Structural defects and chemical interaction of implanted ions with substrate structure in amorphous SiO2.

Abstract

Structural defects in ${\mathrm{SiO}}_{2}$ glasses implanted with ${\mathrm{Li}}^{+}$, ${\mathrm{N}}^{+}$, ${\mathrm{O}}^{+}$, ${\mathrm{F}}^{+}$, ${\mathrm{Si}}^{+}$, and ${\mathrm{P}}^{+}$ ions were examined by vacuum-ultraviolet-absorption and electron-paramagnetic-resonance spectroscopies as well as thermal-gas-release analysis. The chemical interaction of implanted ions with substrate structure was considered on the basis of the obtained results. It is found that the type of predominant defects is controlled by the electronegative nature of implants. Silicon-silicon homobonds, which are oxygen-vacancy-type defects, are produced by electropositive implants (i.e., Li, P, and Si) at concentrations comparable to those of the implants. On the other hand, in the case of electronegative implants (F and O) ${\mathrm{O}}_{2}$ molecules and peroxy radicals (POR), both of which may be regarded as oxygen-interstitial-type defects, are the major defects and the total concentrations of these two defects are comparable to implant concentrations. These results indicate that chemical interaction of implanted ions with ${\mathrm{SiO}}_{2}$ is primarily controlled by the electronegative nature of implants. Electropositive implants (M) react chemically with oxygen atoms in the substrate structure to form M-O bonds, leaving Si-Si bonds. Electronegative implants (A) react chemically with silicon atoms to form Si-A bonds and oxygen atoms recoiled with implants combine with each other to form ${\mathrm{O}}_{2}$ molecules or react with the silica-network structure to form POR's. Concentrations of these predominant defects relative to implants can be used quantitatively to describe the strength of chemical interactions. When the chemical interaction is strong, both concentrations are comparable. On the other hand, when the chemical interaction is weak, concentrations of these defects are much smaller than those of implants because the major fraction of implants occur in a neutral state without forming chemical bonds with constituents of the substrate. Nitrogen is an example of this category and the major fraction of implanted nitrogen atoms are present as ${\mathrm{N}}_{2}$ molecules.