Tungsten film forming apparatus

Details Tungsten film forming apparatus Tungsten film forming apparatus

1990-11-21

1992-09-22

Bueker, Richard

Coating apparatus

Gas or vapor deposition

With treating means

427253, 4272551, C23C 1600

Patent

active

051493780

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a tungsten film forming apparatus.


BACKGROUND OF THE INVENTION

The prior art relating to this invention will be explained by using the example of FIG. 1 where, in order to make an electrical contact with source or drain n.sup.+ regions 82 of an MOS LSI formed on a p type Si substrate, contact holes 85 are formed in an insulating film 81 such as SI0.sub.2, and then tungsten (W) electrodes are attached to the surface of n.sup.+ regions 82 located inside contact holes 85.
As a method for manufacturing the W electrodes, the method that by introducing WF.sub.6 and H.sub.2 gases into a reaction chamber, W electrodes are formed on surface 84 of n.sup.+ region 82 according to the following equation:
The reaction shown as (1) is thought to proceed in such a manner that deposited tungsten works as a catalyst, and the WF.sub.6 is reduced by H.sub.2 as it is adsorbed by the W. Therefore, this reaction is thought to proceed swiftly only in the case in which W has been deposited thicker than some particular thickness and the surface of the metal is kept pure. If the surface of W is not pure, the substrate must be heated to a temperature higher than 600.degree. C. in order for the reaction (1) to proceed. However, when the temperature of the substrate is increased, not only is the quality of the deposited W film reduced because the size of the crystal grain becomes large, but the chance of the formation of an undesired film is also increased as a result of a reaction between tungsten and impurities.
In addition, in the case of the example of FIG. 1, it is necessary to deposit the W film only on the surface of the Si located inside contact holes 85 without depositing it on insulating film 81. For that process to occur, the surface of n.sup.+ region 82 is required to be pure semiconductor. The reason is as follows.
The initial deposition of the W is thought to occur selectively only on the semiconductor surface according to the following reduction reaction Therefore, if some other compounds are formed on the surface of n.sup.+ region and thus the pure semiconductor surface is not preserved, the reaction (2) will not proceed swiftly and, in other words, the selective deposition will not occur.
In order to keep the surface pure, it is important not to allow impurities, especially H.sub.2 O, O.sub.2, and hydrocarbons such as CH.sub.4 to exist in the reaction chamber. When the structure shown in FIG. 1 is adapted to an ultra high integration of LSI, the concentration of these impurities must be suppressed less than several ppb.
However, there exist at the present time no apparatuses which attain such a high purity atmosphere in the reaction chamber. Namely, in the prior art W film forming apparatus, organic materials which are corrosion-resistant to WF.sub.6 are used for the piping system, and metal materials such as stainless steel are used for the reaction chamber. As a result, a large amount of impurities from several ppm to several hundreds ppm, mainly consisting of moisture and hydrocarbons are released from the organic materials. These impurity gases are mixed with source gases, which causes various problems as shown by the following examples. chamber, the following reaction occurs and products such as a gas cause a secondary contamination,
Here, M represents the metal material used for the reaction chamber. according to the reaction,
The surface of the reaction chamber is corroded by HF, and undesirable gases such as oxygen are produced. This case also causes a secondary contamination.
These types of secondary contamination do harm to the semiconductor devices. For example, if H.sub.2 O and O.sub.2 is adsorbed by the surface of the n.sup.+ region 82, the surface 84 will be oxidized. In the case where the substrate is silicon, SiO.sub.2 will be formed on the surface of the n.sup.+ region. Consequently, of n.sup.+ region 82 will not be obtained. In order for the reactions to proceed, the substrate needs to be maintained at a temperature higher than 600.degree. C. Howeve

REFERENCES:
patent: 5009963 (1991-04-01), Ohmi

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