Preparation of p-type silicon films by plasma decomposition of a SiH4/H2/BF3 gas mixture

Abstract

p-Type microcrystalline Si films have been prepared by rf decomposition of SiH4/H2/BF3 gases. The gas composition, substrate temperature, and rf power dependence of film conductivity σ are investigated. The σ increases with increasing BF3 and saturates or takes a maximum at [BF3]/[SiH4]∼1. A fairly high σ value of ∼1.2×10−2 S/cm is obtained for the low rf power (∼0.1 W/cm2). Increasing rf power decreases σ, which is in contrast to the SiH4/H2/B2H6 system. The incorporation rate of boron from gas phase into the film is found to be low (∼4%) by use of secondary ion mass spectroscopy. Increasing hydrogen increases σ. Temperature is found to be the most effective deposition parameter. The σ monotonically increases with an increase of substrate temperature TS. Transmission electron microscopy observation shows that films with higher σ contain higher density or larger size Si crystallites. The crystalline size increases by a short time (≤15 min) annealing at 400 °C. The deposition parameter dependence of σ in comparison to the SiH4/H2/B2H6 system is discussed. The low temperature annealing effect is discussed in terms of film structure.