JPH0375846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an illumination device that can perform illumination with desired coherency using coherent light such as a laser beam.

[Conventional technology]

In the imaging optical system, it is necessary to set the coherency of the illumination to an appropriate value in order to obtain the necessary resolving power, and for this purpose, the σ value (N.
It is known to control the ratio of NA of the illumination system to A.

[Problem to be solved by the invention]

When a coherent light source such as a laser beam is used as the illumination light source, the light source is focused on a spot and scanned by an appropriate size at the pupil position of the imaging optical system. Coherency can be obtained. However, if the area to be scanned is large, the optical system for scanning will be large.
Another drawback is that the time required for scanning is longer.

Therefore, an object of the present invention is to enable uniform illumination with reduced coherency even when using a laser beam with high coherency, and to form a substantially incoherent light source with a simple configuration. It is an object of the present invention to provide an illumination device that enables efficient illumination through an objective optical system.

[Means to solve the problem]

An illumination device according to the present invention includes a laser light source that supplies laser light along a predetermined optical axis, and an optical axis for forming a reflected image of the laser light around the optical axis in a plane perpendicular to the optical axis. a reflective member having a plurality of side surfaces capable of internal reflection disposed around the reflective member; and a reflective member disposed between the reflective member and a light source to direct the incident light beam from the laser light source incident on the reflective member to a desired point around a predetermined point. and a light flux converting means for converting into light that intersects two-dimensionally at an angle of A light source is formed, and an expanded optical system with reduced coherency is formed on the entrance pupil of the objective light source system, and an illuminated object is placed near the exit surface of the reflective member or at a position conjugate thereto. By doing so, the object to be illuminated is uniformly illuminated.

[Effect]

According to the configuration of the present invention as described above, since the angles of the light beam incident on the reflecting member having the side surface capable of internal reflection by the light beam converting means are variously different, the reflection on each reflecting surface of the reflecting member is A large number of light source images are formed on the incident side. Since the optical path length from each of these multiple light source images to the object surface varies depending on the length of the reflected optical path due to internal reflection, it is difficult to reduce the coherency of the multiple light source images as a whole. can. Furthermore, if the light flux conversion means is configured as a scanning means that changes the angle of the light flux incident on the reflecting member over time, it is possible to further reduce the coherency by averaging over time. Therefore, it is also possible to form a substantially incoherent light source.

〔Example〕

Hereinafter, the present invention will be explained based on the illustrated configuration.

FIG. 1 is an optical path diagram showing the basic structure of an illumination device according to the present invention, which illuminates an object plane 10 incoherently using a columnar member made of a transparent material as a light source image forming means. The coherent light from the laser light source 1 is expanded to a predetermined beam diameter by the scanning optical device 20, and is two-dimensionally scanned over a predetermined angular range within the X-Z plane.
The light enters into the quadrangular prism member 9 from the entrance surface 9a of the quadrangular prism member 9 as shown in the perspective view of the figure. A reflective film is deposited on each side surface of the square prism member 9 for internal reflection, and the incident light beam is reflected by the inner surface of the side surface of the rectangular prism member 9 according to the scanning angle θ and reaches the exit surface 9b.
Eject more. FIG. 1 is an optical path diagram showing the state of the scanning light beam in the X-Z plane when the Z-axis is taken in the optical axis direction. As shown in FIG.
The optical axis rotates around the central point A ₀ of , and the angle θ between the optical axis and the optical axis in the X-Z plane changes continuously in the range of +θ ₀ to 0 to −θ ₀ .

To explain the case where the inclination angle θ of the parallel light flux changes clockwise from 0 to θ ₀ , from 0 to θ ₁ the parallel light flux directly reaches the exit surface 9b without being reflected by the side surface, but from θ 1 to θ ₁ . At θ ₂ , it is internally reflected from the lower side surface in Fig. 1 and reaches the exit surface 9b, so in this range, the light beam is emitted as if it were supplied centered on point A ₁ , which is symmetrical to point A ₀ with respect to the lower side surface. It reaches surface 9b. And an even larger angle θ ₂ ~
When θ ₀ , the light beam reaches the exit surface as if it were being supplied centered on point A ₁ and point A 2, which is symmetrical with respect to the upper side surface, because it is reflected at the lower side surface and then also reflected at the _upper side surface. On the other hand, when the inclination angle θ of the parallel light flux changes counterclockwise from 0 to θ ₀ ,
0 to θ ₁ , the luminous flux directly reaches the exit surface 9b, and θ ₁ to _{θ 2}
In the range A ₀
The light reaches the exit surface 9b as if it were supplied from point A ₁ ', which is symmetrical to point A ₁ ', and in the range of θ ₂ to _{θ 0} , the luminous flux is supplied from point A 2 ', which is symmetrical to point A ₁ ' with respect to the lower side surface. The light reaches the exit surface 9b in this manner. Therefore, the first
When the angle of the light beam incident on the quadrangular prism member 9 is scanned for one period from 0 → +θ ₀ →0 → −θ ₀ →0 in the X-Z plan view shown in the figure, the exit surface 9b has the following in sequence:
The luminous flux is sequentially supplied from each point A ₀ , A ₁ , A ₂ , A ₁ , A ₀ , A ₁ ′, A ₂ ′, A ₁ , A ₀ , and the inner surface of the side surface of the quadrangular prism member 9 Due to reflection, a state in which a luminous flux is essentially supplied from a very large light source is created.
This state is also formed in the Y-Z plane perpendicular to the X-Z plane shown in FIG. It will be illuminated from an extremely large area on the X-Y plane including 9a.

Here, as is clear from the optical path diagram in Figure 1,
Since the optical path length from each light source image formed on each point of A ₀ , A 1 A ₁ ′, A ₂ ′A _{2 ′} to the object plane O is different, the spatial A light source with reduced coherency is formed. That is, as shown in FIG. 1, in an enlarged light source consisting of a plurality of light source images formed by reflection on the square prism member 9, from points A ₁ and A ₁ ', which can be called light source images due to one reflection, illumination light, and 2
The illumination light from points A ₂ and A ₂ ′, which can be called light source images due to multiple reflections, has a different optical path length, and also has a different optical path length from the illumination light that does not receive reflection from point A ₀ . This makes it possible to reduce the coherency of light from the When looking at scanning within a predetermined period of time, by changing the position of the light source image within that period of time, coherency can be reduced temporally, making it possible to perform essentially incoherent illumination. Become. In such incoherent illumination, the object plane 1
The numerical aperture NA of the illumination light reaching 0 is determined by the maximum inclination angle of the scanning beam.

In the above configuration, the position of the substantially enlarged incoherent light source surface coincides with the incident surface 9a of the square prism member, which means that the rotation center A ₀ of the scanned light beam is located on the square prism member. Incident surface 9a of 9
This is because the arrangement is not limited to the above arrangement. Furthermore, it goes without saying that the positions of the centers of rotation of the respective scanning light beams do not need to be the same in the Y-Z plane and in the Y-Z plane. In addition, the longer the length of the quadrangular prism member in the optical axis direction, the greater the number of internal reflections, which increases the number of substantial sources of luminous flux, making it possible to form a more uniform light source close to a surface light source. It is desirable to select an appropriate length since a decrease in the light transmission rate and transmittance is unavoidable.

FIG. 3 is a schematic perspective view showing an example of a scanning optical device used in an embodiment of the present invention. Laser light source 1
The beam diameter of the beam from the beam expander 21 is expanded by the beam expander 21.
The light enters the rotating mirror 22, and after being reflected there, passes through the afocal lens system 23 and enters the second rotating mirror 24 having its rotation axis in the X-axis direction. The light beam reflected by the second rotating mirror 24 reaches the scanning surface 3 through a so-called Kepler-type afocal lens system 26 consisting of two positive lens groups 26a and 26b.

Here, as the first and second rotating mirrors 22 and 24 rotate, the light beam incident on the afocal lens system 26 is rotated within a predetermined angle range.
Scan as shown in the figure. The first and second rotating mirrors 22 and 24 can each be configured as a polygonal mirror, and both mirrors are configured in a conjugate position with respect to the afocal lens 23 provided between the first and second rotating mirrors. This is also effective, and the configuration for two-dimensional scanning is not limited to what is illustrated.

FIG. 4 is an optical system layout diagram of an embodiment in which the principle configuration of incoherent illumination shown in FIG. 1 is applied to a projection exposure apparatus. In the configuration example shown in FIG. 4, the rotation center point _A0 of the parallel light beam scanned by the scanning optical device 20' is located away from the incident surface 9a of the square prism member 9, and is located on the X-Y plane including _A0 . A substantially expanded incoherent light source is formed. Then, the reticle R, which is an object to be illuminated and is placed near the exit surface 9b of the quadrangular prism member, is incoherently illuminated, and the pattern on the reticle R is projected onto the wafer W by the projection objective 7'. At this time, it goes without saying that the wafer W as the object to be illuminated is also uniformly illuminated, and the wafer W is arranged conjugately with the vicinity of the exit surface 9b of the quadrangular prism member. The actual light source surface that illuminates the reticle R is A ₀
Therefore, it is desirable that the entrance pupil of the projection objective lens 7' be formed in the vicinity of this point _A0 . Further, when a condenser lens is inserted between the quadrangular prism member 9 and the reticle R, it is desirable to configure the condenser lens so that the entrance pupil of the projection objective lens 7' and the _A0 point are conjugate. In this case, it goes without saying that the reticle R as the object to be illuminated should be arranged conjugately with respect to the condenser lens near the exit surface 9b of the quadrangular prism member.

In addition, in the above embodiment, a substantially enlarged incoherent light source was formed by the square prism member.
As long as it is a columnar member, it is not limited to a square prism. In addition, in a scanning optical device, it is not necessarily necessary to use a beam expander to expand the diameter of the beam from the laser light source, and it is sufficient to simply angle-scan the beam from the laser light source and immediately make it incident on the columnar member. Incoherent illumination can be performed.

As described above, according to the present invention, even when a light source with high coherency is used, an enlarged and large incoherent light source is formed by the light flux converting means and the reflecting member having an inner reflective surface, so that it is easy to use. With this configuration, it is possible to form a light source with reduced coherency, and it is possible to efficiently perform illumination via the objective optical system. If the laser beam is scanned over a small area, a substantially incoherent light source can be formed, and an incoherent illumination device capable of high-speed scanning can be achieved with a simple configuration. .

[Brief explanation of drawings]

Fig. 1 is an optical path diagram showing the principle configuration according to the present invention, Fig. 2 is a perspective view of a columnar member, Fig. 3 is a perspective view of a scanning optical device used in an embodiment, and Fig. 4 is an embodiment according to the present invention. FIG. Explanation of symbols of main parts, 1... Laser light source,
2... Luminous flux conversion means, 7... Objective optical system, 9...
A reflective member having a side surface capable of internal reflection.

Claims (1)

[Scope of Claims] 1. A laser light source that supplies laser light along a predetermined optical axis, and a laser light source for forming a reflected image of the laser light around the optical axis in a plane perpendicular to the optical axis. a reflective member having a plurality of side surfaces capable of internal reflection disposed around an optical axis; and a reflective member disposed between the reflective member and the light source to direct the incident light beam from the laser light source that is incident on the reflective member into a predetermined range. and a light flux converting means for converting light into light that intersects two-dimensionally at a desired angle with a point as the center, and a coherency image consisting of a plurality of light source images distributed around the optical axis by internal reflection of the reflecting member. The enlarged light source with reduced coherency is formed on the entrance pupil of the objective optical system, and the illuminated object is placed near the exit surface of the reflective member or at a position conjugate thereto. An illumination device characterized by uniformly illuminating the illuminated object by arranging. 2. The objective optical system includes a projection objective lens for projecting a reticle having a predetermined pattern onto a wafer, and an enlarged light source with reduced coherency made up of the plurality of light source images is incident on the projection objective lens. 2. The illumination device according to claim 1, wherein the illumination device is formed on a pupil and uniformly illuminates the reticle as the object to be illuminated. 3. The illumination device according to claim 2, wherein the light flux conversion means includes a scanning means for temporally changing the intersection angle of the emitted light flux.