A Transmission Electron Microscopy Study of Process‐Induced Defects in Submicron SOI Structures

Abstract

Novel submicron silicon‐on‐insulator structures were characterized using transmission electron microscopy (TEM). The origin and interaction of defects caused by material processing in the course of fabrication of the structures were investigated and the feasibility of defect‐reduction demonstrated. Fully or partially isolated islands of substrate‐silicon were formed by selective lateral oxidation at the base of 250 nm wide structures. This process produces two adjacent, isolated levels of single‐crystal silicon that could be later processed to fabricate three‐dimensional devices and circuits. Cross‐sectional TEM specimens were prepared for characterization. The majority of the defects observed in the vicinity of partially isolated islands can be explained in terms of dislocations generated as a result of stresses induced during the postprocessing cool‐down to room temperature. These stresses arise due to differences in thermal expansion coefficients of the materials comprising the structure. The dislocations thus formed propagate into the silicon along {111} glide planes. Defect densities depend on the geometry of the structures, suggesting that the critical stress was exceeded in particular structures. Fully isolated silicon islands could be obtained virtually free of defects.