Materials Science Forum Vols. 527-529

Abstract: A new technique that reduces stacking fault (SF) density in 3C-SiC, termed switch-back epitaxy (SBE), is demonstrated regarding its effects on morphological and electrical properties. SBE is a homoepitaxial growth process on backside of 3C-SiC grown on undulant-Si. The key feature of SBE, the surface polarity of residual SFs in 3C-SiC, which cannot be erased by heteroepitaxial growth on undulant-Si, is converted from the Si-face to the C-face. The SF density on the surface of 3C-SiC grown by SBE shows a remarkable decrease to one-seventh lower than that on undulant- Si. The leakage current of pn-diode epitaxially fabricated on the 3C-SiC substrate grown by SBE decreases to as low as one-thirtieth that on 3C-SiC substrate grown without SBE. These results suggest that SBE eliminates the SFs on the surface of 3C-SiC and subsequently reduces the leakage current at pn-junction thus fabricated.

Abstract: Flash lamp annealing of multilayer stack of the type SiC/Silicon overlayer(SOL)/SiC reduces the defect densities in the 3C-SiC/Si heteroepitaxial structure. Ge and C additions to the SOL lead to a substantial increase of the mass transfer from the upper layer to the lower SiC layer. If the Ge content of the SOL and the flash lamp annealing conditions are properly chosen a homogeneous layer with a 3C-SiC thickness between 150 and 200 nm can be achieved corresponding to a growth rate between 7.5 and 10.0 +m/s. The thickening of the lower layer depends on the SOL composition. Ge and/or C incorporation into the SOL and therefore into the Si melt enhances the mass transport from the upper SiC layer to the lower one.

Abstract: 3C-SiC films grown on carbonized Si (100) by plasma-assisted CVD have been investigated with systematic changes in flow rate of monosilane (SiH4) and propane (C3H8) as source gases. The deposition rate of the films increased monotonously and the microstructures of the films changed from 3C-SiC single crystal to 3C-SiC polycrystal with increasing flow rate of SiH4. Increasing C3H8 keeps single crystalline structure but results in contamination of α-W2C, which is a serious problem for the epitaxial growth. To obtain high quality 3C-SiC films, the effects of C3H8 on the microstructures of the films have been investigated by reducing the concentration of C3H8. Good quality 3C-SiC single crystal on Si (100) is grown at low net flow rate of C3H8 and SiH4, while 3C-SiC single crystal on Si (111) is grown at low net flow rate of C3H8 and high net flow rate of SiH4. It is expected that 3C-SiC epitaxial growth on Si (111) will take placed at a higher deposition rate and lower substrate temperature than that on Si (100).

Abstract: Selective epitaxial growth (SEG) of cubic silicon carbide (3C-SiC) was carried out on patterned Si (100) substrates using SiO2 as a mask. The growth was performed by atmospheric pressure chemical vapour deposition in a resistance-heated furnace using hexamethyldisilane (HMDS) as the source. It was observed that voids are the major defect in the case of heteroepitaxial growth of 3C-SiC on Si. Using selective epitaxial growth, the density of voids was reduced. Lateral epitaxial overgrowth (LEO) was achieved at selected areas where windows are arrays of stripes. The effect of temperature, window shape and size, precursor concentration, etc. on the SEG of SiC has been studied. After growth, films have been characterized by Nomarski optical microscopy, SEM, Raman spectroscopy and AFM. Faceted growth was observed along (111) planes inside smaller windows. Raman spectroscopy was used to identify defects and the presence of other polytypes.

Abstract: A hetero-epitaxial 3C-SiC growth process in a low-pressure hot-wall CVD reactor has been developed on planar Si (100) substrates. The growth rate achieved for this process was about 10 μm/h. The process consists of silane/propane/hydrogen chemistry with HCl used as a growth additive to increase the growth rate. 3C-SiC has also been grown on 22, 52 and 123 +m deep etched MEMS structures formed by DRIE of (100) Si at a rate of about 8 +m/h. Secondary electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) were used to analyze the quality of the 3C-SiC films.

Abstract: This paper reports the effect of deposition temperature on the deposition rate, residual stress, and resistivity of in-situ nitrogen-doped (N-doped) polycrystalline 3C-SiC (poly-SiC) films deposited by low pressure chemical vapor deposition (LPCVD). N-doped poly-SiC films were deposited in a high-throughput, resistively-heated, horizontal LPCVD furnace capable of holding up to 150 mm-diameter substrates using SiH2Cl2 (100%) and C2H2 (5% in H2) precursors, with NH3 (5% in H2) as the doping gas. The deposition rate increased, while the residual stress decreased significantly as the deposition temperature increased from 825oC to 900°C. The resistivity of the films decreased significantly from 825°C to 850°C. Above 850°C, although the resistivity still decreased, the change was much smaller than at lower temperatures. XRD patterns indicated a polycrystalline (111) 3C-SiC texture for all films deposited in the temperature range studied. SIMS depth profiles indicated a constant nitrogen atom concentration of 2.6×1020/cm3 in the intentionally doped films deposited at 900°C. The nitrogen concentration of unintentionally doped films (i.e., when NH3 gas flow was zero) deposited at 900°C was on the order of 1017/cm3. The doped films deposited at 900°C exhibited a resistivity of 0.02
-cm and a tensile residual stress of 59 MPa, making them very suitable for use as a mechanical material supporting microelectromechanical systems (MEMS) device development.

Abstract: The main obstacle for the implementation of numerical simulation for the prediction of the epitaxial growth is the variety of physical processes with considerable differences in time and spatial scales taking place during epitaxy: deposition of atoms, surface and bulk diffusion, nucleation of two-dimensional and three-dimensional clusters, etc. Thus, it is not possible to describe all of them in the framework of a single physical model. In this work there was developed a multi-scale simulation method for molecular beam epitaxy (MBE) of silicon carbide nanostructures on silicon. Three numerical methods were used in a complex: Molecular Dynamics (MD), kinetic Monte Carlo (KMC), and the Rate Equations (RE). MD was used for the estimation of kinetic parameters of atoms at the surface, which are input parameters for other simulation methods. The KMC allowed the atomic-scale simulation of the cluster formation, which is the initial stage of the SiC growth, while the RE method gave the ability to study the growth process on a longer time scale. As a result, a full-scale description of the surface evolution during SiC formation on Si substrates was developed.

Abstract: Under forward bias bipolar 4H- and 6H-SiC devices are known to degrade rapidly through stacking fault formation and expansion in the basal plane. It is believed that the ob- served rapid stacking fault growth is due to a recombination-enhanced dislocation glide (REDG) mechanism at the bordering partial dislocations. This degradation phenomenon has generated considerable interest in the involved dislocations — in particular in their atomic and electronic structure, but also in the mechanisms of their glide motion. Fortunately, nowadays advances in computing power and in theoretical methodology allow the ab initio based modelling of some aspects of the problem. This paper therefore gives a brief review of recent activities in this field, and further discusses some general problems of ab initio based modelling of dislocations in compound semiconductors.

Abstract: Structure of the “carrot” defects in 4H-SiC homoepitaxial layers deposited by CVD has been investigated by plan-view and cross-sectional transmission x-ray topography, cross-sectional transmission electron microscopy, atomic force microscopy, and KOH etching. The carrot defects nucleate at the substrate/epilayer interface at the emergence points of threading screw dislocations propagating from the substrate. The typical defect consists of two stacking faults: one in the prismatic plane with second one in the basal plane. The faults are connected by a stair-rod dislocation with Burgers vector 1/n[10-10] with n>3 at the cross-over. The basal plane fault is of Frank-type. Carrot defects are electrically active as evidenced by contrast in EBIC images indicating enhanced carrier recombination rate. Presence of carrot defects in the p-i-n diodes results in higher pre-breakdown reverse leakage current and approximately 50% lower breakdown voltage compared to the nominal value.

Abstract: Raman spectroscopy using deep UV (DUV) light excitation has been applied to characterizing process-induced defects in surface layers in SiC. Raman spectra of P+-ion implanted and post annealed SiC have been measured as a function of dose level and annealing temperature. The recovery of the crystallinity and electrical activity have been evaluated. Precipitation of excess phosphorus was found in heavily doped specimens. High dose implanted and post annealed samples show uneven distribution of residual defects, which is demonstrated by mapping of Raman bandwidth. Damage in 4H-SiC surfaces, which were mechanically polished with various sizes of abrasives, has been evaluated from DUV micro-Raman measurements. The Raman analysis demonstrates that bandwidth and peak frequency can be used as monitors of the polish–induced damage. It is found that localized defects reducing free carrier density remain even after polishing with small sized abrasives.