Large-grained poly-silicon thin films by aluminium-induced crystallisation of microcrystalline silicon

Al-induced crystallisation of microcrystalline Si (μc-Si:H) thin films prepared by electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) on SiO2-coated Si wafers has been studied. The starting structure was substrate/μc-Si:H/Al. Annealing this structure at a temperature of 520 °C resulted in successful layer exchange and the formation of a substrate/Al+Si layer/poly-Si geometry. Grain sizes exceeding ∼60 μm have been achieved in films displaying a preferential (1 0 0) orientation. The length of time the samples are kept under ambient conditions before annealing plays a key role in controlling grain size and orientation. It is likely that this time delay influences the formation of the interface between the Si and Al layers and, hence, the crystallisation process. These poly-Si layers exhibit an average surface roughness (Ra) generally in the range ∼7–12 nm.