Titanium-Silicon Interactions During Ion Beam Irradiation
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TITANIUM-SILICON INTERACTIONS DURING ION BEAM IRRADIATION BRYAN M. TRACY, RAMA K. SHUKLA AND PAUL W. DAVIES Intel Corporation, 3065 Bowers Avenue, Santa Clara,
CA, 95051
ABSTRACT As' ion beam irradiation of thin titanium (~300A) films deposited on silicon substrates at sufficiently high dose and energy has been shown to induce an athermal thin film reaction (as evidenced by insenstivity of the reaction to irradiation current) leading to the formation of a homogeneous titanium subsilicide phase with an extremely smooth interface to the underlying silicon. RBS indicates a stoichiometry of Ti Si4 for this silicide phase. Subsequent rapid thermal annealing (RTA) of this silicide results in the incorporation of additional silicon leading ultimately to the formation of the stable C-54 TiSi 2 phase. Silicided junctions fabricated using a ion beam irradiation show improved sheet resistance uniformity and leakage characteristics when compared with those fabricated using the conventional RTA salicide process. INTRODUCTION Refractory metal silicides are being investigated for applications in both contact and interconnect metal izations in advanced VLSI [1,2). One approach to the formation of silicides is the in-situ thermal reaction between a thin deposited metal film and the underlying silicon substrate. For patterned device wafers comprising regions of silicon dioxide and exposed silicon contact regions, this approach offers the additional advantage of being self-aligned with silicide formation occuring only over those areas were the metal is in direct contact to the silicon. This process is commonly referred to as the Salicide (Self-Aligned Silicide) process [3]. For reliable device performance the silicidi ng reaction must be laterally uniform and reproducible. In practice, the quality of the siliciding
reaction
is
strongly dependent
on the cleanliness of
the
metal/silicon interface. One approach to reducing this dependency is to ion-irradiate the metal-silicon interface in an attempt to break up any interfacial contaminant layer prior to thermal processing [4,5]. In the present study, the effect of ion beam irradiation of sputtered Ti thin films deposited on n* Si has been investigated. The thin film structures formed following ion beam irradiation and during subsequent thermal annealing have been studied using a number of complementary thin film analytical techniques. The structures observed are contrasted with those reported previously for purely thermal silicide formation. In addition the electrical characteristics of junctions fabricated using an ion beam enhanced process are reported. EXPERIMENTAL Thin films of Ti were sputter deposited on single crystal n' silicon wafers. Ion beam irradiation by As' ions was carried out in an energy range choosen in order to maximize damage in the region near the titaniumsilicon interface. Since the maximum in the damage profile for heavy ions implanted into a lighter atomic weight material is shallower than the maximum in the implant, implantation energies were chosen such
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