Low‐Temperature Activation and Recrystallization of B+‐ and  BF 2  +  ‐ Implanted LPCVD Amorphous‐Si Films

Abstract

Low‐temperature (600°C) activation and recrystallization of the low‐pressure chemical vapor deposition (LPCVD) amorphous‐Si films B+‐ and BF2+‐normalImplanted with different implantation dosages and projection ranges have been investigated. The boron dopant in the amorphous‐Si layer can enhance the recrystallization, resulting in the shorter incubation time and smaller grain size then the undoped specimens. For the BF2+‐normalImplanted specimens, the existence of fluorine atoms could postpone the grain nucleation, leading to the longer incubation time and slower nucleation rate for the heavily doped specimens than the undoped ones. For the BF2+‐normalImplanted specimens, as the implantation peak reaches to the α‐normalSi/SiO2 interface, the recoiled oxygen atoms from the oxide substrate would retard the grain nucleation and exhibit a significantly large grain size after a long time annealing. However, the recoiled oxygen atoms and the microdefects in the poly‐Si layers would offset the improvement in hole mobility. Higher hole mobilities and lower trap state densities were also observed for the BF2+‐normalImplanted specimens with respect to the B+‐implanted ones. It is attributed to the passivation effect of fluorine atoms within the poly‐Si layers.

Boron Redistribution During Crystallization of Phosphorus-Doped Amorphous Silicon

“…The crystallization phenomenon is expected to greatly influence the redistribution of the dopants, and may lead to unusual variation of their concentration profiles versus the annealing time. For instance, it has been shown that both the nature of the dopant and its concentration can influence the silicon crystallization [9][10]. Furthermore, dopant diffusion depends on the crystalline state of the Si matrix, being faster in polycrystalline and amorphous Si than in monocrystalline Si.…”