TW531638B - An error evaluation technique for incident angle in a rotating element ellipsometer using quartz crystal - Google Patents

Abstract

A method to evaluate the error in the angle of incidence for a rotating element ellipsometer (REE) using a uniaxial quartz crystal. By comparing the measured ratio of Rp and Rs to its calculated ratio in a full cycle, one can obtain the deviation of the angle of incidence. This invention uses the small difference between the ordinary and extraordinary refractive indices of a uniaxial quartz crystal to evaluate the parasitic error in the angle of incidence of a REE.

Description

531638

V. Description of the invention (l) The present invention is to add a rotatable platform to a unidirectional quartz crystal on a sample holder of a rotary ellipsometry to measure the rotation of the ellipse The resulting incident angle deviation (Figure 1) is generally recognized as a parasitic error of a rotating elliptical polarizer 〇 > Rotating elliptical polarizers have been widely used in spectral measurement because they do not require a complementary plate. However, because of the rotating element, unless the plane of the optical element has no oblique angle, the beam will move, which will cause the parasitic error of the incident angle. This error was disclosed in Zeidler JR et'al · Appl · Opt · as early as 1 974 13, 1938. In addition to the use of expensive optical components, the present invention uses an anisotropic uniaxial quartz to measure and evaluate the parasitic errors in the polarimeter ', thereby eliminating the measurement errors of the ellipsometry. According to US 1998 Yu-Faye Chao et al. Patent 5706088, Polarizer-Sample-Analyzer Intensity

Qudient ellipsometry, take a standard glass and first correct the transmission axis of the polarizer and the analyzer; adjust the transmission axis of the polarizer to ± 45 degrees, and place a rotatable anisotropy on the sample holder. For uniaxial quartz, when the transmission axis of the light analysis plate is zero degrees, the sample is rotated once and its brightness is measured. Weigh, Ip ± 45 ″ When the transmission axis of the light analysis plate is 90 degrees, the sample is rotated one time and s Taking its party degree 'is called is ± 45. Expanded ginseng optimized according to the above patent

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fr J ^ to— = above 11 U + «U (Equation 1) This elliptic polarization parameter Aspnes D. Ε · is indicated in j · 〇pt. S〇C · Am · 70, 1 275 in 1980: The elliptic polarization parameter measured by a uniaxial crystal is equivalent to the polarization parameter of an isotropic medium, and the refractive index of this equivalent nondirectional medium depends on the refractive index of the anisotropic uniaxial refractive index on the reflecting surface. Weight. According to this statement, the present invention compiles a program based on the reflection relationship of the anisotropic uniaxial interface developed in J. Αρρ1 · Phys · 34, 5016 in 1991 by Lekne; r j · for estimating the incident angle deviation (Table 丨). In this paper, Ming uses a birefringent crystal quartz to correct the rotation of an elliptical polarizer. This reduces the measurement error of the system, and can replace polarizers with expensive polarizers. The refractive index of the axial crystal and the position of the optical axis. One feature of the present invention is to provide a birefringent crystalline quartz, the difference between the ordinary refractive index and the extraordinary refractive index is small to achieve a small error in resolving the incident angle. Another feature of the present invention is to measure the ordinary refractive index, extraordinary refractiVe index, and the angle between the optical axis and the tangent plane of the anisotropic uniaxial crystal after correcting the deviation of the incident angle. In order to further disclose the structure, features, and advantages of the present invention, examples are described below with reference to the drawings.

531638 V. Description of the invention (3) According to US patent 5706088, a rotating elliptical polarizer (Figure 1) is set up; the light emitted by the laser (10) passes through a polarizer (20), and its azimuth is placed at ^ 45 degrees 'After being reflected by Shi Yang (3 5) at a specific incident angle (25, 45 degrees in this example)' and then passing through the light analysis sheet (3 0), the azimuth angles are set to 0 and 90 degrees, respectively. ' The brightness measured by the measuring device (40) is converted into an elliptical polarization parameter (refer to the formula lj) by a digital converter (50j input to the computer (60)). The azimuth of the crystal can be controlled by its rotating seat (37). The ratio of the elliptical polarization parameter set by the center to the theoretical value (Figure 2) can clearly detect the error caused by the rotation system. When the incident angle is set to 44.94 degrees, the theoretical value is consistent with the measurement (Figure 3) ). And by measuring γν〇4 in the same way, the angle between the cut plane of the crystal and the optical axis can be found out (Figure 4). Although the present invention has been determined by a preferred example, the uniaxial anisotropy does not depart from the invention The measurement of the constant refractive index of the optical axis and the tangent plane of the crystal, and the uniaxial anisotropic crystal are all within the protection scope of the present invention. However, it is not intended to limit the spirit and scope. If it is applied to the measurement, or its general refractive index and the relative position of the foreign body optical axis to the reference base will be described in the drawing. Figure 1: (a) Basics of a rotating ellipsometry Architecture (b) Symbol description of important components of the quartz crystal and turntable of the present invention

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V. Description of the invention (4) (10) Light source (20) Polarizer (30) Analyzer (37) Sample holder (40) Detector (detector) ) (50) digital converter (a / D converter) (60) personal computer (pc) Figure 2: When the incident angle is 45 degrees, the ellipse parameter values in the various positions of the optical axis of the quartz crystal (-is the theoretical calculation value, • is the measured value) Figure 3: When the incident angle is 44.94 degrees, the ellipse parameter values under the various directions of the optical axis of the quartz crystal (-is the theoretical calculation value, • is the measured value), the incident angle deviation is -0.06 ± 0.01 degrees. Figure 4: When the incident angle is 44. 94 degrees, the ellipse parameter values (-is the theoretical calculation value, _ is the measurement value) under each position of the optical axis of the YV04 crystal, the calculated η〇 = 1.9929 ne = 2.2154; The angle between the cut plane and the optical axis is 136 · 〇1 ± 0 · 01 degrees Table 1: Discrimination process of incident angle deviation ·

531638 V. Description of the invention (5)

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Claims (1)

531638 VI. Application for patent scope 1. The method of parasitic error of the incident angle of a rotating ellipsometry of a s measuring tool, including: a quartz crystal whose optical axis is parallel to the tangent plane for measurement; a rotating frame for placing the quartz crystal ; A theoretical formula to estimate the parasitic error of the incident angle based on the measurement. It is characterized in that: the quartz crystal is placed on a rotating frame and co-located on the rotating ellipse polarizer to be measured; when it is at a certain angle of incidence, the azimuth of the polarizing degree of the elliptical polarizer is placed at ± At 45 degrees, the optimized elliptic parameter ψ of the optical axis at various azimuth angles is measured; the elliptic parameters Ψ of the measurement and theory are compared and the error of the parasitic incident angle is calculated. 2. The method for measuring the parasitic error of the incident angle of a rotating elliptical polarizer as described in item 1 of the scope of the patent application, wherein the optimized ellipse parameter ψ is referred to as the polarization angle at ± 45 degrees and the analysis angle at 0 degrees. Ip ± 45; Polarization angle at 45 degrees, Beam angle at 90 degrees is called Is ± 45 ', and the heart is optimized by the following formula J ^ ΐαηψ = 3. As measured in the scope of the patent application, the rotating ellipse polarizer The method of the parasitic error of the incident angle, in which the theoretical value of the elliptic parameter ψ can be compared with the perceptual value to obtain the error of the parasitic incident angle.