Process flow for two-step collar in dram preparation

Abstract

In a method of forming a DRAM cell in a semiconductor substrate, the improvement of maintaining a substantially full trench opening during trench processing comprising: a) forming a pad nitride on the surface of the substrate and reactive ion etching (RIE) a trench vertically to a first depth; b) depositing a nitride layer in the trench; c) filling the trench with a poly silicon fill; d) recess etching the fill to the collar depth; e) oxidizing to transform the exposed nitride layer into a nitrided oxide collar or depositing an oxide on the layer of nitride; f) reactive ion etching to open the bottom oxide; g) stripping the poly fill trench, and performing a nitride etch selective to oxide; h) expanding the trench horizontally by etching lower trench sidewalls and bottom while masking the upper sidewalls; i) forming a buried plate at the bottom of the trench sidewalls; j) forming the node dielectric in the deep trench to grow a collar oxide that consists of a nitrided oxide and a layer of node nitride; k) filling the trench with a poly fill; l) recess etching the poly fill approximately to the collar bottom; m) depositing a collar oxide; n) reactive ion etching to open the bottom; o) filling the trench with a poly fill; and p) chemically mechanically polishing the semiconductor substrate.