Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-09-19
2002-09-24
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C378S035000
Reexamination Certificate
active
06455204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an X-ray mask employed in fabrication of a semiconductor device, and more particularly to such an X-ray mask including an X-ray absorber composed of an alloy having low stress. The invention relates further to a method of fabricating such an X-ray mask, and still further to a method of fabricating a semiconductor device through the use of such an X-ray mask.
2. Description of the Related Art
As a semiconductor device has been integrated highly, X-ray lithography has been employed for formation of a minute pattern. The X-ray lithography is characterized by features that X-ray has a short wavelength, and that it is relatively easy to have a great depth of focus. The X-ray lithography is suitable particularly for making a small pattern having a length of 10 nm or smaller, or a pattern having a great aspect ratio. The X-ray lithography is employed also in fabrication of a liquid crystal display panel, a charge coupled device (CCD), a thin film magnetic head, and a micro-machine as well as LSI such as memory and logic.
In the X-ray lithography, a resist film is deposited on a wafer, and then, X-ray is radiated onto the resist film through an X-ray mask to thereby make a pattern. Specifically, an X-ray mask composed of X-ray absorber and having a pattern corresponding to a pattern of a semiconductor device to be fabricated is used. The X-ray mask is positioned in the close vicinity of a surface of a wafer on which an X-ray resist film has already been deposited. Then, X-ray is radiated onto the resist film through the X-ray mask to thereby transfer a pattern of the X-ray mask to the resist film.
The above-mentioned X-ray mask is usually comprised of a membrane through which X-ray can pass, X-ray absorbing material arranged on the membrane, a silicon substrate, and a support such as a glass plate for cooperating with the silicon substrate to support the membrane at its periphery.
FIG. 1
illustrates an example of an X-ray mask. The illustrated X-ray mask is comprised of a membrane
2
composed of silicon nitride (SiN), silicon carbide (SiC) or diamond (C) in the form of a thin film, an X-ray absorber
1
formed on the membrane
2
and having a desired pattern, a silicon substrate
3
supporting the membrane
2
at its periphery, and a support ring
4
composed of silicon carbide or quartz glass and cooperating with the silicon substrate
3
to thereby support the membrane
2
.
In conventional X-ray masks, the X-ray absorber
1
has usually been, composed of simple metal such as tungsten (W) and tantalum (Ta).
A method of fabricating the X-ray mask illustrated in
FIG. 1
is explained hereinbelow with reference to
FIGS. 2A
to
2
D.
First, thin films
2
a
are deposited on opposite surfaces of a silicon substrate
3
by chemical vapor deposition. The silicon substrate
3
has a thickness of 1 to 2 mm. The thin films
2
a
are composed of silicon carbide (SiC) and have a thickness of about 1 to 2 &mgr;m. One of the thin films
2
a
will make a membrane
2
.
Then, as illustrated in
FIG. 2A
, a support ring
4
is adhered to a lower surface of the silicon substrate
3
at its periphery by means of an adhesive such as epoxy resin. The support ring
4
is composed of glass or silicon carbide (SiC), and has a thickness of about 5 mm.
Then, as illustrated in
FIG. 2B
, the silicon substrate
3
is back etched from a lower surface thereof by anisotropic etching through the use of KOH aqueous solution. As a result of the etching, a portion of the silicon substrate
3
is removed, and there is formed a membrane
2
on the silicon substrate
3
.
Then, as illustrated in
FIG. 2C
, an X-ray absorbing material
1
is deposited on the membrane
2
by sputtering.
Then, as illustrated in
FIG. 2D
, the X-ray absorbing material
1
is patterned into a desired pattern la by dry etching. Thus, there is completed an X-ray mask having a desired pattern
1
a.
In the method illustrated in
FIGS. 2A
to
2
D, although the silicon substrate
3
is back-etched prior to depositing and patterning the X-ray absorbing material
1
, the silicon substrate
3
may be back-etched after deposition of the X-ray absorbing material
1
.
In order to make a minute pattern of a semiconductor device by means of X-ray lithography, an X-ray absorbing material of which an X-ray mask is composed is required to have the following characteristics.
First, an X-ray absorbing material has to have high ability of disallowing X-ray to pass therethrough, in order to provide sufficient contrast in X-ray exposure. Herein, such ability of disallowing X-ray to pass therethrough is defined as a product of a mass absorption coefficient and a density of an X-ray absorbing material. An X-ray absorbing material is particularly required to have high ability of disallowing passage therethrough of X-ray having a wavelength of about 1 nm, which X-ray is usually used in X-ray lithography.
If an X-ray absorbing material has smaller ability of disallowing X-ray to pass therethrough, a film composed of an X-ray absorbing material, to be formed on a membrane, has to have a greater thickness. In which case, it would be quite difficult to make a minute pattern of the X-ray absorbing material.
In addition, if a film composed of an X-ray absorbing material has a great thickness, problems such as inaccurate transfer of a pattern to an X-ray absorbing material, and difficulty of controlling stress remaining in a film composed of an X-ray absorbing material,would be caused.
Second, an X-ray absorbing material has to have a stress as small as possible, and further have high controllablity of stress.
If a film composed of an X-ray absorbing material, formed on a membrane has a great internal stress, positional accuracy with which a pattern is transferred to an X-ray absorbing material from an X-ray mask would be deteriorated, and as a result, misalignment would be caused in a semiconductor device pattern. Accordingly, an X-ray absorbing material is required to have almost zero internal stress all over a surface of an X-ray mask.
In addition, taking productivity of an X-ray mask into consideration, an X-ray mask is required to not only have an almost zero internal stress, but also be able to be repeatedly fabricated in the same configuration. Furthermore, since an X-ray mask is repeatedly employed, an X-ray mask is required to have stability in stress.
Third, an X-ray absorbing material is required to have a densified crystal structure.
Most metals that have been used as an X-ray absorbing material is changed into a polycrystalline film having a columnar structure when deposited into a film by sputtering. If such a polycrystalline film is patterned, grain boundary would appear at a sidewall thereof, resulting in a side surface of a pattern having much roughness, in which case, it is no longer possible to form a desired pattern of a semiconductor device.
Apart from the above-mentioned characteristics, an X-ray absorbing material is required to have conformity to dry-etching to be carried out in patterning, and to have chemical stability.
However, conventional X-ray absorbing materials used so far cannot meet all of the above-mentioned requirements.
Tungsten (W) and tantalum (Ta) have been conventionally and widely used as an X-ray absorbing material, because these metals meet the above-mentioned first requirement. That is, those metals have sufficient ability of disallowing passage of X-ray therethrough. However, tungsten (W) and tantalum (Ta) cannot meet the above-mentioned second and third requirements, and hence these metals cannot be used for an X-ray mask when a minute pattern of a semiconductor device is to be formed.
If a film is formed of tungsten (W) or tantalum (Ta) by sputtering, a resultant film would be a polycrystalline film having a columnar structure. Hence, when a minute pattern is to be formed of tungsten (W) or tantalum (Ta) by sputtering, grain boundary would be generated at a sidewall of a pattern to thereby rough the sidewall, which is a big hindrance the accompli
NEC Corporation
Rosasco S.
LandOfFree
X-ray mask and method of fabricating the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with X-ray mask and method of fabricating the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and X-ray mask and method of fabricating the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2905461