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Browse Prior Art Database

Selective Extrinsic Base Deposition for an NTX SIGE HBT Process

IP.com Disclosure Number: IPCOM000112364D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 86K

Publishing Venue

IBM

Related People

Comfort, JH: AUTHOR [+2]

Abstract

Disclosed is a process for obtaining a laterally self-aligned SiGe-base Heterojunction Bipolar Transistor (HBT) in the NTx transistor structure [*].

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Selective Extrinsic Base Deposition for an NTX SIGE HBT Process

      Disclosed is a process for obtaining a laterally self-aligned
SiGe-base Heterojunction Bipolar Transistor (HBT) in the NTx
transistor structure [*].

      In the NTx bipolar process, a nitride/oxide stack is used to
obtain self-alignment of the emitter opening to the extrinsic base
region.  This self-alignment is accomplished by using the
nitride/oxide stack to selectively oxidize the extrinsic base region
(60-80 nm of oxide) - the nitride layer over the emitter region
prevents its oxidation (Fig. 1a).  The stack is then used as an
implant mask for the extrinsic base region, with a sidewall sometimes
being formed on the stack to space a second, higher dose implant away
from the emitter region (Fig. 1b).  Finally, the emitter opening is
formed by stripping the nitride layer and the thin oxide (10 nm)
which is underneath (Fig. 1c).

      If this approach were used in the fabrication of a SiGe-base
HBT, selective oxidation of the extrinsic base would result in
oxidation of the SiGe base layer.  This is undesirable because SiGe
oxidation results in Ge pile-up at the interface and a high interface
state density.  In past non-NTx approaches to fabricating SiGe HBTs,
a thin Si layer (< 20 nm) is typically placed above the SiGe layer to
accommodate growth of a thin passivating oxide and arsenic
out-diffusion from the polysilicon during emitter formation.  In the
NTx process, oxidation of the SiGe layer during the selective
oxidation step could be avoided by growing a thicker layer of Si
(40-50 nm) above the SiGe base.  However, this thick Si layer would
not be oxidized away in the active device region and would,
consequently, degrade the performance of the device: the base-emitter
depletion region transit tim...