Low resistivity W using B2H6 nucleation step

Details Low resistivity W using B2H6 nucleation step Low resistivity W using B2H6 nucleation step

2000-06-14

2001-03-27

Bueker, Richard (Department: 1763)

Coating apparatus

Control means responsive to a randomly occurring sensed...

Temperature responsive

C427S253000, C438S685000, C118S668000

Reexamination Certificate

active

06206967

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 tungsten (W) films having decreased resistivity and strong adhesion.
Deposition of 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 oxide 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. One known process that uses this deposition 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.
As advances in integrated circuit technology lead to a scaling down of device dimensions and an increase in chip size and complexity, improved methods of depositing tungsten are continuously being sought. Research has been performed using diborane (B
2
H
6
) and other hydrides of Group III or V in place of or in addition to H
2
in the process gas for both the nucleation and bulk deposition stages of CVD tungsten deposition. Some of this research suggests that tungsten films deposited from a process gas that includes B
2
H
6
exhibit reduced resistivity and increased deposition rates as compared to tungsten films deposited from a process gas without B
2
H
6
.
Despite this discovery, further improvements in the deposition of tungsten films are desirable.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for forming an improved tungsten film. According to the method of the present invention, a multiple step chemical vapor deposition process for depositing the tungsten film over a substrate is taught. A first step of the multistep deposition process includes a nucleation step in which a process gas including a tungsten-containing source, a group III or V hydride and a reduction agent is flowed into a deposition zone of a substrate processing chamber while the deposition zone is maintained at or below a first pressure level. During this first deposition stage, other process variables are maintained at conditions suitable to deposit a first layer of the tungsten film over the substrate. Next, during a second deposition stage after the first stage, the flow of the group III or V hydride into the deposition zone is stopped, and afterwards, the pressure in the deposition zone is increased to a second pressure above the first pressure level and other process parameters are maintained at conditions suitable for depositing a second layer of the tungsten film on the substrate.
In a preferred embodiment, the flow of the tungsten-containing source is stopped along with the flow of the group III or V hydride, and the flow of the tungsten-containing source is restarted when the pressure is in the deposition zone is increased to the secon d pressure level. Preferable, the flow of the tungsten-containing source is stopped for a period of between 5 and 30 seconds.
In another embodiment, N
2
and a silane gas (e.g., SiH
4
) are added to the process gas that includes a tungsten-containing source, B
2
H
6
and a primary reduction agent during the nucleation stage. Preferably, the tungsten-containing source is WF
6
and the primary reduction agent is H
2
. The flow of N
2
, the primary reduction agent and a carrier gas are maintained throughout the nucleation stage until the completion of a bulk deposition stage. In an even more preferred embodiment, a deposition stage prior to the nucleation stage is employed in which a silane source is introduced into the deposition zone along with the primary reduction agent and a carrier gas but without B
2
H
6
and without a tungsten-containing source. Optionally, an N
2
flow may also be introduced during this prior deposition stage.
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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