Optical: systems and elements – Diffraction – From grating
Reexamination Certificate
1998-02-27
2001-07-24
Chang, Audrey (Department: 2872)
Optical: systems and elements
Diffraction
From grating
C359S566000, C355S053000, C355S067000
Reexamination Certificate
active
06266192
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to a projection exposure apparatus and a device manufacturing method. Specifically, the invention is suitably usable in the manufacture of devices with patterns of a size on the order of submicron or quartermicron order or smaller, such as ICs, LSIs, CCDs or liquid crystal panels, for example, based on a projection optical system with a diffractive optical element for projecting and printing a device pattern of a reticle or mask (hereinafter “mask”) on different regions on a wafer through a step-and-repeat procedure or step-and-scan procedure.
Many proposals have recently been made in relation to an optical system having a diffractive optical element. Examples are “SPIE, Vol. 1354, International Lens Design Conference (1990)”, Japanese Laid-Open Patent Applications, Laid-Open No. 213421/1992, No. 324262/1994 and No. 331941/1994, and U.S. Pat. No. 5,044,706, wherein a phenomenon that chromatic aberration of a diffractive optical element is inverse to that of an ordinary refractive lens element is utilized and wherein a diffractive optical element having a positive optical power is formed on the surface of a lens or transparent plate to reduce the chromatic aberration of the optical system.
Further, proposals have been made with respect to a diffractive optical element called a “binary optics element” wherein the units constituting the element are defined by a step-structure of two levels or more. Examples are “G. J. Swanson, Technical Report 854, MIT Lincoln Laboratory, Aug. 14, 1989” and “G. J. Swanson, Technical Report 914, MIT Lincoln Laboratory, Mar. 1, 1991”.
On the other hand, proposals have been made with respect to a projection exposure apparatus for the manufacture of semiconductor devices, which uses a diffractive optical element for correction of aberrations. Examples are Japanese Laid-Open Patent Applications, Laid-Open No. 331941/1994, No. 128590/1995 and No. 17719/1996. In these proposals, a projection optical system includes one or more diffractive optical elements mainly for correction of axial chromatic aberration or magnification chromatic aberration.
With respect to efficiency of the use of light, use of a phase type diffractive optical element may be preferable. In a phase type diffractive optical element, if its kinoform is defined idealistically, it shows a diffraction efficiency of 100%. In a binary optics element, as compared therewith, since its kinoform is defined by approximation with steps, it does not show a diffraction efficiency of 100% even though the element is formed idealistically. With a structure of eight steps, for example, a highest diffraction efficiency will be about 95%. Thus, diffraction light (unwanted diffraction light) not contributable to the imaging, will be produced. Such unwanted diffraction light is not correctly imaged at a desired position, and it produces flare light which reaches the image plane and deteriorates the image quality.
SUMMARY OF THE INVENTION
On an occasion when a diffractive optical element produces unwanted diffraction light such as described above, there are two possibilities: that is, a case in which the unwanted diffraction light is reflected once or more by an inside wall of a lens barrel until it reaches the image plane; and a case in which it passes through the effective diameter of the optical system without such reflection. According to the investigations made by the inventors, it has been found that: of these two types of unwanted diffraction lights, the unwanted diffraction light which is reflected by the lens barrel can be reduced in its intensity to a level that can be disregarded, by means of a barrel design or an anti-reflection treatment to the inside wall of the barrel; whereas the unwanted diffraction light that directly passes through the effective diameter of the optical system may cause non-uniform exposure.
When the effect of unwanted diffraction light upon the image quality is to be evaluated, both (i) the intensity of unwanted diffraction light relative to the diffraction light of design order or orders (the intensity of regular diffraction light to be used for the imaging), upon the image plane, as well as (ii) the intensity distribution of the unwanted diffraction light upon the image plane, should be considered. Of course, it is desirable that the intensity of unwanted diffraction light upon the image plane is nearly equal to zero. However, to accomplish it is very difficult. Through the investigations made by the inventors, it has been found that, even if there is unwanted diffraction light having an intensity of a few percent of the intensity of diffraction light of design orders, there occurs substantially no adverse effect to the image quality provided that the intensity distribution of the unwanted light on the image plane is approximately uniform.
It is accordingly an object of the present invention to provide a unique and improved projection exposure apparatus and a device manufacturing method using the same.
In accordance with a first aspect of the present invention, there is provided a projection exposure apparatus, comprising: an illumination optical system for illuminating a mask with light from a light source; and a projection optical system having a diffractive optical element, for projecting an image of a pattern of the mask, as illuminated, onto a substrate, wherein said diffractive optical element is adapted to produce first diffraction light of a first order to be used for formation of the image and second diffraction light of a second order different from the first order, to be projected on the substrate to provide there a substantially uniform intensity distribution.
In accordance with a second aspect of the present invention, there is provided a projection exposure apparatus, comprising: an illumination optical system for illuminating a mask with light from a light source; and a projection optical system having a diffractive optical element, for projecting an image of a pattern of the mask, as illuminated, onto a substrate, wherein said diffractive optical element is adapted to produce first diffraction light of a first order to be used for formation of the image and second diffraction light of a second order different from the first order, and wherein a portion of the second diffraction light is not to be projected on the substrate and the other portion of the second diffraction light is to be projected on the substrate to provide there a substantially uniform intensity distribution.
In accordance with a third aspect of the present invention, there is provided a projection exposure apparatus for projecting a pattern of a first object onto a second object through a projection optical system, having a feature that said projection optical system comprises first and second diffractive optical elements disposed at or adjacent to the position of an aperture stop, and an aspherical surface lens.
In one preferred form of this aspect of the present invention, when the distance from the aperture stop to the i-th diffractive optical element is d
i
, the distance from the first object to the second object is D, and the height of maximum light height, at the aperture stop position, that determines the numerical aperture of said projection optical system and the incidence height thereof to the i-th diffractive optical element are H and h
i
, respectively, the following relations are satisfied:
0.005
<d
i
/D
<0.12 (1)
0.8
<h
i
/H
<1.2(
i
=1 or 2) (2)
In accordance with a fourth aspect of the present invention, there is provided a projection exposure apparatus for projecting a pattern of a first object onto a second object through a projection optical system, having a feature that said projection optical system includes first and second diffractive optical elements disposed at or adjacent to the position of an aperture stop, and that, when the distance from the aperture stop to the i-th diffractive optical element is d
i
, the distance from the first object to the second objec
Hirose Ryusho
Sekine Yoshiyuki
Canon Kabushiki Kaisha
Chang Audrey
Fitzpatrick ,Cella, Harper & Scinto
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