Batch Reactor Kinetic Studies of Tungsten LPCVD from Silane and Tungsten Hexafluoride

Abstract

The silane reduction of tungsten hexafluoride , used to deposit tungsten during integrated circuit (IC) production, was investigated in a 0.64 liter, 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. The initial partial pressures of and ranged from 0.1 to 0.2 Torr. In each experiment, the kinetic rate dependence on concentration for a wide range of concentrations was observed as the reactants converted to products. Prior to heating the reactive surface, and react at ambient temperature to produce gaseous and . The extent of this reaction can be suppressed by increasing the initial hydrogen partial pressure. On the 95°C surface, tungsten is deposited and is the primary silicon fluoride reaction product for most of the tested conditions. A multiple regression analysis of 1,975 instantaneous composition/rate pairs gives orders of 1.22 in , 0.27 in hydrogen, and −2.17 in . The order of dependencies on and suggests that dissociative silane adsorption is the rate‐limiting step and that is the most abundant surface intermediate. The ratio of to stays low and constant until the gas becomes very silane rich. Plots showing the evolution of the instantaneous rate over time imply that a minimal level of thermal activation of the reactive gas is necessary for the deposition to be surface rate limited.