Low temperature floating plasma oxidation of poly-SiGe

Low temperature oxidation is an essential process for thin-film transistors (TFT) used in active-matrix liquid crystal displays (AMLCD). However, low temperature oxidation gives rise to defects at SiO₂/poly-SiGe interfaces. We have recently developed a novel plasma oxidation method for poly-SiGe materials. The poly-SiGe wafers are soaked in 0.1 Torr pure oxygen RF (Radio Frequency) plasma and isolated. That is, the sample voltage is the same as the sheath potential of the floating wall, which is always negative since electrons move faster than ions. The defects caused by ion impact can therefore be reduced. No heating is applied during oxidation, as the sample is heated slightly by the plasma. Under our conditions, the temperature is below 100 °C even after oxidation for two hours. Depth profiles are acquired by AES and the oxide/substrate interface is examined by XPS. NMOS devices fabricated using this gate oxide show good characteristics.