Optimization of Deposition Parameters for Thin Silicon Films on Flexible Substrates in a Hot-Wire Chemical Vapor Deposition Reactor

Abstract

This paper studies the deposition of thin silicon films from silane on plastic substrates in a recently build hot-wire chemical vapor deposition reactor. Hydrogen dilution of silane was used to induce amorphous-to-nanocrystalline phase transition. Thin-film deposition rate, r d , is roughly proportional to silane concentration during deposition but the proportionality factor depends on filament temperature, T fil . At T fil ∼ 2500°C (1900°C), r d increases from 2.1 A/s (1.2 A/s) at 97% H 2 dilution to 14.5 A/s (10.7 A/s) for films deposited from pure silane. At T fil ∼ 2500°C, films deposited under 80% H 2 dilution were amorphous, under 90% H 2 dilution the crystalline fraction was X C = 49.4% and under 95% H 2 dilution, X C = 52.8%. At T fil ∼ 1900°C, samples were amorphous up to ∼ 95% H 2 dilution where a crystalline fraction of 22.3% was measured. Films with amorphous structure have σ d ∼ 10 -10 -10 -9 Ω -1 cm -1 while those with a measured crystalline fraction have σ d ∼ 10 -7 -10 -5 Ω -1 cm -1 , depending on the amount of crystalline fraction and grain size. Films with lower σ d have optical band gap in the range ∼ 1.85-1.9 eV, typical of hydrogenated amorphous silicon, while those with higher σ d have larger optical band gap (∼2 eV), typical of hydrogenated nanocrystalline silicon. Adhesion of the films to the plastic substrate was good, as they survived bending to small radius of curvature (< 1 mm) without peeling. Structural, optical and transport properties were similar on films deposited both on PEN and on glass under the same deposition conditions.