JPS63232320A - Pattern exposure device - Google Patents

Abstract

PURPOSE:To reduce distortion of an image, by utilizing a phase plate so as to correct phases of lights, which pass through upper and lower ends of a lens, before the lights pass through the lens. CONSTITUTION:Flux of light 1 emitted from a light source is radiated on a mask 2 on which a pattern is formed. An image on the mask 2 is focused on a wafer (substrate) 11 through a projection lens 7. Lights 4, 5, and 10 emitted from a point P2 on the peripheral part of the mask 2 are made to respectively pass through the peripheral and central parts of the lens 7. Since phase differences between their lights are large and so the image distortion is increased upon the focusing on a point P4 on the wafer 11, phases of the lights 4, 5, and 10, which are projected from the point P2 and made to pass near the central part of the mask projection lens 7 and through the peripheral parts on the right and left sides, are regulated by a phase plate 3 before the lights pass through the lens 7, and so the phase difference upon the focusing on the point P4 is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mask pattern exposure method in an LSI 1 manufacturing process, etc., and particularly to a pattern exposure apparatus suitable for exposing a mask pattern consisting of a fine pattern.

[Conventional device]

Conventionally, as described in Japanese Unexamined Patent Publication No. 59-178730, the mask pattern itself has been deformed in order to compensate for transfer distortion caused by aberrations in the optical system of a projection exposure apparatus.

[Problems to be Solved by the Invention] The above-mentioned conventional technology has the problem that it is necessary to perform deformation for each mask pattern to correct transfer distortion of the exposure device, which increases cost.

An object of the present invention is to reduce the transfer distortion of the exposure apparatus optical system itself to a practical value, thereby making deformation of the mask pattern unnecessary and reducing costs.

[Means for solving problems]

The above object is achieved by correcting the aberration of the exposure optical system, which causes butter 1 transfer distortion, by using a phase plate having a thickness distribution, thereby reducing the aberration.

[Effect]

When a mask pattern is transferred to a wafer substrate using an exposure optical system, there is almost no transfer distortion in the center of the mask.
However, transfer distortion is generally large in the peripheral area of the mask (an area where the distance from the center of the optical axis to the image is long and the image height is high). This is because the phase difference (wavefront aberration) of the light rays passing through the upper and lower ends (or left and right ends) of the lens is large.
This is because image distortion increases.

Therefore, in order to eliminate this phase difference, we adopted a method that uses a phase plate to correct the phase of the light beam passing through the upper and lower ends of the lens before passing through the lens. In this way, there is no phase difference when the mask image is formed on the wafer, and image distortion can be reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. A light beam 1 emitted from a light source passes through a mask 2 on which a pattern is formed.
irradiate. An image of the mask 2 is formed onto a wafer (substrate) 11 by a projection lens 7.

Light 6, 8° 9 emitted from a point P1 near the center of the mask passes through the periphery and center of the lens, respectively, and forms an image at a point Pa. The lens has almost no aberration with respect to the center of the mask, and image distortion is extremely small.

On the other hand, the light emitted from the point Pa at the periphery of the mask is 4°5.1o
pass through the periphery and center of the lens, respectively, but the phase difference (wavefront aberration) of the light is large, resulting in large image distortion when focusing on P4.

In an ultra-fine processing process such as a VLSI manufacturing process, the occurrence of such transfer distortion is undesirable because it deteriorates the characteristics of the device and lowers the manufacturing yield.

If the phase difference of light can be reduced and the wavefront aberration can be lowered to a practically negligible level, the distortion of imaging at P4 can be eliminated, and the transfer distortion can be eliminated, allowing ultra-fine processing in the ultra-LSI manufacturing process, etc. It is convenient for the machining process.

Therefore, light that comes out from one point P2 and passes through the left peripheral part near the center of the mask projection lens 7, the right peripheral part, 5, 10, .
The phase (wavefront) of 4 is adjusted by the phase plate 3 to obtain one point P4.
The method for eliminating the phase difference (aberration) during image formation will be explained with reference to FIG. The phase difference between the light 9 coming out of Pz and heading towards the left side periphery of the lens and the light 4 heading towards the right side periphery of the lens is compared. Assuming that the distance between the mask 2 and the phase plate 3 is very small compared to the phase plate-like passage lengths dt and dz of the respective lights, the optical distance Qz between Pz and Ql is Qx t Pz Qz.

respectively, Qt=n, dt+ (dz-dt) (1
)Qz=n,dz (2)
Here, n is the refractive index of the phase plate 3, and the triangle I'zQxQ2
is an isosceles triangle whose base is Q IQ z.

The phase difference T1 is determined from the difference between Ql and Qz, and 'f's=
(n(dz-dx)-(dz-dt))(2g/λ)(
3) = (n 1) (dz-d 5) (2
π/λ) (4) Here, λ is the wavelength of light.

If dz and dz are selected so that the absolute value of the wavefront aberration (phase difference) of the lens itself is equal to the absolute value of 1 and the sign is opposite, then at one point P4, the left and right peripheral parts of the lens The phase difference of the light 10.4 that has passed can be made zero. The phase difference of the light 5 passing near the center of the lens can also be eliminated by a similar method. By performing such calculations for the light passing through each point of the lens, a curve 12 of the ideal thickness distribution of the phase plate can be obtained.

The present invention is also applicable to the case where a plurality of phase plates are used. Furthermore, the present invention also applies to cases where the thickness of the phase plate is distributed not only one-dimensionally but also two-dimensionally. The present invention is also applied to the case of using a projection lens made of a set of lenses made up of a plurality of single lenses. Furthermore, the present invention is applicable not only to refractive lenses but also to cases where an imaging optical system that uses a reflective optical system at least in part is employed.

〔Effect of the invention〕

According to the present invention, it is possible to reduce the transfer distortion of the optical system of the exposure apparatus itself, so that deformation of the mask pattern is unnecessary, and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a pattern exposure apparatus using a phase plate according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the thickness distribution shape design of the phase plate. 1... Luminous flux, 2... Mask, 3... Phase plate, 7.
... Projection height 1 figure I eye+! +-1 House 2 diagram

Claims (1)

[Scope of Claims] 1. A pattern exposure apparatus for forming an image of a mask pattern on a substrate by an imaging optical system, characterized in that an optical phase element is provided near the mask. 2. The pattern exposure apparatus according to claim 1, wherein the optical phase element is an optical phase plate having at least one-dimensional thickness distribution.