Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1997-12-03
2001-08-07
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C427S097100, C427S099300, C427S124000, C427S126400, C438S654000, C438S655000, C438S656000, C438S657000, C438S672000, C438S680000, C438S685000
Reexamination Certificate
active
06271129
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 forming improved refractory metal layers having reduced stress while providing good gap filling properties.
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 low temperature deposition of refractory metals, particularly tungsten, to enhance the gap filling properties and reduce the stress of the same. For purposes of this application, low temperature deposition is defined as a deposition process that occurs at temperatures no greater than 400° C. Traditionally, the gap filling property and the stress are two characteristics of refractory metal layers that have been in conflict. For example, using prior low temperature deposition techniques, refractory metal layers having stress less than 1.5×10
10
dynes/cm
2
have been formed; however, the gap filling properties of these layers have been limited to less than 70%. Alternatively, refractory metal layers having gap filling properties greater than 90% have been formed using the aforementioned prior art deposition techniques. These layers, however, typically exhibit stress much greater than 1.5×10
10
dynes/cm
2
.
What is needed, therefore, is a low temperature deposition process that enables rapid formation of refractory metal layers having reduced stress and superior gap filling properties.
SUMMARY OF THE INVENTION
The present invention provides a method for forming refractory metal layers having reduced stress while maintaining good gap-filling properties. The method does so by including a two-stage nucleation step prior to bulk deposition of a refractory metal.
The method of the present invention includes placing a substrate in a deposition zone, flowing into the deposition zone during a first deposition stage, a silicon source, such as a silane gas, and a tungsten source, such as a tungsten-hexafluoride gas, so as to obtain a predetermined ratio of the two gases therein to commence nucleation of the substrate surface. During a second deposition stage, subsequent to the first deposition stage, the nucleation process is continued with the ratio of the two gases being varied. During the first deposition stage there is a greater quantity of silane gas than tungsten-hexafluoride gas. During the second deposition stage there is a greater quantity of tungsten-hexafluoride gas than silane gas. Also, an additional source of inert gas, such as, argon and/or an additional reducing agent, such as H
2
, may be introduced to stabilize the gas flow during the first and second deposition stages.
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 processing chamber. The silane and tungsten-hexafluoride gases are flowed into the deposition zone at approximately 25-35 sccm and 2-7 sccm, respectively. In this fashion, the flow ratio, in the deposition zone, of silane gas to tungsten-hexafluoride gas is greater than 4.0:1.0. During the second deposition stage, the aforementioned ratio is varied so that the ratio of silane gas to tungsten-hexafluoride gas is less than 0.5:1.0, with the flow rates being 12-17 sccm and 25-35 sccm, respectively. Subsequent to the second deposition stage, a bulk deposition stage occurs to form a metal tungsten layer on the substrate. During the bulk deposition stage, a process gas is introduced into the deposition zone which typically includes argon, nitrogen, tungsten-hexafluoride gas and a reduction agent, such as hydrogen gas. Thereafter, the deposition zone is maintained at process conditions suitable for depositing a tungsten layer on the substrate.
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
Mahajani Maitreyee
Applied Materials Inc.
Berry Renee R.
Nelms David
Townsend and Townsend / and Crew LLP
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