Nitride cap formation in a dram trench capacitor

Abstract

A method for forming an oxygen-impervious barrier on the oxide collar of a trench capacitor in a DRAM cell. The process consists of etching a shallow trench into the oxide collar which surrounds the polysilicon trench fill and isolating it from the single crystal semiconducting substrate material of the DRAM cell to a depth which is at least equal to or larger than the width of the oxide collar. A nitride layer with a thickness equal to or thicker than half of the width of the oxide collar is then deposited on the top surface of the freshly excavated oxide collar such that the aforementioned trench is completely filled with this nitride layer, and the entire surfaces of the substrate and polysilicon trench fill are completely covered. The newly formed nitride layer is then selectively overetched in order to completely remove it from the substrate and polysilicon trench fill surfaces, while still maintaining a sufficient thickness of this layer disposed on the oxide collar sufficient to prevent oxygen diffusion into the oxide collar. Alternatively, the nitride layer may be deposited as a thin layer sandwiched between the original oxide collar and an additional thermally deposited oxide layer.