Reactive Ion Etching of SOI (SIMOX and ZMR) Silicon in Nitrogen Containing CF₄+ O₂ and SF₆+ O₂ Plasmas

The effects of N₂ addition on the etch rate of bulk-silicon and silicon-on-insulator (SOI) separation by implantation of oxygen (SIMOX) and zone melting recrystallization (ZMR) samples using CF₄+ O₂ and SF₆+ O₂ plasmas; as well as the damage assessment of the SF₆+ O₂ plasma are reported. In SF₆+ O₂ plasma, the N₂ additive reduces the etch rate of the masking oxide [chemical vapor deposited (CVD)] while significantly increasing the silicon etch rate and, thus, increasing the selectivity by 44–64 %. In CF₄+ O₂ plasma, the silicon etch rate is increased due to the N₂ addition. However, the increase in selectivity is about 16-45%. The etch rate of SOI silicon especially in SF₆+ O₂ plasma is higher than that of bulk-silicon samples. The higher etch rate of SOI samples appears related to the higher defect density of the SOI silicon. The damage assessment studied through Schottky diode and metal oxide semiconductor (MOS) capacitor samples indicates that SF₆+ O₂ plasma with N₂ additive introduces less damage as compared to without N₂ additive. Furthermore, postmetal annealing at 250°C for 15 min in N₂+ H₂ ambient improves the characteristics of both Schottky diode and MOS capacitor devices. Thus the addition of N₂ improves the etch rate, and selectivity in some cases, and at the same time decreases the damage.