JPH07104563B2 - Illumination optical device for exposure equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to an illumination optical device of a semiconductor exposure apparatus that transfers a mask pattern using a laser beam as an illumination light flux, and in particular, 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 a semiconductor exposure apparatus that transfers a fine mask pattern such as IC and LSI onto a wafer surface, a wavelength of 436n has been conventionally used.
Ultra-high pressure mercury lamps that mainly oscillate m or 365 nm light are widely used, but in order to obtain higher density and finer patterns, a light source that oscillates powerful light at a shorter wavelength is required. . Therefore, the above ultraviolet wavelength range (350 to 450
The exposure apparatus provided with an excimer laser that oscillates a wavelength shorter than 100 nm as an illumination light source is disclosed in, for example, Japanese Patent Laid-Open No.
It is disclosed by the Japanese Patent Publication No. 198631 and is already known.

According to the above publication, an illumination light source (excimer laser)
Light is projected onto the mask through illumination optics using a focusing component and other optical components to uniformly illuminate the entire area of the mask. 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. Further, in order to expand the laser beam to a beam having a desired large diameter, it is also known to use a beam expander composed of two spherical lenses having different focal lengths, which is well known in an optical device using a laser. Technology.

(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 mm × 20 mm. . Therefore, even if the light intensity on the mask is made uniform using the above optical integrator, the cross-sectional shape of the laser light flux is still rectangular, so when the pattern image of the mask is projected through the projection lens, There was a drawback that the resolution was different between vertical and horizontal. Also, since the cross-sectional shape of the laser light flux does not change even if the beam diameter is expanded with a beam expander, when beam shaping into a circular cross section with a diaphragm,
Large vignetting occurs in the longitudinal direction, and in some cases, the exposure amount may be insufficient.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the conventional apparatus and to provide an illumination optical apparatus for a semiconductor exposure apparatus, which can transfer an extremely fine mask pattern efficiently and correctly.

[Structure of Invention]

(Means for Solving the Problems) In order to solve the above problems, in the present invention, a beam shaping optical system including two anamorphic lenses having different refracting powers in only one direction is cross-sectioned. It is technically provided to be provided on the illumination optical path from an excimer laser light source that outputs a rectangular laser light beam, whereby the laser light beam is shaped into a substantially square cross-sectional shape and then the pattern on the mask is illuminated. This is the main point.

(Operation) The laser light flux having a rectangular cross section which is incident by the beam shaping optical systems 3, 13, and 23 has a substantially square shape in which the short side is enlarged or the long side is reduced due to the refracting power in only one direction. The laser beam is shaped into a cross-section. The laser light flux shaped into a square cross section becomes a laser light flux having a substantially circular cross section because only the light fluxes at the four corners are cut by the optical system rotationally symmetric about the optical axis, and after illuminating the pattern area on the mask 6. A pattern image of the mask 6 is formed on the wafer 8 through the entrance pupil of the projection objective lens 7.
Therefore, the laser light flux output from the excimer laser light source is used for projection exposure with a sufficient light amount without being cut wastefully.

(Example) Next, the Example of this invention is described in detail based on an accompanying drawing.

FIG. 1 is an optical system configuration diagram showing an embodiment of the present invention. A laser beam emitted from an excimer laser light source 1 is reflected and diverted downward by a mirror 2 and an analog such as a pair of cylindrical lenses described in detail later. Morphic optical system 3A,
The beam shaping optical system 3 composed of 3B shapes the beam into a predetermined cross section. The beam-shaped laser light flux is divided into a large number of divergent light fluxes by an optical integrator 4 such as a fly-eye lens, as disclosed in, for example, Japanese Patent Laid-Open No. 56-81813. The reticle 6 is focused and uniformly illuminated. In this case, the optical integrator 4 makes a large number of minute light sources on one plane and acts as a secondary light source. The circuit pattern on the reticle 6 that is uniformly illuminated by the 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 chamfered discharge electrodes E ₁ and E ₂ provided in the atmosphere of the enclosed laser medium, as shown in FIG. Flash light generated when a high voltage is applied between ₁ and E ₂ to cause discharge resonates in the longitudinal direction of the electrode and emits light in the direction of arrow L. At that time, the cross-sectional shape of the laser beam is
Although it has characteristics that are greatly influenced by the shapes of E ₁ and E ₂ ,
Excimer lasers currently on the market have a rectangular cross-sectional shape as shown in FIG. 3, in which the discharge direction is the long side (x) and the direction perpendicular to this is the short side (y). Many. In the excimer laser light source 1 shown in FIG. 1, the main discharge electrodes E ₁ and E ₂ are vertically arranged side by side as shown in FIG.
The cross section of the oscillated laser beam is a rectangle that is vertically long. After being turned downward by the mirror 2, this laser light flux has a rectangular cross section that is long in the left and right as shown in FIG. 4 (a), and has a beam shaping optical system 3 that constitutes a main part of the present invention. Incident on.

The beam shaping optical system 3 includes a diverging cylindrical lens 3A and a converging cylindrical lens 3B.
As shown in FIG. 5, the generatrices of both cylindrical lenses 3A and 3B are arranged to be parallel to each other. That is, the rays in the plane including the generatrix pass through without being refracted as shown in FIG. 5 (a), and the rays in the plane perpendicular to the generatrix are refracted as shown in FIG. 5 (b). To do. In this case, set the focal points of both cylindrical lenses 3A and 3B
If they are arranged so that they match each other at O ₁ , an afocal system is formed by both cylindrical lenses, and a parallel light flux parallel to the generatrix incident on one cylindrical lens 3A is also emitted as a parallel light flux from the other cylindrical lens 3B. At that time, only the light rays in the plane perpendicular to the generatrix are expanded in width as shown in FIG.

Now, set the focal length of _one cylindrical lens 3A to f ₁ ,
The focal length of the other of the cylindrical lens 3B and f _2, the long side length of the excimer laser beam x, the length of the short side and _{y, | f 1 | <|} f 2 | to the | f ₂ / f By selecting both focal lengths so that the formula ₁ | = x / y (1) is satisfied, the excimer laser beam with a rectangular cross section can be shaped into a square cross section.

In FIG. 1, the light rays in the plane including the generatrix of the cylindrical lenses 3A and 3B (the plane parallel to the paper surface) are indicated by solid lines, and the light rays in the plane perpendicular to the generatrix (plane perpendicular to the paper surface) are indicated by broken lines. Show. As shown in FIG. 4 (a), the excimer laser light flux having a rectangular cross section with a long side x and a short side y reflected by the mirror 2 is reflected by the divergent cylindrical lens 3A.
Only the long side is enlarged and becomes equal to the long side x, and the parallel luminous flux is emitted by the absorptive cylindrical lens 3B. Therefore, the light beam that has passed through the beam shaping optical system 3 is beam shaped into a square cross section of which one side is x, as shown in FIG. The beam-shaped laser light flux has an optical integrator 4 and a diaphragm having a circular aperture provided in the image plane of the secondary light source formed by the optical integrator 4 or in the vicinity thereof (hereinafter referred to as “α diaphragm”). The pattern area of the mask 6 is uniformly illuminated through the 4A and the condenser lens 5. At that time, the secondary light source formed by the optical integrator 4 into a set of a large number of bright spots also has a substantially square cross-sectional shape with one side x, and the four corners are cut by the α stop 4A to form a substantially circular shape. The shape is as shown in FIG.

The laser light flux illuminating the pattern on the mask 6 passes through the entrance pupil (substantially the diaphragm in FIG. 1) P of the projection objective lens 7 to form a pattern image on the wafer 8. In this case, the α stop 4A is provided at a position conjugate with the entrance pupil P of the projection objective 7, and the image I of the aperture of the α stop 4A is the fourth.
An image is formed in the entrance pupil P as shown in FIG. This α
When the size of the image I of the aperture of the diaphragm 4A (that is, the cross section of the light flux passing through the entrance pupil P) is set to 0.5 to 0.7 with respect to the entrance pupil P, a pattern image with good resolution and contrast on the wafer 8 is obtained. Can be obtained. Therefore, α aperture
By only slightly cutting the laser light flux by 4A, it becomes possible to perform projection exposure by making maximum use of the laser light flux from the excimer laser light source.

The beam shaping optical system 3 is shown in FIG. 6 in place of the anamorphic beam shaping optical system consisting of the divergent (negative) cylindrical lens 3A and the convergent (positive) cylindrical lens 3B shown in FIG. As shown, the anamorphic beam shaping optical system 13 may be configured using only the positive cylindrical lenses 13A and 13B. In this case, both lenses 13
The focal lengths f ₁ and f ₂ of A and 13B are determined by using the above equation (1). Further, both lenses 13A and 13B are arranged so as to be in focus at a point O _{2 as} shown in FIG.

FIG. 7 is an explanatory view showing the relationship between the directions of the generatrixes of the cylindrical lenses 3A, 3B, 13A and 13 constituting the beam shaping optical systems 3 and 13 and the directions of the electrodes E ₁ and E ₂ of the excimer laser light source 1. It is a figure. Each cylindrical lens 3A, 3B, 13A, 13B,
(Indicated by an arrow S _1.) Figure 7 direction of the bus as shown in (a) is, electrodes E _1, E ₂ of the arrangement direction, ie installed so as to be parallel to the longitudinal direction of the rectangular cross section of the laser beam To be done. As a result, the laser light flux goes straight through the cylindrical lenses 3A (13A) and 3B (13B) without refracting in the direction of the generatrix as shown in FIG. 7 (a), but as shown in FIG. 7 (b) and As shown in FIG. 7C, in the direction perpendicular to the generatrix (indicated by the arrow S ₂ ), the luminous flux width is expanded by one of the cylindrical lenses 3A and 13A, and then the other cylindrical lens 3B. , 13B, so that the light flux becomes parallel again. Therefore, this beam shaping optical system 3, 13
By paralleling the direction of the generatrix of the cylindrical lens constituting the above with the discharge direction of the discharge electrodes E ₁ and E ₂ of the excimer laser light source, it is possible to enlarge only the direction of the short side of the laser light flux having a rectangular cross section.

Further, when light is passed from the left side to the anamorphic beam shaping optical systems 3A, 3B, 13A, 13B shown in FIGS. 5 and 6, the light flux width in only the direction perpendicular to the generatrix is shortened. Is possible. Therefore, when the light flux in the output cross section of the excimer laser light source 1 is appropriate in the y direction and too long in the x direction in FIG. 3, for example, in order to reduce the x direction, the expansion type beam shaping optical system is used. And the direction of the busbar is set at right angles 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 illuminate the mask 6 by reducing the longitudinal direction of a laser beam having a rectangular cross section and shaping the beam into a beam having a square cross section. In the optical system layout diagram, (a), (b) of FIG.
(C) and (d) are respectively AA and B of the luminous flux of FIG.
It is a B-C, CC, and DD sectional drawing. It should be noted that parts having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and detailed description of their configuration will be omitted.

In FIG. 8, the laser light flux from the excimer laser light source 1 is reflected by the mirror 2 and enters the reduction type beam shaping optical system 23. The cross-sectional shape of the laser beam at that time is a rectangular shape that is long in the left-right direction as shown in FIG. The beam shaping optical system 23 is composed of a positive cylindrical lens 23A and a negative cylindrical lens 23B having a generatrix in a direction perpendicular to the paper surface, and the laser beam passing through this beam shaping optical system 23 is shown in FIG. 9 (b). As shown, only the left-right direction is reduced and the beam is shaped into a substantially square shape having one side of the short side y of the rectangular cross section of the incident light flux. This laser beam having a square cross section is formed into a circular secondary light source composed of a set of a large number of bright spots by the optical integrator 4 and the α stop 4A having a circular aperture. The light flux from the secondary light source uniformly illuminates the mask 6 via the condenser lens 5. FIG. 9 (c) shows the cross-sectional shape of the light flux that has passed through the aperture of the α stop 4A. The laser light flux illuminating the mask 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. Also in this case, an image I of the α stop 4A is formed on the entrance pupil P with an appropriate size with respect to the entrance pupil P as shown in FIG. 9 (d). Therefore, the luminous flux from the excimer laser light source 1 can be used most effectively. In the second embodiment, the focal length of the positive cylindrical lens 23A is f ₂ , and the negative cylindrical lens 2A is
Since 3B is f ₁ and the afocal system is configured so as to satisfy the above equation (1), the long side x of the excimer laser beam having a rectangular cross section becomes equal to the short side y.

When the square cross section of the beam-shaped excimer laser beam in the embodiment shown in FIG. 1 and FIG.
A general beam expander composed of an afocal system or a reversed version thereof may be added to the optical path between the beam shaping optical systems 13 and 23 composed of cylindrical lenses and the optical integrator 4. In addition, by forming a plane on the side opposite to the cylindrical surface of the cylindrical lens shown in FIGS. 1 and 2 into a spherical surface (positive or negative) having an appropriate curvature, the beam shaped into a square beam can be further formed as a whole. It is also possible to enlarge or reduce the size and perform beam shaping to an appropriate size for the entrance pupil of the projection objective lens.

〔The invention's effect〕

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

[Brief description of drawings]

1 is a layout view 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 portion of an excimer laser light source used in the embodiment of FIG. 1, and FIG. The figure is the second
FIG. 4 is a plan view showing the cross-sectional shape of the excimer laser light flux output from the discharge electrode section in the figure, and FIG. 4 is an explanatory view showing changes in the cross-sectional shape of the excimer laser light flux in the embodiment of FIG.
(A), (b), (c), and (d) are cross-sectional views of the excimer laser light flux taken along the lines AA, BB, CC, and DD in FIG. 1, and FIG. The first, which is an essential part of the present invention
In the explanatory diagram of the beam shaping optical system in the figure, (a) is a transverse sectional view parallel to the generatrix (b) is a longitudinal sectional view of (a), and FIG. 6 is a beam shaping showing an embodiment different from FIG. FIG. 7 is an explanatory diagram showing 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. An optical system layout of a projection exposure apparatus showing an embodiment, FIG. 9 is an explanatory view showing a change in cross-sectional shape of the excimer laser light flux in FIG. 8, (a), (b),
(C) and (d) are AA, BB, and C of FIG. 8, respectively.
FIG. 6 is a cross-sectional view of excimer laser light fluxes on cross sections -C and DD. (Explanation of symbols of main parts) 1 ... Excimer laser light source 3, 13, 23 ... Beam shaping optical system 3A, 3B, 13A, 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) E ₁ , E ₂ ... Main discharge electrode P ... Entrance pupil

Claims (4)

[Claims] 1. A projection exposure apparatus for projecting an image of a pattern on a mask onto a photosensitive substrate using an excimer laser as an illumination light source for exposure, comprising at least two anamorphic lenses having different refractive powers in only one direction. A beam shaping optical system is provided on the illumination optical path from the excimer laser light source, and is configured to illuminate the mask after beam shaping of the light flux cross section of the excimer laser light source into a substantially square shape. Let f _{1 be} the focal length of the lens in the one direction, f _{2 be} the focal length of the other lens in the one direction, x be the long side and y be the short side of the excimer lens light flux having a rectangular cross section, and | f ₁ | < An illumination optical apparatus for an exposure apparatus, characterized in that when | f ₂ |, the relationship of | f ₂ / f ₁ | = x / y is substantially satisfied. 2. The illumination optical apparatus for an exposure apparatus according to claim 1, wherein the beam shaping optical system is formed by cylindrical lenses having different focal lengths. 3. The beam shaping optical system has a refraction surface perpendicular to a generatrix, the discharge electrodes (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 so as to be parallel to the discharge direction between them. 4. The illumination optical device for an exposure apparatus has an optical integrator and a condenser lens arranged in an optical path on the exit side of the beam shaping optical system, and a secondary light source forming surface by the optical integrator has a circular shape. An illumination optical apparatus for an exposure apparatus according to any one of claims 1 to 3, characterized in that a diaphragm having an opening is arranged.