MECHANISMS OF AMORPHIZATION IN ION-IMPLANTED CRYSTALLINE SILICON

The process of ion beam amorphization of crystalline silicon is reviewed in order to elucidate the underlying mechanisms. The role of dopants on this process is also explored studying amorphization of undoped and highly doped crystalline Si in the temperature range 77-423 K and by using Ge ion irradiation at an energy of 400 keV or 1 MeV. At each temperature the amorphous fraction increases more than linearly with the fluence and, at temperatures higher than 300 K, is strongly dependent on dopants. In particular amorphization is retarded by B and enhanced by As doping at concentrations of approximately 10(20)/cm3. These processes are shown to mirror closely ion beam induced amorphization of pre-existing amorphous clusters. The amorphization is modelled in terms of three dimensional nucleation and growth of amorphous Si clusters under ion irradiation. The defects which are not quenched into amorphous regions during the early stages following the collision cascade are long living and interact with the existing amorphous islands inducing their growth. In the presence of B the amorphization rate is reduced while the nucleation rate is unaffected. The As effect is discussed in terms of its strong interaction with point defects.