JP3412212B2 - Interferometer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
Fluctuations, that is, measurement errors due to changes in the refractive index of air, are compensated for.
It relates to a correctable interferometer device. [0002] 2. Description of the Related Art Conventionally, an interferometer device has
Measured value related to the displacement or position of the measured object
Measurement of refractive index of air due to changes in environmental conditions
The error is measured by using the environmental measurement sensor to
Temperature, pressure, and humidity of air near the reciprocating measurement beam
Measurement, etc., and each measurement value and sensor
Based on the measurement value of the object to be measured by the measurement beam,
Was corrected by performing the above calculation. Japanese Patent Application Laid-Open No. 2-1501 discloses FIG.
Interference not affected by changes in the refractive index of air as shown in FIG.
Metering devices have been proposed. FIG. 6 shows the configuration of the interferometer device.
FIG. 7 is a plan view when FIG. 6 is viewed from above.
FIG. 8 is a side view when FIG. 6 is viewed from the left side of the drawing.
You. Therefore, referring to FIG. 6 to FIG.
Will be described. For example, a wafer W is placed as an object to be measured.
A movable mirror 6 is fixed at one end of the stage ST.
The movable mirror 6 moves a predetermined distance l along the measurement direction._TwoOnly
A first reflecting surface 6a and a second reflecting surface arranged to be separated from each other
6b. [0004] The laser beam from the laser light source 1 is shown in FIG.
As shown in the figure, the joint surface of the two prisms (2a, 2b)
The light enters the light splitting prism 2 on which the semi-transmissive surface BS is formed,
The light is split into two vertically by the light splitting surface BS. This
The laser beam reflected from the light splitting surface BS is semi-transmissive prism.
Polarization pre-polarization through the reflection surface R formed on one surface of the
Laser that enters the upper part of the mechanism 3 and passes through the light splitting surface BS
The beam enters the lower part of the polarizing prism 3. This polarization
Rhythm 3 has two right-angle prisms joined to each other.
A polarization separation surface PBS is formed on the mating surface. [0005] The light enters the upper and lower parts of the polarizing prism 3
The laser beam is applied to the polarization splitting surface PBS in the polarizing prism 3.
Polarization separation into reference beam and measurement beam
The polarized light separating surface PBS vibrates in the direction of the paper of FIG.
P-polarized light components are transmitted as reference beams, respectively.
The S polarization component oscillating in the direction perpendicular to the paper of FIG.
Each as a reflection. First, each reference transmitted through the polarization separation surface PBS
The beam is emitted from the exit side of the polarizing prism 3 (the right-angle prism 3).
passing through the 1/4 wavelength plate 4a bonded to one surface
And a reference wavelength provided on the end face of the quarter wavelength plate 4a.
After being reflected by the reflecting mirror 5, the light passes through the quarter-wave plate 4a again and is polarized.
It heads to the light separation surface PBS. At this time, each reference beam is
The polarization plane rotates 90 degrees to reciprocate the quarter-wave plate 4a.
Is converted to S-polarized light. Therefore, each reference beam is polarized
Reflects the separation surface PBS and joins the exit side of the polarizing prism 3
To the polarizing plate 7. On the other hand, each measurement reflecting the polarization separation surface PBS
The beam is emitted from the exit side of the polarizing prism 3 (the right-angle prism 3).
pass through the 1/4 wavelength plate 4b joined to one side of
Then, each of the mirrors 6 is fixed to one end of the stage ST.
Head for it. As shown in FIG.
Reflects the upper part of the remote PBS and the upper part of the 1/4 wavelength plate 4b.
The first measurement beam passing therethrough is the first reflection beam on the upper part of the reflection mirror 6.
Reflects the surface 6a, passes through the quarter-wave plate 4b again, and
It heads to the light separation surface PBS. At this time, each reference beam is
The polarization plane rotates 90 degrees to reciprocate the quarter-wave plate 4a.
Is converted into P-polarized light. Therefore, each measurement beam is polarized
Passes through the separation surface PBS and joins to the exit side of the polarizing prism 3
To the polarizing plate 7. As described above, the light passes through the upper part of the polarization separation surface PBS.
The measurement beam and the reference beam passing through the polarizing plate 7
Interference is caused by passing through the light plate 7, and this interference light is
The first reflecting surface above the reflecting mirror 6 in the one optical path difference detecting device 8a
6A is generated, the output A is generated, and the polarization
Measurement beam passing through the lower part of the remote PBS and going to the polarizing plate 7
The beam and the reference beam are dried by passing through the polarizing plate 7.
The interference light is reflected by the second optical path difference detecting device 8b by a reflecting mirror.
The output A relating to the amount of displacement of the second reflecting surface 6b at the lower part of
Is done. The two signals from each optical path difference detecting device (8a, 8b)
The two outputs are input to the arithmetic unit 9 where predetermined arithmetic operations are performed.
It is. Here, the output A of the first optical path difference detecting device 8a is
X_A, The output B of the second optical path difference detection device 8b_B, Stay
The displacement amount of the ST is x, the origin of the measurement where the displacement amount is zero (measurement
The refractive index of air at the start of reset or at reset) is n,
The amount of change in the refractive index of air due to fluctuations in
Air between launch surface 6b and quarter-wave plate 4b (or interferometer)
The distance in l₁, The first reflecting surface 6a and the second reflecting surface 6b
Distance in air_TwoAnd each optical path difference detection device
(8a, 8b), two outputs (X_A, X_B) Is
Equation 1 is obtained. [0010] (Equation 1)The arithmetic expression in the arithmetic unit 9 is the above equation.
Given by eliminating Δn by the two equations by 1
The following Equation 2 is obtained. [0012] (Equation 2) The operation according to the above equation (2) is performed by the arithmetic unit 9.
Is affected by changes in the refractive index of air.
No output result is generated and the stage ST
Measurement was possible. [0014] SUMMARY OF THE INVENTION In the above-mentioned prior art,
Is that the errors of the two interferometer devices themselves increase in principle.
There is a fatal problem of being spanned. Also, the measured object
Between two reflective surfaces formed at one end on the stage as
Distance l_TwoIs smaller, the air
The problem is that the accuracy with which the refractive index change of
is there. Therefore, the present invention, as described above,
The errors of the two interferometers themselves are amplified
To solve fatal problems and reduce the fluctuations of gas such as air.
Accurately corrects measurement errors caused by changes in the refractive index
An interferometer that can always provide high accuracy and stable measurement
It is intended to provide. [0016] SUMMARY OF THE INVENTION The present invention is directed to the above-mentioned object.
To achieve this, for example, as shown in FIGS.
Are provided at predetermined positions along the
First and second units provided integrally movable along the directions.
Reflection means for measurement, and first reflection means fixed at predetermined positions, respectively.
And second reference reflecting means, and light source means for supplying a light beam
Based on the light flux from the light source means,
Reciprocate in the gas along the measurement direction via the reflection means
Gas through the first measurement optical path and the first reference reflecting means.
A first reference optical path reciprocating in the interior, and the first measurement optical path
And the first measurement output by each light beam passing through the first reference optical path.
First interferometer means for generating a force, and light from the light source means
On the basis of the bundle, the second
1. Reciprocate in gas along a direction almost parallel to the measurement optical path
In the gas through the second measurement optical path and the second reference reflecting means
And a second reference optical path for reciprocating the second measurement optical path.
And a second measurement output by each light beam passing through the second reference light path.
Second interferometer means for generating the first and second measurement outputs.
Calculating means for performing a predetermined calculation based on the force,
The first interferometer means to the first reference reflecting means;
The first reference optical path is connected to the second reference light path from the second interferometer means.
Optical path equal to the second reference path up to the reflection means for use
A first reflection from the first interferometer means for the first measurement
The optical path length of the first measurement path up to the reference position of the means
To l_M1From the second interferometer means.
Optical path of the second measurement path to the reference position of the launching means
Length is l_M2The first reference reflection from the first interferometer means.
The optical path length of the first reference path to the means_R1,Previous
Before the second interferometer means to the second reference reflecting means;
The optical path length of the second reference light path is l_R2, The reference position
Let x be the displacement of the first and second measuring reflecting means.
At this time, the first and second measuring reflecting means are in the following range:
Can be moved at least, or a part of the following
It is configured so that it can be moved without it. L_R1−l_M1≦ x ≦ l_R2−l_M2 [0018] [Operation] Before explaining the principle of the present invention, first, FIG.
Explanation of the measurement error in the conventional device shown in FIG.
I do. First reciprocating on the first reflecting surface 6a above the reflecting mirror 6
First reference optical path reciprocating between the measurement optical path and the upper part of the reflecting mirror 5
Is formed, and the first measurement output is obtained by each light beam passing through each optical path.
The first interferometer device for generating the force A (the polarization prism shown in FIG. 6)
Upper part of the unit 3 and upper parts of the quarter-wave plates 4a and 4b
The upper part of the polarizing plate 7 and the first optical path difference measuring device 8a)
Is the quantization error (or resolution) of_AAt the bottom of the reflector 6
Under the second measuring optical path reciprocating on the second reflecting surface 6b and the reflecting mirror 5
Form a second reference optical path reciprocating on the side part, and pass through each optical path
Second interference that produces a second measurement output B with each of the luminous fluxes
6 (the lower part of the polarizing prism 3 shown in FIG.
The lower part of the four-wavelength plates 4a and 4b, the lower part of the polarizing plate 7,
And the quantization error (or decomposition) of the second optical path difference measuring device 8b)
Function) to δ_BFrom the first interferometer device shown in FIG.
Is the original measurement signal X_AThe quantization error δ_A
And the second interferometer shown in FIG.
The measurement output B from the device is the original measurement signal X_BQuantized to
Error δ_BIs added. Therefore, the quantization error due to each interferometer device is
When the error amount added to the measurement result is Δx,
Equation (2) becomes like Equation (3) below. [0020] (Equation 3)When the above equation (3) is transformed, the following equation is obtained.
Equation 4 is obtained. [0022] (Equation 4) Here, the output by the first and second interferometer devices is shown.
The force is X as shown in Equation 1. _A= Xn + (l₁+
l_Two+ X) Δn, X_B= Xn + (l₁+ X) Δn
Therefore, from this relationship and Expression 4, Expression 5 shown below is derived.
Will be issued. [0024] (Equation 5) Here, assuming that n + Δn ≒ 1, the above equation
5 finally becomes the following Expression 6. [0026] (Equation 6) Therefore, the quantization error is calculated based on the above equation (6).
Maximum value Δx of quantity Δx_MAXTo consider. Now the first
And the quantization error of the second interferometer (δ_A, Δ_B) Maximum
And the minimum values are e and −e, respectively, and the quantum of each interferometer device is
-E ≦ δ_A≦ e, −e ≦ δ_B≤ e
When it is possible, the maximum value | Δ
x_MAX| Here, as is apparent from FIG.₁>
0, l_Two> 0, x ≧ −l₁Since the relationship is established,
(X + 1)₁+ L_Two) And (xl₁) Is
Always positive. Therefore, the quantization error amount according to the above equation (6)
Maximum value | Δx_MAX| Is finally given by the following equation 7.
Become. [0029] (Equation 7)Here, the maximum of the quantization error amount in the above equation (7) is obtained.
Value | Δx_MAX| Is the vertical axis, and the position x of the stage ST is the horizontal axis.
FIG. 9 shows a graph. Shown in FIG.
As described above, the stage ST includes the first and second interferometers (1/4 wavelength
As the distance from the plate 4a) increases, the quantization error increases.
Maximum value of difference | Δx_MAX| Becomes larger and the total
It can be understood that the measurement error is so large that it cannot be ignored. As an example, l₁= 0.3m, l_Two= 0.1m,
When the moving range of the stage ST is -0.3m ≦ x ≦ 0.3m,
Maximum value of quantization error | Δx_MAX| Is the largest
The position of the stage ST is determined by the first and second interferometers (1/4 wavelength
Distance from the plate 4a) to the second reflecting surface 6b below the reflecting mirror 6
When the separation is 0.6m (x = 0.3m), the quantization error at this time
From the above equation 7, the maximum value of the quantity is calculated as in the following equation 8.
You. [0032] (Equation 8) Therefore, the quantization of the first and second interferometer devices
Assuming that the error e is about 10 nm,
According to Equation 8, the measured value reaches 130 nm.
An error will be added. Also, from the above equation 8,
As can be seen, it is placed at one end on the stage as the object to be measured.
Between two reflecting surfaces (6a, 6b) in the placed reflecting mirror 6
Distance l_TwoIs reduced, the maximum value of the quantization error amount | Δx
_MAX| Can be understood to increase. This will be described in detail._Two’= L
_Two/ Max of quantization error amount when / 2_MAX| ’
Then, this error amount is calculated from the above equation 7 by the following equation 9.
Like that. [0035] (Equation 9) As an example, as described above, l₁= 0.3m, l
_Two= 0.1m, the movement range of stage ST is -0.3m ≤x≤0.3m
Then, l_TwoValue is 0.05m, which is half of 0.1m.
In this case, the first and second interferometers (1/4 wavelength plate 4a)
0.6m from the mirror to the second reflecting surface 6b below the reflecting mirror 6
The stage ST is located at a position where (x = 0.3 m).
At this time, the maximum value of the quantization error amount | Δx_MAX| ’Is the largest
And the maximum value of the quantization error amount at this time | Δx_MAX| ’
From the above equations 8 and 9, the following equation 10 is obtained.
You. [0037] (Equation 10) Therefore, from the above equations 8 and 10, the measured
In the reflecting mirror 6 formed at one end on the stage as an object
Distance l between the two reflecting surfaces (6a, 6b)_TwoHalve
Then, the maximum value of the quantization error amount is about twice (| Δx_MAX| ’
/ | Δx_MAX| Times), the first and second dried
Assume that the quantization error e of the interferometer is about 10 nm.
And the finally obtained measurement value,
A measurement error of about 250 nm will be added. The conventional interferometer device described above has
In order to solve the fatal problem, the present invention
If the reference optical path lengths formed by the
Each measurement light also formed by the two interferometer means
The path length is varied by a predetermined length, and the
Reference position of each interferometer means is
Of the predetermined relationship such that the position of the shooting means is at least internally divided
First, move the measuring reflector of each interferometer.
It is something that has been done. Thus, the reference member passing through a gas such as air can be obtained.
When there is a change in the refractive index between the illumination path and the measurement path
In each reference optical path, the effect of the refractive index change is substantially the same.
While measuring, the refractive index according to the optical path length in each measurement optical path
Gases such as air due to environmental changes because they are affected by changes
Two different measurement outputs containing information on the refractive index change of
Can be And based on these two measurement outputs
By performing a predetermined calculation, the refractive index in each optical path is calculated.
Measurement errors due to changes can be removed. Furthermore, the two reflecting means for measurement are moved to a predetermined position.
At least the movable range or a part of the range can be moved
By configuring, the quantum that the two interferometer means themselves have
Can significantly reduce the effects of
Improvement in measurement accuracy can be achieved. In addition, each interference
Each measurement optical path formed by the
Refractive index change in gas such as air may occur
In each case, a reference formed by each interferometer means
It is desirable that each of the optical path and the measurement optical path be close to each other.
New Referring to FIG. 4 below, the principle of the present invention will be described.
explain about. FIG. 4A shows a first interferometer device of the present invention.
FIG. 4B is a diagram showing the configuration of the second interference according to the present invention.
It is a figure showing composition of a meter device. First, as shown in FIG.
As described above, the light beam supplied from the first light source 11
Split into two light beams by beam splitter 12 as material
The beam transmitted through the beam splitter 12 is
Room L_{twenty one}Are the left and right sides of FIG.
Reflection member 14 for measurement (first member)
Of the beam splitter
Head to Tar 12. On the other hand, the beam splitter 12
The other beam L₃₁Is a reflector as a reference beam
13 and the measuring beam L_{twenty one}Air path close to air
Measurement beam L in gas such as_{twenty one}Proceed parallel to
I do. After that, beam L₃₁Is for reference, fixed on the base
The light is reflected by the reflection member 15 (first reference reflection means), and is again measured.
Measurement beam L_{twenty one}In gas such as air close to the optical path of
Beam L_{twenty one}And the reflecting mirror 13
Through the beam splitter 12. And bee
Measurement beam L_{twenty one}And for reference
Beam L₃₁Together with the beam L₄₁As the first
The light is received by the sea bar 16 (first detector), and
Of the reflecting member 14 is detected. Here, the first interferometer shown in FIG.
Beam splitter 12, reflector 13, and first receiver
-16 and the optical path of the reference optical path in the gas.
Target optical path length is l_R1The reflecting member 15 for reference is
Predetermined optical distance l for one interferometer_R1Just separated by the base
It is fixed to. The reflection member 14 for measurement is
Optical path of the measuring optical path in the gas at each reference position
Length is l_M1From the first interferometer for measurement
The optical distance to the reference position of the material 14 is l_M1So that
It is set to be movable. On the other hand, FIG.
In the vertical direction, the second interferometer device as shown in FIG.
Are arranged in parallel, and in the second interferometer device, the reflection
The mirror 23 and the reflecting member 25 for reference are the gas of the second interferometer.
Optical path length l of the reference optical path inside_R2Is the gas of the first interferometer
Optical path length l of the reference optical path inside_R1To be equal to
Each is fixed. Also, beam splitter 2
2 and the reflection member 24 for measurement (reflection means for measurement)
At the reference position of the shooting member 24, the second interferometer in the gas
Optical path length l of the measuring path_M2Is in the gas of the second interferometer
Optical path length l of reference light path_M1Against it differently
The other settings are shown in FIG. 4 (a).
It is basically the same as the first interferometer device shown. As shown in FIG. 4B, the second light source 21
The luminous flux supplied from the beam splitter
The beam is split into two light beams by the
Beam L passing through the_{twenty two}Is the measurement bee
The reflection member 24 for measurement (the second reflection hand for measurement)
Head to the stage). This reflecting member 24 is shown in FIG.
4B together with the reflecting member 14 in the left and right direction.
It is provided movably. And a reflective member for measurement
Beam L heading to 24_{twenty two}Is reflected by the reflecting member 24
Then, the beam again goes to the beam splitter 22. On the other hand,
Beam L that reflects the beam splitter 22₃₂Is
The reflection mirror 23 is reflected as a reference beam, and a measurement beam is reflected.
L_{twenty two}Measurement beam L in a gas such as air close to the optical path of
_{twenty two}Proceed so as to be parallel to. After that, beam L₃₂Is
The reference reflecting member 25 fixed to the base (second reference member)
And the measuring beam L again_{twenty two}Light path and proximity
Measurement beam L in a gas such as compressed air_{twenty two}Will be parallel to
The beam splitter 2 via the reflecting mirror 23
Head to 2. And by the beam splitter 22
Measurement beam L_{twenty two}And reference beam L₃₂And together
Beam L₄₂As the second receiver 26 (second detection
The reflection member 24 as an object to be measured.
The momentum is detected. The second interferometer shown in FIG.
Beam splitter 22, reflector 23, and second receiver
26. With the above configuration,
The reflection members 14 and 24 as objects are
When moved physically, the first receiver 1 of the first interference device
6 and the second receiver 26 of the second interference device
Two different detection signals are output. Now, the first receiver 16 of the first interference device
Output from X_A, The second receiver 2 of the second interference device
X output from 6_BIn the reference optical path of the first interferometer.
Light at the part affected by the change in the refractive index of the gas
Path length (the distance between the first interferometer and the first reference reflector)
1 The optical path length of the reference light path in gas) is l_R1(=
l _R), The refractive index of the gas in the reference optical path of the second interferometer.
The length of the optical path at the part affected by the change (second
Gas in the second reference optical path between the interferometer and the second reference reflector
The optical path length in_R2(= L_R1= L_R), Measurement open
The reference position of the initial measuring reflection means at the beginning (at reset)
Of the refractive index of the gas in the measurement optical path of the first interferometer
The length of the optical path of the part affected by the change (the first interferometer and the
The optical path of the first measurement optical path between the reference position of the measuring reflection means
Optical path length)_M1, Such as at the start of measurement (at reset)
Measurement light of the second interferometer at the reference position of the measurement reflection means
The optical path of the part affected by the change in the refractive index of the gas in the path
Length (between the second interferometer and the reference position of the measuring reflecting means)
Is the optical path length of the second measurement optical path)_M2, First and second
Each of the measurement optical paths is affected by changes in the refractive index of the gas.
The length of the optical path at the part where_M1, L_M2When
Reference position of the object to be measured (the first and second measuring reflecting means)
Let x be the displacement from the position (origin). However, this displacement x
Is positive when the measured object moves to the right from the origin.
The time when the measured object moves to the left from the origin is defined as negative. In the case of the present invention also,
Holds, and the relationship of the following Expression 11 also holds.
Stand up. [0048] [Equation 11] Therefore, from the above equations (6) and (11),
Equation 12 holds. [0050] (Equation 12) Therefore, according to the present invention,
Maximum value Δx of quantization error amount Δx in interferometer device_MAX
To consider. Now, the quantum of the first and second interferometer devices
Error (δ_A, Δ_B) Is the maximum value and the minimum value of e,
−e, and the quantization error of each interferometer device is −e ≦ δ_A≤
e, −e ≦ δ_BWhen the range of ≦ e can be taken, the above equation 12
Value of quantization error due to_MAX|
Cases can be divided into three cases (i) to (iii).(I) In the case of l _R −l _M1 ≦ x ≦ l _R −l _M2 (however, l _M1
> L _M2 ) In this case, x + 1_M1−l_R≧ 0, x + 1_M2−l_R≤
0, the maximum value of the quantization error amount | Δx_MAX|
From Expression 11, Expression 12 is obtained. [0052] (Equation 13) [0053](Ii) When x> l _R -l _M2 (however, l _M1
> L _M2 ) In this case, x + 1_M1−l_R> 0, x + 1_M2−l_R>
0, the maximum value of the quantization error amount | Δx_MAX|
From Expression 12, Expression 14 is obtained. [0054] [Equation 14] [0055](Iii) When x <l _R -l _M1 (where l
_M1 > l _M2 ) In this case, x + 1_M1−l_R<0, x + 1_M2−l_R<
0, the maximum value of the quantization error amount | Δx_MAX|
From Expression 12, Expression 15 is obtained. [0056] (Equation 15) The quantities obtained by the above equations (13) to (15)
Maximum value of emulation error | Δx_MAX| Is the vertical axis, stage ST
When a graph is plotted with the position x of the horizontal axis as shown in FIG.
Become. Therefore, using Expressions 13 to 15 and FIG.
Thus, high accuracy is assured for the entire interferometer apparatus shown in FIG.
Movement of reflective members (14, 24) for measurement
Consider range x. Gas refraction due to fluctuation of gas such as air
High accuracy as an interferometer while compensating for the effects of rate changes
In order to guarantee, realistically, the measurement output of the interferometer
The maximum value of the added quantization error (| Δx_MAX|) Is 4e or less
It is preferable to suppress it. Therefore, in the following,
Quantization error e added to the measurement output of the measuring device is 4 times to 1 time or less
The reflection member for measurement (1
The optimal movement range x of (4, 24) will be described.(I) The maximum value | Δx _MAX | of the quantization error is suppressed to 4e or less.
If In this case, the reflection member (14, 24)
Appropriate moving range x (where x ≧ −l_M2) Is the expression 13 to the number
From Expression 15 and FIG. 5, the following Expression 16 is obtained. [0059] (Equation 16) As an example, the first interference shown in FIG.
Of the interferometer and the second interferometer shown in FIG. 4B
Each error e (or resolution) is 0.5 nm,_M1= 0.
7m, l_M2= 0.5m, l_R= L_R1= L_R2= 0.6
The quantization error added to the measurement output of the interferometer.
Large value (| Δx_MAX|) Is less than 4e
The movement range x of the reflection member (14, 24) will be described. In this case, the above equation 16 is used for measurement.
The moving range x of the reflection member (14, 24) is -0.4m to 0.4m.
The accuracy of the interferometer as a whole is 2.0 nm (= 4e)
It can be understood that is guaranteed.(II) The maximum quantization error | Δx _MAX | is suppressed to 3e or less.
If In this case, the reflection member (14, 24)
Appropriate moving range x (where x ≧ −l_M2) Is the expression 13 to the number
From Expression 15 and FIG. 5, the following Expression 17 is obtained. [0062] [Equation 17] As an example, the first interference shown in FIG.
Of the interferometer and the second interferometer shown in FIG. 4B
Each error e (or resolution) is 0.5 nm,_M1= 0.
7m, l_M2= 0.5m, l_R= L_R1= L_R2= 0.6
The quantization error added to the measurement output of the interferometer.
Large value (| Δx_MAX|) Is less than 3e
The movement range x of the reflection member (14, 24) will be described. In this case, the above equation 17 is used for measurement.
The moving range x of the reflection member (14, 24) is -0.3m to 0.3m.
Therefore, the accuracy of the entire interferometer device is 1.5 nm (= 3e)
It can be understood that is guaranteed.(III) The maximum value of the quantization error | Δx _MAX |
If suppressed In this case, the reflection member (14, 24)
Appropriate moving range x (where x ≧ −l_M2) Is the expression 13 to the number
From Expression 15 and FIG. 5, the following Expression 18 is obtained. [0065] (Equation 18) As an example, the first interference shown in FIG.
Of the interferometer and the second interferometer shown in FIG. 4B
Each error e (or resolution) is 0.5 nm,_M1= 0.
7m, l_M2= 0.5m, l_R= L_R1= L_R2= 0.6
The quantization error added to the measurement output of the interferometer.
Large value (| Δx_MAX|) Is less than 2e
The movement range x of the reflection member (14, 24) will be described. In this case, the above equation 18
The moving range x of the reflecting members (14, 24) is -0.2m to 0.2m.
The accuracy of the interferometer as a whole is 1.0 nm (= 2e)
It can be understood that is guaranteed.(IV) The maximum value Δx _MAX of the quantization error is suppressed to e or less
If In this case, the reflection member (14, 24)
Appropriate moving range x (where x ≧ −l_M2) Is the expression 13 to the number
From Expression 15 and FIG. 5, the following Expression 19 is obtained. [0068] [Equation 19] As an example, the first interference shown in FIG.
Of the interferometer and the second interferometer shown in FIG. 4B
Each error e (or resolution) is 0.5 nm,_M1= 0.
7m, l_M2= 0.5m, l_R= L_R1= L_R2= 0.6
The quantization error added to the measurement output of the interferometer.
Large value (| Δx_MAX|) Is less than e
The movement range x of the shooting member (14, 24) will be described. In this case, the above equation 19
The moving range x of the reflection member (14, 24) is -0.3m to 0.3m.
Therefore, the accuracy of 0.5 nm (= e) is
It can be understood that it is guaranteed. As described above, according to the present invention,
High accuracy even if the refractive index of the gas changes due to environmental changes
It can be understood that stable measurement can be realized under the condition.
Moreover, in the present invention, the object to be measured (for the first and second measurement)
(Reflection means) within the range satisfying Expression 19
Then, in principle, the quantization error e (or the min.
Resolution) can be reduced to 1 times or less.
Stable and accurate measurement can be achieved. In addition, two interference
The accuracy must be less than 1 times the total quantization error e (or resolution).
If not determined, the object to be measured (for the first and second measurement)
(Reflecting means) is in the range or
May be provided at least movably. [0071] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of an interferometer according to an embodiment of the present invention will be described below.
This will be described with reference to FIGS. In this example, FIGS.
The conventional interferometer described with reference to FIG.
A reference light path that passes through the air between the light source and each of the reference reflecting means
Are formed, and are the same as those shown in FIGS.
1 to 3 have the same reference numerals.
Is attached. Here, FIG. 1 shows the interferometer device of the present embodiment.
FIG. 2 shows the state when viewed from the side, and FIG.
The state of the interferometer device of the example when viewed from directly above is shown.
3 shows the interferometer of the present embodiment when viewed from the left side of FIG.
2 shows a side view of the device. In the first embodiment shown in FIGS.
Provided at different positions along the direction X
A first meter provided integrally movable along the measurement direction X
Reflecting means for measurement (first movable mirror 6a) and second reflecting hand for measurement
The step (second movable mirror 6b) and the same position are fixed to each other.
First reference reflecting means (first fixed mirror 5a) and second reference
Reflection means (second fixed mirror 5b) for coherent light flux
Light source means for supplying (laser light source 1, light splitting prism 2)
Based on the light flux from the light source means (1, 2)
1 Air along the measuring direction X via the measuring reflecting means 6a
First measurement optical path OP that makes a round trip_M1And the first reference reflecting means 5
a first reference optical path OP that reciprocates in the air via a_R1And form
And the first measurement optical path OP_M1And the first reference optical path OP_R1
Measurement output X by each light beam passing through_AGenerate
First interferometer (polarization separating prism 3, quarter-wave plate 4a,
4b, polarizer 7, first detector 8a) and light source means
Second measuring reflecting means based on the light flux from (1, 2)
(6b) First measurement optical path OP_M1Direction almost parallel to
Measurement optical path OP reciprocating in the air along the path_M2And second part
Second reference light reciprocating in the air via the illumination reflecting means 5b
Road OP_R2And the second measurement optical path OP_M2And the second
Reference optical path OP_R2Measurement output by each light beam passing through
X_BInterferometer (polarization splitting prism 3, 1 /
4 wavelength plates 4a, 4b, polarizing plate 7, second detecting device 8b)
And the first and second measurement outputs (X_A, X_B) Based on
And an arithmetic processing unit 9 for performing a constant operation.
You. As shown in FIGS. 1 to 3, coherent light
The laser light source 1 as a light source for supplying a bundle has a first frequency
f₁(Hereinafter, referred to as a first beam) and a second round
Wave number f_Two(Hereinafter, referred to as a second beam).
And the first and second beams are supplied to the light splitting prism 2.
Incident. This light splitting prism 2 is a parallelogram-shaped prism.
The rhythm 2a is composed of a right angle prism and a right angle prism.
A light splitting surface BS for amplitude splitting light is formed on the joint surface.
You. First, the light is reflected by the light splitting surface BS and reflected by the first interferometer.
To explain the first and second beams going to
The first and second beams reflected by the light splitting surface BS are prisms.
Reflected by the reflection surface R of the polarization separation prism 3
Incident on the part. The polarization splitting prism 3 has two right angle prisms.
Rhythm 3a, 3b is constituted by joining, this joint surface
Has a polarization separation surface PBS for polarizing and separating light.
You. Here, the upper part of the polarization splitting prism 3 is incident.
The first beam is incident on the plane of incidence of the polarization splitting surface PBS.
Is vibrated by linearly polarized light (hereinafter, referred to as P-polarized light).
And the other second beam is incident on the polarization separation surface PBS.
Linearly polarized light oscillating in a plane perpendicular to the
Name. ). Then, 4
The first beam of P-polarized light incident at an incident angle of 5 ° is polarization-separated
Pass through the surface PBS and enter at 45 ° to the polarization separation surface PBS.
The second beam of S-polarized light incident at an angle of incidence is a polarization separation surface PBS.
Is reflected. First, the light passes through the upper part of the polarization splitting surface PBS.
The first beam of P-polarized light will be described.
After the beam passes through the polarization separation surface PBS, the polarization separation prism
The light passes through the quarter-wave plate 4a joined to 3 and changes into circularly polarized light.
The first upper part of the fixed mirror 5 for reference
Head to fixed mirror 5a. The first fixed mirror 5a has a first reference optical path.
OP_R1The gas optical path length (air optical path length) within the predetermined length l
_R1A predetermined distance from the quarter-wave plate 4a so that
l_R1The first fixed
It is integrally formed with the second fixed mirror 5b disposed below the mirror 5a.
Has been established. The circularly polarized light reflected by the first fixed mirror 5a
One beam passes through the quarter-wave plate 4a again and becomes S-polarized light.
After being converted, the polarization separation surface PBS in the polarization separation prism 3
reflect. After that, the polarized light joined to the polarization splitting prism 3
Light enters the light plate 7. This polarizing plate 7 is used for the S-polarization of the first beam.
Transmits linearly polarized light at 45 ° to the direction of light
So that the polarization component of a part of the first beam is
The light passes through the polarizing plate 7 and is detected by the first optical path difference detecting device 8a.
Will be issued. On the other hand, the light is reflected on the upper part of the polarization separation surface PBS.
The S-polarized second beam will be described.
After the beam is reflected by the polarization separation surface PBS, the polarization separation prism
The light passes through the 1/4 wavelength plate 4b joined to 3 and changes into circularly polarized light.
Is replaced with the first upper part of the movable mirror 6 for measurement.
Head to the moving mirror 6a. The first fixed mirror 6a has a first measurement optical path.
OP_M1The optical path length within the predetermined length l_M1So that
To the quarter-wave plate 4b (or the first interferometer).
Fixed distance l_M1It is arranged only at a distance, as will be described later,
At a lower portion of the first movable mirror 6a, a predetermined
Integrally with the second movable mirror 6b which is arranged shifted by a distance.
It is configured to be movable. In addition, the movable mirror 6 for measurement
Is fixed to one end of the stage ST for holding the wafer W.
And moves with the movement of the stage ST. The circularly polarized light reflected by the first movable mirror 6a
The second beam passes through the quarter-wave plate 4b again and becomes P-polarized light.
, And the polarization separation surface PBS in the polarization separation prism 3
Through the polarizing plate 7 joined to the polarization separating prism 3
Incident. This polarizing plate 7 is, in other words, the second beam
Transmits linearly polarized light at 45 ° to the direction of P-polarized light
And a polarization component of a portion of the first beam.
The light passes through the polarizing plate 7 and a part of the first beam is polarized.
Along with the light component, it is detected by the first optical path difference detecting device 8a.
You. Next, the light is reflected by the light splitting surface BS of the light splitting prism 2.
The first and second beams going to the second interferometer will be described.
Then, the first and second beams passing through the light splitting surface BS
Enter the lower part of the polarization splitting prism 3. Here, the lower part of the polarization splitting prism 3 is incident.
One of the first beams is a polarization separation plane P, as described above.
Linearly polarized light oscillating in the plane of incidence of the BS (hereinafter P-polarized light)
Called. ), And the other second beam is a polarization separation surface.
Linearly polarized light oscillating in the plane perpendicular to the plane of incidence of the PBS
(Hereinafter, referred to as S-polarized light). And polarization separation
First P-polarized light incident on the surface PBS at an incident angle of 45 °
The beam passes through the polarization separation plane PBS, and the polarization separation plane PBS
The second beam of S-polarized light incident at an incident angle of 45 ° with respect to
Reflects the polarized light separating surface PBS. First, the light passes below the polarization separation surface PBS.
The first beam of P-polarized light will be described.
After the beam passes through the polarization separation surface PBS, the polarization separation prism
The light passes through the quarter-wave plate 4a joined to 3 and changes into circularly polarized light.
The second lower part of the fixed mirror 5 for reference
Head to fixed mirror 5b. The second fixed mirror 5b includes the first fixed mirror 5
a and the second reference optical path OP_R2At the inner
Has a gas optical path length (air optical path length) of the first reference optical path OP._R1At the inner
Length l equal to the gas optical path length (air optical path length)
_R2(= L_R1), The １ ／ wavelength plate 4a (or
A predetermined distance l to the second interferometer_R2(= L_R1) Only
It is arranged. The circularly polarized light reflected by the second fixed mirror 5b
One beam passes through the quarter-wave plate 4a again and becomes S-polarized light.
After being converted, the polarization separation surface PBS in the polarization separation prism 3
reflect. After that, the polarized light joined to the polarization splitting prism 3
Light enters the light plate 7. This polarizing plate 7 is used for S polarization of the first beam.
Transmits linearly polarized light at 45 ° to the direction of light
So that the polarization component of a part of the first beam is
The light passes through the polarizing plate 7 and is detected by the second optical path difference detecting device 8b.
Will be issued. On the other hand, the light is reflected at the lower part of the polarization splitting surface PBS.
The S-polarized second beam will be described.
After the beam is reflected by the polarization separation surface PBS, the polarization separation prism
The light passes through the 1/4 wavelength plate 4b joined to 3 and changes into circularly polarized light.
Is replaced with a second lower part constituting a part of the movable mirror 6 for measurement.
Head to the moving mirror 6b. The second fixed mirror 6b
1st fixed mirror 6a with the movement of the stage ST
The second measurement optical path
OP_M2The optical path length in the chamber is the first measurement optical path OP_M1Sky in
A predetermined length l that is shorter than the air path length_M2So that
A predetermined distance l with respect to the / 4 wavelength plate 4b_M2Just separated
Have been. The circularly polarized light reflected by the second movable mirror 6b
The second beam passes through the quarter-wave plate 4b again and becomes P-polarized light.
, And the polarization separation surface PBS in the polarization separation prism 3
Through the polarizing plate 7 joined to the polarization separating prism 3
Incident. This polarizing plate 7 is, in other words, the second beam
Transmits linearly polarized light at 45 ° to the direction of P-polarized light
And a polarization component of a portion of the first beam.
The light passes through the polarizing plate 7 and a part of the first beam is polarized.
Along with the light component, it is detected by the second optical path difference detecting device 8b.
You. As described above, the first optical path difference detection
In the device 8a, the gas optical path length (air optical path length) is l_R1
First reference optical path OP_R1The first beam passing through
The body optical path length (air optical path length) is l_M1First measurement optical path OP
_M1And the second beam passing through
Become. For this reason, the light inside the first optical path difference detecting device 8a is
From the electric detector, the first movable mirror 6a is opposed to the first fixed mirror 5a.
And stopped, the frequency is (f1-f2)
A beat signal is output, and the first movable mirror 6a moves in the X direction
Then, a beat signal whose frequency is modulated is output. Obedience
Therefore, the first optical path difference detecting device 8a
By integrating the changes, the first movable mirror 6a and the first fixed
The relative movement amount with respect to the mirror 5a can be detected. Therefore, the first reference optical path OP_R1Gas optical path length
(Air optical path length) l_R1To l_R, First measurement optical path OP_M1Gas
The optical path length (air optical path length) is l_M1At the start of measurement (reset
Time), the initial refractive index of gas such as air is n,
The change in the refractive index of the body is Δn, and the first measurement optical path OP_M1Gas light of
Path length (air path length) is l_M1The first movable mirror 6a when
(Or stage ST) reset position (coordinate original
From the reset position, the first movable mirror 6a (or
Or stage ST) When the displacement amount is x, the first optical path difference
In the detection device 8a, xn + (l_M1−l_R+ X) phase for Δn
Applicable signal X_AIs output to the arithmetic unit 9. On the other hand, in the second optical path difference detecting device 8b,
Means that the gas optical path length (air optical path length) is l _R2The second reference light
Road OP_R2The first beam passing through the
Road length) is l_M2Second measurement optical path OP_M2Second via
And the beam respectively enter. For this reason,
From the photoelectric detector inside the second optical path difference detecting device 8b,
The second movable mirror 6b is stopped with respect to the second fixed mirror 5b
In the state, a beat signal whose frequency is (f1-f2) is output
When the second movable mirror 6b moves in the X direction, the frequency changes.
The adjusted beat signal is output. Therefore, this second
The optical path difference detection device 8b integrates the change in the frequency.
The relative movement between the second movable mirror 6b and the second fixed mirror 5b
A large amount of movement can be detected. Therefore, the second reference optical path OP_R2Gas optical path length
(Air optical path length) l_R2(= L_R1) To l_R, The second measurement optical path O
P_M2Is the gas optical path length (air optical path length) of l_M2At the start of measurement
The initial refractive index of gas such as air (at reset) is n,
The change in the refractive index of a gas such as air is Δn, and the second measurement optical path OP
_M2The gas optical path length (air optical path length) is l_M2The second shift when
Reset position of moving mirror 6b (or stage ST)
(Coordinate origin) and the second movable mirror from this reset position
6b (or stage ST), when the displacement amount is x, the second
In the optical path difference detecting device 8b, xn + (l_M2−l_R+ X)
Signal X corresponding to Δn_BIs output to the arithmetic unit 9. The arithmetic processing section 9 stores a predetermined arithmetic expression.
Molified, for example, as shown below
Expression 2 derived from Expression 2 and Expression 11 is stored.
ing. [0090] (Equation 20) Therefore, the arithmetic unit 9 is provided with the first and second optical signals.
The output signal (X) from the road difference detection device (7a, 7b)_A, X
_B) And the initial gas refractive index n at the start of measurement
Based on the output n from a refractive index detector (not shown)
Then, the calculation as shown in the above equation (20) is executed, and the gas
Measurement errors due to changes in the refractive index of the gas caused by turbulence
The first movable mirror 6a and the second movable mirror 6a
Movement amount or coordinates of movable mirror 6b (or stage ST)
Calculate the position. Thereby, the first movable mirror 6a and the accurate
And the position of the second movable mirror 6b (or stage ST)
I can do it. Therefore, the calculation result of the calculation device 9 is not shown.
May be displayed through the display unit of
Based on the movement amount or coordinate position information calculated from the
Although not shown, a drive for moving the stage ST
The drive amount of the system may be controlled by a control system. Then, Expressions 16 to 19 are satisfied.
The first movable mirror 6a and the second movable mirror 6b (or
Stage ST), the interferometer device
Quantization error e added to force is 4 times to 1 time or less
It becomes possible to suppress to. As described above, according to this embodiment,
For example, the configuration is such that each measurement optical path and each reference optical path are close to each other.
Changes in the refractive index of the gas generated in the measurement optical path.
Correction of the measurement error due to the movement of the movable mirror 6 with high accuracy
And position can be detected. In addition, according to this example, the two movable mirrors
Two fixed mirrors are divided internally so that the distance between them is
Very high precision
Accurate measurement is guaranteed. In each of the above embodiments, the
Rodyne type laser interferometer to which the present invention is applied
However, the present invention similarly applies to a homodyne interferometer.
Can be applied. In this embodiment, the position of the first movable mirror 6a is set.
By giving a difference between the position and the position of the second movable mirror 6b,
The difference between the gas path lengths in the two measurement paths (l_M1−l_M2) Raw
It's terrifying, but not limited to this. For example, the first
The position of the movable mirror 6a is matched with the position of the second movable mirror 6b.
And the first and second interferences which are integrally formed
(Polarization separating prism 3, quarter-wave plates 4a, 4b,
The light plate 7) has an upper part as a first interferometer and a second interferometer.
And the lower part, and measure the two interferometers
Gas path lengths in the two measurement optical paths
Difference (l_M1−l _M2) May be caused. Moreover,
The position of the first movable mirror 6a is equal to the position of the second movable mirror 6b.
So that both moving mirrors are integrated,
The inside is vacuum and the length along the measurement optical path
If a sealed tube of length L is arranged, only the length L of the sealed tube is required.
Optical path length difference (L = | l_M1−l_M2|) Can be caused
Noh. A gas having a predetermined refractive index is placed in this sealed tube.
A medium such as a body, a liquid, and a solid may be enclosed. In this embodiment, the position of the first fixed mirror 5a is
By matching the position of the second fixed mirror 5b with the
The gas path length in the reference light path of
It is not limited to this. For example, the first fixed mirror 5a and the second fixed mirror 5a
The mirror 5b is shifted from the mirror 5b by a predetermined distance.
First and second interferometers (polarized light
Separating prism 3, quarter-wave plates 4a and 4b, polarizing plate 7)
With the upper part as the first interferometer and the upper part as the second interferometer
Divided into two parts, the lower part, and the two interferometers
Staggered to equalize the gas paths in the two reference paths
You can do it. Further, in each of the embodiments described above,
In at least one of the optical path of the interferometer measurement optical path and the reference optical path
An optical path deflecting member for bending the optical path is appropriately arranged, and the entire device is bent.
It is possible to route each optical path so that it becomes compact
It is. Thus, the present invention is not limited to the above-described embodiment.
Various configurations are possible without departing from the gist of the present invention.
You. [0097] As described above, according to the present invention, air or the like
Even if gas fluctuations occur, measurement errors are extremely small,
In addition, high-performance interference that enables high-precision measurement in principle
A measuring device can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view showing the interferometer apparatus of the present embodiment when viewed from the side. FIG. 2 is a plan view showing a state when the interferometer apparatus of the present embodiment shown in FIG. 1 is viewed from directly above. FIG. 3 is a side view showing the state of the interferometer apparatus of the present embodiment when viewed from the left side of FIG. FIG. 4A is a conceptual diagram of a first interferometer showing the principle of the present invention, and FIG. 4B is a conceptual diagram of a second interferometer showing the principle of the present invention. 5 is a diagram showing a relationship between a maximum value of a quantization error and a moving amount of a stage by the interferometer apparatus according to the present invention shown in FIG. FIG. 6 is a side view showing a state when a conventional interferometer apparatus is viewed from the side. FIG. 7 is a plan view showing a state when the conventional interferometer device shown in FIG. 6 is viewed from directly above. FIG. 8 is a side view showing a state of the conventional interferometer apparatus when viewed from the left side of FIG. 9 is a diagram showing a relationship between a maximum value of a quantization error and a moving amount of a stage by the conventional interferometer apparatus shown in FIGS. 6 to 8. FIG. [Description of Signs of Main Parts] 1 ... Laser light source 2 ... Light splitting prism 3 ... Polarization splitting prisms 4a, 4b ... 1/4 wavelength Plates 5, 5a, 5b Fixed mirrors 6, 6a, 6b Moving mirror 7 Polarizing plate 8a First optical path difference detecting device 8b ..... 2nd optical path difference detection device 9 ..... calculation device

Claims (1)

(57) [Claim 1] First and second measuring reflecting means provided integrally movable along a measuring direction, and first and second reflecting means fixed at predetermined positions, respectively. A second reference reflecting unit, a light source unit for supplying a light beam, and a first measurement reciprocating in the gas along the measurement direction via the first measurement reflecting unit based on the light beam from the light source unit. An optical path and a first reference optical path reciprocating in the gas via the first reference reflecting means are formed, and a first measurement output is generated by each light beam passing through the first measurement optical path and the first reference optical path. (1) an interferometer means, and a second measurement optical path reciprocating in a gas along a direction substantially parallel to the first measurement optical path via the second measurement reflection means based on a light beam from the light source means. A second reference optical path reciprocating in the gas via the second reference reflecting means; A second interferometer means for generating a second measurement output by each light beam passing through the second measurement light path and the second reference light path; and a calculation means for performing a predetermined calculation based on the first and second measurement outputs. And wherein the first reference optical path from the first interferometer means to the first reference reflection means is provided by the second interferometer means from the second interferometer means.
The optical path length of the first measurement optical path from the first interferometer means to the reference position of the first measurement reflection means has an optical path length equal to the second reference light path up to the reference reflection means. Is 1 _M1 , the optical path length of the second measurement optical path from the second interferometer means to the reference position of the second measurement reflection means is 1 _M2 , and the first interferometer means is used for the first reference. The optical path length of the first reference light path to the reflection means is l _R1 , the optical path length of the second reference light path from the second interferometer means to the second reference reflection means is l _R2 , When the displacement of the first and second measurement reflection means from a position is x, the first and second measurement reflection means are movable at least in the following range, or at least part of the following range. An interferometer device configured to be movable. l _R1 -l _M1 ≤x≤l _R2 -l _M2