Titanium diboride is an interesting new candidate for VLSI interconnection applications due to its high electrical conductivity and its excellent chemical inertness at high temperatures.
A thermodynamic analysis of the chemical vapor deposition of TiB2 from gaseous mixtures of TiCl4, B2H6 and H2 onto silicon or SiO2 substrates was performed using the SOLGASMIX computer program. Results indicate that at an input gas ratio corresponding to stoichiometry, TiB2 should form in the solid phase. For non-stoichiometric input gas mixtures, other solid phases, including oxides and silicides, are expected to result from the reaction with the Si or SiO2 substrate. Both the addition of hydrogen to the system and increased deposition temperature are expected to enhance the deposition efficiency of TiB2.
Thin films of TiB2, 50 – 120 nm thick, were experimentally deposited on thermally grown SiO2 by low pressure CVD using various gas mixtures in the temperature range 400 – 700°C. Depth profiling of the deposited films, using XPS and RBS, indicated the successful growth of a uniform, stoichiometric TiB2 film. After deposition, the films were rapid thermal annealed at various temperatures in an effort to reduce their resistivity. Resistivity was reduced by 80 % after an 1150°C, 10 sec RTA in Ar to a value as low as 40μΩ-cm, only 4 times larger than that reported for hot pressed polycrystalline TiB2. X-ray diffraction of as-deposited samples showed no crystalline peaks; however, annealed films exhibited the expected TiB2 peaks as well as those of Ti3O5 and TiO2. The titanium oxide was most likely produced during annealing due to trace amounts of oxygen in the Ar atmosphere. The average grain size measured 0.1μm via TEM. More careful control of growth and annealing conditions is expected to result in even lower resistivity TiB2 films.