ABSTRACT
The aggressive scaling of silicon-based high-performance integrated circuits [1] has led to device
dimensions and junction depths that require ultralow thermal processing budgets. For example, state-
of-the-art CMOS gate lengths have shrunk below 100 nm over the past few decades. The current
International Technology Roadmap for Semiconductors (ITRS) projects physical gate lengths in micro-
processors and ASICs of 40 nm in the near future and 10 nm beyond 2015. Without considering
suppression and enhancement effects, such as substitutional carbon or transients, the classical dopant
diffusion alone (e.g., boron: D0 0.67 cm2/sec, EA 3.46 eV [2]) exhibits comparable 2 ffiffiffiffiffi
Dt p
values at
9008C for minute-scale durations. Growth techniques that employ low temperatures (7008C) for homo-and hetero-epitaxy are necessary to maintain abrupt doping profiles and prevent, nearly
eliminate, dopant and alloy diffusion, especially in high-performance BiCMOS integration schemes.
In particular, pseudomorphically grown silicon-germanium has emerged as an important alloy due to
its bandgap properties and strain-induced effects on carrier mobility [3]. Among others, substrate-
compliant epitaxial SiGe is utilized in the fabrication of heterojunction diodes [4], resonant tunneling
diodes [5], heterojunction bipolar transistors [6], modulation-doped field-effect transistors [7],
MOS field-effect transistors [8], and photodetectors [9]. Today, the most commonly employed low-
temperature epitaxial deposition methods are molecular beam epitaxy (MBE) [10], gas-source MBE
(GSMBE) [11], and chemical vapor deposition (CVD) [12]. The deposition using chemical vapors is
practical in a commercial manufacturing environment because it offers high wafer-throughputs by batch
processing, outstanding film uniformities, excellent control over alloy composition and dopant concen-
tration, and selective epitaxial growth. However, chemical vapor deposition at atmospheric pressures
and in low vacuum was traditionally restricted to high substrate temperatures. Although improvements
in gas purity, chamber cleanliness and design, precursor chemistry, and interface cleanliness soon
enabled further temperature reductions, only a concurrent and significant reduction in deposition
pressure provided the key to defect-free low-temperature epitaxy and manufacturing-friendly batch
processing of silicon and silicon-germanium [13, 14].
