LOW-TEMPERATURE ACTIVATION AND RECRYSTALLIZATION OF B+-IMPLANTED AND BF2+-IMPLANTED LPCVD AMORPHOUS-SI FILMS

Abstract

Low-temperature (600 degrees C) activation and recrystallization of the low-pressure chemical vapor deposition (LPCVD) amorphous-Si films B+- and BF2+-implanted 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+-implanted 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+-implanted specimens, as the implantation peak reaches to the alpha-Si/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+-implanted specimens with respect to the B+-implanted ones. It is attributed to the passivation effect of fluorine atoms within the poly-Si layers.