JPS62280818A - Illuminating optical system - Google Patents

Abstract

PURPOSE:To reduce a speckle generated on the irradiated surface by placing an electro-optical element having a prism type electro-optical crystal and an electrode in a luminous flux between a light source and an illuminating lens system, and varying a voltage impressed to the electro-optical element within a pulse light emission time of the light source. CONSTITUTION:A laser luminous flux 11 which has been oscillated from an eximer laser 1 is made incident on an electro-optical element 31, and the electro- optical element 31 is constituted of two prism type electro-optical crystals whose optical axes are orthogonal to each other, makes an emitted laser luminous flux 12 pass through an electro-optical element 32, and thereafter, light-leads it to an illuminating lens system 5. Also, when a luminous flux whose coherent range is large, what is called, whose interference property is good, such as laser, etc. is used, an uneven illumination caused by a speckle becomes large. Therefore, by varying continuously and quickly a voltage applied to an electrode within the pulse light emission time in the course of oscillation of the laser, a wave front of the laser luminous flux is inclined continuously by DELTAtheta radians. In this way, intensity of the speckle can be reduced.

Description

Detailed Description of the Invention Detailed Description of the Invention (Industrial Field of Application) The present invention relates to illumination optical systems, particularly in semiconductor manufacturing, and in applications where light sources such as high-intensity lasers with good coherence are used. It reduces uneven illumination caused by interference fringes on the irradiated surface, so-called speckles, that occur due to light interference when illuminating the entire irradiated surface, such as a mask surface or reticle surface on which fine patterns such as electronic circuits are formed. This relates to an illumination optical system that performs illumination.

(Conventional technology) Recent semiconductor manufacturing technology (with the increasing integration of electronic circuits)
There is a need for phosphorography technology that can form highly dense electronic circuit patterns.

Generally, when an electronic circuit pattern on a mask or reticle surface is transferred onto the eight surfaces of the sea urchin, the solution of the electronic circuit pattern to be transferred onto the eight surfaces of the sea urchin is tilj! @ is proportional to the wavelength of the light source. For this purpose, for example, ultra-high pressure mercury lamps, xenon mercury lamps, etc., which oscillate short wavelengths in the far ultraviolet (deep UV region) of 200 to 300 n@, are used. However, these light sources have low brightness and no directionality, and the photoresist applied to the eight surfaces of the sea urchins has low photosensitivity, resulting in a long exposure time and a reduction in overall photoresist quality.

Recently, a light source called exekmar laser, which has oscillation and long metal in the deep UV region, has been developed.
Due to its high brightness, monochromaticity, and good directivity, its application to phosphorography technology has been extensively studied. However, when using an excimer laser, in many cases irregularities may occur on one mask surface or eight surfaces due to imperfections on the mask surface or the surface of the sea urchin or the optical characteristics of the illumination system due to the unique coherency of the laser. So-called speckles, which are caused by interference fringes, occur.

These speckles cause uneven lighting and burn-in errors, and are a major cause of deterioration in the interpretation of mask butter/1 elephant.

(Problems to be Solved by the Invention) The present invention reduces speckles that occur when using a high-f4 light source with good coherence such as a laser, and enables uniform illumination of the illuminated area 1'J. The purpose is to provide a Toshiji illumination optical system.

A further object of the present invention is to reduce speckles that occur on the mask surface and the surface of the sea urchin when using a light source that oscillates pulsed light with good coherence, such as an excimer laser. Exposure VC for semiconductor manufacturing that made it possible to
An object of the present invention is to provide an illumination optical system suitable for fiL.

(Ninth means to solve all problems) When illuminating a surface to be illuminated by an illumination lens system using a light beam from a light source with good coherence, 1. The light beam between the light source and the illumination lens system. Prism type electro-optic crystal and electrode inside? Speckles generated on the irradiated surface by changing the voltage applied to the electro-optical elements within the pulse emission time of the light source.
This has been reduced.

Other features of the invention are described in the Examples.

(Implementation row) FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention. In the figure, 1 is a laser oscillator S31 when an excimer laser is used as a light source, 32 are each electro-optical elements, 41 is an electrode of the electro-optic element 31, 42 is an electrode of the Fi electro-optic element 32, and 5 is an irradiated object of a semiconductor exposure device. An illumination lens system for illuminating a mask surface, a reticle surface, etc. (hereinafter referred to as 1-mask surface). 6 is a high voltage oscillator for the electrode 41, and 7 is a high voltage generator for the electrode 42. Vessel, II, 1
2 and 13h are each a laser beam.

In this embodiment, the laser beam ll emitted from the excimer laser 1 is made incident on the electro-optical element 31. ``The optical element 31 is composed of two prism-type electro-optic crystals whose optics are orthogonal to each other.

And the laser beam L2i emitted from the electro-optical element 31
After passing through the electro-optical element 32't')'r, the light is guided to the illumination lens system 5. The electro-optical element 32 and the direct-air optical element 31 have a structure in which the electro-optical element 32 and the direct-air optical element 31 are rotatable by 90 degrees with respect to the center of the traveling beam of the laser beam.

In this implementation, electricity (the original plate surface of the laser that passes through the entire optical element 31 is divided into polar regions and the high voltage V7.c- generated by the high voltage generator 6 is applied) is shown in the figure. X
-1-''P- Fanning is performed within the song.

Let tθ be the clear month in this case. Here n. is the refractive index of the ordinary ray of the optical crystal, 1γ is the Pockels coefficient, ■ is the Ll voltage, t is the distance between 100,000,000, and t and W are the length and width of the electro-optical element, respectively.

In general, when using light beams with good coherence, the reason why speckles occur on the mask surface, which is the irradiated surface, is that among these light beams, the light beams within the spatially coherent range are irregular with each other. This is because they overlap with a certain phase difference within the irradiation time. Therefore, the coherence range of lasers etc. is large.
The more a so-called coherent light beam is used, the more uneven illumination caused by speckles becomes.

Therefore, in this embodiment, the wavefront of the p laser beam is continuously tilted by Δθ radians by changing the voltage applied to the electrode continuously and quickly within the pulse emission time during laser oscillation.

That is, the laser beam is deflected by the wavefront tΔθ.

As a result, for example, if the phase difference of 92 points separated by a distance d on the cross section of the laser beam is defined as the improvement tλ of the laser beam, then it is changed by 2rd·Δθ/λ.

Therefore, in this embodiment, d>λ/Δθ is set, and the amount of phase change is set to be 2 or more. A suitable time? They are mixed and their intensities cancel each other out, resulting in the same effect as if the light beams passing through the two points do not interfere at all.

The deflection angle θ is continuously changed by Δθ by the electro-optical element 31 during the pulse emission time during oscillation of the laser beam, and the interference range in the X direction is effectively changed to λ/Δθ. are roughly equivalent. Therefore, the laser beam 11
Speckle intensity on the mask surface, which is the irradiated surface, is approximately (λ/Δθ)/L over the entire interference range.

For example, if KDP (IJ potassium dihydrogen phosphate) is used as the electro-optic crystal, r -18-9,7X 10-12 m/Vno-1,6. w −t −1crt: * L −2cm
+λ-248n@, then λ/Δθ-0.25m at V-15KV. The cross section of the laser beam 11 is l cm
If the speckle intensity is spatially coherent within this range, the total speckle intensity A(-G, 2
5crIT/1m).

Furthermore, in this embodiment, the interference range in the Y direction is similarly shortened isometrically by interposing the electro-optical element 31 entirely through the electro-optical element 32 having a dot rotated by 90 degrees with respect to the center of the traveling light beam. This reduces the heckle strength of the varnish to about that of maple.

FIG. 2 is a partial explanatory diagram of another embodiment of the present invention. This embodiment is an example in which the spatial coherence range of the laser beam in the X direction is shorter than the width of the laser beam (this is the case in this embodiment).

In this implementation 1j, three electro-optical elements 33 similar to those shown in FIG.
Two laser beams 21 are arranged in parallel for each coherent range of the incident laser beam 21 in the X direction. As a result, the speckle intensity caused by the laser beam 22 emitted in the range between each
-Reduced. Furthermore, as is clear from equation (1), by making the length t of the electro-optical element small (in this embodiment, it is a length), it is easier to manufacture, and furthermore, the absorption loss of the laser beam by the crystal is reduced.

Note that 8 is a high voltage generator and 43 is an electrode.

In the above embodiments, if the amount of deflection angle by the electro-optical element is insufficient, a plurality of electro-optical elements may be arranged in series.

(Effects of the Invention) According to the present invention, by controlling the direct pressure applied to the electro-optic element made of a prism-type electro-optic crystal, the lateral coherence range of the laser beam can be increased. It is possible to achieve an illumination optical system that is suitable for 1, especially half-four exposure illumination, which completely improves the H (1 degree unevenness) on the illuminated surface due to the influence of speckle. .

[Brief explanation of the drawing]

FIG. 1 is a 9-detour diagram of ``Embodiment 1'' of the present invention, and FIG. 2 is a partial explanation of the Ike no Eiho I of the present invention. In the figure, 1 is a laser oscillator, 31, 32, 33d Taniya'Kamekigen'? Elements 6, 7.8 are high 4 pressure generators, 4
1, 42, 43 are each 4 koshi, 5 is a lighting system,
11, 12, 13, 21, and 22 are laser beams.

Claims (4)

[Claims] (1) When illuminating a surface to be illuminated by an illumination lens system using a light beam from a light source with good coherence, a prismatic electro-optic crystal is included in the light beam between the light source and the illumination lens system. An illumination device characterized in that speckles occurring on the irradiated surface are reduced by arranging an electro-optical element having an electrode and changing the voltage applied to the electro-optical element within the pulse emission time of the light source. Optical system. (2) The illumination optical system according to claim 1, wherein the electro-optic element has two prism-type electro-optic crystals whose optical axes are orthogonal to each other. (3) A laser is used as the light source, and two of the electro-optical elements are arranged at positions rotated 90 degrees from each other with respect to the center of the traveling light beam of the laser. Or the illumination optical system according to item 2. (4) The illumination optical system according to claim 1, wherein a plurality of the electro-optical elements are arranged in parallel according to the lateral coherence range of the light beam from the light source.