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Post Emitter Polysilicon Trench Isolation

IP.com Disclosure Number: IPCOM000049706D
Original Publication Date: 1982-Jul-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Antipov, I: AUTHOR [+2]

Abstract

Device isolation by means of refilled deep trenches is I will known in LSI (large-scale integration). The filling material is either an oxide or an oxide nitride polysilicon combination in which the polysilicon is either undoped and isolated, or doped and in contact with the substrate at the bottom of trenches. In general, the oxide nitride polysilicon filled trenches are produced at early processing stages and therefore undergo all heat cycles of subsequent process steps. The application of high temperature heat cycles to deep trenches may, however, cause the generation of defects, leading to an increase of junction leakage currents. Therefore, moving the formation of deep trenches to later processing stages and, in particular, to post emitter formation is advantageous.

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Post Emitter Polysilicon Trench Isolation

Device isolation by means of refilled deep trenches is

I will known in LSI (large-scale integration). The filling material is either an oxide or an oxide nitride polysilicon combination in which the polysilicon is either undoped and isolated, or doped and in contact with the substrate at the bottom of trenches.

In general, the oxide nitride polysilicon filled trenches are produced at early processing stages and therefore undergo all heat cycles of subsequent process steps. The application of high temperature heat cycles to deep trenches may, however, cause the generation of defects, leading to an increase of junction leakage currents. Therefore, moving the formation of deep trenches to later processing stages and, in particular, to post emitter formation is advantageous. A preferred way of producing oxide-nitride polysilicon filled trenches after formation of the emitter is described below.

Most of the process steps through emitter doping (diffusion or ion implantation/anneal) are conventional, and not relevant to the formation of the trench isolation. An exception may be the subcollector which can be formed by a blanket diffusion if the polysilicon trench refill comes into contact with the substrate. The starting structure before the trench formation is shown in Fig. 1. It is obtained with the following conventional process steps: subcollector diffusion/oxidation, epi layer deposition/oxidation, reach-through diffusion/oxidation, and base diffusion 1/oxidation followed by deposition of Si(3)N(4) layer 2, definition of all contacts 3 in Si(3)N(4) and underlying oxide, forming screen oxide 4 and ion implantation/anneal of emitter 5.

Formation of post emitter trenches starts with a deposition of thin S...