Modification of silicon-carbon film properties under high energy ion beam irradiation

Changes induced to the properties of amorphous hydrogenated silicon carbon layers by 2 MeV 4He+ ion irradiation during Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) measurements are reported. Thin films have been deposited at low temperatures ranging from 60 C to 300 C by photo-CVD using a Xe2* excimer lamp from different gas mixtures (acetylene, ethylene, silane and disilane). Additional techniques, such as ellipsometry and infrared spectroscopy have been employed to complete the film characterization. Hydrogen is removed from the material during the sample irradiation, and an exponential decrease of the ERDA counts with increasing the number of ions impinging the surface is observed. Ellipsometric measurements reveal that this effect depends on the film properties, since for films produced from ethylene and disilane, a linear relationship between the relative amount of the removed hydrogen and the index of refraction was found. It is known that silicon carbide presents an aging process when exposed to atmospheric conditions, consisting basically of film oxidation and the consequent diminution of the refractive index values. The effects of the ion beam irradiation on the physico-chemical structure of the films and their aging process are also reported. (orig.)