JPH06109445A - Interferometer device - Google Patents

Abstract

PURPOSE:To perform an adjustment easily and quickly by a simple constitution by a method wherein a tool is constituted of a pinhole-shaped spatial filter which can be mounted on a movement stage and of a concave mirror whose curvature central position coincides with the center of a pinhole. CONSTITUTION:A tool 101 for optical-axis adjustment is constituted of a pinhole-shaped spatial filter which can be replaced and of a high-surface-accuracy concave mirror 2 which is provided with a high-accuracy polished spherical surface and with a rough- planed plane in such a way that they are held by a tube 3. A pinhole in the filter 1 is arranged so as to coincide with the central position of the convex mirror 2. The tool 101 is fixed onto a movement stage 102 in a state that the filter 1 is detached and that is it mounted, interference fringes are observed from the side of an interferometer, the front-faced relationship between the interferometer and the tool 101 and the parallelism dislocation at the right and the left as well as the upper part and the lower part of the tool 101 and the inclination of the stage 102 are adjusted. Then, a final lens for the interferometer is replaced by a lens 6 whose back focus is long and which is provided with a reference spherical surface 6a, the interference fringes are observed, and the parallelism displacement and the inclination of a rail 5 for movement are adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer device for measuring the shape of a rough surface.

[0002]

2. Description of the Related Art An interferometer (interferometer device) has conventionally been recognized as a measuring instrument which has high precision but requires fine adjustment, and requires skill and labor for setting. However, in recent years, as the accuracy of the optical system has become more and more required, the measurement of the radius of curvature of the lens, etc. is changed from the mechanical contact type measurement such as the spherometer to the measurement using an interferometer with higher accuracy. The law is changing to the mainstream. Also,
Interferometers are often used to measure aberrations such as wavefront aberrations of optical systems.

In such an ordinary interferometer, a stage that can be moved along the interferometer main body in the optical axis direction of the interferometer at the time of use, and a scale that can read the amount of movement of the stage.
A moving rail with a rule is required. The delicate adjustment is necessary because the required accuracy is the order of the wavelength used, that is, the accuracy of less than a micron. Therefore, the optical axis of the interferometer and the axis of the stage and rail are required. Must be matched with extremely high precision.

Conventionally, laser beams have been used to achieve this accuracy.
I make adjustments by making a reference with a lens, or by repeating trial and error while observing the interference fringes due to the reflection on the curved surface, and adjusting the optical axis.

On the other hand, it is expected that the measurement by the interferometer will be applied to another field, in particular, the field of flatness measurement of glass or metal having a rough surface which cannot be observed by the normal interferometric measurement by specular reflection.

[0006] Conventionally, as an interferometric measurement of the flatness of an object that cannot be measured by specular reflection, measurement by oblique incidence is known. The oblique incidence has an effect of removing the influence of fine irregularities on the surface of the test object and extracting only the specular reflection component from the surface.

FIG. 5 is a schematic diagram showing a conventional method of forming an interference fringe by making a plane wave obliquely incident on a test object 20 using a prism 22. The prism 22 is arranged close to or slightly apart from the test object 20, and the lower surface 22a of the prism 22 facing the test object 20 serves as a reference surface. Object 20
In order to observe widely, it is necessary to enlarge the prism 22 according to the size of the test object 20.

In the method of oblique incidence, the required incident angle differs depending on the degree of rough surface, and the greater the degree of rough surface, that is, the larger the unevenness of the surface, the larger the incident angle is required. In the prism method of FIG. 5, since the angular relationship is clearly determined in advance by the prism 22, the degree of freedom in the device configuration is small, the incident angle is limited, and there is a drawback in that flexibility is applied to various rough surfaces.

As a method of removing such a restriction on the shape measurement of the rough surface, as shown in FIG. 6, a semi-transparent mirror 29, 30, a reflecting mirror 24, and a reference mirror 27 are combined to obtain a physique.
There is known a method of forming an interferometer, collimating light from a light source 25 with a lens 26 to make the light obliquely incident on an object 20 to be inspected, and observing interference fringes on an observation surface 31.

[0010]

However, the above-mentioned conventional example has a drawback that the adjustment of the optical axis of the interferometer is delicate and there are many uncertain factors. In the case of using a normal interferometer, there are factors such as vertical and horizontal tilts and parallel shifts of the interferometer body, while there are tilts and parallel shifts on the stage and rail sides. There are many optical axis misalignment factors. Since the wavelength order accuracy is required for adjustment,
If a conventional trial-and-error method is used for optical adjustment during installation, use, or periodic maintenance of the apparatus, re-adjustment of the optical axis requires a great deal of labor and time. In addition, there is a problem that only a skilled person can make highly accurate adjustments.

The same applies to the case of constructing a general-purpose non-prism type interferometer for measuring the shape of a rough surface.
As shown in FIG. 6, since the number of components is large, adjustment is complicated and difficult, and skill is also required. Further, in the case of measuring the shape of a rough surface, there is another problem that the apparatus becomes large in size when the rough surface interferometer portion is installed on an existing interferometer.

[0012]

In order to solve the above problems, the present invention is characterized by adding a special tool or mechanism for adjusting the optical axis to an interferometer. The relative position of the interferometer with the moving stage and the rail is characterized by using a tool having a pinhole-shaped special filter and a concave mirror that can be exchanged.

In the case of rough surface measurement, the structure of the interferometer constituting the oblique incidence interferometer is changed to monitor the rotation angle of the arm mechanism rotatable about the axis perpendicular to the optical axis of the interferometer. And an object holder that is rotatable and has a tilt adjustable in the vicinity of a rotation axis on the arm mechanism, and a tilt-adjustable high-precision plane mirror at the end of the arm mechanism. To do. The arm mechanism is attached to a conventional interferometer and together constitutes an interferometer for rough objects.

According to the present invention, as a result of adding a tool or a stage mechanism having a simple structure to the conventional interferometer, the adjustment which requires skill is facilitated, and the adjustment can be performed in a short time even by a non-expert. It was done like this.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a tool 10 used in the interferometer device of the present invention.
1 is a schematic diagram of Embodiment 1 of Example 1 and shows an optical axis adjusting tool in the configuration of a normal interferometer. In the figure, reference numeral 1 denotes various interchangeable pinhole-shaped special filters, 2 denotes a concave mirror polished to a highly accurate spherical surface, and the other surface which is not a spherical surface is a flat surface. Is a face. A lens barrel 3 holds the spatial filter 1 and the concave mirror 2. The pinhole of the special filter 1 is arranged so as to coincide with the central position of the concave mirror 2.

FIG. 2 shows a method of aligning and adjusting the optical axis of the interferometer and the axes of the moving stage and the rail by using the tool 101 of the optical axis adjustment 2 of FIG. Tool 1 in Figure 1
First, 01 is fixed on the moving stage 102 with the special filter 1 removed as shown in FIG.

Reference numeral 4 denotes a final lens of the interferometer, the final surface of which is a reference spherical surface. In the arrangement of FIG. 2A, the reference spherical surface 4a has a short back focus. Next, the interference fringes are observed in the same manner as the surface accuracy of the concave mirror 2 is observed, and adjustment is performed so that the number of interference fringes observed on the interferometer side is one or less.
It means that the tilt of the interferometer and the optical axis adjusting tool has been adjusted in a face-to-face relationship at the position A when the adjustment is completed. This is a rough adjustment in the initial state of the relative relationship between the interferometer, the moving stage 5, and the rail.

Then, the adjustment proceeds to the state shown in FIG. In FIG. 2B, the special filter 1 is attached to the tool 101 for adjusting the optical axis, and the same interference fringes as in FIG. 2A are observed. The center of the special filter 1 is made to coincide with the center of the concave mirror 2 in advance.

Since the adjustment of FIG. 2A is a rough adjustment, it is not always guaranteed that the convergence point of the light from the reference spherical surface 4a generated from the interferometer coincides with the center of 1. If the interferometer and the tool 101 for adjusting the optical axis have a parallel shift, the light flux from the reference spherical surface cannot pass through the special filter 1 and the interference fringes cannot be confirmed. If the interference fringes cannot be confirmed, the parallel displacement of the tool 101 in the vertical and horizontal directions is adjusted by moving the stage 102, and the interference fringes become one color.
The inclination of the stage 102 is also adjusted so that it becomes as follows.

When the optical axis shift is large in the adjustment of FIG. 2B, it is advisable to start the adjustment with the special filter 1 having a larger diameter first and then proceed with the procedure while replacing the filter with a smaller diameter one by one. Further, since the second surface side of the reflecting mirror 2 of the adjusting tool 101 is a rough surface, when the light beam can pass through the special filter 1, the light from the reference spherical surface 4a reaches the rough surface. Then, it is scattered and the passing state of the light beam can be monitored. Therefore, if the second surface of the reflecting mirror can be observed, it can be used for rough adjustment. The above procedure completes the adjustment of the relative relationship between the interferometer and the stage at a position close to the interferometer.

Then, the adjustment proceeds to the adjustment of the relative relationship between the interferometer and the stage 102 at different positions in the optical axis direction of FIG. 2C. In FIG. 2 (C), first, the reference spherical surface 4 is back-focused.
The lens 6 is changed to a reference spherical surface 6a having a long dregs, and the interferometer and the stage 102 are moved so that the interference fringes of the concave mirror 2 can be observed at the position B, and the parallel shift of the rails,
Adjust the tilt.

The series of steps shown in FIGS. 2A to 2C constitutes one loop, and when these operations are repeated to move the stage 102 from the position A to the position B, both positions are moved. Then, the interference fringes are observed, and the adjustment of the optical axis is completed. Many three-dimensional parameters such as parallel shift and tilt
In order to manipulate the device to adjust the device, it is most certain that the tool 101 as in the present invention is used to gradually drive in, and this is a technique that does not require skill.

On the other hand, the construction of an interferometer for measuring the shape of a rough surface also requires skill. FIG. 3 is a schematic view of the essential portions of Embodiment 2 of the present invention, in which interferometer measurement of a rough surface is simplified by adopting a new stage mechanism and configuration.

In the figure, 11 is a transmission reference plane of the interferometer, and 12
Is an optical axis of the interferometer, and a rotary arm 16 having a shaft 13 perpendicular to the optical axis 12 as a center of rotation is arranged.
An object holder 14 that can be rotated and tilted is attached near the rotary shaft 13 on the position 6. Further, a mirror holder 17 whose tilt can be adjusted is attached to the tip of the rotary arm 16. 15 is a rotary stage with a scale,
The rotation angles of the object holder 14 and the arm 16 can be directly read.

FIG. 4 is an explanatory view of the operation of the system of FIG. The interferometer 18 used is a general Fizeau interferometer having an alignment structure inside the main body. First, interferometer 1
The transmission reference plane 11 is attached to 8 and the internal alignment of the interferometer 18 itself is performed.

Next, the test object holder 14 is attached to the test rough surface member 20.
Is attached, the test object is rotated by an appropriate angle according to the roughness of the rough surface member 20, and the system is set so that the light beam from the interferometer is obliquely incident on the test surface. The appropriate angle according to the roughness means the angle at which the influence of surface irregularities is eliminated by oblique incidence and the specular reflection from the surface becomes dominant. However, since the measurement sensitivity decreases as the angle of incidence on the surface to be inspected increases, it is preferable to make the angle as small as possible when accuracy is required.

When the arm 16 is rotated with the interferometer in alignment and the plane mirror 21 attached to the mirror holder 17 is adjusted, the reflected light from the rough surface 20 is reflected by the plane mirror 2.
By 1, the light is reflected, goes backward, and returns to the interferometer, so that the alignment of the entire rough surface interferometer becomes possible. In the case of a rough surface interferometer, the rough surface can be considered as a simple mirror surface due to the effect of oblique incidence.

When alignment is completed and interference fringes are observed, the angle of rotation of the object to be measured with respect to the interferometer optical axis is rotated.
Read from the scale on page 15. When the read angle is θ, the observed interference fringes appear under the condition that the optical path difference satisfies mλ / 4cosθ m = 1,2,3, ... Therefore, the surface accuracy of the rough surface 20 can be read from the interference fringes.

Since the pitch of the interference fringes becomes coarser as the angle θ becomes larger, it is determined in consideration of the roughness of the rough surface 20 and the measurement accuracy as described above. In the embodiment shown in FIG. 3, the incident angle with respect to the object to be inspected can be freely changed, and an interferometer with high flexibility can be assembled.

In the embodiment shown in FIG. 3, since the subject is placed obliquely with respect to the inspection light beam, it is not necessary to form a prism having the same size as the object to be inspected, unlike the conventional prism system. As a result,
The conventional interferometer can be easily used as a rough surface interferometer.

In this embodiment, the rotary stage 15 is provided only around the shaft 13, but in addition to the rotary stage 15, a mirror is provided.
If the holder 17 is also provided with the rotation stage 15 and the mirror holder 17 on the arm 16 is rotated by θ degrees when the rotation stage 15 is rotated by θ degrees, the rotation of the test object 20 is accompanied. The tilt of the optical axis is automatically corrected, and only the fine adjustment of the plane mirror 21 remains, so that the operability is further improved.

Since it is known that the interference fringes appear in λ / 4cosθ in advance, the rotary stage 15 is marked in advance so that the pitch of the interference fringes can be easily handled so that the measurement is convenient. It may be attached to make it easier to set, or when the rotation is automated, it is possible to automatically select a place where the pitch becomes a sharp numerical value.

[0033]

As described above, according to the present invention, the conventional interferometer is provided with a tool having a simple structure of a special filter and a concave mirror, and a simple mechanism having a structure of a rotary stage and a single plane mirror. Only by adding, it is possible to greatly simplify and facilitate the adjustment of the interferometer, which has conventionally been said to be complicated and requires skill and time.

As a result, it becomes easy to match the optical axis of the interferometer with the axis of the rail of the moving stage, and the flatness of rough glass, metal, etc. can be obtained by using an ordinary interferometer. It became possible to easily measure while adjusting the sensitivity.

[Brief description of drawings]

FIG. 1 is a schematic view showing an optical axis adjusting tool according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a method of using the adjusting tool according to the first embodiment.

FIG. 3 is a schematic view of a main part showing a stage for measuring a rough surface according to a second embodiment of the present invention.

FIG. 4 is a schematic view of a main part for explaining a measuring method performed by using the stage of Example 2.

FIG. 5 is an explanatory view showing an oblique incidence interferometry method using a conventional prism.

FIG. 6 is an explanatory diagram showing oblique incidence interferometry using a conventional reflecting mirror and semi-transparent mirror.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Special filter 2 High-accuracy concave mirror 3 Lens barrel 4, 6 Transmission reference spherical surface 5 Moving rail 11 Transmission reference plane of interferometer 12 Optical axis of interferometer 13 DUT perpendicular to optical axis of interferometer Rotation axis of holder 14 Test object holder 15 Rotation stage 16 Rotation arm 17 Miller holder 18 Interferometer 20 Test object (rough surface object) 21 Planar reflecting mirror 22 Prism 25 Laser light source 26 Collimator lens 27, 28 plane mirror 29, 30 semi-transparent mirror 31 observation surface

Claims (2)

[Claims] 1. An interferometer having an interferometer, a moving stage for placing an object to be examined at various positions on the optical axis of the interferometer, and a rail for guiding the moving stage. , A pinhole-shaped special filter mountable on the moving stage and a concave mirror whose center of curvature coincides with the center of curvature of the pinhole. An interferometer device capable of observing interference fringes when aligning a stage in the optical axis direction. 2. In an interferometer device for measuring the surface shape of a rough surface body by oblique incidence, an interferometer that generates a plane wave that serves as a reference wave, and an interferometer that is rotatable about an axis perpendicular to the optical axis of the interferometer. An arm mechanism and a monitor mechanism for the rotation angle; and a hold mechanism for arranging a rough surface body, which is an object to be inspected, near the rotation axis of the arm mechanism to make the incident angle variable. An interferometer device comprising a plane mirror at a tip of a mechanism for reflecting light reflected from the rough surface body and returning the light to the rough surface body again.