Laboratory batch reactor method for kinetic study of chemical vapor deposition

Abstract

AbstractA lab‐scale nonflowing reactor was built to study chemical vapor deposition reactions. Mass spectrometry is used to follow reaction pathways and to determine instantaneous reaction rates throughout film growth. In each experiment, the kinetic rate dependence on concentration for a wide range of concentrations is observed as reactants convert to products. This method of obtaining kinetic data is efficient in terms of sample loading, gas usage, and time, since over 200 instantaneous rate/composition pairs can be determined from one 30‐min deposition. Because the rate is determined from gas‐mass balance, rather than film‐thickness measurements, an unlimited number of rate studies can be made on one sample. As a test case, the SiH4 reduction of WF6, used to deposit tungsten during integrated‐circuit production, was investigated in the 0.64‐L nonflowing laboratory reactor. Gas compositions were measured 2 mm from the growing surface, throughout time, with a mass spectrometer equipped with a capillary sampling tube. Tungsten was deposited on the 95°C surface, and SiHF3 was the primary silicon fluoride reaction product for most tested conditions. A multiple‐regression analysis of 1,975 instantaneous composition/rate pairs gives orders of 1.22 in silane, 0.27 in hydrogen, and −2.17 in WF6. The ratio of SiF4 to SiHF3 stays low and constant until the gas becomes silane‐rich. The evolution of the instantaneous rate over time implies that a minimal level of thermal activation of the reactive gases is necessary for the deposition to be surface‐rate‐limited. Preliminary heat‐transfer models of the wire substrate imply that heat transfer to the gas phase is in the Knudsen regime.