JPH0552487B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an illumination device that can perform illumination with desired coherency using coherent light such as laser light.

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. 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, when the area to be scanned is large, the optical system for scanning becomes large and the time required for scanning becomes long.

An object of the present invention is to provide an incoherent illumination device for supplying incoherent illumination from coherent light, in which the optical system for scanning coherent light is small, the time required for scanning is short, and high-speed scanning is possible. Our goal is to provide the following.

An illumination device according to the present invention includes a laser light source with high coherency, a scanning means for changing the optical path of an emitted light beam with respect to an incident light beam from the laser light source,
a fly-eye lens that forms a light beam from the scanning means into a plurality of light source images distributed on a predetermined plane using a plurality of lens elements; an aperture stop disposed on the exit side of the fly-eye lens; It has a condenser lens for forming an image on the entrance pupil of the objective optical system, and each of the plurality of light source images formed on the exit side of the fly-eye lens is displaced within its corresponding lens element. The scanning means is caused to vibrate minutely, thereby forming a substantially incoherent light source on the entrance pupil of the objective optical system.

Hereinafter, the present invention will be explained in detail based on Examples.

An embodiment of the present invention is an application of the present invention to a projection type exposure apparatus that uses a so-called fly's eye lens as a light source image forming means to project a pattern on a reticle onto a wafer, as shown in FIG. 1A. . Coherent light supplied from a laser light source 1 is focused onto a spot by a scanning optical device 2, and is scanned two-dimensionally on a scanning surface 3. A collimator lens 4 having a focal point on the scanning surface 3 converts the light beam from the scanning surface 3 into a parallel light beam and enters the fly's eye lens 5 . As shown in the plan view of FIG. 2, the fly's eye lens 5 has a substantially circular shape made up of a large number of square prisms joined together, and both end surfaces of each square prism are formed into convex spherical surfaces, so that it has the action of a positive lens. ing. Since the focal length of the convex surface on the side of the entrance surface 5a is approximately equal to the length of this quadrangular prism, that is, the thickness of the fly's eye lens, the parallel light beam incident on the fly's eye lens is transmitted to the exit surface 5b by each quadrangular prism lens element. The light is focused near each convex surface on the side and a spot image is formed. Therefore, when the scanning optical device 2 scans the spot light on the scanning surface 3, on the exit surface 5b of the fly's eye lens 5, spot images equal in number to the number of rectangular prism lens elements constituting the fly's eye lens are scanned. be done. That is, for example, when the spot light is scanned with a trajectory as shown in the perspective view of the scanning surface 3 in FIG.
As shown in the perspective view of the fly's eye lens exit surface 5b, on the exit surface of each quadrangular prism lens element, all spot images are scanned with a trajectory similar to the trajectory on the scanning surface 3, and the exit surface of the fly's eye lens 5 is Side 5
A large number of spot images are simultaneously scanned over b.
As a result, a large enlarged incoherent light source surface is formed on the exit surface 5b of the fly's eye lens. Since the plurality of light sources formed on the exit surface of the fly's eye lens are mutually coherent at a certain moment, interference fringes are formed on the irradiated surface due to the interference of the light beams from the plurality of light sources, resulting in uneven illumination. However, at the next instant, when the position of the multiple coherent light sources formed by the fly's eye lens changes, the relative phase difference between the multiple light sources changes. The interference fringes at will also change. Therefore, by scanning over a certain period of time, the interference fringes on the irradiated surface are made uniform, and multiple coherent light sources can be regarded as substantially incoherent light sources. be.

Then, by illuminating the reticle R as the object to be illuminated by the condenser lens 6 and forming an enlarged image of the light source plane on the pupil plane 7a of the projection objective lens 7, so-called Koehler illumination is achieved. At this time, the pattern on the reticle R is projected onto the wafer W by the projection objective lens 7. In addition, an aperture stop 8 is provided near the exit surface 5b of the fly-eye lens 5, and by changing the diameter of this aperture, the NA of the illumination system, that is, the size of the light source image on the pupil plane 7a of the projection objective lens can be changed. By changing the σ value, it is possible to perform illumination with an arbitrary σ value.

An example of a specific configuration of the scanning optical device 2 is shown in the perspective view of FIG. The beam diameter of the beam from the laser light source 1 is expanded by the beam expander 21, and Y
It enters a first rotating mirror 22 having a rotation axis in the axial direction, and after reflection there, an afocal lens system 23
and enters a second rotating mirror 24 having a rotation axis in the X-axis direction. The light beam reflected by the second rotating mirror 24 passes through the condenser lens 25 and passes through the scanning surface 3.
The light is focused on the top. As the first and second rotating mirrors rotate, the spot light scans the scanning surface 3 along a trajectory as shown in FIG. 1A, for example. First and second rotating mirrors 22, 24
can each be configured as a polyhedral mirror, and it is also effective to configure both mirrors in a conjugate position with respect to the afocal lens provided between the first and second rotating mirrors, and for two-dimensional scanning. The configuration of is not limited to that shown in the drawings.

The area scanned by the spot light on the scanning surface 3 is
As shown in the above example, since independent scanning is performed in each direction of X and Y, the shape must generally be rectangular, and in an optical system that is rotationally symmetrical about the optical axis, the illumination efficiency will inevitably decrease. However, in this embodiment, the fly's eye lens 5 is formed as a bundle of many lens elements combined in a substantially circular shape as shown in FIG. Good lighting is possible. The fly's eye lens 5 can be formed not only from a combination of square prism lens elements as described above, but also from hexagonal prism or octagonal prism lens elements.
Furthermore, as shown in the sectional view of FIG. 4A, for example, it is also possible to form a fly's eye lens using two lenticular lenses 5a' and 5b' instead of the columnar lens elements described above. In this case, it is desirable that the distance d between the respective lenticular lenses is approximately equal to the focal length of the lenticular lens 5a' on the incident light side, and the distance d between the lenticular lenses is substantially equal to the focal length of the lenticular lens 5b' on the exit light side. An incoherent light source surface is formed. At this time, the lenticular lens 5b' on the exit light side has a function as a field lens and plays the role of increasing illumination efficiency, but is not necessarily necessary. These lenticular lenses 5a' and 5b' are shown in FIG. 4B.
As shown in the plan view, it is desirable to have a substantially circular shape, and it can be easily manufactured from transparent plastic.

By the way, if the scanning by the scanning optical device is too large, vignetting will occur in each lens element of the fly-eye lens, resulting in a decrease in illumination efficiency, as well as sending light to unnecessary areas, causing flares, ghosts, etc. Since there is a risk of uneven illumination, it goes without saying that the scanning means is slightly vibrated to the extent that the light source image is displaced within each lens element. Furthermore, the present invention is not limited to illumination non-uniformity caused by interference phenomena such as regular or irregular interference fringes, and can provide good uniform illumination for non-uniformity caused by various causes.

In FIG. 1, in order to make it easier to understand the operation of the present invention, the fly-eye lens 5 is shown particularly large, and the reticle R as the object to be illuminated is shown relatively small. The size of 5 is arbitrarily determined according to the size required as a surface light source, and the size and number of each lens element constituting the fly-eye lens are also arbitrarily determined as necessary. Needless to say.
Further, the collimator lens 4 is used to make the light beam incident on the fly-eye lens 5 into a parallel light beam, but it can be omitted if the numerical aperture NA of the light beam supplied from the scanning optical device 2 is small. It is.

As described above, according to the present invention, by simply scanning a small area with coherent light, a large enlarged incoherent light source is formed using the fly's eye lens as a light source image forming means.
An incoherent illumination device is achieved in which the scanning device becomes compact and can scan at high speed.

In the above explanation, in order to make it easier to understand, a substantial incoherent light source is formed from a coherent light source, but as is clear from the configuration of each of the above embodiments, a scanning means and a plurality of light sources are used. Needless to say, partially coherent illumination is performed by the light source and image forming means that form an image. As described above with reference to FIG. 1A, by changing the diameter of the aperture stop and changing the σ value, it is possible to change the degree of coherence.

[Brief explanation of drawings]

FIG. 1A is an optical configuration diagram of a first embodiment of the present invention, FIGS. 1B and 1C are perspective views showing how spot light is scanned, FIG. 2 is a plan view of a fly-eye lens, and FIG. 3 is a perspective view of the scanning optical device used in the first embodiment, FIG. 4A is a sectional view showing another example of the fly's eye lens, and FIG. 4B is a plan view thereof. Explanation of symbols of main parts: 1...coherent light source, 2...scanning optical means, 5...fly's eye lens.

Claims (1)

[Scope of Claims] 1. A laser light source with high coherency, a scanning means for changing the optical path of an emitted light beam with respect to an incident light beam from the laser light source, and a plurality of lens elements to scan the light beam from the scanning means on a predetermined plane. a fly's eye lens that forms a plurality of light source images distributed over the area; an aperture stop disposed on the exit side of the fly's eye lens; and a condenser lens that forms the plurality of light source images on an entrance pupil of an objective optical system. Further, the scanning means is caused to minutely vibrate so that each of the plurality of light source images formed on the exit side of the fly-eye lens is displaced within the corresponding lens element, so that the incident light of the objective optical system is An illumination device characterized by forming a substantially incoherent light source on the pupil. 2. In the illumination device according to claim 1, the objective optical system includes a projection objective lens for projecting a reticle having a predetermined pattern onto a wafer, and the condenser is configured to An illumination device characterized in that it forms an image of an incoherent light source on the entrance pupil of the projection objective.