JPH05164991A - Interferometer device - Google Patents

Abstract

PURPOSE:To prevent a return light from serving as a secondary light source to generate a noise even when reflected light from the reference surface of a reference primary standard and a body to be inspected is reflected by a polarization beam splitter toward a pinhole member by using a polarizing element. CONSTITUTION:The polarizing element such as a polarizing film 20, a polarized light diffraction grating 21, and a 2nd polarization beam splitter 23 is interposed between the pinhole plate 3 and polarization beam splitter 23, etc., and this polarizing filter 20 reflects the reflected light from the reference surface 7b of the primary standard 7 and the body 8 to be inspected by the polarized light reflecting surface 4a of the polarization beam splitter 4 to absorb and attenuate the light returning to the side of the pinhole plate 3 or scatter the light except to the optical path. Further, light of a polarized component of the incident light which is reflected by the polarized light reflecting surface 4a of the polarization beam splitter 4 is transmitted without being attenuated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer device using a laser light source.

[0002]

2. Description of the Related Art An interferometer device forms an interference fringe by reflected light from a reference surface of a reference prototype and reflected light from a test surface of a subject, thereby determining the state of the surface of the subject,
For example, the surface finish accuracy of a lens is inspected, and various types of interferometer devices have been developed and put into practical use. Among them, for example, the Fizeau interferometer device uses a polarization beam splitter, and a reference prototype and a subject are sequentially arranged on the optical axis of the reflected light by the polarization reflection surface of the polarization beam splitter, and a laser light source is used. The emitted laser beam is reflected by the polarization beam splitter, the reflected light is reflected by the reference surface and the test surface of the reference standard, and is transmitted through the polarization beam splitter to form an interference fringe on the interference fringe image forming means. It is designed to form an image, and the device configuration is simple and can be formed in a small size and compact. Moreover, since the polarization beam splitter is used, there is an advantage that the loss of light amount can be reduced. Therefore, it is widely used as an apparatus for inspecting the surface condition of various test objects.

An interferometer device of this type has the structure shown in FIG. That is, 1 indicates a laser light source,
The laser beam emitted from the laser light source 1 is condensed by the condensing lens 2 and passes through the pinhole 3a of the pinhole plate 3 arranged at the condensing point of the condensing lens 2, so that the next time It becomes divergent light excluding diffracted and scattered light due to folding light and dust in the optical system. Here, if there is birefringence due to the condenser lens 2 described above, the linearly polarized light is thereby split into two linearly polarized light components. The transmitted light of the pinhole 3a is reflected by the polarization reflection surface 4a of the prism type polarization beam splitter 4 such that one polarization component (for example, S polarization component) of the two linear polarization components is reflected and the other polarization component (for example, S polarization component). The P-polarized component) is transmitted and radiated outside the optical system. The polarization reflection surface 4a of the polarization beam splitter 4 has an angle of 45 ° with respect to the incident optical path, and therefore the light reflected by the polarization reflection surface 4a has its optical path bent by 90 °, and the quarter wavelength plate Circularly polarized by 5,
Further, the collimator lens 6 irradiates the reference standard 7 as parallel light. The reference prototype 7 has an antireflection coating on its incident surface 7a. On the other hand, the surface opposite to the incident surface 7a is a reference surface 7b which is finished to be a precise surface, and the light incident on the reference standard 7 is the reference surface 7b.
Part of the light reflected by and the light transmitted through the reference prototype 7
A subject 8 such as an optical lens disposed in the front position of the optical path
And is reflected by the subject 8. Where 1 /
By making the four-wave plate 5 slightly tilted, unnecessary reflected light is emitted to the outside of the optical system.

The reflected light from the subject 8 and the reflected light from the reference surface 7b of the reference standard 7 are made to converge by passing through the collimator lens 6 and transmitted through the quarter-wave plate 5 to make incident light. Is polarized in a direction orthogonal to. The light thus polarized passes through the polarization reflection surface 4a of the polarization beam splitter 4, passes through the low-pass filter 9 provided at the rear focal position f of the collimator lens 6, and further passes through the imaging lens 10 for solid-state imaging. Image plane 11 made up of devices, etc.
An interference fringe can be observed by the interference action between the reflected light from the subject 8 and the reflected light from the reference surface 7b after being imaged on the top.

[0005]

Thus, the incident optical path E of the laser beam from the laser light source 1 to the subject 8 is
Of the reflected optical path R from the subject 8 to the image forming surface 11, the optical path from the polarization reflection surface 4a of the polarization beam splitter 4 to the subject 8 is an incident / reflected optical path E + R in which the incident optical path and the reflected optical path are common. Is becoming Therefore, there are excellent advantages such that the entire structure of the interferometer device can be made small and compact. However, when the incident light path and the reflected light path are shared in this way, the reflected light does not completely pass through the polarization reflection surface 4a of the polarization beam splitter 4 and is reflected by the polarization reflection surface 4a so as to return to the incident light path side. And as a result,
There is a drawback that the returned light is reflected by the pinhole plate 3 and becomes a secondary light source to generate noise.

The cause of the above-mentioned return light is as follows.
First, there is a case where there is a problem in the arrangement relationship of each member forming the optical system, particularly the polarization beam splitter 4, the quarter-wave plate 5, the collimator lens 6, and the like. If these members are not accurately aligned, the reflected light will not be completely transmitted through the polarization reflection surface 4a of the polarization beam splitter 4, and a part will be reflected by the polarization reflection surface 4a to the pinhole plate 3. .. Further, due to the influence of birefringence or the like due to the internal distortion of the condenser lens 2, the light is split into two linearly polarized light components that are orthogonal to each other, which also causes a return light. Therefore, it is necessary to position the respective members in an extremely strict positional relationship and to use an excellent condenser lens 2 having no birefringence. As a result, there are problems that the assembly of the device becomes extremely troublesome and difficult, and the cost becomes high.

Moreover, the above-mentioned members are strictly arranged,
Further, even if a high quality condenser lens is used, it is not always possible to completely prevent the light returning to the pinhole plate 3. That is, the collimator lens 6 is interposed between the quarter-wave plate 5 and the reference standard 7, and the collimator lens 6 not only fulfills the function of making incident light parallel light, but also the reference standard. Since the reflected light from the reference surface 7b of 7 and the subject 8 also has a function of focusing the light at the position of the low-pass filter 9, when the reflected light is incident on the polarization beam splitter 4, it is naturally parallel. It is not light. As a result, the reflected light does not completely pass through the polarization reflection surface 4a of the polarization beam splitter 4, and a part of the reflected light is reflected to generate return light to the pinhole plate 3 side. In order to prevent such a situation, the rear focal length of the collimator lens 6 must be lengthened, the optical path length is significantly lengthened, and the device configuration can be made smaller and more compact. It will be gone.

The present invention has been made in order to solve the problems of the prior art as described above, and the reflected light from the reference surface of the reference prototype and the object is reflected by the polarization beam splitter toward the pinhole member. Even so, it is an object of the present invention to provide an interferometer device in which the returned light to the pinhole member does not become a secondary light source.

[0009]

In order to achieve the above-mentioned object, the present invention allows primary incident light from the laser light source side to pass between a pinhole member and a polarization beam splitter, but a pinhole member. It is characterized in that it has a configuration in which a polarizing element for preventing the return light from the optical system to the side from passing through is interposed.

[0010]

With this structure, the reflected light from the reference surface of the reference prototype and the object to be examined does not completely pass through the reflecting surface of the polarization beam splitter, but is partially reflected to the pinhole member side. Even if it returns, this return light will be absorbed or attenuated by the polarizing element, or will be reflected out of the optical path. As a result, the reflected light of the pinhole member does not become a secondary light source that is incident on the reference prototype side, noise is not generated in the interference fringes imaged on the interference fringe image forming means, and a very good image quality is obtained. Interference fringes are obtained, and the accuracy of inspection and measurement of the surface condition of the subject is improved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an overall configuration diagram of an interferometer device showing a first embodiment of the present invention. In the figure, the same or equivalent components as those of the interferometer device according to the prior art shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

Thus, the interferometer device in FIG. 2 has no particular difference in the basic structure itself from that of the prior art described above. Therefore, the polarization filter 20 as a polarization element is interposed between the pinhole plate 3 and the polarization beam splitter 4. The polarization filter 20 has a function of absorbing the light reflected from the reference surface 7b of the reference prototype 7 and the subject 8 at the polarization reflection surface 4a of the polarization beam splitter 4 and returning to the pinhole plate 3 side. It is a thing. Further, this polarization filter 20 transmits the incident light from the laser light source 1, and therefore, of the incident light, the polarization reflection surface 4 of the polarization beam splitter 4 is included.
The light component reflected by a is transmitted without being attenuated.

By adopting the above-mentioned structure, the return light reflected by the polarization reflection surface 4a of the polarization beam splitter 4 is absorbed or attenuated when passing through the polarization filter 20, and the light slightly passing through is again filtered by the polarization filter. By passing through 20, the light is almost completely absorbed and attenuated and does not serve as a secondary light source. Therefore, the light transmitted through the polarization reflection surface 4a of the polarization beam splitter 4 is only the reflection light of the direct light from the laser light source 1 from the reference surface 7a of the reference standard 7 and the reflection light from the subject 8, The interference fringes imaged on the image plane 11 are of high quality without noise. Generally, in forming the interference fringes, it is preferable that the reflectance from the reference surface 7a of the reference prototype 7 and the reflectance from the subject 8 be substantially equal to each other. Although the reflectance from the surface 7a may be increased or decreased, as described above, the reflectance from the reference surface 7a can be arbitrarily set in order to reliably suppress the generation of the secondary light source due to the returning light. It is possible to set to, and it is possible to form higher quality interference fringes, and it is possible to perform inspection and measurement of the surface state of the subject 8 with extremely high accuracy.

The above-mentioned polarization filter 20 may be arranged at a position between the pinhole plate 3 and the polarization beam splitter 4, and as shown in FIG. Or, as shown in FIG. 4,
You may make it adhere | attach and fix to the pinhole board 3. As described above, when the polarization filter 20 is fixed and integrated with the pinhole plate 3 or the polarization beam splitter 4, the number of parts of the interferometer device is substantially reduced by that amount, and the alignment work at the time of assembly becomes easy. Moreover, it is possible to prevent dust and the like from adhering to the joint surface of the polarization filter 20.

Further, FIG. 5 shows a polarizing element using a polarization diffraction grating 21 in place of the polarization filter 20. The polarization diffraction grating 21 is configured to diffract the return light on the incident optical path E in a direction other than the direction of the pinhole plate 3. Therefore, most of the return light reflected by the polarization reflection surface 4a of the polarization beam splitter 4 is diffracted by the polarization diffraction grating 21 to be diverged to the outside of the system, and the light slightly transmitted is also the polarization diffraction grating. The light is attenuated when passing through 21, and it is possible to prevent the generation of the secondary light source due to the return light, as in the first embodiment described above.

Further, FIGS. 6 and 7 show a laser light source 1
The prism type second polarization beam splitter 22 is used as a polarization element in the same manner as the main polarization beam splitter 4 that reflects the light from the reference standard 7 and the reflected light from the reference surface 7a of the reference standard 7 and the subject 8. The configuration is shown in. The reflection surface 22a of the second polarization beam splitter 22 is, for example, 45 ° with respect to the incident optical path E.
By inclining, the light reflected on the reflecting surface 22a can be diverged in a direction other than the incident optical path E.

By adopting such a structure, the return light reflected by the polarization reflection surface 4a of the main polarization beam splitter 4 can be diverged in the direction orthogonal to the incident optical path E. Further, as shown in FIG. 8, the second polarization beam splitter 22 may be bonded and fixed to the polarization beam splitter 4, and further, as shown in FIG.
It is also possible to use an integrated polarization beam splitter 23 in which both polarization beam splitters are integrally formed. As described above, by using the same prism type beam splitter as the main polarization beam splitter 4 as the polarizing element and only changing the direction of the reflecting surface, it is possible to reduce the number of parts constituting the device. Moreover, by joining the two polarization beam splitters 4 and 22 or by using the integrated polarization beam splitter 23, the surface to be coated with the antireflection coating can be reduced and its processing becomes easy.

Further, as shown in FIG. 10, a flat plate-shaped polarization beam splitter 24 is used instead of the prism type polarization beam splitter 22, and the flat plate-shaped polarization beam splitter 24 is arranged so as to be inclined at a predetermined angle. However, the same effect can be obtained. Further, if a transparent optical member having the same optical path length as that of the polarizing element and having antireflection treatment on both surfaces is arranged at an angle of about 45 ° in the opposite direction to the polarizing element, the optical element generated by the polarizing element arrangement will be generated. Astigmatism can be canceled.

[0019]

As described above, according to the present invention, by providing the polarizing element between the pinhole member and the polarization beam splitter, the light is reflected by the polarization beam splitter and is incident on the subject from the reference prototype. In an interferometer device of the type that shares the optical path of the light with the optical path of the reflected light from the reference surface of the reference prototype and the subject, some alignment may occur due to the assembly error of the polarization beam splitter 1/4 wavelength plate, collimator lens, etc. Error, the birefringence of the condenser lens, the reflected light toward the polarization beam splitter is not parallel light, etc., the light is reflected by the polarization beam splitter and returns to the pinhole member side. Also, by reliably absorbing and attenuating this return light or by diverging it to other than the optical path, it is possible to reliably prevent it from becoming a secondary light source, and to prevent interference. It is possible to improve the quality of the interference fringes are imaged on the imaging means.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an interferometer device according to a conventional technique.

FIG. 2 is a schematic configuration diagram of an interferometer device showing a first embodiment of the present invention.

FIG. 3 is a configuration diagram of a main part of an interferometer device showing a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a main part of an interferometer device showing a third embodiment of the present invention.

FIG. 5 is a configuration diagram of a main part of an interferometer device showing a fourth embodiment of the present invention.

FIG. 6 is a layout explanatory diagram of two polarization beam splitters of the interferometer apparatus of FIG.

FIG. 7 is a main part configuration diagram of an interferometer device showing a fifth embodiment of the present invention.

FIG. 8 is a main part configuration diagram of an interferometer device showing a sixth embodiment of the present invention.

FIG. 9 is a configuration diagram of main parts of an interferometer device showing a seventh embodiment of the present invention.

FIG. 10 is a main part configuration diagram of an interferometer apparatus showing an eighth embodiment of the present invention.

[Description of symbols] 1 laser light source 2 condenser lens 3 pinhole plate 4 polarization beam splitter 4a polarization reflection surface 5 1/4 wavelength plate 6 collimator lens 7 reference prototype 7b reference surface 8 subject 11 imaging surface 20 polarization filter 21 Polarization Diffraction Grating 22 Second Polarization Beam Splitter 22a Reflective Surface 23 Integrated Polarization Beam Splitter 24 Flat Plate Polarization Beam Splitter

Claims (6)

[Claims] 1. A linearly polarized laser light emitted from a laser light source is reflected by a polarization reflection surface of a polarization beam splitter through a pinhole member, converted into circularly polarized light by a ¼ wavelength plate, and applied to a reference prototype. A part of the reference surface of the reference prototype is reflected, and the light transmitted through the reference prototype is reflected on the test surface of the subject, and the reflected light from the reference surface and the test surface is reflected by the 1 Again linearly polarized by the / 4 wavelength plate and transmitted through the polarization beam splitter,
In the case where an image is formed on the interference fringe image forming means,
Between the pinhole member and the polarization beam splitter,
Interference characterized by interposing a polarizing element for transmitting primary incident light from the laser light source side but not returning light from the optical system to the pinhole member side. Measuring device. 2. The interferometer apparatus according to claim 1, wherein the polarization element is a polarization filter, a polarization diffraction grating, or a second polarization beam splitter. 3. The second polarization beam splitter is a prism type polarization beam splitter or a flat plate type polarization beam splitter, and its reflection surface is in a direction orthogonal to an optical path between the pinhole and the polarization beam splitter. The interferometer device according to claim 2, wherein the interferometer device is arranged in a direction other than the above. 4. The interferometer apparatus according to claim 3, wherein the polarization element is fixed to the polarization beam splitter or the pinhole member. 5. The interferometer device according to claim 3, wherein the second polarization beam splitter is configured as a prism type polarization beam splitter integrated with a main polarization beam splitter. 6. An optical member, which is transparent and has an anti-reflection treatment on both sides and has the same optical path length as that of the polarizing element, is arranged at an angle of about 45 ° in the opposite direction to the polarizing element. The interferometer device described.