Role of rapid thermally grown sacrificial oxides in the yield improvement of SRAMs

Yield improvement of high-density SRAM devices with low V_dd has been one of the challenges confronting the wafer fabrication industry. A number of parametric and functional failure modes were observed for these devices in advanced technologies. It is argued that the combined influence of high temperature processing and mechanical stresses generated during Shallow Trench Isolation (STI) formation lead to some of these fails. It is thus critical to have good isolation patterning and trench profile, minimal thermal mismatch during oxidation and dislocation-free high-temperature annealing for good STI integrity. In this paper, the merits of Rapid Thermal Oxidation (RTO) as an effective means of reducing STI related stress and in improving yield of SRAMs by reducing soft fails has been discussed with emphasis on the sacrificial oxide grown following the stripping of pad layers.