STABILITY OF PLASMA-DEPOSITED AMORPHOUS HYDROGENATED BORON FILMS

An investigation of radio-frequency plasma-deposited amorphous hydroge nated boron films was conducted in order to determine the influence of the substrate temperature T-S and d.c. self-bias U-SB on the physical properties and film stability. We found three different regions of st ability depending on T-S and U-SB. Films prepared at high d.c. self-bi as and substrate temperature are mechanically unstable due to internal stress. They peel off during the deposition process or on first conta ct with the ambient atmosphere. Films deposited at low self-bias and s ubstrate temperature were found to be chemically unstable. Exposed to the ambient atmosphere, they undergo chemical changes and incorporate large amounts of oxygen and carbon. These two different regions of ins tability are separated by chemically and mechanically stable films. Th e chemical composition and the structural properties of chemically sta ble and unstable films were determined by Fourier transform infrared s pectroscopy, X-ray induced photoelectron spectroscopy and ion beam ana lysis. These measurements show that chemical stability correlates with the boron density. Chemically stable films reveal densities of more t han 68% up to 99% of the density of crystalline boron. In general, ele vated substrate temperature and ion energy cause densification of the films and increasing internal stress. Densification leads to chemical stability, while internal stress is the reason for mechanical instabil ity. (C) 1997 Elsevier Science S.A.