TW452649B - Azimuthal alignment technique for PEM ellipsometry at a fixed incident angle - Google Patents

Abstract

A fixed incident angle technique is proposed to align the azimuths of polarizer (P), analyzer (A) and optical axis of photoelastic modulator (PEM) in the PEM ellipsometry. Using the intensity ratio technique, two options are proposed: two pre-designed samples or two wavelengths are used to align the azimuths of P and A to the incident plane. Then, the azimuth of optical axis of the PEM is aligned by a direct determination technique.

Description

V. Description of the invention (1) The present invention is a method for correcting each polarization angle with a photoelastic modulator ellipsometry of a single incident angle. "This method can be applied to a closed system that has been designed, such as plasma Etching (p 1 asmaetching system), mineral film (fi 1m de ρ 〇 siti ο η) and other systems. In general, plasma etching or coating systems have multiple monitoring instruments to monitor the manufacturing process. In recent years, elliptical polarimeters have been able to accurately measure film thickness, so they have been regarded as one of the monitoring instruments in the system. However, such systems are mostly closed, and the chamber and the production equipment are often customized by different manufacturers. Due to the extremely high accuracy of the ellipsometry, the operating principles of the systems are related to the various angles of the optical components in the system. Related, so the accuracy of the ellipsometry is determined by the correction of the azimuth zero point of the optical elements in the system. According to Yu-Faye Chao et al. Patent 5,706,088 in 1998, Polarizer-Sample-Analyzer Intensity Quotient ellipsometry, two angles of incidence must be used; direct photometry in 1999 by the same author as Jpn · J. Appl · Phys · 38,691 9 The optical axis of the photoelastic modulator of the elastic modulation polarizing instrument must also use the penetration and operating angle of incidence. Neither of these methods can be applied to the fabricated cavity shell. The invention is based on U.S. 1998 Yu-Faye Chao et al. Patent 5706088 '' Polarizer-Sample-Analyzer Intensity

The brightness ratio concept in Quotient el 1 ipsometry, but using two well-designed test strips or two wavelengths instead of two incidence angles, so that the polarization axis of the polarizer and the analyzer can be calibrated at a single incidence angle to Incident surface; then

Page 4 45 264 9 V. Description of the invention (2) = Bomb: The controller is placed in the optical path to imitate ⑻ "Αρρΐ 38,6919 The direct measurement of the optical axis of the photoelastic modulator. The main purpose of the present invention is to replace the two angles of incidence with the function # u / ^ A ^ test piece (or two wavelengths) to weight the polarizing angle of the polarizer and the analyzer (Uzimuth angu). This method can be applied to a required angle of incidence Corrected system. The optical axis of the present invention is to use the direct measurement method to measure the photoelastic modulator to suppress the biggest feature of the present invention: to provide a photoelastic modulation elliptical polarizer with a single incident angle to correct each optical element Azimuth. The following describes the correction of the polarizing angle of the polarizer and the light-resolving sheet of the present invention: the brightness measured in the PSA (polarizing sheet p-test sheet s-light-receiving sheet a) / (ΛZ) · [[sm * PsinM + tanVeos1 j〇co? where Ψ and △ are ellipSometric para-meters of the test piece, and P and a are the polarizing angles of the polarizer and the light-resolving plate, respectively; assuming α and / 3 are the polarizing plate and the light-removing light, respectively The small deviation rj of the sheet azimuth angle, * X u 丄 ni (45 + txj) R _ ΙΜ ^ + α, β) (deviation), if the brightness ratio. , The first approximation of the small angle expansion is

(1) a V. Description of the invention (3)

-{cos Δ J] β E when Ά-a. Using two different chirps and deltas (can be caused by two test strips or two wavelengths, the aforementioned patent consists of two incident angles) to form a set of binary once-in-one cubic equations' whose only solution is the zero point, which is the reflecting surface. After determining the zero point of the polarizer and the analyzer, put P at 45 degrees, and then place the photoelastic modulator in the optical path to form a P-PEM-SA ellipse polarizer (Figure 1). The measured brightness is (2) / (^ 4) = 3 ^ 4 + jWcos3 tan3 ^ + ATsm j4 cosA] where each parameter of L, M, N is defined as follows: L = 0.5f [+ cosA ^ M = 0.5 f \-\ ~ cosAp cos) (\ +)) ^ ~~ ^ c〇s ^ p-(\ -cos) cosA & Jtanifrcosti. ~ sinK9 cos 2θίαηψ3ΐκ Δ θ 'Δρ is the optical axis of the photoelastic modulator. Azimuth and phase delay Substituting the azimuth angle A = 0 ° and 90 ° of the light-reflector into equation (2) gives-0.5 / ff tan < p (1 + Δ, + (1 — cos Δ,) (1 + sin 4 (3) '(90,): Ci.5L {l + cosA, + (l-cosAj) (1_sm4W (4) The phase delay of the photoelastic modulator is Δ, = Δ, M, where △. Is the phase amplitude of the photoelastic modulator 'ω is the modulation frequency. For Δρ we can use the Fourier expansion (Fourier expansi) expression as follows:

Page 6 5. Description of the invention ¢ 4) 5. Description of the invention ¢ 4) sin Ap = 2Jl (Δρ) cos at-2J2 (Afl) cos 3〇Jt. CosAp = Ja (Aa) -2J: l (Afi) cos2iU ............ Substituting into equations (3) and (4) and taking the DC component Id of the light intensity. , And we know that / „(△,) = 0 When 1 = 0.383 乂 (λ is the wavelength), we can get the following result / rff (0 *) = 0.5 / ,, tan3 ^ (2 + sin Λθ) (5) 4 (90 ·) = 0.5 // 2-sin 4 (6) The azimuth angle β of the optical axis of the photoelastic modulator can be calculated from θ = & + ◦ and “min + 45 ° ide light intensity, see the following formula smAS = 2 IiA〇 ^ ic (〇) pjp. + 0 *) pj. + 45 * (7) The ellipse parameter of the test piece can also be calculated from the following formula (8): v = K0. Enter 90 '-~ this The invention uses two test strips (or two wavelengths) to complete the correction of the azimuth angles of the polarizer, light splitter, and optical axis of the photoelastic modulator under the structure of a single incident angle. The function of instant measurement has been completed. In order to further disclose the structure, features and advantages of the present invention, the following

V. Description of the invention (5) Examples of illustrations are as follows. Please refer to Figure 1 for the day and month ending 2gg _ As far as possible, the first-bounce modulation elliptical polarizer includes: light source device 10 ′ a polarizer 20, a light modulator 30, two adjustable size Apertures 37 and 38, a light analysis sheet 40 == continued i is placed on the frame 35 to be measured, there are two apertures 37 and 38 in front and back, for correcting the optical path after changing the standard or wavelength, and between the light The elastic modulator 30 and the light analysis sheet 40 through the controller 32 of the optical elastic modulator are used to modulate the phase of the optical elastic modulator and the reference frequency for supplying the phase-locked amplifier ^, and control the brightness obtained by the photodetector 50 by a signal. The control unit 60 is divided into a DC voltage (Vdc) 64 and an AC voltage (Vac) 66, which is amplified by a lock-in amplifier (10ck_in ampUfier) 34 and sent to a computer 70 for calculation and analysis. Use two designed test strips (a silicon wafer and a thin film wafer with silicon dioxide of about 100 nm selected in this example) instead of two incident angles, and polarizers at a single incident angle And the transmission axis of the light analysis plate is aligned to the incident surface. From the intersection of the two simultaneous equations in the theoretical program (Figure 2), the actual zero point of the polarizer and light analysis plate can be obtained. According to the present invention, the direct current signal (Vdc) measured from the azimuth of the photoelastic modulator and the theoretical value (Figure 3) 'can clearly determine the position of the optical axis of the photoelastic modulator' via a theoretical formula (Equation 7 ), Can directly measure the optical axis of the photoelastic modulator

Page 8- ^ 3452649 V. Description of the invention (6) The azimuth zero point deviation is 0.28. When the photoelastic modulator azimuth is corrected by 0.28 degrees, the theoretical value and measured value are more consistent (Figure 3) . The elliptic parameter 量 of the platinum film test strip (Eq. 8) measured directly by the present invention in the calibration program is 34.89 degrees (optimized measurement values according to the 1998 Yu-Faye Chao et al. Patent 570 6088), and the test strip is commercially available. As measured by a Rodulgh AutoEL III, the ellipse parameter Ψ is 34.52 degrees. In order to explain the operation procedure of the present invention, the azimuth deviation determination flowchart (Fig. 4) is drawn in order to understand the applicable conditions and requirements of the online correction method.

V. Description of the invention (7) Symbols of important components (10) Light source (20) Polarizer (30) Photoelastic modulator head 0A is its optical axis (32) Photoelastic Photoelastic modulator controller (34) Ioc-in amplifier (35) Sample holder (36) GPIB cable (3 7) Adjustable Aperture size 1 (38) Adjustable size aperture 2 (40) Analyzer (5 0) Price measurement device (detector) (60) Signal control unit (64) DC voltage ( Vdc) (66) AC voltage (Vac) (68) GPIB cable (70) Personal computer (PC)

Page 10 452649 V. Description of the invention (8) Description of the drawings Figure 1: Basic structure of photoelastic modulation ellipsometry Figure 2: Zero calibration of two standard films Two designed test pieces are incident at 70 degrees Diagram of the calibration of the transmission axis of the polarizer and light-reflector under the angle (-is the theoretical calculation value, * is the measured value, 〇 is the measured value) Figure 3: DC measured by rotating the photoelastic modulator azimuth Signal graph After the photoelastic modulator azimuth zero point is corrected to 0.27 64 degrees, the direct current signal graph (Vdc) measured by rotating the photoelastic modulator azimuth. (-Is the theoretical calculation value, * is the measured value) Figure 4: Azimuth deviation discrimination flowchart

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Claims (1)

^ 4 5 2 64 9 VI. Patent application scope 1_ The method of correcting the azimuth of each element on a certain angle of incidence line includes: two standard films, a theoretical program to simulate the illustration of two simultaneous equations at this specific incident angle, A theoretical formula 'uses the measured ellipse parameters to infer the exact value of the incident angle. State eight ΛΙ, optical path _ ... one is: first place a standard film on a rotating elliptical polarization with only polarizers and 2 On the test stand of the instrument, using the brightness ratio correction method 1, the linear relationship between the azimuth angles of the light sheet and the light-resolving sheet; then change the linear relationship between the azimuth angles of the second standard sheet polarizer and the light-resolving sheet; J type = zero point of the retroreflective surface. Place the azimuth of the polarizer in the 45 J 2 4.6 converter and place it in the optical path, and adjust its phase amplitude to 1 g-when the azimuth is 0 degrees, measure the signal of vdc; ^ = modulation theft Rotate 45 degrees and then measure the azimuth of the optical axis of the Vdc 3 ten different light bomb modulator.彳 d This is the amount of the patent application. The first item is determined from # 六 T, one of which is the normal method, and the j card can also be completed by a standard 6-wavelength method. —The quasi-film is selected from the diagrams of the two-pound simulation modeled by the theoretical process of the corner correction method. Page 12 6. Scope of patent application 4. If the fixed angle correction method of item 1 of the scope of patent application is adopted, the fixed angle can be deduced from the elliptic parameters obtained by the bilinear relationship to the exact value of the incident angle. 5. For the fixed angle correction method of item i in the scope of patent application, in which the azimuth of the optical axis of the photoelastic modulator is measured: P is set at 45 degrees and A is set at 0 degrees; the phase of the photoelastic modulator Set the amplitude at 0.383 again, take the DC brightness Id. (0 °) θ. ， Rotating photoelastic modulator 45 degree re-directed DC brightness Idc (0 °) e〇 + 45 > The azimuth angle can be calculated by the following formula: ΑΓι η) p.P + 0 * sin% 2 2-;-;-) w, # +4 (〇) From, + servant. 6. For the fixed angle correction method in the first scope of the patent application, the optical axis of the photoelastic modulation at 0 degrees is set to 0 at A. +45 degree DC brightness Ide (0〇) &+45; and A is set at 90 degrees, and the optical axis of the photoelastic modulation is at Θ. Degree of direct current brightness Ι ^ (9〇 °) θϋ Page 13