JPH02188716A - Optical device with polarizing means - Google Patents

Abstract

PURPOSE:To utilize luminous flux efficiently by separating incident luminous flux in a random polarized state into two pieces of linear polarized luminous flux which cross each other at right angles by a polarization beam splitter and projecting them in the same polarized state. CONSTITUTION:The incident luminous flux in the random polarized state is split by the polarization beam splitter 1 into the two pieces of linear polarized luminous flux which cross each other at right angles, and the P-polarized luminous flux is passed through a lambda/2 plate 2 to rotate the polarization azimuth by 90 deg., then comes to S-polarized luminous flux L2S, which is reflected by a mirror 5, then guided to an optical multiplexing member 6 composed of a reflecting prism. On the other hand, S-polarized luminous flux L which is reflected by a polarized light splitting surface 1a is reflected by a reflecting surface 1b, then projected from the polarization beam splitter 1 and reflected by a mirror 4, and guided to the optical path multiplexing member 6. The S-polarized luminous flux L1 is multiplexed by the optical path multiplexing member 6 with the S-polarized luminous flux L2S reflected by the mirror 5 to equalize their polarized states, and the resulting light is outputted as linear polarized luminous flux L3 form the optical device 10. Consequently, the luminous flux can be utilized effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical device having a polarizing means, for example, for illuminating an object such as a mask or a reticle using a polarized light beam vibrating in a predetermined direction. The present invention relates to an optical device having a polarizing means suitable for an illumination system in an exposure apparatus for manufacturing semiconductor devices, an illumination system of a microscope for illuminating an observation object, and the like.

(Prior Art) Conventionally, optical devices that divide a light beam from a light source into multiple parts or combine multiple light beams and then guide the light onto an object surface to illuminate the object surface are used, such as illumination systems and measuring threads. It is used in various fields.

Generally, when a non-polarized light beam is used and the light beam is split into multiple parts or combined, the amount of light is lost at the light splitting plane.For example, when a non-polarized light beam passes through a polarizing beam splitter, Half of the light is lost.

For this reason, optical systems have conventionally used linearly polarized or circularly polarized light to split or combine the light beam, using phase correction plates, polarizing beam splitters, etc. to prevent loss of light quantity when dividing into one beam. system is used.

Particularly in recent years, with the development of lasers and the ability to treat the polarization state as a piece of coded optical information, various optical devices that utilize the polarization state of light are used to control light in high-precision optical systems. It is being

(Problem to be Solved by the Invention) However, in general, when a polarizing means such as a polarizing beam splitter is used to extract an unpolarized light beam as a polarized light beam that oscillates in a predetermined direction and uses it, in the initial stage. There was a problem in that approximately half of the light amount was lost due to the polarizing means.

For this reason, when a light source that emits a non-polarized light beam is used, compared to a light source that emits a completely polarized light beam, twice the amount of light is required to obtain the same amount of light.

The present invention uses a light source that emits an unpolarized light beam to reuse the amount of light that is lost in the initial stage when it is extracted as a light beam with a predetermined polarization state and is used, so that the light beam from the light source is emitted with the same polarization state. It is an object of the present invention to provide an optical device having a polarizing means suitable for an illumination system, a measurement system, etc., which makes efficient use of the total luminous flux.

(Means for solving the problem) In the present invention, an incident light beam having a random polarization state is split into two linearly polarized light beams orthogonal to each other by a polarizing beam splitter, and the polarization direction of one of the polarized light beams is changed to a phase. It is characterized in that, after being displaced by 90 degrees through a correction plate, it is combined with the other polarized light beam through an optical path combining member to align the polarization state and output it.

(X Example) FIG. 1 is a schematic diagram of the main parts of an optical system according to a first example of the present invention.

In the figure, lO is an optical device having a polarizing means.

l is a polarizing beam splitter as a polarizing means, and 1
In this embodiment, an incident light beam having an incoherent random polarization state is divided into two mutually orthogonal linearly polarized light beams L1. It is divided into L2.

In this embodiment, the polarization splitting surface 1a allows a P-polarized light beam L2 having a vibrating plane within the plane of the paper to pass therethrough, and reflects an S-polarized light beam having a vibrating plane within a plane perpendicular to the plane of the paper.

Then, the P-polarized light beam emitted from the polarizing beam splitter 1 passes through the λ/2 plate 2, rotates the polarization direction by 90 degrees, and becomes the S-polarized light beam L2S. After reflecting by the mirror 5, the light combining member 6 consists of a reflecting prism. It guides light.

The S-polarized light beam Ll reflected by the one-way polarization splitting surface 1a is reflected by the reflecting surface tb, outputted from the polarizing beam splitter 1, reflected by the mirror 4, and then guided to the optical path combining member 6. Then, the S-polarized light beam Ll is combined with the S@light light beam L2S reflected by the mirror 5 by the optical path combining member 6, and then outputted from the optical device W11O as a linearly polarized light beam L3 having one vibration plane in a predetermined direction. ing.

The linearly polarized light beam L3 is then guided to, for example, an illumination system or a measurement system (not shown).

In this embodiment, when the incident light beam is a coherent random polarized light beam, if the difference in optical path length between the two light beams reaching the optical path combining member 6 is small, they may interfere with each other. For this purpose, for example, an optical path length adjusting member that can provide a predetermined optical path length difference with respect to the P-polarized light beam L2 is disposed in the optical path of the S-polarized light beam Ll. After imparting an optical path length difference to the S-polarized light beams, they are combined at the light combining member 6, thereby increasing the optical path length difference between the two light beams L1 and L2S. W
The light is emitted from 110.

The structure of the optical path length adjusting member 3 is, for example, a box made of a hollow transparent member, and the internal air pressure can be controlled online or offline with a pump, or the internal temperature can be adjusted with a heater or the like. In this embodiment, any means can be applied as long as it can impart a predetermined optical path length difference to the passing light beam.

In this embodiment, an image rotor cheater may be used instead of the λ/2 plate 2 to shift the polarization direction of one light beam by 90 degrees, and a second reflective prism 6 may be used as the light combining member instead of the reflecting prism 6. It may also be constructed from a prism reflector 7 that uses internal reflection twice as shown in the figure.

In this embodiment, by setting each element as described above, all of the incident light beams in random polarization states are extracted as linearly polarized light beams vibrating in a predetermined direction, thereby making effective use of the light beams.

FIG. 3 is a schematic diagram of the main parts of an optical system according to a second embodiment of the present invention.

In this example, a polarizing beam splitter is used as a polarizing means.
The polarization splitting surface 8a and the reflecting surface 8b of No. 8 are not parallel to each other as in the first embodiment, but are constituted by a wedge-shaped prism body having a predetermined angle a.

Then, the S-polarized light beam Ll that has been reflected and split by the polarization splitting surface 8a is reflected by [1j8b, emitted from the polarization beam splitter 8, and incident on an optical pipe 9 as a light combining member at an incident angle of 1%.

On the other hand, the P-polarized light beam L2 that is transmitted through the polarization splitting surface 8a is λ
The S-polarized light beam L2S is made to have the same polarization state as the light beam L1 through the /2 plate 2, and is made incident on the optical pipe 9 at the same incident angle i as the light beam L1.

This allows the use of the light beam with uniform polarization state emitted from the optical pipe 9.

In this embodiment, the incident angle i of the light beam on the optical pipe 9
The orientation characteristics of the light emitted from the optical pipe 9 are controlled by the optical pipe 9, and the light is guided to, for example, an illumination system (not shown) as a light beam having predetermined light distribution characteristics.

Compared to the first embodiment shown in FIG. 1, this embodiment does not use a mirror, so it is easier to downsize the entire AM.

FIG. 4 is a schematic diagram of the main parts of an optical system according to a third embodiment of the present invention.

In this example, a polarizing beam splitter is used as a polarizing means.
The light beams from two semiconductor lasers 41 and 42 are made incident on one laser beam.

P of the light beam from the semiconductor laser 41 at the polarization splitting plane la
The polarized light beam is passed through, and the S-polarized light beam is reflected. Also, out of the light beam from the semiconductor laser 42, P at the polarization splitting plane 1a
The polarized light beam is reflected and the S-polarized light beam is transmitted. The two S-polarized light beams are reflected by the reflecting surface 1b and then guided to the light combining member 6 via the mirror 4. On the other hand, the two P-polarized light beams are guided through a λ/2 plate as S-polarized light beams to a light combining member 6 via a mirror 5, and these light beams are combined with the same polarization direction and emitted.

In general, semiconductor lasers have different spread angles of light in the vertical and horizontal directions. Therefore, in this embodiment, for example, when the light beams from two semiconductor lasers are combined at infinity, the light intensity distribution of the light beam is 5th.
Each element is set as shown in the figure.

As a result, for example, when used in an illumination system, the effective sigma σ of the illumination system, that is, the ratio of the numerical aperture of the imaging lens to the numerical aperture of the illumination system, becomes the light flux 53 that is a composite of the light fluxes 51.52 shown in the same figure. Therefore, the vertical and horizontal sides are the same compared to when using a semiconductor laser alone, and it can be used in a nearly circular state.

In this way, in this embodiment, the luminous fluxes from the two semiconductor lasers are efficiently combined and used, and the effective σ value of the illumination system is appropriately determined without using a cylindrical lens or the like.

In the embodiment shown in FIG. 3, 1w, and 44, if coherent light is used for the randomly polarized light beam, if the optical path length adjustment member 3 is provided in the optical path of one of the light beams as shown in the same figure, the result as shown in FIG. The same effects as in the first embodiment can be obtained.

(Effects of the Invention) According to the present invention, as described above, by using a polarizing beam splitter as a polarizing means and a polarizing element that shifts the polarization direction by 90 degrees, random unpolarized light can be generated regardless of coherent light or incoherent light. It is possible to achieve an optical device having a polarizing means suitable for, for example, an illumination system, which can efficiently extract the luminous flux of a predetermined polarized layer from the luminous flux of , while preventing loss of light quantity;

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the main parts of the optical system of the first embodiment of the present invention, FIG. 2 is a schematic diagram of another embodiment of a part of FIG. 1, and FIG.
FIG. 4 shows the second embodiment of the present invention. A schematic diagram of the main parts of the optical system of the third embodiment, and FIG. 5 is an explanatory diagram of the intensity distribution when the luminous flux is combined in FIG. , 3 is an optical path length adjustment member, 4.5 is a mirror, and 6.
7 is a photosynthesis member, 41.42 is a semiconductor laser, and 9 is an optical pipe.

Claims (2)

[Claims] (1) An incident light beam with a random polarization state is split into two linearly polarized light beams orthogonal to each other by a polarizing beam splitter, and after displacing the polarization direction of one of the polarized light beams by 90 degrees via a polarizing element, the optical path is 1. An optical device having a polarizing means, characterized in that the polarized light beam is combined with the other polarized light beam via a combining member and emitted with the polarized state aligned. (2) A polarizing beam splitter splits the incident light beam in a coherent random polarization state into two linearly polarized light beams orthogonal to each other, and shifts the polarization direction of one of the polarized light beams by 90 degrees via a polarizing element. After imparting a predetermined optical path length difference between one of the two linearly polarized light beams to the other light beam through an optical path length adjustment member so that the two light beams do not interfere, the two light beams are optically combined. 1. An optical device having a polarizing means, characterized in that the polarizing means is combined by a member so that the polarized light direction is aligned and the light is emitted.