Method of silicon oxynitride arc removal after gate etching

Abstract

A method is taught for removing a silicon oxynitride ARC from over a polysilicon gate after the gate is patterned. The ARC is removed by wet etching without damaging or undercutting the polysilicon gate. This is accomplished by protecting the lateral sides of a polysilicon gate with a thin silicon oxide layer prior to the performing the wet etch. The method is primarily directed towards removal of a silicon oxynitride ARC layer from the upper surface of the polysilicon gate electrode in a salicide process, although a silicon nitride layer may also be removed by the same method. The protective silicon oxide is formed by rapid thermal oxidation in O or by plasma oxidation in O and H O. After oxidation, the ARC is removed with hot H PO . The protective silicon oxide protects the lateral surfaces of the polysilicon gate from attack by the acid. Following implantation of LDD regions, a conformal sidewall layer is deposited and the sidewalls formed in the conventional manner. When oxide/nitride sidewalls are formed, the protective oxide serves as a pad layer under the nitride. The method is particularly effective in preventing stress induced cracks in a composite oxide/nitride sidewall which has a foot. Elimination of gate undercutting by gate edge protection, according to the method described, eliminates excessive sidewall thickness in the vicinity of the corner at the foot and thereby minimizes stress in this region.