Tungsten chemical vapor deposition characteristics using SiH4 in a single wafer system

Abstract

Several workers have recently begun using silane as a high-rate, low-temperature alternative to hydrogen for the reduction of WF6 in the chemical vapor deposition of W. The deposition and film characteristics of both selective and blanket W using this new chemistry are explored in a radiantly heated single wafer system using closed-loop temperature control with a thermocouple in direct contact with the backside of the wafer. Selective W deposition rates of up to 1.5 μm/min were measured over the temperature range 250–550 °C with blanket W rates typically 2–5× lower. Resistivity is in the 10–15 μΩ cm range at 300 °C for SiH4/WF6 ratios of 0.2 to 1.0, while above 400 °C the range is 7.5–8.5 μΩ cm. Si content in the W films is quite low at 1016 to 1017 atoms/cm3. Adhesion to silicon is excellent at temperatures of 350 °C and above. Selective W using SiH4 reduction for doped silicon contact fill shows none of the consumption or encroachment problems common to H2 reduction, although selectivity is more sensitive. Contact resistance for p+ and n+ silicon contacts are comparable to aluminum controls and to previously published data. Blanket deposition into narrow geometries gives ≥90% step coverage and without keyholes in the 250–450 °C deposition temperature range. For low-SiH4 flows, deposition at 500 °C causes small keyholes, while at 550 °C even larger keyholes result. At higher SiH4 flows, keyholes are typically not seen from 250 to 550 °C. The SiH4-reduced films are much smoother as indicated by reflectivities that are 2–4×higher than for the H2-reduced films.