Interference of arsenic diffusion by argon implantation

In the study of ion implantation, electrically active ions or noble gas ions are often used for damage study, range profiling, etc. Very seldom are both electrically active ions and noble gas ions implanted at about the same depth. In the work reported here, argon and arsenic ion implants and their interference in diffusion were studied by using backscattering, electrical measurements, and transmission electron microscopy (TEM). Several unexpected phenomena were observed.

First, when both Ar and As are implanted in high doses (about 10¹⁶/cm²), at depths around a few hundred nanometers, the Ar significantly hampers the As diffusion, and the As prevents the outdiffusion of the Ar. The interference occurs regardless of which ion is implanted first.

Second, when Si wafers uniformly doped with about 4 × 10¹⁹ As/cm³ are ion-implanted with log¹⁶ Ar/cm² at 130 keV, the As atoms stay uniformly distributed. When the sample is annealed at a temperature between 900 and 1100°C in a nitrogen ambient, however, double peaks for both Ar and As are observed by backscattering. The nonuniform distribution of As after the heat treatment of the uniformly distributed As is puzzling.

Finally, the As profile for an As capsule diffused on a silicon wafer is greatly altered when the wafer has been pre-implanted with Ar. Arsenic atoms tend to build up at the same depth as the Ar atoms.

Several other observations concerning Ar and As are equally puzzling. This paper discusses the observations and some plausible explanations.