JP3883145B2 - Interferometer alignment device - Google Patents

Description

BACKGROUND OF THE INVENTION
The present invention relates to an alignment apparatus for an interferometer. More specifically, the light beams from a reference surface and a test surface are condensed on the alignment inspection surface, and the relative inclination of the both surfaces is adjusted so that the focused spot is matched. The present invention relates to an alignment apparatus for an interferometer to be adjusted.
[Prior 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, and forms interference fringes on a screen by the interference action of the two reflected light beams. By observing the interference fringes, the uneven shape of the test surface can be evaluated.
In order to accurately perform the test surface evaluation in this interferometer, it is important that the reference surface and the test surface are accurately arranged in the 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, a test surface alignment apparatus in a Fizeau interferometer includes an alignment optical system 160 built in the interferometer body 110a and a tilt for mechanically adjusting the tilt of the test surface 102a. An adjustment mechanism (two-axis stage) 120 is included. The alignment optical system 160 separates the light beam by a beam splitter 162 disposed in the optical path between the light source 112 and the reference surface 118a, and forms a light spot of the light source 112 on the alignment screen 166 by the imaging lens 164. It is like that. Then, on the alignment screen 166, the tilt adjustment mechanism 120 is operated 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 are overlapped with each other. The inclination angle is adjusted.
Further, instead of providing the alignment optical system 160 as described above, it is also possible to perform a surface alignment using a television camera. That is, as shown in FIG. 8, the normal television camera 126 functions as a screen on which the imaging plane 126a forms the interference fringes, but the imaging plane 126a is changed by changing the focal length of the lens system of the television camera. If the light beam from the light source 112 is focused on the CRT 128a of the television monitor 128, the two light spots formed by the reflected lights from the reference surface 118a and the test surface 102a overlap each other. It is possible to operate the adjustment mechanism 120 to adjust the inclination of the test surface 102a.
[Problems to be solved by the invention]
However, the range that can be observed with the alignment screen 166 or the CRT 128a is limited, and when the inclination of the reference surface 118a is large, the light spot by the reflected light from the reference surface 118a can be observed in the initial state before the inclination adjustment. However, there also occurs a situation in which 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 in which direction the light spot due to the reflected light from the test surface 102a is, and adjustment for moving the light spot within the observation range is extremely difficult. It becomes.
The present invention has been made in view of such circumstances, and even when at least one of the light spots formed by reflected light from the reference surface and the test surface is deviated from the observation surface, the position of the light spot is It is an object of the present invention to provide an interferometer alignment apparatus that can easily recognize the above.
[0008]
[Means for Solving the Problems]
The present invention irradiates a light beam from a light source to a reference surface and a test surface via a diverging lens and a collimator lens, and causes reflected light beams carrying shape information of these surfaces from these two surfaces to interfere with each other. Then, the interference fringes are observed, and the reflected light beams from the two surfaces are respectively focused on the alignment inspection surface, and at least one of the two surfaces is matched so that the obtained two light spots are matched. In an interferometer alignment apparatus that adjusts the alignment of these two surfaces by adjusting the tilt,
At the time of alignment adjustment of the two surfaces, a flat diffraction grating is inserted in the common optical path of the irradiation light beam directed toward the two surfaces or in the common optical path of the reflected light beam from the two surfaces. It is characterized by.
[0009]
The interferometer alignment apparatus according to the present invention is characterized in that the diffraction grating is movable between two positions, a position in the common optical path and a position outside the common optical path. It is.
Further, the diffraction grating can be formed to have vertical and horizontal striped gratings, and vertical, horizontal and diagonal striped gratings.
The interferometer is a Fizeau interferometer, and the diffraction grating is disposed in an optical path between the diverging lens and the collimator lens or in an optical path between the collimator lens and the reference plane. Can be.
Operation and effect of the invention
According to the interferometer alignment apparatus of the present invention, during the alignment of the test surface, the optical path of the interferometer (the common optical path of the irradiation light beam toward the reference surface and the test surface or the common optical path of the reflected light beam from these two surfaces) A diffractive optical element is inserted into the condensing spot formed by the reflected light of the reference surface and test surface, which appears on the alignment observation surface, so that a bright tail is formed around the center of the light spot. Even if these light spot centers deviate from the observation plane, the position of the light spot center can be recognized if the bright tail is within the observation plane. It is possible to enlarge.
In addition, if the diffractive optical element can be moved mechanically between the position in the optical path and the position outside the optical path, the diffractive optical element can be smoothly inserted into the optical path during alignment adjustment. Can be convenient.
In addition, if the diffractive optical element is a flat diffraction grating and the grating shape is vertical, horizontal, or vertical, horizontal, left and right diagonal grating stripes, the shape has a bright tail in all directions or around the light spot center. The observable range of the light spot can be expanded in all directions.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an alignment apparatus for an interferometer according to the present invention will be described.
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 test surface alignment apparatus according to this embodiment, an outline of the Fizeau interferometer 10 will be described first.
The Fizeau interferometer 10 includes a laser 12, a diverging lens 14, a collimator lens 16, a reference plate 18, a tilt adjustment mechanism 20, a beam splitter 22, an imaging lens 24, a television camera 26, and a television. A monitor 28 is provided, and other than the reference plate 18, the tilt adjustment mechanism 20 and the television monitor 28 are built in the interferometer body 10a, and the reference plate 18 and the tilt adjustment mechanism 20 are attached to the interferometer body 10a, and The monitor 28 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 the collimator lens 16 and then enters the reference plate 18. The reference plate 18 is a flat plate member having a semi-transparent plane 18a (reference plane) with extremely high flatness on the anti-collimator lens side, and parallel light from the collimator lens 16 is incident on the semi-transparent plane 18a from the vertical direction. It has been positioned in advance.
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 distance from the reference plate 18. The subject 2 has a collimator lens side surface that is a test plane 2a (test plane), and the test plane 2a is parallel to the semi-transparent plane 18a of the reference plate 18 so that the tilt adjustment mechanism 20 The inclination angle of the test plane 2a is adjusted by this operation.
The beam splitter 22 is provided in an optical path between the diverging lens 14 and the collimator lens 16, and a part of the return light from the collimator lens 16 reflected by the semi-transparent plane 18a and the test plane 2a is obtained. An image is formed on an image forming surface 26 a made of a CCD of the television camera 26 via the image forming lens 24. This image information signal is input to the television monitor 28 and 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 plane 18a and the reflected light from the test plane 2a. Since interference fringes are formed on the image formation surface 26a of the camera 26, by observing the interference fringes on the CRT 28a of the television monitor 28, it is possible to evaluate the uneven shape of the plane 2a to be examined. It has become.
In order to accurately perform the test surface evaluation in the Fizeau interferometer 10, it is necessary to perform the above evaluation in a state in which the test plane 2a is arranged in parallel with the semi-transparent plane 18a.
For this reason, the test surface alignment is performed prior to the test surface evaluation. This is because the reflected light of the test surface 2a and the semi-transparent plane 18a is converted to the television camera 26 by moving the imaging lens 24. The light spot is converged on the image forming surface 26a and the light spot is formed, and the inclination of the test plane 2a is adjusted by the operation of the inclination adjusting mechanism 20 so that these light spots coincide on the CRT 28a. A sufficient degree of parallelism between the mirror plane 18a and the test plane 2a is secured.
However, when the inclination of the test plane 2a in the initial state is large and the light spot formed by the reflected light from the test plane 2a deviates from the observation range on the CRT 28a, the tilt adjustment mechanism 20 is moved in any direction. It is difficult to determine whether or not the light spot can be matched if adjusted to.
Therefore, in this embodiment, during alignment adjustment, the diffraction grating 30 is inserted into the optical path between the beam splitter 22 and the collimator lens 16, and the CRT 28a formed by the reflected light from the test plane 2a and the semi-transparent plane 18a. Even if the light spot center 40 deviates from the observation field of view of the CRT 28a by forming the upper light spot in such a shape that a bright tail is formed around the light spot center 40 as shown in FIG. It is easy to recognize the position. 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 diagonal parallel lines.
Next, the operation procedure of alignment adjustment will be described with reference to FIG. 4. As shown in FIG. 4A, the light spot 42 a by the reflected light from the semi-transparent plane 18 a is displayed at the center of the observation visual field 45, while the observation visual field 45 is displayed. If a part of the bright tail of the light spot 42b by the reflected light from the test plane 2a is displayed at the end of the test plane, the tilt adjustment mechanism 20 adjusts the tilt of the test plane 2a, and (B) As shown in FIG. 4, the light spot 42b is placed in the observation visual field 45, and the tilt adjustment operation is continued. As shown in (C), the tilt adjustment operation is performed at a position where both the light spots 42a and 42b coincide with each other. To stop. In this state, the test plane 2a faces the semi-transparent plane 18a, and the alignment adjustment is completed.
When the alignment of the test surface is completed, the diffraction grating 30 is moved out to the position 30a outside the optical path to prepare for interference fringe evaluation on the CRT 28a of the television monitor 28.
The diffraction grating 30 is inserted into the optical path when adjusting the alignment, and retracts out of the optical path when observing the interference fringes. The insertion / removal operation may be performed manually by the operator. For example, the actuator 50 as shown in FIG. 5 is used, and the insertion / removal operation of the diffraction grating 30 is performed by the operator's ON / OFF switch switching operation. You can squeeze it.
[0023]
Specifically, the actuator 50 is inserted with a gripping portion 51A for gripping the diffraction grating 30, a diffraction grating movable portion 51 having a shaft portion 51B following the gripping portion 51A, and the shaft portion 51B. , And a solenoid portion 52 that performs electromagnetic suction and discharge operations of the shaft portion 51B in response to an instruction signal from a switch (not shown).
Thus, according to the present embodiment, the light spot recognition range in the alignment of the test surface can be expanded without incurring an increase in size and cost of the Fizeau interferometer 10.
In the present embodiment, the insertion location of the diffraction grating 30 is set between the beam splitter 22 and the collimator lens 16, but the insertion location is within the common optical path of the irradiated light beam toward the two surfaces. Alternatively, the diffraction grating may be inserted in the optical path between the collimator lens 16 and the reference plate 18 as long as it is in the common optical path of the reflected light beams from the two surfaces.
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 that can widen the spot recognizable range. The shape as shown in FIG. 6 having a bright tail 41a may be used.
[0026]
Grating shape of the diffraction grating 30 which can form a light spot shown in FIG. 6, as shown in FIG. 7, the vertical, a horizontal stripe shape.
In addition, although the case where alignment adjustment is performed using the imaging optical system has been described in the above embodiment, an alignment optical system 60 as shown in FIG. 1 is provided separately from the imaging optical system and separated by the beam splitter 62. The light beam may be focused on the screen 66 using the condenser lens 64, and the light spots 42a and 42b may be observed on the screen 66.
In the above embodiment, the test surface alignment 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 beam toward the test surface and the reference surface Alternatively, the test surface alignment can be performed in the same manner by inserting a diffractive optical element into the common optical path of the reflected light beams from these two surfaces.
In the above embodiment, a diffraction grating is used as the diffractive optical element, but other diffractive optical elements that generate a diffraction phenomenon, such as a hologram and a diffractive lens, can be used.
[Brief description of the drawings]
FIG. 1 is a view showing an embodiment in which an interferometer alignment apparatus according to the present invention is applied to a Fizeau interferometer. FIG. 2 is a view showing a light spot shape appearing on a CRT in the embodiment shown in FIG. FIG. 4 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 / retraction operation of the diffraction grating. FIG. 7 is a diagram showing a light spot different from FIG. 2. FIG. 7 is a diagram schematically showing the grating shape of the diffraction grating when the light spot shown in FIG. 6 is generated.
2 Subject 2a Test plane (test surface)
DESCRIPTION OF SYMBOLS 10 Fizeau type interferometer 10a Interferometer main body 12 Laser 14 Divergent lens 16 Collimator lens 18 Reference plate 18a Mirror plane (reference plane)
20 Tilt adjustment mechanism 22, 62 Beam splitter 24 Imaging lens 26 Television camera 28 Television monitor 28a CRT
30 Diffraction grating 30a Position 40, 40a outside optical path Light spot center 41, 41a Bright tail 42a, 42b Light spot 45 Observation range 50 Actuator 60 Alignment optical system

Claims (5)

The light beam from the light source is irradiated to the reference surface and the test surface through the diverging lens and the collimator lens, and the reflected light beam carrying the shape information of each surface from these two surfaces is caused to interfere with the interference. While observing the stripes, the reflected light beams from the two surfaces are each focused on the alignment inspection surface, and the inclination of at least one of the two surfaces is adjusted so that the two obtained light spots are matched. In the interferometer alignment device that adjusts the alignment of these two surfaces,
At the time of alignment adjustment of the two surfaces, a plate-like diffraction grating is inserted into the common optical path of the irradiation light beam toward the two surfaces or the common optical path of the reflected light beam from the two surfaces. An interferometer alignment apparatus characterized by comprising: The interferometer alignment apparatus according to claim 1 , wherein the diffraction grating is movable between two positions, a position in the common optical path and a position outside the common optical path. The diffraction grating, interferometer alignment system as in claim 1 or 2, wherein the formed by forming a stripe-shaped grid of vertical and horizontal. The diffraction grating, vertical, horizontal, interferometer alignment system as in claim 1 or 2, wherein the formed by forming a diagonal striped grid. The interferometer is a Fizeau interferometer, and the diffraction grating is in an optical path between the diverging lens and the collimator lens, or the collimator lens and the reference surface.
The interferometer alignment apparatus according to claim 1, wherein the interferometer alignment apparatus is disposed in an optical path between the interferometer and the interferometer.

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