DRAM CELL HAVING SEMICONDUCTOR SUBSTRATE AND TRENCH

摘要

PROBLEM TO BE SOLVED: To block diffusion of oxygen into an oxide collar by arranging a barrier means for blocking diffusion of oxygen from the surface of a substrate into an isolation collar in a trench and on the isolation collar. SOLUTION: An oxide collar 32 forms a barrier between the single crystal substrate 30 and the polysilicon trench fill 35 of a DRAM in order to block diffusion of a dopant from a deep trench into the substrate material. A shallow trench deep in the vertical direction is made by performing a recess etching process on the oxide collar 32. A low pressure CVD nitride 40 is then deposited on the upper surface of the oxide collar 32 and on the entire surface of the single crystal substrate 30 and the polysilicon trench fill 35 thus filling the shallow trench fully. Finally, the low pressure CVD nitride 40 is removed by isotropic etching.