Disorder produced in SiC by ion bombardment

Abstract

We have measured the amount of residual lattice disorder produced in α-Sic after implantation of 40-keV Sb⁺ and 30-keV N⁺. The implantations were performed at 23°C and, to avoid channeling effects, at a preselected random equivalent orientation of the target with respect to the ion beam. The disorder, defined as the number of lattice atoms displaced greater than ∼0.2Å from lattice sites, was determined by backscattered energy analysis of 280-keV He⁺⁺ and 140-keV H⁺ incident along the channel and in a random direction. The amount of disorder increased linearly with dose of the heavy ion (Sb⁺) to a saturation condition, corresponding to the formation of an amorphous layer at a dose of ∼10¹⁴ Sb⁺/cm². The disorder produced by the light ion (N⁺) at first increased as the square root of N⁺ dose but at ∼10¹⁴ N⁺/cm² increased approximately linearly with dose to a saturation value at ∼10¹⁵ N⁺/cm². Similar behavior for these two ions has been observed in Si. The number of displaced atoms of Si and C produced by an Sb ion is ≈ 2400. Comparison of this result with Sb ion displacement in Si indicates a displacement energy E_d for Sic of 17- to 30-eV. A significant annealing of lightly disordered regions in the Sb⁺ and N⁺ implanted layers is observed after 500°C. More heavily damaged layers anneal at 750°C and above. Little disorder remains after a 1200°C anneal. Annealing at 1650°C or greater produces evidence of decomposition, although there are indications that the implanted species inhibits further decomposition. There is no evidence of outdiffusion of TI after 1650°C anneal and only slight evidence of outdiffusion of Sb after 1700°C anneal. Channeling analysis of Sb⁺ implants after a 1500°C anneal indicate that ∼50 percent of the Sb ions are located along the atomic rows.