G. G. Fountain

Low interface trap density for remote plasma deposited SiO2 on n‐type GaN

Metal‐oxide‐semiconductor capacitors were prepared with remote plasma‐enhanced chemical vapor deposition of SiO2 at ∼300 °C on an n‐type GaN epitaxial layer grown by atmospheric pressure metalorganic chemical‐vapor deposition on a sapphire substrate. No hysteresis was observed in the high‐frequency capacitance‐voltage (C−V) measurements, and the measured C−V curve agreed with the C−V behavior calculated for an ideal oxide with the same flat‐band voltage as the measured C–V curve. The absence of hysteresis and stretchout in the measured C–V curve and the increase of capacitance with incident ultraviolet light while in deep depletion suggest a low concentration of interface traps. These results demonstrate previous predictions of the absence of Fermi‐level stabilization at the interface for the ionic crystal GaN.

Remote plasma‐enhanced chemical‐vapor deposition of epitaxial Ge films

Epitaxial Ge films have been deposited at 300 °C using a remote plasma‐enhanced chemical‐vapor deposition technique where metastable He atoms flow downstream from the plasma region to dissociate GeH4 molecules into deposition precursor species. Ge epitaxy is demonstrated on Ge(111), Si(100), and GaAs(111)Ga face substrates. An in situ cleaning process that involves a moderate thermal bake at 300 °C and a hydrogen plasma etch of the native oxides is integral to the process. Reflection high‐energy electron diffraction is used to examine surface quality just prior to and after deposition. Uniform integral order diffraction streaks and fractional order reconstruction features observed from the Ge epilayers indicate that high quality Ge epitaxial layers can be grown using remote plasma‐enhanced chemical‐vapor deposition.

On the feasibility of growing dilute CxSi1−x epitaxial alloys

Dilute CxSi1−x epitaxial films have been grown on Si(100) by remote plasma‐enhanced chemical vapor deposition. Carbon concentrations of ∼3 at.% have been achieved at a growth temperature of 725 °C. No evidence for the formation or precipitation of SiC was found using x‐ray diffraction and transmission electron microscopy.

Low interface state density SiO2 deposited at 300 °C by remote plasma‐enhanced chemical vapor deposition on reconstructed Si surfaces

A 300 °C process has been used to deposit high‐quality SiO2 on Si. The process is based on remote plasma‐enhanced chemical vapor deposition. In this process excited species from a remote oxygen plasma interact with silane in the deposition zone. A hydrogen plasma is used to clean the silicon surface in situ just prior to deposition. After a 400 °C post‐metallization anneal, interface‐state densities as low as 3.7×1010 cm−2 eV−1 were measured with a fixed charge density of 2×1011 cm−2. The films exhibited good breakdown integrity, sustaining fields of 9–10 MV cm−1. The Si/SiO2 interface‐state density directly correlates with the quality of reflection high‐energy electron diffraction patterns from the silicon surface just prior to oxide deposition.

In situ cleaning of GaAs surfaces using hydrogen dissociated with a remote noble-gas discharge

In situ cleaning of GaAs surfaces has been achieved at 350 °C with a novel technique employing hydrogen that is excited and dissociated using a remote Ar discharge. Reconstructed surfaces characteristic of clean, As‐stabilized GaAs surfaces have been observed with reflection high‐energy electron diffraction following the cleaning treatment. Auger electron spectroscopy analyses confirm that such a treatment removes both carbon and oxygen contamination from the surface. X‐ray photoelectron spectroscopy shows the removal of oxygen bonded to both Ga and As on the surface. Emission spectroscopy shows evidence of excited molecular and atomic hydrogen with the downstream‐excitation process.

SECONDARY ELECTRON EMISSION ENHANCEMENT AND DEFECT CONTRAST FROM DIAMOND FOLLOWING EXPOSURE TO ATOMIC HYDROGEN

Polished nominal (100) surfaces of four types of diamonds were exposed to atomic hydrogen by hot filament cracking of H2 gas or by immersion in a H2 plasma discharge. Both types IIa and IIb (100) diamond surfaces exhibited the following characteristic changes: (a) secondary electron (SE) yield increased by a factor of ∼30 as measured in a scanning electron microscope (SEM), (b) near‐surface, nontopographical defects were observable directly using the conventional SE mode of the SEM, (c) surface conductance increased by up to 10 orders of magnitude. These changes were observed only weakly in nitrogen‐containing types Ia and Ib diamonds.

Demonstration of an n-channel inversion mode GaAs MISFET

Summary form only given. An operational GaAs inversion mode n-channel MISFET has been demonstrated using a composite SiO/sub 2/ (15 nm)/Si (1 nm)/GaAs structure. This result is based on an in situ hydrogen cleaning process (used to prepare the GaAs surface just prior to the Si-SiO/sub 2/ deposition), a low-temperature pseudomorphic Si deposition process, and a low-temperature high-quality SiO/sub 2/ deposition process, all performed sequentially in an ultrahigh-vacuum/load locked system. The first working devices exhibit a DC transconductance of 0.26 mS/mm at a gate length and width of 2 mu m and 50 mu m, respectively. Capacitance-voltage analysis of MIS capacitors on chip with the transistors indicates that the midgap electron trap density is on the order of 4*10/sup 11/ cm/sup -2/.<<ETX>>

Gating of germanium surfaces using pseudomorphic silicon interlayers

A novel insulator structure for gating of germanium surfaces has been developed. The structure consists of a very thin (on the order of 10 A) pseudomorphic silicon layer deposited on the germanium surface prior to deposition of a silicon dioxide insulating layer. Both the silicon and silicon dioxide layers were deposited at low temperature by remote plasma‐enhanced chemical vapor deposition. Low interface state densities and surface inversion have been obtained for both n‐ and p‐type germanium substrates. X‐ray photoelectron spectroscopy and ion scattering spectroscopy analysis indicate that the thin pseudomorphic silicon layer provides complete silicon coverage of the germanium surface. The silicon layer protects the germanium surface from undesirable oxidation during the silicon dioxide deposition. The electrical properties of germanium metal‐insulator‐semiconductor structures which incorporated the silicon interlayer were much improved compared to structures in which the silicon dioxide was deposited d...

The role of an ultrathin silicon interlayer at the SiO2‐Ge interface

Recent studies [Hattangady et al., Appl. Phys. Lett. 57, 581 (1990)] have shown greatly reduced interface state densities (5×1010 cm−2 eV−1) in Ge‐based, metal‐insulator‐semiconductor structures with the use of an ultrathin, pseudomorphic Si interlayer between the gate dielectric, SiO2, and the Ge semiconductor substrate. The Si and the SiO2 layers are deposited in situ and sequentially at low temperature (300 °C) in a remote‐plasma‐enhanced chemical‐vapor‐deposition system. This report presents an analysis of the Si‐Ge heterostructure before and after the SiO2 deposition. Low‐energy He ion scattering spectroscopy shows that the silicon layer (28 A) provides complete coverage of the Ge surface prior to the deposition of the SiO2 film. The existence of the silicon interlayer after the remote‐plasma‐enhanced deposition of 150 A of the SiO2 film is established by x‐ray photoelectron spectroscopy (XPS). Throughout a cumulative series of thin (∼10 A) oxide depositions, XPS showed no evidence of Ge oxidation st...

Epitaxial silicon deposition at 300 °C with remote plasma processing using SiH4/H2 mixtures

Epitaxial Si films have been deposited on Si(100) at 300 °C by remote plasma‐enhanced chemical vapor deposition using SiH4/H2 mixtures with deposition rates as high as 25 A/min at these low temperatures. Hall measurements of the film show an unintentional doping level of about 1×1017 cm−3 with electron mobilities of 700 cm2 V−1s−1. Critical to the process is the in situ cleaning of the silicon substrate surface prior to deposition.