JPH0575246B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides an oblique interferometer device capable of inspecting the flatness of an object by using interference fringes formed by interference of light. It is related to.

[Conventional technology]

Conventionally, a Fizeau type interferometer, for example, has been known as an interferometer. That is, as shown in FIG. 10, the interference fringes caused by the light reflected from the surface of the transparent reference plate p1 and the light reflected from the surface of the object p2 are observed, and the object is determined when the reference plane of the reference plate is used as a reference. It is used as a means of measuring the surface shape of a specimen, and when a light beam of wavelength λ is used, one interference fringe is visible at every distance of λ/2 with respect to the unevenness difference Δh on the surface of the subject. It's summery.

However, this type of interferometer has a drawback that it cannot measure if the difference in unevenness of the object is too large because of its high measurement sensitivity.

Therefore, an oblique-incidence interferometer that can measure objects with large unevenness has been developed. That is, as shown in FIG. 11, a coherent laser beam emitted from a laser oscillator a is made into a parallel beam by a lens k, and this beam is diffracted by a first diffraction grating b. For example, +1 out of the diffracted light
The second-order light is reflected on the surface of the object c, and the reflected +1st-order light and the 0th-order light that has passed through the first diffraction grating b are superimposed by the second diffraction grating e. This causes interference to form interference fringes, and the shape of the surface to be examined of the object c is measured using the interference fringes.

In this grazing incidence interferometer, the 12th
As shown in the figure, the pitch of the first diffraction grating b is set to d,
When the diffraction angle θ and the wavelength of the laser beam used are λ, generally sinθ/λ=1/d...(a) holds true, and on the other hand, when the unevenness difference of the object c is h, the unevenness difference h The optical path difference Δl of the +1st order light generated by can be expressed as Δl=2hsinθ.

By the way, when one interference fringe is generated due to this optical path difference Δl, Δl=2hsinθ=λ holds, so the unevenness h in this case represents the sensitivity, and h=λ/2sinθ=d/ 2 (from formula ∵(a)).

Therefore, in this equation, for example, if the wavelength λ of the loser light is 632.8 nm and the diffraction angle θ of the +1st order light is 9.1 degrees (in this case, the pitch d of the first diffraction grating is 4μ).
m), the sensitivity is 2 μm.

[Problem to be solved]

By the way, as explained earlier, this type of interferometer has lower sensitivity than the Fizeau type interferometer, and therefore can measure large height differences on the surface to be measured. 1. The second diffraction grating must be manufactured with high precision.
For example, if these optical components have aberrations, eccentricity, etc., there is a risk that the test surface cannot be measured correctly.

Therefore, in view of the above-mentioned conventional circumstances, the present invention has been made,
It is an object of the present invention to provide an oblique interferometer device that can accurately measure a surface to be measured without requiring very high accuracy of a collimator lens and first and second diffraction gratings.

[Means for solving problems]

That is, the grazing incidence interferometer device of the present invention includes an outputting means for outputting coherent light, an optical means for diverging the light emitted from the outputting means, and a parallel beam of light after passing through the optical means. a first diffraction grating that divides the light that has passed through the parallel beam forming means into a diffracted beam that is diffracted in a specific direction and a transmitted beam that is transmitted straight; a mounting means for three-dimensionally displacing and moving the specimen; a diffracted light beam diffracted by the first diffraction grating and reflected on a reference surface of a reference body mounted on the mounting means; and the transmitted light beam. A second diffraction grating is formed by superimposing and interfering with each other, and the diffracted light beam diffracted by this second diffraction grating is diffracted by the first diffraction grating, and then reflected by the surface to be measured and passes through the second diffraction grating. It is equipped with a hologram lens that changes the direction in which interference fringes formed by interference with transmitted light rays are observed.

[Effect]

In the grazing incidence interferometer device of the present invention, a second diffraction grating is holographically formed using a first diffraction grating and a reference surface of a reference body, and a second diffraction grating formed on the holographic is used to receive a target. By measuring the specimen, the collimator lens and the first
Even if the precision of optical components such as a diffraction grating is somewhat low, the low precision can be compensated for by common bus interference, which is one of the characteristics of holography. Therefore, it is possible to accurately measure the flatness of the object, and the grazing incidence interferometer device of the present invention is equipped with a hologram lens so that the interference fringes can be read as an accurate image from directly above the optical axis. It is designed to ensure that the inspection surface of the subject can be observed and read.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

1a and 1b show a grazing incidence interferometer device according to the present invention, which includes a laser oscillator 1, a diverging lens 2, a collimator lens 3, and a first diffraction grating. 4 and the mounting table 5
, a second diffraction grating 6, a hologram lens 7,
It is equipped with an adjustment hologram lens 8. Note that reference numeral 9 in the figure is a reflecting prism that bends the optical path by 90 degrees. Reference numeral 10 denotes a pinhole, and the pinhole 10 removes harmful scattered light and the like generated by dust and the like attached to the diverging lens 3 and the like.
11 is a reflecting mirror that bends the optical path by 90 degrees. E is a viewpoint. The entire oblique incidence interferometer device composed of these optical components is placed on a vibration isolator (not shown) to prevent it from vibrating due to unnecessary external factors.

The laser oscillator 1 constitutes an emitting means for emitting coherent light, and in this embodiment, a helium neon (He-Ne) laser with an output of 15 mmW is used.
ne) A red light beam of 632.8 nm emitted from a laser is used as a light beam for measuring the object, which will be explained later.

The diverging lens 2 constitutes a diverging means for diverging the laser light emitted from the laser oscillator 1.

The collimator lens 3 is used as a parallel beam forming means for collimating the laser beam that has passed through the pinhole 10 and reflected by the reflection mirror 11, and is made by combining a plurality of various conventionally known lenses. It is structured as follows.

The first diffraction grating 4 is for diffracting the laser beam that has been made into a parallel beam by the collimator lens 3, and in this embodiment, the first diffraction grating 4 is mechanically engraved on a flat surface to form a large number of fine grooves. However, it is of course possible to use a so-called holographic grating formed by recording interference fringes on an emulsion or a photosensitive resin, which will be explained in detail later. In the oblique incidence interferometer device of this embodiment, the +1st order light α of the laser light diffracted by the first diffraction grating 4 is
and 0 which passes straight through without being diffracted by the first diffraction grating 4.
The secondary light β is used as a light beam for measuring the object.

The mounting table 5 is moved in the direction in which gravitational acceleration acts (hereinafter referred to as the Z direction) and
It is designed so that it can be rotated and moved in a direction perpendicular to the direction (hereinafter referred to as the XY direction), or in other words, it can be moved three-dimensionally. In this embodiment, as shown in FIG. 2, the mounting table 5 includes a jacking mechanism 5a, a base 5b that is mounted on the jacking mechanism 5a and moves in the Z direction by the jacking mechanism, and three screws 5c. is supported on the base 5b on the jacking mechanism 5a by operating the screws 5c.
It consists of a circular table 5d that rotates and moves in the XY direction, and the flatness of the surface of the subject T is inspected by placing the subject T on this circular table 5d. It's summery.

The second diffraction grating 6 is composed of a holographic grating, and due to the unique holographic properties of this holographic grating itself, the precision of the collimator lens 3 and the first diffraction grating 4 is manufactured to be somewhat low. Even if the object T is to be inspected, it is now possible to perform an accurate face reduction test.
Further, as shown in FIG. 3, this first diffraction grating 6 is decomposed by the first diffraction grating 4 to
The +1st-order light α reflected by the inspection surface and the 0th-order light β transmitted straight through without being diffracted by the first diffraction grating 4.
overlap and interfere. In other words, the 0th order light β is -1
It is diffracted in the next direction and converted into −1st-order light β′, and +
The first-order light α is passed through in the -first-order direction without being diffracted as it is to become the -first-order light α'.

Note that, as shown in FIG. 4, for example, the method for manufacturing the second diffraction grating 6 is based on the +1st-order light α diffracted by the first diffraction grating 4 and reflected by the reference plate S whose surface is mirror-finished, and its second order light α. A recording medium such as an emulsion dry plate is placed at a position where the zero-order light β passing through the first diffraction grating 4 intersects, and interference fringes are recorded on the recording medium by these light beams, and then the recording medium is developed. It is now being manufactured using

The hologram lens 7 is a transmission type hologram lens, and among the +1st-order light α and the 0th-order light β, each of the light rays α′, which are diffracted in the −1st-order direction after passing through the second diffraction grating 6 or are transmitted in a straight line, The interference image formed by the interference of β′ with a reduced shape in a specific direction is converted into an interference image observed from the front (hereinafter referred to as a front image), and in this embodiment,
It is possible to view from a viewpoint directly above the optical axis A, where the zero-order light travels without being diffracted, that is, from a point E.

Regarding the manufacturing method of this hologram lens 7, for example, as shown in FIG.
A parallel beam of light is made incident on the recording medium so as to be incident at the same angle as , and a ray from the same light source as the previous parallel beam is made to enter the recording medium from point E, which is the viewpoint. The recording medium is manufactured by recording interference fringes on the recording medium and then developing the recording medium. By the way, when manufacturing a hologram lens by the method shown in FIG. 5, unlike the method shown in FIG. 6, there is no need to use a lens L having a large outer diameter. When using the hologram lens manufactured in this manner, the light beams α' and β' after passing through the second diffraction grating 6 may be incident as reproduction light from the direction opposite to that during recording.

The adjustment hologram lens 8 adjusts the test surface of the test object T to be approximately flush with the reference surface of the reference object S when the test object T is placed on the mounting table 5 and its shape and dimensions are different from those of the reference object. This is for aligning and setting the top. The adjustment hologram lens 8 is manufactured in substantially the same manner as the hologram lens 7 described above. And this adjustment hologram lens 8
When adjusting the position of the surface to be inspected visually, first, as shown in the plan view of FIG. A diffusion screen 13 is installed. Next, the converging point P where the diffracted light (indicated by the dashed-dotted line) that was reflected by the test surface of the subject T and then diffracted by the second diffraction grating is focused by the adjustment hologram lens 8 is transferred to the first diffraction grating. The mounting table 5 is adjusted by the eye M so that the 0th order light (indicated by a solid line) transmitted through the grating and the second diffraction grating matches the focal point F focused by the adjustment hologram lens 8.

After the adjustment is completed, by placing the eye at the viewpoint E shown in FIG. 1b, the entire image of the interference fringes representing the contour lines of the surface to be examined of the subject T can be viewed from the front.

Furthermore, when measuring the surface shape of the object T using the grazing incidence interferometer device according to the present invention, since the adjustment hologram lens 8 focuses the zero-order light onto the screen 13, the mounting Place stand 5 to 3
By dimensional movement and adjustment, accurate positioning adjustment of the subject T can be performed quickly and reliably without relying on intuition.

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

A holographic grating is used as the first diffraction grating in this embodiment, and is configured to function as both a collimator lens and a first diffraction grating. Note that the first diffraction grating having such a function is manufactured as follows.

That is, as shown in FIG. 8, first, the collimator lens 15 is used to make the parallel laser beam γ incident perpendicularly onto the recording medium 14, and the collimator lens 16 is used to make the parallel laser beam γ incident on the recording medium 14 at a specific angle. θ, that is, the light having the same angle as the diffraction angle in the previous embodiment, is obliquely incident as a parallel beam δ, and a diverging beam ε is incident on the recording medium 14 at an arbitrary angle θ′ using the lens 17. let In other words, using light from the same light source,
They are simultaneously made incident on the recording medium 14 from both directions. The holographic grating 14' can be manufactured by developing the recording medium 14 on which interference fringes due to the interference of these lights have been recorded.

When using the holographic grating 14' manufactured in this way as a first diffraction grating,
The collimator lens 3 shown in FIG. 1 is not required, and when reading the inspection surface (not shown) of the subject T, only the previous divergent light beam ε is used as a reference light and is applied to the holographic grating 14' at the same angle θ'. It is better to make it obliquely incident.

Note that it is of course possible to form the first diffraction grating with a hologram without adding a function as a collimator lens. That is,
In this case, as shown in FIG. 9, using light from the same light source (however, the laser oscillator 1 is omitted), a laser beam ζ parallel to the surface of the recording medium 18 is made perpendicularly incident, and recording is performed. A holographic grating 18' is formed by making a parallel laser beam η forming a specific angle θ incident on the medium, and during reading, the holographic grating 18' is irradiated with the previous parallel beam ζ as reference light. .

〔effect〕

As explained above, according to the grazing incidence interferometer device according to the present invention, the second diffraction grating is constituted by a holographic grating, and the collimator lens and the first diffraction grating are manufactured with somewhat low precision. As a result, even if there is some aberration in the parallel plane wave, for example, by adjusting the test surface of the test object to approximately the same position as the reference surface of the reference object and placing it on the mounting table, Accurate flatness measurement can be performed on the object.

Further, according to the grazing incidence interferometer device according to the present invention, a hologram lens is provided that converts interference fringes that were conventionally observed from an oblique angle so that they can be observed from the front. This makes it possible to observe interference images and, in turn, provide a high-quality interferometer.

[Brief explanation of the drawing]

1A and 1B are respectively a plan view and a side view showing a grazing incidence interferometer device according to the present invention, FIG. 2 is a schematic perspective view showing a mounting means for the grazing incidence interferometer device according to the present invention, and FIG. FIG. 4 is an explanatory diagram illustrating the function of the second diffraction grating according to the present invention, FIG. 4 is an explanatory diagram showing the positional relationship of the recording medium when manufacturing the second diffraction grating, and FIGS. 5 a and b are diagrams illustrating the invention. FIG. 6 is an optical path diagram showing the light irradiation means during recording and reproduction of the hologram lens of the oblique incidence interferometer device according to the present invention, and FIG. 6 is an optical path diagram showing another method of manufacturing the hologram lens of the oblique incidence interferometer device according to the present invention. Fig. 7 is an explanatory diagram when adjusting the position of the object using the adjustment hologram lens of the oblique incidence interferometer device according to the present invention, and Fig. 8 is an illustration of another first diffraction grating according to the present invention. FIG. 9 is an optical path diagram showing the irradiation state of the light beam when manufacturing still another first diffraction grating according to the present invention, and FIG. FIG. 11 is a block diagram showing a conventional oblique-incidence interferometer, and FIG. 12 is an optical path diagram for determining a formula giving the sensitivity of the oblique-incidence interferometer device. 1... Laser oscillator (emission means), 2... Diverging lens (diverging means), 3... Collimator lens (parallel beam forming means), 4... First diffraction grating, 5...
...Placement table, 6...Second diffraction grating, 7...Hologram lens, 8...Adjustment hologram lens, α...
...Diffraction ray, β...Transmitted ray, T...Object, S
...Reference body.

Claims (1)

[Scope of Claims] 1. An output means for outputting coherent light; an optical means for diverging the light beam emitted from the output means; and a parallel light beam forming unit for forming the light beam after passing through the optical means into a parallel light beam. means, a first diffraction grating that divides the light after passing through the parallel beam forming means into a diffracted ray that is diffracted in a specific direction and a transmitted ray that is transmitted straight; a mounting means that is displaced and moved by the first diffraction grating, and the diffracted light beam diffracted by the first diffraction grating and reflected by the reference surface of the reference body placed on the mounting means and the transmitted light beam are superimposed. A second diffraction grating formed by interfering with each other; a transmitted light beam that has passed straight through the first diffraction grating is diffracted by the second diffraction grating; and a diffraction light beam that is diffracted by the first diffraction grating and then detected. reflected by the surface and the second
A grazing incidence interferometer device comprising: a hologram lens that changes the direction in which interference fringes formed by interference with light beams transmitted through a diffraction grating are observed; 2. Claims in which an adjustment hologram lens for adjusting the position of the subject is disposed on the output light side of the second diffraction grating, and a screen is disposed on the focal plane on which the light of the adjustment hologram lens is focused. The grazing incidence interferometer device according to item 1.