Drastic improvements of gate oxide reliability by argon annealing compared with hydrogen annealing

Ar annealing considerably improves the gate oxide reliability of Czockralski (CZ) grown silicon wafers as well as H-2 annealing. For both argon and hydrogen annealing at 1200 degrees C for 1 h, the yield of the intrinsic breakdown is drastically improved to a level higher than 90% from the initial value of about 30%. This is established by a significant reduction of near-surface defects. Ar annealing, similar to H-2 annealing, drastically reduces the near-surface defects, such as oxygen precipitates and grown-in defects (laser scattering tomography defects and crystal-originated particles). However, even a small quantity of O-2 gas engulfed in the ambient gas suppresses these reductions due to the restraint in oxygen out-diffusion. Consequently, O-2 annealing improves the gate oxide reliability insufficiently. The roughnesses of the wafer surface after Ar and H-2 annealings are almost comparable. To reduce the near-surface defects and improve the gate oxide reliability of CZ silicon wafers, it is essential to avoid the engulfment of O-2 into the ambient gas during annealing.