BATCH REACTOR KINETIC-STUDIES OF TUNGSTEN LPCVD FROM SILANE AND TUNGSTEN HEXAFLUORIDE

The silane (SiH4) reduction of tungsten hexafluoride (WF6), used to de posit tungsten during integrated circuit (IC) production, was investig ated in a 0.64 liter, nonflowing laboratory reactor. Gas compositions were measured 2 mm from the growing surface, throughout time, with a m ass spectrometer equipped with a capillary sampling tube. The initial partial pressures of SiH4 and WF6 ranged from 0.1 to 0.2 Ton: Ln each experiment, the kinetic rate dependence on concentration for a wide ra nge of concentrations was observed as the reactants converted to produ cts. Prior to heating the reactive surface, SiH4 and WF6 react at ambi ent temperature to produce gaseous SiHF3 and SiF4. The extent of this reaction can be suppressed by increasing the initial hydrogen partial pressure. On the 95 degrees C surface, tungsten is deposited and SiHF3 , is the primary silicon fluoride reaction product for most of the tes ted conditions. A multiple regression analysis of 1,975 instantaneous composition/rate pairs gives orders of 1.22 in SiH4, 0.27 in hydrogen, and -2.17 in WF6 The order of dependencies on SiH4 and WF6 suggests t hat dissociative silane adsorption is the rate-limiting step and that WF, is the most abundant surface intermediate. The ratio of SiF4 to Si HF3 stays low and constant until the gas becomes very silane rich. Plo ts showing the evolution of the instantaneous rate over time imply tha t a minimal level of thermal activation of the reactive gas is necessa ry for the deposition to be surface rate limited.