Fill and etchback process using dual photoresist sacrificial layer and two-step etching process for planarizing oxide-filled shallow trench structure

摘要

To planarize an oxide-filled shallow trench-isolated semiconductor architecture, a composite photoresist sacrificial layer is initially formed on the oxide-filled structure. The composite photoresist layer contains photoresist plugs which are reflowed to fill depressions in the oxide fill layer overlying the trench, and an overlying photoresist layer which effectively planarizes the depression-filled trench oxide layer. Respective photoresist and oxide selective etching chemistries are then successively applied to first etch the composite sacrificial photoresist layer and then etch the trench fill oxide layer down to the surface of an etch stop polysilicon layer. Since the thickness of the polysilicon etch stop layer is initially formed so as to extend above the mesa layer of the trench-isolated semiconductor structure by a relatively nominal height, after planarization, the top surface of the trench fill oxide layer still extends above the surface of the mesa to prevent shorting of a subsequently formed polysilicon gate layer with underlying mesa material, while being sufficiently low enough to avoid sidewall stringer formation.