Sealed-interface local oxidation technology

Abstract

A new regime of local oxidation, dubbed SILO for Sealed-Interface Local Oxidation, is explored. In SILO processing, a of silicon nitride is in intimate contact with the silicon surface. The ubiquitous native oxide is effectively eliminated by using nitrogen ion implantation into silicon or plasma-enhanced nitridation to form a film of approximately 100 A in thickness. The oxidation rate of both types of films is characterized and found to be nearly equivalent. A 100-A can mask the growth 0f 7000 A of oxide in wet oxygen at 950° C. With a sealed interface it is found that the usual beak formation is completely suppressed in local oxidation. An approximate theoretical analysis shows that even a very thin interfacial oxide, acting as a lateral diffusion path for the oxidant species, can lead to a significant bird's beak. With a sealed interface using a 90-A film, the thick-oxide to bare-silicon transition region is chisel shaped, with approximately 45° slopes. The transition region is even more abrupt if a conventional LPCVD nitride is deposited on the sealing before patterning. However, for total nitride thicknesses greater than about 300 A, defects are generated along the pattern edges aligned in [110] directions. Crystal damage generated during oxidation is found to be due to the intrinsic stress in the LPCVD nitride film. Argon-ion implantation into LPCVD nitride is found to be effective in reducing the defect density. A defect-free abrupt profile is produced by combining SILO with a nitride-oxide sandwich.