Browse Prior Art Database

Process for Fabricating Polysilicon and Single-Crystal Emitter Bipolar Transistors

IP.com Disclosure Number: IPCOM000108901D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 1 page(s) / 43K

Publishing Venue

IBM

Related People

Crabbe, EF: AUTHOR [+3]

Abstract

Disclosed is a process for reducing lateral oxide etching prior to emitter polysilicon deposition or single-crystal emitter formation, thus greatly reducing small-emitter effects.

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Process for Fabricating Polysilicon and Single-Crystal Emitter Bipolar Transistors

      Disclosed is a process for reducing lateral oxide etching prior
to emitter polysilicon deposition or single-crystal emitter
formation, thus greatly reducing small-emitter effects.

      Prior to polysilicon deposition for emitter formation of
bipolar devices, the wafers typically receive a dilute HF dip to
remove the native oxide film present on the Si surface.  This HF dip
causes lateral undercut of the oxide creating a "worm hole".  This
"worm hole" fills with small-grain polysilicon which, after implant
and anneal, is not as heavily doped as the bulk of the polysilicon.
This leads to small-emitter effects, nominally enhanced effective
recombination velocity at the emitter perimeter and a non-uniform
doping front in the substrate.  Furthermore, these "worm holes"
result in higher reverse emitter-base perimeter leakage and degrade
the reliability of the device.

      The invention disclosed here uses NH4F to remove native oxide
and provide a bare silicon surface prior to emitter formation without
etching oxide and creating a perimeter "worm-hole".  One simply
replaces the dilute HF dip immediately prior to polysilicon
deposition with a NH4F ammonium fluoride dip.  Etch rates of thermal
oxides are on the order of 0.1 nm/min in a 40% NH4F solution compared
to 40nm/min in 10:1 DHF.  Residues observed on Si and SiO2 surfaces
following NH4F exposure have been found to be...