Enhanced crystallinity of microcrystalline silicon thin films using deuterium in reactive magnetron sputter deposition at 230 °C

We analyze the formation kinetics and microstructure of hydrogenerated vs. deuterated microcrystalline (μc-Si:H or D) thin films using real-time spectroscopic ellipsometry, post-deposition thermal hydrogen evolution, and TEM. The films are deposited by reactive magnetron sputtering of a silicon target in Ar (1.65 mT) with added partial pressures of H₂ or D₂ (0-5.5 mT) on Corning 7059 glass substrates at 230 °C. Amorphous films are deposited when P_H2 = 0. When hydrogen is added to the chamber, the reactive magnetron sputtering process generates a flux of fast neutral H which promotes μc-Si growth. The substitution of D for H varies the kinetics of hydrogen reflection from the target and implantation into the growing film. We analyze the amorphous to microcrystalline transition as a function of the isotope (H₂ or D₂) and pressure used in the deposition process. We find that the films enter the microcrystalline regime at lower D₂ pressures that H₂ pressures. Furthermore, the 〈ε₂〉 data determined by ellipsometry have a different shape for deuterated films, compared to hydrogenerated films at similar growth pressures. This indicates changes in band structure which we interpret as evidence for enhanced crystallinity.