METHOD FOR ETCHING SINGLE-CRYSTAL SEMICONDUCTOR SELECTIVE TO AMORPHOUS/POLYCRYSTALLINE SEMICONDUCTOR AND STRUCTURE FORMED BY SAME

A method of forming a vertical DRAM device. A lower trench is filled with polycrystalline or amorphous semiconductor for a capacitor. An upper trench portion has exposed sidewalls of single-crystal semiconductor. The method then includes etching the single-crystal semiconductor sidewalls to widen the of the upper trench portion beyond the exposed upper surface of the semiconductor fill of the capacitor to form exposed regions of single-crystal semiconductor on a bottom portion of the upper trench adjacent to the exposed upper surface of the semiconductor fill. A trench top insulating layer is deposited on the bottom portion of the upper trench, over the upper surface of the semiconductor fill and over the adjacent regions of single-crystal semiconductor. The method then includes forming a vertical gate dielectric layer, wherein the trench top insulating layer extends below the vertical gate insulating layer.