POSITRON-ANNIHILATION SPECTROSCOPY APPLIED TO POROUS SILICON FILMS

A monoenergetic slow positron beam has been used for the first time to profile porous silicon films. High values of the Doppler-broadened li ne shape parameters are observed, which correspond to positron annihil ation within the porous layers and these are attributed to the decay o f para-positronium. After allowing for the reduced density of the poro us film, fitted values of thickness were deduced which were in reasona ble agreement with values obtained from ellipsometry measurements. Low values of the Doppler parameters observed for the two samples with th e thinnest films are attributed to oxide residing at the interface of the porous and bulk silicon regions. Etching the samples in a solution of 48% hydrogen fluoride reduced the porous film thickness significan tly, suggesting that a considerable amount of the film consists of SiO 2. A four-component convolution analysis routine is used to analyze th e individual 511 keV annihilation peaks, the result of which confirms the formation of positronium within the porous layer. Positron annihil ation is shown to be a promising method for the nondestructive investi gation of thin porous films. (C) 1995 American Institute of Physics.