Materials Science Forum Vols. 615-617

Abstract: A novel method for growing highly-crystalline 3C-SiC on an oxide release layer via a poly-Si seed layer is reported. Silicon carbide’s potential role as a ubiquitous material for MEMS fabrication lies in its dual role as an electronic and mechanical material. Unfortunately, due to residual stresses and crystal defects stemming from the large lattice constant mismatch and the thermal expansion coefficient difference between SiC and Si, the use of SiC in Si-based MEMS fabrication techniques has been very limited. The growth of 3C-SiC on a poly-Si seed layer deposited on oxide on (111)Si substrates (i.e., p-Si/ SiO2/(111)Si) provides an alternative fabrication method to expensive, traditional SOI bonding techniques for producing free-standing 3C-SiC MEMS structures. 3C-SiC grown with a poly-Si seed layer on SiO2 should experience reduced residual stress and far fewer defects due to the compliance of the SiO2 layer. Although poly-Si is utilized as a seed layer in this process, a well-ordered monocrystalline 3C-SiC layer was achieved and the process and film properties reported.

Abstract: In order to demonstrate the formation of 3C-SiC film on Si (111) at low substrate temperature, the effects of C3H8 on the crystallinity of the films on Si (111) have been investigated by changing the flow rate of C3H8 at the substrate temperature of 850 °C. Oriented polycrystalline 3C-SiC film grew under the C/Si of 3 – 5 with a-C. It is suggested that etching effects of growing surface by hydrogen radicals generated from C3H8 decomposition is lowered by lowering the substrate temperature. The crystallinity has been investigated by 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: Single-crystalline 3C-SiC epitaxial layers were grown on on-axis Si (001) substrates by low-pressure hot-wall chemical vapour deposition. Aluminium from a trimethylaluminium (TMA) source was used for p-type doping. The atomic Al and carrier concentrations in the layers were determined as a function of the partial pressure of the TMA source gas. Secondary ion mass spectroscopy (SIMS), Hall-effect measurements at room temperature and four-point electrical resistivity method were applied to measure the atomic and electrically active Al concentrations. The crystalline perfection of the layers was characterized by high-resolution x-ray diffraction (HRXRD). At TMA-partial pressures ranging from 510-7 mbar up to 1.510-4 mbar corresponding aluminium concentrations from 21015 cm-3 up to 1.31019 cm-3 were measured in the epitaxial layers. On increasing the Al concentration from 1x1017 cm-3 to 1x1019 cm-3 the layer electrical resistivity decreases from 17 cm to 0.8 cm, while no influence on the crystalline quality of the layers was observed. The average full width at half maximum (FWHM) of the rocking curve for a 5µm thick 3C-SiC layer is about 500 arcsec. With increasing layer thickness (up to 16 µm) the FWHM of the rocking curve decreases to about 300 arcsec.

Abstract: We analyze in detail the evolution of curvature of 3C-SiC layers grown on vicinal silicon substrates. A common feature of (100) and (111) oriented layers is a strongly asymmetric wafer bending that may suggest an anisotropic stress relaxation within the layer. A comparative study of the curvature, lattice parameter, surface morphology and structural defects for the off-angles ranging from 0.5° to 6° is performed in order to confirm or disprove this hypothesis. We find a homogeneous, tensile in-plane lattice deformation. We also show the correlation of the orientation of the high and low curvature axes with the morphology and defect pattern of the layer.

Abstract: The possibility of silicon carbide films production out of organosilicon chlorine-containing monomers is under analysis in this research. Silicon carbide films samples were produced by chemical deposition method out of gas phase in reactor with “cold walls”, in the conditions of low pressure. The influence of monomer type, substrate temperature on crystalline SiC films composition is also under consideration. The results of infrared spectroscopy, Raman scattering spectrometry and x-ray phase analysis are presented.

Abstract: Highly doped p-3C-SiC layers of good crystal perfection have been grown by sublimation epitaxy in vacuum. Analysis of the photoluminescence (PL) spectra and temperature dependence of the carrier concentration shows that at least two types of acceptor centers at ~EV + 0.25 eV and at EV + 0.06-0.07 eV exist in the samples studied. A conclusion is made that layers of this kind can be used as p-emitters in 3C-SiC devices.

Abstract: The present paper deals with morphological and structural investigation of 3C-SiC layers grown by sublimation epitaxy on on axis 6H-SiC(0001) at source temperature 2000 °C, under vacuum conditions (<10-5 mbar) and different temperature gradients in the range of 5-8 °C/mm. The layer grown at a temperature gradient 6 °C/mm has the largest average domain size of 0.4 mm2 assessed by optical microscope in transmission mode. The rocking curve full width at half maximum (FWHM) of (111) reflection is 43 arcsec which suggests good crystalline quality. The AFM image of the same layer shows steps with height 0.25 nm and 0.75 nm which are characteristic of a stacking fault free 3C-SiC surface and c-axis repeat height, respectively.

Abstract: The use of Ge very rich Si-Ge liquid phase during the heteroepitaxial growth of 3C-SiC on Si-face, on-axis 6H-SiC(0001) substrate by vapour-liquid-solid mechanism leads to the formation of Ge based precipitates inside the 3C layer. These Ge based features are investigated by TEM and atomic models of the Ge clustering are proposed by means of high resolution TEM image simulation. Conventional TEM shows only a few small precipitates sparsely distributed near the interface, as well as dislocations and stacking faults starting from the interface in an almost regular manner. High resolution TEM shows fine structural imperfections in the form of Guinier Preston zones also near the interface. It is concluded that the high Ge content creates an enlargement of the SiC lattice leading to a misfit with the substrate. This could be the driving force for the formation of all the observed features.

Abstract: The initial stage of heteroepitaxial growth of 3C-SiC and homoepitaxial growth of 6H-SiC on nominal 6H-SiC on-axis substrates has been studied. Before 3C-SiC starts to nucleate, 6H-SiC grows in a step-flow growth mode due to a slight off-orientation of the substrate surface already at about 1500oC. In the 1650-1700oC temperature interval 3C-SiC nucleates as 2D islands. A distance away from the 3C-SiC island 6H-SiC grows in step-flow mechanism. In the vicinity of the 3C-SiC islands the 6H-SiC growth steps start to change direction and even split into two steps with the equal height of 0.5 nm, which is approaching the unit cell size of cubic SiC. When the supersaturation is lower in comparison with the conditions for 3C-SiC growth, there is only formation of 6H-SiC, i.e. homoepitaxial growth. The growth mode of 6H-SiC is dependent on temperature. At the lowest temperature there is spiral growth while at higher temperature 2D nucleation is preferred.

Abstract: Like on 6H-SiC substrates, 3C-SiC islands precipitation was found to be the initial stage of the VLS growth of 3C-SiC layers on 4H-SiC surfaces. This precipitation happens between 1100 and 1200°C with a heating rate of 2.8°C.s-1, without addition of propane. The islands size increases in a similar manner whether the final temperature increases (for a given heating rate) or the heating rate decreases (for a given final temperature). This enlargement can give rise to a complete cubic layer for the highest temperatures or the slowest heating rates. It is suggested that the carbon atoms involved in the enlargement process (after the nucleation) come from the graphite crucible.