Materials Science Forum Vols. 556-557

Abstract: 3C-SiC epitaxial layers with a thickness of up to 100 μm and area of ~0.3-0.5 cm2 have been grown by sublimation epitaxy on hexagonal (6H-SiC) substrates at a maximum growth rate of about 200 μm per hour. The epilayers obtained are of n-type (Nd-Na ~ 1017 -1018 cm-3). According to X-ray data, the epitaxial layers are composed of the 3C-SiC polytype, without inclusions of other polytypes. The donor-acceptor (Al-N) recombination band with hνmax ~ 2.12 eV predominates in the photoluminescence (PL) spectrum. A detailed analysis of a PL spectrum measured at 6 K is presented. A conclusion is made that the epitaxial layers can be used as substrates for electronic devices based on 3C-SiC.

Abstract: 3C-SiC is a promising material for the development of microelectromechanical systems (MEMS) applications in harsh environments. This paper presents the LPCVD growth of heavily nitrogen doped polycrystalline 3C-SiC films on Si wafers with 2.0 μm-thick silicon dioxide (SiO2) films for resonator applications. The growth has been performed via chemical vapor deposition using SiH4 and C2H4 precursor gases with carrier gas of H2 in a newly developed vertical CVD chamber. NH3 was used as n-type dopant. 3C-SiC films were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and room temperature Hall Effect measurements. It was shown that there is no voids at the interface between 3C-SiC and SiO2. Undoped 3C-SiC films show n-type conduction with resisitivity, Hall mobility, and carrier concentration at room temperature of about 0.56 ⋅cm, 54 cm2/Vs, and 2.0×1017 cm-3, respectively. The heavily nitrogen doped polycrystalline 3C-SiC with the resisitivity of less than 10-3 ⋅cm was obtained by in-situ doping. Polycrystalline SiC resonators have been fabricated preliminarily on these heavily doped SiC films with thickness of about 2 μm. Resonant frequency of 49.1 KHz was obtained under atmospheric pressure.

Abstract: The effects of C3H8 on the microstructures of the films on Si (111) have been investigated by changing the concentration of C3H8 from 0.5% to 5%. 3C-SiC film on Si (111) grown at the C3H8 concentration of 1% with relatively high flow rate of SiH4 (30 sccm) is single crystal and free from the contamination of W2C. By comparing the deposition rates of the films on Si (111) and Si (100) at different concentrations of C3H8, SiC growth on Si (111) is much more dependent on C3H8 concentration than that on Si (100). From these results it is suggested that SiC growth on Si (111) is strongly influenced by hydrogen radicals generated from C3H8 decomposition by the plasma and forms single crystal easier than on Si(100). It is expected that 3C-SiC epitaxial growth on Si (111) has higher deposition rate and lower substrate temperature than on Si (100). The crystallinity has been investigated by a reflection electron diffraction (RED) and a X-ray diffraction (XRD). The thickness and the surface roughness of the films were investigated by an ellipsometric measurement.

Abstract: We report on the heteroepitaxial growth of 3C-SiC layers by Vapor-Liquid-Solid (VLS) mechanism on various α-SiC substrates, namely on- and off-axis for both 4H and 6H-SiC(0001), Si and C faces. The Si-Ge melts, which Si content was varied from 25 to 50 at%, were fed by 3 sccm of propane. The growth temperature was varied from 1200 to 1600°C. It was found that singledomain 3C-SiC layers can be obtained on 6H-SiC off and on-axis and 4H-SiC on-axis, while the other types of substrate gave twinned 3C-SiC material. As a general rule, one has to increase temperature when decreasing the Si content of the melt in order to avoid DPB formation. It was also found that twinned 3C-SiC layers form at low temperature while homoepitaxy is achieved at high temperature.

Abstract: Growth rates from 10 to 38 μm/h of single crystal 3C-SiC on planar Si (001) substrates have been obtained in a low-pressure horizontal hot-wall CVD reactor. The propane-silanehydrogen gas chemistry system with HCl added as a growth additive, which allows an increased amount of silane to be introduced into the reactor during growth, was used. The 3C-SiC film growth rate versus silane mole fraction was found to be a linear function in the range from 0.43x10-3 to 1.50x10-3. Nomarski optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, atomic force microscopy and X-ray diffraction were used to characterize the deposited layers. The X-ray rocking curve taken on the (002) diffraction plane of a 12 μm thick 3CSiC (001) layer displayed a FWHM of 360 arcsec, which indicates the films are mono-crystalline.

Abstract: The effect of initial growth condition of 3C-SiC growth on the C-face of 6H-SiC has been studied in sublimation epitaxy. The initial temperature increase to initiate the sublimation has a strong effect on the polytype formation using on-axis substrates. Polytype inclusions of 6H-SiC in the 3C-SiC layers is found to be related to spiral growth. The micropipe dissociation process is discussed. At the slowest ramp-up of the temperature the 3C-SiC does not contain any inclusions. In 1 degree off-oriented substrates there were no 3C-SiC formation. In this case the different ramp-up conditions has an influence on the heights of the steps.

Abstract: The development of 3C-SiC crystals from <0001> oriented hexagonal seed has always suffered from the systematic twinning which appears during the nucleation step of the layer. Using the continuous feed – Physical Vapour Transport (CF-PVT) growth process, we succeeded in growing single domain 3C-SiC crystals. To explain that, we propose in this work, a model based on the interaction between the lateral expansion anisotropy of 3C-SiC nuclei and the step flow growth front. Depending on the step edges direction, we can obtain one 3C orientation developing simultaneously with the vanishing of the other one. This model is confirmed by cross sectional HRTEM observation of the α-β interface.

Abstract: The influence of the growth conditions on the 3C-SiC layer quality in terms of crystallinity, morphology and residual strain was investigated. In dependence on the chosen growth conditions the stress state can be varied between inhomogeneous and homogeneous strain. For the reduction of the residual strain an alternative route for the improvement of the epitaxial growth of 3CSiC( 100) on Si(100) was developed. It consists in covering the silicon wafers with germanium prior to the carbonization step. The achieved improvement in the residual strain and crystalline quality of the grown 3C-SiC layers is comparable to SOI substrates. These beneficial effects were reached by using a Ge coverage in the range of 0.5 to 1 monolayer with respect to the silicon surface.

Abstract: We have investigated the influence of several growth parameters on the incorporation of doping species in the case of 3C-SiC layers grown by CVD on silicon. This includes nitrogen (both intentional and residual) as well as residual aluminum. All concentrations have been determined by SIMS (Secondary Ion Mass Spectrometry). First, we investigated the effect of the growth temperature, growth rate and C/Si ratio on the doping level of (100) oriented layers. Then, we compared the change in nitrogen incorporation versus nitrogen flow rate for layers grown on (100), (111), (110) and (211) oriented wafers.

Abstract: Double and triple crystal rocking curve and peak position maps are constructed for a 4HSiC wafer for the symmetric (0 0 0 8) reflection in the normal position, the same reflection for a sample rotated 90º, and an asymmetric (1 23 6) reflection for the wafer in the normal position. These measurements were corrected for the ‘wobble’ in the instrument by scanning a 4” (1 1 1) Si wafer and assuming that the Si wafer was perfect and attributing the variations in the measurements to instrumental error. The x-ray measurements are correlated with a cross polar image, etch pit density map, white beam transmission x-ray topograph, and a laser light scan.