JPH0540011A - Gauge interferometer - Google Patents

Abstract

PURPOSE:To reduce the number of parts used for a gauge interferometer and make the constitution of the interferometer compact by photoelectrically detecting two luminous fluxes split through a polarization beam splitter after the fluxes are reflected by an x- and y-axis movable mirrors and respectively superimposed upon reference light through beam splitters. CONSTITUTION:The p-polarized component 14 made incident to an interference optical system 1 advances toward an x-axis movable mirror 2 after the component 14 passes through a polarization beam splitter(PBS) 5 and its plane of vibration is rotated by 45 deg. by means of a pi/4 rotator 7. The luminous flux reflected by the mirror 2 is again reflected by a mirror M after passing through PBSs 5 and 6 and advances toward a signal detecting optical system 4. Another luminous flux reflected by a y-axis movable mirror 3 is made incident to a corner cube 11 after it is transformed into p- polarized light and passed through the PBS 6. The reflected luminous flux again advances toward the mirror 3 and the returned luminous flux advances toward the optical system 4 after it is reflected by the PBSs 6 and 5. On the other hand, the s-polarized light component 15 advances as reference light and its reflected light is superimposed upon object light from the mirror through a pi/4 rotator 8. As a result, a buffer signal is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer, which is used for measuring microscopes, coordinate measuring machines and the like, for measuring the amount of movement of an object such as an xy stage.

[0002]

2. Description of the Related Art Conventionally, as an instrument for measuring the amount of movement of an xy stage in the two axial directions, there is an instrument as shown in FIG. The xy stage (23) can move on the table (25) in the x and y directions, and its movable range is a range surrounded by a dotted line as illustrated. Moving mirrors (34) and (41) are installed on the stage (23). This length measuring device is a laser light source (30),
It is composed of a half mirror (31), an x-axis length measuring unit (47), and a y-axis length measuring unit (48). Each length measuring unit includes a polarization beam splitter (hereinafter abbreviated as PBS) (32), (39), λ / 4.
Plates (33), (40), signal detectors (37), (44)
And corner cubes (35), (3) that are optical elements that reflect parallel to the incident direction regardless of the direction of the incident light.
6), (42) and (43).

The luminous flux emitted from the light source (30) is divided into two by a half mirror (31) into a luminous flux (45) to be reflected and a luminous flux (46) to be transmitted. The luminous flux (45) is P
The p-polarized light component incident on the BS (32) is transmitted through the PBS (32) and the λ / 4 plate (33) to be converted into circularly polarized light, which is further advanced by the moving mirror (34). The reflected light beam is again converted into s-polarized light by the λ / 4 plate (33), and then the corner cube (35) and PBS are used.
It is reflected by (32) and again travels to the moving mirror (34). Then, the light flux reflected by the moving mirror (34) returns to p-polarized light by the λ / 4 plate (33), and P
It passes through the BS (32) and enters the signal detector (37).

On the other hand, the s-polarized component of the light beam (45) is PB.
The corner cube for reference (3
6), and the light flux reflected here is PBS (3
It is reflected again at 2), but at this time, the moving mirror (3
4) The light flux from 4) is overlapped and travels to the signal detector 37, where an interference signal is detected. In the above process, the length measurement in the x-axis direction is performed.

The other light beam (46) split into two by the half mirror (31) is reflected by the mirror (38) to generate PB.
The s-polarized light component of the incident light that is incident on S (39) is PBS
After being reflected by (39), transmitted through the λ / 4 plate (40), converted into circularly polarized light, and reflected by the moving mirror (41), λ / 4
It passes through the plate (33) and is converted into p-polarized light.
After passing through 9), it enters the corner cube (43).
The light beam reflected by the corner cube (43) again travels to the moving mirror (41), and the returned light is reflected by the λ / 4 plate (4).
0) to be returned to s-polarized light, reflected by the PBS (39) and incident on the signal detector (44).

Further, the p-polarized component of the light beam (46) is P
After passing through the BS (39) and being reflected by the corner cube (42), the PBS (39) overlaps the light flux from the moving mirror (41), and the interference signal is detected by the signal detector (44). The length measurement in the y-axis direction is performed.

However, in such a conventional length measuring method, in order to measure the x-axis and the y-axis separately, at least two sets of interference sections and two sets of signal detection sections ( Three
7, 44) are required, which increases the number of parts,
I needed to take up a lot of space. SUMMARY OF THE INVENTION It is an object of the present invention to provide a biaxial interferometer for an xy stage that solves the above-mentioned drawbacks of the related art, requires a small number of parts, and has a compact table structure.

[0007]

In order to achieve the above object, an interferometric length measuring instrument according to the present invention is an interferometric length measuring instrument for measuring a moving distance of an object movable in two axial directions of x and y. A reflection member attached to the object and oriented in the x and y directions, a laser light source, a beam splitter that splits the light from the laser light source into first and second light fluxes, and the first light flux. A polarization beam splitter that divides the first and second polarized light components into the first and second polarized light components and directs the first and second polarized light components to the reflecting member in the x direction and the y direction, respectively, and a part of the second light flux and the first polarized light component. An interference optical system that includes an interference optical path that interferes with a polarized component and an interference optical path that interferes with the second polarized component with another part of the second light flux, and an interference signal that receives both interference patterns and outputs an interference signal. And an interference signal detection unit for detecting Is shall.

[0008]

The two light beams split by the polarization beam splitter are reflected by the x- and y-axis direction moving mirrors, respectively, superposed on the reference light separately by the beam splitter, and photoelectrically detected by the respective interference signal detecting portions. It

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the present invention will be described in detail below with reference to the drawings.
FIG. 1 is a plan view showing an outline of an embodiment of an interferometer according to the present invention, which is capable of simultaneously measuring the lengths of the x-axis and the y-axis in two axial directions by a set of interferometers and a signal detector. It is a figure.

This interferometer is composed of an interference optical system (1), an x-axis moving mirror (2), a y-axis moving mirror (3) and a signal detecting optical system (4). It is applied to a stage (object) that can move in both directions.

Further, the interference optical system (1) includes polarization beam splitters (5), (6) and a π / 4 rotator (7).
(8), λ / 4 plates (9) and (10), corner cubes (11) and (12), and an optical path correcting optical system (13).

First, the coherent linearly polarized light (14) emitted from a light source (not shown) enters the interference optical system (1). Of this incident light, the p-polarized component (14) is transmitted through a polarized beam sputter (hereinafter abbreviated as PBS) (5) and becomes π / 4.
The rotator (7) rotates the direction of the vibrating surface by 45 °. The p-polarized component (14b) of the light beam (14) that has passed through the π / 4 rotator (7) and has its vibrating surface rotated is
The light passes through the PBS (6), passes through the λ / 4 plate (9), is converted into circularly polarized light, and travels toward the mirror (2) that moves in the x-axis direction. The light beam reflected by the x-axis moving mirror (2) is again λ / 4.
The light is transmitted through the plate (9), converted into s-polarized light, reflected by the PBS (6), and then enters the corner cube (11). The light flux reflected by the corner cube (11) is reflected by the PBS (6) and reciprocates between the mirror and the x-axis moving mirror (2). The returned luminous flux is returned to p-polarized light by the λ / 4 plate (9) and
(6), transmitted through the PBS (5) and reflected by the mirror M toward the signal detection optical system (4).

The other s-polarized light component (1
4a) is reflected by the PBS (6) and is reflected by the optical path correction optical system (1
3), the light passes through the λ / 4 plate (10) and becomes circularly polarized light toward the y-axis moving mirror (3). Here, the optical path correction optical system (13) functions to change the direction of the light beam (14a) so that it enters the y-axis moving mirror (3) at an appropriate position in parallel with the y-axis. In this embodiment,
The board is used.

The luminous flux reflected by the y-axis moving mirror (3) is λ
It is converted into p-polarized light by the / 4 plate (10), passes through the optical path correcting optical system (13) and PBS (6), and enters the corner cube (11). The light flux reflected by the corner cube (11) again travels to the y-axis moving mirror (3), and the returned light flux becomes s-polarized light, PBS (6), PBS (5).
It is reflected by and goes to the signal detection optical system (4).

On the other hand, the s-polarized component (15) of the light beam incident on the interference optical system (1) is reflected by the PBS (5) and goes to the corner cube (12) as reference light.
The light reflected by the corner cube (12) is rotated by 45 ° by the π / 4 rotator (8), and the PBS vibrates.
The s-polarized light component is divided into two by (5) and the x-axis moving mirror (2)
And the interfering signal is detected by superimposing it on the object light from.

Similarly, the p-polarized component is superimposed on the object light from the y-axis moving mirror (3), and the interference signal is detected.

The signal detection method of this embodiment will be described below. The signal detection optical system (4) includes a λ / 4 plate (16), a beam splitter (abbreviated as BS) (17), a π / 4 rotator (18), PBSs (19) and (20), a photodetector (PD). ) (21a) to (21h).

The s-polarized component of the reference light and the object light from the x-axis moving mirror (2) are superposed by the PBS (5), reflected by the mirror (M), and transmitted through the λ / 4 plate (16). Then, they are converted into circularly polarized lights having mutually opposite rotations, and divided into two by the BS (17). Of these, the light flux reflected by the BS (17) is further divided by the PBS (20) into an s-polarized component and a p-polarized component, which are respectively incident on PDs (21d) and (21g) to detect interference signals S4 and S7. To be done. PD (21d),
The incident light on (21g) has different vibrating planes by 90 °, so if S4 = 1 + Sin (ψ _x −ψγ), then S7
= 1-Sin (ψ _x −ψγ), and the interference signals S4 and S7
Has a phase difference of π. Here, ψ _x is the phase of the light from the x-axis moving mirror (2), and ψ _γ is the phase of the reference light.

On the other hand, the luminous flux transmitted through the BS (17) is π /
After passing through the 4 rotator (18), it is divided into a p-polarized component and an s-polarized component by the PBS (19), and the PD (21b),
The interference signals S2 and S5 are detected by being incident on (21e). It may be considered that the signal is detected by rotating the PBS (19) around 45 °. Therefore, the incident light on the PD (21b) is the same as the incident light on the PD (21b) with the direction of the vibrating surface being shifted by 45 °, and the interference signal S2 = 1 + Cos (ψ _x −ψγ), S5 = 1-Cos (ψ _x −ψ
γ), the phase difference between the interference signals S4 and S2 is π / 2.
Becomes Since the phase difference between the interference signals S5 and S2 is π, four signals of 0, π / 2, π and 3π / 2 are finally obtained. Further, interference signals S2-S5 and interference signals S4-S7
By detecting, a two-phase signal with no DC component can be obtained, and length measurement in the x-axis direction including the direction of movement is possible.

After the p-polarized components of the object light and the reference light from the y-axis moving mirror (3) are also superposed by the PBS (5),
Similarly, the interference signals S1, S3, S6 and S8 are detected, and the length measurement in the y direction becomes possible. Regarding the y-axis direction,
The interference signal _{S1 = 1 + Cos (ψ y} -ψγ), S3 = 1 + Sin
_{(ψ y -ψγ), S6 =} 1-Cos (ψ y -ψγ), S8 =
It becomes _{1-Sin (ψ y -ψγ)} . Where ψ _y is the phase of the light from the y-axis moving mirror (3).

FIG. 2B shows x using the interferometer length measuring device 22.
It shows a situation in which both movements of the y stage (23) are measured. In the figure, a sample stage (24) is mounted on an xy stage (23) so as to be movable integrally with the xy stage (23), and an x-axis moving mirror (2),
The y-axis moving mirror (3) is installed on this xy stage (23). The xy stage (23) is movable on the table (25) in the xy directions. The length measuring instrument (22) is arranged and fixed inside the table (25) so that the extension of the measurement optical axes of the x and y axes passes through the center of the visual field and hits the respective moving mirrors (2) and (3). There is.
The xy stage (23) does not need to be a mechanism that can move in any of the xy directions, and can be simply x or y.
By stacking two stages that can move only in one direction,
A sample table (24) having a mirror installed thereon may be stacked. It is of course possible to directly measure the movement of the stage divided into two stages of x and y.

A second embodiment is shown in FIGS. (3) and (4). In this embodiment, the interference optical system (1) and the signal detection optical system (4) are constructed vertically so that the space in the horizontal direction (plane) is omitted as much as possible, and the incident light is taken in from below. The structure is almost the same as that of the first embodiment, but the x stage (26) and the y stage (27) use stages movable only in the x-axis and y-axis directions, respectively.
Right-angle prisms (13a) and (13b) are used in the x-axis and y-axis directions, respectively, in the optical path correcting optical system (13).

In the above first and second embodiments, the corner cubes (11) and (12) can be replaced with cat's eyes, and when the stage is stable and the vertical swing is small, Right angle prisms may be used. The π / 4 rotators (7) and (8) are λ / 2.
It is also possible to use plates or λ / 4 plates.

Further, in this embodiment, in order to detect the moving direction of the mirror, polarized light is used to obtain a signal whose phase is shifted by π / 2. For this reason, the polarization beam splitter is inevitably used as a component of the interference optical system 1, but it is also possible to use the heterodyne method or the like as a signal detecting method. In that case, an ordinary beam splitter can be used instead of the polarized light, so that the polarization conversion element is unnecessary and the π / 4 rotators (7) and (8) are unnecessary.

[0025]

Since the incident light is divided and the length measuring device in the x-axis and y-axis directions is performed by the set of the interference optical system and the signal detecting optical system, the number of elements can be gradually reduced and the space can be reduced as much as possible. Can be made smaller.

[Brief description of drawings]

FIG. 1 is a schematic plan view of an interferometer, which measures an xy stage movement amount according to the present invention.

FIG. 2 is a perspective view showing a relational position between the same stage and the length measuring unit.

FIG. 3 is a perspective view of a main part of an interferometer according to a second embodiment.

FIG. 4 is a perspective view showing relative positions of a stage and a length measuring unit according to a second embodiment.

FIG. 5 is a schematic plan view showing the configuration of a conventional stage movement amount measuring device that does not use the present invention.

[Explanation of symbols]

 1 Interference Optical System 2 x-axis Moving Mirror 3 y-axis Moving Mirror 4 Signal Detection Optical System 5 Polarizing Beam Splitter (PBS) 6 Polarizing Beam Splitter (PBS) 7 π / 4 Rotator 8 π / 4 Rotator 9 λ / 4 Plate 10 λ / 4 plate 11 corner cube 12 corner cube 13 optical path correction optical system 14 luminous flux (14a, 14b) 15 luminous flux 16 λ / 4 plate 17 beam splitter (BS) 18 π / 4 rotator 19 polarizing beam splitter (PBS) 20 polarizing beam splitter (PBS) 21 Photo detectors (21a to 21h) 22 Length measuring device 23 Stage 24 Sample stage 25 Table 26 x stage 27 y stage M Mirror S Interference signal (S1 to S8)

Claims (1)

[Claims] 1. An interferometer, which measures a moving distance of an object movable in two axial directions of x and y, wherein a reflection member attached to the object and oriented in the x and y directions, and a laser light source. A beam splitter that divides the light from the laser light source into first and second luminous fluxes, and divides the first luminous flux into first and second polarized light components, and divides the first and second polarized light components into A polarization beam splitter directed to the reflecting member respectively facing the x direction and the y direction, an interference optical path for causing a part of the second light flux and the first polarization component to interfere with each other, and another part of the second light flux. And an interference optical path including an interference optical path that causes the second polarized component to interfere with each other, and an interference signal detector that receives the interference patterns and detects an interference signal.