Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – Insulated gate formation
Reexamination Certificate
2001-01-11
2004-11-23
Coleman, W. David (Department: 2823)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
Insulated gate formation
C438S595000, C438S684000, C257S407000, C257S412000, C257S413000, C257S900000
Reexamination Certificate
active
06821874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a semiconductor device. More specifically, the invention relates to a method for depositing a tungsten silicide film for use in a gate electrode/wiring (a gate electrode and/or a wiring), and a method for preparing a gate electrode/wiring.
2. Description of Related Background Art
In semiconductor devices, such as LSIs, a so-called polycide structure comprising a polysilicon layer
10
and a tungsten silicide layer
20
stacked thereon as shown in
FIG. 3
is widely used as a gate electrode and/or a wiring in order to lower the resistance of the gate electrode and wiring. The tungsten silicide layer serving as a top layer of the polycide structure is generally deposited by the CVD method using WF
6
/SiCl
2
H
2
/Ar as a reactive gas. Therefore, in the conventional thin-film deposition method, a desired film quality of tungsten silicide layer is obtained by controlling the deposition temperature, the pressure of the reactive gas, and the flow rate and flow ratio of the gas. In
FIG. 3
, reference number
30
denotes a silicon substrate,
31
denotes a silicon oxide film,
40
denotes a silicon oxide film,
50
denotes a silicon nitride film, and
60
denotes a side wall of a silicon oxide film.
However, in the present circumstances, if an electrode and/or wiring having a polycide structure, which is scaled down as small as possible, is prepared by a conventional method for depositing a tungsten silicide film, there are some cases where a void V is formed in the electrode and/or wiring in the producing stage as shown in FIG.
3
. Although the void has little influence on the productivity of semiconductor devices in the present stage, it is predicted that the influence of such a void becomes obvious to lower yields if the scale down and lowering of resistance of the electrode and/or wiring further proceed in future.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a method for depositing a tungsten silicide film and a method for preparing a gate electrode/wiring, which can enhance yields in future without forming any voids in the electrode and/or wiring having a polycide structure. It is another object of the present invention to provide a gate electrode/wiring structure which is prepared by the gate electrode/wiring preparing method according to the present invention.
The inventors found that depressions V′ corresponding to voids existed in the central portion of the surface of a polysilicon layer
10
when a tungsten silicide layer
20
was peeled off from the polysilicon layer
10
after a side wall oxidizing step of an electrode/wiring preparing process was completed in order to identify a void occurring step (see FIG.
4
). On the basis of this, the inventors predicted that voids occur at the side wall oxidizing step by trying the identification of void existing places and existing step, and carried out the side wall oxidizing process while varying process temperature and process time. As a result, the inventors found that voids occurred at a high process temperature although no void occurred when the process time was short and/or when the process temperature was low. From this fact, the inventors presumed that since more lattice defects and interstitial atoms concentrate on the interface between the polysilicon layer
10
and the tungsten silicide layer
20
than other portions, silicon atoms in the surface of the polysilicon layer
10
use lattice defects as media to diffuse to be consumed for the side wall oxidation to produce voids, as shown in
FIG. 3
by an arrow, when the side wall oxidizing step is carried out at a high temperature. The side wall oxidizing step means a step of forming an oxide film on the side wall of the tungsten silicide layer
20
and on the side wall of the polysilicon layer
10
in order to prevent impurities from being injected into the tungsten silicide layer
20
and the polysilicon layer
10
from oblique directions when the impurities are ion-implanted.
Therefore, the inventors studied various tungsten silicide film depositing methods and gate electrode/wiring preparing methods which do not fear that silicon atoms are consumed even at the side wall oxidizing step. As a result, the inventors knew that the above described objects of the present invention can be accomplished by depositing a tungsten silicide film or preparing a gate electrode/wiring on specific conditions.
The present invention has been made on the basis of the above described knowledge. In order to accomplish the aforementioned and other objects, according to a first aspect of the present invention, there is provided a method for depositing a tungsten silicide film, wherein when a tungsten silicide layer is formed on a polysilicon layer, a phosphorus atom containing gas is added to a reactive gas at least in the initial stage that the tungsten silicide layer is formed, and the amount of the added phosphorus atom containing gas is set to be in the range of from 0.2 vol. % to 0.45 vol. %.
According to a second aspect of the present invention, there is provided a method for depositing a tungsten silicide film, wherein when a tungsten silicide layer is formed on a polysilicon layer, a phosphorus atom containing gas is added to a reactive gas at least in the initial stage that the tungsten silicide layer is formed, and a tungsten silicide layer forming temperature is set to be a temperature at which silicon atoms of the polysilicon layer are activated.
In the second aspect of the present invention, the tungsten silicide layer forming temperature is preferably set to be at least 700° C.
In the first and second aspects of the present invention, the method preferably includes a first stage in which the phosphorus atom containing gas is added to the reactive gas, and a second stage in which the phosphorus atom containing gas is not added to the reactive gas.
According to a third aspect of the present invention, there is provided a method for preparing a gate electrode/wiring, which comprises the steps of depositing a tungsten silicide layer on a polysilicon layer, and depositing a silicon layer on the tungsten silicide layer.
According to a fourth aspect of the present invention, there is provided a method for preparing a gate electrode/wiring, which comprises a step of depositing a tungsten silicide layer on a polysilicon layer, a step of oxidizing a side wall of a gate electrode/wiring layer containing the polysilicon layer and the tungsten silicide layer, and a short-time annealing step carried out between the depositing and oxidizing steps.
According to a fifth aspect of the present invention, there is provided a gate electrode/wiring structure which comprises a polysilicon layer, a tungsten silicide layer formed on the polysilicon layer, and a silicon layer formed on the tungsten silicide layer.
The tungsten silicide film depositing method (which will be hereinafter referred to as a “deposition method”) according to the present invention is characterized in that a tungsten silicide layer is formed on a polysilicon layer, which has been previously formed by a conventional well-known method, by a method which will be described later. According to the present invention, the phosphorus atom containing gas is a gaseous molecule bonded to phosphorus atoms, and is preferably phosphine (PH
3
). The reactive gas is a mixed gas composition comprising various gases required when tungsten silicide is produced, and is preferably a mixed gas of tungsten hexafluoride (WF
6
), dichlorosilane (SiCl
2
H
2
) and argon (Ar). The composition ratio of the gases (WF
6
/SiCl
2
H
2
/Ar) can be suitably set.
In the deposition method according to the present invention, a gas composition, which comprises a reactive gas and a phosphorus atom containing gas added to the reactive gas at least in the initial stage that a tungsten silicide layer is formed, is used when a tungsten silicide layer is formed on a polysilicon layer. By
Matsudo Masahiko
Okubo Kazuya
Suzuki Kenji
Coleman W. David
Nguyen Khiem
Smith , Gambrell & Russell, LLP
Tokyo Electron Limited
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