Multiple exposure device formation

Details Multiple exposure device formation Multiple exposure device formation

2001-02-15

2003-03-18

Young, Christopher G. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Making electrical device

C430S030000, C430S328000, C430S394000

Reexamination Certificate

active

06534242

ABSTRACT:

FIELD OF THE INVENTION AND RELATED ART
This invention relates to an exposure method, an exposure apparatus and a device manufacturing method. In one preferred embodiment, the invention is concerned with a dual or multiple exposure method for printing a fine circuit pattern on a photosensitive substrate, and an exposure apparatus and a device manufacturing method based on the dual (multiple) exposure method. The exposure method and apparatus of the present invention are suitably usable in the manufacture of microdevices such as semiconductor chips (e.g., IC or LSI), display devices (e.g., a liquid crystal panel), detecting devices (e.g., a magnetic head), or image pickup devices (e.g., a CCD), for example.
In the manufacture of devices such as IC, LSI, or liquid crystal panels, for example, on the basis of photolithography, generally, a projection exposure method and a projection exposure apparatus are used, in which a circuit pattern of a photomask or reticle (hereinafter “mask”) is projected by a projection optical system onto a photosensitive substrate (hereinafter “wafer”) such as a silicon wafer or glass plate having a photoresist coating applied thereto, for example, whereby the pattern is transferred or printed on the substrate.
In order to meet further increases in the density of integration of such devices, further miniaturization of a pattern to be transferred to a wafer (that is, further improvement of resolution) as well as a further increase of the area of a single chip are required. In projection exposure methods and projection exposure apparatuses which are the primary types of microfabrication technology, attempts have been made to improve the resolution and the exposure area that an image of a size (linewidth) of 0.5 micron or less can be formed in a wide range.
FIG. 19
is a schematic view of a projection exposure apparatus of a known type. Denoted in
FIG. 19
at
191
is an excimer laser which is a light source for deep ultraviolet light exposure. Denoted at
192
is an illumination optical system, and denoted at
193
is illumination light. Denoted at
194
is a mask, and denoted at
195
is object-side exposure light which, after being emitted from the mask
194
, enters an optical system
196
. The optical system
196
comprises a reduction projection optical system. Denoted at
197
is image-side exposure light which, after being emitted from the optical system
196
, impinges on a photosensitive substrate
198
. The substrate
198
comprises a wafer. Denoted at
199
is a substrate stage for holding the photosensitive substrate
198
.
Laser light emitted by the excimer laser
191
is directed by a guiding (or directing) optical system to the illumination optical system
192
. By means of the projection optical system
192
, the light is adjusted or transformed into illumination light
193
having a predetermined light intensity distribution, an orientation distribution, and an opening angle (numerical aperture NA), for example. The illumination light
193
illuminates the mask
194
. The mask
194
has a fine pattern of chromium, for example, formed on a quartz substrate. The pattern has a size corresponding to an inverse (e.g., 2×, 4×, or 5×) of the projection magnification of the projection optical system
192
. The illumination light
193
is transmissively diffracted by the fine pattern of the mask
194
, whereby object-side exposure light
195
is provided. The projection optical system
196
serves to transform the object-side exposure light
195
into image-side exposure light
197
with which the fine pattern of the mask
194
is imaged upon the wafer
198
, at the above-described projection magnification and with sufficiently small aberration. As illustrated in an enlarged view at the bottom of
FIG. 19
, the image-side exposure light
197
is converged upon the wafer
198
with a predetermined numerical aperture (NA=sin &thgr;), whereby an image of the fine pattern is formed on the wafer
198
. For sequentially printing the fine pattern on different regions (shot regions, each being a region for the production of one or plural chips), the substrate stage
199
moves stepwise along an image plane of the projection optical system to change the position of the wafer
198
with respect to the projection optical system
196
.
Practically, however, with current projection exposure apparatuses having an excimer laser as a light source, it is difficult to form a pattern of 0.15 micron or less.
In the projection optical system
196
, there is a limitation in resolution due to a tradeoff between optical resolution and depth of focus which is attributable to the wavelength of exposure light (hereinafter “exposure wavelength”). The relation between resolution R and depth of focus DOF of a projection exposure apparatus can be expressed in accordance with Rayleigh's equation, such as equations (1) and (2) below:
 R=k
1
(&lgr;/NA)  (1)
DOF=k
2
(&lgr;/NA
2
)  (2)
where &lgr; is the exposure wavelength, NA is the image-side numerical aperture that represents brightness of the projection optical system
196
, and k
1
and k
2
are constants which are usually about 0.5-0.7. It is seen from equations (1) and (2) that, in order to provide higher resolution with a smaller resolution value R, the numerical aperture NA may be enlarged (enlargement of NA). However, in a practical exposure process, the depth of focus DOF of the projection optical system
196
should be not less than a certain value and, therefore, enlargement of the numerical aperture NA beyond a certain level is not practicable. Thus, for higher resolution, it is necessary to make the exposure wavelength &lgr; shorter (shortening of wavelength).
However, shortening of the wavelength raises a serious problem. That is, there is no lens glass material available for the projection optical system
196
. Almost all glass materials have about a zero transmissivity to the deep ultraviolet region. While there is a fused silica which can be produced as a glass material in an exposure apparatus with an exposure wavelength about 248 nm in accordance with a special manufacturing method, the transmissivity of even such fused silica decreases drastically to an exposure wavelength not longer than 193 nm. Thus, it may be very difficult to develop a practical glass material having a sufficiently high transmission factor in a region not longer than an exposure wavelength of 150 nm, corresponding to a fine pattern of 0.15 micron or less. Further, the glass material to be used in the deep ultraviolet region should, to some extent, satisfy several other conditions such as durability, uniformness of birefringence or refraction factor, optical distortion, and workability or machining characteristic, for example. For these reasons, development of a practical glass material for use in an exposure wavelength region not longer than 150 nm will not easily be accomplished.
In conventional projection exposure methods and projection exposure apparatuses, such as described, for the formation of a pattern of 0.15 micron or less upon a wafer
198
, the exposure wavelength should be shortened to about 150 nm or less. Nevertheless, since there is no practical glass material available for such a wavelength region, practically, it is very difficult to form a pattern of 0.15 micron or less on the wafer
198
.
U.S. Pat. No. 5,415,835 shows a process of forming a fine pattern by use of dual-beam interference exposure (also known as “double-beam interference exposure”). This exposure process involves the use of two mutually coherent light beams that interfere with each other to produce an interference fringe. With this dual-beam interference exposure process, a pattern of 0.15 micron or less may be formed on a wafer.
Referring to
FIG. 15
, the principle of dual-beam interference exposure will be explained. In accordance with dual-beam interference exposure, laser light from a laser
151
which comprises parallel light having coherency is divided by a half mirror
152
into

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