JPS633288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an illumination optical system for projecting a predetermined pattern, and particularly to a mask illumination optical system for transferring an IC pattern from a mask to a wafer using a contact method or a proximity method.

Conventionally, various illumination optical systems used in IC pattern transfer devices are known. For example, as in US Pat. Some devices illuminate a predetermined region of a surface (mask surface) with a parallel light beam within a predetermined collimation half angle (the maximum angle that the illumination light makes with the normal to the object surface). Here, the fly-eye lens is used to remove the diffraction image caused by the mask and to obtain even and uniform illumination by forming multiple secondary light sources and illuminating the mask surface with a large number of light beams. Such means are called optical integrators. Generally, the illumination optical system using an elliptical mirror has a power distribution of 2
It is broadly divided into One is to focus a light source image near the optical integrator using an elliptical mirror, and the other is as described in the above-mentioned US Patent Specification No. 3,296,923.
The light beam from the circular mirror is converted into parallel light by a diverging collimator lens and guided to the optical integrator. From the point of view of light collection efficiency, the latter is relatively superior because there is less vignetting of the light in the optical integrator, but it is still not completely satisfactory. In particular, PMMA, a typical photoresist, has low sensitivity when using deep ultraviolet light, so increasing the light collection efficiency of the illumination optical system has been a major challenge.

An object of the present invention is to provide a mask illumination optical system that is uniform and has higher light collection efficiency while eliminating the influence of a diffraction image caused by a mask.

Hereinafter, the present invention will be explained based on examples. FIG. 1 is a schematic cross-sectional view showing an embodiment of the illumination optical system according to the present invention.

The arc tube 1 has a high-intensity light source a that emits ultraviolet rays and deep ultraviolet rays, and this light source a is located approximately at the first focal point of the rectangular mirror 2. Horenkyo 2 is the second one.
An image a' of the light source a is formed at the focal position. The cold mirror 3 transmits most of the infrared rays and reflects most of the deep ultraviolet light, and is generally made of a multilayer coating. A collimation lens 4 consisting of two positive lenses is arranged so that its front focal point coincides with the light source image a', and converts the light from the light source image a' into a parallel beam of light. An optical integrator 5 is arranged to form a large number of secondary light sources in this parallel light beam, and substantially generates a large number of light beams. Specifically, the optical integrator 5 is a hexagonal prism of glass, with both end surfaces processed into convex lenses, which are bundled together in a honeycomb shape, as shown in the longitudinal cross-sectional view of FIG. 2a and the cross-sectional view of FIG. 2b. The front small lens 11 and the rear small lens 12 have almost the same refractive power, and the distance between them is equal to the back focal length of the front small lens 11 and, of course, the front focal length of the rear small lens 12. equal. The front small lens 11 and the rear small lens 12 have a one-to-one correspondence, and the rear small lens 12
has the function of focusing the image of the corresponding front small lens 11 on the object plane (mask plane). Therefore, the shape of the aperture of the front small lens 11 and the illumination area on the object plane are similar, and here, since the individual small lenses are hexagonal in shape, the illumination area is also hexagonal. As shown in the longitudinal cross-sectional view of FIG. 3a and the cross-sectional view of FIG. It is also possible to configure it accordingly.

Returning to FIG. 1, a positive lens 6 is disposed immediately after the optical integrator 5, and an aperture 7 is disposed immediately after this, and the light beam reflected by the reflector 8 is directed to an object by a collimator lens 9. The light is focused on the surface 10. The aperture of the collimator lens 9 can be made small by the action of the positive lens 6, and the distance between the collimator lens 9 and the object plane 10 can be made small, so that the entire apparatus can be constructed more compactly. However, the distance between the collimator lens 9 and the object plane is a so-called working distance, and if it is desired to increase the working distance for some purpose, a negative lens can be placed in place of the positive lens 6. The aperture 7 is used to change the collimation half angle of the illumination light by changing its aperture. The reflector 8 simply serves to bend the traveling direction of the light beam by 90 degrees. The collimator lens 9 is arranged so that its front focus matches the position of the secondary light source image formed by the rear surface of the optical integrator 5, that is, the front small lens 11 of the optical integrator. The diverging light beams from each of the lenses 12 are converted into parallel light beams, and the parallel light beams are completely superposed on the object plane 10.

In the configuration of the present invention as described above, the light source a is not a complete point light source, but has a certain size in the light source image a', so the light flux exiting the collimation lens 4 corresponds to the size of the light source image a'. It becomes a diverging beam of light that spreads at an angle of . Here, collimation lens 4
Due to the convergence action, an image b' of the aperture surface b of the rectangular mirror 2 is formed at a distance d behind the collimation lens 4, as shown in FIG. 4, so the optical integrator 5 is placed at this position. This arrangement can prevent vignetting. If the collimation lens is a concave diverging lens as in the past, the image b' of the aperture surface b of the rectangular mirror 2 will be formed in front of the collimation lens, making it impossible to prevent vignetting. .

As shown in Figure 4, the collimation lens 4
When the distance between the aperture b of the rectangular mirror 2 and the collimation lens 4 is l, the distance d between the collimation lens 4 and the image b' of the aperture b of the rectangular mirror 2 is , as is well known, is expressed as d=·l/l−.

As mentioned above, vignetting can be almost completely eliminated by arranging the optical integrator at a position conjugate with the aperture surface of the rectangular mirror with respect to the collimation lens 4; The problem is the heterogeneity of That is, in an actual condensing system using a circular mirror, at a position conjugate with the aperture surface b of the circular mirror 2 with respect to the collimation lens 4, an annular shape is formed reflecting the light intensity distribution of the aperture surface b of the circular mirror 2. Because of the light amount distribution, non-uniformity also occurs in the illumination onto the object plane 10. Figure 5 is an aperture image of the collimation lens 4 and the oval mirror.
This figure shows the light amount distribution at four locations A, B, C, and D between the point and the point b'. The light intensity along the beam cross section at each position of A, B, C, and D is shown with reference lines x ₁ , x ₂ , x ₃ , and x ₄ at each position as zero intensity, and the left side as high intensity. . As shown in the figure, at position D, where image b' of the aperture surface of the rectangular mirror is formed, the light intensity is almost zero at the center, but it is somewhat averaged at position C, and at position B, which is approximately in the middle, the light intensity is almost zero at the center. The intensity has increased considerably and is almost uniform at position A. For this reason, it is desirable that the optical integrator 5 be placed as close to the collimation lens 4 as possible. However, since the light source has a size, the closer the light source is to the collimation lens 4, the larger the luminous flux width becomes, making it necessary to make the aperture of the optical integrator 5 larger. In reality, it is desirable to arrange the optical integrator 5 at a position closer to the collimation lens 4 than at the intermediate position B. That is, it is desirable that the distance D between the collimation lens 4 and the optical integrator 5 satisfy the following condition: D<d/2=.l/2(l-).

Here, as mentioned above, the image of the front small lens 11 of the optical integrator 5 is
0, the front small lens of the optical integrator is formed on the elliptical mirror aperture image.
It is clear that the non-uniformity of illumination on the object plane is most significant at position D where b' is formed. Therefore, the distance D between the collimation lens 4 and the optical integrator 5 under the above conditions is practically the distance D between the collimation lens 4 and the optical integrator 5.
It goes without saying that this should be configured as the distance between the lens and the front small lens of the optical integrator.

If the above conditions are not met, it tends to be advantageous to prevent vignetting and maintain high lighting efficiency, but the position of the optical integrator approaches the position where an annular light intensity distribution occurs, so the optical integrator is Even if it is used, illumination unevenness will be significant, making it difficult to prevent vignetting and maintain uniform illumination at the same time.

In the above configuration, the collimation half angle can be changed by changing the aperture diameter of the diaphragm, but when increasing the diaphragm diameter as shown in Figure 6a, the collimation lens has a large focal length. In addition, when reducing the aperture diameter as shown in FIG. 6b, by replacing the aperture with one with a smaller focal length, the highest light collection efficiency can always be maintained without loss.

As described above, according to the present invention, a mask illumination optical system that is uniform and has extremely high light collection efficiency while sufficiently eliminating the influence of the diffraction image due to the mask has been achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the illumination optical system according to the present invention, FIG. 2 a is a vertical cross-sectional view of an optical integrator, FIG. 2 b is a cross-sectional view thereof, and FIG. 3 a is an optical integrator. 3b is a cross-sectional view thereof, and FIG. 4 is an explanatory diagram in which the image of the aperture surface of the rectangular mirror is formed at a distance behind the collimation lens.
Figure 5 is an explanatory diagram showing the light intensity distribution at four locations A, B, C, and D between the collimation lens and the aperture image of the rectangular mirror, and Figure 6 a is when increasing the aperture diameter of the diaphragm. FIG. 6b is an explanatory diagram showing the types of collimation lenses used when reducing the aperture diameter. [Explanation of the symbols of the main parts], 2...Oroen mirror, 3...
Cold mirror, 4... Collimation lens, 5
...Optical integrator.

Claims (1)

[Claims] 1. An elliptical mirror having first and second focal points, and an arc tube disposed at the first focal point of the elliptical mirror, and an annular light amount on the aperture surface of the elliptical mirror. a light source device for condensing the light beam from the arc tube onto a second focal point with a distribution; a parallel light beam conversion means for converting the light beam from the light source device into a parallel light beam; an optical integrator having a front small lens group and a rear small lens group arranged at a distance approximately equal to each other's focal length to form a multiple light beam by a secondary light source image and the secondary light source image; In the illumination optical system including a convergent lens for guiding the light flux from the optical integrator toward the object side, the parallel light flux conversion means includes a convergent collimation disposed on the exit light side of the second focal point of the elliptical mirror. A lens, arranged so that the front focal point of the convergent collimation lens substantially coincides with the second focal point of the elliptical mirror, and arranged in a parallel light beam on the exit light side of the convergent collimation lens. The optical integrator is disposed between the convergent collimation lens and an image position of the elliptical mirror aperture surface formed on the exit light side of the collimation lens by the convergent collimation lens,
When the focal length of the collimation lens is f and the distance from the aperture of the elliptical mirror to the collimation lens is l, the distance D between the front small lens group of the optical integrator and the collimation lens is , D<f·l/2(l−f).