Method of making a three-dimensional memory device using silicon nitride etching end point detection

Abstract

A method of making three-dimensional memory device includes forming a stack of insulating layers and silicon nitride sacrificial layers over a substrate, forming memory stack structures in the alternating stack, forming a trench through the alternating stack, selectively etching the silicon nitride sacrificial layers through the trench using a phosphoric acid solution, filling a sample container with a fixed quantity of the phosphoric acid solution that was used to etch the silicon nitride sacrificial layers, determining a weight of the sample container, determining if a threshold value indicative of the etching end point has been reached or exceeded based on the determined weight, stopping the etching of the silicon nitride sacrificial layers in response to determining that the threshold value indicative of the etching end point has been reached or exceeded to leave recesses between the insulating layers, and filling the recesses with electrically conductive layers.