JP3230280B2 - Interferometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention corrects a measurement error due to a temperature change by an optical configuration, and more accurately measures a fluctuation of air, especially a measurement error due to a change in refractive index of air. The present invention relates to an interferometer capable of correcting the measurement error.

[0002]

2. Description of the Related Art A laser interferometer (or laser length measuring device) is known as a device capable of measuring a change in relative distance between a first point and a second point with high accuracy. The laser interferometer changes the interference fringes when the difference between the optical path length of the first laser beam reflected from the first point and the optical path length of the second laser beam reflected from the second point changes. Alternatively, a change in the beat signal is converted into a count pulse. For example, a relative distance can be obtained by integrating and counting this count pulse.

In this case, the optical path length is the product of the actual length of the optical path of the laser beam and the refractive index of the medium through which the beam passes. For example, as disclosed in Japanese Patent Application Laid-Open No. 63-228003, the optical path length generally has a portion caused by many optical paths of a laser beam passing through air having a small refractive index (close to 1) and a refractive index. And a portion of the laser beam that passes through a medium such as glass having a high refractive index due to multiple optical paths. Therefore, when the temperature inside the medium such as glass changes due to a change in the surrounding temperature or a change in the heat of the supporting member, and the refractive index changes, the relative distance between the first point and the second point changes. The difference in optical path length may change even though the distance is not changed, and a change in distance may be erroneously detected by the laser interferometer.

In recent years, laser interferometers have been used for applications requiring extremely high measurement accuracy, such as displacement detectors of projection exposure apparatuses for manufacturing semiconductor devices, and have been subject to measurement errors due to thermal factors. It is desired to eliminate as much as possible. JP-A-63-228003 mentioned above proposes the following interferometer as an interferometer capable of reducing a measurement error due to thermal factors and detecting a change in distance with high accuracy even at a high temperature. I have.

FIG. 3 (a) shows the conventional interferometer. In FIG. 3 (a), reference numeral 1 denotes a laser light source for a two-frequency laser. The first beam having a frequency f1 linearly polarized in a parallel direction and the frequency f linearly polarized in a direction perpendicular to the plane of FIG.
2 (f2 ≠ f1) is emitted in the X direction in a mixed form. Reference numeral 2 denotes a prism body formed by bonding a right-angle prism 3 and a parallelepiped 4 having a parallelogram parallel to the paper surface of FIG. 3A, and the bonding surface of the right-angle prism 3 and the parallel hexahedron 4 is The surface becomes a polarization separation surface 2a, and one surface of a parallelepiped parallel to the surface 2a is a reflection surface 2b. The reflection surface 2b may be a mirror using total reflection. That is, the prism body 2 has a polarization separation surface 2a and a reflection surface 2b.
Can also be regarded as an optical member arranged in parallel.
The polarization separation surface 2a is perpendicular to the plane of FIG.
The prism body 2 is arranged so as to cross the direction at 45 °.

[0006] Laser beams (first and second beams) from the laser light source 1 are incident on the polarization separation surface 2 a of the prism body 2 at an incident angle of 45 °. The first beam is P-polarized light with respect to the surface 2a, passes through the surface 2a as it is, enters the reference mirror 6 via the quarter-wave plate 5, and is reflected by the reference mirror 6. Is again incident on the polarization separation surface 2a of the prism body 2 via the quarter-wave plate 5. At this time, since the first beam is S-polarized with respect to the surface 2a due to the reciprocation of the quarter-wave plate 5, the first beam is reflected by the surface 2a and travels toward the corner cube 7.

The first light reflected by the corner cube 7
The beam is incident on the polarization splitting surface 2 a of the prism body 2 after the polarization plane is rotated by 90 ° by the half-wave plate 8. The position of incidence on the surface 2a is a position shifted from the emission position in a direction parallel to the plane of FIG. 3A. In this case, since the first beam is P-polarized by the half-wave plate 8,
After passing through the surface 2a as it is, the light is reflected by the reflection surface 2b, and then enters the reference mirror 6 via the quarter-wave plate 5. The first beam reflected by the reference mirror 6 again is a quarter-wave plate 5
Are reflected by the reflection surface 2b of the prism body 2 and enter the polarization separation surface 2a. In this case, the first beam is converted into S-polarized light by reciprocating through the quarter-wave plate 5, so that the first beam is reflected by the surface 2a and enters the receiver 10. The receiver 10 contains an analyzer and a light receiving element.

On the other hand, the second beam of the laser beam incident on the polarization splitting surface 2a of the prism body 2 from the laser light source 1 is S-polarized with respect to the surface 2a, and this second beam is reflected by the surface 2a. Later, the light is reflected by the reflection surface 2b. Thereafter, the second beam enters the movable mirror 9 via the quarter-wave plate 5. The movable mirror 9 is wider than the reference mirror 6 and is movably held in the X direction in a region shifted in the X direction. The second beam reflected by the movable mirror 9 passes through the quarter-wave plate, is reflected again by the reflection surface 2b of the prism 2, and enters the polarization separation surface 2a. At this time, since the second beam is P-polarized with respect to the surface 2a by reciprocating through the quarter-wave plate 5, the second beam passes through the surface 2a and travels toward the corner cube 7.

The second light reflected by the corner cube 7
The beam is incident on the polarization splitting surface 2 a of the prism body 2 after the polarization plane is rotated by 90 ° by the half-wave plate 8. In this case, since the second beam is converted into S-polarized light by the half-wave plate 8, the second beam is reflected by the surface 2a and then enters the movable mirror 9 via the quarter-wave plate 5. The second beam reflected by the movable mirror 9 again passes through the quarter-wave plate 5 and enters the polarization splitting surface 2a of the prism body 2. This time, 1/4 wavelength plate 5
Reciprocating, the second beam becomes P-polarized light, so that it passes through the surface 2 a and enters the receiver 10. In the receiver 10, the first beam reflected twice by the reference mirror 6 and the second beam reflected twice by the movable mirror 9 are incident on the light receiving element with their polarization directions aligned by the analyzer.

From the light receiving element of the receiver 10, the movable mirror 9
Is stopped, a beat signal having a frequency of (f1-f2) is output, and when the movable mirror 9 moves, a beat signal whose frequency is modulated is output. Therefore, by integrating the change in the frequency, the amount of movement of the movable mirror 9 in the X direction with respect to the reference mirror 6 can be detected. FIG.
(B) shows the prism body 2 of the interferometer of FIG.
Assuming that the width of the prism body 2 in the X direction is d11 and the length in the direction orthogonal to the X direction is d12, the following relationship is obtained.

D12 = 2 · d11 When the beam diameter of the laser beam is φ, the width d1
1 needs to be about 2φ or more.

[0012]

The optical path of the first beam and the second beam in the prism body 2 in the interferometer of FIG. 3A will be discussed with reference to FIG. As shown in FIG. 3B, inside the parallelepiped 4 of the prism body 2, the optical paths of the first beam and the second beam are T11 and T21, respectively, except for a common optical path, and the right-angle prism 3
, The optical paths of the first beam and the second beam are T12 and T22, respectively, except for the common optical path. Since T11 + T12 = T21 + T22 holds, the optical path of the first beam and the second
It is equal to the optical path of the beam.

However, when the parallelepiped 4 and the rectangular prism 3 are individually examined, the parallelepiped 4 has a T
11> T21 holds, and T12 <T22 holds for the right-angle prism 3. Therefore, the parallelepiped 4
Even if the refractive indexes of the right-angle prism 3 and the right-angle prism 3 are equal, if the temperatures of the two become different, the optical path difference between the first beam and the second beam changes, and the moving mirror 9 stops. Nevertheless, it is detected that the movement amount has changed. That is, in the configuration of FIG. 3A, there is a disadvantage that a measurement error occurs when a temperature difference occurs between the optical members constituting the prism body 2.

As shown in FIG. 3B, the width of the prism body 2 in the X direction is d11. However, since two laser beams must pass in parallel between the widths d11, the width is d11. There is also an inconvenience that d11 becomes large and the prism body 2 itself is large. Such a large prism body 2 means that the internal temperature difference is likely to be further increased.

Further, in the interferometer, since there is an optical path passing over the air, a measurement error occurs due to fluctuations of the air, particularly, a change in the refractive index of the air. There is a problem that cannot be done. SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-precision interferometer that solves all of the above problems and has a very small measurement error even when a temperature change occurs between optical members and air fluctuations occur.

[0016]

In order to achieve the above object, the present invention provides a light source means (1) for supplying a coherent light beam as shown in FIG. 1 and a first light beam and a second light beam. A first optical member (11) having a polarized light separating surface (11a) for separating polarized light into a light beam and a reflecting surface (11b) orthogonal to the polarized light separating surface (11a); and a first optical member (11) facing the first optical member (11). The arranged first reflection member (15) and the first light beam passing through the polarization splitting surface (11a) are reflected by the polarization splitting surface (11a) and the first reflection member (15).
To and from the polarization separation plane (11
a), the first and second quarter-wave plates (14a, 14a, 14a, 14b) provided in each reciprocating optical path between the first optical member (11) and the first reflection member (15). 14b) and its polarization separation surface (1
A deflecting member (17) for deflecting the first light beam emitted from the first light beam and the second light beam reflected by the polarization separation surface (11a) toward the polarization separation surface (11a) again; and the deflecting member (17). First through
The deflecting member (17) and its polarization separating surface are used to reflect the light beam on the polarization separating surface (11a) and transmit the second light beam via the deflecting member (17) through the polarization separating surface (11a). (11
a) a phase member (18) arranged between the optical paths of
A second reflecting member (16) disposed opposite to the optical member (11);
And a second light beam passing through the polarization separation surface (11a) reciprocates between the polarization separation surface (11a) and the second reflection member (16) in separate optical paths, respectively. Third and fourth quarter-wave plates (14e, 14f) provided on each reciprocating optical path between the first optical member (11) and the second reflection member (16) so as to emit light. And a first light beam reflected by the polarization splitting surface (11a) and a second light beam emitted from the polarization splitting surface (11a) are received, and the first reflection member (15) and the second reflection member (16) are received. And a first detecting means (10a) for detecting a relative movement amount.

Based on the above basic structure, the present invention divides the first light beam emitted from the polarization separation surface (11a) and the second light beam reflected from the polarization separation surface (11a), and splits the first light beam. In order to reflect the split first light beam on the polarization separation surface (11a) and transmit the split second light beam on the polarization separation surface (11a), the polarization separation surface (11a) and the deflection member (17) are used. )
And a split second light beam passing through the polarization splitting surface (11a) through the second optical member (19) and the polarization splitting surface (11a). ) And the first or second reflecting member (15, 16) so as to reciprocate in separate optical paths, respectively, and emit the polarized light separating surface (11a). 1 or 2nd reflection member (15,1
6) The fifth and sixth ones provided in each round-trip optical path between
波長 wavelength plate (14c, 14d) and a fifth 1/1 between the first optical member (11) and the first or second reflecting member (15, 16).
A first correction member (22) provided in an optical path reciprocating through a four-wavelength plate (14c), and a first correction member (22) between the first optical member (11) and the first or second reflection member (15, 16). The sixth quarter wave plate (14
d) a second correction member (22) provided in the optical path reciprocating in
And a second light beam that reflects the polarized light separating surface (11a) and a second light beam that is emitted from the polarized light separating surface (11a) to detect a change in the refractive index of air. 2 detecting means (10b).

[0018]

According to the interferometer of the present invention, the first reflecting member (15) and the second reflecting member (16) are arranged with respect to the first direction (X direction) which is the traveling direction of the first light beam. Can be staggered in the vertical direction. Then, the first light flux reflected twice by the first reflection member (15) and the second reflection member (1).
6) and the second light flux reflected twice by the first detecting means (10).
The light is mixed and received in a).

Therefore, when the relative position of the first reflecting member (15) and the second reflecting member (16) in the X direction changes, the first reflecting member (15) and the second reflecting member (16) change.
The optical path length between the light beam and the second light beam changes and the light receiving means (10
Since the interference fringe or the beat signal in a) changes, the relative movement amount of both members (15, 16) can be detected. Further, a part of the second light beam reflected when the light beam from the light source means (1) passes through the first optical member (11) is converted by the first or second reflecting member (15, 16) through the correction member into a second part. The secondly reflected correction light beam and a part of the light beam twice reflected by the first or second reflection member (15, 16) are mixed and received by the second detection means (10b).

Therefore, the optical path length of the first optical member (11) and the first or second reflecting member (15, 16) due to the fluctuation of the air (change in the refractive index of the air) in the optical path exposed to the air. The change, that is, the change in the optical path length in the air with respect to the length of the correction member having a predetermined length in the X direction can be accurately detected by the second detection means. Therefore, by applying correction to the measurement signal obtained by the first detection means (10a) by the correction signal obtained by the second detection means, measurement with extremely excellent accuracy can be achieved.

As described above, according to the present invention, a part of the measuring optical path of the interferometer is used as one of the correcting optical paths for detecting a change in the air refractive index.
Since the optical path for correction reference, which is a reference for the change of the air refractive index, is formed in parallel with the common optical path in parallel with the common optical path, the interferometer is actually received while the configuration of the interferometer is made compact. Measurement errors due to the refractive index of air can be detected more accurately.

Further, the interferometer according to the present invention has a configuration capable of eliminating a measurement error due to a temperature change, and this will be specifically described. First, in the first optical member (11), for example, as shown in FIG. 1B, a polarization separation surface (11a) and a reflection surface (11b) are arranged orthogonally. The width (height) of the first optical member (11) in the X direction is d1.
Then, the length d2 of the member in the direction perpendicular to the X direction has a relationship of d2 = 2 · d1.

First, when examining the optical path for measurement, if the first optical member (11) is composed of only a triangular prism (13) having a right-angled isosceles triangular cross section, the first optical member (11) will be described. An optical path through which the first light beam reflected twice by the one reflecting member (15) passes through the first optical member (11) (solid line optical path T1 inside the prism 13 shown in FIG. 1B).
And an optical path (a dotted optical path T2 inside the prism 13 shown in FIG. 1B) through which the second light flux reflected twice by the second reflecting member (16) passes through the first optical member (11). Since the light passes through optical paths of the same length vertically separated from each other and the temperature of the prism 13 changes, the optical path difference between the two does not change, and measurement can be performed with higher accuracy.

Further, as shown in FIG. 1, two prisms each having a triangular prism shape having a cross section of a right-angled isosceles triangle, that is, right-angle prisms (12, 13) are integrated into a first optical member (1).
Even in the case of 1), the first light beam and the second light beam have the same length on the optical path above and below the optical member (11) (FIG. 1B).
The optical path T1 of the solid line and the optical path T2 of the dotted line shown in FIG. Therefore, the right angle prism (12) and the right angle prism (1
3), the optical path difference between the first light beam and the second light beam does not change, and more accurate measurement is guaranteed.

Next, considering the correction optical path, first, when the first optical member (11) is composed of only the right-angle prism (12), as shown in FIG. The light path of the light beam affected by the fluctuation of air in 12) is T1 or T2, and the light path of the light beam serving as the correction reference via the correction member is T3. Therefore, the optical path T
1 (or T2) and the optical path T3 have the same length, and the optical path difference between the two does not change even if the temperature of the prism 13 changes, so that the optical path length due to the fluctuation of air (change in the refractive index of air). Changes can be measured with high accuracy.

Further, as shown in FIG. 1, two right angle prisms (12, 13) are integrated to form a first optical member (11).
1D, as shown in FIG. 1D, in the right-angle prism (12), the optical path length (T1 or T2) of the luminous flux affected by the fluctuation of the air and the correction reference through the correction member. The light path affected by the fluctuation of air in the right-angle prism (13) is equal to the light path serving as a correction reference through the correction member. Therefore, the right angle prism (12) and the right angle prism (1
3), the difference in the optical path length between the light beam affected by the fluctuation of air and the light beam serving as the correction reference through the correction member does not change, and is always accurate. The change in the optical path length due to the fluctuation of the air (change in the refractive index of the air) can be measured.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An interferometer according to a first embodiment of the present invention will be described below with reference to FIG. Note that the laser light source 1 and the receiver 10 of this embodiment are denoted by the same reference numerals as those of the conventional example shown in FIG. FIG. 1A shows a main part of the laser interferometer of the present embodiment. In FIG.
Is a first prism body (first optical member: a first optical member: a first rectangular member 12 and a second rectangular prism 13) bonded together.
Hereinafter, it is referred to as a prism body 11. ). As shown in FIG. 1B, the prism body 11 has a hypotenuse of a right-angle prism 12 having a hypotenuse inclined at 45 ° with a length of an orthogonal side d1 and a length d2 (= 2 · d1). The right-angle prism 13 having a hypotenuse inclined at 45 ° is bonded to one of two orthogonal sides. The bonding surface (the surface on one side of the two orthogonal sides of the right-angle prism 13) is a polarization separation surface (polarization beam splitter surface) 11a.
The surface on the other side of the two orthogonal sides of the right-angle prism 13 is formed by the reflection surface 11b. In addition,
The reflection surface 11b may be configured so that light is totally reflected without providing a reflection film on the reflection surface 11b.

Here, the prism body 11 only needs to have the polarization separation surface 11a and the reflection surface 11b arranged orthogonally in principle, and may be constituted by only the right-angle prism 13. Also, for example, as shown in FIG. 1C, three right-angle prisms 111 to 113 are bonded together to form a prism body 1.
10, the bonding surface of the right-angle prisms 111 and 112 is formed by the polarization splitting surface 110a.
If the surface outside 13 is a reflection surface 110b, this prism body 110 can be used in place of the prism body 11.

Referring back to FIG. 1A, the direction in which two laser beams (first and second beams) having different frequencies are emitted from the laser light source 1 is defined as the X direction, and the prism 11 Prism body 11 is arranged such that the polarization separation surface 11a of the
A first movable mirror 15 and a second movable mirror 16, each of which is a movable flat mirror, are displaced in a direction perpendicular to the X direction in the X direction so as to face the prism body 11.

The two orthogonal sides (11a, 11a,
In the vicinity of the transmission surface 11c forming an oblique side forming an equal angle with respect to 11b), each of the six quarter-wave plates 14a to 14c
14f are arranged in parallel with each other.
1/4 wavelength plates (14c, 14d) and first movable mirror 1
5, two quarter-wave plates (14)
A closed tube 22 (correction member) is provided which is separated from the surroundings by a predetermined length of two reciprocating optical paths which reciprocate by the first movable mirror 15 via the respective c and 14d).

The sealed tube 22 is a member formed of a hollow cylinder having at least both ends transparent and a predetermined length, and the inside thereof is filled with air. The inside of the sealed tube 22 may be evacuated. Further, the prism body 11
A deflecting prism (right-angle prism) 17 as a deflecting member for deflecting the light emitted from the polarization separating surface 11a by 180 ° is disposed in the direction in which the laser beam from the laser light source 1 is reflected by the polarization separating surface 11a. . In this case, assuming that the laser beam is returned to the polarization separation surface 11a again by the two total reflections in the deflection prism 17, the polarization separation surface 11a and the reflection surface 11b of the prism body 11 are assumed.
The deflecting prism 17 is positioned so that the plane including the optical path deflected by the prism body 11 is parallel to the ridge line of the deflecting prism 17.

A half-wave plate 18 is arranged in the middle of one optical path between the prism body 11 and the deflecting prism 17, and a laser beam from the deflecting prism 17 is reflected by the polarization separating surface 11a. In the direction, a first receiver 10 for detecting a relative movement amount of the first and second movable mirrors (15, 16) is arranged. Also, the half-wave plate 18
A second prism member 19 (second optical member: hereinafter, referred to as a prism member 19) having a shape similar to the prism member is provided between the first prism member 19 and the deflecting prism 17 . The prism body 19 includes two right-angle prisms (20, 2).
1), and a bonding surface thereof (a surface on one side of two orthogonal sides of the right-angle prism 20) is formed by a light splitting surface (beam splitter surface) 19a. The surface on the other side of the two orthogonal sides 20 is formed by a reflection surface 19a.

In the direction in which the beam split and deflected by the prism 19 via the half-wave plate 18 is reflected by the polarization splitting surface 11a of the prism 11, the prism 1
A second receiver 10b for detecting a change in the refractive index of air between the movable mirror 1 and each of the movable mirrors (15, 16) is arranged.
Instead of the 波長 wavelength plate 18, a ４ wavelength plate is arranged so as to cover the entire entrance and exit surfaces of the deflection prism 17, and a 波長 wavelength plate is provided on the exit surface of the prism body 19. A １ ／ wavelength plate may be arranged on three optical paths between the prism body 19 and the prism body 11. At this time, the 波長 wavelength plate may be joined to the surface of the right-angle prism 12 of the prism body 11.

Next, the operation of this embodiment will be described. First,
Laser beams (first beam and second beam) from the laser light source 1 are incident on the polarization splitting surface 11a of the prism body 11 at an incident angle of 45 °. The first beam of P-polarized light with respect to the surface 11a passes through the surface 11a as it is, is converted into circularly polarized light via the quarter-wave plate 14a, and is again quarter-wavelength-converted by the first moving mirror 15. The light enters the polarization splitting surface 11a of the prism body 11 via the plate 14a. At this time, the first beam reciprocates through the quarter-wave plate 14a, and
Since the light enters the polarized light separating surface 11a in the state of polarized light, it is reflected by the polarized light separating surface 11a. Then, the first beam reflected by the polarization separation surface 11a is reflected and deflected by 90 ° at the reflection surface 11b, converted into circularly polarized light via the quarter-wave plate 14b, and again by the first movable mirror 15 1/4 wavelength plate 14b
Reflected toward. The first through the quarter-wave plate 14b
The beam is reflected again by the reflection surface 11b to form the polarization separation surface 11b.
a. At this time, the first beam is a １ ／ wavelength plate 14.
By reciprocating through b, the light enters the surface 11a in the state of P-polarized light, and passes through the surface 11a and travels toward the half-wave plate 18. The first beam having passed through the half-wave plate 18 is converted into S-polarized light by rotating the polarization plane by 90 °, and is then split into two by the light splitting surface 19a of the prism body 19.

First, one of the first beams passing through the light splitting surface 19a of the prism body 19 is reflected and deflected by 180 ° by the deflecting prism 17, and re-enters the polarization splitting surface 11a of the prism body 11. At this time, since the first beam has been converted into S-polarized light by the half-wave plate 18, the first beam is reflected by the polarization separation surface 11a and received by the first receiver 10a.

On the other hand, the other first beam reflected by the light splitting surface 19a of the prism body 19 is reflected and deflected by 90 ° at the reflecting surface 19b, and re-enters the polarization splitting surface 11a of the prism body 11. At this time, since the first beam has been converted into S-polarized light by the half-wave plate 18, its polarization separation surface 11a
And is received by the second receiver 10b. Next, the polarized light separating surface 1 of the prism body 11 is
The second S-polarized beam is reflected by the surface 11a of the surface 11a of the laser beam incident on
It goes to the two-wavelength plate 18. The second beam having passed through the half-wave plate 18 is converted into P-polarized light by rotating the polarization plane by 90 °, and is then split into two by the light splitting surface 19a of the prism body 19.

First, one second beam passing through the light splitting surface 19a of the prism body 19 is reflected and deflected by 180 ° by the deflecting prism 17, and re-enters the polarization splitting surface 11a of the prism body 11. At this time, the first beam has been converted into P-polarized light by the half-wave plate
After passing through 1a and being reflected and deflected by 90 ° on the reflection surface 11b, the light is converted into circularly polarized light via the 波長 wavelength plate 14e.
The light is reflected by the second movable mirror 15 again toward the quarter-wave plate 14e. Then, the second beam having passed through the quarter-wave plate 14e is reflected again by the reflection surface 11b and is incident on the polarization separation surface 11a. At this time, since the second beam reciprocates on the quarter-wave plate 14e and enters the polarization separation surface 11a in the state of S-polarized light, the second beam is reflected by the polarization separation surface 11a and travels toward the quarter-wave plate 14f. This quarter wave plate 14f
After being converted into circularly polarized light, the second beam is reflected by the second moving mirror 16 again toward the quarter-wave plate 14f and enters the polarization splitting surface 11a. At this time, since the second beam reciprocates through the quarter-wave plate 14f and enters the polarization splitting surface 11a in a P-polarized state, the polarization splitting surface 1a
The light passes through 1a and is received by the first receiver 10a.

On the other hand, the other second beam reflected by the light splitting surface 19a of the prism body 19 is reflected and deflected by 90 ° at the reflecting surface 19b, and re-enters the polarization splitting surface 11a of the prism body 11. At this time, since the second beam has been converted into P-polarized light by the 波長 wavelength plate 18, the second beam passes through the surface 11a and is reflected and deflected by 90 ° on the reflection surface 11b. Is converted into circularly polarized light. Thereafter, the second beam passes through the sealed tube 22 having a predetermined length in the x direction, is reflected by the first movable mirror 15, passes through the sealed tube 22 again, and travels toward the quarter-wave plate 14c. . And this one
The second beam passing through the ／ wavelength plate 14c is reflected by the reflection surface 11b.
And is incident again on the polarization splitting surface 11a of the prism body 11. At this time, the second beam is a quarter-wave plate 14c.
Is reciprocated, the polarization splitting surface 11a in the state of S-polarized light
, Is reflected by the polarization separation surface 11a, and
It goes to the 波長 wavelength plate 14d. The second beam having passed through the quarter-wave plate 14d is converted into circularly polarized light, passes through the closed tube 22, is reflected by the first movable mirror 15, and is again returned to the closed tube 22.
Head for. The second beam that has passed through the sealed tube 22 is １ ／
The light is converted into P-polarized light via the wave plate 14d,
The second receiver 10a is transmitted through the first polarization separation surface 11a.
Is received at.

As described above, in the interferometer of the first embodiment according to the present invention, a part of the measuring optical path of the interferometer is shared as a part of the correcting optical path for detecting a change in the refractive index of the air, and this shared part is further shared. Since it has a characteristic configuration that forms an optical path for a correction reference that is a reference for a change in air refractive index in parallel with the optical path, measurement errors due to the refractive index of air actually received by the interferometer can be more accurately determined. It is possible to detect.

In the receiver 10a, the polarization direction of the first beam reflected twice by the first movable mirror 15 and the second beam reflected twice by the second movable mirror 16 are aligned by the analyzer. Incident on the light receiving element. Here, from the light receiving element of the receiver 10a, when the first movable mirror 15 and the second movable mirror 16 are relatively stopped in the X direction, a beat signal having a frequency of (f1-f2) is generated. When both are relatively moved in the X direction, a beat signal whose frequency is modulated is output. Therefore, by integrating the change in the frequency, the relative movement amount of the first movable mirror 15 and the second movable mirror 16 in the X direction can be detected.

In this case, in this example, as is clear from FIG. 1A, the first and second beams for measurement pass through the same optical path inside the right-angle prism 12 of the prism body 11. Further, inside the right-angle prism 13 of the prism body 11, the first and second beams for measurement are vertically separated from each other by an optical path of the same length (that is, an optical path T1, indicated by a solid line in FIG. 1B).
The light passes through a dotted optical path T2). Therefore, the right-angle prism 1
Even if a temperature difference occurs between the second prism 13 and the right-angle prism 13, the first
Since the difference in the optical path length between the beam and the second beam does not change, the relative movement amount in the X direction between the first movable mirror 15 and the second movable mirror 9 is always measured with high accuracy. be able to.

On the other hand, in the second receiver 10b,
The first beam reflected twice by the first movable mirror 15 (the beam actually affected by the change in the refractive index of air) and the first beam reflected twice by the first movable mirror 15 via the sealed tube 22. The second beam (a beam for correction reference serving as a reference for the change in the refractive index of the air) is incident on the light receiving element after the polarization directions thereof are aligned by the analyzer.

From the light receiving element of the second receiver 10b,
In the state where the optical path length difference due to the fluctuation of the air (change of the refractive index of the air) does not occur, the beat signal having the frequency (f1−f2) is output, and the fluctuation of the air (the change of the refractive index of the air) causes the X direction. When a difference in the optical path lengths occurs, a beat signal whose frequency is modulated is output. Therefore, by integrating the change in the frequency, it is possible to detect the amount of change in the optical path length in the X direction due to air fluctuation (change in the refractive index of air).

In this case, in this example, as is clear from FIG. 1A, inside the right-angle prism 12 of the prism body 11, the first and the second for detecting the change in the refractive index of air.
The beam passes through the same optical path. In addition, prism body 1
As shown in FIG. 1D, the first and second beams for detecting a change in the refractive index of air pass through the optical paths T1 and T3 inside the right-angle prism 13 as shown in FIG.
The length of the optical path T1 is equal to the length of the optical path T3. Therefore,
Even if a temperature difference occurs between the right-angle prism 12 and the right-angle prism 13, the difference between the optical path lengths of the first and second beams does not change, and the air fluctuation (air flow) always occurs with high accuracy. The change in the optical path length in the X direction due to the change in the refractive index can be measured.

As described above, the first and second receivers (1)
0a, 10b) are input to an unillustrated arithmetic processing system (arithmetic means), and the arithmetic processing system converts the signals into signals containing air fluctuation information output from the second receiver. By performing a predetermined operation based on the first and second movable mirrors (15, 1) with higher accuracy by correcting the measurement signal output from the first receiver.
The relative movement amount of 6) can be detected.

As described above, the first type described with reference to FIG.
When the embodiment is used as an interferometer for detecting a two-dimensional position of an XY stage on which a wafer of a projection exposure apparatus for manufacturing a semiconductor is mounted, for example, a projection objective for projecting a pattern on a reticle onto the wafer. It is preferable that the first movable mirror 15 be fixed to the lens barrel, and the first movable mirror 16 be fixed to one end on the XY stage. At this time, the sealed tube 22
One end of the (correction member) may be connected to the first movable mirror 15, but the force due to vibration or expansion due to external factors causes the first movement mirror
This is not preferable because it may be transmitted to the moving mirror 15 and the projection objective lens.

In the first embodiment shown in FIG. 1A, a case where six quarter-wave plates (14a to 14f) are formed has been described.
A 構成 wavelength plate may be used. In the first embodiment shown in FIG. 1A, the deflecting prism 17 and the prism 11
The prism body 19 is disposed in the upper optical path between the deflecting prism 17 and the prism body 11, and the prism body 19 is disposed in the lower optical path between the deflecting prism 17 and the prism body 11. The (correction member) may be arranged between the prism body 11 and the second movable mirror 16.

Further, in the first embodiment shown in FIG. 1 (a), the closed pipe 22 covers two correction optical paths which reciprocate the first movable mirror 15 through the prism 19 two times.
Although the (correction members) are arranged, the closed tubes 22 (correction members) may be arranged in the respective correction optical paths, and further, the 1/4 arranged in the respective correction optical paths.
The wave plates (14c, 14d) and the sealed tube 22 may be interchanged to be arranged in an opposite manner.

In the embodiment shown in FIG. 1A, the laser light source 1 and the two receivers (10a, 10a) are placed on the first surface side of a rectangular prism 12 having two surfaces orthogonal to each other.
b), and a half-wave plate 18, a prism body 19 and a right-angle prism 17 are arranged on the second surface side. However, without being limited to this arrangement, the laser light source 1 and the two receivers (10a, 10b) are arranged on the second surface side of the right-angle prism 12, and 1 / 2 wavelength plate 18, prism body 1
9 and the right-angle prism 17 may be arranged, and further, the laser light source 1 and two receivers (10a, 10a) are provided.
The arrangement may be such that either one of b) is replaced.

It is needless to say that one of the first and second movable mirrors (15, 16) in the first embodiment shown in FIG. 1A can be used as a fixed mirror and the other can be used as a movable mirror. No. Next, an interferometer according to a second embodiment of the present invention will be described with reference to FIG. This example is shown in FIG.
In this embodiment, the deflection prism 17 (right-angle prism) is arranged in a state of being laid sideways and is configured in a planar manner. In FIG. 2, portions corresponding to FIG. The detailed description is omitted.

FIG. 2 shows the structure of a main part of the laser interferometer of this embodiment. In FIG. 2, reference numeral 220 denotes a rod-shaped correction member having a predetermined length and a very small coefficient of thermal expansion. Is fixed to a fixed mirror 15 (in this embodiment, the surface mirror 15 is a fixed mirror and the surface mirror 16 is a movable mirror), and the other end is provided with a reflecting mirror 220a. In the second embodiment, the prism 11
6 quarter-wave plates (14a to 14a)
14f) is different from the first embodiment in which 1f
Only the wave plate is arranged.

Next, the routed optical path of this embodiment will be described with reference to FIG. First, the laser beams (first and second beams) from the laser light source 1 are incident on the polarization splitting surface 11a of the prism body 11 at an incident angle of 45 °. The first beam of P-polarized light passes through the polarization splitting surface 11a as it is, passes through the quarter-wave plate 14, is reflected by the fixed mirror 15, and is again quarter-waved.
After passing through the wavelength plate 14, the light is reflected by the polarization separation surface 11a. The first beam reflected by the polarization separation surface 11a is reflected by the fixed mirror 15 via the reflection surface 11b and the １ ／ wavelength plate 14, and is again polarized via the ４ wavelength plate 14 and the reflection surface 11b. After passing through the surface 11a, the half-wave plate 18
Head for. The first beam having passed through the half-wave plate 18 is split into two by a light splitting surface 19 a of the prism 19.

One first beam passing through the light splitting surface 19a of the prism 19 is reflected by the polarization splitting surface 11a via the deflecting prism 17 and received by the first receiver 10a. The other first beam reflected by the light splitting surface 19a is reflected by the polarization splitting surface 11a via the reflecting surface 19b and received by the second receiver 10b.

Next, from the laser light source 1 to the prism 11
Among the laser beams incident on the polarization separation surface 11a, the second beam of S-polarized light with respect to the polarization separation surface 11a is reflected by the polarization separation surface 11a and travels toward the half-wave plate 18. The second beam having passed through the half-wave plate 18 is split into two by a light splitting surface 19 a of the prism body 19. First, one second beam passing through the light splitting surface 19a of the prism body 19 passes through the polarization splitting surface 11a via the deflecting prism 17, and passes through the reflecting surface 11b and the quarter-wave plate 14 to move the movable mirror 16a. Is reflected by Then, the second beam reflected by the moving mirror 16 is reflected again by the polarization separation surface 11a via the quarter-wave plate 14 and the reflection surface 11b, and is again reflected by the quarter beam.
It goes to the wave plate 14. The second beam having passed through the quarter-wave plate 14 is reflected again by the moving mirror 16 toward the quarter-wave plate 14, transmitted through the polarization splitting surface 11a, and received by the first receiver 10a.

On the other hand, the other second beam reflected on the light dividing surface 19a of the prism 19 is reflected by the reflecting surface 19b, passes through the polarization separating surface 11a of the prism 11, and is reflected by the reflecting surface 11b. Then, the second beam is １ ／
Bar-shaped member 2 fixed to fixed mirror 15 via wave plate 14
20 is reflected by a reflection surface 220a provided at one end of
The light is again reflected by the polarization separation surface 11a via the quarter-wave plate 14 and the reflection surface 11b, and travels toward the quarter-wave plate 14.
The second beam passing through the 波長 wavelength plate 14 is
After being reflected by the reflection surface 220a provided at one end of the
Transmitted through the polarization separation surface 11a through the quarter wavelength plate 14,
The light is received by the second receiver 10b.

As described above, the interferometer of the second embodiment according to the present invention also has one of the measuring optical paths of the interferometer as in the first embodiment.
The characteristic configuration is such that the portion is shared as a part of a correction optical path for detecting a change in air refractive index, and further, an optical path for a correction reference serving as a reference for a change in air refractive index is formed in parallel with the shared optical path. This makes it possible to more accurately detect a measurement error due to the refractive index of air actually received by the interferometer.

Therefore, the fixed mirror 1 is used by the first receiver 10a.
The amount of movement of the movable mirror 16 with respect to 5 can be detected with high accuracy, and the amount of change in the optical path length in the X direction due to air fluctuation (change in the refractive index of air) can be detected with high accuracy by the second receiver 10b. Therefore, a predetermined operation is performed based on the signal output from the second receiver, and the measurement signal output from the first receiver is corrected, thereby detecting the movement amount of the movable mirror 16 with higher accuracy. can do.

Here, in this example, as is clear from FIG. 2A, the first and second beams for measurement pass through the same optical path inside the right-angle prism 12 of the prism body 11, and the air The first and second beams for measuring the fluctuation also pass through the same optical path. Also, inside the right-angle prism 13 of the prism body 11, the first and second beams for measurement are transmitted through optical paths T1 and T2, respectively, as shown in FIG.
, But the length of the optical path T1 is equal to the length of the optical path T2. Further, inside the right-angle prism 13 of the prism body 11, the first and second beams for measuring the fluctuation of the air are transmitted through optical paths T1 and T3, respectively, as shown in FIG.
, But the length of the optical path T1 is equal to the length of the optical path T3.

Therefore, even if a temperature difference occurs between the right-angle prism 12 and the right-angle prism 13, the first and second measurement
The difference between the optical path lengths of the beams does not change, and the difference between the first and second beam optical path lengths for measuring air fluctuation does not change. Thus, right angle prism 1
Even if a temperature difference occurs between the fixed mirror 15 and the right-angle prism 13, the relative movement amount of the fixed mirror 15 and the movable mirror 16 in the X direction is always measured with high accuracy while the fluctuation of air (refractive index of air) ), The amount of change in the optical path length in the X direction can always be measured with high accuracy, so that the amount of movement of the movable mirror 16 can be detected with higher accuracy.

In the second embodiment shown in FIG.
Although the case where one quarter wavelength plate 14 is formed is shown, the quarter wavelength plate 14a may be arranged in each of the six reciprocating optical paths that reciprocate by reflection of the fixed mirror 15 and the reflection surface 220a. . In the second embodiment shown in FIG.
First of a right angle prism 12 having two surfaces orthogonal to each other
Laser light source 1 and two receivers (10a, 1
0b), and the half-wave plate 18,
The prism body 19 and the right-angle prism 17 are arranged. However, without being limited to this arrangement, the laser light source 1 and the two receivers (10a, 10b) are arranged on the second surface side of the right-angle prism 12, and 1 / 2 wavelength plate 18, prism body 1
9 and the right-angle prism 17 may be arranged, and further, the laser light source 1 and two receivers (10a, 10a) are provided.
The arrangement may be such that either one of b) is replaced.

Further, instead of the half-wave plate 18 of the second embodiment shown in FIG. 2A, a quarter-wave plate is arranged so as to cover the entire entrance and exit surfaces of the right-angle prism 17. At the same time, a quarter-wave plate may be arranged on the exit surface of the frit body 19, and further, a quarter-wave plate is arranged on three optical paths between the frit body 19 and the prism body 11, which will be described later. May be. At this time, the 波長 wavelength plate is connected to the prism 1
The 直 wavelength plate 14 may be joined to and integrated with the surface of the right-angle prism 13 of the prism body 11.

Although the above embodiment is an example in which the present invention is applied to a heterodyne type laser interferometer, the present invention can be similarly applied to a homodyne type interferometer. Further, a corner cube or the like may be used instead of the right-angle prism 17. As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0063]

As described above, according to the present invention, a high-precision interferometer with a very small measurement error can be achieved with a compact configuration even when a temperature change occurs between optical members and air fluctuations occur. . Moreover, since the interferometer of the present invention can be realized with a relatively small number of parts, it is extremely advantageous in terms of cost reduction.

[Brief description of the drawings]

1A is a perspective view showing a first embodiment of an interferometer according to the present invention, FIG. 1B is a plan view showing a state of a measurement optical path passing through a prism body 11 of the first embodiment, and FIG. FIG. 4 is a plan view illustrating another example of the prism body of the first embodiment, and FIG. 4D is a plan view illustrating a state of an optical path for measuring fluctuation of air passing through the prism body 11 of the first embodiment.

FIG. 2A is a configuration diagram showing a second embodiment of the interferometer according to the present invention, and FIG. 2B is a plan view of a prism body 11 of the second embodiment.

3A is a configuration diagram showing a conventional interferometer, and FIG. 3B is a plan view of a conventional prism body 2. FIG.

[Description of Signs of Main Parts]

 1 Laser light source 10a, 10b Receiver 11 First prism 14 (14a to 14f) 1/4 wavelength plate 15 First moving mirror 16 Second moving mirror 17 Deflection prism (right-angle prism) 18 Half-wave plate 19 First prism body 22 ···· Correction member

Claims (5)

(57) [Claims] A light source means for supplying a coherent light beam; a first optical member having a polarization separation surface for separating the light beam into a first light beam and a second light beam; and a reflection surface orthogonal to the polarization separation surface. A first reflection member disposed to face the first optical member, and a first light beam passing through the polarization separation surface reciprocates between the polarization separation surface and the first reflection member in separate optical paths. A first and a second quarter-wave plate provided on each reciprocating optical path between the first optical member and the first reflection member so as to emit the polarization separation surface; A deflecting member that deflects the emitted first light beam and the second light beam that reflects the polarization splitting surface again toward the polarization splitting surface, and reflects the first light beam passing through the deflecting member on the polarization splitting surface; In order to transmit the second light beam through the deflecting member through the polarization splitting surface, A phase member disposed between the optical paths of the deflecting member and the polarization separation surface, a second reflection member disposed to face the first optical member, and a second light beam passing through the polarization separation surface being polarized light. It is provided on each reciprocating optical path between the first optical member and the second reflecting member so as to reciprocate between the separating surface and the second reflecting member in separate optical paths and emit the polarized light separating surface. And the third and fourth quarter-wave plates, the first light beam that reflects the polarization splitting surface, and the second light beam that exits the polarization splitting surface. First detecting means for detecting a relative movement amount of the first light beam, a first light beam emitted from the polarization splitting surface, and a second light beam reflecting the polarized light splitting surface. In order to transmit the second light beam reflected by the separation surface and split by the polarization separation surface, A second optical member disposed between the polarization splitting surface and the deflecting member; and a split second light beam passing through the polarization splitting surface via the second optical member, the split second light beam passing through the polarization splitting surface and the second optical member. 1st or 2nd
Fifth light paths provided in each reciprocating optical path between the first optical member and the first or second reflecting member so that the light beam reciprocates between the first optical member and the first or second reflecting member while reciprocating between the first and second reflecting members and the reflecting member. A first correction provided in an optical path reciprocating through the fifth quarter wave plate between the first optical member and the first or second reflection member, and a sixth quarter wave plate. A member, a second correction member provided in an optical path reciprocating through the sixth quarter-wave plate between the first optical member and the first or second reflection member, and the polarization separation surface. The reflected first split light beam and the split second light beam exiting the polarization splitting surface
An interferometer comprising: a second detection unit that receives a light beam and detects a change in the refractive index of air. 2. The interferometer according to claim 1, wherein said first and second correction members are constituted by a sealing member in which a vacuum or air is sealed. 3. The first and second correction members are rod-shaped members having little thermal expansion, and one end of the rod-shaped member is fixed to the first or second reflection member. The interferometer according to claim 1, wherein one end has a reflecting surface. 4. The interferometer according to claim 1, wherein said first and second correction members are integrally formed. 5. The interferometer according to claim 1, wherein said first to sixth quarter-wave plates are integrally formed.