out is needed to be exactly calibrate and self calibration compensator C1 and C2 of two wherein, the i.e. phase delay of Accurate Determining two compensators at each wavelength place, to eliminate the inaccurate systematic error brought of spectrometer receiving end calibration.The calibration mode of usual employing is as document [R.W.Collins and J.Koh, J.Opt.Soc.Am.A, 16,1997 (1999)] described in, namely the output photoelectric stream of CCD pixel is first measured, then Fourier analysis is done to it, solve wherein each fourier coefficient respectively, then apply mechanically the phase-delay quantity that certain formula tries to achieve each compensator in ellipsometer.

But the program limits (this instrument is applied in infrared band usually) by the measurement wavelength coverage of fourier transform analysis instrument used, the many and solution procedure relative complex of source of error.Other instrument (ellipsometer as commercial in other) can certainly be adopted to measure respectively two compensators rotating double compensation device formula ellipsometer, and then assemble, the greatest problem of this scheme is that the phase delay spectral property of compensator restricts by the measure spectrum scope of ellipsometer used, and process is more complicated.

Measuring the method for Phase Retardation of Wave Plate has a variety of, but the retardation of wave plate under being often only applicable to measure a certain specific monochromatic wavelength, can not measure the phase delay spectral characteristic of wave plate in multi-wavelength situation simultaneously.And some measuring methods, can but be merely able to the phase delay spectral characteristic measuring single wave plate, the phase delay spectral characteristic of two wave plates to be measured can not be measured simultaneously.

Although Chinese patent CN1743796 and CN100340838C etc. all once can read the measurement data of multi-wavelength simultaneously, the phase delay spectral characteristic of two wave plates cannot be measured simultaneously.

The method of Chinese patent CN1632501, CN201032473Y and CN102589850A etc. also needs to select single wavelength by monochromator at every turn, carry out the feature measurement of single wave plate to be measured, requiring that the occasion of ease for operation and the measuring speed measured is more limited.

Chinese patent (application number: 201110344206, patent name: broadband waveplate and realize the equal method of phase delay and Polarization Controller), the content of this patent how to utilize dispersion element spatially separated by wideband spectrum and realize in broad frequency range, obtain equal phase delay, and how to utilize this wide wave plate combined to become Polarization Controller, do not relate to the measurement problem of broadband waveplate phase delay spectral characteristic at all.

Summary of the invention

Object of the present invention is exactly that provide a kind of measuring method and device of phase delay spectral characteristic of wave plate, it belongs to non-cpntact measurement in order to solve the problem, and can automatically measure two unknown Phase Retardation of Wave Plate spectrums in wide spectral range simultaneously; Efficiently easy to use, both can be used for measuring the phase delay spectral characteristic rotating two rotating wave plates in double compensation device formula wide spectrum ellipsometer, eliminate the inaccurate systematic error brought of its calibration; Can be used for again the direct calibration of the phase-delay quantity spectral characteristic of simultaneously carrying out two unknown wave plates in actual production and research work, and measurement result is not subject to the impact of light source and detector spectrum characteristic.

To achieve these goals, the present invention adopts following technical scheme:

A kind of measurement mechanism of phase delay spectral characteristic of wave plate, comprise a wideband light source, the multi-wavelength continuous light of its outgoing is successively by after collimating apparatus, the polarizer, the first wave plate to be measured, the second wave plate to be measured, analyzer and optical splitter, through multi-wavelength photoelectric detector, data collecting card is transferred data to after reception, the data of data collecting card are transferred to computing machine, and described first wave plate to be measured and the second wave plate to be measured are arranged on the precise rotating platform of Non-follow control.

A kind of measurement mechanism of phase delay spectral characteristic of wave plate, comprise a wideband light source, the multi-wavelength continuous light of its outgoing successively by after collimating apparatus, the polarizer, the first wave plate to be measured, the second wave plate to be measured, analyzer and optical splitter, through multi-wavelength photoelectric detector; Described first wave plate to be measured and the second wave plate to be measured are all connected with same motor or are connected respectively with two motors; The data upload of described multi-wavelength photoelectric detector is in data collecting card, and data collecting card transfers data to computing machine, and computing machine connects motor.

Described light source is the continuous spectrum light source that output characteristics is stable, and the spectral range of this light source can cover the phase delay spectral characteristic scope of wave plate to be measured.

Described collimating apparatus adopts the optical fiber collimator of accurately being located by tail optical fiber and GRIN Lens, is transformed into collimated light for the light sent by wideband light source.

The described polarizer and analyzer all adopt the one in the dichroism polarizer or the birefringence polarizer.

Two described wave plates to be measured to be delay scope be zero-th order waveplates of 0 ° ~ 180 °, especially broadband zero-th order waveplates, for by the true zero-th order waveplates of crystalline material or polymeric material or compound zero-th order waveplates.

Described optical splitter can adopt the satisfactory color dispersion-type optical splitter such as Amici prism or grating, for being launched by the wavelength of multi-wavelength composite light beam, and is detected by each wavelength signals feeding multi-wavelength light electric explorer launched.

Described multi-wavelength light electric explorer is multi-wavelength photodiode array, photomultiplier tube array or CCD(Charge-coupled Device) linear array or area array sensor, be preferably CCD linear array or area array sensor, carry out data processing for the multi-wavelength light detected current signal is reached computing machine through data collecting card.

Described motor and motor driver select servomotor, p-m step motor or reaction stepping motor and corresponding driver thereof.

Described first wave plate to be measured and the second wave plate to be measured manually rotate or are rotated by driven by motor.

Described computing machine sends the rotation status of pulse signal through motor driver adjustment motor by data collecting card.

The measuring method that the measurement mechanism of phase delay spectral characteristic of wave plate adopts, mainly comprises the steps:

Step one: regulate the quick shaft direction of the first wave plate to be measured parallel with analyzer with the polarizer, the quick shaft direction of the second wave plate to be measured is vertical with the first wave plate to be measured;

Step 2: open wideband light source, the parallel beam of the continuous wavelength of outgoing successively by after collimating apparatus, the polarizer, the first and second wave plates to be measured, analyzer and optical splitter, through multi-wavelength photoelectric detector; Computing machine is by analyzing Data Control driven by motor two wave plates to be measured of data collecting card collection with same angular velocity w rotating Vortex;

Step 3: come relative to the photocurrent values collection under several absolute rotation angle of reference position by wave plate to be measured, by being obtained the phase-delay quantity δ of any af at wavelength lambda first wave plate to be measured by phase-delay quantity formula and measuring system overall performance formula ₁, the second wave plate to be measured phase-delay quantity δ ₂, and characterize the parameter η of this wavelength place measuring system overall performance, and then obtain the phase delay spectral characteristic of two wave plates to be measured;

Step 4: according to all δ in the measurement wavelength coverage of described measurement mechanism ₁, δ ₂with η data, draw corresponding δ ₁(λ), δ ₂(λ) with η (λ) curve, finally obtained curve is gone to the smoothing processing of " burr ", reduce error further.

The concrete steps of described step 3 are: wave plate to be measured is denoted as α relative to the absolute rotation angle of reference position and has α=wt, and the initial time of t=0 corresponds to α=0, every anglec of rotation step delta θ, wherein 0 < Δ θ≤π/4; Data collecting card gathers primary photoelectric current and passes to computing machine, like this when driven by motor wave plate to be measured rotates a circle, all obtains at least eight group photocurrent data at each wavelength place; Due to when stable system performance, photocurrent I(α) about the periodic function of independent variable α to be the cycle be π; So at arbitrary wavelength place, consider that all emphatically α gets several special angle, described special angle is α=k π, k π+π/4, k π+pi/2, the value of k π+3 π/4 place photocurrent I, k is integer and k>=0, is then obtained the phase-delay quantity δ of any wavelength first wave plate to be measured by phase-delay quantity formula and measuring system overall performance formula ₁, the second wave plate to be measured phase-delay quantity δ ₂, and characterize the parameter η of this wavelength place measuring system overall performance, and then obtain the phase delay spectral characteristic of two wave plates to be measured.

The phase-delay quantity δ of the in described step 3 first wave plate to be measured ₁, the second wave plate to be measured phase-delay quantity δ ₂, and characterize the parameter η of this wavelength place measuring system overall performance, as shown in following formula;

$\mathrm{\&eta;}=\frac{1}{8}\&CenterDot;\left\{\begin{array}{c}I\left(\mathrm{k\&pi;}\right)+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{4})+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})+I(\mathrm{k\&pi;}+\frac{3\mathrm{\&pi;}}{4})+\\ \sqrt{{[I\left(\mathrm{k\&pi;}\right)+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{4})+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})+I(\mathrm{k\&pi;}+\frac{3\mathrm{\&pi;}}{4})]}^2-16\&CenterDot;I\left(\mathrm{k\&pi;}\right)\&CenterDot;I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})}\end{array}\right\}$

${\mathrm{\&delta;}}_1={\cos }^{-1}[I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})/\mathrm{\&eta;}-1]$

δ ₂＝cos ^-1[I(kπ)/η-1]。

Beneficial effect of the present invention:

1) measuring method of the present invention belongs to non-cpntact measurement, the phase delay spectral characteristic of two unknown broadband waveplates can be measured simultaneously, efficiently easy to use, both can be used for the phase delay spectrum measuring two rotating wave plates in PCSCA type ellipsometer, eliminate the inaccurate systematic error brought of its calibration; Can be used for again the direct calibration of the phase-delay quantity simultaneously carrying out two unknown zero-th order waveplates in actual production and research work, and measurement result is not subject to the impact of light source and analyzer spectral characteristic.

2) when the characteristic of each probe unit and incident intensity the unknown, do not need complicated Fourier analysis and solve to demarcate two zero-th order waveplates to be measured rapidly and accurately in the phase delay spectrum waiting to investigate wave band in multi-wavelength light electric explorer simultaneously; Meanwhile, also can obtain measuring system at the parameter η waiting to investigate band operation performance, the fault investigating measuring system of the present invention is contributed to the analysis of this parameter, and analyze, the serviceability of each building block in calibration measurements system; Such as, when the spectral characteristic of wideband light source and the known and multi-wavelength light electric explorer spectral characteristic the unknown of each device loss characteristic, η (λ) characteristic can be utilized to demarcate, analyze the spectral characteristic of multi-wavelength light electric explorer.

3) measuring error that forward and reverse rotation of motor and the angular displacement of corresponding measurement elimination element orientation cause can be utilized, and the quick high accuracy utilizing error correction measure to achieve any zero-th order waveplates is further measured.

4) the present invention can measure the phase delay spectral characteristic of two zero-th order waveplates simultaneously, and relative to other measuring method, measured zero-th order waveplates phase delay ranges is wider, can be both quarter wave plate, and may not be quarter wave plate.

Accompanying drawing explanation

Fig. 1 is the device schematic diagram of phase delay spectral characteristic of wave plate measurement mechanism when adopting Electric Machine Control wave plate to be measured to rotate involved in the present invention;

Fig. 2 is the universal architecture schematic diagram of the measurement mechanism of phase delay spectral characteristic of wave plate involved in the present invention.

Wherein, 1, wideband light source, 2, collimating apparatus, 3, the polarizer, the 4, first wave plate to be measured, the 5, second wave plate to be measured, 6, analyzer, 7, optical splitter, 8, multi-wavelength light electric explorer, 9, data collecting card, 10, computing machine, 11, motor.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the invention will be further described.

Innovative point of the present invention is to adopt method for self-calibrating to achieve the real-time measurement of the phase delay spectral characteristic of two unknown wave plates simultaneously.Its embodiment is as follows:

First, the present invention needs the measurement mechanism building phase delay spectral characteristic of wave plate, then realizes object of the present invention by the technical scheme such as method for self-calibrating and forward and reverse mensuration.

As shown in Figure 1, a kind of measurement mechanism of phase delay spectral characteristic of wave plate, comprise a wideband light source 1, the multi-wavelength continuous light of its outgoing, successively by after collimating apparatus 2, the polarizer the 3, first wave plate 4, second to be measured wave plate 5 to be measured, analyzer 6 and optical splitter 7, receives through multi-wavelength light electric explorer 8; Described first wave plate 4 to be measured is connected with motor 11 with the second wave plate 5 to be measured, and the data upload that described multi-wavelength light electric explorer 8 receives is in data collecting card 9, and data collecting card 9 transfers data to computing machine 10, and computing machine 10 controls motor 11.

As shown in Figure 2, a kind of measurement mechanism of phase delay spectral characteristic of wave plate, comprise a wideband light source 1, the multi-wavelength continuous light of its outgoing is successively by after collimating apparatus 2, the polarizer the 3, first wave plate 4, second to be measured wave plate 5 to be measured, analyzer 6 and optical splitter 7, receive through multi-wavelength light electric explorer 8, described first wave plate 4 to be measured and the second wave plate 5 to be measured are arranged on the precise rotating platform of Non-follow control.The data upload that described multi-wavelength light electric explorer 8 receives is in data collecting card 9, and data collecting card 9 transfers data to computing machine 10.

Described collimating apparatus 2 can adopt optical fiber collimator of accurately being located by tail optical fiber and GRIN Lens etc., and the light that wideband light source 1 sends can be transformed into the optical device of collimated light (directional light) function by all.

Described wideband light source 1 is the continuous spectrum light source that output characteristics is stable, and the spectral range of this light source can cover the phase delay spectral range of wave plate to be measured.

The described polarizer 3 and analyzer 6 all adopt the one in the dichroism polarizer or the birefringence polarizer.

Two described wave plates to be measured to be delay scope be zero-th order waveplates of 0 ° ~ 180 °, especially broadband zero-th order waveplates, for by the true zero-th order waveplates of crystalline material or polymeric material or compound zero-th order waveplates.

Described multi-wavelength light electric explorer 8 is multi-wavelength photodiode array, photomultiplier tube array or CCD linear array or area array sensor, is preferably CCD linear array or area array sensor.

Described motor 11 selects servomotor, p-m step motor or reaction stepping motor and corresponding driver thereof.

Described optical splitter 7 can adopt the satisfactory color dispersion-type optical splitter such as Amici prism or grating, for being launched by the wavelength of multi-wavelength composite light beam, and is detected by each wavelength signals feeding detector array launched.

The rotation of two described wave plates to be measured, except employing motor 11 controls, also realizes by manual or alternate manner.

The type that described computing machine 10 and data collecting card 9 adopt and model are not limit, and mutually mate.

Described computing machine 10 is gathered by data collecting card 9, is calculated data, and sends the driver of pulse signal to two motors 11 to control motor 11 with fixed step size rotating wave plate.

Principle of work of the present invention and the course of work specific as follows:

Step one: the first wave plate 4 to be measured and the second wave plate 5 to be measured are placed among the polarizer 3 of the parallel placement in the direction that shakes and the light path of analyzer 6 successively, regulate the quick shaft direction of the first wave plate 4 to be measured parallel with analyzer 6 with the polarizer 3, the quick shaft direction of the second wave plate 5 to be measured is vertical with the first wave plate 4 to be measured;

Step 2: open wideband light source 1, the parallel beam of the continuous wavelength of outgoing, successively by after collimating apparatus 2, the polarizer 3, first wave plate 4 to be measured and the second wave plate 5 to be measured, analyzer 6 and spectroscope, receives through multi-wavelength light electric explorer 8; Computing machine 10 controls motor 11 by data collecting card 9 and drives two wave plates to be measured with same angular velocity w rotating Vortex, wave plate is denoted as α relative to the absolute rotation angle of reference position and has the initial time of α=wt(t=0 to correspond to α=0), every anglec of rotation step delta θ, data collecting card 9 gathers primary photoelectric current and passes to computing machine 10, wherein 0 < Δ θ≤π/4; Like this when motor 11 drives wave plate to be measured to rotate a circle, all can obtain at least eight group photocurrent data at each wavelength place.According to the correlation theory of polarization optics, the Stokes of the constrained input light signal in Fig. 1 or Fig. 2 shown device represents, i.e. S _inand S _outbetween meet following relation:

S _out＝M _AR(-C ₂)M _C2(δ ₂)R(C ₂)R(-C ₁)M _C1(δ ₁)R(C ₁)M _pS _in

$=\left(\begin{array}{cccc}1& 1& 0& 0\\ 1& 1& 0& 0\\ 0& 0& 0& 0\\ 0& 0& 0& 0\end{array}\right)\&CenterDot;\left(\begin{array}{cccc}1& 0& 0& 0\\ 0& \cos C_2& -\sin C_2& 0\\ 0& \sin C_2& \cos C_2& 0\\ 0& 0& 0& 1\end{array}\right)\&CenterDot;\left(\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 0& 0& \cos {\mathrm{\&delta;}}_2& \sin {\mathrm{\&delta;}}_2\\ 0& 0& -\sin {\mathrm{\&delta;}}_2& \cos {\mathrm{\&delta;}}_2\end{array}\right)\&CenterDot;\left(\begin{array}{cccc}1& 0& 0& 0\\ 0& \cos C_2& \sin C_2& 0\\ 0& -\sin C_2& \cos C_2& 0\\ 0& 0& 0& 1\end{array}\right)\&CenterDot;---\left(1\right)$

$\&CenterDot;\left(\begin{array}{cccc}1& 0& 0& 0\\ 0& \cos C_1& -\sin C_1& 0\\ 0& \sin C_1& \cos C_1& 0\\ 0& 0& 0& 1\end{array}\right)\&CenterDot;\left(\begin{array}{cccc}1& 0& 0& 0\\ 0& 1& 0& 0\\ 0& 0& \cos {\mathrm{\&delta;}}_1& \sin {\mathrm{\&delta;}}_1\\ 0& 0& -\sin {\mathrm{\&delta;}}_1& \cos {\mathrm{\&delta;}}_1\end{array}\right)\&CenterDot;\begin{array}{c}\left(\begin{array}{cccc}1& 0& 0& 0\\ 0& \cos C_1& \sin C_1& 0\\ 0& -\sin C_1& \cos C_1& 0\\ 0& 0& 0& 1\end{array}\right)\&CenterDot;\left(\begin{array}{cccc}1& 1& 0& 0\\ 1& 1& 0& 0\\ 0& 0& 0& 0\\ 0& 0& 0& 0\end{array}\right)\&CenterDot;\left(\begin{array}{c}{S}_0\\ S_1\\ S_2\\ S_3\end{array}\right)\end{array}$

In formula (1), M _p, M _a, M _c1, M _c2be respectively the Muller matrix of the polarizer 3, analyzer 6, first wave plate 4 to be measured and the second wave plate 5 to be measured; R (C ₁), R (C ₂), R (-C ₁) and R (-C ₂) be the transformation matrix of coordinates corresponding when rotating of the first wave plate 4, second to be measured wave plate 5 to be measured, δ ₁be the phase-delay quantity of the first wave plate 4 to be measured, δ ₂it is the phase-delay quantity of the second wave plate 5 to be measured.Because the direction that thoroughly shakes of the quick shaft direction of the first wave plate 4 to be measured and the polarizer 3, analyzer 6 is parallel to each other (being 0), the quick shaft direction of the second wave plate 5 to be measured is vertical with the first wave plate 4 to be measured, and both are with same angular velocity w rotating Vortex, the anglec of rotation C of the first wave plate 4 to be measured ₁=wt=α, the anglec of rotation C of the second wave plate 5 to be measured ₂=pi/2+α, (w is the angular velocity that wave plate rotates, and t represents Measuring Time, measures initial time t=0 and corresponds to α=0), then the Stokes expression formula of output optical signal can turn to further:

$S_{\mathrm{out}}=\left(\begin{array}{cccc}A& A& 0& 0\\ A& A& 0& 0\\ 0& 0& 0& 0\\ 0& 0& 0& 0\end{array}\right)\&CenterDot;\left(\begin{array}{c}{S}_0\\ S_1\\ S_2\\ S_3\end{array}\right)=B\&CenterDot;\left(\begin{array}{c}{S}_0+S_1\\ S_0+S_1\\ 0\\ 0\end{array}\right)---\left(2\right)$

Wherein B is α and δ ₁, δ ₂function, its expression is as follows:

$B(\mathrm{\&alpha;},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)=1+({\sin }^2\mathrm{\&alpha;}+{\cos }^2\mathrm{\&alpha;}\&CenterDot;\cos {\mathrm{\&delta;}}_2)\&CenterDot;({\cos }^2\mathrm{\&alpha;}+{\sin }^2\mathrm{\&alpha;}\&CenterDot;\cos {\mathrm{\&delta;}}_1)$

$+[\frac{1}{4}\&CenterDot;{\sin }^{2}2\mathrm{\&alpha;}\&CenterDot;(1-\cos {\mathrm{\&delta;}}_1)\&CenterDot;(1-\cos {\mathrm{\&delta;}}_2)]-\frac{1}{2}\sin 2\mathrm{\&alpha;}\&CenterDot;\sin {\mathrm{\&delta;}}_1\&CenterDot;\sin {\mathrm{\&delta;}}_2---\left(3\right)$

Due at any wavelength place, the output photoelectric stream of the receiving end photodetector unit of measurement mechanism of the present invention is proportional to this wavelength place output optical signal S ₀the light intensity of component, namely

$I\left(\mathrm{\&alpha;}\right)=\frac{1}{4}\&CenterDot;K\&CenterDot;(S_0+S_1)\&CenterDot;B(\mathrm{\&alpha;},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)$

$=\frac{1}{2}\&CenterDot;K\&CenterDot;{\left|E_p\right|}^2\&CenterDot;B(\mathrm{\&alpha;},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)---\left(4\right)$

$\begin{array}{cc}=\mathrm{\&eta;}\&CenterDot;B(\mathrm{\&alpha;},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)& \mathrm{\&eta;}=\frac{1}{2}\&CenterDot;K\&CenterDot;{\left|E_p\right|}^2\end{array}$

Wherein K be consider that the impact of the factor such as detective quantum efficiency introduces be less than 1 scale-up factor, E _pfor analyzer 6 shakes the light amplitude in direction thoroughly.Photocurrent I is actually α herein, δ ₁, δ ₂and the function of wavelength X, be the convenience that follow-up formula (6.a ~ 6.d) and (7.a ~ 7.c) represent, be abbreviated as I (α) herein.As can be seen here, the characteristic such as quantum efficiency of the output photoelectric stream of detector and the light intensity (this light intensity is determined by factors such as the loss of each device of measurement mechanism and the spectral characteristics of light source) of measurement mechanism receiving end light signal and detector itself is directly related.Because composition device each in the actual measurement device that the present invention relates to all exists certain insertion loss, and the spectral characteristic of this loss and actual wideband light source 1 may and uneven, so the very difficult E directly being obtained each wavelength place by simple theory calculate _pvalue (but these influence factors hardly in time pass change).And for the sensitive detection parts of reality, the spectral response curve of its output photoelectric stream is also also uneven, namely K value becomes with wavelength variations.Be example with the spectral response curve of the Hamamatsu company ultraviolet area array CCD of current international mainstream (without glass vision panel, 25 DEG C), in the wavelength coverage of 200nm-400nm, quantum efficiency changes within the scope of 35-65%.Accordingly by formula (4) known, be difficult to directly obtain a η value accurately by the index of each device.So in the process of measurement two phase delay spectral characteristic of wave plate to be measured, if the impact of η can be avoided, directly record δ ₁, δ ₂ideal; Certainly, if η can be recorded simultaneously, and come duty and the investigation fault of further analysis measuring device with it, achieve many things at one stroke especially.Study formula (4) and (5) for this reason further, following regular formula can be obtained:

B(α,δ ₁,δ ₂)＝B(kπ+α,δ ₁,δ ₂)＝I(α)/η＝I(kπ+α)/η （5）

This shows when stable system performance, at the wavelength place that any one is determined, and photocurrent I(α) and B(α, δ ₁, δ ₂) about the function (k is integer and k>=0) of independent variable α to be all cycles be π, and have following relation to occur in several special angle:

B(0,δ ₁,δ ₂)＝B(kπ,δ ₁,δ ₂)＝I(0)/η＝1+cosδ ₂（6.a）

$B(\frac{\mathrm{\&pi;}}{2},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)=B(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)=I\left(\frac{\mathrm{\&pi;}}{2}\right)/\mathrm{\&eta;}=1+\cos {\mathrm{\&delta;}}_1---(6.b)$

$B(\frac{\mathrm{\&pi;}}{4},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)=B(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{4},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)=I\left(\frac{\mathrm{\&pi;}}{4}\right)/\mathrm{\&eta;}=\frac{3}{2}+\frac{1}{2}\cos ({\mathrm{\&delta;}}_1+{\mathrm{\&delta;}}_2)---(6.c)$

$B(\frac{3\mathrm{\&pi;}}{4},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)=B(\mathrm{k\&pi;}+\frac{3\mathrm{\&pi;}}{4},{\mathrm{\&delta;}}_1,{\mathrm{\&delta;}}_2)=I\left(\frac{3\mathrm{\&pi;}}{4}\right)/\mathrm{\&eta;}=\frac{3}{2}+\frac{1}{2}\cos ({\mathrm{\&delta;}}_1-{\mathrm{\&delta;}}_2)---(6.d)$

So it is that several special angle is (as α=k π that the starting point of measuring method of the present invention is measured at arbitrary wavelength place α exactly, k π+π/4, k π+pi/2, during k π+3 π/4) photocurrent numerical value (k is integer and k>=0), then obtained the phase-delay quantity δ of this wavelength first wave plate 4 to be measured by formula (6.a ~ 6.d) ₁, the second wave plate 5 to be measured phase-delay quantity δ ₂, and characterize the parameter η of this wavelength place measuring system overall performance, as shown in formula (7.a ~ 7.c).

$\mathrm{\&eta;}=\frac{1}{8}\&CenterDot;\left\{\begin{array}{c}I\left(\mathrm{k\&pi;}\right)+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{4})+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})+I(\mathrm{k\&pi;}+\frac{3\mathrm{\&pi;}}{4})+\\ \sqrt{{[I\left(\mathrm{k\&pi;}\right)+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{4})+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})+I(\mathrm{k\&pi;}+\frac{3\mathrm{\&pi;}}{4})]}^2-16\&CenterDot;I\left(\mathrm{k\&pi;}\right)\&CenterDot;I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})}\end{array}\right\}---(7.a)$

${\mathrm{\&delta;}}_1={\cos }^{-1}[I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})/\mathrm{\&eta;}-1]---(7.b)$

δ ₂＝cos ^-1[I(kπ)/η-1] （7.c）

Step 3: the impact considering measuring error, can calculate several groups of δ at Same Wavelength place more ₁, δ ₂with η data, and get its average respectively.Finally, can according to all δ in the measurement wavelength coverage of measurement mechanism of the present invention ₁, δ ₂with η data, draw corresponding δ ₁(λ), δ ₂(λ) with η (λ) curve, certain algorithmic rule is finally set, obtained curve is gone to the smoothing processing of " burr ", reduce error further.

The specific algorithm flow process of measuring method of the present invention is exemplified below:

First, configure measuring system of the present invention according to above-mentioned measuring process, and open light source and other each building block of system.Then, after waiting various parts stable, can start to measure.Setting wave plate anglec of rotation step-length is π/4; First the I (0) at each wavelength place is read at measurement initial time; Then two wave plates to be measured are all rotated π/4, read the I (π/4) at each wavelength place; Again two wave plates to be measured are rotated π/4, read the I (pi/2) at each wavelength place; By that analogy, when wave plate rotates a circle from initial time, the I (3 π/4) at each wavelength place, I (π), I (5 π/4), I (3 pi/2), I (7 π/4) and I (2 π) can be obtained subsequently successively.For eliminating the impact of two wave plate anglec of rotation deviations to be measured etc., send drive singal to circle by wave plate is counter, obtain the I ' (7 π/4) at each wavelength place, I ' (3 pi/2), I ' (5 π/4), I ' (π), I ' (3 π/4), I ' (pi/2), I ' (π/4) and I ' (0) respectively successively.For reducing error further, the following root-mean-square valve AvaI (π) of each wavelength place photocurrent, AvaI (π/4), AvaI (3 π/4), AvaI (pi/2) can be calculated respectively, then obtain corresponding δ by formula (7.a ~ 7.c) ₁, δ ₂computing machine 10 is saved in η data.Finally, draw the δ 1(λ in the measurement wavelength coverage of measurement mechanism of the present invention), δ 2(λ) and η (λ) curve, and to carry out curve fitting, obtained curve gone to the smoothing processing of " burr ", further reduction error, preserves data and end operation.

$\mathrm{AvaI}\left(\mathrm{\&pi;}\right)=\sqrt{\frac{{\left[I\left(0\right)\right]}^2+{\left[I\left(\mathrm{\&pi;}\right)\right]}^2+{\left[I\left(2\mathrm{\&pi;}\right)\right]}^2+{\left[I^{\&prime;}\left(\mathrm{\&pi;}\right)\right]}^2+{\left[I^{\&prime;}\left(0\right)\right]}^2}{5}}$

$\mathrm{AvaI}\left(\frac{\mathrm{\&pi;}}{4}\right)=\sqrt{\frac{{\left[I\left(\frac{\mathrm{\&pi;}}{4}\right)\right]}^2+{\left[I\left(\frac{5\mathrm{\&pi;}}{4}\right)\right]}^2+{\left[I^{\&prime;}\left(\frac{5\mathrm{\&pi;}}{4}\right)\right]}^2+{\left[I^{\&prime;}\left(\frac{\mathrm{\&pi;}}{4}\right)\right]}^2}{4}}$

$\mathrm{AvaI}\left(\frac{3\mathrm{\&pi;}}{4}\right)=\sqrt{\frac{{\left[I\left(\frac{3\mathrm{\&pi;}}{4}\right)\right]}^2+{\left[I\left(\frac{7\mathrm{\&pi;}}{4}\right)\right]}^2+{\left[I^{\&prime;}\left(\frac{7\mathrm{\&pi;}}{4}\right)\right]}^2+{\left[I^{\&prime;}\left(\frac{3\mathrm{\&pi;}}{4}\right)\right]}^2}{4}}$

$\mathrm{AvaI}\left(\frac{\mathrm{\&pi;}}{2}\right)=\sqrt{\frac{{\left[I\left(\frac{\mathrm{\&pi;}}{2}\right)\right]}^2+{\left[I\left(\frac{3\mathrm{\&pi;}}{2}\right)\right]}^2+{\left[I^{\&prime;}\left(\frac{3\mathrm{\&pi;}}{2}\right)\right]}^2+{\left[I^{\&prime;}\left(\frac{\mathrm{\&pi;}}{2}\right)\right]}^2}{4}}$

In fact, can depend on actual need the need of drafting and matching η (λ) curve and determine actually herein.Because to the analysis of this parameter mainly in order to investigate the fault of measuring system of the present invention, and analyze, the serviceability of each building block in calibration measurements system.Such as, when the spectral characteristic of wideband light source 1 and the known and multi-wavelength light electric explorer 8 spectral characteristic the unknown of each device loss characteristic, η (λ) curve and formula (4) can be utilized to demarcate, analyze the spectral characteristic of multi-wavelength light electric explorer 8.

Utilize the measuring method of wave plate spectral characteristic of the present invention, also directly can realize the measurement of two broadband quarter wave plate phase delay spectral characteristics in PCSCA type ellipsometer.First, PCSCA type ellipsometer is set to direct mode operation, regulate initial orientation angle α (quick shaft direction) parallel with analyzer 6 with the polarizer 3 (α=0) of the first wave plate 4 to be measured, the initial orientation angle of the second wave plate 5 to be measured is vertical with the first wave plate 4 to be measured, and both synchronized, unique step rotating Vortexes; At arbitrary wavelength place, consider that all emphatically α gets several special angle, as α=k π, k π+π/4, k π+pi/2, the photocurrent numerical value (k is integer and k>=0) during k π+3 π/4, is then obtained the phase-delay quantity δ of any wavelength first wave plate 4 to be measured by formula ₁, the second wave plate 5 to be measured phase-delay quantity δ ₂, and characterize the parameter η of this wavelength place measuring system overall performance, and then obtain the phase delay spectral characteristic of two wave plates to be measured.

The present invention is also noted that in the specific implementation and ensures that the operating wavelength range of all optical components (as wideband light source 1, the polarizer 3, analyzer 6, multi-wavelength light electric explorer 8 etc.) in measuring system of the present invention can cover the operating wavelength range of wave plate to be measured.This realizes than being easier in actual applications.For the wave plate often adopted in ellipsometer, the operation wavelength of such wave plate, substantially all within 200nm ~ 1100nm scope, can adopt operation wavelength at 190nm ~ 2500nm for this reason, be furnished with the xenon lamp of high-precision regulated power supply as wideband light source 1; Operation wavelength is adopted to be that the quartzy wollaston prism of 200 ~ 2300nm is as the polarizer 3 and analyzer 6; Operation wavelength is adopted to be that the back-illuminated type area array CCD (such as shore pine FFT-CCD detector) of 200 ~ 1100nm is as multi-wavelength light electric explorer 8; Etc..

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.

Claims (9)

1. the measuring method of phase delay spectral characteristic of wave plate, is characterized in that, mainly comprises the steps:

Step one: regulate the quick shaft direction of the first wave plate to be measured parallel with analyzer with the polarizer, the quick shaft direction of the second wave plate to be measured is vertical with the first wave plate to be measured;

Step 2: open wideband light source, the parallel beam of the continuous wavelength of outgoing successively by after collimating apparatus, the polarizer, the first and second wave plates to be measured, analyzer and optical splitter, through multi-wavelength photoelectric detector; Computing machine is by analyzing Data Control driven by motor two wave plates to be measured of data collecting card collection with same angular velocity w rotating Vortex;

Step 3: come relative to the photocurrent values collection under several absolute rotation angle of reference position by wave plate to be measured, by being obtained the phase-delay quantity δ of any af at wavelength lambda first wave plate to be measured by the formula of phase-delay quantity formula and measuring system overall performance ₁, the second wave plate to be measured phase-delay quantity δ ₂, and characterize the parameter η of this wavelength place measuring system overall performance, and then obtain the phase delay spectral characteristic of two wave plates to be measured;

The phase-delay quantity δ of the in described step 3 first wave plate to be measured ₁, the second wave plate to be measured phase-delay quantity δ ₂, and characterize the parameter η of this wavelength place measuring system overall performance, as shown in following formula;

$\mathrm{\&eta;}=\frac{1}{8}\&CenterDot;\left\{\begin{array}{c}I\left(\mathrm{k\&pi;}\right)+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{4})+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})+I(\mathrm{k\&pi;}+\frac{3\mathrm{\&pi;}}{4})+\\ \sqrt{{[I\left(\mathrm{k\&pi;}\right)+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{4})+I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})+I(\mathrm{k\&pi;}+\frac{3\mathrm{\&pi;}}{4})]}^2-16\&CenterDot;I\left(\mathrm{k\&pi;}\right)\&CenterDot;I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})}\end{array}\right\}$

${\mathrm{\&delta;}}_1={\cos }^{-1}[I(\mathrm{k\&pi;}+\frac{\mathrm{\&pi;}}{2})/\mathrm{\&eta;}-1]$

δ ₂＝cos ^-1[I(kπ)/η-1]；

Step 4: according to all δ in the measurement wavelength coverage of described measurement mechanism ₁, δ ₂with η data, draw corresponding δ ₁(λ), δ ₂(λ) with η (λ) curve, finally obtained curve is gone to the smoothing processing of " burr ", reduce error further.

2. the measuring method of a kind of phase delay spectral characteristic of wave plate as claimed in claim 1, it is characterized in that, the concrete steps of described step 3 are: wave plate to be measured is denoted as α relative to the absolute rotation angle of reference position and has α=wt, and the initial time of t=0 corresponds to α=0; Every anglec of rotation step delta θ, wherein 0 < Δ θ≤π/4, data collecting card gathers primary photoelectric current and passes to computing machine, like this when driven by motor wave plate to be measured rotates a circle, all obtains at least eight group photocurrent data at each wavelength place; Due to when stable system performance, photocurrent I (α) is about the periodic function of independent variable α to be the cycle be π; So at arbitrary wavelength place, consider that all emphatically α gets the value of several special angle time electric current I, described special angle is α=k π, k π+π/4, k π+pi/2, k π+3 π/4, wherein k is integer and k>=0, is then obtained the phase-delay quantity δ of any wavelength first wave plate to be measured by the formula of phase-delay quantity formula and measuring system overall performance ₁, the second wave plate to be measured phase-delay quantity δ ₂, and characterize the parameter η of this wavelength place measuring system overall performance, and then obtain the phase delay spectral characteristic of two wave plates to be measured.

3. the measurement mechanism that adopts of the method for claim 1, it is characterized in that, comprise a wideband light source, the multi-wavelength continuous light of its outgoing is successively by after collimating apparatus, the polarizer, the first wave plate to be measured, the second wave plate to be measured, analyzer and optical splitter, through multi-wavelength photoelectric detector, transfer data to data collecting card after reception, the data of data collecting card are transferred to computing machine, and described first wave plate to be measured and the second wave plate to be measured are arranged on the precise rotating platform of Non-follow control.

4. the measurement mechanism that adopts of the method for claim 1, comprise a wideband light source, the multi-wavelength continuous light of its outgoing successively by after collimating apparatus, the polarizer, the first wave plate to be measured, the second wave plate to be measured, analyzer and optical splitter, through multi-wavelength photoelectric detector; Described first wave plate to be measured is all connected with same motor with the second wave plate to be measured, or is connected respectively with two motors; The data upload of described multi-wavelength photoelectric detector is in data collecting card, and data collecting card transfers data to computing machine, and computing machine controls motor.

5. the measurement mechanism as described in claim 3 or 4, is characterized in that,

Two described wave plates to be measured to be delay scope be zero-th order waveplates of 0 ° ~ 180 °, described zero-th order waveplates is by the true zero-th order waveplates of crystalline material or polymeric material or compound zero-th order waveplates.

6. the measurement mechanism as described in claim 3 or 4, is characterized in that,

Described collimating apparatus adopts the optical fiber collimator of accurately being located by tail optical fiber and GRIN Lens, is transformed into collimated light for the discrete light sent by wideband light source; The described polarizer and analyzer all adopt the one in the dichroism polarizer or the birefringence polarizer; Described optical splitter adopts Amici prism or grating dispersion type optical splitter, for being launched by the wavelength of multi-wavelength composite light beam, and is detected by each wavelength signals feeding multi-wavelength light electric explorer launched.

7. the measurement mechanism as described in claim 3 or 4, is characterized in that,

Described wideband light source is the continuous spectrum light source that output characteristics is stable, and the spectral range of this light source can cover the required phase delay spectral characteristic of wave plate scope measured.

8. the measurement mechanism as described in claim 3 or 4, is characterized in that,

Described multi-wavelength light electric explorer is multi-wavelength photodiode array, photomultiplier tube array or CCD linear array or area array sensor, be preferably CCD linear array or area array sensor, carry out data processing for each wavelength light current signal detected is reached computing machine through data collecting card.

9. measurement mechanism as claimed in claim 4, is characterized in that,

Described motor selects the motor of servomotor, p-m step motor or reaction stepping motor and corresponding driver thereof; Described computing machine sends the rotation status of pulse signal through motor driver adjustment motor by data collecting card.