Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-07-26
2002-12-10
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06492070
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron beam exposure mask and a method for manufacturing the electron beam exposure mask and more particularly to the electron beam exposure mask and the method for manufacturing the electron beam exposure mask capable of forming fine patterns without losing mechanical strength.
2. Description of the Related Art
In manufacturing a semiconductor device represented by a LSI (Large-Scale Integrated)circuit, a lithography technology is essential in order to pattern various kinds of films, including insulation films such as a silicon oxidation film and a silicon nitride film formed on a semiconductor substrate and conductive films such as an aluminum alloy film and a copper alloy film, into desired shapes.
Conventionally, in this lithography technology, a photolithography technology is widely applied, in which a photoresist film is formed by coating photoresist having photosensitivity for ultraviolet rays, ultraviolet rays are irradiated (exposed) onto the photoresist film through a mask pattern, an ultraviolet ray irradiation area is made soluble (a positive type) or an ultraviolet ray non-irradiation area is made soluble (a negative type).
Now, as integration is improved with sophistication of the LSI, a lithography technology capable of further fine-processing is required. With this requirement, an electron beam lithography technology has been developed in which an electron beam of a wavelength shorter than that of the ultraviolet ray is used as an exposure medium.
In this electron beam lithography technology, an electron beam resist being photosensitive to an electron beam is used, and a desired pattern is represented by irradiating and exposing the electron beam to the electron beam resist. When the desired pattern is represented on the electron beam resist, a stencil mask, namely, an aperture mask (hereafter, called an electron beam exposure mask) is used. For the electron beam exposure mask, a material efficient in electron dispersion and in absorption and suitable for a fine process is used and generally a semiconductor film such as a silicon film is used.
FIG. 3
is a sectional view showing a conventional structure of an electron beam exposure mask.
An electron beam exposure mask
51
, as shown in
FIG. 3
, is provided with a substrate portion
52
formed from a silicon single crystal or a like and provided with an aperture
53
and a thin film portion
54
supported by the substrate portion
52
.
The thin film portion
54
is provided with a semiconductor active film
56
formed from a silicon single crystal through an buried insulation film
55
formed from a silicon oxide film or a like. The semiconductor active film
56
is provided with a pattern portion
57
provided with apertures
58
conducting to the semiconductor active film
56
.
Here, the aperture
53
of the substrate portion
52
and the apertures
58
of the semiconductor active film
56
become electron beam passages during the electron beam exposure.
Explanations will be given of a method of manufacturing an electron beam exposure mask with reference to
FIGS. 4A
,
4
B,
4
C,
4
D and
4
E in accordance with a procedure.
First, as shown in
FIG. 4A
, a semiconductor substrate
60
formed from a silicon single crystal is used and an etching mask
61
formed from silicon oxide film, a silicon nitride film or a like is formed on a reverse of the semiconductor substrate
60
by a CVD (Chemical Vapor Deposition) process or a like.
Second, by applying a known SIMOX (Separation by IMplanted OXygen) technology to an obverse of the semiconductor substrate
60
, oxygen ions are implanted to form the buried insulation film
55
of silicon oxide. The semiconductor active film
56
separated from the semiconductor substrate
60
by the buried insulation film
55
is formed.
Third, as shown in
FIG. 4C
, by applying a known photolithography process, necessary areas in the obverse of the semiconductor active film
56
are covered with photoresist film
62
and then dry etching is executed using the photoresist film
62
as a mask in order to form the semiconductor active film
56
in a desired shape, namely, in order to execute patterning. With this process, the pattern portion
57
of a desired shape having the apertures
58
is formed.
Fourth, after selectively etching the buried insulation film
55
exposed in the apertures
58
, as shown in
FIG. 4D
, necessary areas in the etching mask are covered with photoresist film
63
and then dry etching is executed using the photoresist film
63
as a mask in order to form the etching mask
61
in a desired shape, namely, in order to execute patterning.
Fifth, after removing the photoresist film
63
, wet etching is applied to the reverse of the semiconductor substrate
60
using the etching mask
61
as a mask and the semiconductor substrate
60
is selectively etched to form the apertures
53
.
Finally, the etching mask
61
and the buried insulation film
55
exposed in the apertures
53
are removed by dry etching, and thereby the electron beam exposure mask
51
shown in
FIG. 3
is completed.
Now, in a conventional electron beam exposure mask, there is a problem in that it is difficult to change a pattern accuracy partially since the semiconductor active film forming a pattern portion of a film portion supported by a substrate is formed wholly in a same film thickness.
In other words, concerning the electron beam exposure mask, though there is a case in that a pattern accuracy is changed partially on one mask and a fine pattern is formed on only a part of the mask according to a design rule, a film thickness of the above-mentioned semiconductor active film must be made thinner as to a processing precision to form such fine pattern.
However, when the film thickness of the semiconductor active film is made thin, mechanical strength of a mask deteriorates accordingly and a mask tolerance deteriorates. Therefore, the film thickness of the semiconductor active film must be thick to improve the mechanical strength of the mask.
For example, when the semiconductor active film is optimized to make a film thick in order to obtain mechanical strength, an aspect ratio becomes large in areas requiring a fine pattern. As a result, it is difficult to form fine apertures since a processing precision lacks. On the contrary, when the semiconductor active film is optimized to make a film thin, a fine pattern can be formed easily. However, the mechanical strength deteriorates since the whole mask becomes thin.
As above described, in manufacturing the electron beam exposure mask, forming the fine pattern is contrary to improving mechanical strength. Conventionally, since a film thickness of a semiconductor active film in which a pattern is formed is set to an identical thickness, there is a limitation in that a mask can be manufactured only from the viewpoint of forming the fine pattern or improving the mechanical strength.
Further, conventionally, instead of the semiconductor substrate, an SOI (Silicon On Insulator) substrate being two laminated substrates is manufactured. However, these two substrates are laminated under high tension, therefore, a mask is flexible under tension when the mask is made thinner. In addition, there are cases in that evenness during laminating deteriorates and in that since voids are apt to occur, etching liquid seeps in the voids in the manufacturing process and thereby the pattern is broken.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide an electron beam exposure mask and a method of manufacturing the electron beam exposure mask, in which forming a fine pattern is compatible with improving mechanical strength.
According to a first aspect of the present invention, there is provided an electron beam exposure mask provided with a substrate portion, a thin film portion supported by the substrate portion, and a pattern portion formed into a desired shape in a semiconductor film formed through a buried insulation film i
Huff Mark F.
Mohamedulla Saleha R.
Young & Thompson
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