JP3340824B2 - Optical system including total reflection prism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system including a total reflection prism used for changing a distance between two objective lenses of a photomask inspection apparatus while keeping a light receiving side fixed.

[0002]

2. Description of the Related Art In a photomask inspection apparatus for inspecting a defect of a photomask having a predetermined pattern, light is irradiated to mutually corresponding regions of the photomask through two objective lenses, and the reflected light or the transmitted light is transmitted. Defects are detected by calculating a difference between signals obtained from light. In such a photomask defect inspection apparatus, the interval between the two objective lenses can be changed while the light receiving side is fixed so that the same portion of the object can be simultaneously detected.

FIG. 5 is a schematic configuration diagram of a conventional optical system including a total reflection prism. In the optical system including the total reflection prism, a first parallelogram total reflection prism 1 is provided with a second parallelogram total reflection prism 2, and a third parallelogram total reflection prism 3 is provided with a fourth parallelogram. The first and third total reflection prisms 1 and 3 are arranged such that the first and third total reflection prisms 1 and 3 are centered on the optical axis of light incident on the third total reflection prism from the first total reflection prism. To rotate mutually. Using the optical system including such a total reflection prism, the distance between the optical axes of the two objective lenses can be changed.

In recent years, lasers emitting linearly polarized light have been used as irradiation light sources. However, when the above-described optical system is used, there is a problem that the rotation of a total reflection prism or the like affects the polarization characteristics. It has become. That is, when linearly polarized light is incident on the total reflection surface, the phase difference between the P-polarized light component and the S-polarized light component on one total reflection surface is determined by the angle of incidence on the surface and the refractive index. When the reflection surface rotates around the axis, the ratio of the amplitude of the P-polarized light component to the amplitude of the S-polarized light component changes. Changes between polarizations. FIG. 6 is a schematic configuration diagram of an optical system in which two parallelogram total reflection prisms 1 and 3 in FIG. 5 are combined.
As shown in FIG. 6, when the optical system in which two parallelogram prisms are combined is relatively rotated about the axis G , the polarization characteristics of the axes F and G are not the same. In order to eliminate such inconveniences, in the optical system shown in FIG. 5, the first and third total reflection prisms 1 and 3 are respectively coupled to the second and fourth total reflection prisms so that the PS polarization component To cancel the phase difference.

[0005]

However, in an optical system including a total reflection prism as shown in FIG. 5, it is necessary to use as many as four total reflection prisms. There is a disadvantage that the resolution is reduced due to integration. In addition, desired optical characteristics due to various problems such as deviation of incident light and outgoing light due to an error of adjustment of mechanical dimensions such as an offset amount of an optical axis, a twist when bonding a total reflection prism, and the like. There is a disadvantage that can not be obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to accurately and simply equalize the polarization characteristics of incident light and outgoing light of a total reflection prism without causing the above-mentioned problems, and as a result, to obtain desired optical characteristics. It is an object of the present invention to provide an optical system including a total reflection prism capable of obtaining the following.

[0007]

SUMMARY OF THE INVENTION An optical system including a total reflection prism according to the present invention has an entrance surface and an exit surface parallel to each other,
And having at least one total reflection surface, configured to rotate about an input optical axis passing through the incident surface or an output optical axis passing through the output surface, and between the P component and the S component of the incident linearly polarized light. A total reflection prism that introduces a phase difference of 90 °, a quarter-wave plate disposed opposite the entrance surface or the emission surface of the total reflection prism, and a direction of the crystal axis of the quarter-wave plate. The direction with respect to the total reflection surface of the total reflection prism is defined as P
Adjusted so that the phase difference between the component and the S component becomes zero, so that the polarization characteristics do not change when the total reflection prism rotates about the incident optical axis or the output optical axis. Means for setting a relative position between the total reflection surface and the quarter-wave plate.

Further, the optical system including the total reflection prism of the present invention has an entrance surface and an exit surface parallel to each other, and first and second total reflection surfaces parallel to each other.
A first parallelogram total reflection prism that introduces a phase difference of 90 ° between the component and the S component, an input surface and an output surface that are parallel to each other, and first and second total reflection surfaces that are parallel to each other. A second parallelogram total reflection prism for introducing a phase difference of 90 ° between the P component and the S component of the incident linearly polarized light; and a second parallelogram total reflection prism facing the incident surface of the first total reflection prism. A first quarter-wave plate, and a second quarter-wave plate disposed opposite to the emission surface of the second total reflection prism. 1 total reflection surface and 1 /
The direction of the crystal axis of the four-wave plate, the direction of the crystal axis of the second total reflection surface of the second total reflection prism, and the direction of the crystal axis of the second quarter-wave plate are determined between the P component and the S component of the output linearly polarized light. Is adjusted to be zero, and the optical axis between the second total reflection surface and the exit surface of the first total reflection prism, the entrance surface of the second total reflection prism, and the first The first total reflection prism and the first 1 /
A four-wave plate can be integrated to rotate around the optical axis.
And the second total reflection prism and
The second quarter-wave plate is integrated with the optical axis as a center.
It is characterized in that it is configured to be able to rotate mutually .

[0009]

In an optical system including a total reflection prism of the present invention, when a total reflection prism that gives a phase difference of 90 ° between the P component and the S component of linearly polarized light is used, the linearly polarized light is applied to the total reflection prism. When incident, circularly polarized light or elliptically polarized light is emitted as described above, and conversely, when circularly polarized light or elliptically polarized light is incident, linearly polarized light is emitted. The quarter-wave plate also has a similar function. Therefore, the total reflection prism and 1/4
The phase difference between the P component and the S component can be reduced to zero by adjusting the direction of the total reflection surface and the direction of the crystal axis of the quarter-wave plate in combination with the Can be made equal in polarization characteristics. That is, when linearly polarized light is incident, linearly polarized light having the same polarization plane can be emitted.

In addition, in the present technology, one total reflection prism can be manufactured with sufficient mechanical precision, so that the use of a large number of reflection surfaces as described above causes a decrease in resolution, an offset amount of the optical axis, and a total amount of offset. The problem of adjusting mechanical dimensions such as torsion when attaching the reflecting prism is eliminated, so that the polarization characteristics of the outgoing light can be accurately and easily matched with the polarization characteristics of the incident light, and an optical system with good optical characteristics Can be realized.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical system including a total reflection prism according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic structural view of an optical system including a total reflection prism according to a first embodiment of the present invention. In FIG. 1, an optical system including a total reflection prism includes a parallelogram total reflection prism 11 for introducing a phase difference of 90 ° between the P component and the S component of linearly polarized light, and an incident surface 12 of the total reflection prism. And a quarter-wave plate 13 arranged opposite to the first. In this example, the total reflection prism 11 is, for example,
This is for a He-Ne laser (wavelength 632.8 nm) and uses LLF1 as a glass material.
An antireflection film of 632.8 nm is formed. The angle θ ₁ between the entrance surface 12 and the first reflection surface 14 and the exit surface 15
The angle θ ₂ with the reflecting surface 16 is set to 45.54 ± 0.03 °. In the present invention, in order to cancel the phase difference introduced by the total reflection prism 11, a quarter-wave plate 13 is provided, and its crystal axis is adjusted with respect to the directions of the total reflection surfaces 14, 16. .

In the optical system of this embodiment, the total reflection prism 1
The relative position between the 1/4 wavelength plate 13 and the 1/4 wavelength plate 13 can be adjusted by various methods. First, a basic adjustment method will be described. First, the crystal axis of the quarter-wave plate 13 is adjusted to be inclined by 45 ° with respect to the polarization direction of the incident laser light 17 that has been linearly polarized. For this purpose, it is preferable to provide a mechanism for supporting the quarter-wave plate 13 rotatably in the plane thereof. With this adjustment, the linearly polarized laser beam 17 becomes 1 /
The light is converted into circularly polarized light by the four-wavelength plate 13 and emitted. This circularly polarized light is incident on the incident surface 1 of the total reflection prism 11.
2 to the first total reflection surface 14 and then to the second
Is reflected by the total reflection surface 16 and exits from the exit surface 15.
This total reflection prism has an effect of generating a phase difference of 90 ° between the P-polarized light and the S-polarized light as described above. However, when linearly polarized light is incident, the incident surface and the total reflection surface Circularly polarized light or elliptically polarized light is emitted depending on the relative positional relationship of. Therefore, in this example, the total reflection prism 1 is used to convert incident circularly polarized light into linearly polarized light.
Adjust 1 With this adjustment, the linearly polarized incident laser light 17 passes through the quarter-wave plate 13 and the total reflection prism 11, so that the phase difference between the P component and the S component becomes zero and the amplitude becomes zero. Are emitted from the exit surface 15 of the total reflection prism 11 as linearly polarized light having the same polarization characteristics as the incident laser light 17.

Another example of the method for adjusting the optical system according to the present invention will be described. In this example, first, after fixing the position of the incident surface 14 of the total reflection prism 11, linearly polarized light is made incident, and the / 4 wavelength plate 1 is made to emit linearly polarized light from the total reflection prism.
Adjust the rotation of 3 and fix it. With this adjustment, linearly polarized light is always emitted regardless of how the optical system is set for incident linearly polarized light unless the relative positions of the total reflection prism 11 and the quarter-wave plate 13 are changed. Become. Therefore, even if the optical system is rotated about the incident optical axis A, the polarization characteristics do not change.

As described above, according to the present invention, the polarization characteristics introduced by the total reflection prism 11 can be adjusted by adjusting the total reflection prism 11 and the quarter-wave plate 13 or the quarter-wave plate. The opposite polarization characteristic can be canceled out by generating the same in the quarter-wave plate 13, and the polarization characteristic of the outgoing light can be made equal to the polarization characteristic of the incident light. In this case, the total reflection prism 11 and / or 1 /
The adjustment of the four-wavelength plate 13 can be made much easier and more accurate than in the case of using a conventional total reflection prism.

FIG. 2 is a schematic structural view of an optical system including a total reflection prism according to a second embodiment of the present invention. In the embodiment shown in FIG. 1, the linearly polarized light is made incident on the quarter-wave plate 13 and then made incident on the total reflection prism 11. In this example, however, this relationship is reversed, and the linearly polarized light is first made incident on the total reflection prism 21. After being incident, it is incident on the quarter-wave plate 22. In this example, the incident linearly polarized light is converted by the total reflection prism 21 into circularly polarized light or linearly polarized light.
Since the light is returned to the linearly polarized light by 2, the polarization characteristic of the outgoing light can be made to match the polarization characteristic of the incident light as in the previous example. Also in this example, even if the total reflection prism 21 and the quarter-wave plate 22 are rotated together about the output optical axis B, the polarization characteristics of the output light are not affected.

FIG. 3 is a perspective view showing the structure of an optical system including a total reflection prism according to a third embodiment of the present invention, and FIG. 4 is a front view thereof. The optical system of this example can be used as an optical system for adjusting the distance between the optical axes of two objective lenses in the above-described photomask defect inspection apparatus. In FIG. 4, an optical system including a total reflection prism has a first material and the same shape as those of the total reflection prism 11 of FIG.
And the second total reflection prisms 31 and 32, a first quarter-wave plate 34 disposed opposite the incident surface 33 of the first total reflection prism 31, and an output of the second total reflection prism 32. Second quarter-wave plate 36 arranged opposite surface 35
And Further, the exit surface of the first total reflection prism 31 and the entrance surface of the second total reflection prism 32 are opposed to each other, and both prisms are coupled so as to be relatively rotatable about the axis C.

The total reflection surface of the first total reflection prism 31 and the crystal axis of the first quarter wave plate 34 are adjusted as described in the embodiment shown in FIG. Linear polarization 3 on wave plate
When 7 is incident, linearly polarized light is emitted from the exit surface of the first total reflection prism. Similarly, the total reflection surface of the second total reflection prism 32 and the crystal axis of the second quarter-wave plate 36 are adjusted as described in the embodiment shown in FIG. When the linearly polarized light is incident on the incident surface, the linearly polarized light is emitted from the second quarter-wave plate.

In this embodiment, when linearly polarized light 37 is incident on the first quarter-wave plate 34, linearly polarized light having the same polarization characteristics as the incident linearly polarized light is emitted from the second quarter-wave plate 36. That is, the relationship is that the first quarter-wave plate 34 and the first total reflection prism 31 are integrally rotated about the axis D, or the second quarter-wave plate 36 and the second Does not change even if the total reflection prism 32 of FIG. That is, when the optical system of the present example is applied to the above-described photomask defect inspection apparatus, even if the optical system is rotated to change the distance between the optical axes of the objective lens, the polarization characteristics do not change at all.

[0019]

As described above, according to the optical system including the total reflection prism of the present invention, the phase difference between the P-polarized light component and the S-polarized light component introduced by the total reflection prism is canceled by the quarter-wave plate. Therefore, the polarization characteristics of the incident light and the output light can be made equal. In this case, since the adjustment of the total reflection surface of the total reflection prism and the crystal axis of the quarter-wave plate can be performed very easily and accurately, desired optical characteristics can be easily obtained. Further, when the optical system of the present invention is used in, for example, a photomask inspection device, the polarization characteristics do not change even if the distance between the optical axes of the two objective lenses is adjusted, so that the optical characteristics of the entire device change. Not even.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of an optical system including a total reflection prism of the present invention.

FIG. 2 is a schematic configuration diagram of a second embodiment of the optical system including the total reflection prism of the present invention.

FIG. 3 is a schematic configuration diagram of a third embodiment of the optical system including the total reflection prism of the present invention.

FIG. 4 is a side view of a third embodiment of the optical system including the total reflection prism of the present invention.

FIG. 5 is a schematic configuration diagram of an optical system including a conventional total reflection prism.

FIG. 6 is a schematic configuration diagram of an optical system in which two parallelogram total reflection prisms are combined.

[Explanation of symbols]

 11, 21, 31, 32 Total reflection prism 12 Incident surface 13, 22, 34, 36 Quarter-wave plate 14 First reflecting surface 15, 35 Outgoing surface 16 Second reflecting surface 17, 37 Laser light A, B, C , D, E axis

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-47506 (JP, A) JP-A-3-284706 (JP, A) JP-A-59-48716 (JP, A) JP-A 52-187 40350 (JP, A) JP-A-2-304724 (JP, A) JP-A-61-121379 (JP, A) JP-A-1-257216 (JP, A) JP-A-2-192043 (JP, A) JP-A-64-27057 (JP, A) JP-A-3-36504 (JP, A) JP-A-59-75220 (JP, A) JP-A-5-127103 (JP, A) (58) (Int.Cl. ⁷ , DB name) G01B 11/00-11/30 G01J 4/00-4/04 G01N 21/17-21/61 G01N 21/84-21/958 G02B 5/00-5/136 G02B 5/30 G02B 21/00-21/36 G02B 26/00-26/08 G02B 27/28

Claims (2)

(57) [Claims] 1. An optical system, comprising: an incident surface and an outgoing surface parallel to each other; and at least one total reflection surface, and rotated about an incident optical axis passing through the incident surface or an outgoing optical axis passing through the outgoing surface. A total reflection prism configured to introduce a phase difference of 90 ° between the P component and the S component of the incident linearly polarized light, and a / 4 wavelength disposed opposite to an entrance surface or an exit surface of the total reflection prism. The direction of the crystal axis of the quarter-wave plate and the direction of the total reflection surface of the total reflection prism are adjusted so that the phase difference between the P component and the S component of the output linearly polarized light becomes zero. Then, the total reflection surface and the 1/4, so that the polarization characteristics do not change when the total reflection prism is rotated about the incident optical axis or the output optical axis.
Means for setting a relative position with respect to the wave plate. 2. An incident plane and an exit plane, which are parallel to each other, and first and second total reflection planes, which are parallel to each other, wherein a phase difference of 90.degree. A first parallelogram total reflection prism to be introduced, an entrance surface and an exit surface parallel to each other, and a first parallel surface
A second parallelogram total reflection prism that has a 90 ° phase difference between the P component and the S component of the incident linearly polarized light, and the first total reflection prism. A first quarter-wave plate disposed opposite to the entrance surface of the second total reflection prism; and a second quarter-wave plate disposed opposite to the exit surface of the second total reflection prism. A first total reflection surface of the first total reflection prism and a first total reflection surface;
The direction of the crystal axis of the 1/4 wavelength plate and the direction of the second total reflection surface of the second total reflection prism and the direction of the crystal axis of the second 1/4 wavelength plate are defined as the P component and the S component of the linearly polarized light. And the optical axis between the second total reflection surface and the exit surface of the first total reflection prism, and the entrance surface of the second total reflection prism. First
The first total reflection prism and the first quarter-wave plate are integrated with each other so that they can mutually rotate around the optical axis, An optical system including a total reflection prism, wherein the second total reflection prism and the second quarter-wave plate are integrally formed so as to be mutually rotatable around the optical axis.