JPH11108611A - Alignment device for interferometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a light spot to be recognized easily even when the center of the spot is shifted from an alignment observing surface, at the time of adjusting the alignment of the surface to be inspected of an interferometer, by making bright tails to be formed around the light spot appearing on the observing surface by inserting a diffraction optical element into the optical path of a light beam. SOLUTION: At the time of adjusting the alignment of an interferometer, bright tails are made to be formed by reflected rays of light from a flat surface 2a to be inspected and the flat surface 18a of a semi-transparent mirror in the radial direction around a center 40 of a light spot formed on a CRT 28a, by inserting a diffraction grating 30 into the optical path between a beam splitter 22 and a collimator lens 16. Therefore, the position of the light spot 40 can be-recognized even when the center 40 of the light spot is shifted from the observing visual field of the CRT 28a. In other words, the recognizable extent of the center 40 of the light spot is made wider than the observing extent of the CRT 28a.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment apparatus for an interferometer, and more particularly, to a method of converging a light beam from a reference surface and a test surface onto an alignment test surface and matching the condensed spots. The present invention relates to an alignment device for an interferometer that adjusts a relative inclination of both surfaces.

2. Description of the Related Art In general, an interferometer reflects a light beam from a light source on a reference surface and a test surface arranged in a predetermined positional relationship, respectively, and interferes the reflected two light beams on a screen. The apparatus is configured to form interference fringes, and by observing the interference fringes, it is possible to evaluate the uneven shape and the like of the test surface. In order to accurately perform the test surface evaluation in this interferometer, it is important that the reference surface and the test surface be accurately arranged in the above-described predetermined positional relationship. For this reason, conventionally, a test surface alignment device that adjusts the position of the test surface so as to obtain the predetermined positional relationship is provided in the interferometer. For example, as shown in FIG. 8, an alignment apparatus for a test surface in a Fizeau interferometer has an alignment optical system 160 built in an interferometer main body 110a and a tilt for mechanically adjusting the tilt of the test surface 102a. And an adjustment mechanism (two-axis stage) 120. The alignment optical system 160
Are separated by a beam splitter 162 disposed in an optical path between the light source 112 and the reference plane 118a, and the alignment screen 1 is formed by an imaging lens 164.
A light spot of the light source 112 is formed on the light source 66. Then, the tilt adjusting mechanism 120 is operated on the alignment screen 166 so that the light spot due to the reflected light from the reference surface 118a and the light spot due to the reflected light from the test surface 102a overlap one another.
The inclination angle of 2a is adjusted. Also, instead of providing the alignment optical system 160 as described above,
It is also possible to perform test surface alignment using a television camera. That is, as shown in FIG. 8, the television camera 126 normally has its image forming surface 126a functioning as a screen on which the above-mentioned interference fringes are formed.
If the light flux from the light source 112 is focused on a,
The tilt adjusting mechanism 120 is operated by operating the tilt adjusting mechanism 120 so that two light spots formed by the respective reflected lights from the reference surface 118a and the test surface 102a on the CRT 128a of the television monitor 128 overlap. Adjustments can be made.

However, the range that can be observed on the alignment screen 166 or the CRT 128a is limited, and when the inclination of the reference plane 118a is large, the reference plane 118a is shifted from the reference plane 118a in the initial state before the inclination adjustment. Although the light spot due to the reflected light can be observed, the light spot due to the reflected light from the test surface 102a cannot be observed. In such a case,
It is difficult for the operator to determine the direction of the light spot due to the reflected light from the test surface 102a, and it is extremely difficult to adjust the light spot to be moved within the observation range. The present invention has been made in view of such circumstances, and even when at least one of the light spots formed by the reflected light from the reference surface and the test surface is deviated from the observation surface, the position of the light spot is also determined. It is an object of the present invention to provide an alignment apparatus for an interferometer that can easily recognize the alignment.

SUMMARY OF THE INVENTION The present invention irradiates a light beam from a light source to a reference surface and a surface to be inspected, and emits light from these two surfaces.
The reflected light beams carrying the shape information of the respective surfaces are caused to interfere with each other to observe the interference fringes, and the reflected light beams from the two surfaces are respectively focused on the alignment inspection surface to obtain two light beams. In an interferometer alignment apparatus for adjusting the alignment of at least one of the two surfaces by adjusting the inclination of at least one of the two surfaces so as to match the spots, the two surfaces may be adjusted at the time of alignment adjustment of the two surfaces. The diffractive optical element is configured to be inserted into a common optical path of the irradiation light beam toward the optical path or a common optical path of the light beam reflected from the two surfaces. In the alignment apparatus for an interferometer according to the present invention, the diffractive optical element can be moved between two positions: a position in the common optical path and a position outside the common optical path. Things. Further, it is preferable that the diffractive optical element is formed of a flat diffraction grating. Further, the diffraction grating may be a vertical or horizontal striped grating, a vertical,
It can be formed to have horizontal and oblique striped grids.

According to the interferometer alignment apparatus of the present invention, the optical path of the interferometer (the common optical path of the illuminating light beam directed to the reference plane and the test plane or the two paths) is adjusted when the alignment of the test plane is adjusted. (A common optical path of the reflected light beam), a condensed spot formed by the reflected light of the reference surface and the test surface, which appears on the alignment observation surface, has a bright tail around the center of the light spot. Since the shape is formed, even if the center of these light spots deviates from the observation plane, if the bright tail is within the observation plane, the position of the center of the light spot can be recognized, Thus, the light spot recognizable range can be expanded. If the diffractive optical element can be mechanically moved between two positions inside the optical path and outside the optical path, the diffractive optical element can be smoothly inserted into the optical path when performing alignment adjustment. Is convenient. In addition, if the diffractive optical element is a flat diffraction grating and the grid shape is vertical, horizontal, or vertical, horizontal, left and right diagonal grid stripes, a shape having a bright tail in all directions or eight directions around the center of the light spot. Thus, the observable range of the light spot can be expanded in all directions or all directions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an alignment apparatus for an interferometer according to the present invention will be described. FIG.
FIG. 1 is a configuration diagram illustrating a Fizeau interferometer 10 on which a test surface alignment is performed according to the present embodiment. Before describing the alignment apparatus for a test surface according to the present embodiment, an outline of the Fizeau interferometer 10 will be described first. The Fizeau interferometer 10 includes a laser 12 and a diverging lens 14.
, Collimator lens 16, reference plate 18, tilt adjustment mechanism 20, beam splitter 22, and imaging lens 24
, A television camera 26, and a television monitor 28, except for the reference plate 18, the tilt adjustment mechanism 20, and the television monitor 28, which are built in the interferometer main body 10 a. The television monitor 28 is attached to the meter main body 10a, and is connected to the television camera 26. The light beam emitted from the laser 12 and diverged by the diverging lens 14 is collimated by a collimator lens 16.
After being converted into parallel light, the light enters the reference plate 18. The reference plate 18 has a semi-transparent mirror plane 18a (reference plane) having extremely high flatness on the side opposite to the collimator lens.
And is positioned in advance so that the parallel light from the collimator lens 16 is incident on the semi-transparent mirror plane 18a from the vertical direction. On the anti-collimator lens side of the reference plate 18, the subject 2 is supported by the tilt adjustment mechanism 20 at a predetermined interval from the reference plate 18. The surface of the subject 2 on the side of the collimator lens is a test surface 2a (test surface), and the test surface 2a is
The tilt angle of the test plane 2a is adjusted by operating the tilt adjusting mechanism 20 so as to be parallel to the semi-transparent mirror plane 18a of FIG. The beam splitter 22 is provided in an optical path between the diverging lens 14 and the collimator lens 16, and includes the semi-transparent mirror plane 18a and the test plane 2a.
A part of the return light from the collimator lens 16 reflected by the
An image is formed on an image forming surface 26a composed of. Then, this image information signal is input to the television monitor 28, and is displayed as an image on the CRT 28a. If the test plane 2a has irregularities or the like, a phase shift occurs between the reflected light from the semi-transparent mirror plane 18a and the reflected light from the test plane 2a. Since interference fringes are formed on the image plane 26a of the camera 26, the CRT 28a of the television monitor 28
By observing the interference fringes above, it is possible to evaluate the uneven shape and the like of the test plane 2a. In order to accurately evaluate the test surface in the Fizeau interferometer 10, the test surface 2a must be
It is necessary to perform the above-mentioned evaluation in a state of being arranged exactly parallel to a. Therefore, prior to the test surface evaluation,
Alignment of the test surface is performed. This is because the reflected light of the test surface 2a and the reflected light of the semi-transparent mirror plane 18a are converted into the image-forming lens 2
4, the light is converged on the image plane 26a of the television camera 26 to form a light spot.
This operation is performed by adjusting the tilt of the plane 2a to be inspected by the operation 0, whereby the semi-transparent mirror plane 18a and the plane 2a to be inspected are adjusted.
To ensure sufficient parallelism. However, the inclination of the test plane 2a in the initial state is large,
If the light spot formed by the reflected light from the test plane 2a has deviated from the observation range on the CRT 28a, it is necessary to determine in which direction the tilt adjustment mechanism 20 should be adjusted to match the light spot. It is difficult to judge. Therefore, in the present embodiment, at the time of alignment adjustment, the diffraction grating 30 is inserted into the optical path between the beam splitter 22 and the collimator lens 16, and the test plane 2a is adjusted.
The light spot on the CRT 28a formed by the reflected light from the semi-transparent mirror plane 18a is shaped such that bright tails are formed around the light spot center 40 in all directions as shown in FIG. 40 is CRT 28a
This makes it easy to recognize the position even if it deviates from the observation field of view. That is, the recognizable range of the light spot center 40 is wider than the observation range. FIG. 3 shows the grating shape of the diffraction grating 30, which is formed by vertical, horizontal, and left and right oblique parallel lines. Next, the operation procedure of the alignment adjustment will be described with reference to FIG. 4. As shown in FIG. 4A, the light spot 42a due to the light reflected from the semi-transparent mirror plane 18a is displayed at the center of the observation field 45, while the observation field 45 is displayed. Light spot 42b due to the reflected light from the test plane 2a
If a part of the bright tail is displayed, the inclination of the test plane 2a is adjusted by the inclination adjusting mechanism 20 to obtain (B)
As shown in (c), the light spot 42b is put into the observation field of view 45, and the operation of the tilt adjustment is further continued. As shown in FIG. To stop. In this state, the test plane 2a faces the semi-transparent mirror plane 18a, and the alignment adjustment is completed. When the alignment of the test surface is completed, the diffraction grating 30 is retracted to the position 30a outside the optical path to prepare for the evaluation of interference fringes on the CRT 28a of the television monitor 28. The diffraction grating 30 is inserted into the optical path when adjusting the alignment, and retreats outside the optical path when observing interference fringes. The insertion and exit operations may be performed manually by an operator.
The insertion / removal operation of the diffraction grating 30 may be performed by an operator using an actuator 50 as shown in FIG. Specifically, the actuator 50 includes a holding portion 51A for holding the diffraction grating 30, a diffraction grating movable portion 21 having a shaft portion 51B following the holding portion 51A, and the shaft portion 51B inserted. , And a solenoid 52 that electromagnetically suctions and discharges the shaft 51B in response to an instruction signal from a switch (not shown). As described above, according to the present embodiment, the light spot recognition range in the alignment of the test surface can be expanded without increasing the size and cost of the Fizeau interferometer 10. In the present embodiment, the insertion point of the diffraction grating 30 is set between the beam splitter 22 and the collimator lens 16.
It suffices that the diffraction grating is inserted in the optical path between the collimator lens 16 and the reference plate 18 within the common optical path of the irradiation light beam directed to one surface or the common optical path of the reflected light beam from the two surfaces. You may. Further, the shapes of the light spots 42a and 42b are not limited to those described above, and it is sufficient that the light spots 42a and 42b have a bright tail around the center of the light spot so as to expand the spot recognizable range.
It may have a shape as shown in FIG. 6 having bright tails 41a on all sides around a. The light spots 42a and 4a shown in FIG.
The grating shape of the diffraction grating 30 that can form 2b is a vertical and horizontal stripe shape as shown in FIG. Note that, in the above-described embodiment, the case where the alignment adjustment is performed using the imaging optical system is described, but separately from this imaging optical system,
An alignment optical system 60 as shown in FIG. 1 is provided, and the light beam separated by the beam splitter 62 is focused on a screen 66 using a condenser lens 64.
6, the light spots 42a and 42b may be observed. In the above-described embodiment, the alignment of the test surface in the Fizeau interferometer 10 has been described. However, in other interferometers such as the Michelson type and the Mach-Zehnder type, in the common optical path of the irradiation light beams traveling toward the test surface and the reference surface. Alternatively, by inserting a diffractive optical element in the common optical path of the reflected light beams from these two surfaces, the alignment of the test surface can be similarly performed. In the above embodiment, a diffraction grating is used as a diffractive optical element, but other diffractive optical elements that cause a diffraction phenomenon, such as a hologram and a diffractive lens, can be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment in which an interferometer alignment apparatus according to the present invention is applied to a Fizeau interferometer.

FIG. 2 is a diagram showing a light spot shape appearing on a CRT in the embodiment shown in FIG. 1;

FIG. 3 is a perspective view schematically showing a grating shape of a diffraction grating.

FIG. 4 is a diagram for specifically explaining an alignment adjustment operation;

FIG. 5 is a perspective view showing an actuator for performing insertion / removal operation of a diffraction grating.

FIG. 6 is a diagram showing a light spot different from FIG. 2;

FIG. 7 is a diagram schematically showing a grating shape of a diffraction grating when the light spot shown in FIG. 6 is generated.

FIG. 8 is a diagram showing a conventional technique.

[Explanation of symbols]

 Reference Signs List 2 object 2a object plane (object surface) 10 Fizeau interferometer 10a interferometer body 12 laser 14 divergence lens 16 collimator lens 18 reference plate 18a mirror plane (reference surface) 20 tilt adjusting mechanism 22, 62 beam splitter 24 Image lens 26 Television camera 28 Television monitor 28a CRT 30 Diffraction grating 30a Position outside optical path 40, 40a Light spot center 41, 41a Bright tail 42a, 42b Light spot 45 Observation range 50 Actuator 60 Alignment optical system

Claims (5)

[Claims] 1. A light beam from a light source is irradiated on a reference surface and a test surface, and reflected light beams carrying shape information of these surfaces from these two surfaces interfere with each other to observe interference fringes. By converging the reflected light beams from the two surfaces on the alignment inspection surface, and adjusting the inclination of at least one of the two surfaces so as to match the two obtained light spots, In an alignment apparatus for an interferometer that performs surface alignment adjustment, at the time of the alignment adjustment of the two surfaces, a common light path of the irradiation light beam directed to the two surfaces or a common light path of the reflected light beam from the two surfaces is used. An alignment apparatus for an interferometer, wherein a diffraction optical element is inserted. 2. An interferometer alignment apparatus, wherein the diffractive optical element is movable between two positions: a position in the common optical path and a position outside the common optical path. 3. An alignment apparatus for an interferometer according to claim 1, wherein said diffractive optical element comprises a plate-like diffraction grating. 4. An alignment apparatus for an interferometer according to claim 3, wherein said diffraction grating is formed as a vertical and horizontal stripe-like grating. 5. An alignment apparatus for an interferometer according to claim 3, wherein said diffraction grating is formed as a vertical, horizontal, or oblique striped grating.