Silicon Carbide Thin Films Research Articles

Aluminum doped silicon‐carbon alloys prepared by hot wire chemical vapor deposition

AbstractAluminum doped stoichiometric microcrystalline silicon carbide (µc‐SiC:H) thin films deposited by Hot Wire Chemical Vapor Deposition (HWCVD) technique have been studied. Without Al‐doping, highly crystalline µc‐SiC:H thin films prepared from monomethysilane (MMS) and hydrogen are mainly cubic polytype and are unintentionally doped into n‐type. Trimethyaluminum (TMAl) is used as a source of Aluminum. By increasing the TMAl/MMS ratio (rdoping), the dark conductivity of µc‐SiC:H thin film firstly decreases and then increases. This variation indicates the compensation from n‐type to p‐type, which is confirmed by the thermo‐power measurements. It is observed in the infrared spectra that the crystallinity of µc‐SiC:H thin film deceases with increasing rdoping. In order to improve the crystallinity of this conductive p‐type µc‐SiC:H thin film, the effect of deposition pressure (pdepo) has been investigated. With increasing pdepo, the crystallinity is improved and the structure of SiC alloys changes according to the Raman spectra. A maximum dark conductivity of 1.3×10–1 S/cm has been achieved at rdoping = 0.0620 and pdepo = 100 Pa. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanocrystallites formation in a‐SiC by low power plasma enhanced chemical vapour deposition

AbstractFormation of nanocrystallites in the amorphous silicon carbide thin films deposited from silane methane mixture diluted in argon by plasma enhanced CVD has been studied under different levels of rf power density and Ar dilution. Systematic transformations between different polymorphic phases of SiC have been observed with changes in rf power and Ar dilution. At low Ar dilution no H‐SiC (α‐SiC) nanocrystallites was observed. Only traces of β‐SiC of Si were observed. With increase in Ar dilution formation of α‐SiC nanocrystallites was observed. Increase of rf power density at this dilution enhanced α‐SiC nanocrystallites but reduced β‐SiC slightly. Variation of SiC peak in the infra red absorption corresponds closely with the changes in β‐SiC nanocrystallites in the layers. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of porous silicon carbide as a new material for environmental and optoelectronic applications

In this paper, we present an experimental study on the chemical and electrochemical etching of silicon carbide (SiC) in different HF-based solutions and its application in different fields, such as optoelectronics (photodiode) and environment (gas sensors). The thin SiC films have been grown by pulsed laser deposition method. Different oxidant reagents have been explored. It has been shown that the morphology of the surface evolves with the etching conditions (oxidant, concentration, temperature, etc.). A new chemical polishing solution of polycrystalline 6H-SiC based on HF:Na 2O 2 solution has been developed. Moreover, an electrochemical etching method has been carried out to form a porous SiC layer on both polycrystalline and thin SiC films. The PL results show that the porous polycrystalline 6H-SiC and porous thin SiC films exhibited an intense blue luminescence and a green-blue luminescence centred at 2.82 eV (430 nm) and 2.20 eV (560 nm), respectively. Different device structures based on both prepared samples have been investigated as photodiode and gas sensors.

Spectral tuning of near-field radiative heat flux between two thin silicon carbide films

Spectral distributions of radiative heat flux between two thin silicon carbide films separated by sub-wavelength distances in vacuum are analysed. An analytical expression for the near-field flux between two layers of finite thicknesses in terms of film reflection and transmission coefficients is derived for the first time. The resulting equation clearly shows the resonant modes of thermal emission, absorption and the cross-coupling of surface phonon-polaritons (SPhPs) between the layers. When the films are of the same thickness, the resonant frequencies maximizing near-field thermal emission almost match those of absorption. The small discrepancies, due to SPhP coupling between the films, lead to loss of spectral coherence affecting mostly the low frequency mode. The flux profiles also show that splitting of the resonance into two distinct frequencies happens when the ratio thickness of the film over the separation gap is less than unity. When the thickness of one film increases relative to the other, spectral distributions of flux are significantly altered due to an important mismatch between the resonant frequencies of high emission and absorption. This modification of the near-field flux is mostly due to weaker SPhP coupling within the layer of increasing thickness. Based on an asymptotic analysis of the dispersion relation, an approximate approach is proposed to predict the resonant modes maximizing the flux between two films, which can be potentially extended to multiple thin layers. The outcome of this work would allow tailoring near-field radiative heat transfer, and can eventually be used to design customized nanostructures for energy harvesting applications.

CVD에 의한 고전력 디바이스용 단결정 3C-SiC 박막 성장

This paper describes that single crystalline 3C-SiC (cubic silicon carbide) thin films have been deposited on carbonized Si(100) substrates using hexamethyldisilane (HMDS, Si2(CH3)6) as a safe organosilane single precursor and a nonflammable mixture of Ar and H2 gas as the carrier gas by APCVD at 1280°C. The deposition was performed under various conditions to determine the optimized growth condition. The crystallinity of the 3C-SiC thin film was analyzed by XRD (X-ray diffraction). The surface morphology was also observed by AFM (atomic force microscopy) and voids between SiC and Si interfaces were measured by SEM (scanning electron microscopy). Finally, residual strain and hall mobility was investigated by surface profiler and hall measurement, respectively. From these results, the single crystalline 3C-SiC film had a good crystal quality without defects due to viods, a low residual stress, a very low roughness.

Technology roadmap for development of SiC sensors at plasma processes laboratory

Recognizing the need to consolidate the research and development (R&D) activities in microelectronics fields in a strategic manner, the Plasma Processes Laboratory of the Technological Institute of Aeronautics (LPP-ITA) has established a technology roadmap to serve as a guide for activities related to development of sensors based on silicon carbide (SiC) thin films. These sensors have also potential interest to the aerospace field due to their ability to operate in harsh environment such as high temperatures and intense radiation. In the present paper, this roadmap is described and presented in four main sections: i) introduction, ii) what we have already done in the past, iii) what we are doing in this moment, and iv) our targets up to 2015. The critical technological issues were evaluated for different categories: SiC deposition techniques, SiC processing techniques for sensors fabrication and sensors characterization. This roadmap also presents a shared vision of how R&D activities in microelectronics should develop over the next five years in our laboratory.

Effects of substrate temperature on microstructural and photoluminescent properties of nanocrystalline silicon carbide films

Nanocrystalline silicon carbide (nc-SiC) thin films have been grown on silicon (1 0 0) substrates by helicon wave plasma enhanced chemical vapor deposition technique and the photoluminescence of the films has been tuned from yellow to blue by changing the substrate temperatures ( T s). The resulting nc-SiC films show a microstructure of 3C–SiC nanocrystallites embedded in hydrogenated amorphous SiC matrix. Detailed analysis of the infrared absorption reveals that the degree of crystallization of the films increases with the increase of T s while the content of hydrogen-related bonds in the films is decreased. The photoluminescence spectra of the nc-SiC films are found to be composed of two Gaussian components. As the T s increases, the component with higher energy shows a growing trend and the corresponding peaks move to high energy side, indicating that the main luminescence mechanism in the films changes from the defect-related carrier recombination to the quantum confinement effect.

Preparation and characterizations of amorphous nanostructured SiC thin films by low energy pulsed laser deposition

Amorphous silicon carbide (SiC) thin films were deposited on silicon substrates by pulsed laser ablation at room temperature. Thicknesses and surface morphology of the thin films were characterized using optical profilers, atomic force and field emission scanning electron microscopy. Nanohardnes, modulus and scratch resistance properties were determined using XP nanoindenter. The results show that crack free, smooth and nanostructured thin films can be deposited using low laser energy densities.

Design and Performance of an LPCVD Reactor for the Growth of 3C-Silicon Carbide

This paper discusses the design of a low pressure chemical vapor deposition (LPCVD) reactor and growth of β silicon carbide (3C-SiC) thin films on Si. The reactor’s hot-zone configuration radiatively couples the graphite heater (no physical contact) to Si substrates with realized temperatures . We implemented a four-stage growth procedure using silane and propane precursors and hydrogen as the carrier gas. Temperatures, pressures, and flows varied from , from , and from during growth, respectively. Growth of 3C-SiC was confirmed using X-ray diffraction (XRD) with the observation of a (200) peak located at 41.4°. Activation energies of 21.5 and were calculated for the kinetically and mass-transport-limited regimes for polycrystalline 3C-SiC growth. The polycrystalline 3C-SiC films with fewest defects and smallest XRD full width at half-maximum were deposited at with a growth rate of using flow rates of , , and of (conc. 1.16%). The composition of the films measured by X-ray photoelectron spectroscopy shows that the films are slightly carbon rich with oxygen as the main source of contamination. Voids were observed at the film–substrate interface for samples grown at high precursor concentrations.

Silicon carbide thin films for EUV and soft X-ray applications

We have deposited SiC thin films using two different deposition tech- niques, Pulsed Electron Deposition (PED) and Pulsed Laser Deposition (PLD). The PED technique is a relatively new technique where a pulsed electron flux with high energy directly hits the target surface producing a plasma in a very similar way to PLD, where, instead, a pulsed laser beam is used. These two techniques can give very dense thin films with stoichiometry much closer to the target one's compared to others physical vapour deposition techniques (sputtering, e-beam). The major drawback of PED is that the thin film surface is affected by the pres- ence of particulate, due to the impact of the high energy electron beam with the target. In the PLD system we used a magnetic field to curve the plasma path in the vacuum and we placed the substrate at 90 ◦ with respect to the target allowing the deposition of particulate-free samples. The characterization of the films has been made by measuring the optical reflectance vs angle of incidence in the EUV region (from 121.6 nm down to 40.7 nm), taking measurements at different time from deposition. X-ray photoemission measurements have been also carried out to show stoichiometry and the presence of contaminants. Other measurements such as X-ray diffraction, atomic force microscopy and profiling were also carried out to check crystalline domains and surface roughness.

Modeling and Simulation of Boron-Doped Nanocrystalline Silicon Carbide Thin Film by a Field Theory

This paper presents the application of a multiscale field theory in modeling and simulation of boron-doped nanocrystalline silicon carbide (B-SiC). The multiscale field theory was briefly introduced. Based on the field theory, numerical simulations show that intergranular glassy amorphous films (IGFs) and nano-sized pores exist in triple junctions of the grains for nanocrystalline B-SiC. Residual tensile stress in the SiC grains and compressive stress on the grain boundaries (GBs) were observed. Under tensile loading, it has been found that mechanical response of 5 wt% boron-SiC exhibits five characteristic regimes. Deformation mechanism at atomic scale has been revealed. Tensile strength and Young's modulus of nanocrystalline SiC were accurately reproduced.

Enhancement of the corrosion resistance of a Ti-based alloy by ion beam deposition methods

Physical vapour deposition (PVD) and ion beam assisted deposition (IBAD) were applied to produce silicon carbide (SiC) thin films on the surface of Ti–6Al–4V alloy (T6A4V) aiming at the improvement of its corrosion resistance. Diamond-like carbon (DLC) coatings were also prepared using the above techniques in combination with plasma enhanced chemical vapour deposition (PECVD). The Si-, C- and O-content and depth distribution in the films was determined using Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). The corrosion resistance of the coated samples was investigated under aggressive conditions (0.5M H2SO4 at R.T and 5M HCl at 50°C) using polarization techniques. The surface morphology and microstructure of the initial and the corroded samples were examined by scanning and transmission electron microscopy (SEM and TEM). The thickness of the coatings remained practically unchanged after the corrosion attack, whereas the corrosion resistance of the coated materials seems to be related with the amorphous structure of the modified surface.

Growth of silicon carbide thin films by hot-wire chemical vapor deposition from SiH 4/CH 4/H 2

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition from SiH 4/CH 4/H 2 and their structural properties were investigated by X-ray diffraction, Fourier transform infrared absorption and Raman scattering spectroscopies. At 2 Torr, Si-crystallite-embedded amorphous SiC (a-Si 1 − x C x :H) grew at filament temperatures ( T f) below 1600 °C and nanocrystalline cubic SiC (nc-3C-SiC:H) grew above T f = 1700 °C. On the other hand, At 4 Torr, a-Si 1 − x C x :H grew at T f = 1400 °C and nc-3C-SiC grew above T f = 1600 °C. When the intakes of Si and C atoms into the film per unit time are almost the same and H radicals with a high density are generated, which takes place at high T f , nc-3C-SiC grows. On the other hand, at low T f the intake of Si atoms is larger than that of C atoms and, consequently, Si-rich a-Si 1 − x C x :H or Si-crystallite-embedded a-Si 1 − x C x :H grow.

Importance of H 2 gas for growth of hot-wire CVD nanocrystalline 3C-SiC from SiH 4/CH 4/H 2

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition from SiH 4/CH 4/H 2 and the influence of H 2 gas flow rate ( F(H 2)) on the film properties was investigated. The SiH 4 gas flow rate was 1 sccm. At the CH 4 gas flow rate ( F(CH 4)) of 1 sccm, nanocrystalline cubic SiC (nc-3C-SiC) grew even without H 2. On the other hand, at F(CH 4) = 2 sccm, amorphous SiC grew without H 2 and nc-3C-SiC grew above F(H 2) = 50 sccm. As F(H 2) was increased, the crystallinity improved both at F(CH 4) = 1 and 2 sccm. However, the mean crystallite size decreased at F(CH 4) = 1 sccm and increased at F(CH 4) = 2 sccm. We discuss growth mechanisms of nc-3C-SiC.

Microcrystalline silicon carbide thin films grown by HWCVD at different filament temperatures and their application in n-i-p microcrystalline silicon solar cells

To optimize the performance of microcrystalline silicon carbide (µc-SiC:H) window layers in n-i-p type microcrystalline silicon (µc-Si:H) solar cells, the influence of the rhenium filament temperature in the hot wire chemical vapor deposition process on the properties of µc-SiC:H films and corresponding solar cells were studied. The filament temperature T F has a strong effect on the structure and optical properties of µc-SiC:H films. Using these µc-SiC:H films prepared in the range of T F = 1800–2000 °C as window layers in n-side illuminated µc-Si:H solar cells, cell efficiencies of above 8.0% were achieved with 1 µm thick µc-Si:H absorber layer and Ag back reflector.

Room-Temperature Wet Etching of Polycrystalline and Nanocrystalline Silicon Carbide Thin Films with HF and HNO3

Polycrystalline 3C-SiC films deposited using low-pressure chemical vapor deposition from the precursors 1,3-disilabutane and dichlorosilane (DCS) are etched at room temperature in a mixed acid solution consisting of a 1:1 mixture of . DCS flow rate fractions from 0 to 0.47, which yield a range of films with varying grain sizes, are examined. Etch rates vary from for smaller grained films to for larger grained films. A kinetic model of the etch rate with first-order dependence on free silicon concentration and inverse power-law dependence on grain size is developed that fits the data well. The change in roughness of most polycrystalline SiC films is nominal upon etching; however, films deposited with 0.16 DCS fraction exhibit an increase in roughness accompanied by the exposure of larger grains at the etched surface. Furthermore, films deposited without DCS exhibit an increase in roughness accompanied by the formation of deep “nanocraters” on the surface of individual grains. The room-temperature wet-etch capability thus presented enables new process flows for the realization of micro- and nanoelectromechanical system devices for harsh environments.

Fabrication of amorphous silicon carbide films using VHF-PECVD for triple-junction thin-film solar cell applications

Preparation of intrinsic hydrogenated amorphous silicon carbide (i-a-SiC:H) thin films for use as a top cell of triple junction solar cells is presented. These films were deposited using very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique with monomethyl silane (MMS) gas as the carbon source. Deposition conditions were explored to obtain films with a wide gap and low defect density. It was confirmed that the hydrogen dilution ratio plays an important role in enhancing the film properties. Employing a-SiC:H film as an intrinsic layer of single junction cell, open-circuit voltage as high as 0.99 V has been achieved.

Fracture Properties of Silicon Carbide Thin Films by Bulge Test of Long Rectangular Membrane

Fracture Properties of Silicon Carbide Thin Films by Bulge Test of Long Rectangular Membrane

Modeling of plasma process data using a multi-parameterized generalized regression neural network

For characterization or optimization process, a computer prediction model is in demand. A new technique, to improve the prediction performance of conventional generalized regression neural network (GRNN) of plasma process data was presented. Genetic algorithm (GA) was applied to optimize multi-parameterized training factors of GRNN. To evaluate the technique, two data sets were collected from the etchings of silica and silicon carbide (SiC) thin films in inductively coupled plasmas. Both data sets called Data I and Data II were statistically characterized by means of 2 3 and 2 4 full factorial experiment plus one center point. The GRNN models trained with these data were tested with additional six and 16 experiments. A total of eight etch outputs were modeled and compared with conventional GRNN and statistical regression models. The five etch outputs comprising Data I include silica etch rate, aluminum (Al) etch rate, Al selectivity, profile angle, and DC bias. Data II consisted of three etch outputs, including SiC etch rate, surface roughness, and profile angle. Compared to GRNN models, GA-GRNN models yielded more than 40% and 15% improvements for all etch outputs comprising Data I and Data II, respectively. Similar improvements were also demonstrated with respect to statistical regression models. All these results reveal that a multi-parameterization of training factors and GA optimization is an effective technique to considerably improve the prediction performance of conventional GRNN model.

Etching Characteristics and Surface Morphology of Nitrogen-Doped a-SiC Films Prepared by RF Magnetron Sputtering

Amorphous nitrogen-doped silicon carbide (a-SiCxNy) thin films were deposited on Si substrates by RF magnetron sputtering of a SiC target in a N2+Ar atmosphere. The N2/Ar flow ratio was adjusted by varying the N2 flow rate and maintaining constant the Ar flow rate. In order to investigate the influence of N2/Ar flow ratio on composition, bonding structure, morphology and surface roughness of the deposited films, the following techniques were used: Rutherford backscattering spectroscopy (RBS), Raman spectroscopy and atomic force microscopy (AFM). Moreover, using a reactive ion etching (RIE) system the a-SiCxNy samples were etched in SF6+O2 gases mixtures. To better understand the variation of the etching rate as a function of the nitrogen content in the film, temporal mass spectrometry analysis of main effluents generated during etching process was performed.