Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-03-03
2001-09-25
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S685000, C438S656000, C438S648000
Reexamination Certificate
active
06294468
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of semiconductor manufacturing, and more particularly, this invention relates to the chemical vapor deposition of a tungsten film on a semiconductor substrate.
BACKGROUND OF THE INVENTION
Tungsten (W) films are deposited as a blanket layer using chemical vapor deposition (CVD) techniques during semiconductor manufacturing. The tungsten can be deposited through a chemical reduction of tungsten hexafluoride (WF
6
) using a hydrogen (H
2
) or silane (SiH
4
). Usually, the tungsten is deposited at temperatures ranging from 425° C. to as high as 475° C., such as disclosed in the upper range of temperatures in U.S. Pat. No. 5,795,824. In this prior art process, tungsten film is grown on a semiconductor substrate by positioning the semiconductor substrate within a chemical vapor deposition chamber having a number of different pedestals that are heated. Initiation gases, such as hydrogen and silane, are provided to initiate a growth at temperature ranges of 350 to 475° C., followed by nucleation with a gas flow that replaces the initiation gases, where tungsten film is formed at a rate in excess of approximately 100 NM/MIN on the surface. The hydrogen and silane gas flow occurs without argon gas at a first pedestal. The substrate is repositioned at a second deposition station or pedestal within the deposition chamber, followed by successive positioning at other pedestals.
However, the current chemical vapor deposition tungsten processes are not adaptable for use with low-K dielectrics because the stability of dielectrics are compromised by the high tungsten deposition temperatures of 425 to 450° C. Thus, those processes that can be used with these higher temperatures are not adaptable for use with the low-K dielectrics requiring low temperature applications. It is difficult to fabricate any chemical vapor deposition tungsten plugs at temperatures around 375° C. without extensive hardware modifications. More optimal gas species combinations, gas flows and gas flow sequences are required in the chemical vapor deposition chambers, such that a low resistivity, high reflectivity, and smaller grain size tungsten plug could be obtained at the lower temperatures compared to the prior art using the 425 to 450° C. range. It would also be advantageous if there could be little hardware changes to existing chemical vapor deposition chambers. Instead, changes in the gas flow and gas species combinations and gas flow sequences are the better design choice.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for depositing tungsten at low temperatures of about 360 to about 390° C. onto a semiconductor substrate having low-K dielectric materials.
In accordance with the present invention, a method for depositing tungsten on a semiconductor substrate comprises the step of receiving the semiconductor substrate at a first deposition station within a chemical vapor deposition chamber having a plurality of discrete deposition stations. The semiconductor substrate is heated to a temperature between about 360 and about 390° C. Initiation gases are introduced into the first deposition station to form an amorphous, monolayer of silicon. The initiation gases comprise a silane (SiH
4
) gas that flows at a rate of about 40 to about 48 standard cubic centimeters per minute.
Nucleation gases are introduced into the first deposition station to form a silane reduced tungsten layer. These nucleation gases comprise a silane gas flow of about 20 to about 30 standard cubic centimeters per minute and a tungsten hexafluoride (WF
6
) gas that flows at a rate of about 300 to about 350 standard cubic centimeters per minute.
The hydrogen reducing gas flow is introduced to form a layer of hydrogen reduced bulk tungsten. The hydrogen reducing gas flow comprises a hydrogen gas flow of about 7,000 to about 8,500 standard cubic centimeters per minute gas flow and a tungsten hexafluoride gas flow of about 300 to about 350 standard cubic centimeters per minute. A bulk hydrogen reduced tungsten is then deposited at successive deposition stations.
In another aspect of the present invention, a continuous flow of argon is introduced with the initiation and nucleation gas flows. Argon can be introduced in a continuous flow rate of about 10,000 to about 12,000 standard cubic centimeters per minute with the initiation and nucleation gas flows. In one aspect of the present invention, there are five deposition stations and argon is introduced at a continuous flow rate of about 10,000 to about 12,000 standard cubic centimeters per minute at all deposition stations. The total tungsten film thickness can be about 3,000 angstroms. Hydrogen gas flow can also be introduced at a gas flow of about 7,000 to about 8,500 standard cubic centimeters per minute with the initiation gas flow. In still another aspect of the present invention, the semiconductor substrate is heated to about 375° C.
In still another aspect of the present invention, the process for depositing tungsten on a semiconductor substrate comprises the steps of receiving the semiconductor substrate at a first deposition station within a chemical vapor deposition chamber having a plurality of discrete deposition stations. The semiconductor substrate is heated to a temperature between about 360 and about 390° C. Initiation gases are introduced for about 10 seconds into the first deposition station to form an amorphous, monolayer of silicon The initiation gases comprise a silane (SiH
4
) gas flow at a rate of about 40 to about 48 standard cubic centimeters per minute.
Nucleation gases are then introduced for about 10 seconds into the first deposition station to form a silane reduced tungsten layer of about 400 angstroms. The nucleation gases comprise a silane gas flow of about 20 to about 30 standard cubic centimeters per minute and a tungsten hexafluoride (WF
6
) gas flow of about 300 to about 350 standard cubic centimeters per minute. A hydrogen reducing gas flow is introduced for about 20 seconds into the first deposition station to form a layer of hydrogen reduced bulk tungsten of about 370 angstroms. The hydrogen reducing gas flow comprises a hydrogen gas flow of about 7,000 to about 8,500 standard cubic centimeters per minute gas flow, and a tungsten hexafluoride gas flow rate of about 300 to about 350 standard cubic centimeters per minute.
The semiconductor substrate is then received into successive deposition stations. At each successive deposition station, a gas flow is introduced for about 30 seconds to deposit a bulk, hydrogen reduced tungsten. The gas flow comprises a tungsten hexafluoride gas flowing at a rate of about 300 to about 350 standard cubic centimeters per minute and hydrogen flowing at a rate of about 7,000 to about 8,500 standard cubic centimeters per minute.
In yet another aspect of the present invention, the semiconductor substrate is received on a heated platen at a first deposition station within a chemical vapor deposition chamber that has a plurality of discrete deposition stations with heated platens. The heated platens heat the semiconductor substrate to between about 360 to about 390° C., and preferably to about 375° C. At the same time, a backside gas flow is introduced against the semiconductor substrate and heated platen for preventing backside deposition and preventing front side edge deposition, e.g., edge exclusion, and maintaining the backside gas flow in subsequent processing.
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Patent Abstracts of Japan, vol. 013, No. 429, Sep. 2
Gould-Choquette Adrienne
Merchant Sailesh
Agere Systems Guardian Corp.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Bowers Charles
Nguyen Thanh
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