High density trench isolation for MOS circuits
AssigneeNorth American Philips Corporation, Signetics Division
InventorsWayne I. Kinney, John P. Niemi, Jonathan E. Macro, David Back
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Abstract
A method of forming isolation trenches in CMOS integrated circuits is disclosed. The trench side walls are covered by a thin oxide layer, and the trenches are filled with a highly doped polysilicon. The doped polysilicon has a high work function which prevents oxide charges from inverting the trench side walls and thereby turns off the parasitic transistors at these side walls to reduce latchup.
Claims4
A method of forming isolating trenches in dual-well integrated circuits formed on an n-type silicon substrate, comprising:
- forming a first isolating trench in said substrate, said first trench having a first preselected depth;
- oxidizing the side walls of said first trench;
- filling said first trench with an n+ polysilicon material having a work function sufficient to prevent electrical conduction at the trench side walls;
- forming n-well and p-well regions in said substrate on opposite sides of said first trench, said well regions having depths in said substrate less than the depth of said first trench;
- forming a second isolating trench in said p-well region closely adjacent to said first trench, said second trench having a second preselected depth less than the depth of said p-well region;
- and
- filling said second trench with a p+ polysilicon material.
A method of forming isolating trenches in dual-well integrated circuits formed on a silicon substrate which is moderately of a first conductivity-type, comprising:
- forming a first isolating trench in said substrate;
- oxidizing the side walls of said first trench;
- filling said first trench with a polysilicon material which is strongly of said first conductivity type and having a work function sufficient to prevent electrical conduction at the trench side walls;
- forming in said substrate a first well region on one side of said first trench and a second well region on the opposite side of said first trench, said first well region being of said first conductivity-type and said second well region being of a second conductivity-type the opposite of said first conductivity-type;
- forming a second isolating trench in said second well region closely adjacent to said first trench;
- and
- filling said second trench with a polysilicon material which is strongly of said second conductivity-type.
Dependencies are inferred from the claim text.