APPLIED PHYSICS LETTERS 92, 223501 ͑2008͒
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D. Shahrjerdi,
D. I. Garcia-Gutierrez, E. Tutuc, and S. K. Banerjee
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Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758, USA
Advanced Technology Development Facility (ATDF-SEMATECH), Austin, Texas 78741, USA
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Received 20 January 2008; accepted 7 May 2008; published online 2 June 2008͒
In this work, we study the chemical and physical properties of the interface between Al O and
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GaAs for different surface treatments of GaAs. The interfacial layer between the high- layer and
GaAs substrate was studied using x-ray photoelectron spectroscopy ͑XPS͒ and transmission electron
microscopy ͑TEM͒. The reduction in native oxide layer was observed upon atomic layer deposition
of Al O on nontreated GaAs using trimethyl aluminum precursor. It was also observed that the
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sulfide treatment effectively mitigates the formation of the interfacial layer as compared to the
surface hydroxylation using NH OH. The electrical characteristics of GaAs capacitors further
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Recently, III-V materials have attracted substantial inter-
est as alternative channel materials to silicon for complemen-
tary metal-oxide-semiconductor ͑CMOS͒ applications at the
chemical treatment in altering the GaAs surface properties,
four different sample preparation procedures were devised. It
should be noted that all the samples underwent identical pro-
cessing steps, with the exception of the surface treatment
prior to high- deposition and postdeposition annealing
͑PDA͒ step. In addition, the results of the XPS, TEM, and
electrical measurements were obtained from the samples of
the same batch. Samples 1, 2, 3, and 4 denote nontreated,
HF-last, hydroxylated, and sulfide-treated GaAs substrates,
22 nm technology node and beyond. The poor gate oxide/
III-V interface quality, however, has long hindered fabrica-
tion of high-performance enhancement-mode ͑E-mode͒ III-V
metal-oxide-semiconductor field-effect transistors ͑MOS-
FETs͒. Hence, there has been tremendous effort to examine
the interface between III-V materials and various
dielectrics. Moreover, the studies on the thermal oxidation
of GaAs revealed that the presence of arsenic oxides, which
are intrinsically thermally unstable, could give rise to the
formation of electronic defects, thereby leading to Fermi
sulfide treatment were described elsewhere. The HF-last
sample was treated in a 1% diluted HF solution for 1–2 min,
whereas the nontreated sample underwent no chemical treat-
ment. After each surface treatment, samples were immedi-
ately transferred into a hot-wall ALD reactor, where ϳ82 Å
thick Al O was grown by alternating trimethyl aluminum
level pinning.
It is known that atomic layer deposition ͑ALD͒ offers a
precise control over the uniformity and thickness of the de-
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posited film through a self-limiting reaction. Furthermore,
͑TMA͒ and water precursors at 250 °C. Then, samples 3 and
atomic layer deposition could potentially offer the advantage
4 were annealed at 550 °C for 5 min in N ambient. Samples
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and 2, however, did not undergo PDA, due to their rela-
the precursor chemistry.
As a result, ALD could facilitate
tively poor interface properties. For the XPS samples, the
developing a simple recipe without requiring elaborate in
situ clean. Nevertheless, integrating ALD high on III-V
materials necessitates the use of an effective chemical sur-
face treatment protocol. This is to alter the III-V surface
properties in order to ensure full surface coverage from the
beginning of ALD runs, while preventing the regrowth of
native oxides during the ex situ sample transfer into the ALD
reactor. As a result, we have recently developed an effective
Al O layer was thinned down to ϳ20 Å in a dilute HF
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solution under a controlled etching condition, in order to
enhance corresponding signal/noise ratio for chemical bonds
at the Al O /GaAs interface. For the TEM studies and elec-
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trical measurements, GaAs MOS capacitors were fabricated
by TaN metal gate deposition using a dc magnetron sputter-
ing system, followed by patterning using standard photoli-
thography and reactive ion etch.
chemical surface treatment protocol which has enabled fab-
Figure 1 illustrates the As 3d and Ga 2p XPS spectra of
sample 1 before and after Al O deposition. The As 3d and
rication of inversion-type E-mode GaAs nMOSFETs with
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ALD-Al O gate dielectric. This work intends to examine
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Ga 2p spectra were fitted using Gaussian curves. In order to
obtain a valid fit for the As 3d spectra, we have considered
doublets for As bonding, where they have a peak ratio of 3:2
with a separation of ϳ0.7 eV. Moreover, all the As 3d and
Ga 2p spectra were normalized with respect to their corre-
sponding As–Ga and Ga–As bonding, respectively. A re-
markable reduction in arsenic oxides was observed upon
ALD growth of Al O using TMA, whereas the reduction in
the chemical and physical characteristics of the interface be-
tween ALD-Al O and GaAs substrates, using x-ray photo-
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electron spectroscopy ͑XPS͒ and high-resolution transmis-
sion electron microscopy ͑HRTEM͒. The correlation
between XPS and TEM results, coupled with the electrical
properties of the interface, will be further discussed.
In order to investigate the impact of chemical surface
cleaning and obtain a better understanding of the role of each
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Ga–O bonding was not significant. This facilitates the forma-
tion of high quality gate stack on GaAs by reduction in a
potentially regrown native oxide layer during the sample
a͒Electronic mail: davood@mail.utexas.edu.
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Shahrjerdi
