Selective Rapid Thermal Chemical Vapor Deposition of Titanium Silicide.

Scaling of MOSFET device dimensions into the deep submicron regime requires source/drain junction depths on the order of a few tens of nanometers. Considerable work has been carried out to form such ultra-shallow junctions. Formation of reliable, low resistivity contacts to these junctions is also a challenging task. The presently available self -aligned silicide technology suffers from substrate consumption during silicide formation, which makes the process unsuited for ultra-shallow junctions. Selective rapid thermal chemical vapor deposition of TiSi_2 is one of the promising alternatives currently considered for contact formation. In this process, Ti and Si are provided in the gas phase. The process relies on the hypothesis that by supplying optimum amounts of Ti and Si, substrate consumption can be minimized or eliminated. In previous studies as well as this one, the source gas for Ti has been TiCl_4. For Si, SiH _4 and rm SiH_2Cl_2 have both been considered. From the beginning, the objective of this work has been to increase fundamental understanding on selective chemical vapor deposition of TiSi_2. The work includes investigations of TiSi _2 nucleation on Si, reaction pathways, selectivity and chamber contamination. Nucleation studies in this work emphasize surface preparation for TiSi_2 . In-situ cleaning as well as in-situ selective deposition of different layers prior to TiSi_2 deposition have been investigated. As part of these studies, a new in-situ low temperature surface cleaning method using rm SiH_2Cl_2/H _2 has been developed. Potential mechanisms that retard TiSi_2 nucleation below 800^circC have been proposed. Results suggest that surface morphology may be a key factor in TiSi_2 nucleation. Silicon substrate etching during TiSi_2 deposition has been studied in detail via thermodynamic equilibrium simulations. It has been determined that Si etching occurs via formation of SiCl_4 and SiCl_2. Hydrogen has been determined as an extremely useful ingredient to suppress substrate etching. The simulation results have also been confirmed by experiments. Silicon substrate consumption has been studied under different deposition temperatures and using different gas compositions. A process window for consumption -free TiSi_2 deposition has been determined. Deposition selectivity with respect to silicon dioxide and silicon nitride has been investigated. A novel approach that combines SiH_4 and rm SiH_2Cl_2 has been developed for enhanced selectivity.