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Prevention of Boron Penetration in a Passivated P+ Polysilicon Gated Mosfet Structure

IP.com Disclosure Number: IPCOM000120761D
Original Publication Date: 1991-Jun-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 47K

Publishing Venue

IBM

Related People

Sun, YC: AUTHOR [+3]

Abstract

Disclosed in this article is a method to avoid boron penetration from P+ polysilicon through thin oxide in polysilicon/oxide/silicon MOSFET structures passivated by LPCVD insulators.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 70% of the total text.

Prevention of Boron Penetration in a Passivated P+ Polysilicon Gated
Mosfet Structure

      Disclosed in this article is a method to avoid boron
penetration from P+ polysilicon through thin oxide in
polysilicon/oxide/silicon MOSFET structures passivated by LPCVD
insulators.

      Boron diffusion in oxide is enhanced by orders of magnitude in
the presence of hydrogen or water.  The deposition of PSG or BPSG for
passivation/gettering/reflow purposes by LPCVD or PECVD methods at
around 400oC can incorporate hydrogen byproduct in the glass as well
as in the oxide between boron doped polysilicon gate electrode and
the silicon substrate.  The incorporated hydrogen can enhance boron
diffusion in the gate oxide during subsequent annealing (>800oC) of
the passivation oxide (glass) -*-. Once boron has penetrated the thin
oxide into the silicon substrate, the MOSFET threshold voltage will
shift positively which renders the device inoperative.

      The proposed technique calls for a medium temperature anneal
after the LPCVD of passivation oxide to evolve hydrogen from the
structure.  The idea is based on the fact that hydrogen diffuses
faster in the oxide than boron does, even though the diffusivity of
boron is enhanced in the presence of hydrogen.  The temperature for
the hydrogen evolution step can be chosen to minimize the annealing
time with little boron diffusion, e.g., 600oC.

      In the case of nitride capping of p+-poly MOS structures,
windows may have...