Infrared ellipsometric study of SiO2 films: relationship between LO mode frequency and porosity

A method for evaluating the pore volume fraction of silica films for differ ent pore connectivities is presented. A series of SiO2 films, evaporated by electron gun with or without ion bombardment, have been studied using visi ble and infrared ellipsometry. The TO and LO mode frequencies are deduced f rom the dielectric function calculated from infrared ellipsometric data. Th e study of both TO and LO mode frequencies is shown to bring independent in formation on the film microstructure. The TO mode frequency (near 1075 cm(- 1)) varies mainly with the density of the silica matrix. On the other hand, variation in the LO mode frequency (near 1245 cm(-1)) is mainly due to cha nges in porosity. In the case of films with pores largely connected, the ev aluation of the pore volume fraction from the LO frequency is compared to t hat obtained from the analysis of the large water absorption band near 3300 cm(-1) (H-OH and Si-OH stretching absorption band). (C) 2000 Elsevier Scie nce B.V. All rights reserved.