JP5432680B2 - Oblique incidence interferometer - Google Patents

Description

  The present invention relates to an oblique incidence interferometer.

Conventionally, a laser light source that emits laser light, a separation unit that separates the laser light into reference light and measurement light, and that emits measurement light obliquely with respect to the measurement surface, and the reference light and measurement surface There is known an oblique incidence interferometer that includes a combining unit that combines reflected measurement light to form interference light, and measures the shape of the surface to be measured based on the interference light (see, for example, Patent Document 1). .
The oblique incidence interferometer described in Patent Document 1 includes a laser (laser light source) and two diffraction gratings (separation means and synthesis means), and analyzes the interference fringes based on the interference light to thereby measure the surface to be measured. The shape is being measured.

  In such an oblique incidence interferometer, the interference fringe sensitivity Λ / 2, which is the difference in height between adjacent fringes in the interference fringes, is expressed by the wavelength λ of the laser light as shown in the following equation (1): It is determined based on the incident angle θ of the measurement light with respect to the surface to be measured.

  That is, in such an oblique incidence interferometer, when changing the interference fringe sensitivity Λ / 2, it is necessary to change at least one of the wavelength λ of the laser light and the incident angle θ of the measurement light with respect to the measured surface. Cost.

FIG. 6 is a schematic diagram showing an example of an oblique incidence interferometer that can change the incident angle θ. In FIG. 6, the optical path in the oblique incidence interferometer is indicated by a solid line.
The oblique incidence interferometer 100 includes a laser light source 110, a separating unit 120, and a combining unit 130, and measures the measurement surface W.

The separating unit 120 includes a beam splitter 121 disposed in the downstream of the optical path of the laser light emitted from the laser light source 110, a beam splitter 121, and a mirror 122 disposed between the measurement target surface W.
The beam splitter 121 has a function of separating laser light emitted from the laser light source 110 into reference light and measurement light. Specifically, the beam splitter 121 separates the laser light by reflecting a part of the laser light as reference light and transmitting the other as measurement light.
The mirror 122 reflects the measurement light separated by the beam splitter 121 and emits it obliquely with respect to the measured surface W.

The synthesizing unit 130 includes a mirror 131 and a beam splitter 132 that are arranged in the latter stage of the optical path of the measurement light reflected by the measurement surface W.
The mirror 131 reflects the measurement light reflected by the surface to be measured W so as to enter the beam splitter 132.
The beam splitter 132 combines the reference light separated by the beam splitter 121 and the measurement light reflected by the mirror 131 into interference light. Specifically, the beam splitter 132 reflects a part of the reference light separated by the beam splitter 121 and transmits a part of the measurement light reflected by the mirror 131 to combine it with the interference light. To do.

  Further, the oblique incidence interferometer 100 includes a rotation mechanism (not shown) that rotates the mirrors 122 and 131 about the axis perpendicular to the paper surface in FIG. The oblique incidence interferometer 100 can change the incident angle θ by rotating the mirrors 122 and 131 by a rotating mechanism, and can change the interference fringe sensitivity Λ / 2.

JP-A-4-221704

However, when the interference fringe sensitivity Λ / 2 is changed by mechanically changing the incident angle θ as in the case of the oblique incidence interferometer 100 described above, there is a problem that a very advanced technique is required.
In addition, a general-purpose tunable laser light source that can change the wavelength of the laser light is adopted as the laser light source, and the interference fringe sensitivity Λ / 2 is changed by changing the wavelength λ of the laser light emitted from the tunable laser light source. It is also possible. However, in an oblique incidence interferometer in which the incident angle θ is set to be close to 90 °, the change in the interference fringe sensitivity Λ / 2 with respect to the change in the wavelength λ is linear. The effect on Λ / 2 is much smaller than when the incident angle θ is changed. Therefore, when the interference fringe sensitivity Λ / 2 is changed by changing the wavelength λ, there is a problem that an expensive laser light source capable of changing the wavelength λ within a large range is required.

  An object of the present invention is to provide an oblique incidence interferometer capable of changing the interference fringe sensitivity without requiring an advanced technique or an expensive laser light source.

An oblique incidence interferometer according to the present invention includes a laser light source that emits laser light, and a separating unit that separates the laser light into reference light and measurement light, and emits the measurement light obliquely with respect to a surface to be measured. And oblique incidence interference for measuring the shape of the surface to be measured based on the interference light, and combining means for combining the reference light and the measurement light reflected by the surface to be measured into interference light A first reflecting mirror that is disposed between the separating unit and the surface to be measured and reflects the measurement light, and is disposed between the surface to be measured and the combining unit; A second reflecting mirror that reflects the measurement light, wherein the laser light source is a wavelength tunable laser light source capable of changing a wavelength of the laser light, and the separating unit is configured to change the measurement light according to the wavelength of the laser light. The emission angle is changed.

  According to such a configuration, the separating unit can change the emission angle of the measurement light by changing the wavelength of the laser light emitted from the wavelength tunable laser light source, and consequently the measurement light with respect to the surface to be measured. The incident angle can be changed. Therefore, the oblique incidence interferometer can change the interference fringe sensitivity without requiring an advanced technique or an expensive laser light source.

In the present invention, as described above, the first reflecting mirror that is disposed between the separating unit and the surface to be measured and reflects the measurement light, the surface to be measured, and the combining unit is disposed. is set, characterized in that it comprises a second reflecting mirror for reflecting the measurement light.

Here, when the separating means and the synthesizing means are configured so that the incident angle becomes smaller as the wavelength of the laser light becomes longer and the incident angle becomes larger as the wavelength of the laser light becomes shorter, the above equation (1) is used. As shown, since the increase and decrease of the wavelength of the laser beam and the incident angle work to cancel each other with respect to the interference fringe sensitivity, there is a problem that the efficiency of changing the interference fringe sensitivity is lowered.
According to the present invention, the oblique incidence interferometer includes the first reflecting mirror and the second reflecting mirror. Even in such a case, the incident angle increases as the wavelength of the laser light increases, and the laser light As the wavelength of becomes shorter, the incident angle becomes smaller. Therefore, the oblique incidence interferometer can efficiently change the interference fringe sensitivity.

  In the present invention, the separating means and the synthesizing means are preferably diffraction gratings.

  According to such a configuration, since the diffraction angle of the diffracted light in the diffraction grating changes according to the wavelength of the laser light incident on the diffraction grating, the specularly reflected light in the diffraction grating is used as the reference light, and the diffracted light is used as the measurement light. By doing so, the separating means and the synthesizing means can be configured. Therefore, since the separating means and the combining means can be configured by one optical element, the number of parts of the oblique incidence interferometer can be reduced and the oblique incidence interferometer can be miniaturized.

In the present invention, the separating means, first emitting a first beam splitter for separating the laser beam, the measurement light separated by the first beam splitter obliquely with respect to the surface to be measured e Bei a prism, said combining means, said a second prism and a second beam splitter disposed on the optical path downstream of the measuring light reflected by the measurement surface, the second prism Emits the measurement light to the second beam splitter side, and the second beam splitter is emitted from the reference light separated by the first beam splitter and the second prism. It is preferable that the measurement light is combined and emitted as interference light .

  According to such a configuration, the same operational effects as the oblique incidence interferometer described above can be obtained.

The schematic diagram which shows the oblique incidence interferometer which concerns on 1st Embodiment of this invention. The schematic diagram which shows the oblique incidence interferometer which concerns on 2nd Embodiment of this invention. The enlarged schematic diagram which shows the 1st diffraction grating, the 1st reflective mirror, and the to-be-measured surface in the said embodiment. The schematic diagram which shows the oblique incidence interferometer which concerns on 3rd Embodiment of this invention. The schematic diagram which shows the oblique incidence interferometer which concerns on 4th Embodiment of this invention. The schematic diagram which shows an example of the oblique incidence interferometer which can change an incident angle.

[First Embodiment]
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an oblique incidence interferometer 1 according to the first embodiment of the present invention. In FIG. 1, the optical path in the oblique incidence interferometer 1 is shown by a solid line. The same applies to the following drawings.
As shown in FIG. 1, the oblique incidence interferometer 1 includes a laser light source 2, a first diffraction grating 3, and a second diffraction grating 4, and measures a surface to be measured W.
The laser light source 2 emits laser light, and is composed of a wavelength tunable laser light source that can change the wavelength of the emitted laser light.

  The first diffraction grating 3 as the separating means is formed of a reflection type diffraction grating, and is disposed in the latter stage of the optical path of the laser light emitted from the laser light source 2, and the laser light emitted from the laser light source 2 is referred to as reference light, And has a function of emitting the measurement light obliquely with respect to the surface W to be measured. Specifically, the first diffraction grating 3 uses specularly reflected light (light passing through the upper optical path in FIG. 1) as reference light and diffracted light (light passing through the lower optical path in FIG. 1) as measurement light. It is arranged like this.

  Here, the diffraction angle of the diffracted light in the first diffraction grating 3 changes according to the wavelength of the laser light incident on the first diffraction grating 3. Specifically, in the present embodiment, the first diffraction grating 3 increases the diffraction angle when the wavelength of the laser beam is increased (arrow A in FIG. 1), and decreases the diffraction angle when the wavelength of the laser beam is decreased (FIG. 1). 1 arrow B). That is, the first diffraction grating 3 changes the emission angle of the measurement light according to the wavelength of the laser light. Therefore, the incident angle θ decreases as the wavelength of the laser light increases, and the incident angle θ increases as the wavelength of the laser light decreases.

  The second diffraction grating 4 as the combining means is arranged in the latter stage of the optical path of the measurement light reflected by the measurement surface W, and is separated from the reference light separated by the first diffraction grating 3 and the measurement surface W. It has the function of combining reflected measurement light into interference light. Specifically, the second diffraction grating 4 has the same configuration as the first diffraction grating 3 and is arranged so that the specularly reflected light is the reference light and the diffracted light is the measurement light.

  Laser light emitted from the laser light source 2 is separated into reference light and measurement light by the first diffraction grating 3. The reference light separated by the first diffraction grating 3 is incident on the second diffraction grating 4. The measurement light separated by the first diffraction grating 3 is emitted obliquely with respect to the measurement surface W, reflected by the measurement surface W, and incident on the second diffraction grating 4. The reference light and the measurement light incident on the second diffraction grating 4 are combined by the second diffraction grating 4 and become interference light. The oblique incidence interferometer 1 measures the shape of the measurement target surface W by analyzing the interference fringes based on the interference light.

According to this embodiment, there are the following effects.
(1) The first diffraction grating 3 can change the emission angle of the measurement light by changing the wavelength of the laser light emitted from the laser light source 2, and thus the incident angle of the measurement light with respect to the measured surface W θ can be changed. Therefore, the oblique incidence interferometer 1 can change the interference fringe sensitivity without requiring an advanced technique or an expensive laser light source.
(2) The separating means and the synthesizing means are a first diffraction grating and a second diffraction grating. Accordingly, since the separating means and the combining means can be configured by one optical element, the number of parts of the oblique incidence interferometer 1 can be reduced and the oblique incidence interferometer 1 can be miniaturized. .

[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. In the following description, parts that have already been described are assigned the same reference numerals and description thereof is omitted.
FIG. 2 is a schematic diagram showing an oblique incidence interferometer 1A according to the second embodiment of the present invention.
In the present embodiment, the oblique incidence interferometer 1A is arranged between the first diffraction grating 3 and the surface to be measured W as shown in FIG. A first reflecting mirror 5 that reflects and a second reflecting mirror that is disposed between the surface to be measured W and the second diffraction grating 4 and reflects the measurement light reflected by the surface to be measured W is provided. This is different from the first embodiment.

FIG. 3 is an enlarged schematic view showing the first diffraction grating 3, the first reflecting mirror 5, and the surface to be measured W. In FIG. 3, the shapes of the first diffraction grating 3 and the surface to be measured W are simplified for the sake of explanation.
As shown in FIG. 3, the angle of the normal line on the diffraction surface of the first diffraction grating 3 with respect to the normal line of the surface to be measured W is a, and the angle of the normal line on the reflection surface of the first reflecting mirror 5 is b. The incident angle of the laser beam with respect to the first diffraction grating 3 is α, and the diffraction angle of the diffracted light at the first diffraction grating 3 is β. In FIG. 3, the laser light is incident on the first diffraction grating 3 so that the incident angle α = angle a. In this case, the incident angle θ of the measurement light with respect to the measured surface W is represented by an angle b, an incident angle α, and a diffraction angle β as shown in the following formula (2).

  The diffraction angle β is represented by the incident angle α, the wavelength λ of the laser light, and the pitch d of the first diffraction grating 3 as shown in the following formula (3).

  Here, as described above, the first diffraction grating 3 increases the diffraction angle β when the wavelength of the laser beam is increased, and decreases the diffraction angle β when the wavelength of the laser beam is decreased. Therefore, as shown in Equation (2) described above, the incident angle θ increases as the wavelength of the laser light increases, and the incident angle θ decreases as the wavelength of the laser light decreases. That is, the oblique incidence interferometer 1A includes the first reflecting mirror 5 and the second reflecting mirror 6, thereby reversing the relationship between the wavelength λ of the laser light and the incident angle θ.

In this embodiment as well, the same operations and effects as those of the first embodiment can be achieved, and the following operations and effects can be achieved.
(3) Since the oblique incident interferometer 1A includes the first reflecting mirror 5 and the second reflecting mirror 6, the incident angle θ decreases as the wavelength of the laser light increases, and the incident angle θ decreases as the wavelength of the laser light decreases. Even when the separating means and the synthesizing means are configured so as to increase, the incident angle θ increases as the wavelength of the laser light increases, and the incident angle θ decreases as the wavelength of the laser light decreases. Therefore, the oblique incidence interferometer 1A can efficiently change the interference fringe sensitivity.

[Third Embodiment]
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.
FIG. 4 is a schematic diagram showing an oblique incidence interferometer 1B according to the third embodiment of the present invention.
In the second embodiment, the oblique incidence interferometer 1A includes the reflective first diffraction grating 3 and the second diffraction grating 4 as the separating means and the synthesizing means. On the other hand, in the present embodiment, the oblique incidence interferometer 1B includes a transmission type first diffraction grating 3A and a second diffraction grating 4A as separation means and synthesis means, as shown in FIG. It is different in point.

  The first diffraction grating 3A is composed of a transmissive diffraction grating, and is disposed in the latter stage of the optical path of the laser light emitted from the laser light source 2, and the laser light emitted from the laser light source 2 is used as reference light and measurement light. While separating, it has the function to radiate | emit measurement light with respect to the to-be-measured surface W diagonally. Specifically, the first diffraction grating 3 uses transmitted light (light passing through the upper optical path in FIG. 4) as reference light and diffracted light (light passing through the lower optical path in FIG. 4) as measurement light. It is arranged.

  The second diffraction grating 4A is disposed downstream of the optical path of the measurement light reflected by the measurement surface W, and the reference light separated by the first diffraction grating 3A and the measurement reflected by the measurement surface W. It has the function of combining light into interference light. Specifically, the second diffraction grating 4A has the same configuration as the first diffraction grating 3A, and is arranged so that the transmitted light is the reference light and the diffracted light is the measurement light.

  In this embodiment, the same operations and effects as those of the second embodiment can be achieved.

[Fourth Embodiment]
Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings.
FIG. 5 is a schematic diagram showing an oblique incidence interferometer 1C according to the fourth embodiment of the present invention.
In the second embodiment, the oblique incidence interferometer 1A includes the first diffraction grating 3 and the second diffraction grating 4 as the separating means and the synthesizing means. On the other hand, in this embodiment, the oblique incidence interferometer 1C is different in that it includes a separating unit 7 and a combining unit 8 as shown in FIG.

The separating means 7 includes a beam splitter 71 disposed in the latter stage of the optical path of the laser light emitted from the laser light source 2, a beam splitter 71, and a prism 72 disposed between the measured surface W.
The beam splitter 71 has a function of separating laser light emitted from the laser light source 2 into reference light and measurement light. Specifically, the beam splitter 71 separates the laser light by reflecting a part of the laser light as reference light and transmitting the other as measurement light.
The prism 72 is formed in a triangular prism shape and radiates the measurement light separated by the beam splitter 71 obliquely with respect to the measured surface W.

The synthesizing unit 8 includes a prism 81 and a beam splitter 82 that are arranged in the latter stage of the optical path of the measurement light reflected by the measurement surface W.
The prism 81 is formed in a triangular prism shape, and refracts the measurement light reflected by the surface to be measured W so as to enter the beam splitter 82.
The beam splitter 82 has a function of combining the reference light separated by the beam splitter 71 and the measurement light refracted by the prism 81 into interference light. Specifically, the beam splitter 82 reflects a part of the reference light separated by the beam splitter 71 and transmits a part of the measurement light refracted by the prism 81 to combine it with the interference light. To do.

  In this embodiment, the same operations and effects as those of the second embodiment can be achieved.

[Modification of Embodiment]
Note that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope in which the object of the present invention can be achieved are included in the present invention.
For example, in each of the above-described embodiments, the separating unit and the synthesizing unit are configured such that the incident angle θ decreases as the wavelength of the laser light increases, and the incident angle θ increases as the wavelength of the laser light decreases. On the other hand, the separating means and the combining means may be configured such that the incident angle increases as the wavelength of the laser light increases, and the incident angle decreases as the wavelength of the laser light decreases. In this case, the oblique incidence interferometer can efficiently change the interference fringe sensitivity without including the first reflecting mirror and the second reflecting mirror.
In each of the embodiments, the separating unit and the combining unit are configured by a diffraction grating, a beam splitter, and a prism, but may be configured by any optical element.

  The present invention can be suitably used for an oblique incidence interferometer.

1, 1A, 1B, 1C ... oblique incidence interferometer 2 ... laser light sources 3 and 3A ... first diffraction grating (separating means)
4, 4A ... Second diffraction grating (synthesizing means)
5 ... 1st reflecting mirror 6 ... 2nd reflecting mirror 7 ... Separation means 8 ... Composition means

Claims (3)

A laser light source that emits laser light; a separation unit that separates the laser light into reference light and measurement light; and that emits the measurement light obliquely with respect to a surface to be measured; the reference light; and the measured light A grazing incidence interferometer for measuring the shape of the surface to be measured based on the interference light, comprising combining means for combining the measurement light reflected by a surface to form interference light,
A first reflecting mirror disposed between the separating means and the surface to be measured and reflecting the measurement light;
A second reflecting mirror disposed between the surface to be measured and the combining means and reflecting the measurement light;
The laser light source is a tunable laser light source capable of changing the wavelength of the laser light,
The oblique incidence interferometer characterized in that the separating means changes an emission angle of the measurement light according to a wavelength of the laser light. The grazing incidence interferometer according to claim 1 ,
The oblique incidence interferometer, wherein the separating unit and the combining unit are diffraction gratings. The grazing incidence interferometer according to claim 1 ,
The separating means includes
A first beam splitter for separating the laser beam;
E Bei a first prism for emitting obliquely the measurement light separated by the first beam splitter to the measurement surface,
The synthesis means includes
A second prism and a second beam splitter disposed in the latter stage of the optical path of the measurement light reflected by the measurement surface;
The second prism emits the measurement light to the second beam splitter side,
The second beam splitter synthesizes the reference light separated by the first beam splitter and the measurement light emitted from the second prism and emits them as the interference light. Oblique incidence interferometer.

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