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Method to Dope Lower Portions of Sidewalls of Trenches in Silicon

IP.com Disclosure Number: IPCOM000119803D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Bracchita, JA: AUTHOR [+2]

Abstract

By using a removable material as a temporary partial trench fill and forming a protective collar at the top, the lower portion of the trench may be selectively doped after removing the trench fill material. This technique is useful for control of certain types of leakage and other purposes, e.g., doping tailoring in channels of trench sidewall vertical field-effect transistors.

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Method to Dope Lower Portions of Sidewalls of Trenches in Silicon

      By using a removable material as a temporary partial
trench fill and forming a protective collar at the top, the lower
portion of the trench may be selectively doped after removing the
trench fill material.  This technique is useful for control of
certain types of leakage and other purposes, e.g., doping tailoring
in channels of trench sidewall vertical field-effect transistors.

      Referring to Fig. 1, a trench is defined and etched through
oxide 10 and into silicon substrate 12 by a standard process.  A
selectively removeable material 14, e.g., parylene, is deposited
conformally to completely fill the trench and etched back to a level,
as shown.

      Referring to Fig. 2, protective sidewall coating 16 is formed
by conformal deposition of a material, e.g., silicon dioxide, and
anisotropic etching to leave only coating 16 as shown.  Material 14
shown in Fig. 1 is then selectively removed by an isotropic etching
process.  Diffusion of a dopant, e.g., boron, is used to form doped
region 18.

      Coating 16 may be removed to result in the cross section shown
in Fig. 3 wherein diffusion 18 is formed below a controlled depth in
the lower portion of a trench wall.