DIRECT OBSERVATION OF WATER INCORPORATION IN PECVD SIO2-FILMS BY UV-VISIBLE ELLIPSOMETRY

Post-deposition exposure to the ambient of SiO2 PECVD thin films is in vestigated by phase modulated ellipsometry. Real time and static measu rements show evidence of changes in the structure of hygroscopic films due to water incorporation. These films show changes in the IR spectr a associated with the development of the bands centered at 3450 cm(-1) and 950 cm(-1) assigned to OH and SiOH bonds. The evolution of the De lta = f(psi) curves exhibits two different kinetics and it appears tha t more than 50% of the incorporated water is present within a few seco nds after the contact with air. If the exposure time does not exceed a few minutes, incorporated water molecules can be reversibly desorbed. Three models based on BEMA are proposed to account for the experiment al data. (C) 1997 Elsevier Science S.A.