Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2002-02-13
2003-07-01
Goudreau, George (Department: 1763)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C438S725000, C438S717000, C438S714000, C438S704000, C438S750000, C134S001200, C134S001300
Reexamination Certificate
active
06586145
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device and a semiconductor device, and more specifically, it relates to a method of fabricating a semiconductor device capable of forming a precision fine pattern not implementable solely by photolithography and a semiconductor device.
2. Description of the Prior Art
Following improvement in the degree of integration of a semiconductor device such as a DRAM (dynamic random access memory), a fine pattern having a size smaller than the wavelength of a light source employed for photolithography must be formed on a semiconductor substrate. Such a fine pattern can be formed by a method of preparing a gate electrode from polycrystalline silicon (hereinafter referred to as polysilicon).
This method is now described with reference to
FIGS. 23
to
27
. Referring to
FIG. 23
, a gate insulator film
113
is formed on a silicon substrate
101
, and a polysilicon film
108
is deposited thereon. A silicon oxide film
109
is arranged on the polysilicon film
108
, and a photoresist pattern
111
is formed thereon. This photoresist pattern
111
is employed as a mask for dryly etching the silicon oxide film
109
as shown in
FIG. 24. A
pattern
109
a
obtained from the silicon oxide film
109
is dipped in a chemical solution containing hydrofluoric acid, to be thinned. In other words, the width of the pattern
109
a
is narrowed for obtaining a precision-made pattern
109
b
(FIG.
25
). Thereafter the precision-made pattern
109
b
is employed as a mask for dryly etching the polysilicon film
108
. Consequently, a polysilicon pattern
108
a
for defining a gate electrode is obtained (FIG.
26
).
Silicon oxide films are deposited on the aforementioned polysilicon pattern
108
a
for forming side wall spacers
114
. Consequently, a gate electrode having a small width can be formed (FIG.
27
).
In order to deposit cobalt on the polysilicon pattern
108
a
for forming an electrode of cobalt silicide through a salicide process, however, the silicon oxide film
109
b
employed as the mask must be removed with hydrofluoric acid or the like. When the silicon oxide film
109
b
is removed with hydrofluoric acid or the like, however, the gate oxide film
113
and the patterns of the silicon oxide films such as the side wall spacers
114
around the gate electrode are also etched at the same time. Such etching is disadvantageous. Thus, awaited is a method of forming a fine pattern not implementable solely by photolithography with no pattern shifting etching unnecessary portions or the like.
When a MOS transistor is fabricated in practice, a silicon oxynitride film
112
may be deposited between the silicon oxide film
109
and the photoresist pattern
111
as an antireflection film for photolithography, as shown in FIG.
28
. In order to etch the polysilicon film
108
through the pattern
109
b
of the silicon oxide film
109
thinned by wet etching, this antireflection film
112
must be removed before the wet etching. If the antireflection film
112
is removed by wet etching employing phosphoric acid or the like, however, the silicon oxide film
109
for forming the mask
109
b
is also etched. Therefore, the size of the finally obtained polysilicon pattern
108
a
disadvantageously fluctuates.
Further, the pattern
109
b
of the silicon oxide film
109
employed as the mask for dry etching as described above must be finally removed. However, a chemical solution employed for removing the pattern
109
b
of the silicon oxide film
109
by wet etching inevitably etches the remaining silicon oxide films forming the peripheral portions and the silicon oxynitride film
112
. When the mask pattern
109
b
of the silicon oxide film
109
is removed, therefore, the gate electrode and a portion around a contact hole are also etched to deteriorate dimensional accuracy.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of fabricating a semiconductor device having a fine structure not implementable solely by photolithography with no pattern shifting on a peripheral oxide film or when removing an antireflection film as well as a mask pattern, and the semiconductor device.
The method of fabricating a semiconductor device according to the present invention comprises steps of forming a base film of either a silicon film or a silicon compound film on a semiconductor substrate and forming a hard film of either a metal film or a metal compound film in contact with the upper portion of the base film. The method also comprises steps of forming a photoresist pattern in contact with the upper portion of the hard film and dryly etching the hard film through the photoresist pattern serving as a mask for forming a hard pattern. The method further comprises steps of dryly etching the base film through the hard pattern serving as a mask and removing the hard pattern by wet etching with a chemical solution not substantially etching at least the base film.
According to this structure, the hard film is formed by a metal-based film, and the base film is formed by a film mainly composed of silicon. In the step of removing the hard pattern by wet etching, therefore, the chemical not etching the pattern of the base film can be selected with no significant difficulty. The above wording “chemical solution not substantially etching at least the base film (but etching the hard film)” stands for a chemical solution having large etch selectivity for the hard film with respect to the base film. When the base film is formed by a polysilicon film and the hard film is formed by a metal film of tungsten or the like, for example, a chemical solution containing an oxidant such as hydrogen peroxide water or ozone water corresponds to this chemical solution.
Thus, the pattern of the base film formed by dry etching is not influenced by the aforementioned chemical solution. Therefore, neither a gate electrode nor a contact hole causes pattern shifting in the aforementioned wet etching for removing the hard pattern. Thus, a semiconductor device having a fine precision structure can be obtained. Consequently, the semiconductor device having a fine structure can be fabricated with an excellent yield. The base film may be in contact with the upper portion of the semiconductor substrate, or may be formed on another film interposed between the same and the semiconductor substrate.
The aforementioned method of fabricating a semiconductor device according to the present invention further comprises a step of wetly etching the hard pattern with a chemical solution substantially not etching at least the base film for forming a precision-made hard pattern between the step of forming the hard pattern and the step of dryly etching the base film. In the step of dryly etching the base film, the base film can be dryly etched through the precision-made hard pattern serving as a mask.
According to this structure, a precision hard pattern not implementable solely by photolithography can be obtained without exerting bad influence such as pattern shifting on at least the base film or the remaining portions. Further, the hard pattern can be removed without exerting bad influence on at least the base film or the remaining portions as hereinabove described.
When this precision-made hard pattern is employed, a fine gate electrode and a precision contact hole can be formed in a refined MOS transistor.
The aforementioned method of fabricating a semiconductor device according to the present invention further comprise a step of removing the photoresist pattern after the step of forming the hard pattern by dry etching.
When the base film is dryly etched through the mask of the aforementioned hard pattern, the photoresist pattern may remain in contact with the upper portion of the hard film. However, precision may be more readily improved if the photoresist pattern is removed. Therefore, the photoresist pattern is preferably removed by ashing or the like before the step of etching the base film through the mask of
Asaoka Yasuhiro
Muranaka Seiji
Nagai Toshihiko
Tanaka Hiroshi
Yokoi Naoki
Goudreau George
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
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