Hideki Nakazawa

Low-temperature formation of an interfacial buffer layer using monomethylsilane for 3C–SiC/Si(100) heteroepitaxy

By using monomethylsilane (MMS:H3Si–CH3), we have formed a Si1−xCx interfacial buffer layer for 3C–SiC/Si(100) heteroepitaxy at substrate temperature Tf of as low as 450–650 °C, which is compared to the conventional carbonization temperature of 900 °C or higher. The buffer layer allows the subsequent growth of high-quality single-crystalline 3C–SiC films at 900 °C without formation of voids in the Si substrate at the interface. The grown 3C–SiC films degrade for Tf 650 °C. The low processing temperature as well as the suppressed Si outdiffusion can be related to the inclusion of both Si–H and Si–C bonds within the MMS molecule.

Structure, Chemical Bonding and These Thermal Stabilities of Diamond-Like Carbon (DLC) Films by RF Magnetron Sputtering

We have deposited diamond-like carbon (DLC) films using RF magnetron sputtering techniques, and investigated structure, chemical bonding of deposited films and these thermal stabilities by Raman spectroscopy and photoelectron spectroscopy. It has been found that the film deposited under typical conditions is amorphous carbon (a-C) with 62% sp2 and 38% sp3 bonds. Ordering of a-C has been observed with an increase in substrate temperature during deposition and similarly observed after postannealing, although the sp3/sp2 ratio in a film does not change even at 900°C. The absence of conversion between sp3 and sp2 bonds indicates that the DLC films have high thermal stabilities.

Gas-source MBE of SiC/Si using monomethylsilane

Abstract We have conducted a systematic series of gas-source MBE experiments of 3C–SiC on Si(100) using monomethylsilane (MMS), and have investigated the relation between growth parameters (MMS pressure and growth temperature) and the grown film quality using atomic force microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Auger electron spectroscopy. As a result, it was clarified that there exists a set of optimum growth parameters for the best surface morphology and crystallinity. The optimum temperature lowered with decreasing MMS pressure, and the crystallinity of the SiC film improved at the same time. In particular, a high quality 3C–SiC film on Si(100) was successfully grown at T = 900°C.

Formation of quasi-single-domain 3C-SiC on nominally on-axis Si(001) substrate using organosilane buffer layer

Quasi-single-domain 3C-SiC films have been successfully grown on nominally on-axis Si(001) substrate. The starting surface is either of 2×1 quasi-single-domain or of 2×1+1×2 double-domain. The point here is to use dc-resistive heating of the substrate and to form a low-temperature (650 °C) interfacial buffer layer using monomethylsilane (H3 C-SiH3). The dc resistive heating serves to form a single-domain Si(001)-2×1 or 1×2 starting surface or to develop a single-domain 3C-SiC(001)-2×3 or 3×2 surface on a 2×1+1×2 double-domain Si(001) substrate. When a single-domain Si(001) starting surface is utilized, it is not the dc polarity during growth but the surface reconstruction of the starting surface that determines the dominant domain in the 3C-SiC film. The thickness of the single-domain 3C-SiC film is as thin as ∼45–200 nm, which is about three orders of magnitude smaller than that required in a previous study (>5 μm).

Dissociative adsorption of monomethylsilane on Si(100) as revealed by comparative temperature-programmed desorption studies on H/, C2H2/, and MMS/Si(100)

Abstract Dissociative adsorption of monomethylsilane (MMS), a promising precursor gas for low-temperature SiC, has been investigated on Si(100) by using temperature-programmed desorption (TPD) method after its comparison with H/ and C 2 H 2 /Si(100) surfaces. For both MMS/ and C 2 H 2 /Si(100), the β 1 peak from SiH species showed a shift to higher temperatures in the presence of surface C atoms, while two new peaks appeared separately for the two gases: γ peak (∼640°C) for the C 2 H 2 / and δ peak (∼870°C) for the MMS/Si(100). The γ peak is suggested to be from hydrogen desorption from SiH species at which a C atom is inserted to its backbond. The δ peak is related to desorption from surface CH x species. The absence of the γ peak on MMS/Si(100) suggests absence of atomic exchange between surface C and substrate Si atoms on its adsorption.

Temperature-programmed-desorption study of the process of atomic deuterium adsorption onto Si(100)2×1

Abstract The process of atomic deuterium adsorption onto Si(100)2×1 surfaces was investigated by the temperature-programmed-desorption (TPD) method, whose spectrum was successfully decomposed into contributions from mono- and dihydride phases. The time evolutions of these phases were described quite well with a model that involves an initial formation of the monohydride phase from surface bare Si atoms, followed by a delayed development of the dihydride phase. Although their qualitative behavior agreed with kinematical considerations, quantitative analysis indicates a difference in the dynamical factors in these processes. The observed saturated surface coverage (1.56 ±0.18 ML) below 2 ML was also interpreted as being determined by a balance of mutual conversions between monohydride and dihydride phases.

Thin-Film Deposition of Silicon-Incorporated Diamond-Like Carbon by Plasma-Enhanced Chemical Vapor Deposition Using Monomethylsilane as a Silicon Source

We have deposited Si-incorporated diamond-like carbon (DLC) films by radio-frequency plasma-enhanced chemical vapor deposition using methane, argon, and monomethylsilane (MMS; CH3SiH3) as a silicon source, and have investigated the structural and mechanical properties of the films. The deposition rate and Si atomic fraction [Si/(Si+C)] in the DLC films increased with increasing MMS flow ratio. The Si fraction was approximately 13% at a MMS flow ratio [MMS/(MMS+CH4)] of 3%, showing that the deposition using a combination of CH4 and MMS produces films with high Si content compared with those deposited using conventional C and Si sources. The Si fraction was also found to increase with a decrease in Ar flow rate under a constant MMS flow ratio. Many particles composed mainly of Si, whose size was 0.3–1 µm in diameter, were observed on the surface when deposition was carried out at MMS flow ratios of 15 and 30%. Compressive internal stress in the films decreased with the MMS flow ratio and/or with the Ar flow rate. The decrease in internal stress is probably due to the relaxation of a three-dimensional rigid network by the formation of Si–C and Si–H bonds in the films as well as Ar+ ion bombardment.

Observation of hydrogen-coverage- and temperature-dependent adsorption kinetics of disilane on Si(100) during Si gas-source molecular beam epitaxy

Precise measurements of the growth rate, R g, and the surface hydrogen coverage, θ H, of the gas-source-molecular-beam-epitaxy-grown Si(100) surface using disilane have been conducted to obtain the reaction order m of the adsorption process. The data points separated into three regions: region (I) for 1-θ H 0.75 ML with m=4, which was successfully interpreted by a hydrogen-coverage- and temperature-dependent adsorption kinetics model.

Role of hydrogen prepairing in the hydrogen desorption kinetics from Si(100)-2×1: effects of hydrogenating-gas and thermal history

Hydrogen desorption kinetics from Si(100)-2×1:H has been systematically investigated using temperature-programmed desorption (TPD) on several hydrogenating gases and thermal conditions. As a result, the desorption kinetic order with the hydrogen coverage was found to increase in the order: atomic hydrogen<disilane<silane and room-temperature adsorption<high-temperature adsorption<post-annealing. These variations in kinetic order, depicted as a TPD peak shift at low hydrogen coverages, are universally described with a single surface parameter, γ0, the fractional coverage of unpaired hydrogen atoms. Fitting with obtained TPD spectra demonstrates that γ0 is a delicate function of the hydrogenating gas and thermal history.

Structural and electrical properties and current–voltage characteristics of nitrogen-doped diamond-like carbon films on Si substrates by plasma-enhanced chemical vapor deposition

We have deposited nitrogen-doped diamond-like carbon (N-DLC) films by plasma-enhanced chemical vapor deposition using CH4, N2, and Ar, and investigated the effects of N doping on the structure and the electrical, mechanical, and optical properties of the N-DLC films. We fabricated undoped DLC/p-type Si and N-DLC/p-type Si heterojunctions and examined the current–voltage characteristics of the heterojunctions. When the N2 flow ratio was increased from 0 to 3.64%, the resistivity markedly decreased from the order of 105 Ωcm to that of 10−2 Ωcm and the internal stress also decreased. The resistivity gradually increased with increasing N2 flow ratio from 3.64 to 13.6%, and then it decreased at a N2 flow ratio of 13.6%. These behaviors can be explained in terms of the clustering of sp2 carbons and the formation of sp3C–N, sp2C=N, sp1C≡N, and C–H n bonds. The rectification ratio of the heterojunction using the N-DLC film prepared at 3.64% was 35.8 at ±0.5 V.