JPS63298107A - Slant incident interferometer device - Google Patents

Abstract

PURPOSE:To measure the irregularities of a surface to be checked accurately with interference fringes, by providing image forming lenses on a light path between a second diffraction grating and a hologram screen, and providing the image forming relation of a equal multiplication. CONSTITUTION:Laser light from a laser oscillator 1 is inputted into a first diffraction grating 4 through a diverging lens 2 and collimator lenses 3. A body under test is mounted on a mounting stage 5 and the flatness of the surface to be checked is checked. The light, which is inputted on the surface to be checked of the body under test and reflected, is made to interfere in a second diffraction grating 6. The luminous flux through the second diffraction grating 6 undergoes equimultiple image forming action through a lens system comprising image forming lenses 20 and 22. The diffracted light from the peripheral part of the surface to be checked is condensed at a point corresponding to a hologram screen 7. Therefore, the roundness at the peripheral part of the interference fringes is eliminated. Mutually parallel interference fringes are formed. Even if diffraction occurs at the peripheral part of the surface to be checked, the effect is not received, and the flatness of the surface is accurately checked.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is an improvement of a grazing incidence interferometer device capable of inspecting the flatness of an object by using interference fringes formed by interference of light. It is related to.

(Prior Art) In recent years, a grazing incidence interferometer device has been developed as an interferometer device that can accurately measure the surface of an object to be examined even if the surface has a large unevenness difference. Figure 3 ta'l and (b)
1 shows an incident oblique interferometer device proposed by the applicant for the patent on January 31, 1986.

In this grazing incidence interferometer device, the laser beam with a wavelength of 632.8 nm emitted from the He-Ne laser oscillator 1 is
The optical path is bent by the prism emitting mirror 9 and the diverging lens 2
incident on . This laser beam is expanded by a diverging lens 2, bent by a mirror 11, and then enters a collimator lens 3. The laser beam that has been made into a parallel beam by the collimator lens 3 is divided into +1st-order parallel light α, which is diffracted in the +1st-order direction by the first diffraction grating 4, and O-order parallel light β, which is transmitted straight without being diffracted. divided into This +1st order light α
is incident on the test surface of the subject T placed on the mounting table 5 , is reflected, and enters the second diffraction grating 6 . As shown in FIG. 5, the second diffraction grating 6 converts the 0th-order light β into 0th-order light A, which is transmitted straight without being diffracted, and 11th-order M light β′, which is diffracted in the direction of the 1st-order light. At the same time, the light α reflected by the test surface of the subject T is transmitted to become transmitted light α′. This transmitted light creates interference fringes. This interference fringe is the hologram screen 7
This allows for a frontal view from viewpoint E.

Note that the adjustment hologram 8 focuses diffracted light that is reflected by the surface to be inspected and diffracted by the second diffraction grating 6 onto the screen 12 . In order to be able to observe the interference fringes, the observer adjusts the height and inclination of the surface to be measured by adjusting the mounting table 5, and aligns the focal point of the reference surface on the screen 12 with that of the surface to be measured. This makes it possible to match the light points.

(Problems to be Solved by the Invention) By the way, in the interferometer device, the first diffraction grating 4
When the +1st-order diffracted light α of the parallel light diffracted by the +1st-order diffracted light spreads beyond the surface to be examined of the object T and enters the same, a diffraction phenomenon occurs at the peripheral edge T1 regardless of the shape of the surface to be examined. When this diffraction phenomenon occurs, the wavefront of the light reflected from the periphery of the test surface no longer has a perfect plane wave shape, but instead has a wavefront shape with rounded edges.

- For example, when the object T is circular and has an inclination, the transmitted light α' that is reflected from the object surface and transmitted without being diffracted by the second diffraction grating 6 is diffracted by the second diffraction grating 6. First plowing 4
The interference fringes caused by the ffl light β' do not become mutually parallel interference fringes as shown in Fig. 6 (al), but due to the influence of the diffracted light at the peripheral edge T of the test surface, as shown in Fig. 6 (bl). This results in rounded interference fringes at the periphery.Therefore, there is a risk that the periphery TI of the surface to be inspected may be mistakenly recognized as if surface sagging exists.

Therefore, in view of the above circumstances, the present invention provides a grazing incidence interferometer device that can correctly inspect a surface to be measured without adding a diffraction effect to the interference fringes even if a diffraction phenomenon occurs at the periphery of the surface to be measured. The purpose is to provide

(Means for Solving the Problems) The grazing incidence interferometer device of the present invention includes an emitting means for emitting coherent light, an optical means for diverging the light beam emitted from the emitting means, and an optical means for emitting coherent light. a first diffraction grating that divides the light beam after passing through the parallel light beam forming means into a diffracted light ray α that diffracts in a specific direction and a transmitted light ray β that passes straight through; , a mounting means for placing and displacing and moving an object to be inspected, and a light ray α diffracted by the first diffraction grating and reflected by the test surface of the object as a transmitted light ray α'; a second diffraction grating that diffracts the transmitted light beam β in a specific direction to form a diffracted light beam β′ and interferes with both the light beams α′ and β′; An imaging lens system that images a subject at the same magnification, and a hologram screen on which interference fringes transmitted through the imaging lens system are projected and an image of the subject is formed by the imaging lens system. It is something.

(Function) In the grazing incidence interferometer device of the present invention, the test surface of the test object is
An image at the same magnification is formed on the hologram screen by an imaging lens system provided in the optical path between the second diffraction grating and the hologram screen. Therefore, the diffracted light generated at the peripheral edge of the surface to be inspected is focused on the corresponding imaging point on the hologram screen, and the interference fringes on the hologram screen are no longer affected by the diffracted light.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings. In FIGS. 1(a) and (ill), 1 emits coherent light such as a laser beam. Laser oscillator, 2 is a diverging lens, 3 is a collimator lens, 4 is a first diffraction grating, 5 is a mounting table, 6
is a second diffraction grating, 20.22 is an imaging lens, 7 is a hologram screen (also called a hologram lens), 9 is a reflection prism, IO is a pinhole, 11 is a reflection mirror, 3
0 indicates an imaging lens, and 40 indicates a television camera.

The laser oscillator 1 uses helium neon (He-Ne) with an output of 15 mW, which is a red coherent light beam with a wavelength of 632.8 nm.
) emits laser light. This laser light is linearly polarized light. The diverging lens 2 is a lens that diverges the laser beam emitted from the laser oscillator 1, and may be composed of a plurality of lenses.

The collimator lens 3 converts a diverging laser beam that passes through a pinhole 10 for removing harmful light and is reflected by a reflection mirror 11 into a parallel light beam, and is composed of a plurality of lenses.

The first diffraction grating 4 splits the laser beam, which has been made into a parallel beam by the collimator lens 3, into the first-order light α, which is diffracted in the +1st-order light direction, and the O-order light β, which is transmitted straight without being diffracted. It is. This first diffraction grating 4 is constructed by mechanically carving a plane to form a large number of fine grooves, but for example, the grating can be formed by recording interference fringes on an emulsion or a photosensitive resin. Holographic gratings may also be used.

The mounting table 5 is a table on which the subject is placed. This mounting table 5
As shown in FIG. 4, there is a jack mechanism 5a, a base 5b that is mounted on the jack mechanism 5a and moves in the vertical direction (Z direction) by the jack mechanism, and is supported on the base 5b by three screws 5c. and a circular table 5d for adjusting the inclination of a plane perpendicular to the Z direction (XY plane) by operating these screws 5c. This circular table 5
A subject T is placed on the test surface d, and the flatness of the surface of the subject T is inspected.

The second diffraction grating 6 is formed similarly to the first diffraction grating 4. As shown in FIG. 5, this second diffraction grating 6 diffracts the +1st order light α which is diffracted by the first diffraction grating 4 in the +1st order direction and reflected after being incident on the test surface of the subject T. The 11th-order light α' that passed straight through without being diffracted by the first diffraction grating 4, and the 11-order light that diffracted the 0th-order light β that passed straight through the first diffraction grating 4 in the 11th-order direction.
This is to superimpose and interfere with the secondary light β'.

The imaging lens 20 is a lens having a positive focal length f. This imaging lens 20 is provided at a distance f from the center point O of the surface to be examined of the object 5, and the second diffraction grating 6
This is to condense the collimated light beam in the interference state emitted from the point to point p.

The imaging lens 22, like the imaging lens 20, is a lens having a positive focal length f. The imaging lens 22 is provided at a distance f from the focal point p, and returns the light beam focused by the imaging lens 20 into a parallel light beam. Therefore, the imaging lenses 20 and 22 are arranged symmetrically with the focal point p as the center, and both lenses have the same lens.
It is installed diagonally corresponding to the surface to be inspected, and a lens system consisting of imaging lenses 20 and 22 allows it to be viewed at the same magnification as the surface to be inspected.
-1 times).

On the other hand, interference fringes due to the unevenness of the surface to be inspected are projected onto the hologram screen 7 . Here, as an example, the shape of interference fringes when a circular object is tilted to its XY plane will be described.

Since the light beam passing through the second diffraction grating 6 is a parallel light beam, its wavefront looks like a plane wave when viewed from the direction of the imaging lens 20. However, in reality, it becomes a light-tinged quasi-plane wave. When this pseudo-plane wave interferes with the one-dimensional plane wave β', an image is formed at the same magnification in the form of interference fringes, so that the peripheral edge T of the surface to be inspected.

Since the diffracted light from the hologram screen 7 is focused on the corresponding point T1' of the hologram screen 7, the roundness of the peripheral edge of the interference fringes disappears and the interference fringes become parallel to each other.

The photographing lens 30 forms an image of the interference fringes on the hologram screen 7 on the imaging surface of an imaging tube built into the television camera 40. The interference fringes can also be observed by placing the observer's eyes at the position of the photographing lens 30.

Next, another embodiment of the grazing incidence interferometer device according to the present invention will be described.

FIG. 2 shows a side view of the main parts of a grazing incidence interferometer device according to another embodiment of the present invention, from the first diffraction grating 4 to the television camera 40, and shows the configuration from the laser oscillator 1 to the collimator lens 3. It is the same as FIG. 1(a) and (bl).

In FIG. 2, the same symbols and numbers have the same functions as those in FIGS. 1(a) and (b).

24 is a polarizing beam splitter, 26 is a quarter wavelength plate, 2
8 indicates a rear mirror. In FIG. 2, the not-illustrated structure from the laser oscillator 1 to the collimator lens 3 and the structure from the first diffraction grating 4 to the second diffraction grating 6 are the same as those described above, and therefore their explanations will be omitted.

The polarizing beam splitter 24 is provided at an angle of 45 degrees with respect to the 1st-order light α' emitted from the second diffraction grating 6, and transmits the linearly polarized light beam from the second diffraction grating 6.

The imaging lens 20 has a focal length f, is provided at a distance f from the center 0 of the surface to be examined of the object, and focuses the parallel light beam from the polarizing beam splitter 24 on a point p separated by a distance f. .

The 1/4 wavelength plate 26 is provided in the condensed light beam of the imaging lens 20, and circularly polarizes the light beam from the imaging lens 20.

The back mirror 28 has a reflective surface 28b, and the reflective surface 28b
is provided so as to coincide with the focal point p. This back mirror 28 reflects the light beam circularly polarized by the quarter-wave plate 26 on a reflecting surface 28b and returns it to the original optical path. The light beam reflected by the back mirror 28 is polarized into linearly polarized light orthogonal to the light beam by the quarter-wave plate 26, and then becomes a parallel light beam from the imaging lens 20 again. The parallel light beam emitted from the imaging lens 20 is reflected by the polarizing beam splinter 24 and reaches the hologram screen 7 with its optical path bent. The center 0' of the hologram screen 7 is located at a distance f from the imaging lens 20, and is inclined at an angle θ with respect to the light beam in correspondence with the surface to be inspected. In other words, the surface to be inspected and the hologram screen 7 have an image formation relationship of equal magnification (-1 times).

On this hologram screen 7, interference fringes are formed based on the image of the surface to be inspected and the irregularities of the surface to be inspected.

Since the hologram screen 7 bends the light beam, the photographing lens 30 forms an image on the imaging surface of the television camera 40 . In this embodiment, since the polarizing beam splitter 24 and the back reflecting mirror 28 are used, it is sufficient to provide only one imaging lens 20, which is inexpensive and allows the overall length to be shortened.

(Effects) As explained above, the grazing-incidence interferometer device according to the present invention provides an imaging lens in the optical path between the second diffraction grating and the hologram screen to provide a same-magnification imaging relationship. Therefore, the interference fringes formed on the hologram screen can accurately measure the uneven state of the test surface without being affected by diffraction.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(a) are a plan view and a side view, respectively, showing an embodiment of a grazing incidence interferometer device according to the present invention. FIG. 2 is a side view of main parts of another embodiment of the grazing incidence interferometer device according to the present invention. FIGS. 3 fal and (bl are a plan view and a side view, respectively, of a conventional grazing incidence interferometer device. FIG. 4 is a diagram showing a mounting table of the grazing incidence interferometer device according to the present invention. Fig. 5 is a diagram explaining the action of the second diffraction grating of the grazing incidence interferometer device according to the present invention. Fig. 6 fal and (b) respectively show interference fringes based on the grazing incidence interferometer device according to the present invention. 1 is a diagram showing interference fringes based on a conventional oblique incidence interferometer device. 1--Laser oscillator, 3--Collimator lens, 4--First diffraction Lattice, 5---
-----Placement table, 6------Second diffraction grating, 7-------Hologram screen, 20.22.
----m-imaging lens.

Claims (1)

[Claims] 1. An emitting means for emitting coherent light, an optical means for diverging the light emitted from the emitting means, a parallel light beam forming means for forming a light beam after passing through the optical means into a parallel light beam, and a parallel light beam forming means for forming a parallel light beam after passing through the optical means. A first diffraction grating that divides the light flux after passing through the light flux forming means into a diffracted light ray α that diffracts in a specific direction and a transmitted light ray β that passes straight through;
The light ray α diffracted by the moving mounting means and the first diffraction grating and reflected by the test surface of the object is defined as a transmitted light ray α′, and the transmitted light ray β is diffracted in a specific direction to perform diffraction. a second diffraction grating that causes the two light beams α' and β' to interfere with each other as a light beam β'; and an imaging lens that refracts and transmits the light beam from the second diffraction grating and forms an image of the subject at the same magnification. A grazing incidence interferometer apparatus comprising: a hologram screen on which interference fringes transmitted through the imaging lens system are projected and on which an image of a subject is formed by the imaging lens system.