Patent ID: 6225158
Filing Date: 2001-05-01
Classification: H01L

Abstract:
A method of forming a dynamic random access memory cell, said cell having a vertical transfer device, said method comprising the steps of:forming a plurality of oxide filled trenches in a silicon substrate;etching a multiplicity of deep trenches, said deep trenches being deeper than said oxide filled trenches;selectively coating a lower portion of sidewalls of said deep trenches with a glass containing a dopant and driving said dopant into said substrate at said lower portion;removing said glass;forming a node dielectric;filling said deep trenches with a first polysilicon deposit and recessing said first polysilicon deposit below an upper surface of said silicon substrate;depositing a collar oxide in said recesses and directionally etching to form a collar around a periphery of said deep trenches;refilling said deep trenches with a second polysilicon deposit at least to a top of said collar oxide;recessing said collar and node dielectric;performing a third fill and recess of a third polysilicon deposit in said deep trenches to just above said collar oxide;forming a gate oxide along exposed sidewalls in said deep trenches; positioning only within said deep trenches a gate polysilicon;implanting bit line diffusion into said substrate surface between said deep trenches;depositing an insulating material;etching said insulating material to form a multiplicity of word line trenches in said insulating material;filling said word line trenches with a conductive metal to form word lines in said word line trenches which contact a planarized surface of said gate polysilicon; andforming a bit line contact to said bit line diffusion and depositing conductive bitlines.