Pattern formation of silicon nitride

Abstract

A plasma etch method for forming a patterned silicon nitride layer within an integrated circuit. There is first provided a substrate having formed thereover a blanket silicon nitride layer. There is then formed upon the blanket silicon nitride layer a patterned photoresist layer. Finally, there is etched through a plasma etch method while employing the patterned photoresist layer as an etch mask layer the blanket silicon nitride layer to form a patterned silicon nitride layer. The plasma etch method employs an etchant gas composition comprising a perfluorocarbon etchant gas, a hydrofluorocarbon etchant gas and an oxygen etchant gas at a perfluorocarbon etchant gas flow rate, a hydrofluorocarbon etchant gas flow rate and an oxygen etchant gas flow rate which yields substantially no plasma etch bias of the patterned silicon nitride layer with respect to the patterned photoresist layer. When the patterned silicon nitride layer is employed within a thermal oxidation mask, the blanket silicon nitride layer is only nearly completely patterned through the plasma etch method. The nearly completely patterned silicon nitride layer is then completely patterned and over-etched through a second plasma etch method, where the second plasma etch method employs a second etchant gas composition comprising a perfluorocarbon etchant gas, a hydrofluorocarbon etchant gas and an oxygen etchant gas at a perfluorocarbon etchant gas flow rate, a hydrofluorocarbon etchant gas flow rate and an oxygen etchant gas flow rate which minimizes etching of a blanket silicon oxide layer formed beneath the patterned silicon nitride layer within the thermal oxidation mask.