JPH09138105A - Device for measuring moving quantity of moving body by interferometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand a dynamic range by arranging two measuring mirrors for one measuring axis in the opposite direction to each other and selecting the other beat signal when one beat signal from one interferometer of two ones cannot be measured. SOLUTION: Measuring mirrors MA and MB are fitted in the opposite direction to each other on both sides at a stage 2 in an x direction, so that the measuring lights of interferometers A and B are refelcted therefrom. When the stage 2 is shifted in an x minus direction, a frequency f2 of the measuring lights of the interference A increases, and its beat frequency increases more than the reference beat frequency at the time when the stage 2 is stopped. In addition, the measuring frequency f4 of the interferometer B is decreased, and the beat frequency is decreased at least at the intial time more than the reference beat frequency at the time when the stage 2 is stopped. When the stage 2 is shifted in an x puls direction, the phenomenon become reverse. Even when one interferometer is in an unmeasurable area, the other one is measurable, and the interferometer modulated to the high-frequency side is delected so as to expand the dynamic range of a measuring device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the amount of movement of a moving body using a light wave interferometer.

[0002]

2. Description of the Related Art In semiconductor manufacturing equipment, it is necessary to accurately measure the amount of movement of the stage. Conventionally, the stage position measurement of a semiconductor manufacturing apparatus has been performed by an interferometer using a heterodyne light source, as shown in FIG. That is, the light flux from the heterodyne light source 1 is split by the half mirror HM, one light flux is guided to the interferometer A, the other light flux is guided to the interferometer B, and the position of the stage 2 in the x direction is measured by the interferometer A. The position of the stage 2 in the y direction was measured by the interferometer B. Thus, in the related art, the movement amount for one measurement axis (x or y) is 1
It was measured by two interferometers (A or B).

As the heterodyne light source 1, a helium neon laser using the axial Zeeman effect is mainly used. The axial Zeeman laser is a laser that coaxially generates a right circularly polarized light beam and a left circularly polarized light beam whose frequencies are slightly different from each other. The typical value of the wavelength λ of both beams is λ
= 633 nm. A typical value of the difference between the frequencies f ₁ and f ₂ of both light fluxes is 1.8 MHz. Therefore, the difference between the wavelengths or the frequencies of the two beams is on the order of 10 ⁻⁹ of the wavelengths or the frequencies of the two beams.

FIG. 12 shows an example of the structure of the interferometer A shown in FIG. 11, and the same applies to the interferometer B. The right circularly polarized light beam and the left circularly polarized light beam whose frequencies are slightly different from each other are
It is converted into two linearly polarized light beams orthogonal to each other by the / 4 plate 3 and enters the polarization beam splitter 4. The s-polarized reference light b ₁ of the two linearly polarized lights is reflected by the polarization beam splitter 4 and the reference mirror 6, and λ
It is converted into p-polarized light by passing back and forth through the / 4 plate 5, and therefore passes through the polarization beam splitter 4 and enters the analyzer 8. On the other hand, the p-polarized measuring light b ₂ of the two linearly polarized lights passes through the polarization beam splitter 4 and is reflected by the measuring mirror M attached to the stage 2 of the semiconductor measuring device, and the λ / 4 plate 7 is placed between them. It is converted into s-polarized light by passing back and forth, and therefore is reflected by the polarization beam splitter 4 and similarly enters the analyzer 8.

In the above description, it is assumed that the reference light b ₁ is initially s-polarized light, so that it is reflected by the polarization beam splitter 4 and then transmitted therethrough, and the measurement light b ₂ is initially p-polarized light. Although it is assumed that the light is transmitted through the beam splitter 4 and then reflected, the relationship may be reversed. That is, the reference light b ₁ initially passes through the polarization beam splitter 4 and is then reflected, and the measurement light b ₂ initially transmits the polarization beam splitter 4.
It may be configured so that it is reflected by and then transmitted.

The reference light b ₁ and the measurement light b ₂ are measured by the analyzer 8
The polarized light interferes with the light by passing through the light and the intensity of the interfered light is detected by the photodetector 9. Here, both luminous fluxes b ₁ ,
Since the frequencies f ₁ and f ₂ of b ₂ are slightly different, interference results in a beat or beat. The beat frequency observed by the photodetector 9 is f ₀ = | f ₁ −f ₂ | when the measuring mirror M is stopped. The reference beat frequency f ₀ is the reference interferometer 13
Is measured by That is, the light from the light source 1 is separately split by the optical path splitting means (not shown), and the reference light b ₁
And the measurement light b ₂ which does not reach the measurement mirror M are caused to interfere with each other, and the reference interferometer 13 measures the reference beat frequency f ₀ .

By the way, when the measurement mirror M is moving, the frequency f ₂ of the measuring light b ₂ is modulated by the Doppler shift, the _{f 2 '= f 2 ± Δf} . Here, the frequency change Δf has a positive value. When the measuring mirror M moves toward the interferometer A, that is, in the x-minus direction, the compound signal is positive because it modulates to the high frequency side, and when it moves in the opposite direction, the compound signal is negative. Therefore, the beat frequency is also modulated from f ₀ , Becomes The frequency change Δf is given by Δf = 2v / λ 2 when the measuring mirror M is moving at a constant speed v (> 0), for example. Here, the refractive index of the air filling the optical path is 1. The coefficient 2 on the right side of the above formula means the round trip of light. The frequency change Δf is measured by the phase counter 10.

The phase counter 10 includes a reference interferometer 13
From the reference beat signal f ₀ = | f ₁ −f ₂ |
The beat signal f measured by is input, and the difference ΔN = (f−f ₀ ) in the number of beats of both signals f ₀ and f during ΔT seconds
ΔT can be obtained. Difference in beat counts ΔN and ΔT
Since there is a relationship of ΔL = ΔN · λ / 2 between the mirror movement distances ΔL per second, the total movement amount of the measurement mirror M is known by accumulating the count number ΔN for ΔT seconds by the phase counter 10. be able to.

In the above description, the case where the measurement light b ₂ is reflected by the measurement mirror M only once is described as a single path. However, the interferometer is configured such that the measurement light b ₂ is reflected by the measurement mirror M a plurality of times. It may be a multipath that reflects light. A case of the double pass of the multi-pass will be described with reference to FIG. 13. The right circularly polarized light beam and the left circularly polarized light beam having slightly different frequencies are converted into two linearly polarized light beams orthogonal to each other by the λ / 4 plate 3. And enters the polarization beam splitter 4. The s-polarized reference light b ₁ of the two linearly polarized light is reflected by the polarization beam splitter 4 and
It is reflected twice by the prism 11, and the polarization beam splitter 4
It is reflected by and enters the analyzer 8.

On the other hand, the measurement light b of the p-polarized light of the two linearly polarized light
_The light ₂ passes through the polarization beam splitter 4, is reflected by the measuring mirror M, and is converted into s-polarized light by passing back and forth through the λ / 4 plate 7, while being reflected by the polarization beam splitter 4. Further, the measurement light b _{2 that} has become s-polarized light is
The light is reflected twice by the measurement triangular prism 12, reflected by the polarization beam splitter 4 and reflected again by the measurement mirror M, and is converted into p-polarized light by passing back and forth through the λ / 4 plate 7 during this time, and thus is polarized. The light passes through the beam splitter and enters the analyzer 8.

In the case of this double pass, the optical path length of the measuring light b ₂ changes by 4 times the moving amount of the measuring mirror M,
The modulation amount Δf of the optical beat frequency is Δf = 4v / λ. That is, generally, when the number of reflections is m, the modulation amount Δf of the optical beat frequency is Δf = 2mv / λ (2).

As is clear from the above description, when the measuring mirror M moves toward (or separates from) the interferometer, the frequency f ₂ of the measuring light b ₂ from the interferometer is measured by the measuring mirror M. , It is observed with a slight shift to the high frequency side (or low frequency side) due to the Doppler effect. Further, the frequency f ₂ of the measurement light from the measurement mirror M shifted to the high frequency side (or the low frequency side) is further shifted to the high frequency side (or the low frequency side) and observed by the interferometer. In the case of multipath, this process is doubled by the number of paths.

In this way, the frequency f ₂ of the measuring light b ₂ is modulated by Δf = 2 mv / λ from the frequency when the measuring mirror M is stopped. Along with this, the beat frequency f is also modulated by Δf from the reference frequency f ₀ when the measuring mirror M is stopped. The frequency modulation amount Δf is negligibly small for the frequency f ₂ of the measurement light b ₂ . Reference light b
Since the difference between the _first frequency f ₁ and frequency f ₂ of the measurement light b ₂ is small, for the beat frequency f, modulation amount Δf is large.

Therefore, when f ₁ <f ₂ , when the frequency f _{2 of the} measurement light is modulated to the high frequency side, the beat frequency f is simply modulated to the high frequency side. However, when the frequency f _{2 of the} measurement light is modulated to the low frequency side, the beat frequency f is initially modulated to the low frequency side, but it is so low that the frequency f _{2 of the} measurement light matches the frequency f _{1 of the} reference light. When modulated to the side, the beat disappears. Further, when the frequency f _{2 of the} measurement light is modulated to the low frequency side so that it becomes smaller than the frequency f _{1 of the} reference light, the beat frequency f becomes 0
Gradually increases from. Similarly, when f ₁ > f ₂ , when the frequency f _{2 of the} measurement light is modulated to the low frequency side, the beat frequency f is simply modulated to the high frequency side, but the frequency f of the measurement light is f
_{When 2} is modulated to the high frequency side, the beat frequency f is modulated to the low frequency side, becomes zero beat, and then increases.

However, there is a limit to the beat frequency f that can be detected by the phase counter 10. That is, assuming that the maximum and minimum frequencies at which the optical beat detection system can electrically respond are e _max and e _min , the maximum frequency f _max of the beat frequency f accompanying the movement of the measuring mirror is f _max <e _max.
Must be the minimum frequency f _{min of the} beat frequency f
Must also be f _min > e _min . FIG.
(A) and (B) are measurement mirrors M when f ₁ <f _2.
In the direction approaching the interferometer (x minus direction)
The optical beat frequency f in the prior art when moving in the direction away from (x plus direction) is shown. (A) in the figure
And (B) also use the measuring mirror M when f ₁ > f ₂ ,
The optical beat frequency f in the prior art when moving in a direction away from the interferometer (x plus direction) and moving in a direction approaching (x minus direction) are shown. As shown in the figure, in the prior art, the optical beat frequency f has been used in a range within the electrical response range [e _min , e _max ] of the optical beat detection system.

[0016]

In the prior art, when the measuring mirror M moves at high speed, or when the number of passes m is large, the beat frequency f is the response range [e _min , e _max of the electric circuit of the detection system. ], That is, the beat frequency f may enter the unmeasurable region X in FIG. In particular, the response range of the beat detection system [e
_min, e _max] of, it is possible to increase the upper limit e _max, it is not possible to 0 for the lower limit e _min, it was sometimes falls below this order limit e _min . In such a case, the phase counter 10
Did not work properly and there was a problem that the position could not be measured.

The reason why such a phenomenon occurs is that the modulation amount Δf = 2mv / λ of the beat frequency depends on the moving speed v of the stage 2 and the number of paths m of the interferometer. This will be described with specific numerical values. Table 1 shows that the maximum moving speed v _max of the stage is 400 mm / s and 800 mm / s.
s, and the number of passes m is m = 1 (single pass) and m = 2
Modulation amount of beat frequency when (double pass) Δ
f is shown. However, the wavelength λ of the light source is λ = 63
It is set to 3 nm.

[0018]

[Table 1] v _max 400 mm / s 800 mm / s Δf (single pass) 1.3 MHz 2.6 MHz Δf (double pass) 2.6 MHz 5.2 MHz

The range [f _min , f _max ] of the optical beat frequency f during movement of the stage can be estimated by f ₀ ± Δf from Δf in Table 1. Now, the reference beat frequency f ₀ when the stage is stopped is set to f ₀ = 1.8 MHz, and the electrical response range of the optical beat detection system is from e _min = 100 KHz to e _max.
= 8 MHz. From Table 1, v _max = 400 m
In the case of a single pass at m / s, the range of the optical beat frequency f during the movement of the stage is 500 KHz ≦ f ≦ 3.1 MHz. Therefore, in this case, the optical beat frequency f is included in the electrical response range, and the position can be measured.

However, in the case of v _max = 400 mm / s and double pass, 0 Hz ≦ f ≦ 4.4 MHz. Therefore, in this case, the area of 100 KHz or less that could not be electrically responded was included, and the stage position could not be measured. That is, when f ₁ <f ₂ moves the stage in the x-minus direction, or when f ₁ > f ₂ moves the stage in the x-plus direction, FIG.
As shown in (A), the optical beat frequency is within the electrical response range, and the phase of the optical beat can be detected. However, f ₁ <
When the stage moves in the x plus direction at f ₂ , or f ₁
When the stage moves in the x minus direction with> f ₂ , as shown in FIG. 15 (B), it passes through the unmeasurable region X of e _min or less, and the phase of the optical beat in this range is detected. I can't. Note that, in FIG. 15B, the portion where the beat frequency f becomes negative is folded back with respect to the time axis. This is as shown in the equation (1).
This is because the beat frequency f is obtained as the absolute value of the difference between the frequency f _{1 of the} reference light and the frequency f ₂ ′ of the measurement light.

Next, in the case of single pass with v _max = 800 mm / s, the range of the optical beat frequency f is 0 Hz ≦ f ≦ 4.4 MHz, and in the case of double pass with v _max = 800 mm / s, 0 Hz ≦ f ≦ 7.0 MHz. In both cases, the measurement impossible region (100 KHz or less) was included, and the stage position could not be measured.

As described above, in the prior art, when the speed of the stage 2 is increased and the multipath of the interferometer is performed, the optical beat frequency f becomes the frequency response range [e _min , e _max ] of the optical beat detection system.
However, the position may not be measured because the value may be below the lower limit e _min . Therefore, an object of the present invention is to provide a movement amount measuring device having a wide dynamic range.

[0023]

The above problem is that two measuring mirrors are arranged in opposite directions with respect to one measuring axis, and a heterodyne interferometer is constructed for each of the two measuring mirrors. It was possible to solve the problem by arranging the magnitude relations between the frequencies of the reference light and the measurement light, and selecting one of the optical beat signals of the two interferometers when the other beat signal cannot be measured.

The principle of the present invention will be described with reference to FIG. In the figure, only the x-axis direction is extracted and shown. Measuring mirrors M _A and M _B are attached in parallel to each other in opposite directions on both sides of the stage 2 in the x direction so that the measuring light beams of the interferometer A and the interferometer B can be reflected. The frequencies of the reference light of the interferometer A, the measurement light, and the measurement light reflected by the measurement mirror M _A are f ₁ , f ₂ , and f ₂ ′, respectively, and the reference light, the measurement light, and the measurement mirror of the interferometer B are set. If the frequencies of the measurement light reflected by M _B are f ₃ , f ₄ , and f ₄ ′, the beat frequencies f _A and f _B of both interferometers _A and _B are It is. The two interferometers with the movement of the stage A, the modulation amount Delta] f _A of the beat frequency of B, Delta] f _B is the two interferometers A, each wavelength of the light source of B lambda _A, as _{λ B, Δf A = 2mv /} λ _A Δf _B = 2 mv / λ _B.

In the present invention, however, either f ₁ <f ₂ and f ₃ <f ₄ (3) or f ₁ > f ₂ and f ₃ > f ₄ (4) Both interferometers A and B are configured.

First, the direction of modulation in the case of the equation (3) is such that when the stage 2 moves in the x minus direction, that is, when the stage approaches the interferometer A, the interferometer A is used.
The frequency f ₂ of the measuring light of is increased to f ₂ ′. Therefore, since f ₁ <f ₂ , the beat frequency f _A = | f ₁ −
f ₂ '| increases from the reference beat frequency f _A0 at the time of stop. Further, at this time, since the stage is separated from the interferometer B, the frequency f ₄ of the measurement light of the interferometer B decreases to f ₄ ′, but f ₃ <f ₄ , so the beat frequency of the interferometer B is f
_{B = | f 3 -f 4 '} | , the reference at the time of stopping the beat frequency f _B0
More, at least initially.

On the contrary, when the stage 2 moves in the x plus direction, that is, when the stage is separated from the interferometer A, the frequency f ₂ of the measuring light of the interferometer A decreases and the interferometer A
Beat frequency f _A of, at least initially decreases. Further, at this time, since the stage approaches the interferometer B, the frequency f ₄ of the measuring light of the interferometer B increases and the beat frequency f _B of the interferometer _B increases. That is, the beat frequency of one interferometer increases and the beat frequency of the other interferometer decreases at least initially regardless of the moving direction of the stage.

On the other hand, the direction of modulation in the case of the equation (4) is that when the stage 2 approaches the interferometer A, the frequency f ₂ of the measurement light of the interferometer A increases and f ₁ > f ₂ is satisfied. , Beat frequency f _A = | f ₁ −f ₂ '| decreases at least initially. Further, since the stage is separated from the interferometer B, the frequency f ₄ of the measuring light of the interferometer B is reduced, and f ₃ > f
_Therefore , the beat frequency of the interferometer B is f _B = | f ₃ −
f ₄ '| increases.

On the contrary, when the stage 2 is separated from the interferometer A, the frequency f ₂ of the measuring light of the interferometer A decreases and the beat frequency f _A of the interferometer _A increases. Further, since the stage approaches the interferometer B, the frequency f ₄ of the measuring light of the interferometer B is
Increases and the beat frequency f _B of interferometer B decreases, at least initially. That is, also in the case of Expression (4), the beat frequency of one interferometer increases and the beat frequency of the other interferometer decreases at least initially regardless of the moving direction of the stage.

As described above, according to the present invention, unless the median value of the frequency response range [e _min , e _max ] of the optical beat detection system is the reference beat frequencies f _A0 and f _B0 of both interferometers A and B, respectively. Even if one of the interferometers enters the non-measurable region X, the other interferometer can measure, so that the movement amount of the stage can be measured by either one of the interferometers. In particular, as the stage moves, the beat frequency of one of the interferometers is modulated to the low frequency side and is likely to fall below the lower limit e _min of the frequency response range of the optical beat detection system. Since it is modulated on the high-frequency side, it is possible to avoid entering the non-measurable region, so that by selecting an interferometer modulated on the high-frequency side, the dynamic range of the measuring device can be expanded.

Regarding the method of selecting the interferometers A and B, refer to the electric signal sent from the CPU for controlling the stage to the stage moving motor when the stage is moved,
Alternatively, it can be performed by referring to a signal from the motor. For example, if the interferometer is configured to satisfy the expression (3), the control device issues a signal to move in the x-plus direction, and when the stage moves in the x-plus direction, the interferometer The procedure of adopting the data of B is C
It can be done in the PU. This data can be selected before the stage is moved so that only the data of the interferometer B is acquired, but on the other hand, the data of both interferometers are always acquired and after the stage is moved, the CP
It is also possible to take the procedure of selecting the data of the interferometer B according to the electrical signal issued by U. When the stage is stopped or is moving at a low speed and the optical beat frequency is within the electrical response range, position measurement can be performed by either one or both interferometers.

In the above description, it was explained that f _{1 to} f ₄ are all different, but it is sufficient that the formula (3) or (4) is satisfied,
Not all frequencies need to be different. In particular, f ₁ = f ₃ , f
_{If 2} = f ₄ , then either equation (3) or (4) is always satisfied. This corresponds to the case where the same light source is used as the heterodyne light source and the interferometers A and B have the same configuration. Further, although the case of the x direction has been described above, the y direction can be configured by the same principle. Although the interferometer has been described above in the air (refractive index = 1), when it is in another medium (refractive index n),
Replace lambda _A to λ _A / n, it may be replaced with lambda _B to lambda _B / n.

[0033]

Embodiments of the present invention will be described.
FIG. 2 shows a first embodiment of the invention, in which the frequencies f ₁ ,
A right circularly polarized light beam and a left circularly polarized light beam having slightly different f ₂ are coaxially generated from the axial Zeeman laser light source 2. The difference between the frequencies of the two light beams, that is, the reference beat frequency f
₀ is f ₀ = | f ₂ −f ₁ | = 1.8 MHz, and the wavelength λ of the light source is λ = 633 nm.

The light quantities of both light fluxes are three half mirrors HM.
1, HM2 and HM3 divide the signal into four 25% blocks, which are guided to interferometers A1, A2, B1 and B2, respectively. On the four sides of the stage 2, measurement mirrors M1 to M4 each having a rectangular shape are attached, and therefore M1 and M3, and M2 and M4 are attached in opposite directions. Measuring mirrors M1, M
2, M3 and M4 are interferometers A2, B2, A1 respectively.
And B1 measurement mirrors.

Each interferometer is composed of the single path shown in FIG. 12, and in each interferometer, the beam splitting by the polarization beam splitter is performed with the reference light at the frequency f ₁ and the measurement light at the frequency f _2. Is set so that
Further, in this embodiment, f ₁ <f ₂ , so that the frequency f ₁ of the reference light is lower than the frequency f _{2 of the} measurement light in all interferometers.

The optical beat detection system of each interferometer is connected to a CPU (not shown) that controls the movement of the stage. The range of the electrical response frequency of the optical beat detection system of each interferometer is e
_{From min} = 100 KHz to e _max = 8 MHz. Which of the four beat outputs is adopted is selected by the CPU. The CPU also controls the driving of a motor (not shown) for moving the stage 2 in the x and y directions. The maximum moving speed of the stage 2 by the x-direction motor and the y-direction motor is 800 mm / sec. The change Δf of the beat frequency f when the stage is moving at the maximum speed is 2.6 MHz from Table 1.

FIG. 3 is a diagram showing the time change of the optical beat frequency f of each interferometer when the stage 2 moves, and FIG.
Shows the case of moving in the x plus direction or the y plus direction, and FIG. 3 (B) shows the case of moving in the x minus direction or the y minus direction. As shown in FIG. 3, the beat frequency f of the interferometer that is modulated to the high frequency side with the movement of the stage 2 is f ₀ = 1.8 MHz, and f = f ₀ +2.6 at the highest.
Modulate up to MHz = 4.4 MHz. Further, the beat frequency f of the interferometer that is modulated to the low frequency side as the stage 2 moves decreases from f ₀ = 1.8 MHz to 0 Hz and then increases to f = 2.6 MHz−f ₀ = 0.8 MHz. To do. Therefore, if an interferometer that modulates to the high frequency side as the stage 2 moves is used, the amount of movement of the stage can be constantly monitored, but an interferometer that modulates to the low frequency side as the stage 2 moves is used. Sometimes f <100KH
The amount of movement of the stage cannot be monitored when z.

Therefore, in the present embodiment, the CPU selects an interferometer that modulates to the high frequency side as the stage 2 moves. From FIG. 3, it is understood that the combination of the moving direction of the stage 2 and the interferometer in which the optical beat frequency becomes high has the following one-to-one correspondence relationship. When moving in the plus direction: Interferometer A1 When moving in the minus direction: Interferometer A2 When moving in the plus direction: Interferometer B1 When moving in the minus direction: Interferometer B2 CPU emits CPU Four optical beat outputs are selected based on the control signals to the x-direction motor and the y-direction motor. The same applies to the movement in an oblique direction that is not parallel to the x axis and the y axis.

FIG. 4 shows an example of the movement path of the stage 2. In this example, the stage 2 starts from the coordinate P ₁ ,
It moved to P ₂ , P ₃ , P _4, and finally to P ₁ . The selection of the interferometer in this case will be described. First, the case of moving from P ₁ to P ₂ will be described. The xy coordinate of the stage 2 when stopped at P ₁ is (x ₀ , y ₀ ). The CPU sends a signal to the x-direction motor to move the stage 2 in the x-plus direction by Δx. The x-direction motor moves the stage 2 from P ₁ to P ₂ ,
Stop at ₂ . With the above signal, the CPU selects the interferometer A1,
The amount of movement in the x plus direction is obtained as Δx according to the output data of the interferometer A1. The movement amount in the y direction is obtained as 0 according to the output data of the interferometer B1 or B2. Thus, the xy coordinates of the stage 2 are determined as (x ₀ + Δx, y ₀ ).

Next, the case of moving from P ₂ to P ₃ will be described. The CPU sends a signal to the y-direction motor to move the stage 2 in the y-plus direction by Δy. The y-direction motor moves the stage 2 from P ₂ to P ₃ ,
Stop at ₃ . With the above signal, the CPU selects the interferometer B1,
The amount of movement in the y-plus direction is obtained as Δy according to the output data of the interferometer B1. The amount of movement in the x direction is obtained as 0 according to the output data of the interferometer A1 or A2. Thus, the xy coordinates of stage 2 are (x ₀ + Δx, y ₀ + Δy)
Is determined.

Next, the case of moving from P ₃ to P ₄ will be described. The CPU sends a signal to the x-direction motor to move the stage 2 in the negative x direction by Δx. The x-direction motor moves the stage 2 from P ₃ to P ₄ ,
Stop at ₄ . With the above signal, the CPU selects the interferometer A2,
The amount of movement in the negative x direction is obtained as Δx according to the output data of the interferometer A2. The movement amount in the y direction is obtained as 0 according to the output data of the interferometer B1 or B2. Thus, the xy coordinates of the stage 2 are determined as (x ₀ , y ₀ + Δy).

Next, the case of moving from P ₄ to P ₁ will be described. The CPU sends a signal to the y-direction motor to move the stage 2 in the negative y direction by Δy. The y-direction motor moves the stage 2 from P ₄ to P ₁ ,
Stop at ₁ . With the above signal, the CPU selects the interferometer B2,
The amount of movement in the negative y direction is obtained as Δy according to the output data of the interferometer B2. The amount of movement in the x direction is obtained as 0 according to the output data of the interferometer A1 or A2. Thus, the xy coordinates of the stage 2 are determined as (x ₀ , y ₀ ).
By measuring the amount of movement as described above, it was possible to accurately measure the position of the route shown in FIG.

Next, description will be given of the case of moving diagonally from P ₁ to P ₃ in FIG. The xy coordinate of the stage 2 when stopped at P ₁ is (x ₀ , y ₀ ). The CPU sends a signal to the x-direction motor to move the stage 2 by Δx in the x-plus direction, and sends a signal to the y-direction motor to move the stage 2 in the y-plus direction by Δy. The x-direction motor and the y-direction motor move the stage 2 from P ₁ to P ₃ and stop at P ₃ . The above signals cause the CPU to interferometer A1 and interferometer B.
1 is selected, the movement amount in the x plus direction is obtained as Δx according to the output data of the interferometer A1, and the movement amount in the y plus direction is obtained as Δy according to the output data of the interferometer B1. Thus, the xy coordinates of stage 2 are (x ₀ + Δx,
y ₀ + Δy).

Although f ₁ <f ₂ is set in this embodiment,
It is also possible to make f ₁ > f ₂ , that is, the frequency f ₁ of the reference light can be higher than the frequency f _{2 of the} measurement light in all interferometers. However, in this case, the combination of the moving direction of the stage and the interferometer that modulates the optical beat frequency to the high frequency side has the following correspondence. When moved in the x-plus direction: A2 When moved in the minus direction: A1 When moved in the y-direction: B2 When moved in the y-direction: B1

Further, in the present embodiment, the four interferometers use the luminous fluxes of frequencies f ₁ and f ₂ generated from the same light source, but the frequency of each interferometer is the combination of two opposing interferometers. As long as the magnitude relationship between the reference light and the measurement light is aligned so that the frequency of the measurement light is higher or the frequency of the measurement light is lower, the frequency values themselves are all different. Good. Further, in the present embodiment, each interferometer has been described as being configured with a single path, but each interferometer may be configured with multiple paths.

Next, FIG. 5 shows a second embodiment. In the first embodiment, only one light source for the heterodyne interferometer is used,
The luminous flux from this light source was distributed to the four interferometers A1, A2, B1 and B2. In this second embodiment, two axial Zeeman lasers 1A and 1B are used, and the luminous flux from the axial Zeeman laser 1A interferes with two. The light flux from the axial Zeeman laser 1B is distributed to the two interferometers A2 and B2.
Is distributed to. With this configuration, the light quantity of the optical beat detector can be doubled. It is also possible to use four light sources, ie different light sources for each interferometer.

Next, FIG. 6 shows a third embodiment. In the first or second embodiment, the four measuring mirrors M1 to M4 are arranged on the four sides of the stage 2, but in the third embodiment, two measuring mirrors M1, M3; M2, M4 in opposite directions are arranged. Are arranged back to back and are arranged on two adjacent sides of the stage 2. With this configuration, it is easy to parallelize the two mirrors M1, M3; M2, M4 opposite to each other.

Next, FIG. 7 shows a fourth embodiment. In each of the above-mentioned embodiments, the measuring lights of the interferometers A1, A2; B1, B2 facing each other are arranged coaxially, and therefore, the rotation angle of the stage 2 in the xy plane cannot be measured. So this 4th
In the embodiment, an interferometer A3 is separately introduced, and x of stage 2 is introduced.
The rotation angle in the y plane can be measured.

Next, FIG. 8 shows a fifth embodiment. Although the total number of interferometers is five in the fourth embodiment, this fifth
In the embodiment, one of the interferometers A1 and A2 facing each other among the measurement lights of the interferometers A1 and A2; B1 and B2 facing each other is arranged parallel to each other and not coaxially. With this configuration, the total number of interferometers is four, and in addition to the movement amount of the stage 2 in the x direction and the y direction, the rotation angle in the xy plane can be measured.

In each of the above embodiments, the interferometer data is selected by referring to the drive signal of the stage moving motor, but the interferometer data can be selected by another method. . Since the movement amount is measured by the interferometer by counting the frequency of the optical beat, the higher the count number is, the higher the beat frequency is modulated. That is, if all the beat signals of the four interferometers are measured, A1 in the x direction
The number of counts of the interferometer of either B1 or B2 should be large in the direction of A2 or y. The amount of movement in the x and y directions can be obtained from the two interferometer data having a large count number.

Further, in the above description, as the interferometer selection method, only one of the interferometers A1, A2; B1, B2 facing each other is always used, but this is not always necessary. It is absolutely necessary to use the high frequency side only for the data in the non-measurable region X.
A sixth embodiment will be described with reference to FIG. 9 in which opposed interferometers are appropriately switched without always using only one of the opposed interferometers A1 and A2; B1 and B2. FIG. 9 shows f
_{If 1} <f ₂ , the stage moves in the x plus direction, or f
The time change of the optical beat frequencies of the interferometers A1 and A2 when the stage moves in the x minus direction with ₁ > f ₂ is shown. Therefore, in this case, the interferometer A1 modulates to the high frequency side and A2 modulates to the low frequency side. Interferometer A that stores the data of two interferometers in the CPU and modulates it to the low frequency side
The data of No. 2 is mainly selected, but the data of interferometer A1 is selected only when the data of interferometer A2 cannot be obtained by unmeasurable region X. Therefore, in the figure, the data of interferometer A2 is used for routes R1, R3, and R5, and the data of A1 is used for routes R2 and R4.

FIG. 10 shows a seventh embodiment. In this embodiment, the interferometer A1 modulated to the high frequency side is initially selected, and the interferometer A2 modulated to the low frequency side passes through the unmeasurable region X and ends. After that, the interferometer A2 is selected.
Therefore, in the figure, data of interferometer A1 is used for routes R1 and R3, and data of A2 is used for route R2.
That is, according to the seventh embodiment, the switching frequency of the interferometer is reduced as compared with the sixth embodiment.

The advantage of the method of switching the interferometer as in the sixth or seventh embodiment is that the dynamic range is further expanded. That is, the reference beat frequency is f ₀ = 1.8.
MHz, and the electrical response range of the optical beat detection system is e
_{If min} = 100 KHz and e _max = 8 MHz,
The dynamic range (Δf) _max of the prior art is (Δ
f) was _{max = f 0 -e min = 1.7MHz} . On the other hand,
When only one of the facing interferometers is always used, the dynamic range is (Δf) _max = e
_It was expanded to _max −f ₀ = 6.2 MHz. However, as in the sixth or seventh embodiment, if one of the interferometers facing each other is used, the dynamic range is (Δf) _max = f ₀ + e _max = 9.8 MH.
Expand further with z.

Obviously, if only one of the interferometers facing each other is always used, the data processing time is saved. Without switching of the interferometer, in the case of using only the same interferometer, the widening of the dynamic range, the reference beat frequency f ₀ slightly higher than the response limit e _min of optical beat detection system, or the upper limit e _It should be slightly lower than _max . A lateral Zeeman laser can be used as the heterodyne light source having a small reference beat frequency f ₀ . However, since the output of the lateral Zeeman laser is linearly polarized light, the configuration of the interferometer needs to be slightly changed. If one of the facing interferometers is used as long as it can be used, in order to expand the dynamic range, the interferometer on the low frequency side should be measured just before the interferometer on the high frequency side becomes unmeasurable. F can be measured, f
_It suffices to make ₀ slightly lower than (e _max −e _min ) / 2.

[0055]

As described above, according to the present invention, since the dynamic range is expanded, the moving object can be moved without any trouble even when the moving speed of the moving body is increased or when the interferometer is multipathed. The amount of body movement can be measured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the principle of the present invention.

FIG. 2 is a configuration diagram showing a first embodiment.

FIG. 3 is a diagram showing a time change of an optical beat frequency according to the first embodiment.

FIG. 4 is a diagram showing an example of a movement path of a stage.

FIG. 5 is a configuration diagram showing a second embodiment.

FIG. 6 is a configuration diagram showing a third embodiment.

FIG. 7 is a configuration diagram showing a fourth embodiment.

FIG. 8 is a configuration diagram showing a fifth embodiment.

FIG. 9 is a diagram showing the time change of the optical beat frequency of the sixth embodiment.

FIG. 10 is a diagram showing the time change of the optical beat frequency of the seventh embodiment.

FIG. 11 is a block diagram showing a conventional example.

FIG. 12 is a configuration diagram showing an example of a single-pass interferometer.

FIG. 13 is a configuration diagram showing an example of a multipath interferometer.

FIG. 14 is a diagram showing a temporal change of an optical beat frequency in a conventional example.

FIG. 15 is a diagram showing a time change of an optical beat frequency which causes a problem in a conventional example.

[Explanation of symbols]

1 ... Axis Zeeman laser 2 ... Stage 3, 5, 7 ... λ / 4 plate 4 ... Polarization beam splitter 6 ... Reference mirror 8 ... Analyzer 9 ... Photodetector 10 ... Phase counter 11 ... Reference triangular prism 12 ... Measurement use triangular prism 13 ... reference interferometer A, B, A1, A2, A3, B1, B2 ... interferometer M _A, M _B, M1~M4 ... measuring mirror b ₁ ... reference beam b ₂ ... measurement light

Claims (7)

[Claims] 1. A reference light and a measurement light having different frequencies,
Two sets having a measurement mirror are prepared, and the magnitudes of the frequencies of the reference light and the measurement light are set so that the frequencies of the reference light of both sets are both higher or lower than the frequencies of the measurement light of the set. Aligning the relationship for both sets, the measurement mirrors of both sets are attached to the same moving body so that their reflection surfaces are opposite to each other. For each of the two sets, the reference light and the measurement light are Prepare a reference beat frequency caused by interference, and, after reflecting the measurement light by the measurement mirror, interfere the measurement light and the reference light, to measure the beat frequency caused by the interference of both light beams, The moving amount of the moving body is obtained based on the difference between the beat frequency and the reference beat frequency. When the moving frequency cannot be measured in one set when the moving body moves, the other set is selected. By choosing
An apparatus for measuring a moving amount of a moving body by an interferometer capable of measuring the moving amount of the moving body. 2. A group having a wider measurable margin of the beat frequency when the mobile body is moved is selected based on a signal to or from a drive device for moving and driving the mobile body. 1. A moving amount measuring device of a moving body by the interferometer according to 1. 3. For each of the both sets, the beat frequency when the moving body is stopped is set lower than the center of the measurable area of the beat frequency, and the beat frequency increases when the moving body moves. The moving amount measuring device of a moving body by an interferometer according to claim 1, wherein a set is selected. 4. When the moving body moves, one of the two sets is selected until the set in which the beat frequency is lowered enters the unmeasurable region of the set in which the beat frequency is lowered, When the decreasing set passes through the unmeasurable region of the decreasing set, a set other than the decreasing set is selected, and the decreasing set is The moving amount measuring apparatus of a moving body by an interferometer according to claim 1, wherein after passing through the non-measurable region of the lower group, the lower group is selected. 5. The interferometer movement according to claim 1, wherein both sets of the measurement light beams are reflected by the measurement mirror a plurality of times and then interfere with the reference light beam. Body movement measuring device. 6. An apparatus for measuring the amount of movement of a moving body by an interferometer according to claim 1, wherein both sets of the measuring lights are arranged in parallel and not coaxially. 7. The moving body moves two-dimensionally or three-dimensionally, and the measuring device according to claim 1 is provided for each moving direction of the moving body. Measuring device for moving amount of moving body by interferometer.