Compositions – Etching or brightening compositions
Reexamination Certificate
2000-10-04
2004-05-04
Norton, Nadine G. (Department: 1765)
Compositions
Etching or brightening compositions
C252S079400, C438S745000, C134S001200
Reexamination Certificate
active
06730239
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a cleaning agent, and more specifically, it relates to a cleaning agent for cleaning a semiconductor substrate subjected to dry etching. The present invention also relates to a method of fabricating a semiconductor device including a step of cleaning a semiconductor substrate subjected to dry etching with such a cleaning agent.
2. Description of the Prior Art
The pattern of a semiconductor integrated circuit device is increasingly refined in order to improve the speed and the performance of the device. Not only a transistor part influencing the performance of the device but also a capacitor and a multilayer wiling step are refined
In order to form a fine pattern by dry etching employing a resist film as a mask, refinement of the resist pattern and dry etching having higher anisotropy are required. Consequently, a large amount of resist residue adheres onto the fine pattern after ashing for removing the resist film employed for dry etching, and it is difficult to remove the residue with a conventional cleaning liquid.
Further, the target grain size of particles remarkably influencing the, yield of the device is also reduced following refinement of the pattern, and it is necessary to remove smaller particles.
At present, a mixed solution (hereinafter abbreviated as APM) of ammonia and aqueous hydrogen peroxide is widely employed for removing the resist residue and the particles in general. APM, which is an alkaline cleaning liquid, has an effect of finely etching a device material such as a silicon oxide and removing the resist residue and the particles. It has been reported in a learned society or the like that particles hardly adhere to a silicon substrate in an alkaline aqueous solution since the silicon substrate and the particles are negatively charged, and this phenomenon is regarded as the reason for the high cleaning effect of APM.
In a device following a design rule of not more than 0.15 &mgr;m, wires for a gate electrode, a bit line and the like are prepared from a metal material such as tungsten or a tungsten alloy having low resistance. Tungsten or an alloy such as tungsten nitride is dissolved due to reaction with aqueous hydrogen peroxide contained in APM. If such a material is exposed, therefore, APM cannot be used. When employing a mixed solution (dilute aqueous ammonia)-of ammonia and water containing no aqueous hydrogen peroxide as a cleaning liquid for preventing dissolution of the material, a silicon material such as silicon forming a semiconductor substrate or polysilicon or amorphous silicon employed as a wire material or an electrode material for a capacitor is dissolved due to reaction with ammonia although dissolution of tungsten is suppressed.
While alkaline cleaning liquids include an aqueous solution (generally used as a developer) of tetramethylammonium hydroxide (TMAH), a water-soluble organic solvent containing organic amine and the like in addition to the aforementioned aqueous ammonia, all these cleaning liquids dissolve silicon and have low cleaning ability.
Thus, there is no proper cleaning liquid removing a resist residue and particles in a state simultaneously exposing tungsten or an alloy such as tungsten nitride and silicon under the present circumstances.
Problems of a conventional method of fabricating a semiconductor device having a step simultaneously exposing tungsten and silicon are now described.
FIG. 2
is a sectional view of a semiconductor device fabricated with a conventional cleaning agent. An isolation insulator film
2
for isolating element regions from each other is provided on a major surface of a semiconductor substrate
1
. A gate electrode
6
is formed by stacking a polysilicon film
4
and a tungsten (or tungsten alloy) film
5
on the semiconductor substrate
1
through a gate insulator film
3
. An interlayer isolation film
7
is formed on the semiconductor substrate
1
to cover the gate electrode
6
. A connection hole
7
a
exposing the surface of the semiconductor substrate
1
and a connection hole
7
b
reaching the surface of the gate electrode
6
are formed in the interlayer isolation film
7
, and embedded conductive layers
8
consisting of tungsten are embedded in the connection holes
7
a
and
7
b
respectively. A bit line
9
consisting of tungsten or a tungsten alloy is provided on the interlayer isolation film
7
, to be connected with the embedded conductive layers
8
. Interlayer isolation films
10
and
11
are provided on the interlayer isolation film
7
, to cover the bit line
9
. A connection hole
12
a
exposing the surface of the semiconductor substrate
1
is formed through the interlayer isolation films
11
,
10
and
7
. An embedded conductive layer
12
consisting of tungsten is provided to cover the side wall surface and the bottom surface of the connection hole
12
a
. This embedded conductive layer
12
, which must essentially be completely embedded in the connection hole
12
a
, is not completely embedded in the prior art.
An aluminum wiling layer
13
consisting of aluminum or an aluminum alloy is provided on the interlayer isolation film
11
, to be connected with the embedded conductive layer
12
. The conventional semiconductor device shown in
FIG. 2
is fabricated through steps shown in
FIGS. 3
to
15
.
The problems of the method of fabricating the conventional semiconductor device shown in
FIG. 2
are now described.
First Problem
Tungsten or a tungsten alloy is used as an electrode material in the conventional semiconductor device, and a gate electrode made of such a material is generally referred to as a metal gate. Tungsten silicide (WSi) was employed as a previous electrode material.
Referring to
FIG. 3
, the isolation insulator film
2
is formed on the semiconductor substrate
1
. Then the surface of the semiconductor substrate
1
is oxidized for forming the gate insulator film
3
. The polysilicon film
4
and the tungsten film
5
serving as electrode materials are successively formed on the gate insulator film
3
, and a resist pattern
14
is formed thereon.
Referring to
FIG. 4
, the resist pattern
14
is employed as a mask for performing reactive ion etching (dry etching) on the tungsten film
5
and the polysilicon film
4
, thereby forming the gate electrode
6
.
Referring to
FIGS. 4 and 5
, the resist pattern
14
is removed by plasma treatment (referred to as ashing) with a gas containing oxygen. At this time, upwardly extending resist residues
15
adhere to the side walls of the gate electrode
6
.
Referring to
FIGS. 5 and 6
, the resist residues
15
are removed by treatment with a cleaning agent. The cleaning agent is prepared from a mixed solution (dilute aqueous ammonia) of ammonia and water. The dilute aqueous ammonia, having small dissolubility for tungsten, dissolves polysilicon due to reaction with ammonia. Therefore, the polysilicon film
4
forming the gate electrode
6
is transversely etched to narrow the width of the gate electrode
6
. Consequently, the electric characteristics of a transistor are disadvantageously deteriorated. When the cleaning agent is prepared from APM, the tungsten film
5
is remarkably dissolved although the polysilicon film
4
is not etched. Thus, APM cannot be used in practice.
While this prior art is described with reference to dry etching employing a resist mask, a similar problem arises also when employing a silicon nitride film as a mask.
Second Problem
A second problem of the method of fabricating the conventional semiconductor device having a step simultaneously exposing tungsten and silicon is now described.
Referring to
FIG. 7
, the gate electrode
6
is formed on the semiconductor substrate
1
and the interlayer isolation film
7
is formed thereon. A resist pattern
14
is formed on the interlayer isolation film
7
.
Referring to
FIG. 8
, the resist pattern
14
is employed as a mask for performing reactive ion etching (dry etching) on the interlayer isolation film
7
, thereby forming contact holes
Ichiki Naoki
Kanno Itaru
Morita Hiroshi
Nezu Hideaki
Takashima Masayuki
Norton Nadine G.
Umez-Eronini Lynette T.
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