Radiant energy – Radiation controlling means
Reexamination Certificate
1998-09-03
2001-03-06
Anderson, Bruce C. (Department: 2881)
Radiant energy
Radiation controlling means
C430S005000
Reexamination Certificate
active
06198109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus including an aperture through which electron beams are radiated onto a patterned photoresist film formed on a semiconductor substrate for forming a circuit pattern thereon, and a holder for fixedly supporting the aperture therewith. The invention relates also to a method of fabricating such an apparatus.
2. Description of the Related Art
There has been widely used photolithography for forming a small pattern on a wafer as a semiconductor substrate. In such photolithography, there has been employed a step and repeat exposure system (stepper) in order to expose a patterned photoresist film to light. The stepper first employed ultra-violet ray beams as a light source. However, in these days, a light source emitting a light having a smaller wavelength has been employed in order to form a pattern in a smaller size. For instance, g-ray having a wavelength of 436 nm in a mercury lamp, i-ray having a wavelength of 365 nm in a mercury lamp, and then, KrF eximer laser beam having a wavelength of 249 nm have been employed so far.
A resolution can be increased by using a light source emitting a light having a smaller wavelength. However, such a light source is accompanied with reduction in a depth of focus, which causes a problem that sharpness of a pattern is degraded due to blooming.
For this reason, electron beam exposure draws attention, because it has a significantly greater depth of focus than light exposure. The electron beam exposure makes it possible to form a more highly resolved pattern than the light exposure, but has a shortcoming that it has a low throughput.
However, there has been developed an exposure process which solves the above-mentioned problem, namely, significant increases in throughput. In the exposure process, electron beams are focused into rectangular patterns in certain sizes by means of an aperture, the thus focused patterns are all transferred to a wafer at a time, and those patterns are connected to one another to thereby transfer all circuit patterns onto a wafer.
FIGS. 1A
to
1
D are cross-sectional views of an aperture used in the above-mentioned exposure system, illustrating respective steps of a method of fabricating the aperture.
As illustrated in
FIG. 1A
, first and second silicon substrates
1
a
and
1
b
are adhered to each other to thereby form a wafer
1
. The first and second silicon substrates
1
a
and
1
b
are adhered to each other at a boundary surface
2
. Then, the wafer
1
is formed at a surface thereof having a plane azimuth of (
100
) with a desired pattern of opening
1
c
by conventional photolithography and etching. Then, a protection film
3
for protecting the wafer
1
from wet etching is formed all over upper, side and lower surfaces of the wafer
1
by chemical vapor deposition (CVD). For instance, the protection film
3
is a silicon nitride film.
Then, as illustrated in
FIG. 1B
, a photoresist film is formed on a lower surface of the wafer
1
, and then, is patterned so that the photoresist film has an opening below the openings
1
c
of the wafer
1
. Then, the protection film
3
is dry etched with the patterned photoresist film
4
being used as a mask, to thereby form a window
5
in the protection film
3
.
Then, as illustrated in
FIG. 1C
, the wafer
1
is etched back at a lower surface thereof at an area exposed through the window
5
. The wafer
1
is etched by means of a wet etching solution until the first silicon substrate
1
a
appears. Namely, the second silicon substrate
1
b
is etched by an entire thickness thereof as well as the boundary surface
2
. Thus, there is formed an opening
6
at a lower surface of the wafer
1
. For instance, there may be used heated alkaline solution such as potassium hydroxide and hydrazine, as the wet etching solution.
Since a plane azimuth (
111
) appears in the opening
6
during the wet etching, the opening
6
can be designed to have a tapered wall.
Then, as illustrated in
FIG. 1D
, the patterned photoresist film
4
and the protection film
3
are all removed. Thereafter, an electrically conductive film
7
is formed on an upper surface of the wafer
1
by sputtering in order to prevent charge-up which would occur when electron beams are radiated onto an upper surface of the wafer
1
. For instance, the electrically conductive film
7
is composed of Au.
Thus, there is completed an aperture
10
as illustrated in
FIGS. 2A
to
2
C, wherein
FIG. 2A
is a cross-sectional view of the aperture
10
,
FIG. 2B
is a top plan view of the aperture
10
, and
FIG. 2C
is an enlarged view of the opening
6
. As illustrated in
FIG. 2B
, the opening
6
formed in the aperture
10
consists of smaller openings
6
a
arranged in 4×3. Each of the openings
6
a
is designed to have a pattern as illustrated in FIG.
2
C. That is, each of the openings
6
a
includes a plurality of horizontally extending slits
6
b
in parallel with one another. When electron beams are radiated to a photoresist film through the opening
6
having a plurality of the smaller openings
6
a
each of which includes the slits
6
b,
portions of the photoresist film in alignment with the slits
6
b
are exposed, and hence, such portions of the photoresist film are etched out, or are not etched out.
The thus completed aperture
10
is fixed onto a holder
20
, as illustrated in
FIGS. 3A and 3B
. The holder
20
is constructed as a frame having a central window
21
through which the opening
6
of the aperture
10
is exposed, and has a stepped portion
22
having a reduced thickness, around the central window
21
. The stepped portion
22
has an upper surface as an adhesion surface
23
on which the aperture
10
is adhered at its marginal portion by means of an adhesive layer
30
composed of silver paste, for instance. For instance, the aperture
10
is fixed onto the stepped portion
22
of the holder
20
by first applying the adhesive on the adhesion surface
23
, and compressing the aperture
10
onto the stepped portion
22
.
The apparatus including the aperture
10
fixed onto the holder
20
, which has been explained with reference to
FIGS. 1A
to
3
B, has a problem that a portion
30
a
of the adhesive
30
may be forced out into the central window
21
of the holder
20
, or a portion
30
b
may be forced out onto an upper surface of the aperture
10
, passing between the aperture
10
and the holder
20
. Those portions
30
a
and
30
b
of the adhesive
30
contaminates the apparatus, and causes problems of reduction in an accuracy of painting with electron beams, and reduction in a lifetime of the aperture
10
.
In particular, if the portion
30
a
of the adhesive
30
is forced out into the central window
21
in a significantly excessive amount, the portion
30
a
may disadvantageously reach the opening
6
of the aperture
10
, and may partially cover the slits
6
b
of the opening
6
therewith, as illustrated in FIG.
4
B. If electron beams are radiated onto a photoresist film with the slits
6
b
being covered with the adhesive
30
b,
there would be generated a defect
31
in a photoresist pattern PR, as illustrated in FIG.
4
C.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an aperture apparatus and a method of fabricating the same both of which are capable of preventing an adhesive from being forced out into an opening of an aperture or onto an upper surface of an aperture.
In one aspect of the present invention, there is provided an apparatus used for forming a pattern on a substrate by photolithography with electron beams, the apparatus including (a) an aperture formed with at least one opening through which electron beams are to pass, and (b) a holder for fixedly supporting the aperture therewith by means an adhesive. A surface of the aperture and/or a surface of the holder, at which the aperture and the holder are adhesively fixed to each other, are(is) formed with at least one groove for excessive portion of the adhesive to flow in.
For instance,
Anderson Bruce C.
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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