Three-dimensional memory device with charge-trapping-free gate dielectric for top select gate electrode and method of making thereof

Abstract

A portion of a charge trapping layer adjacent to a select drain gate electrode can be removed employing a differential-rate etch process that provides an accelerated etch rate to a doped portion with respect to an undoped portion. If a silicon nitride layer is employed as the charge trapping layer, then angled ion implantation of boron atoms to an upper portion of the silicon nitride layer can increase the etch rate of the boron-doped portion of the silicon nitride layer in phosphoric acid. The charge trapping layer is etched back such that a remaining portion of the charge trapping layer can be present only at levels of control gate electrodes, and absent at each level of select drain gate electrodes. Threshold voltage shift for the select drain gate electrodes can be eliminated or reduced by removal of the charge trapping layer at each level of the select drain gate electrodes.