Abstract
Experimental rate data on the chemical vapor deposition of boron by reduction of boron trichloride with hydrogen are analyzed to determine the reaction mechanism. The experiments were conducted at atmospheric pressure. Tungsten was used as the substrate. It has been found that deposited film is WB. The region of mass transport control could be separated from that of chemical reaction control; in the former the mass increase of the sample depends on the total flow rate of the gas, and in the latter the mass increase does not. The activation energies in the higher temperature range and in the lower temperature range have been determined to be 17.1 and 127.9 kJ/mol, respectively. The values of activation energies also indicate that the reaction is controlled by mass transport at higher temperatures. When mass transport limitation is absent, the reaction orders with respect to boron trichloride and hydrogen are one-third and one-half, respectively. By comparing these orders with those obtained from Langmuir-Hinshelwood type equations, the rate controlling mechanism has been identified to be the desorption of hydrogen chloride from the substrate.
