Aluminum CVD for Interconnect Thin Films
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ALUMINUM CVD FOR INTERCONNECT THIN FILMS DONNA M. SPECKMAN The Aerospace Corporation, Electronics Technology Center, P.O. Box 92957, Los Angeles, CA 90009 ABSTRACT Aluminum thin films were deposited by chemical vapor deposition on Si02 substrates using trimethylamine alane (TMAA) in a standard low pressure CVD reactor system, with argon as a carrier gas. Film quality and morphology were found to be a sensitive function of reactor flow dynamics. High purity films were obtained with resistivities of -5.0 g0-cm and grain sizes of 1-2 gim in diameter, but many of these films also exhibited aluminum whiskers, which caused VLSI processing problems. The CVD aluminum films exhibited conformal deposition over 0.5gm topographies, and also demonstrated electromigration lifetimes comparable to those of sputtered aluminum films. Aluminum films deposited using TMAA were also found to be selective at 90'C for titanium oxide. INTRODUCTION As device design rules continue to decrease for VLSI and ULSI applications, and as demands for multilevel metallization escalate due to greater device packing densities, interconnect metallization must be capable of providing adequate step coverage over the increasingly harsh topographies of high aspect ratio contact windows and via holes. Aluminum and aluminum-silicon-copper alloys are the most commonly used metallization materials for VLSI and ULSI structures. Conventional, line-of-site sputtering techniques are currently employed to deposit these materials, but problems of poor step coverage on state-ofthe-art integrated circuits are occurring with increasing frequency. Chemical vapor deposition (CVD) is a technique that can deposit thin films conformally over a variety of topographies. The use of aluminum CVD for interconnect applications has received moderate, ongoing attention over the years, with the bulk of the studies performed to date centered on the use of TIBA (triisobutylaluminum) as a precursor reagent. TIBA has produced excellent aluminum films, but has several disadvantages including having a low vapor pressure and depositing small-grain aluminum, which may be limit its electromigration resistance [1]. In contrast, trimethylamine alane ({CH 3 }3 N)A1H 3 ; TMAA) has recently shown promise for the deposition of high purity aluminum thin films [2]. TMAA is a stable, white solid with a higher vapor pressure than that of TIBA (-2 Torr at 25'C), and has been found to deposit high purity aluminum thin films in both hot- and cold-wall reactors at low pressures. We wish to report here the results from a series of aluminum deposition experiments we have carried out using TMAA as the precursor. The influence of different CVD reactor designs on film quality and morphology will be described, and the results from some preliminary step coverage experiments performed on VLSI topography structures, as well as some electromigration studies of the aluminum films, will be presented. We will also discuss results from a study of low-temperature selectivity on a variety of substrates using TMAA. EXPERIM
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