IMPLANTATION DAMAGE AND ANOMALOUS DIFFUSION OF IMPLANTED BORON IN SILICON THROUGH SIO2-FILMS

Boron is implanted in crystalline silicon through oxide layers with di fferent thicknesses. The implantation is carried out at various doses and energies of interest in ultra large scale integration (ULSI) appli cation. Rapid thermal annealings (RTA) are used to obtain shallow junc tions and electrical activation of the B atoms. However, transient enh anced diffusion induced by implantation damage can be observed. The bo ron concentration profiles before and after annealing are obtained wit h secondary ion mass spectrometry (SIMS). It is found that the diffusi on transient in the tail region of the boron profile increases with de creasing oxide thickness. Even more, if the implantation damage concer ns mostly the oxide, i.e. when the concentration peak is located in th is oxide, the oxygen knocked into the silicon substrate could play thi s way an important role in restricting the boron diffusion, which is g ood to obtain very shallow junctions. On the other hand, for thinner o xide, boron enhanced diffusion is attributed to the implantation induc ed damage into silicon at high doses. The diffusion process of boron i n oxide and monocrystalline silicon during rapid thermal annealing is investigated. The boron diffusion profiles obtained by computer simula tion are compared with the measured results. It is shown by this compa rison that the intrinsic coefficient cannot be considered as constant along all the silicon depth.