Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1997-11-25
2001-03-20
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S683000, C438S685000, C438S780000, C427S124000, C427S126100, C427S126200
Reexamination Certificate
active
06204174
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the fabrication of integrated circuits. More particularly, the invention provides a technique, including a method and apparatus, for improving the deposition rate of refractory metal layers.
Deposition of refractory metals, such as tungsten, over a semiconductor substrate is a common step in the formation of some integrated circuit (IC) structures. For example, tungsten is commonly used to provide electrical contact to portions of a semiconductor substrate. These electrical contacts are usually provided through openings in an insulation layer, such as a silicon dioxide layer, formed over the substrate. One method used to form such contacts includes the chemical vapor deposition (CVD) of tungsten to fill the opening after an initial layer of titanium nitride has been deposited in the opening. As another example, tungsten is sometimes used to form metal lines over a semiconductor substrate.
One CVD technique that has been employed to deposit tungsten films in the semiconductor industry uses tungsten hexafluoride (WF
6
) and a hydrogen reducing agent, e.g., H
2
, as precursor gases. This technique includes two main steps: nucleation and bulk deposition. The nucleation step grows a thin layer of tungsten which acts as a growth site for subsequent film. In addition to WF
6
and H
2
, the process gas used in the nucleation step of this technique includes silane (SiH
4
), and may also include nitrogen (N
2
) and argon. A bulk deposition step then is used to form the tungsten film. The bulk deposition gas is a mixture containing WF
6
, H
2
, N
2
, and Ar.
Advances in integrated circuit technology have lead to a scaling down of device dimensions and an increase in chip size and complexity. This has necessitated improved methods for deposition of refractory metals, particularly tungsten which has led to a constant endeavor to decrease the quantity of impurities, such as ethylene, deposited in the refractory metal layers. The aforementioned impurities may have deleterious effects on the refractory metal layer, depending upon the nature of the impurity and the quantity present therein. Over the past ten years, impurity control has been successful in substantially reducing impurities attributable to the ambient environment in which refractory metal layers are formed so that greater than 80% of all impurities now present are a direct result of the process. One such source is the contaminants present in the process gases employed to form refractory metal layers. As a result, many process gases are produced in purified form so that there is less than ten, 10, parts of contaminants for every one billion, 1,000,000,000 parts of process gas. Such purification greatly increases the cost of the process gas and, therefore, the cost of depositing a refractory metal layer.
What is needed, therefore, is an improved method for depositing refractory metal layers that lowers the cost of producing the same.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for controlling a deposition rate of a refractory metal layer, such a tungsten, on a silicon substrate, as a function of an amount of contaminants present in a process gas. The present invention is based upon the discovery that the presence of ethylene, C
2
H
4
, in a process gas has an effect on the deposition rate of a tungsten layer.
The method of the present invention includes placing a substrate in a deposition zone, of a semiconductor process chamber, flowing, into the deposition zone, a process gas including a refractory metal source, an inert carrier gas, and a hydrocarbon. Typically, the refractory metal source is tungsten hexafluoride, WF
6
, the inert gas is argon, Ar, and the hydrocarbon is ethylene, C
2
H
4
. The ethylene may be premixed with either the argon gas or the tungsten hexafluoride source to form a homogenous mixture. However, it is also possible to mix the ethylene with either the argon gas or the tungsten hexafluoride source, in situ, anterior to the process chamber.
In an exemplary embodiment of the method in accordance with the present invention, a substrate having an anisotropic surface is placed in a deposition zone of a substrate process chamber. The flow rate of the WF
6
gas is between 60 and 200 sccm, with 95 sccm being preferred. The flow rate of the Ar gas is between 1,000 and 6,000 sccm, depending upon the chamber temperature. Were the ethylene premixed with the argon gas or the tungsten hexafluoride source, the minimum quantity of ethylene present would be no less than 100 parts for every 1,000,000,000 parts of the process gas. The maximum quantity of ethylene present would be no greater than 10,000 parts for every 1,000,000,000 parts of the process gas. Were the ethylene mixed, in situ with either the argon gas or the tungsten hexafluoride source, the mixture rate would be established so that the aforementioned quantities are obtained in the process chamber.
These and other embodiments of the present invention, as well as its advantages and features are described in more detail in conjunction with the text below and attached figures.
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Ghanayem Steve
Glew Alexander D.
Johnson Andrew D.
Rajagopalan Ravi
Applied Materials Inc.
Berry Renee R.
Nelms David
Townsend and Townsend and Crew
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