The effect of HF processing on gate oxide degradation in aggressive poly buffered LOCOS isolation

We have investigated gate oxide degradation in metal-oxide semiconductor (MOS) devices associated with aggressive Poly Buffered Locos (PBL) isolation. Defects in the gate oxide resulting in severe degradation of charge-to-breakdown (Q/sub bd/) occurring at the interface between field oxide and active silicon have been shown to be a result of local Si surface roughness. Capacitor I-V data was used to quantify the Si roughness. It is shown that NH/sub 4/F-H/sub 2/O-HF (BOE) etchback chemistry provides significant improvement in gate oxide Q/sub bd/ for capacitors fabricated using PBL isolation. This Q/sub bd/ improvement is correlated to a decrease in Si roughness at the active silicon edge.