A thin amorphous silicon buffer process for suppression of W polymetal gate depletion in PMOS

The mechanism of gate depletion in PMOS W polymetal (W/WN/sub x//poly-Si) gate was investigated. It was found for the first time that the pile-up of boron (B) occurred at the WN/sub x//poly-Si interface due to B-N formation and the B concentration in poly-Si decreased resulting in gate depletion. In order to prevent the B pile-up, we developed a new process module and succeeded in suppressing the gate depletion without B penetration into Si substrate by using a thin amorphous Si buffer (ASB) layer combined with miniaturization of poly-Si grain-size.