X-ray or gamma ray systems or devices – Specific application – Lithography
Reexamination Certificate
1998-04-17
2001-04-17
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Lithography
C378S035000, C378S084000
Reexamination Certificate
active
06219400
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to an X-ray optical system wherein X-rays such as radiation from a charged particle accumulation ring are used as exposure light. In another aspect, the invention is concerned with an X-ray exposure apparatus and a semiconductor device manufacturing method which uses such X-ray optical system.
In order to meet recent miniaturization of a pattern of semiconductor devices, various exposure apparatuses which enable transferring and printing a pattern with a minimum linewidth of 0.15 micron (1 gigabit DRAM) have been developed. Among them, X-ray exposure apparatuses wherein X-rays such as radiation from a charged particle accumulation ring are used as exposure light are attractive in respect to both of good transfer and printing precision and good productivity.
As shown in
FIG. 1A
, X-rays (synchrotron radiation light) such as charged particle accumulation ring radiation are produced from a light emission point as a sheet-like beam having a small thickness in the direction (Y-axis direction) perpendicular to the orbit of a light source
101
such as a charged particle accumulation ring. The sheet-like beam is then expanded by a beam expander such as an expanding mirror
102
, in the Y-axis direction. The expanded beam L
0
being thus expanded to a required exposure picture angle, is introduced into an exposure chamber through a beryllium window
103
, and it irradiates a mask M
0
and then a wafer, not shown.
The beam duct from the light source
101
to the beryllium window
103
of the exposure chamber is controlled to provide therein a ultra-high vacuum ambience, to prevent attenuation of X-rays. Also, the inside of the exposure chamber is controlled to provide therein a reduced pressure ambience of helium gas, for example.
The expanding mirror
102
comprises a cylindrical mirror having a reflection surface being curved into a cylindrical shape. It is suspended within a vacuum chamber, not shown. If the relative position of the reflection surface of the expanding mirror
102
and the X-rays, that is, the position of incidence of X-rays, changes in the Y-axis direction, the X-ray intensity distribution of the expanded beam L
0
varies largely. It causes large non-uniformness of intensity within the exposure picture angle, and disables uniform exposure. In consideration of this, an actuator
104
is provided to shift the expanding mirror
102
in the Y-axis direction and, additionally, a position sensor
105
for detecting relative positional deviation, in the Y-axis direction, of the X-rays impinging on the expanding mirror
102
. The position sensor
105
is provided integrally with the expanding mirror
102
, and the output of the position sensor
105
is supplied to a controller
106
to control the actuator
104
.
There is another type exposure apparatus wherein the whole surface of a mask is exposed while being scanned with a sheet-like X-ray beam.
FIG. 1B
shows an X-ray mirror system used in such apparatus and a coordinate system therein. Synchrotron radiation light from a light source
101
is scanningly deflected in Y direction by swinging a flat X-ray mirror
102
by use of driving means, not shown, so as to irradiate the whole surface of a mask M
0
with the synchrotron radiation light. In this mirror system, the synchrotron radiation light is directly projected to the mask surface. In such system, control is made to prevent deviation, only in the Y direction, of the center of the intensity distribution of the synchrotron radiation light in the Y direction with respect to the reflection surface of the X-ray mirror
102
. This is because a deviation in the Y direction between the synchrotron radiation light and the reflection surface of the X-ray mirror causes a large change in the intensity of X-rays projected on the mask, whereas a deviation in X direction or a rotational deviation wY about the Y axis does not produce a large influence. More specifically, in an X-ray illumination system without light convergence, the reflection surface of an X-ray mirror
102
is flat with respect to the X direction and, as a result of this, a deviation in X direction between the synchrotron radiation light and the mirror reflection surface does not produce an intensity variation in X-rays upon the mask surface. Also, a rotational deviation in wY direction has a small influence. In consideration of the above, a synchrotron radiation light position sensor
105
is used and, on the basis of an output of this sensor, Y-axis mirror driving means
104
is controlled through a controller
106
so as to prevent relative shift of the Y-axis center of the intensity distribution of the synchrotron radiation light with reference to a predetermined position.
There is another type X-ray exposure apparatus wherein an expanding mirror is used to expand X-rays such as charged particle accumulation ring radiation in Y-axis direction and, additionally, a light collecting mirror is provided to collect X-rays in X-axis direction, at a position upstream of the expanding mirror, whereby an expanded beam of higher intensity is produced. The light collecting mirror comprises a concaved surface mirror for converging X-rays of sheet-like beam in the X-axis direction. With this enlargement of intensity of X-rays, the exposure time can be reduced considerably. That is, in such structure, an X-ray illumination system having two mirrors is used to enable simultaneous exposure of the whole surface of a mask with strong X-rays, to thereby improve the productivity of the X-ray exposure apparatus.
With the above-described structure, however, when two or more mirrors (expanding mirror and collecting mirror) are used, only adjustment of the expanding mirror position based on detection of the incidence position of X-ray beam with respect to Y-axis direction such as described above, is insufficient to provide uniform X-ray intensity distribution. If the X-ray incidence position relative to the collecting mirror shifts in the X-axis direction or if the optical axis of the X-rays tilts, the reflection angle of the collecting mirror changes largely, and it causes two-dimensional variation of X-ray intensity distribution within the exposure picture angle.
As described above, X-ray exposure apparatuses having an illumination system with a light collecting mirror, for example, involve a difficulty in achieving sufficient transfer precision.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an X-ray optical system by which X-ray intensity distribution of X-rays to be projected on an original, such as a mask, through two or more mirrors can be controlled to provide uniform distribution, and by which the transfer precision or productivity of an X-ray exposure apparatus can be improved significantly.
It is another object of the present invention to provide an X-ray exposure apparatus and/or a semiconductor device manufacturing method which is based on such X-ray optical system as described above.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5073918 (1991-12-01), Kamon
patent: 5285488 (1994-02-01), Watanabe
patent: 5394451 (1995-02-01), Miyake
patent: 5448612 (1995-09-01), Kasumi
Hasegawa Takayuki
Watanabe Yutaka
Canon Kabushiki Kaishi
Kim Robert H.
Schwartz Michael J.
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