Effect of interfacial and bulk organic contamination on the quality of thin silicon oxide

The effect of organic contamination of silicon (HF-last cleaned) and silicon dioxide (as-received) wafer surfaces on the quality of gate oxide was studied. Controlled contamination by model organics as well as cleanroom contamination conditions were investigated. Wafers were oxidized under oxidizing or inert ramp-up ambient to grow ultrathin thermal oxides (30 A). Surface and electrical characterization of the oxides was done by Auger sputter profiling, tunneling atomic force microscopy (TAFM) and gate oxide integrity (GOI) measurements. For oxides grown in an inert ambient during ramp-up, HF-last cleaned wafers had a large number of carbon-based defects as compared to as-received wafers. Oxygen in the ramp-up ambient oxidized and volatilized organics resulting in good quality thin gate oxides for HF-last cleaned wafers. However, for as-received wafers, the defect density was increased in an oxidizing ramp-up ambient. A probable mechanism for degradation of the gate oxide quality on HF-last wafers in an inert ramp-up ambient is investigated.