KINETICS OF TUNGSTEN LOW-PRESSURE CHEMICAL-VAPOR DEPOSITION USING WF6 AND SIH4 STUDIED BY INSITU GROWTH-RATE MEASUREMENTS

The kinetics of tungsten low-pressure chemical-vapor deposition (LPCVD) using WF6 and SiH4 have been studied in a vertical hot-wall reactor equipped with a microbalance. In situ growth-rate measurements were performed by monitoring the sample weight during tungsten film deposition. The kinetics of the LPCVD process appear to be determined by the ratio of the partial pressures of SiH4 and WF6. At low SiH4/WF6 ratios, i.e., p(SiH4)/P(WF6) less-than-or-equal-to 0.3, the kinetics are first and zeroth order with respect to p(SiH4) and p(WF6), respectively. At higher ratios, i.e., 0.5 less-than-or-equal-to p(SiH4)/p(WF6) less-than-or-equal-to 1.0, the deposition rate is second and minus first order with respect to p(SiH4) and p(WF6), respectively. In both kinetic regimes a zeroth-order dependence on p(H-2) was observed. The growth rate does not vary substantially in the temperature range 200-400-degrees-C. Maximum rate values are observed near 300-degrees-C. An attempt has been made to interpret the observed kinetic behavior in terms of a Langmuir-Hinshelwood model. The proposed surface reaction mechanism involves reaction between chemisorbed SiH species and chemisorbed WF6 molecules. Different surface reaction pathways, governed by different rate-limiting steps, have been proposed in order to explain the observed kinetics in the two regimes.