Optical spectroscopic analyses of OH incorporation into SiO2 films deposited from O-2/tetraethoxysilane plasmas

Silicon dioxide thin films are deposited on (100) silicon substrates at low pressure (5 mTorr), from O-2/tetraethoxysilane (TEOS) helicon plasmas. The reactor is operated at 300 W radio frequency power without any intentional heating or biasing of the substrate. The samples are characterized using i nfrared spectroscopy, ultraviolet-visible ellipsometry, and complementary d ensity measurements. Changes in film properties are observed varying the TE OS fraction in the gas mixture. Good quality SiO2 films, insensitive to pos tdeposition exposure to atmospheric water, are deposited for low TEOS fract ions (<5%) in the mixture. As the O-2 flow rate decreases, porous SiO2 and polymeric SiOxCyHz samples are successively obtained. Aging over 5 months o f intentionally produced porous films has been investigated using Fourier-t ransform infrared spectroscopy. The 2900-3800 cm(-1) OH absorption stretchi ng band is quantitatively analyzed with three deconvolution bands. These fi lms are hygroscopic and they show changes in the infrared spectra indicatin g an incorporation of additional highly associated hydroxyl groups. In addi tion, the development of the 935 cm(-1) Si-OH stretching band and the evolu tion of the Si-O-Si stretching peak are due to interactions between the air borne absorbed water and silica network. On the other hand, isolated silano l species are rather insensitive to the postdeposition exposure to the atmo spheric water. The respective contribution of growth induced and after grow th ex situ incorporated Si-OH groups is established. Using the Bruggeman ef fective medium approximation, we found that water molecules account well fo r the dielectric properties of these highly associated SiOH groups mainly o riginating from postdeposition silica hydrolysis. (C) 2000 American Vacuum Society. [S0734-2101(00)05305-7].