Nanocrystalline Si formation in the a-Si/Al system on polyimide and silicon dioxide substrates

Polysilicon (poly-Si) films fabricated on flexible substrates are of considerable interest because of their potential application in flexible displays. In this study, an 800 nm layer of amorphous silicon (a-Si), followed by a 20 nm layer of aluminum (Al), were deposited on polyimide/silicon and silicon dioxide/silicon (SiO₂/Si) substrates. Samples on polyimide were rapid thermal annealed at 900 °C for 20 s, while those on SiO₂/Si were vacuum annealed at temperatures between 200 and 600 °C for 1 h. Film properties were analyzed using Rutherford backscattering spectrometry, cross-section transmission electron microscopy, and X-ray diffraction. Silicon films containing nanocrystallites and pores were obtained, with a pore formation activation energy (E_A) of 0.59 eV. A short-range self-diffusion model is proposed for the formation of Si crystallites in cases where the solid-solubility limit for Si dissolution into Al has not been reached.