Title page for ETD etd-03312004-172745

Type of Document

Dissertation

Author

Kang, Inkuk ,

Author's Email Address

inkuk.kang@spansion.com

URN

etd-03312004-172745

Title

Formation of N+P Junctions Using In-situ Phosphorus Doped Selective Si1-xGex Alloys for CMOS Technology Nodes Beyond 50nm.

Degree

PhD

Graduate Program

Electrical Engineering

Advisory Committee

Advisor Name	Title
Mehmet C, Ozturk	Committee Chair

Keywords

BTBT Tunneling
gated diode
Raised source and drain
SiGe
In-situ phosporus doping
Selective Epitaxial growth

Date of Defense

2004-03-31

Availability

unrestricted

Abstract

As CMOS integrated circuits are scaled beyond the 50nm regime, conventional
source/drain junction and contact technologies can no longer satisfy the requirements of
MOSFETs, which require super-abrupt doping profiles and extremely low contact
resistivities. To address these challenges, selective Si1-xGex source/drain technology was
proposed by this laboratory. In this approach, in-situ doped Si1-xGex layers are selectively
deposited in recessed source/drain regions. Since the dopants occupy substitutional sites
during epitaxial growth, high temperature annealing is not required for dopant activation,
which eliminates diffusion and provides abrupt doping profiles. Furthermore, smaller
bandgap of Si1-xGex reduces the metal-semiconductor barrier height, an essential
requirement for achieving a substantial reduction in contact resistivity.
This thesis focuses on selective rapid thermal chemical vapor deposition of in-situ
phosphorus doped Si1-xGex alloys intended for this application. Experiments were carried
out to study electrical properties of the in-situ doped layers with emphasis on maximizing
the active carrier concentration. Active phosphorus levels in the range of 2 ? 5 x 1020 cm-3
were obtained.
The deposited layers were used to fabricate pn junctions with excellent reverse
leakage characteristics. Junctions fabricated on lightly doped substrates exhibited behavior
equivalent to best junctions in spite of the lattice mismatch between the Si substrate and the
phosphorus doped Si1-xGex. Junctions fabricated on heavily doped substrates suffered from
band to band tunneling, which is expected regardless of the junction formation technique.
Deposition selectivity of the process was studied and determined that high flows of
PH3 could degrade the selectivity. An alternative deposition process based on alternating
periods of deposition and etching was developed, which provided substantial improvements
in deposition selectivity.

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