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Browse Prior Art Database

PNP Superlattice 1/N Memory Cell

IP.com Disclosure Number: IPCOM000109519D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 3 page(s) / 156K

Publishing Venue

IBM

Related People

Harame, DL: AUTHOR [+3]

Abstract

A vertical PNP is fabricated with a single crystal emitter consisting of the emitter portion and a memory cell superlattice portion. The memory cell portion is etched, passivated, and filled to form a stacked plate capacitor over the active emitter. Multiple emitters are made in the same isolation well. The memory cell circuit is identical to the 1/N cell (1).

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PNP Superlattice 1/N Memory Cell

       A vertical PNP is fabricated with a single crystal
emitter consisting of the emitter portion and a memory cell
superlattice portion.  The memory cell portion is etched, passivated,
and filled to form a stacked plate capacitor over the active emitter.
Multiple emitters are made in the same isolation well.  The memory
cell circuit is identical to the 1/N cell (1).

      Bipolar memory cells have not been envisioned as high density
alternatives to the MOS counterparts partly because of device and
circuit limitations.  Previously a version of the 1/N cell was
proposed which used a capacitor between the emitter and wordline but
the stacked capacitor was low in capacitance and this limited the
usefulness.  It has been found that UHV/CVD can be used to fabricate
high density large capacitance structures and also high performance
single crystal emitter PNP transistors (2).  The present stacked
capacitor is thus formed by first depositing a doped superlattice
consisting of alternating intrinsic and heavily boron doped layers,
then RIE etching a center hole through these layers, using KOH to
laterally etch intrinsic silicon, forming insulating thin
dielectrics; and redepositing heavily boron doped silicon again with
UHV/CVD.  The resulting arrangement combines the single crystal
emitter and stacked capacitor in a novel structure.

      The fabrication process is illustrated in Figs. 1-4.  Fig. 1
shows the starting point of...