Studies on Correlation between Diluted NH₄OH Concentration of Pre-GOX Clean SC1 and GOX Breakdown Induced by Silicon Surface Oxides

Studies on effect of diluted ammonium hydroxide (NH4OH) in standard clean 1 (SC1) on failure rate of dielectric breakdown due to gate oxide (GOX) rupture of a Metal Oxide Field Effect Transistor (MOSFET) device was performed. For an experimental bath (EB) of SC1 chemistry, the bath was purposely processed until its total organic carbon (TOC) level reached 25.0 ppm while the NH4OH is at similar to 0.3%, which is about 0.1% lower compared to the clean bath (CB) with 0 ppm TOC. Using Auger surface scanning method, enhanced chemical oxides were found on pre-GOX silicon substrate surface cleaned in EB chemistry. Further studies on lower (0.2%) and higher (0.5%) NH4OH were carried out in an EB SC1. The results shown that the wafers cleaned in 0.2% NH4OH SC1 has significant trend of GOX breakdown compared to the one cleaned in 0.5% NH4OH SC1. The high failure rate of GOX breakdown can thus be attributed to deteriorated thermal GOX quality when it was grown on the silicon substrate surface with enhanced chemical oxides. These could be due to in-sufficient oxide dissolution in EB SC1 chemistry at the possibly combined effect of lower NH4OH with higher TOC concentration.