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(bd)) occuring 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 NH4F:H2O:HF (BOE) etchback chemistry provides significant improvement in gate oxide Q(bd) for capacitors fabricated using PBL isolation, This Q(bd) improvement is correlated to a decrease in Si roughness at the active silicon edge.