Atomistic Modeling of Amorphization in Si

The dimensional and electrical features of current Si devices require high dose and very low energy implants, which cause amorphization in the regions of high dopant concentration. The simulation of dopant diffusion and damage evolution is frequently done using the "+1" model, but this approximation is not valid when a large fraction of the implanted ions are within the amorphous region. Monte Carlo and molecular dynamics simulations have been used to study the amorphization and recrystallization processes and the interaction between dopants and defects for amorphizing implants. Molecular dynamics simulations are used to examine the extent of ion-induced amorphization and the mobility and recombination of defects, together with the recrystallization of amorphous pockets. For the Monte Carlo approach, we have modified the code DADOS in order to include the formation of amorphous regions, which allows accurate simulations of high implant doses. Amorphous regions are simulated as aggregates of point defects, with Frankel-pair recombination rates reduced in regions of high point defect density. For the low implant temperatures, the damage is accumulated, with little diffusion of defects and dopants during the implant. When the dose exceeds the amorphization threshold and the amorphous layer extends to the surface, the transient diffusion of the dopant atoms is reduced. Most of the "+1" interstitials in the amorphous layer are displaced to the free surface as this layer is recrystallized, and hence rendered ineffective for transient diffusion. Using this model, we discuss dopant diffusion accompanying amorphizing implants for a range of conditions. Good agreement with experiments is obtained.