SiO2 films deposited on Si substrates studied by monoenergetic positron beams

Abstract

Variable-energy positron beams were utilized to study SiO2 films grown on Si substrates. Annihilation characteristics of positrons in the SiO2 films were found to be dominated by the formation probability of positronium (Ps). For the SiO2 film grown by wet oxidation, a high formation probability of Ps was found by measurements of Doppler broadening profiles of the annihilation radiation and those of lifetime spectra. For SiO2 films grown by an atmospheric-pressure chemical vapor deposition technique using tetraethylorthosilicate and ozone, however, the formation probability of Ps drastically decreased. The inhibition of the Ps formation was attributed to interactions between positrons and –OH bonds.

Characterization of the interface region during the agglomeration of silicon nanocrystals in silicon dioxide

“…18 During post-growth annealing, hydrogen diffuses towards the surface of SiO 2 so that it is nearly uniformly distributed in the SiO 2 layer. 18 Because hydrogen introduces low S values in SiO 2 by reducing the positronium formation probability, 20,21 we see a clear decrease in S after the virgin SiO 2 /Si sample is annealed at 1100°C in nitrogen ͑Figs. 2-4͒.…”

Depth Profiling of Defects in He Implanted SiO2

“…1) is well fitted with three layers: SiO 2 , SiO 2 /Si interface (3 nm thickness) and the Si substrate. In SiO 2 positrons are known from lifetime measurements to form Ps [8,9,20], the 3/4 of positronium forms o-Ps (ortho-Ps) and annihilate via pick-off with an electron of the environment into two gamma rays and a lifetime in the 1-2 ns range. The fraction of p-Ps (para-Ps) self annihilate directly into two gammas.…”

“…Ion implantation induces several type of defects in silicon dioxide [14]. Moreover, the analysis of the positron measurements becomes more complicated due to the formation of Ps in SiO 2 [8,20]. Positronium formation depends on the grown condition of the silicon oxide (for example, thermal or wet) and its pick-off is influenced by the radiation induced defects and by the change in the silicon dioxide morphology.…”

Annealing properties of open volumes in strained SiN films studied by monoenergetic positron beams

“…The incorporation of positron annihilation with oxygen valence electrons is known to decrease the S value for amorphous materials such as SiO 2 and metal oxides. 17,20,21 For the as-deposited tensile film, oxygen atoms could therefore diffuse into the film because of the roughness of the surface and the low film density. The diffusion path was blocked by the densification of films after annealing at 500°C.…”