JPS63255685A - Length measuring apparatus by laser - Google Patents

Abstract

PURPOSE:To enable the detection of an absolute position of an object to be measured, by providing a device which calculates a distance to the object from phase data and period data. CONSTITUTION:When an injection current is varied linearly by a modulation circuit 1, a frequency-modulated light is emitted from a semiconductor laser 2. The light emitted from the laser 2 is made to enter a light receiver 7, as a reference light, through a collimator lens 3, a beam splitter 4, a reference mirror 5 and the splitter 4. Meanwhile, a measured light passing through the splitter 4, striking at a moving mirror 6 and reflected therefrom enters the light receiver 7 through the splitter 4. The reference light and the measured light are composed in the light receiver 7 and an electric signal is obtained therefrom. Next, a period Tb is measured in a period counting circuit 8, while a rough measured value is determined from the period Tb in a wave number counting circuit 9 and further the number (n) of cycles one of which is a 1/2 wavelength is determined therein. In a phase detection circuit 10, a phase theta of a beat signal for a prescribed time being synchronized with the modulation signal of the circuit 1 is detected. In a distance detection circuit 11 a distance R is determined from the number (n) of cycles and the phase theta, and it is outputted 12 therefrom.

Description

【発明の詳細な説明】 〔産業上の利用分野〕 本発明は半導体製造工程などにおけるＸ−Ｙステージな
ど粒密に位置決めを行なう装置において測長を行なうレ
ーザ測長装置に関する。DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser length measuring device that measures length in a device that performs positioning in a precise manner, such as an X-Y stage in a semiconductor manufacturing process.

〔従来の技術〕[Conventional technology]

従来のレーザ測長装置は単一周波または２周波レーザ光
を用い、測定光と基準光との干渉による縞移動変化から
被測定物の変位量を計測していた。Conventional laser length measuring devices use single-frequency or dual-frequency laser light to measure the amount of displacement of the object to be measured from changes in fringe movement due to interference between measurement light and reference light.

第２図は上述したレーザ測長装置のブロック図、第３図
は縞移動変化を示す図である。FIG. 2 is a block diagram of the laser length measuring device described above, and FIG. 3 is a diagram showing changes in fringe movement.

このレーザ測長装置は、Ｈｅ−Ｎｅなとの単一周波レー
ザ光２１を発射し、ビームスプリッタ２２で参照鏡２３
と移動ステージ３１（ステージモータ３２で駆動される
）上の移動鏡２４に２分し、参照鏡２３および移動鏡２
４で反射してきた光をビームスプリッタ２２でミキシン
グし、分割ミラー２５で分割した後受光器２６．２７で
検出し、プリアンプ２８により第３図に示すような９０
°の位相差の出力を得、該出力を可逆カウンタ２９でカ
ウントし、ＣＰＵ３０で移動ステージ３１の移動量を演
算するものである。This laser length measuring device emits a single frequency laser beam 21 such as He-Ne, and uses a beam splitter 22 to connect a reference mirror 23 to a reference mirror 23.
and a movable mirror 24 on a movable stage 31 (driven by a stage motor 32), a reference mirror 23 and a movable mirror 2.
4 is mixed by a beam splitter 22, divided by a splitting mirror 25, detected by a light receiver 26, 27, and then detected by a preamplifier 28 as shown in FIG.
An output of a phase difference of degrees is obtained, the output is counted by a reversible counter 29, and the amount of movement of the moving stage 31 is calculated by the CPU 30.

〔発明が解決しようとする問題点〕[Problem that the invention seeks to solve]

上述した従来のレーザ測長装置は、単一周波数レーザ光
または２周波レーザ光を用い被測定物の移動量を変位と
して計測しており、検出されるイ１；号はステージ移動
に伴なうくり返し信号でありインクリメンタルな変位計
測であるため、たとえば、なんらかの障害物が光路中を
瞬時たりとも通過した場合、その時点で被測定物の位置
情報か失なわれるという欠点があり、ざらにＨａ　−Ｎ
　ｅなと比較的大きな形状のカスレーザを用い、また光
学系も複雑になるため装置が大型化し、かつ高価になる
という欠点かある。The above-mentioned conventional laser length measuring device uses a single frequency laser beam or a dual frequency laser beam to measure the amount of movement of the object to be measured as a displacement, and the detected a. Since it is a repetitive signal and incremental displacement measurement, there is a drawback that, for example, if some obstacle passes through the optical path even momentarily, the position information of the object to be measured is lost. N
The e type uses a comparatively large shaped laser beam and has a complicated optical system, which has the disadvantage of making the device larger and more expensive.

本発明の目的は、被測定物の絶対位置を検出てき、した
がって外乱の影響に強いレーザ測長装置を提供すること
にある。An object of the present invention is to provide a laser length measuring device that can detect the absolute position of an object to be measured and is therefore resistant to the influence of disturbances.

〔問題点を解決するための手段〕[Means for solving problems]

本発明のレーザ測長装置は、 半導体レーザを用い直線的に周波数変調したレーザ光を
放射し、被測定面で反射して来たレーザ光と基準光路を
通るレーザ光をミキシングしてビート信号を検出する装
置と、 前記ビート信号の周期を計数する装置と、変調周期のあ
る一定時刻におけるヒートイ菖号の位相を検出する装置
と、 前記位相データと周期データより被測定物までの距離を
演算する装置とをイｆする。The laser length measurement device of the present invention uses a semiconductor laser to emit linearly frequency-modulated laser light, and generates a beat signal by mixing the laser light reflected from the surface to be measured and the laser light passing through the reference optical path. a device for detecting the beat signal; a device for counting the period of the beat signal; a device for detecting the phase of the Heati irises at a certain time in the modulation period; and a device for calculating the distance to the object to be measured from the phase data and the period data. If the device.

〔作用〕[Effect]

半導体レーザで周波数変調したレーザ光を用い測定光と
基準光をミキシングすることによって発生するビート信
号の周期データから距離の粗測定を行ない、また変調信
ぢに同期した一定時刻での位相測定から密測定を行ない
、両者を合成することにより、高精度な絶対距離測定が
可能になり、したかりて障害物通過の影響もなく、また
光学系も小型、簡単になる。The distance is roughly measured from the cycle data of the beat signal generated by mixing the measurement light and the reference light using a laser light frequency modulated by a semiconductor laser, and the fine distance is measured from the phase measurement at a fixed time synchronized with the modulated signal. By performing measurements and combining the two, highly accurate absolute distance measurement becomes possible, and therefore there is no influence from passing obstacles, and the optical system can also be made smaller and simpler.

〔実施例） 次に、本発明の実施例について図面を参照して説明する
。[Example] Next, an example of the present invention will be described with reference to the drawings.

第１図は本発明のレーザ測長装置の一実施例のブロック
図である。FIG. 1 is a block diagram of an embodiment of the laser length measuring device of the present invention.

本実施例は、半導体レーザ２と、半導体レーザ２の出射
光を直線的に周波数変調するだめの注入電流を直線的に
変化させる変調回路工と、レーザ光をコリメートするコ
リメータレンズ３と、参照鏡５と、ステージモータ】４
で駆動される移動ステージ１３上に設りられた移動鏡６
と、レーザ光を参照鏡５用、移動鏡６用へと２分し、ま
た反射光をミキシングするだめのビームスプリッタ４と
、ミキシングにより生じるビート信号を検出する受光器
７と、ビート信号の周期Ｔｂを十分に高い周波数のクロ
ックを用いて計測する周期計数回路８と、周期データよ
り移動鏡６の位置の粗測定値ｎを演算する波数計数回路
９と、変調回路１の変調信号と同期したある時刻でのビ
ート信号の位相θを検出する位相検出回路】０と、波数
データｎ、位相信号θおよび波長λより移動鏡６の位置
Ｒを演算する距ｒａ演算回路１１と、位置Ｒを出力する
出力回路１２とで構成されている。This embodiment includes a semiconductor laser 2, a modulation circuit that linearly changes the injection current to linearly frequency modulate the output light of the semiconductor laser 2, a collimator lens 3 that collimates the laser light, and a reference mirror. 5 and stage motor】4
A movable mirror 6 installed on a movable stage 13 driven by
, a beam splitter 4 that splits the laser beam into two for the reference mirror 5 and the movable mirror 6 and mixes the reflected light, a light receiver 7 that detects the beat signal generated by the mixing, and a beat signal period. A period counting circuit 8 that measures Tb using a clock with a sufficiently high frequency, a wave number counting circuit 9 that calculates a rough measurement value n of the position of the movable mirror 6 from the period data, and a wave number counting circuit 9 that is synchronized with the modulation signal of the modulation circuit 1. A phase detection circuit that detects the phase θ of a beat signal at a certain time; a distance ra calculation circuit 11 that calculates the position R of the movable mirror 6 from the wave number data n, the phase signal θ, and the wavelength λ; and outputs the position R. The output circuit 12 is composed of an output circuit 12 and an output circuit 12.

次に、本実施例の動作について説明する。Next, the operation of this embodiment will be explained.

半導体レーザ２は周波数が急激に変化するモードホップ
を起こさない周波数範囲内（約０．１零以下）であれば
注入電流に比例して周波数を変化させることができる。The semiconductor laser 2 can change the frequency in proportion to the injected current as long as it is within a frequency range (approximately 0.1 zero or less) that does not cause mode hopping where the frequency changes rapidly.

すなわち注入電流を直線的（実際には三角波状に変化さ
せる）変化させわば次式（１）で示される周波数ｆの周
波数変調された光が半導体レーザ２から出てくる。That is, by changing the injected current linearly (actually, in a triangular waveform), frequency-modulated light with a frequency f expressed by the following equation (1) is output from the semiconductor laser 2.

ｒ　＝　ｆｏ　＋　ｆｔ　　＝・（１）ただし、ｆｏは
変調開始点のレーザ光周波数、？は周波数変化率、ｔは
時間 今、半導体レーザ２からコツメータレンズ３を通りビー
ムプワッタ４で９０°方向が曲げられ、参照鏡５に当り
反射され、ビームスプリッタ４を通り受光器７に到る基
準光が次式（２）で表わされるものとする。r = fo + ft = · (1) where fo is the laser light frequency at the modulation start point, ? is the rate of frequency change, and t is the time.The reference beam from the semiconductor laser 2 passes through the meter lens 3, is bent by 90 degrees at the beam splitter 4, is reflected by the reference mirror 5, passes through the beam splitter 4, and reaches the photoreceiver 7. It is assumed that light is expressed by the following equation (2).

Δ−Δ、ｅｘｐ　（−２πｊ（ｆｏ＋ｆｔ）　ｔ　）　
−（２）ただし、八、は基準光の強度 一方、ビームスプリッタ４を通過し、移動鏡６に当り反
射されビームスプリッタ４で９０°方向が曲げられ受光
器７に到る測定光は基準光に対する時間遅れをτ、光路
差をＲとすれば次式（３）で表わされる。Δ−Δ, exp (−2πj(fo+ft) t )
-(2) However, 8 is the intensity of the reference light.On the other hand, the measuring light that passes through the beam splitter 4, hits the movable mirror 6, is reflected, is bent by the beam splitter 4 by 90 degrees, and reaches the light receiver 7 is the reference light. Letting τ be the time delay and R be the optical path difference, it is expressed by the following equation (3).

Ｂ＝Ｂ＋ｅｘｐ［−２πｊ　　（（ｆｏ＋ｆ（ｔ−−τ
）　　）　　（ｔ−τ）コ・・・　（３） たたし、＋１．は測定光の強度、 τ＝２８．＃：、　Ｃは光速 受光器７ては、２．Ｌ−準光と測定光のミキシングによ
り次式（４）で表わさねる電気信号Ｖ、が得られる。B=B+exp[-2πj ((fo+f(t--τ
) ) (t-τ)ko... (3) Tatami, +1. is the intensity of the measurement light, τ=28. #:, C is the speed of light receiver 7, and 2. By mixing the L- quasi-light and the measurement light, an electric signal V expressed by the following equation (4) is obtained.

ｖｌ−）Ａ十Ｂ（２ ＝Ａ、’＋Ｂ、’＋２Ａ山ｃｏｓ　（２ｙｒ　（ｆτ＋
ｆτｆ：　−ｆτ２））・・・（４） たたし、　ｆτ２　（＜　ｆτてあり無視てき、また（
４）式の交流分のみをとり出し受光器７の出力を■２と
すれば次式（５）の信号となる。vl-)A0B(2 =A,'+B,'+2A mountain cos (2yr (fτ+
fτf: -fτ2))...(4) Then, fτ2 (< fτ has been ignored, and (
If only the alternating current component of the equation (4) is taken out and the output of the light receiver 7 is set to 2, the signal of the following equation (5) will be obtained.

■２−２八１Ｂ１ｃｏｓ（４πＲ／＾＋　４πｆＲｔ／
Ｃ：　　）　　−（５）たたし、λ・波長 （５）式の第２項がビート信号を表わし、ビート周波数
ｆｂは次式（５）で表わされる。■2-281B1cos (4πR/^+ 4πfRt/
C: ) - (5) and λ/wavelength The second term of the equation (5) represents the beat signal, and the beat frequency fb is expressed by the following equation (5).

ｆｈ　＝　２Ｒ−ｆ／ｃ　　　　　　　　　　　　　−
（［１）（６）式かられかるようにビート周波数ｆｂは
測定距離Ｈに比例する。しかし、周波数工１数では周波
数偏位量を△ｆとずわば、　Ｃ／４△ｆの量子化誤差が
牛しる。今、八ｆ　＝５０ＧＨｚとすればこの量子化誤
差は１．５ｍｍと大きな値となる。周期計数回路８ては
このため周波数を計数するかわりに周期Ｔｂ−１／ｆｂ
を計測する。今、ビート周期ｆｂに対してＩ／Ｎ（たと
えば１０−４から１Ｏ−５）の周期Ｔｃのクロックを用
いてＭ４数すればその量子化誤差△Ｒは次式（７）％式
％ 今、Ｒ＝１０ｍｍで、Ｎ＝１０！′−とすれば量子化誤
差△Ｒは０．１＋１１１１となり、波長以下の精度が得
られる。波数計数回路９では、周期データＴ、より粗測
定値Ｒ“を求め、さらに１７２波長を１サイクルとする
サイクル数を求める。fh = 2R-f/c-
([1) As can be seen from equation (6), the beat frequency fb is proportional to the measurement distance H. However, when the frequency deviation is △f, the quantization error of C/4△f is significant. Now, if 8f = 50 GHz, this quantization error will be as large as 1.5 mm. For this reason, the period counting circuit 8 calculates the period Tb-1/fb instead of counting the frequency.
Measure. Now, if we multiply M4 by using a clock with a period Tc of I/N (for example, 10-4 to 1O-5) for the beat period fb, the quantization error △R is the following formula (7)% formula % Now, R=10mm, N=10! '-, the quantization error ΔR becomes 0.1+1111, and accuracy below the wavelength can be obtained. The wave number counting circuit 9 obtains the period data T, the rough measured value R'', and further calculates the number of cycles in which 172 wavelengths constitute one cycle.

すなわち、サイクル数をｎ、剰余をαとすればＲ’／局
λ：ｎ・・・α　　　　　　　　　　・・・（８）ｇ′
＝　ｃ／（２−ｊ−ｒｂ＞　　　　　　　　　　　　　
−（９）位相検出回路１０では変調回路１の変調信号に
同期した一定時刻のビート信号の位相θを検出する。That is, if the number of cycles is n and the remainder is α, then R'/station λ:n...α...(8)g'
= c/(2-j-rb>
(9) The phase detection circuit 10 detects the phase θ of the beat signal at a fixed time synchronized with the modulation signal of the modulation circuit 1.

今、簡単のため（５）式の時刻１＝０の位相θを検出す
るものとすわば次式（］０）で位相θが表わされる。For simplicity, the phase θ at time 1=0 in equation (5) is detected, and the phase θ is expressed by the following equation (]0).

θ＝　４πＲ／λ　　　　　　　　　　　　　−（１０
）位相Ｏはλ／２を周期としたくり返し信号となり、今
、波長人−０，８μｍとし、位相θを１７１００（３，
６°）の精度で検出すれば４Ｒｍの分解能で測定か可能
となる。距離演算回路１１ては上記サイクル数ｎおよび
位相θより距離Ｒを次式（１１）を用い演算し、出力回
路１２より出力する。θ=4πR/λ−(10
) The phase O becomes a repeating signal with a period of λ/2, and now the wavelength is −0.8 μm and the phase θ is 17100 (3,
If it is detected with an accuracy of 6°), it is possible to measure with a resolution of 4Rm. The distance calculation circuit 11 calculates the distance R from the above-mentioned cycle number n and the phase θ using the following equation (11), and outputs it from the output circuit 12.

Ｒ＝λ／２（ｎ＋θ／２ｒｔ　）　　　　　　　　　−
（１１）〔発明の効果〕 以上説明したように本発明は、小型の半導体レーザを用
い、かつ直線的に周波数変調したレーザ光を用い、距離
に比例したビート信号の周期の測定を行なうと共に変調
信号に同期した一定時刻でのビート信号の位相測定を行
ない、周期データおよび位相データを演算処理すること
により、高精度な距離測定が行なえ、また従来例で述べ
たような変位測定方式ではなく、絶対距離測定方式のた
め、たとえ障害物が光路中を一時的に通過しても通過後
は精密な測定ができ、さらには光学系も比較的簡明であ
り、小型かつ安価な測長器を提供できる効果がある。R=λ/2(n+θ/2rt) −
(11) [Effects of the Invention] As explained above, the present invention uses a small semiconductor laser and linearly frequency-modulated laser light to measure and modulate the period of a beat signal proportional to distance. By measuring the phase of the beat signal at a fixed time synchronized with the signal and processing the period data and phase data, highly accurate distance measurement can be performed. Since it uses an absolute distance measurement method, even if an obstacle temporarily passes through the optical path, accurate measurements can be made after it passes.Furthermore, the optical system is relatively simple, providing a compact and inexpensive length measuring instrument. There is an effect that can be done.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は本発明のレーザ測長装置の一実施例のブロック
図、第２図は従来例のブロック図、第３図は第２図の従
来例におりるステージ移動に伴なうプリアンプ出力の変
化を示す図である。 １・・・変調回路、　　　２・・・半導体レーザ、３・
・・コリメータレンズ、 ４・・・ビームスプリッタ、 ５・・・参照鏡、　　　　６・・・移動鏡、７・・・受
光器、　　　８・・・周期計数回路、９・・・波数５１
数回路、ＩＯ・・・位相検出回路、１１・・・距離演算
回路、１２・・・出力回路。Fig. 1 is a block diagram of an embodiment of the laser length measuring device of the present invention, Fig. 2 is a block diagram of a conventional example, and Fig. 3 is a preamplifier output associated with stage movement in the conventional example of Fig. 2. FIG. DESCRIPTION OF SYMBOLS 1... Modulation circuit, 2... Semiconductor laser, 3...
... Collimator lens, 4... Beam splitter, 5... Reference mirror, 6... Moving mirror, 7... Light receiver, 8... Period counting circuit, 9... Wave number 51
Several circuits, IO...phase detection circuit, 11...distance calculation circuit, 12...output circuit.

Claims (1)

【特許請求の範囲】 半導体レーザを用い直線的に周波数変調したレーザ光を
放射し、被測定面で反射して来たレーザ光と基準光路を
通るレーザ光をミキシングしてビート信号を検出する装
置と、 前記ビート信号の周期を計数する装置と、 変調周期のある一定時刻における前記ビート信号の位相
を検出する装置と、 前記位相データと周期データより被測定物までの距離を
演算する装置とを有するレーザ測長装置。[Claims] A device that detects a beat signal by emitting linearly frequency-modulated laser light using a semiconductor laser and mixing the laser light reflected from a surface to be measured with the laser light passing through a reference optical path. a device for counting the period of the beat signal; a device for detecting the phase of the beat signal at a certain time in the modulation period; and a device for calculating the distance to the object to be measured from the phase data and period data. A laser length measurement device with