JPH05180757A - Polarization analyser - Google Patents

Abstract

PURPOSE:To shorten a required measuring time by the continuation of measuring operation and the simultaneous rotation of a polarizer and an analyser by continuously rotating the polarizer and the analyser at different speeds and calculating the respective azimuth angles of both of them at the point of time when a light detection signal becomes zero from the timewise change of the light detection signal at the time of rotation. CONSTITUTION:A control unit 5 sets respective polarizing elements, that is, a polarizer 1, a 1/4 wavelength plate 2 and an analyser 3 to a reference azimuth and subsequently sets the 1/4 wavelength plate 2 to an azimuth of +45 deg.. Thereafter, the polarizer 1 and the analyser 3 are rotated at predetermined angular velocities omega', omega and the output of a photodetector 4 is sampled at a definite time interval and stored in a memory along with the azimuth angles of the polarizer 1 and the analyser 3 at the time of rotation. Next, the azimuth angle of the wavelength plate 2 is set to -45 deg. to repeat the same measuring operation. When the analyser 3 is rotated at a higher speed, the azimuth of the analyser 3 at the trough where the intensity of light is min. before and after a point of time (t) is a value near to an extinction angle and, when the polarizer is rotated at a higher speed, the extinction angle and azimuth of the polarizer 1 can be also calculated in the same way.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【産業上の利用分野】本発明は偏光解析装置の高速化を
消光法の精度で計るものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims at speeding up of an ellipsometer with the accuracy of an extinction method.

【０００２】[0002]

【従来の技術】従来の消光法型偏光解析装置は図５に示
すような構造になっていた。この図で１は偏光子、２は
１／４波長板、３は検光子でＳは試料である。偏光子１
と１／４波長板との方位角に応じて、試料に入射する光
は長軸方向が或る方位を持った楕円偏光となっている。
試料Ｓは表面に薄膜が形成されており、その屈折率と層
厚さとに応じて入射した楕円偏光は異なる方位と楕円率
を持った楕円偏光となって反射される。この反射光を検
光子を通して光検出器４で検出測定する。測定操作は１
／４波長板の方位角を４５°に設定し、試料に入射させ
る楕円偏光の方位角を一定にして楕円率を色々に変えて
試料からの反射光が直線偏光となるときの偏光子の方位
角と、試料から反射した直線偏光の方位角を測定する。
実際には試料からの反射直線偏光と検光子の方位角が直
交するとき、光検出信号が０になるから、偏光子，検光
子の方位を色々に変えて光検出信号が０になる位置を探
すのである。2. Description of the Related Art A conventional extinction type ellipsometer has a structure as shown in FIG. In this figure, 1 is a polarizer, 2 is a quarter-wave plate, 3 is an analyzer, and S is a sample. Polarizer 1
The light incident on the sample is elliptically polarized light whose major axis direction has a certain azimuth according to the azimuth angle between the ¼ wavelength plate and the ¼ wavelength plate.
A thin film is formed on the surface of the sample S, and the elliptically polarized light incident according to the refractive index and the layer thickness thereof is reflected as elliptically polarized light having different azimuth and ellipticity. This reflected light is detected and measured by the photodetector 4 through the analyzer. Measurement operation is 1
Azimuth of the quarter wave plate is set to 45 °, the azimuth of the elliptically polarized light incident on the sample is kept constant, the ellipticity is changed variously, and the azimuth of the polarizer when the reflected light from the sample becomes linearly polarized light The angle and the azimuth of the linearly polarized light reflected from the sample are measured.
Actually, when the linearly polarized light reflected from the sample and the azimuth angle of the analyzer are orthogonal to each other, the light detection signal becomes 0. Therefore, the position where the light detection signal becomes 0 by changing the azimuths of the polarizer and the analyzer in various ways. Search for it.

【０００３】上述した測定操作は偏光子１を小角度ずつ
ステップワイズに回転させ、偏光子１の各角位置毎に検
光子を一回転させて光検出信号の変化を調べて、光検出
信号が０になる点を見出すのであるから、測定には大変
時間を消費するものである。In the above-described measurement operation, the polarizer 1 is rotated stepwise by a small angle, and the analyzer is rotated once for each angular position of the polarizer 1 to check the change of the light detection signal. It is very time consuming to measure because it finds a point where it becomes zero.

【０００４】[0004]

【発明が解決しようとする課題】測定操作の連続化と、
偏光子，検光子同時回転化により、測定所要時間を短縮
しようとする。SUMMARY OF THE INVENTION A continuous measurement operation,
Simultaneous rotation of the polarizer and analyzer will reduce the time required for measurement.

【０００５】[0005]

【課題を解決するための手段】偏光子，検光子を異なる
速度で連続回転させ、そのときの光検出信号の時間的変
化から、光検出信号が０になる時点の４ゾーンの偏光
子，検光子の方位角を内挿的に算出するようにした。A polarizer and an analyzer are continuously rotated at different speeds, and the four-zone polarizer and detector at the time when the photodetection signal becomes 0 based on the temporal change of the photodetection signal at that time. The azimuth angle of the photon was calculated by interpolation.

【０００６】[0006]

【作用】 偏光子検光子とも連続回転させるから高速回
転が可能であり、そのときの光検出信号の時間的変化か
ら光検出信号が０になるときの偏光子検光子の方位を内
挿的に算出するので、実際に光検出信号が０になる時点
が測定期間中になくてもよく、測定の高速化か達成され
る。Since the polarizer analyzer is also continuously rotated, high-speed rotation is possible, and the azimuth of the polarizer analyzer when the photodetection signal becomes 0 is interpolated from the temporal change of the photodetection signal at that time. Since the calculation is performed, the time at which the photodetection signal actually becomes 0 does not have to be during the measurement period, and the speedup of the measurement is achieved.

【０００７】まず検光子を偏光子より速く回転させる場
合を考える。今偏光子の方位を一定にして検光子を角速
度ωで回転させると、試料からの反射光は楕円偏光であ
るから、光検出器出力即ち検光子透過光強度Ｉは一般的
に光検出出力が０となるときの検光子の方位角をφとし
て Ｉ＝Ａｓｉｎ² （ωｔ−φ）＋Ｂ と書ける。偏光子の方位角を変えるとＡ，Ｂは変化する
から、Ａ，Ｂは偏光子の方位角の関数となる。まずＡの
値は試料からの反射光が直線偏光のとき最大で、このと
きの光検出出力Ｉｏとなり、円偏光のとき０である。他
方Ｂは円偏光のとき最大で（１／２）Ｉｏ、直線偏光の
とき０となる。偏光子の回転角速度をω’とし、反射光
が直線偏光になるときの偏光子の方位角をψとすると、 Ａ＝Ｉｏｓｉｎ² （ω’ｔ−ψ），Ｂ＝（１／２）Ｉｏ
ｃｏｓ² （ω’ｔ−ψ） 従って Ｉ＝Ｉｏ ｓｉｎ² （ω’ｔ−ψ）ｓｉｎ² （ωｔ−
φ）＋（１／２）ｃｏｓ²（ω’ｔ−ψ）…(1) これをグラフに画くと図２のようになる。上式は求める
未知数ψ，φ，Ｉｏの３個を含む時間ｔの関数であるか
ら、原理上最小限３つの時点のＩの測定値からφ，ψを
算定することができる。First, consider the case where the analyzer is rotated faster than the polarizer. When the analyzer is rotated at the angular velocity ω with the azimuth of the polarizer being constant, the reflected light from the sample is elliptically polarized light. Therefore, the photodetector output, that is, the analyzer transmitted light intensity I is generally the photodetection output. When the azimuth angle of the analyzer when it becomes 0 is φ, it can be written as I = Asin ² (ωt−φ) + B. Since A and B change when the azimuth angle of the polarizer is changed, A and B are functions of the azimuth angle of the polarizer. First, the value of A is maximum when the reflected light from the sample is linearly polarized light, which is the light detection output Io at this time, and is 0 when it is circularly polarized light. On the other hand, B is (1/2) Io at maximum for circularly polarized light and 0 for linearly polarized light. When the rotational angular velocity of the polarizer is ω ′ and the azimuth angle of the polarizer when the reflected light is linearly polarized light is ψ, A = Iosin ² (ω′t−ψ), B = (1/2) Io
cos ² (ω′t−ψ) Therefore I = Io sin ² (ω′t−ψ) sin ² (ωt−
φ) + (1/2) cos ² (ω′t−ψ) (1) When this is drawn in the graph, it becomes as shown in FIG. Since the above formula is a function of the time t including three unknowns ψ, φ, Io to be obtained, φ and ψ can be calculated from the measured values of I at a minimum of three points in principle in principle.

【０００８】次に偏光子の方を検光子より速く回転させ
る場合を考える。今検光子を固定して偏光子を回転させ
ると、試料からの反射光は円偏光から直線偏光の範囲で
変化し方位角も変化する。従って検出される光強度Ｉは
偏光子の回転に従って上下変動しながら、検光子の回転
に従ってゆるやかに上下し、図３に示すような変化を示
す。このＩは Ｉ＝Ｉｏ［ｓｉｎ² （ωｔ＋φ）±（１／２）ｓｉｎφ
ｓｉｎ２ωｔ ×｛ｓｉｎ（２ω’ｔ±ψ）±（−１）｝］…(2) となる。上式で正負２重記号の所は１／４波長板の方位
により、上側は方位角＋４５°のとき下側は−４５°の
場合である。上式より最小限３点の測定結果からφ，ψ
を算定することができる。Next, consider the case where the polarizer is rotated faster than the analyzer. When the analyzer is fixed and the polarizer is rotated, the reflected light from the sample changes in the range of circularly polarized light to linearly polarized light, and the azimuth angle also changes. Therefore, the detected light intensity I fluctuates up and down in accordance with the rotation of the polarizer, but gradually rises and falls in accordance with the rotation of the analyzer, and exhibits a change as shown in FIG. This I is I = Io [sin ² (ωt + φ) ± (1/2) sinφ
sin2ωt × {sin (2ω′t ± ψ) ± (−1)}] (2) The positive and negative double symbols in the above equation are for the azimuth of the quarter-wave plate. From the measurement results of the minimum of 3 points from the above equation, φ, ψ
Can be calculated.

【０００９】[0009]

【実施例】図１に本発明の一実施例を示す。Ｌは光源の
レーザ、１は偏光子、２は１／４波長板、３は検光子、
４は光検出器で、Ｓは試料である。これらの基本的な構
成は一般のエリプソメータと同じである。偏光子１，１
／４波長板２，検光子３は夫々装置の光軸を中心として
回転可能に保持され、夫々が独立にステッピングモータ
Ｍ１，Ｍ２，Ｍ３で駆動されるようになっている。１／
４波長板は、試料への入射光の光軸と試料からの反射光
の光軸を含む面に平行な方向を基準方向として、その方
向と＋４５°および−４５°の二種の方位角に設定する
ためモータＭ２で駆動されるようになっている。５は制
御装置でモータドライバ６を介してステッピングモータ
Ｍ１，Ｍ２，Ｍ３を駆動する。Ｐ１，Ｐ２，Ｐ３は夫々
偏光子１，１／４波長板２，検光子３の方位が基準方位
になっていることを検知する光電的検出器で、制御装置
５は各偏光素子１，２，３が基準方位にあることをセン
サＰ１，Ｐ２，Ｐ３の出力によって検知し、その位置か
らステッピングモータＭ１，Ｍ２，Ｍ３に送ったパルス
数を計数して夫々の偏光素子の方位を検知している。光
検出器４の出力はＡ／Ｄ変換器７を介して制御装置５に
取り込まれる。８は制御装置に種々な動作指令を与え、
また各種データを入力するためのキーボードで、９は測
定結果を表示する表示装置である。FIG. 1 shows an embodiment of the present invention. L is a light source laser, 1 is a polarizer, 2 is a quarter-wave plate, 3 is an analyzer,
4 is a photodetector and S is a sample. The basic configuration of these is the same as that of a general ellipsometer. Polarizer 1,1
The / 4 wave plate 2 and the analyzer 3 are rotatably held around the optical axis of the apparatus, and are independently driven by the stepping motors M1, M2 and M3. 1 /
The four-wave plate has a reference direction that is parallel to the plane including the optical axis of the incident light to the sample and the optical axis of the reflected light from the sample, and the two azimuth angles of + 45 ° and −45 °. It is driven by the motor M2 for setting. A controller 5 drives stepping motors M1, M2 and M3 via a motor driver 6. P1, P2, and P3 are photoelectric detectors that detect that the azimuths of the polarizer 1, the quarter-wave plate 2, and the analyzer 3 are the reference azimuths, respectively. , 3 are in the reference azimuth based on the outputs of the sensors P1, P2, P3, the number of pulses sent from the position to the stepping motors M1, M2, M3 is counted to detect the azimuths of the respective polarization elements. There is. The output of the photodetector 4 is taken into the control device 5 via the A / D converter 7. 8 gives various operation commands to the control device,
A keyboard for inputting various data, and 9 is a display device for displaying measurement results.

【０００８】測定動作をスタートさせると、制御装置５
は各偏光素子１，２，３を基準方位に設定し、次いで１
／４波長板２を＋４５°の方位に設定した後、偏光子
１，検光子３を夫々所定の角速度ω’，ωで回転させ、
一定時間間隔で光検出器４の出力をサンプリングし、そ
のときの偏光子１，検光子３の方位角と共にメモリに記
入して行く。この動作は低速回転させている方の偏向素
子の半回転の間行う。次に１／４波長板の方位角を−４
５°に設定して上と同じ測定動作繰り返す。When the measurement operation is started, the controller 5
Sets each polarizing element 1, 2, 3 to the reference direction, and then 1
After setting the / 4 wave plate 2 in the azimuth of + 45 °, the polarizer 1 and the analyzer 3 are rotated at predetermined angular velocities ω ′ and ω, respectively,
The output of the photodetector 4 is sampled at regular time intervals, and the azimuths of the polarizer 1 and the analyzer 3 at that time are recorded in a memory. This operation is performed during the half rotation of the deflecting element which is rotating at a low speed. Next, set the azimuth angle of the quarter-wave plate to -4.
Set to 5 ° and repeat the same measurement operation as above.

【０００９】実際問題として前記(1) 或は(2) の式によ
り３つの時点の光検出強度各偏光素子の方位角からφ，
ψを算出する演算は三角方程式となって大へん面倒であ
る。しかし偏光子１と検光子３の回転速度の比が或る程
度大きいときは図２，３の短周期の変化の包絡線が明確
になって来るので、以下述べるようにして消光点を内挿
的に求めることができる。As a practical matter, the photodetection intensities at three time points can be calculated from the azimuth angle of each polarization element by the equation (1) or (2).
The calculation to calculate ψ becomes a trigonometric equation, which is very troublesome. However, when the rotation speed ratio of the polarizer 1 and the analyzer 3 is large to some extent, the envelope of the change in the short period in FIGS. 2 and 3 becomes clear, and the extinction point is interpolated as described below. Can be asked for.

【００１０】検光子３の方が高速回転の場合図４Ａに示
すような光検出強度のデータが得られる。図は強度変化
の振幅が最大である付近のカーブの下の部分だけを示し
ている。図で点線で示す包絡線の最低位置が消光位置
で、その時点ｔの偏光子１の方位がψを与える。同じ時
点で検光子３の方位が消光角φであれば、ｔ時点で光検
出器出力は最小（原理的には０）になっているが、検光
子の方位は一般にはそのときφではない。偏光子は検光
子に比しゆっくり回っているので、ｔ時点の前後で殆ど
方位は変わっていない。従ってｔ時点の前後の光強度最
小の谷における検光子の方位は消光角に近い値である。
これらの方位角をα，β，γ等とする。βはαと略１８
０°の差があるので、γ，β−１８０°，γ…を図４Ｂ
のように時間軸上にプロットして、一曲線で結びｔ時点
に立てた垂線との交点の高さが検光子３の消光角φを与
える。以上を数式演算で行うには、図４Ａの複数の極小
点の時刻と光強度のデータから包絡線を２次曲線として
最小自乗法で決定し、この包絡線の極小点の時間ｔを算
出する。次に図４Ｂの曲線を時刻と光強度極小点の検光
子の方位角α，β，γ等のデータから２次曲線として上
と同様にして最小自乗法で決定し、ｔ時点の角度を算出
する。When the analyzer 3 rotates at a higher speed, the data of the photodetection intensity as shown in FIG. 4A is obtained. The figure shows only the lower part of the curve near the maximum intensity change amplitude. The lowest position of the envelope shown by the dotted line in the figure is the extinction position, and the azimuth of the polarizer 1 at that time point t gives ψ. If the azimuth of the analyzer 3 is the extinction angle φ at the same time point, the photodetector output is at a minimum (0 in principle) at time t, but the azimuth of the analyzer is generally not φ at that time. . Since the polarizer rotates more slowly than the analyzer, the azimuth hardly changes before and after the time point t. Therefore, the azimuth of the analyzer in the valley with the minimum light intensity before and after the time t is a value close to the extinction angle.
Let these azimuth angles be α, β, γ, etc. β is approximately 18 with α
Since there is a difference of 0 °, γ, β−180 °, γ ...
Plotted on the time axis as above, the height of the intersection of the curve and the perpendicular line standing at time t gives the extinction angle φ of the analyzer 3. To perform the above by mathematical calculation, the envelope is determined as a quadratic curve from the data of the plurality of minimum points in FIG. 4A and the data of the light intensity by the method of least squares, and the time t of the minimum point of this envelope is calculated. . Next, the curve of FIG. 4B is determined as a quadratic curve from the data of the time and the azimuth angles α, β, γ, etc. of the analyzer at the light intensity minimum point by the least square method in the same manner as above, and the angle at time t is calculated. To do.

【００１１】偏光子が検光子より高速回転する場合、図
３で光強度の極小点の包絡線が極小になる位置が消光位
置であるから、この場合も上述と同じにしてφ，ψを求
めることができる。When the polarizer rotates faster than the analyzer, the extinction position is the position where the envelope of the minimum point of the light intensity is the minimum in FIG. 3, and in this case also φ and ψ are obtained in the same manner as described above. be able to.

【００１２】[0012]

【発明の効果】偏光子，検光子の回転速度の速い方を９
００°／秒、遅い方を５°／秒とすると、遅い方を１８
０°回転させることで一回の測定が完了するので、一回
の測定は３６秒で終わり、１／４波長板の方位角＋４５
°と−４５°での測定を合わせて７２秒で完了する。こ
のように本発明によれば、偏向素子を連続回転させて、
低速回転側の半回転で測定を終わることができるので、
偏光解析測定が能率的に行われる。[Effects of the Invention] If the rotation speed of the polarizer or analyzer is higher,
00 ° / sec, slower is 5 ° / sec, slower is 18
Since one measurement is completed by rotating 0 °, one measurement is completed in 36 seconds, and the azimuth angle of the quarter wave plate is +45.
The combined measurements at ° and -45 ° are completed in 72 seconds. Thus, according to the present invention, the deflection element is continuously rotated,
Since the measurement can be completed in half rotation on the low speed rotation side,
Ellipsometric measurement is efficiently performed.

【図面の簡単な説明】[Brief description of drawings]

【図１】本発明の一実施例の平面図FIG. 1 is a plan view of an embodiment of the present invention.

【図２】上記実施例の測定データのグラフFIG. 2 is a graph of measurement data of the above example

【図３】上記実施例の他の場合の測定データのグラフFIG. 3 is a graph of measured data in other cases of the above-mentioned embodiment.

【図４】偏光素子の消光位置の決定手順を説明する図FIG. 4 is a diagram illustrating a procedure for determining an extinction position of a polarizing element.

【図５】従来例の平面図FIG. 5 is a plan view of a conventional example.

【符号の説明】[Explanation of symbols]

１ 偏光子 ２ １／４波長板 ３ 検光子 ４ 光検出器 ５ 制御装置 Ｍ１，Ｍ２，Ｍ３ ステッピングモータ 1 Polarizer 2 1/4 Wave Plate 3 Analyzer 4 Photo Detector 5 Control Device M1, M2, M3 Stepping Motor

Claims (1)

【特許請求の範囲】[Claims] 【請求項１】偏光子と検光子を互いに異なる速度で回転
させる手段と、時間データと各時間に対応する偏光子と
検光子の方位角と光検出信号のデータを採取し記憶する
手段と、上記採取したデータから光検出信号が０になる
時点の偏光子，検光子の方位角を内挿的に算出する手段
とを有する偏光解析装置。1. A means for rotating a polarizer and an analyzer at mutually different speeds, and means for collecting and storing time data, azimuth angles of the polarizer and the analyzer corresponding to each time, and data of a light detection signal. A polarization analyzer having a polarizer and means for interpolating the azimuth angle of the analyzer when the light detection signal becomes 0 from the collected data.