X-ray or gamma ray systems or devices – Specific application – Lithography
Reexamination Certificate
1999-11-12
2002-04-02
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Lithography
C430S005000
Reexamination Certificate
active
06366640
ABSTRACT:
REFERENCE OF RELATED APPLICATION
This application claims the priority right under 35 U.S.C. 119 of Japanese Patent Application No. Hei 10-341058 filed on Nov. 14, 1998, the entire disclosure of which is incorporated by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an X-ray mask blank and a method for manufacturing the same, and an X-ray mask and a method for manufacturing the same.
(2) Description of the Related Art
In the semiconductor industry, as a conventional transfer technique of a fine pattern necessary for preparing an integrated circuit formed of the fine pattern on a silicon substrate, and the like, a photolithography method of using visible or ultraviolet rays as exposure electromagnetic waves to transfer the fine pattern has been used.
In recent years, however, with a progress of semiconductor technique, high integration of semiconductor devices such as an ultra LSI has remarkably progressed, and there arises a demand for a transfer technique of the fine pattern with high precision which exceeds a transfer limit in the visible or ultraviolet rays used in the conventional photolithography method.
In order to realize the transfer of such fine pattern, the development and practical application of an X-ray lithography method using X-rays shorter in wavelength than the visible or ultraviolet rays have been advanced.
X-ray lithography is an equal-size vicinity exposure, and requires an equal-size X-ray mask. The structure of the X-ray mask for use in the X-ray lithography is shown in FIG.
1
.
As shown in
FIG. 1
, an X-ray mask
1
is constituted of an X-ray transmission film (membrane)
12
for transmitting X-rays, and an X-ray absorber pattern
13
a
for absorbing the X-rays, which are supported by a support substrate (support frame)
11
a
formed of silicon. Furthermore, to facilitate the reinforcing and handling, a glass frame
15
having a larger outer diameter than that of the support substrate is bonded to the support substrate. Here, for example, the support substrate with an outer diameter of four inches, and the glass frame with an outer diameter of five inches are used.
A process of preparing an X-ray mask blank to obtain the X-ray mask is shown in FIG.
2
.
First, the X-ray transmission film
12
with a thickness of about 2 &mgr;m is formed on both surfaces of a silicon substrate
11
by CVD method, and subsequently an X-ray absorbing film
13
and an etching mask layer
14
are successively formed on the X-ray transmission film
12
by a sputtering method (
FIG. 2
a
).
Subsequently, an area to form a mask area is removed from the X-ray transmission film (not shown) formed on the back surface of the substrate by dry etching, the X-ray transmission film remaining on an outer peripheral portion is used as a mask to wet-etch the central portion of the back surface of the silicon substrate by hydrofluoric nitrate (mixed solution of hydrofluoric acid and nitric acid) until the back surface of the X-ray transmission film
12
is exposed, and the X-ray transmission film
12
is self-supported (formed into a membrane) (
FIG. 2
b
).
Next, the reinforcing glass frame
15
is bonded by a method such as anodic bonding (
FIG. 2
c
).
As the X-ray transmission film
12
, silicon carbide or another material which has a high Young's modulus and a superior resistance against X-ray radiation is generally used. As the X-ray absorbing film
13
, a material containing tantalum (Ta), tungsten (W), and the like which has a high X-ray absorbing ratio and a superior resistance against X-ray radiation is well used.
In recent years, with the progress of the photolithography technique, the time to introduce the X-ray lithography is fed forward, and in the present situation, the lithography is expected to be introduced from the generation of 1 Gbit-DRAM (design rule: 0.18 &mgr;m). Even if the X-ray lithography is introduced from 1 G, it can be used over a plurality of generations of 4 G. 16 G, 64 G. As the generation advances, strict prescribed properties are required.
Particularly, the X-ray absorbing film is requested to have a high X-ray absorbing ratio, to have a dense crystalline structure to provide an excellent dry etching property and form smooth pattern side walls and upper face, to be able to form a pattern of 0.18 &mgr;m or less and enhance the dimensional precision of the pattern, to have a low stress and no stress nonuniformity, to have no pattern strain or positional fluctuation caused by the stress or stress change and be superior in positional precision, to be superior in X-ray radiation resistance, and to have other strict prescribed properties.
For the positional precision required for the X-ray mask, for example, when the use in 64 G is assumed, the precision becomes stricter, and a high positional precision of 10 nm is necessary. Therefore, the strain attributed to the film stress needs to be as close to zero as possible. Particularly, it is important to minimize the pattern strain attributed to the stress of the X-ray absorbing film. The X-ray absorbing film needs to have an excessively low stress, and to be uniform in a mask area. For example, in the X-ray absorbing film with a thickness of 0.5 &mgr;m, a stress of ±10 MPa or less is required in the mask area of 30 mm square.
Additionally, the stress of the prepared film has to be unchanged and maintained even after the pattern is formed to prepare the mask. If the stress of the film forming the pattern changes, the pattern strain is caused after preparing the mask, which raises a problem.
SUMMARY OF THE INVENTION
The present invention has been developed under the above-described background, and a first object thereof is to provide an X-ray mask blank from which an X-ray mask satisfying strict prescribed properties requested for X-ray masks of 1 Gbit-DRAM and subsequent generations can be manufactured, a method for manufacturing the blank, a method for manufacturing the X-ray mask, and the like.
Another object is to provide an X-ray mask which satisfies strict prescribed properties requested for X-ray masks of 1 Gbit-DRAM and subsequent generations, and particularly a second object is to provide an X-ray mask which has no pattern strain or no positional fluctuation attributed to a change of film stress of an X-ray absorber pattern after preparing the mask and which is superior in positional precision.
To achieve the above-described objects, as a result of intensive researches, the present inventors have found that an X-ray absorbing film containing tantalum (Ta), boron (B), nitrogen and/or oxygen has a high X-ray absorbing ratio, has a dense crystalline structure to provide an excellent dry etching property and form smooth pattern side walls and upper face, can form a pattern of 0.18 &mgr;m or less to enhance a pattern dimensional precision, has a low stress and no stress nonuniformity, has no pattern strain or no positional fluctuation attributed to the stress and stress change to provide a superior positional precision, is superior in X-ray radiation resistance, and satisfies strict prescribed properties required for X-ray masks of 1 Gbit-DRAM and subsequent generations.
Specifically, the present invention is constituted as follows:
(Constitution 1) An X-ray mask blank comprising, on a mask substrate, an X-ray transmission film for transmitting X-rays and an X-ray absorbing film formed on the X-ray transmission film for absorbing the X-rays, the X-ray absorbing film containing tantalum, boron and nitrogen.
(Constitution 2) An X-ray mask blank comprising, on a mask substrate, an X-ray transmission film for transmitting X-rays and an X-ray absorbing film formed on the X-ray transmission film for absorbing the X-rays, the X-ray absorbing film containing tantalum, boron and oxygen.
(Constitution 3) An X-ray mask blank comprising, on a mask substrate, an X-ray transmission film for transmitting X-rays and an X-ray absorbing film formed on the X-ray transmission film for absorbing the X-rays, the X-ray absorbing film containing tantalum, boron, nitrogen an
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Hobden Pamela R.
Hoya Corporation
Porta David P.
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