JP3436407B2 - Grazing incidence interferometer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oblique incidence interferometer device which can be applied to the measurement of the surface shape of a surface on which relatively large irregularities are formed, and more specifically, to a reference light generated by reflection from a reference surface. The present invention relates to an oblique-incidence interferometer device that causes optical interference with object light that is generated by reflection from a surface to be inspected and then re-enters the reference surface.

[0002]

2. Description of the Related Art Conventionally, an oblique incidence interferometer device capable of measuring the surface shape of a surface to be inspected having a certain degree of unevenness by making coherent light obliquely incident on the surface to be inspected and lowering the measurement sensitivity. It has been known.

Various types of such grazing incidence interferometer devices are known, and the birch type as shown in FIG. 4 is a typical one. That is, this birch type grazing incidence interferometer device, as shown in FIG. 4, collimates the laser light emitted from the laser light source 40 with a collimator lens.
A parallel ray bundle is formed at 42, this bundle of rays is diffracted by the first diffraction grating 44, and, for example, + 1st-order light of the diffracted diffracted light is reflected by the test surface of the subject 46, and the reflected +1 0 transmitted through the next light and the first diffraction grating 44
The second light and the second light are superposed by the second diffraction grating 48 to cause interference,
As a result, interference fringes are formed on the screen 50, and the shape of the test surface of the subject 46 is measured by the interference fringes.

However, in an oblique incidence interferometer device, coherent light generally enters and exits the surface to be inspected, so that the device tends to become large in the surface direction of the surface to be inspected, as is apparent from FIG. It is in. Particularly, in the above-mentioned birch type, since members such as a converging lens 49a and a pinhole plate 49b are inserted between the second diffraction grating 48 and the screen 50, the second
There is a problem that the device becomes large due to the space for disposing the members outside the diffraction grating 48.

As an oblique incidence interferometer device which has a simple structure and can be made compact, for example, a structure as shown in FIG. 5 can be considered.

That is, in this oblique incidence interferometer device, the coherent light 54 is obliquely incident on the point 56a of the object 56 through the reference surface 52a of the reference plate 52 at the incident angle i. The reflected light (object light) specularly reflected on the surface 56a to be inspected is made incident vertically on the plane reflection mirror 58, and the object light reflected from this plane reflection mirror 58 is again incident on the point O on the surface 56a to be inspected at an incident angle i. The object light that is specularly reflected by the surface 56a to be inspected is incident on the reference plate.
The reference surface 52a of 52 is made to be incident again.

That is, in this apparatus, the forward path of the bundle of rays reaching the plane reflecting mirror 58 from the reference surface 52a via the surface 56a to be detected and the plane of reflection from the plane reflecting mirror 58 to the reference surface 52a via the surface 56a to be tested. Since the return path of the bundle of rays that overlaps with each other overlaps, when one ray of coherent light is considered, the exit position and the re-incident position on the reference surface 52a are the same position, and the reference surface 52a
In a, the reference light reflected to the light source side and the object light that interferes with this reference light are formed from the same light beam.

[0008]

However, in the apparatus described with reference to FIG. 5 described above, the coherent light 54 transmitted through the reference surface 52a is irradiated on the surface 56a to be inspected on the outward path and the return path. The light is in a state where it is modulated twice by the surface to be inspected. Especially, if the light incident positions on the surface to be inspected on the outward path and the return path are slightly different, the original fringes are generated from the interference fringes generated based on this object light. It becomes difficult to analyze the surface shape of the surface to be inspected 56a, and the measurement accuracy also decreases.

The present invention has been made in view of the above circumstances, and a first object thereof is that the surface shape of the surface to be inspected can be easily and accurately measured from the obtained interference fringes. An object is to provide a simple and compact grazing incidence interferometer device.

Depending on the size of the irregularities on the surface 56a to be tested, it may be necessary to change the incident angle i of the coherent light 54 to the surface 56a to be tested to change the measurement sensitivity. 5
In the apparatus shown in FIG. 1, the light output optical system and the reference plate 52a are rotated in the direction of arrow A about the incident point O of the surface 56a to be detected, and the plane reflection mirror is interlocked with this rotation operation.
It is also necessary to rotate 58 around the incident point O in the direction of arrow B, which complicates the device configuration and lowers measurement accuracy.

Therefore, a second object of the present invention is to simply configure the apparatus and prevent the measurement accuracy from deteriorating when the measurement sensitivity is changed by changing the incident angle of the coherent light on the surface to be measured. An object of the present invention is to provide a grazing incidence interferometer device.

Further, in recent years, it is possible to apply not only the size of the unevenness on the surface to be inspected but also the phase shift method (fringe scanning method) capable of easily determining whether it is concave or convex and analyzing the shape. An interferometer device is required.

Therefore, a third object of the present invention is to provide an oblique-incidence interferometer device which has a simple device configuration and to which the phase shift method can be applied.

[0014]

A first oblique incidence interferometer device of the present invention makes coherent light obliquely incident on a surface to be inspected of a subject through a reference surface of a reference plate, and the coherent light An oblique incidence interferometer device for forming an interference fringe formed on a predetermined screen by optical interference between object light generated by reflection on the surface to be inspected and reference light generated by reflection on the reference surface, It is characterized in that it is provided with a plane reflection mirror arranged so as to be perpendicular to the surface to be inspected so that the object light from is reflected and directly incident on the reference surface again.

The second oblique-incidence interferometer device of the present invention makes coherent light obliquely incident on the surface to be inspected of the object through the reference surface of the reference plate, and the coherent light to be inspected. In an oblique incidence interferometer device that forms an interference fringe generated by optical interference between an object light generated by reflection on a surface and a reference light generated by reflection on the reference surface, on a predetermined screen,
The coherent light transmitted through the reference surface is reflected and made incident on the surface to be inspected, and the reflected light from the surface to be inspected is arranged so as to be perpendicular to the surface to be inspected so as to re-enter the reference surface. It is characterized by having a flat reflecting mirror.

It is necessary that the coherent light has coherency such that interference fringes are formed on the screen even by the reference light and the object light generated by different light fluxes from the same light source. .

Further, a third oblique incidence interferometer device of the present invention is the first or second oblique incidence interferometer device, wherein the phase relationship between the object light and the reference light on the screen is It is characterized in that it is provided with a phase relationship changing means for changing.

Further, it is possible to use a means for changing the reference plate by a minute distance in the light incident direction of the reference plate.

Further, the plane reflecting mirror is arranged so that the object light or the coherent light from the surface to be inspected can be applied to the plane reflecting mirror in accordance with the incident angle of the coherent light to the surface to be inspected. It is also possible to make the mirror movable.

[0020]

According to the oblique incidence interferometer device of the present invention, the object light reflected from the surface to be inspected is made to re-enter the reference surface without being re-injected into the surface to be inspected. Since the coherent light that has passed through the reference surface is radiated only once on the surface to be inspected before returning to the reference surface, the object light returning to the reference surface and this object surface are reflected. The analysis of the interference fringes generated by the optical interference with the reference light shows that the coherent light is irradiated twice on the surface to be inspected,
It is not so difficult, and it is possible to prevent a decrease in measurement accuracy.

Further, in the apparatus of the present invention, the object light is returned in the direction of the reference plane by the reflection mirror, and the optical members other than this reflection mirror are arranged closer to the reference plate than the subject, and the reflection of the reflection member Since the mirror can be brought close to the subject, the width of the device in the plane direction of the test surface can be made smaller than that of the birch oblique incidence interferometer device, and the device can be made compact. Becomes

Further, according to the oblique incidence interferometer device of the present invention, the coherent light which has passed through the reference plane is made into a parallel light flux,
Further, the reflecting mirror is a plane reflecting mirror arranged substantially perpendicular to the surface to be inspected, and when the surface to be inspected is flat, the coherent light of the parallel ray bundle is the surface to be inspected and the surface to be inspected. The bundle of parallel rays that have been specularly reflected by the reflecting mirrors and that have finally passed through the reference surface and the bundle of parallel rays that re-enters this reference surface are parallel regardless of the incident angle of this bundle of parallel rays on the test surface. Thus, it is not necessary to adjust the optical system or the like each time the incident angle is changed, and highly accurate shape measurement can be performed by the object light and the reference light that are two parallel light fluxes parallel to each other.

In the device of the present invention, since the reference light beam and the object light beam generated by the different light fluxes from the same light source interfere with each other on the screen, a high light flux is used. Even if the exit position of the two rays on the reference surface and the re-incident position on the reference surface are different, there is no problem in forming interference fringes.

Furthermore, by providing means for varying the phase relationship between the object light and the reference light by a very small amount in such an apparatus structure, the phase shift method can be introduced with a simple structure.

As the phase relationship changing means, it suffices if the difference in optical path length between the object light and the reference light can be increased or decreased so that the interference fringes are shifted by about one stripe on the screen. It suffices that the reference plate be moved back and forth by a minute amount, and in this case, the reference plate can be slightly oscillated linearly, which facilitates the phase shift operation and increases the measurement accuracy.

Further, when the incident angle of the coherent light on the surface to be inspected is changed, the irradiation position of the object light on the above-mentioned plane reflection mirror is changed, so that the plane is changed according to this irradiation position. If the reflecting mirror is configured to be movable, the object light can always be re-incident on the reference surface even if the size of the plane reflecting mirror is reduced to about the beam diameter of the object light to be irradiated.

[0027]

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

FIG. 2 is a schematic view showing an oblique incidence interferometer device of the present invention. In this device, various optical systems of an interferometer, a monitor and the like are arranged on a vibration isolation table 1 so that the measurement result is not affected by external vibration or the like. The interferometer arranged on the vibration isolation table 1 includes a laser light source unit 3 and
The coherent light beam from the laser light source is used as a parallel light beam bundle, and an optical system 4 for inverting the emission direction of the parallel light beam bundle and a reference plate 5 having a reference plane for vertically injecting the parallel light beam bundle are U-shaped. The optical unit 2 incorporated in the optical unit 2 and the optical unit 2 so that the coherent light 6 is obliquely emitted from the optical unit 2.
A tilt stand 7 for holding the object 9 obliquely on the table, and a test surface position adjusting mechanism 8 for holding the test object 9 on the table of the vibration isolation table 1 and adjusting the tilt and height of the test surface of the test object 9. , Coherent light 6
The object light 12 which is the light reflected from the surface to be inspected is specularly reflected, and the object light 12 is re-incident on the reference surface of the reference plate 5 (and the coherent light 6 is reflected and incident on the surface to be inspected, The reflected light from the surface to be inspected is re-incident on the reference surface, a plane reflection mirror 11 arranged perpendicularly to the surface to be inspected, and this plane reflection mirror.
A mirror holder 10 for holding 11 on the table of the vibration isolation table 1, and an interference fringe formed by optical interference between the reference light, which is the reflected light from the reference surface, and the object light re-incident on the reference surface are imaged. C
A monitor 13 is provided for displaying an image of the interference fringes on the tube surface based on the video signal from the CD light receiving surface 14.

Further, in this apparatus, the incident angle of the coherent light 6 incident on the surface to be examined of the subject 9 can be changed by changing the fixing angle of the light source section 2 to the tilt stand 7. ing. That is, this tilt stand 7
The optical part fixing part 15 has a pair of inner and outer screw hole rows 16 whose center of curvature is the surface to be inspected of the subject 9, and after the optical part 2 is set at an appropriate angle, the optical part fixing part 15 The optical part 2 is sandwiched between the pressing member 17 and the pressing member 17 and can be screwed stepwise.

Instead of the screw hole row 16, a slit extending in the row direction is formed at the position of the screw hole row so that the optical portion 2 can be fixed at a continuous arbitrary angle. Good.

Next, the operation of the apparatus of this embodiment will be described with reference to FIG.

First, the coherent light 21 emitted from the laser light source 20 is made into a divergent ray bundle by the diverging lens 22 and the pinhole plate 23, and thereafter, the reflecting mirror 24 and the half mirror 29.
The direction is changed by the collimator lens 25, and the collimator lens 25 converts the light into parallel rays, which are then irradiated onto the reference surface 26a of the reference plate 26.

The reference surface 26a is a half mirror surface having a high plane accuracy, and transmits a part of the irradiated parallel ray bundle to generate the parallel ray bundle 31 (31a, 31b).
The remaining parallel light flux is reflected to generate the reference light 33 (33a, 33b).

The parallel ray bundle 31 from the reference surface 26a is irradiated onto the test surface 27a of the test object 27 having minute irregularities, is specularly reflected by the test surface 27a, and carries the object carrying the test surface information. Light 32 is generated.

Here, the surface to be inspected 27a is irradiated with a bundle of parallel rays 31a which passes through the reference surface 26a and is directly incident, and a bundle of parallel rays 31b which is incident via a plane reflecting mirror 28, which will be described later. Since the bundles 31a and 31b have the same action, the incident ray bundle 31a and the object light 32a generated thereby are mainly described.

The diagonal lines in FIG. 1 (A) indicate the path of the parallel ray bundle 31a passing through the reference surface 26a and directly incident on the surface 27a to be measured and the path of the object light 32a generated thereby, and also in FIG.
The shaded area in (B) passes through the reference surface 26a and is a plane reflection mirror.
A bundle of parallel rays incident on the surface 27a after being reflected by 28.
31b and the path of the object light 32b generated thereby are respectively shown.

Since the object light 32a is specularly reflected by the plane reflection mirror 28 arranged perpendicularly to the surface 27a to be inspected, it becomes parallel to the bundle of parallel rays 31 from the reference surface 26a and is reflected by the reference surface 26a. Re-inject.

After that, the reference light 33b and the object light 32a pass through the half mirror 29, and the interference fringes formed by the optical interference between the two are imaged on the CCD light receiving surface 30b. The reference light 33a and the object light 32b pass through the half mirror 29, and the interference fringes formed by the optical interference between the two are reflected by the CCD light receiving surface 30b.
Imaged above.

The interference fringe image formed on the CCD light receiving surface 30b is converted into a video signal and displayed on the monitor 13. The same applies to the interference fringe image formed on the CCD light receiving surface 30a.

The interference fringes formed on the light-receiving surface 30a and the light-receiving surface 30b are line-symmetrical to each other, so that two interference-fringe images which are line-symmetrical to each other are displayed on the monitor 13.

The laser light source 1 emits light with high coherence. In this embodiment, the laser light source 1 has a helium neon (He-Ne) laser light source (wavelength 632.8n) with an output of 3 mW.
m) is used.

The reference plate 26 is formed of a quartz glass plate having a reference surface 26a having extremely high flatness.

Further, the plane reflection mirror 28 is constructed by depositing a reflection film on a quartz glass surface having a high degree of flatness.

Further, the reference light 33 and the object light 32 are constructed such that they partially overlap each other on the CCD light receiving surface 30,
Interference fringes are formed in a portion where the two overlap.

According to the apparatus of the embodiment thus constructed, the plane reflection mirror 28 is arranged so as to be perpendicular to the plane surface 27a to be inspected. The object light 32 re-incident on the reference surface 26a is formed so as to be always parallel to the parallel ray bundle 31 of.

That is, even when the incident angle of the parallel light bundle 31 is i'as shown in FIG. 3 (A), and when the incident angle is larger i "as shown in FIG. 3 (B). Even in some cases, the parallel relationship between the parallel ray bundle 31 and the object light 32 is maintained regardless of the value of the incident angle.

This makes it possible to maintain good measurement accuracy even when the incident angle of the parallel light bundle 31 on the surface 27a to be measured is changed in order to change the photometric sensitivity of the device.

The surface to be tested 27a in the apparatus of the above embodiment is
The phase shift method (fringe scanning method) is applied to determine whether a concave portion or a convex portion is formed on the surface of the. The phase shift method (fringe scanning method) is used for not only one interference fringe image but also reference light.
A plurality of interference fringe images are obtained while the phases of 33 and the object light 32 are shifted by 1 pitch from each other, and a phase calculation is performed by a computer based on the brightness of each point in the image at that time to determine the uneven shape on the surface 26a to be inspected. It is a calculation.

In applying this phase shift method (fringe scanning method), as described above, the reference beam 33 is used.
It is necessary to shift the phases of the object light 32 and the object light 32 from each other.
In order to shift the phase, the reference plate 26 may be vibrated by a minute distance in the light incident direction with respect to the reference surface 26a.

Further, in order to vibrate the reference plate 26 by a minute distance, an actuator such as a piezoelectric element capable of minutely changing the position of the member is used.

Further, instead of physically changing these members, a phase shift optical element such as a phase shifter is inserted in the optical path to change the phase difference between the reference light 33 and the object light 32. Good.

If the incident angle of the parallel light flux 31 on the surface 27a to be measured is set to be smaller than that shown in FIG. 3A, the object light 32 from the surface 27a to be measured is plane reflected. mirror
There is a risk of passing above 28. In such a case, if the plane reflecting mirror 28 can be slid up and down (mirror surface direction) or left and right (perpendicular to the mirror surface), the plane reflecting mirror 28 has a large diameter. It is possible to reflect the object light 32 in the direction of the reference plane 26a without doing so.

The movement of the plane reflecting mirror 28 is performed by, for example, engaging the plane reflecting mirror 28 with a rail and changing the movement of the plane reflecting mirror 28 on the rail by changing the incident angle, for example, an optical section. It may be performed according to the angle change of 2.

The oblique incidence interferometer device of the present invention is not limited to that of the above embodiment, and various other modifications can be made.

For example, in the above embodiment, the example of the helium neon (He-Ne) laser was shown as the laser light source, but it is not always necessary to use a gas laser light source such as a helium neon (Ne-He) laser light source. In the case of the device of the present invention, since the re-incident position of one light beam on the reference surface and the exit position of this light beam on the reference surface are not the same, light having high spatial coherence can be obtained to some extent. It is necessary to use a light source that emits light.

Although the CCD light receiving surface is used as the screen for forming the interference fringes in the above embodiment, an optical screen that can be visually recognized by the operator can be used instead.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main part of an oblique incidence interferometer device according to an embodiment of the present invention.

FIG. 2 is a schematic view showing an entire oblique incidence interferometer device according to an embodiment of the present invention.

FIG. 3 is a schematic view for explaining the operation of the embodiment apparatus shown in FIG.

FIG. 4 is a schematic diagram showing a grazing incidence interferometer device according to the prior art.

FIG. 5 is a schematic view showing an oblique incidence interferometer device according to another prior art.

[Explanation of symbols]

1 Vibration isolation table 2 Optics 3,20 laser light source 5,26 Reference plate 9,27 subject 11,28 Plane reflection mirror 12, 32 object light 13 monitor 26a Reference plane 27a Test surface 30 CCD light receiving surface 31 parallel ray bundle 33 Reference light

Claims (5)

(57) [Claims] 1. Coherent light is obliquely incident on a surface to be inspected of a subject through a reference surface of a reference plate, and the coherent light is reflected by the surface to be inspected. In an oblique incidence interferometer device that forms interference fringes generated by optical interference with reference light generated by reflection on a predetermined screen, the object light from the surface to be inspected is reflected and directly incident on the reference surface again. An oblique incidence interferometer device, comprising a plane reflection mirror arranged so as to be perpendicular to the surface to be inspected. 2. Coherent light is obliquely incident on a surface to be inspected of a subject through a reference surface of a reference plate, and the coherent light is reflected by the surface to be inspected and the object light and the reference surface are generated. In an oblique incidence interferometer device that forms an interference fringe caused by light interference with the reference light generated by reflection on a predetermined screen, the coherent light that has passed through the reference surface is reflected and incident on the surface to be inspected, An oblique incidence interferometer device comprising a plane reflection mirror arranged so as to be perpendicular to the surface to be inspected so that the reflected light from the surface to be inspected is re-incident on the reference surface. 3. The oblique incidence interferometer apparatus according to claim 1, further comprising a phase relationship changing means for changing the phase relationship between the object light and the reference light on the screen. 4. The oblique incidence interferometer apparatus according to claim 3, wherein the phase relationship changing means is means for minutely changing the phase of the coherent light reflected from the reference surface. 5. The plane reflection so that the object light from the surface to be inspected or the coherent light can be irradiated to the plane reflection mirror according to a change in an incident angle of the coherent light on the surface to be inspected. The oblique incidence interferometer device according to any one of claims 1 to 4, wherein the mirror is configured to be movable.