Improvement of oxide quality by rapid thermal annealing

Rapid thermal processing as a post-oxidation annealing (POA) process is of considerable influence on the quality of thin thermal oxides: The number of defect-related oxide failures is reduced, together with a slight reduction of the intrinsic oxide quality, but to a degree that is of no importance as regards reliability aspects. According to our investigations, it is important that POA is performed after poly-Si deposition and doping, whereas POA after poly-Si patterning is found to be an undesirable process. Infrared spectroscopy indicates stress relaxation caused by the POA treatment, but no change of the SiO2/Si-interface roughness could be observed by high-resolution electron microscopy. This relaxation process was accompanied by the creation of electron traps. Constant-current investigations indicated an enhanced electron trapping in the oxides after POA. This electron trapping increased with increasing POA temperature. The reduced defect-related oxide failures after POA are attributed to a retarded runaway of the injection current by negative space charges.