Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Patent
1996-08-22
1999-01-26
Bowers, Jr., Charles L.
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
438688, H01L 2144
Patent
active
058638369
DESCRIPTION:
BRIEF SUMMARY
This invention concerns a method of depositing thin metal films, particularly of aluminium.
The deposition of thin films of aluminium is important for a variety of applications, such as the metallisation of silicon devices in VLSI technology, the growth of semi-conducting III-V alloys eg. AlGaAs, AlInAs and AlSb and the growth of dielectrics, such as AlN. In addition, hybrid sensors based on digital recording media are currently under development which require the deposition of aluminium on micron-size steps or holes etched on silicon.
Metalorganic chemical vapour deposition (MOCVD) is an attractive thin film growth technique possessing the advantages of large area growth capability, accurate control of layer thickness and good conformal step coverage. Much effort has, therefore, been directed at developing suitable aluminium CVD precursors.
The use of metalorganic compounds of gallium as CBE precursors has been investigated (see Journal of Crystal Growth 120 (1992) 103-113 and 124 (1992) 81-87; Surface Science 278 (1992) 111-120) including the use of tritertiarybutylgallium, tri-isobutylgallium and tri-isopropylgallium. Whilst all the compounds gave rise to reduced carbon contamination of the metal film, tritertiarybutylgallium had unacceptably low growth rates.
Volatile metalorganic compounds of aluminium have been widely investigated as CVD precursors including trimethylaluminium, dimethylaluminium hydride and higher aluminium alkyls of the formula AlR.sub.3 where R is n-propyl, n-butyl and i-butyl. However, aluminium films grown using these precursors have frequently demonstrated poor morphology and low purity. In particular, carbon contamination has resulted from the decomposition of the organic radical during metalorganic pyrolysis. That has stimulated research into the aluminium hydride based adducts bis-trimethylamine alane and dimethylethylamine alane from which carbon free aluminium and low carbon content AlGaAs have been grown. However, doubts remain about the large scale application of these alane adducts due to an unpredictable gas phase chemistry which can lead to premature decomposition and also their tendency to liberate hydrogen during storage at room temperatures.
The most successful and widely investigated CVD precursor to date has been triisobutylaluminium (TIBA). Detailed surface science studies have shown that at temperatures less than 327.degree. C. the facile .beta.-hydride elimination of iso-butylene leads to carbon free aluminium films. However, at higher temperatures the iso butyl radical can eliminate a .beta.-methyl group which leads to surface methyl radicals and to a significant increase in carbon content of the deposited aluminium film. That limits the temperature range for aluminium deposition from TIBA and precludes its use in the growth of technologically important Al/Si alloys, which require high substrate temperatures, typically above 400.degree. C., to pyrolyze the silicon precursor, typically SiH.sub.4.
Therefore, a need exists for an aluminium precursor which combines the advantages of stability associated with trialkylaluminium compounds with the potential to deposit high purity aluminium films. Analogous indium compounds may also be useful for their deposition.
It has now been surprisingly found that tritertiarybutyl aluminium may be used as a precursor for aluminium deposition.
Accordingly the present invention provides a method of depositing an aluminum or indium film on a substrate comprising the steps of contacting the substrate with an aluminum or indium precursor and treating the precursor to decompose leaving the aluminium or indium deposited on the substrate, wherein the precursor is the tritertiarybutyl compound of aluminium or indium.
The present invention further provides a substrate having an aluminum or indium layer deposited thereon from a precursory decomposing same on the substrate, wherein the precursor is a tritertiary butyl compound of the aluminum or indium.
Aluminium is the metal of most importance for the method of the invention.
In a preferre
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FitzGerald et al., Comparative Studies of the Thermal Decomposition of Tritertiarybutylgallium and Tri-isobutylgallium on GaAs (100) Surface Science, 278 (1992), 111-120.
Jones, et al., New Metalorganic Gallium Precursors For The Growth of GaAs and ALGaAs by CBE, J. of Crystal Growth, 124 (1992) 81-87.
Foord et al., Applications of MBMS and Surface Spectroscopic Techniques in the Study of Reaction Mechanisms in CBE; Investigations of the Reactivity of Tritertiarybutylgallium and Triisobutylgallium as Alternative Precursors for Epilayer Growth, J. of Crystal Growth, 120 (1992) 103-113.
Jones, Growth of aluminum films by low pressure chemical vapor deposition using tritertiarybutylaluminum, Journal of Crystal Growth, 285-289, Jul. 31, 1993.
Berry Renee R.
Bowers Jr. Charles L.
Defense Evaluation and Research Agency
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