Role of chamber pressure on crystallinity and composition of silicon films using silane and methane as precursors in hot-wire chemical vapour deposition technique

Abstract

Hot-wire chemical vapour deposition is a versatile technique to deposit a-Si:H and nc-Si films at higher deposition rate (~5–10 Å/s) as compared to Plasma enhanced chemical vapour deposition (1–2 Å/s). We report the deposition of highly crystalline Si films at very high deposition rate (≥40 Å/s) by adding methane to silane during thermal/catalytic decomposition. A series of films were deposited by varying the chamber pressure between 10 and 100 Pa at a substrate temperature of 300 °C and filament temperature 2000 °C. The hydrogen diluted silane (10% silane in hydrogen) and pure methane were used as precursors and gas flow rate ratio was kept constant at 10. Films prepared at lower pressure (≤20 Pa) were more crystalline and do not contain any trace of carbon atoms. Bandgap was found to increase from 1.24–1.63 eV when pressure was increased. It was observed that chamber pressure plays a key role in determining the crystallinity, disorder and composition of these films. Addition of methane to hydrogen diluted silane increased deposition rate and crystallinity of Si films at low pressure (≤20 Pa). Above 20 Pa pressure, carbon atoms signature was obtained. SiC films were obtained when pressure was >100 Pa.