JPH07190714A - Interferometer - Google Patents

Abstract

PURPOSE:To accurately measure a distance between surfaces by an interferometer having a light path passing through a space between two surfaces with a polarizing prism combined with wave length plates and the like. CONSTITUTION:The interferometer includes a laser 3 generating (p) polarization and (s) polarization which are different in frequency, a light receiving element 9, a polarizing prism 5 having a polarizing film 501, a polarizing plate 8, and 1/4 wave length plates 6 and 7. The polarizing prism and the 1/4 wave length plates 6 and 7 for rotating a polarizing surface are interposed between surfaces 1 and 2 where normal lines are overlapped, an incident (s) polarization component from the laser 3 is made a measuring beam, and the aforesaid measuring beam is reciprocated between the surfaces 1 and 2, so that it thereby enters the light receiving element 9 through the polarizing plate 8. On the other hand, the (p) polarization component of a reference light beam passes through the polarizing prism 5, and enters the light receiving element 9 through the polarizing plate 8. A distance between surfaces can accurately be measured by the interferometer which has both the measuring light beam reciprocating a light path between two surfaces and the reference light beam not passing through the aforesaid light path. The interferometer is small in size and easy to be manufactured as compared with an interferometer measuring the phase of an interference fringe. Scanning enables the profile of a surface, even if it is large, to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer, and more particularly to an interferometer for measuring distance.

[0002]

2. Description of the Related Art In recent years, the need to measure the shape of a surface with high precision has been increasing more and more, and in particular, a measuring method that can guarantee the order of nanometer is required. It is said that this degree of accuracy can be realized by using an interferometer, and therefore, it is desired to develop and put into practical use a new technique for an interferometer suitable for being used for such a purpose. . Conventionally, a method of measuring the phase of so-called interference fringes has been widely used for measuring the surface shape.

[0003]

However, the measurable range in the surface shape measurement is determined by the aperture of the interferometer, and it is impossible to measure a surface having a size larger than that.
Therefore, this method is not suitable for applications in which such a large surface is to be measured as the surface to be measured. In addition, no conventional interferometer for measuring the phase of interference fringes is sufficiently small and easy to manufacture. If an interferometer that can be made compact and easy to manufacture and that can accurately determine the surface spacing can be realized, it will be possible to scan it with high accuracy when measuring various surface shapes. However, no proposal is made for such an interferometer.

The present invention seeks to provide an interferometer suitable for measuring surface spacing. More specifically, it can be advantageously used for highly accurate measurement of surface shape, and even if it is a large surface, it is possible to measure the shape by scanning.
And it is to obtain an interferometer for distance measurement which is small and easy to manufacture.

[0005]

The interferometer of the present invention comprises a polarized light generating means for generating two orthogonal polarized light components, and a first polarized light component and a second polarized light component emitted from the polarized light generating means. At least one polarizing prism that reflects one and transmits the other, at least two wave plates that rotate the polarization plane when transmitting the polarized component, a polarizing plate, the first polarized component and the second polarized component. Having a light receiving element for receiving a polarization component, among the polarization components generated from the polarization generating means,
As a reference light beam a polarized light component that passes through the polarizing prism,
While the reference light beam passes through the polarizing plate, the polarization component reflected by the polarization prism among the polarization components generated by the polarization generation means is used as a measurement light beam, and the measurement light beam passes through one of the wave plates. Then, after reaching / reflecting on the surface to be measured, the wave plate is transmitted, and after passing through at least one of the polarizing prisms, the wave plate and another wave plate are transmitted, and the surface to be measured is After reaching / reflecting on the opposite measurement surface, after passing through the other wave plate, it is reflected by at least one of the polarizing prisms, passes through the polarizing plate, and passes through the polarizing plate. And the measurement light flux is received by the light receiving element.

Also, a set of semi-transparent mirrors having a light source and a light-receiving element and arranged between two surfaces whose normals overlap or substantially overlap each other are formed, and the incident light flux from the light source is reflected. Two of the first semi-transparent mirror, which is used as a measurement light beam and which is transmitted as a reference light beam, and the second semi-transparent mirror which allows the reference light beam to be transmitted and made incident on the light receiving element and reflects the measurement light beam to be made incident. , A semitransparent mirror, an optical system for forming an optical path that guides the reference light flux that has passed through the first semitransparent mirror to the second semitransparent mirror, and two measurement light beams divided by the first semitransparent mirror. Of the first semitransparent mirror and the second semitransparent mirror so as to be incident on the light receiving element from the second semitransparent mirror after being overlapped with the reference light flux by the optical system after passing through the optical path between the surfaces.
Two lenses inserted off-axis at one of the two surfaces and at each position between the second semi-transparent mirror and the other of the two surfaces. It is a thing.

[0007]

In the present invention, the interplanar distance can be accurately measured by an interferometer having two surfaces arranged and having a measurement light beam passing through the optical path between them and a reference light beam not passing through the same optical path.

According to the first aspect of the present invention, the polarization generating means, the polarization prism, the wave plate, the polarizing plate, and the light receiving element can be provided to realize the above, and at least one surface is provided between the two surfaces.
Two polarizing prisms and two wave plates to rotate the plane of polarization
One sheet is arranged so that the measurement light beam reciprocates between the surfaces. The surfaces to be measured have normals that overlap or almost overlap 2
It is a surface of a sheet, and the polarizing prism and the wave plate described above are provided between them, and the measurement is performed. The interferometer itself is smaller than an interferometer that measures the phase of interference fringes and is much easier to fabricate. A small interferometer having a light path that reciprocates between two surfaces by combining such a polarizing prism and a polarizing plate can be easily scanned even when scanning is used when measuring the surface shape. A conventional interferometer is not suitable for measuring a surface having a size exceeding the aperture, but even a surface having such a large size can be measured by scanning.

The present invention can be realized without using a polarizing prism, and the light source, the light receiving element, and
A first semi-transparent mirror and a second semi-transparent mirror, an optical system for forming an optical path, and two lenses, respectively, and two semi-transparent mirrors and two lenses between two surfaces. And an optical system for forming an optical path is arranged so that the measurement light beam passes through the optical path between the surfaces and then is superposed on the reference light beam. This can also achieve the same effect as the above.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In the figure, reference numerals 1 and 2 respectively represent plane mirrors. These constitute two surfaces whose surface spacing is to be measured, and are arranged so that their surface normals overlap. The interferometer according to the present embodiment can be used by being arranged so as to be movable one-dimensionally or two-dimensionally between two planes 1 and 2 where such normals overlap, and here, a two-frequency laser 3 and a light beam are used. Enlarging laser 4, polarizing prism 5, 1
The quarter wave plates 6 and 7, the polarizing plate 8 and the light receiving element 9 are included.

The two-frequency laser 3 has a frequency f1 within the plane of the drawing.
A light source that generates p-polarized light that oscillates at a frequency of s-polarized light and s-polarized light that oscillates at a frequency f2 perpendicular to the paper surface are configured. A light beam expanding lens 4, a polarizing prism 5, and a light receiving element 9 are arranged in this order as shown in the drawing. In the present embodiment, the polarizing prism 5 has a polarizing film 501 on one side, and a quarter wavelength plate 6 for rotating the polarization plane on each side facing the planes 1 and 2.
7 and a polarizing plate 8 on the side facing the light receiving element 9,
Each is provided integrally with the polarization prism 5. The quarter-wave plates 6 and 7 are located between the polarizing prism 5 and the planes 1 and 2, and the polarizing plate 8 is in the optical path from the polarizing prism 5 to the light receiving element 9.

The quarter-wave plates 6 and 7 face the plane 1 so that the planes of polarization of the transmitted polarization components are rotated. , And the quarter-wave plate 7 facing the plane 2 is selected such that the crystal axis is in the direction of 45 degrees with respect to the paper surface, and the polarizing plate 8 has a polarization axis other than the paper surface and the plane perpendicular thereto. Selected within the plane.

In the above-mentioned configuration, in the present embodiment, the s-polarized component of the p-polarized light and the s-polarized light (linearly polarized light) from the two-frequency laser 3 is used as a measurement light flux that reciprocates between the plane 1 and the plane 2. The p-polarized component is used as a reference light beam, and the measurement is performed as described below. In this case, the split measurement light beam of the s-polarized light component combines the p-polarized light component with the reference light beam with an optical path length difference corresponding to the distance between the plane 1 and the plane 2, and these surface distances are equal to this optical path. It will be reflected in the difference. Now, when a light flux is emitted from the laser 3, the emitted light flux is expanded by the light flux expanding lens 4 and enters the polarizing prism 5. The s-polarized light component (measurement light beam) and the p-polarized light component (reference light beam) of the expanded parallel light beam are received by the light receiving element 9 in the following optical paths.
Leading to.

That is, the incident s-polarized component from the laser 3 side is reflected by the polarizing film 501 of the polarizing prism 5 and passes through the quarter-wave plate 6 whose crystal axis is in the direction of 45 degrees with respect to the plane of the drawing to form a plane. To 1. At this time, the linearly polarized light is converted into circularly polarized light, and is incident perpendicularly to the plane 1 and reflected. The light flux thus reflected again passes through the quarter-wave plate 6. Here, the circularly polarized light is converted into the p polarized light by converting the circularly polarized light into the linearly polarized light. Therefore, the polarized light is transmitted through the polarizing film 501 toward the plane 2 side, and the other crystal axis is oriented at 45 degrees with respect to the paper surface. It is reflected by the plane 2 through the quarter-wave plate 7 located at. Then, after passing through the quarter-wave plate 7 after being reflected, this becomes s-polarized light in the process of transmission of the quarter-wave plate 7, reflection on the plane 2 and transmission of the quarter-wave plate 7 described above. As a result, the polarizing film 501
And enters the light receiving element 9 through the polarizing plate 8 whose polarization axis is in a plane other than the plane of the paper and the plane perpendicular thereto. In this way, the polarization prism 5 and the quarter-wave plates 6 and 7 for rotating the polarization plane are arranged between the two planes 1 and 2 so that the incident s-polarized component as the measurement light flux is The optical path on the normal line between them is reciprocated.

On the other hand, the reference light flux reaches the light receiving element 9 without passing through the same optical path. That is, the incident p-polarized light component from the laser 3 side passes through the polarizing prism 5 and the polarizing plate 8 and enters the light-receiving element 9, and interferes with the above-mentioned s-polarized light traveling back and forth between the plane 1 and the plane 2. Then, a beat signal equal to the difference between the two frequencies f1 and f2 is obtained. Then, as is well known, by measuring the phase change of the beat signal, it is possible to measure the change of the optical path length due to the movement. Since this measurement method is known as a heterodyne interferometry method, further explanation is omitted, but the phase of the beat signal when the interferometer is moved along a predetermined path in a plane perpendicular to the optical axis. Change the two surfaces 1 and 2 by a known method.
Can be measured as a change in the interval.

According to the present embodiment, as described above, the surfaces are arranged so that the surface normals are overlapped with each other, and the surface spacing is measured by an interferometer having a measurement light beam that reciprocates on the optical path on the normal line and a reference light beam that does not pass through the optical path. Can be accurately measured. Also, in this case, the interferometer itself is smaller than the interferometer that measures the phase of the interference fringes, and is much easier to manufacture. In this way, an interferometer suitable for measuring the interplanar distance is realized, and it is possible to exert a great effect on the practical application of the ultraprecision length measurement. Furthermore, when the measurable range in surface shape measurement is limited by the aperture of the interferometer,
Although it cannot be applied to the measurement of a larger surface than that, such disadvantages are eliminated, and the shape can be measured by scanning even a large surface.

There are two possible methods for measurement: moving the laser 3 and other interferometer components integrally, or fixing the laser 3 and moving only the other interferometer components. , It does not matter. In any case, those skilled in the art can easily determine how to configure the measurement system, if necessary.

FIG. 2 shows another embodiment (second embodiment) of the present invention. This embodiment is the same as the above-mentioned embodiment (first embodiment).
In addition, as shown in the same drawing, lenses 10 and 11 for condensing the light beams traveling from the polarization prism 5 to the planes 1 and 2 are arranged on the respective planes.

According to the present embodiment, since the light beam is made into a small spot by the lens 10 and the lens 11, the resolution can be improved as much as that in the first embodiment.
That is, the addition of the lens 10 and the lens 11 facilitates more accurate measurement with a small spot diameter. Also, if the focal lengths of the two lenses 10 and 11 are made equal, the wavefront will bend due to defocusing if displaced in the optical axis direction when the interferometer is moved, but it returns to a flat surface when exiting the polarizing prism 5. There is also an advantage that the reduction in the contrast of the interference fringes can be reduced.

Next, in the case where the polarizing prism is used as in the first and second embodiments, another preferable configuration example of the light beam separating and coupling in the polarizing prism will be described.
3, FIG. 4, FIG. 5, and FIG. 6, FIG. 7, and FIG. 8 respectively show the polarization prisms 5 and 1 / in the configuration of FIG.
It is a figure which shows the case where the parts of the four-wavelength plates 6 and 7 and the polarizing plate 8 are made into another structure, and split-combining of a light beam, ie, a measurement light beam (s polarization component) and a reference light beam (p polarization component). It shows a method of separation and a coupling after the separation.

In the following, the main parts of the reflection and transmission modes will be explained. In the structures shown in FIGS. 1 and 2, the polarizing prism 5 having the one-sided polarizing film 501 was used. In the case of FIG. 3, the polarizing prism 5 is configured to have three parallel polarizing films 501, 502, 503. In FIG. 3, the incident s-polarized light component as the measurement light beam is the polarization film 501 and the polarization film 502 of the polarization prism 5.
After being sequentially reflected by, the light is reflected again by the polarizing film 501, then passes through the quarter-wave plate 6 and is reflected by one plane mirror (see plane mirror 1 in FIGS. 1 and 2) not shown. The light beam reflected by the one plane mirror passes through the quarter wavelength plate 6 again, and further passes through the polarizing film 501, the polarization film 503, and the quarter wavelength plate 7 in this order, and the other plane mirror (not shown) (see FIG. 1). , 2 plane mirror 2
(Refer to). Then, the reflected light flux is 1 /
After passing through the four-wave plate 7, the light is reflected by the polarizing film 503 and thus exits from the polarizing prism 5.

On the other hand, the p-polarized light component as the reference light beam is transmitted through the polarizing film 501 and the polarizing film 503 of the polarizing prism 5 in this order and is emitted from the polarizing prism 5. After that, the above s
It is the same as each of the above-described embodiments that it is combined with the polarized component and is detected by the light receiving element as a beat signal through the polarizing plate.

In this configuration example, even if the characteristics of the polarizing film used in the polarizing prism 5 are insufficient, the respective light fluxes are reflected and / or transmitted at least twice, so that the two polarization components are mixed. Can be reduced, and the accuracy of the beat signal phase measurement can be improved. Specifically, looking at the number of reflections of the s-polarized component on the polarizing film, for example, in the cases of FIGS. Once, then polarizing film 50
2 times, once with the polarizing film 501, and once with the polarizing film 50
3 times, 1 time, 4 times in total). When separating the two polarized components, originally, 100% reflection and 100% transmission are ideal, but even if this is not the case, according to the present configuration, the separation can be more sufficient and the separability is improved. More accurate measurement is possible.

FIG. 4 similarly shows still another example of the structure for splitting and combining light beams. In the figure, 5a, 5b and 5c are polarizing prisms each having one polarizing film, 12 is a prism,
04s is a polarizing plate that passes only the s-polarized component, 505p and 5
06p indicates a polarizing plate that passes only the p-polarized component,
In this example, these elements are combined as shown in the figure to form a light beam splitting / combining optical system.

In FIG. 4, the incident s-polarized component is reflected by the polarizing film 501 of the polarizing prism 5a and the prism 12 in this order, and then the s-polarized component is passed through.
After passing through 4s, the light is further reflected by the polarizing film 502 of the polarizing prism 5b, and then passes through the quarter-wave plate 6 and is reflected by one plane mirror (not shown). The reflected light beam is again 1
After passing through the / 4 wavelength plate 6, the polarizing film 502, and the polarizing plate 505p that passes only the p-polarized component in this order, the polarizing film 503 of the polarizing prism 5c and the ¼ wavelength plate 7 further pass in this order, and the other It is reflected by a plane mirror (not shown). The reflected light flux passes through the quarter-wave plate 7, is reflected by the polarizing film 503, and is emitted from the polarizing prism 5c.

On the other hand, for the p-polarized component, the polarizing film 501 of the polarizing prism 5a and the polarizing plate 5 that allows only the p-polarized component to pass therethrough.
06p, and further passes through the polarizing film 503 in this order, and is emitted from the polarizing prism 5c. After that, the s-polarized light component is combined with the s-polarized light component, and is detected as a beat signal by the light receiving element through the polarizing plate, which is the same as in each of the above-described embodiments.

In this configuration example as well, the same operational effects as in the case of FIG. 3 can be obtained, and since the above-mentioned polarizing plates 504s, 505p, and 506p for making the separation more sufficient are used, further separation can be achieved. Can be improved.

FIG. 5 similarly shows still another example of the structure of splitting and combining light beams. This example shows two polarizing prisms 5a and 5b.
And the prism 13 are arranged in a combination as illustrated. The polarizing prisms 5a, 5b and the prism 13 can be arranged in a predetermined positional relationship. In addition, an example in which the quarter-wave plates 6 and 7 are arranged separately is also shown.

In the figure, the incident s-polarized light component of the measurement light beam is reflected by the polarizing film 501 of the polarizing prism 5a and then 1
The light is reflected by one of the plane mirrors (not shown) through the quarter wave plate 6, and again the quarter wave plate 6, the polarization film 501, the polarization film 502 of the polarization prism 5b, and the quarter wavelength plate 7 are arranged in this order. The light is transmitted and reflected by the other plane mirror (not shown). The reflected light flux passes through the quarter-wave plate 7, is reflected by the polarizing film 502, and is emitted from the polarizing prism 5.

On the other hand, the p-polarized light component as the reference light beam is transmitted through the polarizing film 501 of the polarizing prism 5a, then is incident on the prism 13, the optical path is changed, and then the polarizing prism 5b is transmitted through the polarizing film 502. Then, the light is emitted from the polarizing prism 5b. After that, it becomes the same as the s-polarized component and is detected as a beat signal by the light receiving element through the polarizing plate, as in the above-mentioned respective embodiments. After splitting the measurement beam and back and forth between the two surfaces,
Separation and coupling of the reference light beam and the superposed light beam may be performed as in this example. In the case of this example,
The polarizing plate and the light receiving element can be arranged on the same side as the light source of the dual frequency laser.

Next, the structure shown in FIGS. 6 to 8 will be described. FIG. 6 shows an embodiment according to an example of light beam splitting coupling having substantially equal optical path differences. For example, in the configuration of the first embodiment of FIG. 1, the interferometer is related to the optical system of the p-polarized component for the reference light beam. , Another reference reflecting mirror (plane mirror) other than the plane mirrors 1 and 2.
1'and 2'are provided, and a polarizing prism 5'having a polarizing film 502 on one surface and quarter wavelength plates 6'and 7'are respectively added between them, and the polarizing prism 5 and the above-mentioned additional A half-wave plate 14 for rotating the plane of polarization by 90 degrees is further arranged between the polarizing prisms 5 '. In the illustrated example, the half-wave plate 14 is provided on one surface of the polarizing prism 5 side.

In this example, the process until the measurement light beam and the reference light beam component are emitted from the polarizing prism 5 is the same as in the first embodiment. Therefore, the s-polarized component reciprocates between the planes 1 and 2 and then exits from the polarizing prism 5 in the preceding stage, and the p-polarized component passes through this and exits. In this way, the s-polarized light component (measurement light flux) emitted from the polarization prism 5 is
The light passes through the half-wave plate 14 that rotates the plane of polarization by 90 degrees toward the polarizing prism 5 ′ in the subsequent stage, and thus passes through and exits the polarizing prism 5 ′.

On the other hand, the polarizing prism 5 of the previous stage is also used.
The p-polarized light component (reference light beam) emitted from the
After passing through the half-wave plate 14 which is rotated by one degree, the light enters the polarizing prism 5'in the subsequent stage and reciprocates between the reflecting mirrors 1'and 2 '. Thus, in this way, the p-polarized light component emitted from the polarizing prism 5 reciprocates between the reflecting mirrors 1'and 2 ', and then exits from the polarizing prism 5', and is combined with the s-polarized light component.

By doing so, the optical path differences of both components become substantially equal, and there is an advantage that the influence of the atmosphere such as atmospheric pressure and temperature can be canceled.

FIG. 7 shows another example of the structure of an interferometer of the same type as that of FIG. In this example, the four-sided polarizing film 50
1, 502, 503 and 503 ', each having one polarizing film 5a, 5b, 5c
And 5c 'are arranged in combination as shown, and the polarization plane is rotated by 90 degrees between the polarizing prism 5a and the polarizing prism 5c' and between the polarizing prism 5a and the polarizing prism 5c, respectively. 1 to let
This is configured by inserting the / 2 wavelength plates 14 and 15.

FIG. 8 shows a modification of the structure of FIG. That is, this is the same as that of FIG.
01, 502, a quarter wave plate, and a half wave plate, and a polarization film 503, 503 ', and a quarter wave plate are separated as shown in FIG. Is an example of the interferometer.

Detailed explanations of these examples will be omitted because their functions and effects can be easily understood from the above description. For example, if the optical path order in FIG. , Polarizing prism incident → Polarizing film 50
Reflection at 1 → Transmission through quarter wave plate 6 → Reflection at plane → 1/4
Wave plate 6 is transmitted → Polarizing film 501 is transmitted → Polarizing film 502 is transmitted → 1/4 Wave plate 7 is transmitted → Plane is reflected → 1/4 Wave plate 7 is transmitted → Polarizing film 502 is reflected → 1/2 wavelength The order is in the order of transmission through the plate 15 → transmission through the polarizing film 503 → exiting the polarizing prism, and the incident p-polarized component is incident on the polarizing prism → the polarizing film 50.
1 → Transmits 1/2 wavelength plate 14 → Reflects at polarizing film 503 ′ → Transmits 1/4 wavelength plate → Reflects on a plane → Transmits 1/4 wavelength plate → Transmits polarizing film 503 ′ → Polarized The order of the light is transmitted through the film 503, transmitted through the quarter-wave plate 7, reflected on a plane, transmitted through the quarter-wave plate 7, reflected by the polarizing film 503, and emitted from the polarizing prism.

In FIG. 8, the s-polarized component is incident → polarized film 5
Reflection at 01 → Transmission through quarter-wave plate 6 → Reflection at plane 1 → 1
/ 4 Wave plate 6 is transmitted → Polarizing film 501 is transmitted → Polarizing film 50
2 is transmitted → 1/4 Wave plate is transmitted → Reflected by plane 2 → 1 /
In this order, the light is transmitted through the four-wavelength plate 7, is reflected by the polarizing film 502, is transmitted through the half-wave plate 14, is transmitted through the polarizing film 503, and is emitted.
The polarized component is incident → transmitted through the polarizing film 501 → transmitted through the ½ wavelength plate 14 → reflected by the polarizing film 503 ′ → quarter wavelength plate 6 ′
Through → reference surface 1 ′ → through 1/4 wave plate 6 ′ → through polarizing film 503 ′ → through polarizing film 503 → 1/4
The order is transmission of the wave plate 7 ', reflection of the reference surface 2', transmission of the quarter wave plate 7 ', reflection of the polarizing film 503, and emission. The present invention may be implemented with the above-described configuration.

Incidentally, supplementary description of FIGS. 6, 7 and 8 will be made. The interferometer does not perform absolute measurement in the first place but performs relative measurement. Therefore, for example, in FIGS. 6, 7 and 8, when the reference plane is the plane 1, it can be applied to the one for the purpose of relative measurement of the plane 2. In this case, the interval measurement is actually an interval deviation measurement (relative value).

Next, still another embodiment (third embodiment) of the present invention will be shown. FIG. 9 shows an embodiment of an improved interferometer for measuring an optical path, and shows a configuration in which one lens is arranged in a light beam. In this one, as shown in FIG.
The main difference from the embodiment of FIG. 2 is that one lens 10 is arranged in the optical path relating to the round-trip path between the two surfaces, and it is inserted off-axis as shown in FIG. It is that. The main part of the optical path of the measurement light beam will be described below. Of the parallel light beams incident from the light source (not shown), the measurement light beam of the desired polarization component is reflected by the polarizing film 501 of the polarization prism 5 and The light is transmitted through the four-wavelength plate 6, reflected by the plane 1 and again transmitted through the one-quarter wavelength plate 6, and the polarization prism 5
The light is transmitted through the polarizing film 501 and the quarter wave plate 7 in this order.

After that, the lens 1 inserted off-axis
At 0, the light is condensed on the plane 2, reflected there, passes through the lens 10 again as shown in the figure, becomes a parallel light flux, and again enters the plane 1 toward the plane 1 in this embodiment.
By doing so, two reciprocating optical paths are formed between the planes 1 and 2 at equal intervals. That is, the light beam directed to the plane 1 is reflected there, goes back in the optical path and returns to the polarization prism 5 (plane 1 → lens 10 → plane 2 → lens 10 → quarter wave plate 7 → polarization prism 5),
Here, the light is reflected by the polarizing film 501 and thus passes through the polarizing plate 8 and enters the light receiving element 9.

According to this embodiment, it is possible to obtain an interferometer in which the surfaces are arranged so that the surface normals overlap with each other, and the measurement light beam that reciprocates in the optical paths that are parallel and equally spaced apart from each other and the reference light beam that does not pass through the optical path are obtained. In addition to the same operational effects as those of the above-described respective embodiments, such as the ability to measure the surface spacing with high accuracy, there are the following advantages. That is, since the measurement light beam makes two round trips between the plane 1 and the plane 2, the sensitivity is doubled, the surface spacing can be measured more accurately, and the wavefront emitted from the interferometer does not tilt even if the interferometer tilts. The contrast of the interference fringes or the amplitude of the beat signal does not decrease.

As for the measurement of the surface shape, it is possible to measure the shape of a large surface without being restricted by the aperture by scanning with the interferometer according to the present embodiment. In addition, since the surface can be scanned with a light beam having a large diameter with respect to the surface 1, even if the surface 1 has very fine unevenness as compared with the diameter, it can be detected during measurement. There is no such thing. Therefore, when only the surface 2 is desired to be measured, there is also an advantage that a surface having small irregularities and no waviness and having low accuracy can be used as the reference surface.

When the interferometer including the lens 10 is moved integrally, if the distance between the plane 2 and the lens 10 changes,
Since the wavefront exiting the interferometer is curved and the contrast of the interference fringes or the amplitude of the beat signal is reduced, a moving mechanism with high straightness is used as the moving mechanism (not shown) for scanning so that the interval is constant. Is a preferred embodiment. In this case, although the detailed description is omitted, the interval can be known from the contrast of the interference fringes or the amplitude of the beat signal, so that the interval can be controlled to be constant. For example, since the control signal can be obtained by synchronously detecting the amplitude change of the beat signal when the lens 10 is vibrated in the optical axis direction with a constant amplitude, the interval can be controlled to be constant.

As for the splitting / combining of the light fluxes, the method described in the above or the examples shown in the following examples or the like can be used as long as it can reciprocate between the surfaces 1 and 2 by being used in combination with the lens 10. Other methods can be used.

10 and 11 show the essential structure of an embodiment which is an improvement of the embodiment shown in FIG. In addition, this embodiment also shows an example of improvement of the polarizing prism in the case of the configuration in FIG.

In FIG. 10, the incident measurement light flux is obtained by polarizing films 501, 502, 503 and 504 having four surfaces as shown in the figure.
The polarizing film 501 and the polarizing film 502 in the polarizing prism 5 having the
It goes through the / 4 wave plate 6 to the plane to be measured 1 and is reflected here. The reflected light flux passes through the quarter-wave plate 6 again, and this time, the polarization film 501, the polarization films 503, 1 / of the polarization prism 5.
After passing through the four-wave plate 7 and the lens 10 in this order, the light is focused on the measured plane 2 and reflected.

The light beam reflected by the plane 2 returns to a parallel light beam by the lens 10 which is inserted off-axis and travels toward the plane 1 to be measured (see FIG. 11). Here, the light beam reflected by the plane to be measured 1 follows the path opposite to the above (see FIG. 11), enters the polarizing prism 5 and reaches the polarizing film 503, is reflected there, and is further polarized films 504 and 503. The light is reflected in this order, and is thus emitted from the polarizing prism 5. On the other hand, the reference light beam passes through the polarizing film 501 and the polarizing film 503 in the polarizing prism 5 in this order, and is emitted from the polarizing prism 5.

In this embodiment, in addition to the one shown in FIG. 9, since the measurement light beams are reflected by the polarizing films 501 and 502 and 503 and 504, even if the polarizing film used is somewhat incomplete, a desired polarization component (for example, , S component) can be passed through the round-trip optical path between the two planes. Further, since the reference light flux also passes through the polarization films 501 and 503, only a desired polarization component (for example, p component) can pass through. Therefore, the separation is further improved and precise measurement is possible. Moreover, if a highly accurate quarter-wave plate is used, the amount of light returning to the light source can be made extremely small.

FIG. 12 shows still another embodiment of beam splitting / combining. In this example, the direction in which the light travels from the polarized light generating means and the direction in which the light for measuring the distance between the surfaces to be measured are the same. That is, unlike the previous embodiments (in the previous example, they are all orthogonal), the incident light beam is directed in the same direction as the measurement light beam. In the figure, the s-polarized light component of the incident light beam is reflected by the polarizing film 501 of the polarizing prism 5a and the polarizing film 502 of the polarizing prism 5b, reflected by the surface 1 to be measured through the quarter-wave plate 6, and again 1 /Four
After passing through the wave plate 6, this time the polarizing film 50 of the polarizing prism 5b.
2. Through the polarizing film 503 of the polarizing prism 5c and the quarter-wave plate 7, the surface to be measured 2 is reached. The light flux reflected by the plane 2 follows the reverse optical path to reach the polarizing film 503 of the polarizing prism 5c, is reflected there, and is further reflected by the polarizing film 50 of the polarizing prism 5d.
The light is reflected at 4 and exits from the polarizing prism. On the other hand, the p-polarized component of the incident light flux is the polarization film 50 of the polarization prism 5a.
1. After passing through the polarizing film 504 of the polarizing prism 5d, s
It goes with the polarization component. In this embodiment, since the measurement light beams are reflected by the polarizing films 501 and 502 and 503 and 504, a desired polarization component (s component) is obtained even if the polarizing film is somewhat incomplete.
Can only pass through. Since the reference light flux also passes through the polarization films 501 and 504, only the desired polarization component (p component) can pass through. Moreover, if a highly accurate quarter-wave plate is used, the amount of light returning to the light source can be made extremely small. Needless to say, this embodiment can be applied to the embodiment using the above-mentioned lens.

In each of the above examples, a polarizing prism is used. According to them, a surface is formed by combining an polarizing prism and a wave plate to form an interferometer having an optical path that reciprocates between two surfaces. The interval can be measured accurately. As already mentioned above, it is not necessary to integrally configure the components that make up the interferometer. For example, as shown in the embodiment of FIG. It goes without saying that it is okay.

What is shown next by way of example is still another embodiment of the present invention, in which at least one polarizing prism is provided between two surfaces whose normals overlap with each other in FIGS. And a wavelength plate for rotating the plane of polarization was arranged so that the measurement light beam reciprocates between the planes,
The example of FIG. 13 is an example that can be implemented without using a polarizing prism. According to this embodiment, two semi-transparent mirrors, two lenses, and optical components for forming an optical path are arranged between two surfaces whose normals overlap with each other, and a measurement light beam travels back and forth between the surfaces. After that, an interferometer for measuring the distance is obtained which is superposed on the reference light beam.

In FIG. 13, reference numerals 16 and 17 denote semitransparent mirrors, and the light flux from the laser is split here. The interferometer includes semi-transparent mirrors 16 and 17 arranged between the two surfaces 1 and 2 as shown in FIG. It can be configured to include the lenses 10 and 11 that are inserted at the outside, the prism 18 for forming the optical path of the divided transmitted light flux, and the light receiving element 9. The lens 10 is between the semi-transparent mirror 16 and the surface 2, and the lens 11 is between the semi-transparent mirror 17 and the surface 1. The prism 18 guides the light flux transmitted through the semitransparent mirror 16 to the semitransparent mirror 17 arranged in parallel with the semitransparent mirror 16. The semi-transparent mirror 16, the semi-transparent mirror 17, and the prism 18 can be arranged in a predetermined positional relationship with each other.

When a light beam from a laser (not shown) as a light source enters one of the semi-transparent mirrors 16, the light beam is split here by half reflection and half transmission. The reflected light flux (measurement light flux) is directed to one of the lenses 10 and the lens 1
0, surface 2, lens 10, other lens 11, surface 1,
After passing through the lens 11 in this order, the light is reflected by the other semi-transparent mirror 17 and enters the light receiving element 9. In this way, the measured light flux of the reflected light flux follows the optical path between the two surfaces 1, 2. On the other hand, the luminous flux (reference luminous flux) transmitted through the semi-transparent mirror 16 is
After being reflected by the prism 18 and changing the optical path, the semi-transparent mirror 17
To enter the light receiving element 9.

In this way, the two semi-transparent mirrors 16 and 17 are
Using the two lenses 10 and 11 and the prism 18, the luminous flux reflected by the semi-transparent mirror 16 is used as the measuring luminous flux, and the luminous flux passing through is used as the reference luminous flux. The phase difference of the interference fringes, which can result from the measurement light beam and the reference light beam overlapping, can be detected by a known method. Also according to this embodiment, by configuring the interferometer having the optical path for the measurement light flux as described above, it is possible to accurately measure the surface distance without using the polarization prism. Further, like the above-described examples, it can be advantageously used for highly accurate measurement of surface shape, and even if the surface is large, the shape can be measured by scanning. The present invention can also be implemented in this manner.

The present invention is not limited to the above example. For example, in the above description, the heterodyne interferometry method was mainly used as the basis, but various methods are known as the phase measurement method, and it goes without saying that they can be applied. For example, the phase change method is well known, which calculates the phase from a series of interference fringe intensities obtained when the optical path length of the measurement light beam or the reference light beam is changed stepwise at regular intervals. It is also possible to do so easily.

Further, for example, the surface has been described by using the plane in all the embodiments, but it is not necessary that the surface is a plane because it may be arranged so that the normals are substantially overlapped. For example, the interferometer according to the present invention can be used for two cylindrical surfaces sharing an axis or two spherical surfaces sharing a center.

[0058]

According to the interferometer of the present invention, the interferometer suitable for measuring the interplanar distance is provided, and the interferometer having the measurement light beam passing through the optical path between the two surfaces and the reference light beam not passing through the optical path is used. The distance can be accurately measured. In addition, the interferometer itself can be made smaller and much easier to manufacture than an interferometer that measures the phase of interference fringes. Furthermore, it can be advantageously used for highly accurate measurement of surface shape, even if a large surface is used. Even in this case, the shape can be measured by scanning. Further, in the case of the second aspect, this can be realized without using the polarizing prism.

[Brief description of drawings]

FIG. 1 is a diagram showing a distance measuring interferometer according to an embodiment of the present invention.

FIG. 2 is a diagram similarly showing another embodiment of the present invention.

FIG. 3 is a diagram showing another configuration example of light beam division coupling.

FIG. 4 is a diagram showing yet another configuration example of light beam splitting / coupling.

FIG. 5 is a diagram showing still another configuration example.

FIG. 6 is a diagram showing a configuration example of light beam splitting / coupling having substantially equal optical path differences.

FIG. 7 is a diagram showing another configuration example of the light beam splitting / coupling having substantially the same optical path difference.

FIG. 8 is a diagram showing still another configuration example of the light beam splitting / coupling having substantially equal optical path differences, and is a diagram showing a modification example of the configuration of FIG. 7.

FIG. 9 is a view showing still another embodiment of the present invention and is a diagram showing a configuration of an interferometer when one lens is arranged in a light beam.

FIG. 10 is a view showing an interferometer according to another embodiment of the present invention, which is an improved configuration of FIG. 9.

FIG. 11 is a side view of the same.

FIG. 12 is a diagram showing yet another embodiment of beam splitting and combining.

FIG. 13 is a view showing still another embodiment of the present invention and is a diagram showing a configuration in the case where a polarizing prism is not used.

[Explanation of symbols]

1 plane mirror 1'plane mirror (reference reflecting mirror, reference surface) 2 plane mirror 2'plane mirror (reference reflecting mirror, reference surface) 3 2 frequency laser 4 luminous flux expansion lens 5, 5 ', 5a, 5b, 5c, 5c', 5d Polarizing prism 6,6 '1/4 wave plate 7,7' 1/4 wave plate 8 Polarizing plate 9 Light receiving element 10,11 Lens 12 Prism 13 Prism 14 1/2 wave plate 15 1/2 wave plate 16,17 Half Mirror 18 Prism 501,502,503,503 ', 504 Polarizing film 504p, 505p, 506p Polarizing plate

Claims (2)

[Claims] 1. A polarized light generation unit that generates two orthogonal polarized light components, and a polarized light that reflects one of the first polarized light component and the second polarized light component emitted from the polarized light generation unit and transmits the other. There are at least one prism, at least two wave plates that rotate the plane of polarization when transmitting a polarization component, a polarizing plate, and a light receiving element that receives the first polarization component and the second polarization component. Then, of the polarization components generated from the polarization generating means, the polarization component passing through the polarization prism is used as a reference light beam, and while the reference light flux passes through the polarizing plate, among the polarization components generated from the polarization generating means. The polarized light component reflected by the polarizing prism is used as a measuring light beam, and the measuring light beam passes through one of the wave plates and reaches / reflects on a surface to be measured, and then passes through the wave plate, After passing through at least one wave plate, after passing through the wave plate and another wave plate, after reaching and reflecting on a measurement surface opposite to the measurement surface, after passing through the other wave plate , Reflected by at least one of said polarizing prisms,
An interferometer, wherein the reference light flux and the measurement light flux transmitted through the polarizing plate are received by the light receiving element. 2. A set of semi-transparent mirrors, each of which has a light source and a light-receiving element and is arranged between two surfaces whose normals overlap or substantially overlap each other, and reflects an incident light flux from the light source. A first semi-transparent mirror that transmits as a reference light beam while making it a measurement light beam, and a second semi-transparent mirror that allows the reference light beam to pass through and enter the light receiving element while reflecting the measurement light beam.
Two semi-transparent mirrors, an optical system for forming an optical path that guides the reference light beam that has passed through the first semi-transparent mirror to the second semi-transparent mirror, and is divided by the first semi-transparent mirror. After the measured light flux passes through the optical path between the two surfaces, it is superposed on the reference light flux by the optical system and is incident on the light receiving element from the second semi-transparent mirror. Two lenses inserted off axis at respective positions between the one of the two surfaces and between the second semi-transparent mirror and the other of the two surfaces. And an interferometer.