Tomoaki Koui

In-Situ RHEED Monitoring of Hydrogen Plasma Cleaning on Semiconductor Surfaces

The first trial of in-situ reflection high-energy electron diffraction (RHEED) monitoring of cleaning processes on semiconductor surfaces with hydrogen (H) plasma was performed. The cleaning time on (100) GaAs surfaces decreased for the higher temperature, while that on (100) Si surfaces increased for the higher temperature. This opposite tendency in the temperature dependence was studied with the measured temperature dependence of the etch rate and the in-situ quadrupole mass spectroscopy. The dependence of the Si surface reconstruction on the angle of incidence of the H-plasma beam is also reported for the first time.

Atomic layer epitaxy of GaAs and role of As‐source materials on self‐limiting mechanism

Atomic layer epitaxy (ALE) of GaAs using triethylgallium (TEG) with the combination of arsine has been limited to an extremely narrow temperature range. It is demonstrated that the temperature range for ALE using TEG is substantially expanded when arsine is replaced with an alkyl‐As, tris‐dimethylamino‐arsenic {As[N(CH3)2]3}. The role of the As source materials on the self‐limiting mechanism is discussed with the measurement of the surface reaction species employing a transient quadrupole mass spectrometry.

Mass Spectrometric Study and Modeling of Decomposition Process of Tris-Dimethylamino-Arsenic on (001) GaAs Surface

Decomposition process of a new arsenic precursor, As[N(CH3)2]3, for metalorganic molecular beam epitaxy (MOMBE) was studied. It was found that a Ga-stabilized (4×2) GaAs surface turned to an As-stabilized (2×4) surface at a low substrate temperature of ~400°C and with a low As[N(CH3)2]3 pressure of ~10-7 Torr when it was supplied without thermal precracking. This is a marked contrast to conventional As[C2H5]3 with which the As-stabilized GaAs surface is never formed without precracking. The decomposition process was modeled assuming an intermediate-state species adsorbed on the GaAs surface based on a quadrupole mass spectrometric study. The measured temperature dependence was very well explained with the present model.

Catalytic Precracking of Amino-As in Metalorganic Molecular-Beam Epitaxy of GaAs

Precracking of an As source employing the catalytic effect of GaAs is proposed for the growth of GaAs in metalorganic molecular-beam epitaxy. The As source used was an amino-As, tris-dimethylamino-arsenic {TDMAAs, As[N(CH3)2]3}. The enhancement of the growth rate was observed for an optimum combination of the substrate temperature and the cracking temperature. The mechanism of the growth enhancement was studied by means of quadrupole mass spectrometry. It is shown that the intermediate As species of the amino-As play a prominent role in growth enhancement.

Decomposition mechanism of triethyl-arsenic on a GaAs surface for metalorganic molecular-beam epitaxy : role of hydrogen radicals

Growth of GaAs in metalorganic molecular-beam epitaxy using triethyl-arsenic (TEAs) becomes possible only when TEAs is thermally precracked or when hydrogen (H) plasma is irradiated simultaneously. In this paper, it will be shown that the bottleneck in the growth of GaAs with TEAs is the quick desorption of the As-intermediate species before its decomposition to supply As to a GaAs surface. The Ga-stabilized GaAs surface after the TEAs supply is proposed to be covered with stable C2H4 species based on reflection high-energy electron diffraction and quadrupole mass spectrometric measurements. H radicals are shown to be effective in the initial stages of the decomposition process of TEAs, but once the surface is covered stably with C2H4, even the H radicals cannot enhance their desorption.

Metal-Organic Molecular-Beam Epitaxy with a New Arsenic Precursor As[N(CH3)2]3: Characterization of the Decomposition Processes and Growth of GaAs

The decomposition process of a new alkyl-As source, tris-dimethylaminoarsenic (TDMAAs) was studied with RHEED and quadrupole-mass spectrometer (QMS) measurements together with a theoretical modeling. TDMAAs is decomposed efficiently on a GaAs surface and the Ga-stabilized surface turned to the As-one with very-low TDMAAs pressure. Grown GaAs films show small carbon-acceptor peak in PL measurements and were n-type. The origin of the n-type conductivity is discussed. D-4-1

Evaluation of hydrogenation on semiconductor surfaces treated with hydrogen-plasma beam excited by electron cyclotron resonance

Hydrogen (H) plasma excited by electron cyclotron resonance (ECR) offers a powerful technique for cleaning semiconductor surfaces at low temperature and for realizing atomically flat surfaces. This paper evaluates the neutralization of impurities near semiconductor surfaces during the H-plasma cleaning process, which is known as the hydrogenation effect. It was found that hydrogenation in the present ECR cleaning process is quite different from that in the usual radio-frequency plasma. It was found that hydrogenation with the H-plasma excited with ECR is dependent on the angle of incidence of the plasma beam and is also dependent on the presence of the surface oxide and on the related surface flatness in the atomic level.