APPLIED PHYSICS LETTERS 92, 113506 ͑2008͒
K. H. Chung,1,2,a͒ N. Yao,1 J. Benziger,1,3 J. C. Sturm,1,2 K. K. Singh,4 D. Carlson,4 and
S. Kuppurao4
1Princeton Institute of Science and Technology of Materials (PRISM), Princeton University, Princeton,
New Jersey, 08544, USA
2Department of Electrical Engineering, Princeton University, Princeton, New Jersey, 08544, USA
3Department of Chemical Engineering, Princeton University, Princeton, New Jersey, 08544, USA
4Applied Materials, Santa Clara, California 95054-3299, USA
͑Received 13 December 2007; accepted 6 February 2008; published online 18 March 2008͒
A precursor, neopentasilane, is used to produce high-quality silicon epitaxy by chemical vapor
deposition under 700 °C with very high growth rates. Low background dopant concentration
and excellent crystal quality were determined from secondary-ion-mass spectroscopy and cross
sectional transmission electron microscopy. Growth rates as high as 130 nm/min at 600 °C have
been achieved. Growth rates in nitrogen and hydrogen ambients are about equal for neopentasilane,
unlike those for growth with low-order silanes. A concerted reaction, where an open site is generated
at the same time the adatom is adsorbed, is proposed as a possible mechanism for both the high
growth rate with neopentasilane as well as the similar rate with hydrogen and nitrogen carriers.
For silicon epitaxial growth, temperatures under 700 °C
are required for the integration of front-end processes in
very-large-scale integration structures, such as raised
monly used chemical vapor deposition ͑CVD͒ approach,
such low temperatures lead to a large reduction of epitaxial
growth rate. This is significant because high growth rates are
desired for throughput in modern single-wafer processing
tools.
with a hydrogen carrier was used to introduce the NPS to the
chamber.
The neopentasilane partial pressure is not known abso-
lutely. Assuming the hydrogen leaving the bubbler is com-
pletely saturated with NPS ͑bubbler temperature is 35 °C,
vapor pressure is 30 torr͒, then the estimated upper limit of
the vapor pressure in the reactor of NPS is 20 mtorr ͑solid
squares͒. We suspect that the actual partial pressure is up to a
factor of 10 lower than this. The epitaxial growth rates were
measured by step height measurements on patterned oxide
samples. Epitaxial rates were 215, 130, and 54 nm/min at
700, 650, and 600 °C, respectively ͑solid squares, Fig. 1͒.
The growth rate increases linearly with partial pressure
at 600 °C ͑Fig. 2͒. We have yet to observe any saturation of
the growth rate with NPS partial pressures. Classically, the
growth rate at high partial pressures saturates because growth
becomes limited by desorption of hydrogen.5 At a high par-
In this work, we report very high growth rates of high-
quality epitaxial silicon grown by CVD from 600 to 700 °C.
The work was enabled by a silicon precursor, neopentasilane
͑Si5H12͒. Growth was performed on ͑100͒ oriented silicon
wafers. It has been observed that an increased number of
silicon atoms in hydride precursors ͓i.e., switching from sil-
iane ͑SiH4͒ to disilane ͑Si2H6͒, to trisilane, Si3H8͔ leads to
increased epitaxy growth rates at the same temperature
and thus enables lower growth temperatures. For example,
Fig. 1 compares growth rates using dichlorosilane ͑partial
pressure=52 mtorr͒, silane ͑partial pressure=20 mtorr͒, disi-
lane ͑partial pressure=10 mtorr͒, and neopentasilane ͑upper
limit to partial pressure of 20 mtorr͒, with a 6 torr hydrogen
carrier pressure observed in our laboratory At 600 °C,
dichlorosilane growth rates were negligible, the silane
growth rate was 0.6 nm/min, and the disilane growth rate
was 8 nm/min.
In this work, we explored the use of neopentasilane
͑Si5H12͒ in our homemade CVD reactor.3 Prior to loading
into the reactor, the wafers were cleaned using a chemical
mixture of sulfuric acid and hydrogen peroxide, followed by
a 2 min, dilute HF dip.4 The chamber pressure for all experi-
ments was set at 6 torr, with a hydrogen carrier flow of
3 SLPM ͑SLPM denotes standard liters per minute͒. Neo-
pentasilane ͑NPS͒ is a liquid at room temperature: a bubbler
FIG. 1. Comparison of low-pressure CVD epitaxial growth rates vs inverse
temperature for sources of dichlorosilane, silane, dislane, and neopentasilane
͑NPS͒ precursor on ͑100͒ silicon substrates. In all cases, the carrier was
hydrogen at a pressure of 6 torr. The dichlorosilane, silane, disilane, and
NPS partial pressures were 52, 20, 10, and 20 mtorr, respectively. The open
squares are NPS with a partial pressure of 65 mtorr. Estimated temperature
error is Ϯ1% and growth rate error is Ϯ10%.
a͒
Electronic mail: kchung@princeton.edu.
0003-6951/2008/92͑11͒/113506/3/$23.00 92, 113506-1 © 2008 American Institute of Physics
137.189.170.231 On: Fri, 19 Dec 2014 07:35:00