OPTIMIZATION AND CHARACTERIZATION OF LPCVD TIB2 FOR ULSI APPLICATIONS

The chemical vapor deposition of TiB2 from gaseous mixtures of TiCl4, B2H6, and H-2 onto various substrates was studied. A thermodynamic analysis using the SOLGASMIX computer program indicated that at an input gas ratio corresponding to the stoichiometry of TiB2, the amount of secondary-phase deposition would be considerably reduced compared to that of TiB2. For nonstoichiometric input gas mixtures, other solid phases, including oxides and silicides, are expected to result from the reaction with substrates. Experimental depositions of films were carried out in a cold wall system over a broad range of temperatures, pressures, and input gas flow rates. X-ray diffraction and x-ray photoelectron spectroscopy data indicate that the as-deposited films are very fine grained polycrystalline or amorphous, and the films RTA-annealed above 900-degrees-C are crystalline TiB2. Below 550-degrees-C, surface reactions are the dominant factor for the kinetics of TiB2 deposition, while mass transport is a limiting step for deposition above 550-degrees-C. At higher temperatures the deposition rate increases linearly with flow rate and total pressure, suggesting the deposition mechanism is reactant limited. The B/Ti ratio determined via Auger electron spectroscopy approaches the stoichiometric value of two in higher temperature films, while the presence of excess boron and chlorine was detected for low-temperature films. Stoichiometric TiB2 films were deposited over a wide range of input gas mixture B/B+Ti ratios ranging from 0.4 to 0.71. Depletion effects of input gas were observed at low flow rate and high pressure where the residence time of reactants is longer than 10 s.