JP2990913B2 - Interferometer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art An interferometer apparatus forms an interference fringe by using light reflected from a reference surface of a reference prototype and light reflected from a test surface of a test object, thereby obtaining the state of the surface of the test object,
For example, it inspects the surface finish accuracy of a lens and the like, and various types of interferometer devices have been developed and put into practical use. Among them, for example, a Fizeau-type interferometer device uses a polarizing beam splitter, and sequentially arranges a reference prototype and an object on an optical axis of light reflected by a polarization reflecting surface of the polarizing beam splitter, and transmits the reference beam from a laser light source. The emitted laser beam is reflected by the polarizing beam splitter, and the reflected light is reflected by the reference surface and the test surface of the reference prototype, transmitted through the polarizing beam splitter, and the interference fringes are formed on the interference fringe imaging means. An image is formed, the apparatus configuration is simple, the apparatus can be formed small and compact, and the use of a polarizing beam splitter has advantages such as a reduction in light amount loss. Therefore, it is widely used as an apparatus for inspecting the surface state of various types of subjects.

[0003] An interferometer of this type has a configuration schematically shown in FIG. That is, 1 indicates a laser light source,
A laser beam emitted from the laser light source 1 is condensed by a condenser lens 2 and passes through a pinhole 3 a of a pinhole plate 3 disposed at a focal point of the condenser lens 2, so that a high-speed laser beam is emitted. It becomes divergent light excluding folded light and diffraction scattered light due to dust in the optical system. Here, if there is birefringence by the condenser lens 2 described above, this causes the linearly polarized light to be split into two linearly polarized light components. The transmitted light of the pinhole 3a reflects one of the two linearly polarized light components (for example, the S-polarized light component) on the polarization reflection surface 4a of the prism-type polarizing beam splitter 4, and the other polarized light component (for example, the polarized light component). (P-polarized light component) is transmitted and radiated out of the optical system. The polarization reflection surface 4a of the polarization beam splitter 4 has an angle of 45 ° with respect to its incident optical path. Therefore, the light reflected by the polarization reflection surface 4a has its optical path bent by 90 ° to form a 波長 wavelength plate. 5 is circularly polarized,
Further, the collimator lens 6 irradiates the reference prototype 7 as parallel light. The reference prototype 7 is provided with an anti-reflection coating on its entrance surface 7a. On the other hand, the surface opposite to the incident surface 7a is a reference surface 7b finished to a precise surface, and light incident on the reference prototype 7 is reflected on the reference surface 7b.
The light partially reflected by and transmitted through the reference prototype 7 is
A subject 8 such as an optical lens disposed at a position in front of the optical path
And is reflected by the subject 8. Where 1 /
By setting the four-wavelength plate 5 in a slightly inclined state, unnecessary reflected light is emitted out of the optical system.

The reflected light from the subject 8 and the reflected light from the reference surface 7b of the reference prototype 7 are converged by passing through the collimator lens 6, pass through the quarter-wave plate 5, and enter the incident light. Polarized in the 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 point f of the collimator lens 6, and further passes through the imaging lens 10 to solid-state imaging. Image plane 11 composed of devices and the like
An image is formed thereon, and interference fringes can be observed due to the interference between the reflected light from the subject 8 and the reflected light from the reference surface 7b.

[0005]

As described above, the incident optical path E of the laser beam from the laser light source 1 to the subject 8 is
Of the reflected light path R from the object 8 to the imaging plane 11, the light path from the polarization reflection surface 4a of the polarization beam splitter 4 to the object 8 is defined as an incident / reflection light path E + R where the incident light path and the reflection light path are common. Has become. Therefore, there is an excellent advantage that the whole configuration of the interferometer device can be formed small and compact. However, when the incident light path and the reflected light path are shared as described above, the reflected light does not completely pass through the polarization reflection surface 4a of the polarization beam splitter 4, but is reflected by the polarization reflection surface 4a and returns to the incident light path side. As a result,
There is a disadvantage that the return 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 relation of the respective members constituting the optical system, in particular, the polarization beam splitter 4, quarter-wave plate 5, collimator lens 6, and the like. If these members are not correctly aligned, the reflected light does not completely pass through the polarization reflection surface 4a of the polarization beam splitter 4, and a part of the light is reflected by the polarization reflection surface 4a to the pinhole plate 3. . Further, splitting into two mutually orthogonal linearly polarized light components due to the influence of birefringence or the like due to the internal distortion of the condenser lens 2 also causes the generation of return light. Therefore, it is necessary to position the members very strictly and to use an excellent condenser lens 2 having no birefringence. As a result, there are problems in that assembling of the device becomes extremely troublesome and difficult, and it becomes expensive.

In addition, the above-described members are strictly arranged,
Also, just because a high-quality condenser lens is used, it is not always possible to completely prevent light returning to the pinhole plate 3. That is, a collimator lens 6 is interposed between the quarter-wave plate 5 and the reference prototype 7, and this collimator lens 6 not only functions to convert incident light into parallel light, but also 7 also serves to focus the reflected light from the reference surface 7b and the subject 8 at the position of the low-pass filter 9, so that when the reflected light is incident on the polarizing 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 thereof 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 increased, and the optical path length becomes extremely long, so that the device configuration can be reduced in size and size. Will be gone.

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

[0009]

In order to achieve the above-mentioned object, according to the present invention, primary incident light from a laser light source side is transmitted between a pinhole member and a polarizing beam splitter. This is characterized in that a polarizing element for intercepting return light from the optical system to the side is not provided.

[0010]

With this configuration, the reflected light from the reference surface of the reference prototype and the subject does not completely pass through the reflecting surface of the polarizing 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 from the pinhole member does not become a secondary light source that is incident on the reference prototype, and no noise is generated for the interference fringes formed on the interference fringe imaging means, so that extremely good image quality is obtained. Is obtained, and the accuracy of the inspection and measurement of the surface state 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 apparatus 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 denoted by the same reference numerals, and description thereof will be omitted.

The basic configuration of the interferometer shown in FIG. 2 is not significantly different from that of the prior art. However, a polarizing filter 20 as a polarizing element is interposed between the pinhole plate 3 and the polarizing beam splitter 4. The polarization filter 20 has a function of reflecting light reflected from the reference surface 7b of the reference prototype 7 and the subject 8 on the polarization reflection surface 4a of the polarization beam splitter 4, and absorbing light returning to the pinhole plate 3 side. Things. The polarization filter 20 transmits the incident light from the laser light source 1, and therefore, out of the incident light, the polarization reflection surface 4 of the polarization beam splitter 4.
The light component reflected at a is transmitted without being attenuated.

By adopting the above configuration, 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 transmitted slightly is also returned to the polarization filter. By passing through 20, the light is almost completely absorbed and attenuated and does not become 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 prototype 7 and the reflection light from the subject 8, The interference fringes formed on the image plane 11 are of high quality without noise. In general, in forming interference fringes, it is preferable that the reflectance from the reference surface 7a of the reference prototype 7 be substantially equal to the reflectance from the subject 8, and if necessary, the reference Although the reflectivity from the surface 7a may be increased or decreased, as described above, the reflectivity from the reference surface 7a can be arbitrarily set in order to reliably suppress the generation of the secondary light source due to the return light. , And higher quality interference fringes can be formed, and the inspection and measurement of the surface state of the subject 8 can be performed with extremely high accuracy.

The above-described polarizing filter 20 may be provided at a position between the pinhole plate 3 and the polarizing beam splitter 4, and is bonded and fixed to the polarizing beam splitter 4 as shown in FIG. Or as shown in FIG.
It may be bonded and fixed to the pinhole plate 3. As described above, when the polarizing filter 20 is fixedly integrated with the pinhole plate 3 or the polarizing beam splitter 4, the number of parts of the interferometer device is substantially reduced by that much, and the alignment work at the time of assembly is facilitated. In addition, it is possible to prevent dust and the like from adhering to the bonding surface of the polarizing filter 20.

FIG. 5 shows a polarization element using a polarization diffraction grating 21 instead of the polarization filter 20 as a polarization element. The polarization diffraction grating 21 is configured to diffract the return light in the incident light 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 and diverged out of the system. Since the light is attenuated when the light passes through the light source 21, it is possible to prevent the generation of the secondary light source due to the return light as in the first embodiment.

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

By employing such a configuration, the return light reflected by the polarization reflection surface 4a of the main polarization beam splitter 4 can be diverged in a 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.
An integrated polarization beam splitter 23 in which both polarization beam splitters are integrally formed may be used. As described above, by using the same prism type beam splitter as the main polarizing beam splitter 4 as the polarizing element and changing the direction of the reflection surface only, it is possible to reduce the types of components constituting the device. In addition, by joining the two polarizing beam splitters 4 and 22, or by using the integrated polarizing beam splitter 23, the number of surfaces on which the antireflection coating is to be applied can be reduced, and the processing can be facilitated.

Further, as shown in FIG. 10, a plate-shaped polarizing beam splitter 24 is used in place of the prism type polarizing beam splitter 22, and the plate-shaped polarizing beam splitter 24 is disposed so as to be inclined at a predetermined angle. The same effect can be obtained. In addition, if an optical member having the same optical path length as the polarizing element and having been subjected to antireflection treatment on both surfaces is disposed at an angle of approximately 45 ° in the opposite direction to the polarizing element, optical generated by the polarizing element arrangement can be obtained. Astigmatism can be canceled.

[0019]

As described above, according to the present invention, by providing a polarizing element between the pinhole member and the polarizing beam splitter, the light is reflected by the polarizing 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 light with the optical path of the reflected light from the object and the reference surface of the reference prototype, the alignment is slightly adjusted due to the assembly error of the polarizing beam splitter quarter-wave plate, collimator lens, etc. Error, the birefringence of the condensing lens, and the reflected light toward the polarizing beam splitter is not parallel light, it is reflected by the polarizing beam splitter, and the return light to the pinhole member side occurs. Also, by reliably absorbing and attenuating this return light or diverging it outside the optical path, it can be reliably prevented from becoming a secondary light source, and It is possible to improve the quality of the interference fringes are imaged on the imaging means.

[Brief description of the drawings]

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

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

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

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

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

FIG. 6 is an explanatory diagram of an arrangement of two polarization beam splitters of the interferometer apparatus of FIG. 5;

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

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

FIG. 9 is a main part configuration diagram of an interferometer apparatus 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.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Condensing 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 polarizing beam splitter 22a Reflecting surface 23 Integrated polarizing beam splitter 24 Plate-shaped polarizing beam splitter

Claims (6)

(57) [Claims] 1. A linearly polarized laser beam emitted from a laser light source is reflected by a polarization reflecting surface of a polarizing beam splitter through a pinhole member, converted into circularly polarized light by a quarter wavelength plate, and irradiated to a reference prototype. The light reflected from the reference surface of the subject is reflected by a part of the reference surface of the reference prototype, and the light transmitted through the reference prototype is reflected by the surface to be inspected of the subject. Again linearly polarized by a 波長 wavelength plate and transmitted through the polarizing beam splitter,
In what is made to form an image on interference fringe imaging means,
Between the pinhole member and the polarizing beam splitter,
Interference characterized by interposing a polarizing element for transmitting the primary incident light from the laser light source side but not passing the return light from the optical system to the pinhole member side Instrument. 2. The interferometer device according to claim 1, wherein the polarizing element is a polarizing filter, a polarizing diffraction grating, or a second polarizing beam splitter. 3. The polarization beam splitter according to claim 1, wherein the second polarization beam splitter is a prism type polarization beam splitter or a flat plate type polarization beam splitter, and a reflection surface of the second polarization beam splitter is orthogonal to an optical path between the pinhole and the polarization beam splitter. 3. The interferometer device according to claim 2, wherein the interferometer device is disposed in a direction other than the directions. 4. The interferometer apparatus according to claim 3, wherein said polarizing element is fixed to said polarizing beam splitter or a pinhole member. 5. The interferometer apparatus according to claim 3, wherein said second polarization beam splitter is configured as a prism type polarization beam splitter integrated with a main polarization beam splitter. 6. An optical member having the same optical path length as the polarizing element and having a transparent surface and having antireflection treatment applied to both surfaces thereof is disposed at an angle of approximately 45 ° in a direction opposite to the polarizing element. The interferometer device as described.