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Substrate Contact with Closed Bottom Trenches

IP.com Disclosure Number: IPCOM000119755D
Original Publication Date: 1991-Feb-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 53K

Publishing Venue

IBM

Related People

Hsieh, CM: AUTHOR [+2]

Abstract

A process to open a substrate contact that is compatible with standard deep trench isolation has been developed. The method takes advantage of the high conformality of polysilicon and the anisotropic nature of the reactive ion etch (RIE) of polysilicon. This is similar in concept to the sidewall process applied in the emitter-base self-aligned transistors.

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Substrate Contact with Closed Bottom Trenches

      A process to open a substrate contact that is compatible with
standard deep trench isolation has been developed.  The method takes
advantage of the high conformality of polysilicon and the anisotropic
nature of the reactive ion etch (RIE) of polysilicon.  This is
similar in concept to the sidewall process applied in the
emitter-base self-aligned transistors.

      The technique involves etching deep trenches of two distinct
widths; one narrow and the other roughly five times wider.  The
narrow trench is used as isolation between active device areas.  The
wider trench will eventually serve as the substrate contact.  After
etching the trench and forming a thin insulating sidewall, a layer of
poly is deposited.  Due to the conformal nature of the deposition,
the trenches will fill from the sides as well as from the bottom.
The thickness of the deposition is roughly one and a half times the
width of the narrow trench to ensure it has been completely filled.
The wide trench fills partially because it is about five times the
width of the narrow trench.

      The excess polysilicon is etched back to the surface using an
anisotropic RIE.  This removes the poly from the bottom of the wide
trench.  With the polysilicon as sidewall, the bottom of the wide
trench is now about two times the width of the narrow trench.  The
thin dielectrics are then removed to open a contact to the substrate.
A second poly layer i...