Roles of Extended Defect Evolution on the Anomalous Diffusion of Boron in Si during Rapid Thermal Annealing

Abstract

The role of extended defect evolution on the anomalous diffusion of boron during rapid thermal annealing (RTA) was studied by investigating the diffusion behavior of boron implanted into various Si substrates using secondary ion mass spectroscopy and transmission electron microscopy, i.e., predamaged wafers with low dose Si implantation, preamorphized wafers with high dose Si implantation, and single‐crystal wafers without any previous implantation. Low‐dose Si preimplantation reduced the channeled tail significantly in subsequent boron implantation and resulted in a larger anomalous diffusion of boron and faster annealing of extended defect during RTA compared to crystalline Si samples. Diffusion of boron implanted into preamorphized Si was found to be anomalous in nature and its magnitude was dependent upon the RTA temperature. The temperature dependence was found to be due to the difference in the density of dislocation loops formed during RTA at the original amorphous/crystalline (a/c) interface. These loops determined the effectiveness of the trapping Si interstitials diffusing from the crystalline side of the original a/c interface to the epitaxially regrown region. Anomalous diffusion of boron in the crystalline Si samples was found to be a strong function of implant dose. Diffusion displacement increased and anomalous diffusion effect lasted longer with increasing implant dose. Diffusion enhancement for longer periods of time in samples with higher implant doses was related to the formation and annealing of extended defects. At very high doses , where the peak boron concentration was above the solid solubility, excess diffusion in the high boron concentration region was observed. The excess diffusion was explained in terms of segregation of boron into interstitial dislocation loops in the early stage of RTA and the subsequent annealing of these dislocation loops after the initial large anomalous tail diffusion.