Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-08-30
2001-06-12
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S592000, C438S655000, C438S301000
Reexamination Certificate
active
06245673
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of forming a tungsten silicide film used mainly in the manufacture of a semiconductor device, particularly, the tungsten silicide film used for forming a gate electrode/wiring in combination with, for example, a polycrystalline silicon layer and a method of forming the same.
A so-called “polyside structure”, in which, for example, a polycrystalline silicon layer and a tungsten silicide layer are superposed one upon the other, is used for forming a gate electrode and a wiring in a semiconductor device such as LSI in order to lower the resistance of the gate electrode and the wiring. In this case, the tungsten silicide layer constituting the upper layer of the polyside structure is formed in general by a CVD method using WF
6
/SiCl
2
H
2
/Ar as a process gas. In the conventional film forming method, the required properties of the tungsten silicide layer are obtained by controlling the film forming temperature, the pressure of the process gas, the gas flow rate, the flow rate ratio of the gases, etc. Also, it is known to the art that, in order to control the resistivity of the tungsten silicide layer and to increase the resistance to migration, it is necessary to control the crystal grain diameter and the crystal orientation of the tungsten silicide layer.
In the conventional method of forming a tungsten silicide layer, however, it was impossible to control as desired the crystal grain diameter and the crystal orientation of the tungsten silicide layer. For example, the tungsten silicide film formed by the conventional method is large in nonuniformity of the crystal grain diameter. Also, concerning the crystal orientation, (002) faces and (101) faces are present in substantially the same rate. It follows that it is difficult to control the crystal grain diameter and the crystal orientation, leading to the problem that the crystals after the heat treatment are oriented at random.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of manufacturing a tungsten silicide film that makes it possible to align the crystal orientations of tungsten silicide, and to control the nonuniformity in the size of the crystal grains, thereby diminishing the resistivity, improving the resistance to migration and stabilizing the film properties.
A method of forming a tungsten silicide film according to a first aspect of the present invention comprises a first step of forming a first tungsten silicide layer relatively rich in silicon on a substrate using a process gas having a phosphorus atom-containing gas added thereto and a second step of forming a second tungsten silicide layer relatively rich in tungsten on the first tungsten silicide layer.
In this disclosure, a phosphorus-containing gas refers to a gas whose molecule includes one or more phosphorus atom. For example, it is preferable to use phosphine (PH
3
). The process gas used in the present invention is a mixed gas composition consisting of a plurality of kinds of gases required for forming tungsten silicide. For example, it is preferable to use as the process gas a mixed gas consisting of tungsten hexafluoride (WF
6
), dichlorosilane (SiCl
2
H
2
) and argon (Ar). The mixing ratio of the mixed gas (WF
6
/SiCl
2
H
2
/Ar) can be set appropriately. In working the method of the present invention for forming a tungsten silicide film, it is necessary to use a gas composition prepared by adding a phosphorus atom-containing gas to the process gas in order to form at least the first tungsten silicide layer. By using a process gas having a phosphorus atom-containing gas added thereto, it is possible to control appropriately the crystal grain diameter and the crystal orientation of the tungsten silicide film so as to obtain a tungsten silicide film of stable film properties having a low resistivity and excellent in resistance to migration. It is preferable to add a phosphorus atom-containing gas in an amount of about 0.02 to 0.2% by volume based on the process gas amount. If the amount of the phosphorus atom-containing gas is smaller than 0.02% by volume, the effect produced by the addition of the phosphorus atom-containing gas cannot be recognized. If the addition amount exceeds 0.2% by volume, however, the film properties are deteriorated. For example, the adhesion of the tungsten silicide film to the underlying film is lowered.
In the film forming method of the present invention, it is preferable to use a process gas having a phosphorus atom-containing gas added thereto in the step of forming at least the first tungsten silicide layer. The phosphorus atom performs the function of controlling the crystal grain diameter and the crystal orientation within the tungsten silicide film. The phosphorus atom can be introduced into the tungsten silicide film during or after the film forming step. The phosphorus atom can be introduced into the tungsten silicide film by various methods. For example, the process gas having a phosphorus atom-containing gas added thereto can be heated to permit the phosphorus atom to be introduced into the tungsten silicide film simultaneously with formation of the tungsten silicide film. It is also possible to introduce the phosphorus atom into the tungsten silicide film by means of ion implantation using a phosphorus atom-containing gas after formation of the tungsten silicide film by means of CVD. Further, it is possible to introduce the phosphorus atom into the tungsten silicide film by exposing the tungsten silicide film to a plasma of a phosphorus atom-containing gas.
As described above, a process gas having a phosphorus atom-containing gas added thereto is used in the first step. The process gas serves to form a growing nucleus of tungsten silicide so as to control the crystal grain diameter and the crystal orientation. The tungsten silicide layer relatively rich in silicon referred to previously denotes a layer of tungsten silicide (W
x
Si
y
) in which a ratio x/y of the number of tungsten atoms to the number of silicon atoms is lower than ⅖, i.e., a tungsten silicide layer containing a high ratio of silicon atoms.
In the second step, a tungsten silicide film can be formed on the basis of the growing nucleus formed in the first step. In the second step, a tungsten silicide layer relatively rich in tungsten, in which the crystal grain diameter and the crystal orientation are aligned, can be formed by using the process gas alone without using a phosphorus atom-containing gas. The tungsten silicide layer relatively rich in tungsten referred to above denotes a layer of tungsten silicide (W
x
Si
y
) in which a ratio x/y of the number of tungsten atoms to the number of silicon atoms is higher than ⅖, i.e., a tungsten silicide layer containing a high ratio of tungsten atoms. Since the second step should desirably be carried out immediately after the first step, the phosphorus atom contained in the process gas used in the first step remains in the second step even if a phosphorus atom-containing gas is not added to the process gas used in the second step. Therefore, it is possible for the remaining phosphorus atoms in the first step to be mixed in the process gas used in the second step, which does not contain a phosphorus atom, resulting in formation of a tungsten silicide film containing traces of phosphorus atoms. It should also be noted that, even if a process gas that does not contain a phosphorus atom is used in the second step, it is possible for phosphorus atoms to be diffused from the first tungsten silicide layer (lower layer) into the second tungsten silicide layer (upper layer), resulting in formation of a tungsten silicide film containing phosphorus atoms. The second tungsten silicide layer of the present invention substantially free from phosphorus atoms should be interpreted to include a tungsten silicide layer that has been unavoidably allowed to contain phosphorus atoms during the film forming treatment.
A process gas having a phosphorus atom-containing gas added thereto can also be used in th
Aoki Kimiya
Matsuse Kimihiro
Okubo Kazuya
Takahashi Tsuyoshi
Amya Igwe U.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Smith Matthew
Tokyo Electron Limited
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