JPS6380243A - Illumination optical device for exposure equipment - Google Patents

Abstract

PURPOSE:To suppress a loss of the light quantity of a luminous flux from an excimer laser light source to the minimum, and also, to shape a beam so that there is no directivity in a resolving power of a projected pattern image, by using a laser beam shaping optical system which has been constituted of an anamorphic lens. CONSTITUTION:A beam shaping optical system consisting of two pieces of anamorphic lenses 3A, 3B having each different refracting power in only one direction is provided on an illuminating optical path from an excimer laser light source 1 for outputting a laser luminous flux whose cross section is rectangular, by which its laser luminous flux is brought to beam shaping to a sectional form of roughly a regular square. Thereafter, only a luminous flux of four corners is cut to a rotational and symmetrical optical system. Therefore, it becomes a laser luminous flux whose cross section is roughly circular, illuminates a pattern area on a mask 6, and thereafter, passes through an entrance pupil of a projection objective lens 7 and forms a pattern image of the mask 6 on a wafer 8. Accordingly, the laser luminous flux outputted from the excimer laser light source is not cut uselessly, but utilized for a projection exposure by a sufficient quantity.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to an illumination optical device for a semiconductor exposure apparatus that transfers a mask pattern using a laser beam as an illumination light flux, and in particular to an illumination optical device that uses an excimer laser as an illumination light source. The present invention relates to an exposure illumination optical device for a semiconductor exposure apparatus.

(Prior Art) In semiconductor exposure equipment such as ICSLSI that transfers fine mask patterns onto wafer surfaces, ultra-high pressure mercury lamps that mainly emit light with a wavelength of 436 nm or 365n+n, for example, have traditionally been used in many cases. In order to obtain even higher-density and finer patterns, a light source that emits even shorter wavelength and more powerful light is required. Therefore, an exposure apparatus equipped with an excimer laser as an illumination light source which oscillates at a shorter wavelength beyond the above-mentioned ultraviolet wavelength range (350 to 450 nm) is disclosed, for example, in Japanese Patent Application Laid-open No. 57-198631, and is already known.

According to the above publication, the illumination light source (excimer laser)
It is disclosed that light from the mask 3 is projected onto the mask through an illumination optical system using a focusing component and other optical components to uniformly illuminate the entire area. On the other hand, as an optical system for average illumination of a mask in an exposure apparatus, a combination of an optical integrator such as a fly's eye lens and a condenser lens is conventionally known. It is also well known in optical devices that use lasers to use a beam expander composed of two spherical lenses with different focal lengths in order to expand the laser beam into a beam with a desired large diameter. This is the technology of

(Problems to be Solved by the Invention) However, the output cross section of the excimer laser depends on the shape of the electrode, and has a beam shape of a rectangular cross section with different vertical and horizontal lengths, for example, 7 m x 20 mm. Therefore,
Even if the optical integrator described above is used to make the light intensity uniform on the mask, the cross-sectional shape of the laser beam is still rectangular, so when the pattern image of the mask is projected through the projection lens, the resolution of the image is low. There was a drawback that the vertical and horizontal directions were different. Further, even if the beam diameter is expanded using a beam expander, the cross-sectional shape of the laser beam remains the same, and there is a risk that the amount of exposure will be insufficient.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an illumination optical device for a semiconductor exposure apparatus that can solve the problems of the conventional devices described above and can efficiently and correctly transfer even extremely fine mask patterns.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems, in the present invention, a beam shaping optical system consisting of two anamorphic lenses having refractive powers that differ from each other only in one direction is Technically, it is installed on the illumination optical path from an excimer laser light source that outputs a rectangular laser beam, so that the laser beam is shaped into a nearly square cross-sectional shape and then illuminates the pattern on the mask. This is the main point.

(Function) The laser beam having a rectangular cross section that enters the beam shaping optical system 3.13.23 is either enlarged on the short side or reduced on the long side due to the refractive power in only one direction, so that it becomes almost square. The laser beam is shaped into a cross-sectional shape.

This laser beam shaped to have a square cross section becomes a laser beam having an approximately circular cross section because only the light beams at the four corners are canted by the optical system that is rotationally symmetrical around the optical axis, and after illuminating the pattern area on the mask 6, , an image of the pattern of the mask 6 is formed onto the wafer 8 through the entrance pupil of the projection objective 7 . Therefore, the laser beam output from the excimer laser light source is not wasted and is used in sufficient quantity for projection exposure.

(Example) Next, an example of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a configuration diagram of an optical system showing an embodiment of the present invention, in which the beam is shaped into a predetermined cross-sectional shape by a beam shaping optical system 3 consisting of anamorphic optical systems 3A and 3B such as a pair of cylindrical lenses. Ru. This beam-shaped laser beam is divided into a large number of diverging beams by an optical integrator 4 such as a fly's eye lens, and is further divided into a number of diverging beams by a condenser lens 5, as disclosed in Japanese Patent Application Laid-Open No. 56-81813. and is focused to uniformly illuminate the reticle 6. In this case, the optical integrator 4 creates a large number of minute light sources on the -plane and acts as a secondary light source. The circuit pattern on the reticle 6 uniformly illuminated by this laser beam is projected by the projection objective lens 7 onto the wafer 8 placed on the stage 9.

The excimer laser light source 1 has elongated semi-cylindrical discharge electrodes El, Et, as shown in FIG. A flash of light generated when a high voltage is applied between IF and discharge resonates in the longitudinal direction of the electrode and emits light in the direction of the arrow. At this time, the cross-sectional shape of the laser beam has the characteristic that it is greatly influenced by the shape of the electrodes E+ and Ex, but in the excimer lasers currently on the market, the discharge direction is the long side (x), and Many of them have a rectangular cross-sectional shape as shown in FIG. 3, with the short side (y) being perpendicular to the direction. In the excimer laser light source 1 shown in FIG. 1, the main discharge electrodes E1 and E2 are arranged vertically in parallel as shown in FIG. 2, so that the cross section of the emitted laser beam is a vertically long rectangle. After this laser beam is deflected downward by the mirror 2, it has a rectangular cross-sectional shape that is elongated from side to side, as shown in FIG. incident on .

This beam shaping optical system 3 consists of a diverging cylindrical lens 3A and a convergent cylindrical lens 3B, and as shown in FIG.
The generatrix lines of 3B are configured to be parallel to each other.

In other words, rays in a plane including the generatrix pass through without being refracted as shown in Figure 5(a), and rays in a plane perpendicular to this generatrix are refracted as shown in Figure 5(b). do.

In this case, each focal point of both cylindrical lenses 3A13B is set to a point 0. If they are arranged so that they match, an afocal system is formed by both cylindrical lenses, and a parallel light beam parallel to the generatrix that enters one cylindrical lens 3A is also emitted as a parallel light beam from the other cylindrical lens 3B, and its At this time, only the light rays in the plane perpendicular to the generatrix are expanded in beam width and emitted as parallel light beams again, as shown in FIG. 5(b).

Now, the focal length of one cylindrical lens 3A is f.
11 The focal length of the other cylindrical lens 3B is ft.
Let the length of the long side of the excimer laser beam be x1, and the length of the short side be y, and let 1fll<1f21. By selecting the focal length, it is possible to shape an excimer laser beam having a rectangular cross section into a square cross section.

In FIG. 1, a cylindrical lens 3A.

A cross-section reflected by mirror 2, where rays in the plane containing the generatrix of 3B (plane parallel to the paper) are shown as solid lines, and rays in the plane perpendicular to the generatrix (plane perpendicular to the paper) are shown in broken lines. The shape is the fourth
As shown in Figure (a), the excimer laser beam having a rectangular cross section with x on the long side and y on the short side is transmitted through a diverging cylindrical lens 3A.
Only the short side y is expanded to be equal to the long side X,
The light is emitted as a parallel light beam by the absorptive cylindrical lens 3B. Therefore, the light beam passing through the beam shaping optical system 3 is shaped into a square cross section with one side of X as shown in FIG. 4(b). This beam-shaped laser beam is transmitted through an optical integrator 4 and a diaphragm (hereinafter referred to as "α diaphragm") having a circular aperture provided on or near the secondary light source imaging plane of the optical integrator 4. 4A and the condenser lens 5, the pattern area of the mask 6 is uniformly illuminated. At this time, the secondary light source formed by the optical integrator 4 into a set of many bright spots also has a substantially square cross-sectional shape with one side X, and the four corners are cut by the α aperture 4A to form a substantially circular shape. The shape is as shown in Figure (C).

The laser beam illuminating the pattern on the mask 6 forms a pattern image on the wafer 8, which passes through the entrance pupil P (corresponding to a substantial aperture in FIG. 1) of the projection objective lens 7. In this case, the α aperture 4A is provided at a position conjugate with the entrance pupil P of the projection objective lens 7, and the image of the aperture of the α aperture 4A is focused within the entrance pupil P as shown in FIG. 4(d). imaged. The size of the image (i.e., the cross section of the light beam passing through the entrance pupil P) of the aperture of the α aperture 4A is 0.5 to 0.
7, a pattern image with good resolution and contrast can be obtained on the wafer 8.

Therefore, by only slightly cutting the laser beam with the α aperture 4A, it is possible to perform projection exposure by making maximum use of the laser beam from the excimer laser light source.

The beam shaping optical system 3 is the same as shown in FIG. 6 instead of the anamorphic beam shaping optical system consisting of a divergent (negative) cylindrical lens 3A and a convergent (positive) cylindrical lens 3B shown in FIG. As shown, the anamorphic beam shaping optical system 13 may be configured using only positive cylindrical lenses 13A and 13B. in this case,
The focal lengths f, , f of both lenses 13A and 13B are determined using the above-mentioned equation (1). Also, both lenses 13A
, 13B are arranged so that their focal points coincide at point 0□ as shown in FIG.

FIG. 7 is an explanatory diagram showing the relationship between the direction of the generatrix of the millimeter lenses 3A, 3B, 13A, and 13B constituting the beam shaping optical system 3.13 and the direction of the electrodes E+ and Ez of the excimer laser light source 1. be.

As shown in FIG. 7 <a>, each cylindrical lens 3A, 3B, 13A, 13B has a generatrix direction (indicated by arrow Sl) that is aligned with the direction of the electrodes El and Et, that is, the rectangular cross section of the laser beam. installed parallel to the longitudinal direction of the As a result, the laser beam is directed to the seventh point in the direction of the generatrix.
As shown in Figure (a), it passes straight through the cylindrical lenses 3A (13A) and 3B (13B) without being refracted, but perpendicular to the generatrix as shown in Figures 7 (b) and 7 (c). For the direction (indicated by arrow S2), one cylindrical lens 3A.

After the beam width is expanded by 13A, the beam becomes parallel again by the other cylindrical lenses 3B and 13B. Therefore, by making the direction of the generatrix of the cylindrical lens constituting this beam shaping optical system 3.13 parallel to the discharge direction of the discharge electrodes E+ and Ex of the excimer laser light source, only the direction of the short side of the laser beam having a rectangular cross section can be set. can be expanded.

Furthermore, when light passes from the left through the anamorphic beam shaping optical systems 3A, 3B, 13A, and 13B shown in FIGS. 5 and 6, the beam width only in the direction perpendicular to the generatrix can be shortened. is possible. Therefore, excimer laser light source 1
For example, if the beam at the output cross section of the beam in the X direction is appropriate in the X direction in Figure 3, but the X direction is too long, in order to reduce the X direction, the expanding beam shaping optical system should be turned in the opposite direction. ,
If the direction of the generatrix is set perpendicular to the discharge direction of the discharge electrode, it can be used as a reduction type beam shaping optical system.

FIG. 8 shows a projection exposure apparatus according to a second embodiment of the present invention configured to reduce the longitudinal direction of a laser beam having a rectangular cross section and shape the beam into a beam having a square cross section to illuminate a mask 6. Optical system layout diagram, (a), (b), (c) in Figure 9
) and (d) are A-A and B-B of the luminous flux in Fig. 8, respectively.
, CC, and DD sectional views. Note that parts having the same functions as those in FIG. 1 are designated by the same reference numerals as in FIG. 1, and detailed explanations of their configurations will be omitted.

In FIG. 8, a laser beam from an excimer laser light source 1 is reflected by a mirror 2 and enters a reduction type beam shaping optical system 23. In FIG. The cross-sectional shape of the laser beam at that time is
As shown in FIG. 9(a), it has a rectangular shape that is long in the left-right direction. The beam shaping optical system 23 consists of a positive cylindrical lens 23A and a negative cylindrical lens 23B, each having a generatrix perpendicular to the plane of the paper. The laser beam that has passed through this beam shaping optical system 23 is shown in FIG. As shown, only the left and right directions are reduced and the beam is shaped into a substantially square shape with one side being the short side y of the rectangular cross section of the incident light beam. This laser beam with a square cross section is transmitted to the optical integrator 4.
and an α aperture 4A having a circular aperture, a circular secondary light source consisting of a collection of many bright spots is formed. The light flux from this secondary light source uniformly illuminates the mask 6 via the condenser lens 5. FIG. 9(C) shows the cross-sectional shape of the light beam passing through the aperture of the α aperture 4A. The laser beam illuminating the mass 6 passes through the entrance pupil P of the projection objective lens 7 and forms an image on the surface of the wafer 8 on the stage 9 . In this case as well, an image (2) of the α aperture 4A is formed on the entrance pupil P with an appropriate size relative to the entrance pupil P, as shown in FIG. 9(d). Therefore, the light beam from the excimer laser light source 1 can be used most effectively. In this second embodiment, the focal length of the positive cylindrical lens 23A is f2, and the negative cylindrical lens 23B is f, and the above-mentioned (1
Since the system is configured as an afocal system so as to satisfy the following equation, the long side X of the excimer laser beam having a rectangular cross section is equal to the short side y.

When the square cross section of the excimer laser beam that has been beam-shaped in the embodiments shown in FIGS. 1 and 8 is further proportionally expanded or contracted to an appropriate size,
A general beam expander made of an afocal system or its inverted version may be added on the optical path between the beam shaping optical system 13.23 made of a cylindrical lens and the optical integrator 4. In addition, it is also possible to further expand or contract the square beam-shaped beam by forming the square beam into an appropriate size for the entrance pupil of the projection objective lens. be.

〔Effect of the invention〕

As described above, according to the present invention, by using a laser beam shaping optical system configured with an anamorphic lens, the loss of the light beam from the excimer laser light source is minimized, and the projected pattern image is Beam shaping is possible so that there is no directionality in resolution, the configuration is simple, and the luminous flux from the light source can be guided most effectively to the projection lens to form a pattern image with excellent contrast and resolution.

[Brief explanation of the drawing]

1 is a layout diagram of an optical system of a projection exposure apparatus showing a first embodiment of the present invention, FIG. 2 is a perspective view of a discharge electrode section of an excimer laser light source used in the embodiment of FIG. 1, and FIG. The figure is the second
FIG. 4 is an explanatory diagram showing changes in the cross-sectional shape of the excimer laser beam in the embodiment shown in FIG.
a), (b), (C), and (d) are cross-sectional views of the excimer laser beam at A-ASB-B, CC, and D-D cross sections in FIG. 1, respectively, and FIG. 5 is the cross-sectional view of the excimer laser beam of the present invention. An explanatory diagram of the beam shaping optical system in Fig. 1, which is the main part, where (a) is a cross-sectional view parallel to the generatrix, (b) is a longitudinal cross-sectional view of <a>, and Fig. 6 is different from Fig. 5. 7th block diagram of a beam shaping optical system showing an embodiment
The figure clearly shows the relationship between the beam shaping optical system shown in Figs. 5 and 6 and the discharge direction between the discharge electrodes of the excimer laser light source, and Fig. 8 shows the projection exposure method according to the second embodiment. FIG. 9 is an explanatory diagram showing the change in the cross-sectional shape of the excimer laser beam in FIG. 8, showing the arrangement of the optical system of the device.
, (d) are A-A, B-B, and C-C5 in Fig. 8, respectively.
FIG. 3 is a sectional view of an excimer laser beam along the DD cross section. (Explanation of symbols of main parts) 1... Excimer laser light source 3.13.23... Beam shaping optical system 3A, 3B, 1
3A, 13B, 23A, 23B... Cylindrical lens (anamorphic lens) 4... Optical integrator 4A... α aperture 5... Condenser lens 6... Mask 7... Projection objective lens 8. ...Wafer (photosensitive substrate) El, Ez...Main discharge electrode P...Entrance pupil

Claims (3)

[Claims] (1) In a projection exposure apparatus that projects an image of a pattern on a mask onto a photosensitive substrate using an excimer laser as an exposure illumination light source, beam shaping is made up of at least two anamorphic lenses having different refractive powers in only one direction. An illumination optical device for an exposure apparatus, characterized in that an optical system is provided on an illumination optical path from an excimer laser light source, and is configured to illuminate the mask after shaping the beam cross section of the excimer laser into a substantially square beam. (2) The beam shaping optical system includes cylindrical lenses (3A, 3B, 13A, 13B) having different focal lengths.
, 23A, 23B), the focal length of one lens is f_1, the other is f_2, the long side of the excimer laser beam having a rectangular cross section is x, and the short side is y, |f_1|
The illumination optical device for an exposure apparatus according to claim 1, characterized in that the illumination optical device for an exposure apparatus is configured to substantially satisfy the relationship |f_2/f_1|=x/y when <|f_2|. (3) In the beam shaping optical system, the refraction surface perpendicular to the generatrix is the discharge electrode (E_1, E_1, E_1) of the excimer laser light source (1).
_2) The illumination optical device for an exposure apparatus according to claim 1 or 2, wherein the illumination optical device is installed parallel to the discharge direction between the two.