JP2574175B2 - Flatness measurement device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flatness measuring device that measures the flatness of a test object using interference fringes.

[Description of the Related Art] As one of related arts related to the present invention, there is a flatness measuring apparatus described in Japanese Patent Application Laid-Open No. 63-122909 previously proposed by the present applicant. This involves irradiating a single coherent light beam to the measuring section where the object to be measured is placed with the surface to be measured facing the reference surface of the standard prototype, and the measurement of the reference surface of the standard prototype and the An interference fringe corresponding to an optical path difference between the target and the surface is generated to measure the flatness of the target surface of the test object.

[Problems to be Solved by the Invention] In such an apparatus, it is desired to generate only an interference fringe corresponding to an optical path difference, that is, a gap between the reference surface of the reference prototype and the measurement surface of the test object. . If the thickness of the test object is extremely large with respect to the gap between the reference surface of the reference prototype and the measurement surface of the test object, the coherence distance using a single light as in the related art is increased. Even in a long case, it is possible to generate only interference fringes corresponding to the gap between the reference surface of the reference prototype and the measured surface of the test object. On the other hand, when the test object is thin, the optical path difference between the measurement surface and the opposite surface of the test object, that is, the test Interference fringes due to the thickness of the object occur, and this overlaps with the interference fringe corresponding to the gap between the reference surface of the reference prototype and the measurement surface of the test object, making it impossible to determine the target interference fringe However, there is a problem that the measurement becomes difficult.

The present invention has been made based on the above-described viewpoint, and its object is to provide a reference prototype when the thickness of the test object is as thin as the gap between the gaps to be measured and is larger than the gap between the gaps. An object of the present invention is to provide a flatness measuring device capable of generating only interference fringes according to an optical path difference between a reference surface and a measurement surface of a test object.

[Means for Solving the Problems] In the present invention, coherent light is applied to a measuring unit in which a test object is placed with a surface to be measured facing a reference surface of a reference prototype, and In a flatness measuring apparatus for generating an interference fringe according to an optical path difference between a reference surface and a measurement surface of the test object to measure the flatness of the measurement surface, a plurality of laser beams having the same wavelength are used. The above object is attained by a flatness measuring apparatus comprising: a generating means for generating a laser beam;

Further, the irradiating means may include a rotary diffusion plate, and irradiate the superposed laser beams to the measurement unit as the coherent light via the rotary diffusion plate.

[Operation] The coherence length is shortened by superposing a plurality of laser beams, and even when the specimen is thin, the interference fringes due to the thickness of the specimen are not generated, and the reference surface of the reference prototype and the laser beam are not affected. Only interference fringes corresponding to the optical path difference between the object and the surface to be measured are generated.

Further, due to the roughness on the surface of the rotating diffuser and its condensing state, speckle patterns appearing as irregularities in the projected image of the interference fringes are made difficult to see visually, and noise in the projected image of the interference fringes is prevented. In combination with the superposition of a plurality of laser beams, the coherence distance that generates a projection image of only interference fringes corresponding to the optical path difference between the reference surface of the reference prototype and the measurement surface of the test object is determined. An adjusting action can be provided.

[Embodiment of the Invention] FIG. 1 is a configuration diagram showing an embodiment of the present invention.

In the figure, 1 and 2 are laser beams L ₁ and L ₂ having the same wavelength.
Is a collimator lens disposed in front of the laser light sources 1 and 2. In this example, the laser light sources 1 and 2 are, for example, semiconductor lasers having a large spread angle. The laser beams L ₁ and L ₂ of the respective laser light sources 1 and ₂ are
Are collimated, and are incident on the incident surface 4a of the reference prototype 4 at an angle θ with respect to the perpendicular to the incident surface 4a as the coherent light L. Reference prototype 4
A light-transmitting optical member such as a plane-parallel glass, and the incident surface 4a and the reference surface 4b are parallel to each other. Reference prototype 4
On the reference surface 4b side, a light-transmitting test object 5 such as glass is arranged. The test object 5 has the measured surface 5a facing the reference surface 4b of the reference prototype 4 and the reference surface 4b and the measured surface 5a of the reference prototype 4 due to the non-planarity of the measured surface 5a. In order not to disturb the gap 6 between the reference prototype 4 and the reference plane 4b of the reference prototype 4, or simply placed on the reference plane 4b of the reference prototype 4. They are arranged in a form. The space between the gaps 6 is smaller than the thickness of the test object 5, and the thickness of the test object 5 is smaller than the thickness of the reference prototype 4. As is well known, the coherent light L obtained by superimposing the laser beams L ₁ and L ₂ has a single effect due to an effect similar to the phenomenon that the TEM ₀₀ mode shifts to another mode and the coherence length due to multiple oscillations becomes shorter. coherence length compared with the laser light L ₁ or L ₂ has become shorter, thereby, not interference fringes were generated by an optical path difference due to the thickness and the thickness of the reference standard 4 of the test object 5, most Only interference fringes corresponding to the optical path difference due to the short gap 6 are generated. A screen 7 is arranged on a surface 5b of the object 5 opposite to the surface 5a to be measured, and the generated interference fringes are projected.

With the above configuration, when the laser light sources 1 and 2 are driven, the respective laser beams L ₁ and L ₂ become parallel beams superimposed via the collimator lens 3, and become the coherent light L of the reference prototype 4. Obliquely incident on the incident surface 4a at an angle θ and the obliquely incident coherent light L causes an optical path difference between the reference surface 4b of the reference prototype 4 and the measured surface 5a of the test object 5, that is, interference fringes due to the gap 6. Is generated and projected on the screen 7. In other words, it overlaps a light L _A that passes through the reference standard 4, the reference standard 4 and the reflected light of the light L _B toward the reference surface 4b is reflected by the measurement surface 5a of the street specimen 5 the gap 6, An interference fringe corresponding to the unevenness of the interval of the gap 6 is generated by the optical path difference between the two. Since the coherent light L has a shorter coherent distance due to the superposition of the laser beams L ₁ and L ₂ , the optical path due to the thickness of the test object 5 and the thickness of the reference prototype 4 larger than the gap of the gap 6. No interference fringes occur at the difference.

In the embodiment of FIG. 1, it is of course possible to use lasers having a small divergence angle as the laser light sources 1 and 2. In such a case, as shown in FIG.
After increasing the divergence angle of each laser beam through 8 and 9, it is made into parallel light superimposed via the collimator lens 3,
This may be applied as coherent light L.

FIG. 3 is a block diagram showing another embodiment of the present invention, in which the same reference numerals as in FIG. 1 denote the same components.

This is because the laser light L ₁ of the same wavelength from the laser light sources 1 and 2,
L ₂ is superimposed by a condenser lens 10 and condensed on a rotating diffusion plate 11, and the light beam passing through the rotating diffusion plate 11 is
Is converted into parallel light by a spherical mirror 13 through the optical axis, and this light is made to coherently enter the incident surface 4a of the reference prototype 4 at an angle θ with respect to a perpendicular to the incident surface 4a as coherent light L. The rotating diffusion plate 11 has a circular diffusion plate 11a and a motor 11b, and the diffusion plate 11a is driven to rotate by the motor 11b. Such a rotating diffusion plate 11 has a function of making a speckle pattern appearing as unevenness in a projected image of interference fringes difficult to visually recognize and shortening a coherent distance. That is, as the spot diameter of the light beam by the condenser lens 10 on the diffusion plate 11a is increased, the speckle pattern becomes less visible and the coherence distance is reduced.
The spot diameter on the diffusion plate 11a is such that the speckle pattern is difficult to see, and the reference surface 4b of the reference prototype 4 and the specimen 5
The converging lens 10 is set to move along the optical axis so that only interference fringes corresponding to the optical path difference with the surface 5a to be measured are generated. Other configurations are as described in FIG.

According to this example, the speckle pattern appearing as irregularities in the interference fringes projected on the screen 7 becomes difficult to see visually, preventing noise in the projected image of the interference fringes, and superimposing a plurality of laser beams. In conjunction with this, a projection image of only interference fringes corresponding to the optical path difference between the reference surface of the reference prototype and the measurement surface of the test object is given to the screen 7.

In the embodiment shown in FIG. 3, when lasers having a small divergence angle are used as the laser light sources 1 and 2, as shown in FIG. Alternatively, as described with reference to FIG. 2, the spread angle of each laser beam may be increased through a lens, and then the laser beams may be overlapped and condensed by the condensing lens 10.

In each of the embodiments described above, two laser light sources have been described as examples, but the present invention is not limited to this. If the number of laser light sources is further increased, the coherence length can be further shortened by the overlap of the laser beams, so that no interference fringes occur due to the optical path difference due to the thickness of the test object, and the reference surface of the reference prototype The number can be set according to the thickness of the test object so that only interference fringes due to the gap between the test object and the measurement surface of the test object are generated. In the above embodiment, the case where a plurality of laser light sources are used has been described. However, the laser light from a single laser light source may be converted into a plurality of laser lights by optical means, and these may be overlapped. In the above embodiment, the reference prototype having a parallel plane has been described as an example. However, it is needless to say that the invention can be applied to a prism prototype.

[Effects of the Invention] As described above, according to the present invention, a plurality of laser beams are superimposed and irradiated as coherent light, so that the coherent distance of the laser beam irradiated on the measurement surface is reduced, Even when the specimen is thin, only interference fringes corresponding to the optical path difference between the reference surface of the reference prototype and the measurement surface of the specimen are generated without generating interference fringes due to the thickness of the specimen. By using a rotating diffuser, noise in the projected image of interference fringes can be prevented, and in combination with the superposition of a plurality of laser beams, the reference surface of the reference prototype can be covered. It is possible to provide a flatness measuring apparatus that has an effect such as being able to obtain a projection image of only interference fringes according to an optical path difference between the inspection object and a measured surface.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing a main part of an example in which a laser light source having a small divergence angle is used, FIG. 3 is a block diagram showing another embodiment of the present invention, and FIG. 4 is a laser light source having a small divergence angle in FIG. FIG. 4 is a main part configuration diagram showing an example in the case of using. 1,2 ... Laser light source, 3 ... Collimator lens, 4 ...
Reference prototype, 4b Reference surface, 5 ... Test object, 5a ... Measurement surface, 8,9 ... Lens, 10 ... Condenser lens, 11 ... Rotating diffuser, 12 ... Plane mirror, 13 …… Spherical mirror

Claims (2)

(57) [Claims] A coherent light is applied to a measuring section in which a test object is placed with a surface to be measured opposed to a reference surface of a reference prototype, and a reference surface of the reference prototype and an object of the test object are irradiated. Generating means for generating a plurality of laser beams of the same wavelength in a flatness measuring device for generating an interference fringe according to an optical path difference between the laser beam and a measuring surface and measuring the flatness of the surface to be measured; A flatness measuring device comprising: an irradiation unit configured to irradiate the measuring unit with the light as the coherent light by superimposing light. 2. The plane according to claim 1, wherein said irradiating means includes a rotary diffuser, and irradiates each of said superposed laser beams to said measuring section as said coherent light via said rotary diffuser. Degree measuring device.