JPH0562877A - Optical system for lsi manufacturing contraction projection aligner by light - Google Patents

Abstract

PURPOSE:To obtain a mirror type stepper in which a short wavelength ultraviolet ray is used as a light source and which has a deep focal depth, a wide exposure area and a large numerical aperture. CONSTITUTION:A light source is mounted at one focal point of a rotational elliptical concave mirror, the small hole 8 of the mirror 7 is mounted at the other focal point, and the hole 8 also becomes a focal point of a parabolic mirror 10. A high coherent light is used as a light source thereby to deepen a focal depth, to remove various aberrations and to improve an effective numerical aperture. Further, a reticle image is increased larger than an image on a wafer and the width of the wavelength of an illumination light is increased thereby to prevent deterioration of the image due to the use of the coherent light. In this case, its resolution is improved when transparent liquid is filled between optical systems.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system of an LSI manufacturing reduction projection exposure apparatus (stepper) using mirror type light. [0002] [Prior Art] Conventionally, there is a mirror type equal-magnification collective projection exposure apparatus and a lens type stepper. [0003] [Problems to be solved by the invention] In the optical system of the conventional mirror type unit-magnification batch projection exposure apparatus, only a linear image of equal magnification is obtained, so that precise alignment of the mask image is difficult. However, there is a problem in that the influence of dust is great and it is difficult to correct all defects. [0004] In the conventional lens type stepper, there are problems that there are few transparent substances that can be used for a lens with short wavelength ultraviolet rays, low transparency, and durability of the lens. [0005] It is an object of the present invention to provide a stepper having a mirror type optical system capable of using short wavelength ultraviolet rays, having a high resolution, a wide exposure area and a deep depth of focus. [0006] [Means for Solving the Problems] In order to achieve the above object, in the optical system of the stepper of the present invention,
A high-coherent light of a relatively wide wavelength range is used as a light source, and a concentrating concave mirror is used to concentrate the light at one point in front of the reticle. [0007] A small hole on the plane mirror is installed at the one point where the light is concentrated. [0008] A concave mirror is installed on the opposite surface of the plane mirror so that the focal point of the concave mirror and the small hole of the plane mirror coincide with each other.

[0009] The light from the light source irradiates the reticle, passes through the small hole of the plane mirror, becomes a substantially parallel light beam by the concave mirror, and installs an extremely thin transparent window plate that is perpendicular to the parallel light rays traveling by being reflected by the same plane mirror. A wafer is placed in close proximity to the transparent window plate, and a reticle image is reduced and formed on the wafer. [0011] Then, the reticle is formed into a curved surface for correcting the curvature of field. [0012] Fill the space between the optical systems with a transparent liquid,
Circulating the transparent liquid is effective for the reasons described below. [Operation] The light transmitted through the reticle is also highly coherent. Assuming that the wavelength λ, the diameter D of the condenser concave mirror, and the focal length are f, the total light amount is 84. within the radius of γ = 1.22λf / D. 6% are concentrated in the small hole in the plane mirror in front of the reticle. The surrounding area shows the diffraction image of the reticle. [0014] In the present invention, since the reticle and the transparent window plate are made of synthetic quartz, the surface can be polished smoothly, and the influence of the surface due to the use of high coherent light is small. [0015] In the present invention, since it is isolated from the outside world by the transparent window, the convection of air is small and the invasion of dust is prevented. When the entire invention is brought closer to a vacuum, the influence of air convection and dust is reduced. [0016] Conversely, by filling the space between the mirror optical systems with a transparent liquid and circulating the transparent liquid, the influence of the surfaces of the reticle and the transparent window plate is reduced, and the influence of dust is reduced. The change in the refractive index of light due to the temperature rise due to the absorption of light by the transparent liquid is prevented. [0017] Since the transparent window is extremely thin and is installed perpendicularly to the light reflected by the concave mirror and the plane mirror, no chromatic aberration occurs. [0018] In the present invention, since the electrostatic precipitator is installed around the small hole of the flat mirror between the flat mirror and the reticle,
The dust inside the stepper is removed to prevent the dust from entering the mirror optical system through the small hole of the flat mirror. In the present invention, the more transparent the image pattern on the reticle is, the better. Therefore, it is necessary to consider it when forming an image. Depending on the image pattern, it may be better to perform an inversion of the photoresist image. The LSI manufactured by the stepper of the present invention has a defective portion corresponding to the small hole of the flat plate mirror at the center portion, but since the small hole has a diameter of about 1 mm, there is no influence on the LSI integration degree. Of course, if the light quantity of the light source can be increased, the diameter of the small hole can be set smaller. [Embodiment] An embodiment will be described with reference to the drawings. In FIG. 1, a xenon lamp 1, a filter 2,
Slit 3, spheroidal concave mirror 4, reticle 5, plane mirror 7
The small hole 8, the parabolic mirror 10, the plane mirror 7, the transparent window plate 11, and the wafer 12 are installed in this order in the optical path of the light from the xenon lamp 1, and the slit 3 is placed at one focus of the spheroidal concave mirror. , The small hole 8 of the plane mirror 7 is installed at the other focal point. The small hole 8 also serves as the focal point of the parabolic mirror 10. At this time, the mirror surface 9 of the plane mirror 7 is installed to face the parabolic mirror 10, and the electrostatic precipitator 6 is mounted around the small hole 8. There is an example in which the xenon lamp 1 is replaced by several kinds of gases such as AγF and KγF, and an excimer laser that fluctuates the oscillation wavelength is used as a light source. There is an example in which an aberration correction lens is used instead of the transparent window plate 11. [0024] There is an embodiment in which the parabolic mirror 10 is replaced with another concave mirror such as a spherical mirror or a hyperbolic mirror. In the embodiment shown in FIG. 2, the space between the optical systems is filled with a transparent liquid, and the transparent liquid is circulated. The reticle 5 is immersed in a tank 13 filled with a transparent liquid. [0026] [Effect of the Invention] Since the present invention is configured as described above, it has the following effects. [0027] Since the reticle irradiation light source uses high coherent light and is focused on one point in front of the reticle by the spheroidal concave mirror, the wavelength λ, the diameter D of the spheroidal concave mirror,
Assuming that the focal length is f, 84.6% of the total amount of light is concentrated in the small hole of the plane mirror in front of the reticle within the radius of γ = 1.22f / D. The area around the small hole is a diffraction image of the reticle, but the central part of the small hole has an extremely high amount of light compared to the peripheral ring-shaped edge part of the light wavelength width of the small hole. The rate at which light passes through and diffracts is extremely small. Therefore, the decrease in resolution due to the passage of light through the small holes is extremely small. The effect is that small holes are γ =
It increases as the radius approaches 1.22 λf / D. [0028] Since most of the light that reaches each point of the image on the surface of the wafer is reflected by a very small range corresponding to the parabolic mirror, the depth of focus is deep and the image plane curve or image plane is deep. Aberrations other than distortion are extremely small. [0029] Also, most of the light that reaches each point of the image on the surface of the wafer is reflected in a correspondingly small area of the parabolic mirror, so that the computational aperture of the parabolic mirror. The effective numerical aperture is larger than the numerical aperture. [0030] When high coherent light is used as the irradiation light source, speckle noise or the like appears in the diffraction development of the reticle image, but since it is a type that is reduced to about 1/10 of the reticle image, a large reticle image pattern should be used. In addition, since there is no chromatic aberration and the wavelength band is wide because of no chromatic aberration, there is no deterioration of the image even when high coherent light is used as the light source. [0031] With the stepper of the present invention, an exposure area of about 30 mm, a numerical aperture of about 0.35 (the effective numerical aperture is larger) can be obtained. [0032] Since the present invention uses the mirror type optical system, shorter wavelength ultraviolet rays can be used than the lens type optical system stepper. [0033] If the wavelength of light is λ and the refractive index of the transparent liquid is η by filling the space between the optical systems with a transparent liquid, the same effect as using light of λ / η is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the construction of an embodiment of a stepper according to the present invention. FIG. 2 is a configuration diagram of a reticle peripheral portion of an embodiment in which a transparent liquid is filled between the optical systems of the stepper of the present invention. [Explanation of symbols] 1 xenon lamp 2 filter 3 slit 4 spheroidal concave mirror 5 reticle 6 electrostatic precipitator 7 plane mirror 8 small hole 9 plane mirror surface 10 parabolic mirror 11 transparent window plate 12 wafer 13 tank for filling transparent liquid 14 Transparent liquid flow that fills the optical system

Claims (2)

[Claims] [Claim 1] An irradiation mechanism for concentrating light at a point in front of the reticle is provided, a small hole of the plane mirror is aligned with the point at which the light is concentrated, and a plane mirror is installed opposite to the mirror surface of the plane mirror. An optical system of an LSI manufacturing reduction projection exposure apparatus characterized by the above. [Claim 2] An LSI manufacturing reduced projection exposure apparatus according to claim 1, wherein the space between the optical systems is filled with a transparent liquid, and the transparent liquid is circulated.