Enhanced Crystallinity of Microcrystalline Silicon Thin Films Using Deuterium in Reactive Magnetron Sputter Deposition at 230°C

Abstract

We analyze the formation kinetics and microstructure of hydrogenated 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 H₂or D₂(0-5.5mT) on Coming 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 (H₂or D₂) and pressure used in the deposition process. We find that the films enter the microcrystalline regime at lower D₂pressures than H₂pressures. Furthermore, the <ε₂> data determined by ellipsometry have a different shape for deuterated films, compared to hydrogenated films at similar growth pressures. This indicates changes in band structure which we interpret as evidence for enhanced crystallinity.