(183b) Interface Preparation for High Mobility Substrates

Significantly higher electron mobilities compared to silicon
make III-V compound semiconductors the materials of choice for high speed, low
power devices. The poor quality of thermal oxide layers grown on these
surfaces, however, has limited the use of III-V materials in microelectronics.
Recent advances in depositing high-k
films on silicon using atomic layer deposition (ALD) could expand the use of
III-V materials in high volume manufacturing. ALD offers precise control of
film thickness, low processing temperatures, and excellent conformality on high
aspect ratio structures. ALD relies on self-terminating chemisorption of a
reactant on a surface producing up to a monolayer coverage. Recent results show
improved gate stack quality in the absence of interfacial layers that are
formed typically by reoxidation after cleaning or by reaction during high-k deposition. Controlled removal of the native oxide
and passivation/activation of the surface prior to depositing high dielectric
constant materials are important process to develop and understand. Etching
techniques to remove native oxides on III-V compounds such as liquid phase
chemical etching, thermal desorption, and ion bombardment face issues of
partial oxide removal, roughened surfaces, and selective etching, which can
produce changes in surface stoichiometry. Gas phase processing provides an
alternative etching technology that not only addresses the issues of process
repeatability and uniformity, but also reduces environmental impact and thermal
budget by minimizing the use of ultra pure water and reducing the necessity for
recleaning. This study investigated gas phase etching of In-based III-V
materials using mixtures of anhydrous HF and water vapor at a total pressure of
100 Torr and a temperature of 29ûC. Native oxide removal and surface
termination of InAs(100) and InSb(100) using liquid and gas phase HF
chemistries were studied using x-ray photoelectron spectroscopy. Aqueous HF
etching removed the native oxides on InAs and produced elemental As, which
reoxidized when exposed to air. On InSb the native oxides were not completely
removed due to F-termination, which passivated the surface. Gas phase HF
etching of InSb native oxide completely removed Sb₂O₅
producing a stoichiometric semiconductor surface terminated by F atoms on
primarily In sur- face sites. On InAs gas phase HF completely removed As₂O₃
producing two surface stoichiometries. For the majority of HF to water molar
ratios studied, a stoichiometric bulk metal and an As-rich overlayer was
produced. For a lean HF composition, an As-rich bulk metal and In-rich
overlayer was produced. Deposition of Al₂O₃ by atomic
layer deposition (ALD) at 170°C directly onto F-terminated InSb produced a
chemically sharp Al₂O₃/InSb interface. ALD of Al₂O₃
on an In-rich overlayer on InAs resulted in an interfacial layer containing
As-oxide.