Anomalous Diffusion of Boron in Silicon Due to Heavy Ion Bombardment

Anomalous diffusion of impurities and lattice atoms under proton irradiation at high temperatures is well known but less is published for heavy ion bombardment. This paper deals with the redistribution of predoped boron in silicon due to postbombardment with 20Ne and 40Ar ions at elevated temperatures (400 to 850 °C). The observed changes of the initial concentration profiles show a dramatical redistribution of boron, if target temperature during implantation is greater than 600 °C. Due to the additional ion bombardment the diffusity of boron is enhanced up to five orders of magnitude and the profiles are characterized by tails, second peak formation, or steplike distributions. The results depend critically on current density and temperature. The higher mobility of boron atoms under ion bombardment is explained assuming a formation of mobile complexes between a defect and the boron atom.