The diffusion of ion-implanted As was investigated using Rutherford back-scattering spectrometry (table 164). By applying various annealing ambients and by encapsulation with a Si3N4 layer, it was possible to distinguish 3 types of diffusion of implanted As. These were correlated with 2 chemical states of the As. One state, where the As was completely immobile, was typical of implanted As and occurred when no extra O was supplied during annealing. This type of As was associated with As on O sites in the SiO2 network. When extra O was supplied during annealing, As was incorporated on Si sites and exhibited the normal diffusion coefficient of As in SiO2. Diffusion occurred via a mobile As-O complex, formed by reaction with the extra O. When annealing was carried out in an O2/H2O mixture, enhanced diffusion of As was observed. This was attributed to the introduction of hydroxyl groups, into the SiO2 network, which tended to weaken the structure. When P was also implanted, in addition to As, the As became immobile in all annealing ambients.

Diffusion of Ion-implanted As in SiO2. A.H.van Ommen: Journal of Applied Physics, 1984, 56[10], 2708-15

Table 164

Diffusion of Implanted As in SiO2