Papers by Keyword: Polytype

Abstract: The increasing demand for WBG materials like SiC has led STMicroelectronics to expand wafer diameter from 150 mm to 200 mm, enhancing production yield and reducing costs. However, this expansion poses challenges in preserving crystalline quality. This investigation examines the impact of defects on 200 mm wafers, focusing on Total Usable Area (TUA) and electrical performance, particularly in wafers with polytype inclusions and high basal plane dislocation (BPD) density. Although the results for non-standard wafers show a significant reduction in TUA and an increase in electrical failures, the overall distribution of functional and non-functional devices remains stable, indicating process consistency.

Abstract: In the last decade, silicon carbide (SiC) has gained a remarkable position among wide bandgap semiconductors due to its high temperature, high frequency, and high power electronics applications. SiC heterostructures, based on the most prominent polytypes like 3C-SiC, 4H-SiC and 6H-SiC, exhibit distinctive electrical and physical properties that make them promising candidates for high performance optoelectronic applications. The results of simulations of nn-junction 3C-4H/SiC and 6H-4H/SiC heterostructures, at the nanoscale and microscale, are presented in this paper. Nanoscale devices are simulated with QuantumWise Atomistix Toolkit (ATK) software, and microscale devices are simulated with Silvaco TCAD software. Current-voltage (IV) characteristics of nanoscale and microscale simulated devices are compared and discussed. The effects of non-ideal bonding at the heterojunction interface due to lattice misplacements (axial displacement of bonded wafers) are studied using the ATK simulator. These simulations lay the groundwork for the experiments, which are targeted to produce either a photovoltaic device or a light-emitting diode (working in the ultraviolet or terahertz spectra), by direct bonding of SiC polytypes.

Abstract: SiC crystals are grown using a Si-Cr-based solvent by a top-seeded solution growth (TSSG) method by changing the dipping time after when the growth temperature is reached. Step-flow-like curve morphologies were observed for a dipping time after 15 min, while polycrystallization occurred at the periphery for that after 120 min, which corresponded to the dipping under unsaturated and supersaturated carbon in the solvent, respectively. Furthermore, the solution growth of SiC with dipping under unsaturated carbon was easily realized by the growth from the crucible bottom, step-flow-like growth was achieved. Using this technique, dominant polytypes of SiC in various growth conditions after stable seed dipping under the unsaturation in the solvent can be demonstrated.

Abstract: We have succeeded in solution growth of SiC from Cr solvent without Si using ceramic SiC as the SiC source. The effect of the growth conditions, such as the liquid height in the crucible, on the crystal quality in solution growth of SiC from Cr solvent was investigated. For a liquid height in the crucible of up to 10 mm, the growth rate increases with increasing liquid height and the SiC crystals are a single polytype, while the growth rate decreases and the crystals are polycrystalline for a liquid height above 10 mm. In the former case, the balance between dissolution and transportation of the solute are comparable. The latter case is expected to be transportation limited because transportation of free C and Si atoms is inhibited by excrescent crystals in solution and the increase in the distance for solute transportation. In addition, a higher growth temperature leads to growth of only 4H-SiC.

Abstract: A competitive lattice model was developed for the Kinetic Monte Carlo (KMC) simulation of the competition of 4H and 6H polytypes in SiC crystal growth based on the on-lattice model. In the competitive lattice model, site positions are fixed at the perfect crystal lattice positions without any adjustment of the site positions. The effect of surface steps was investigated, and behavior similar to step-controlled homoepitaxy was observed in KMC simulation of PVT grown SiC. Maintaining the step growth mode is an important factor to maintain a stable single polytype during SiC growth.

Abstract: Raman spectroscopy is a well established non-destructive tool for determining crystal polytypes, strain/stress, electronic properties and material quality in SiC. Here we report on the application of ultrafast Raman imaging to a SiC wafer, allowing 870,908 spectra to be collected from a 2 inch 4H-SiC wafer, in 75 minutes. Analysis of the acquired data enabled us to locate and investigate defects and surface contamination and also allowed stress in the wafer to be characterised.

Abstract: Synchrotron white beam x-ray topography (SWBXT), synchrotron monochromatic beam x-ray topography (SMBXT), and high resolution transmission electron microscopy (HRTEM) studies have been carried out on stacking faults in PVT grown 4H-SiC crystal. Their fault vectors were determined by SWBXT to be 1/3<-1100>, 1/2<0001>, 1/6<-2203>, 1/12<4-403>, 1/12<-4403>. HRTEM studies reveal their similarity in stacking sequences as limited numbers of bilayers of 6H polytype structure. Simulation results of the two partial dislocations associated with the stacking faults in SMBXT images reveal the opposite sign nature of their Burgers vectors. A mechanism for stacking fault formation via 2D nucleation is postulated.

Abstract: In this paper we used three dimensional kinetic Monte Carlo simulations on super-lattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on hexagonal 6H-SiC substrates with miscuts towards the <11-20> and <1-100> directions. We analyze the grown film for different miscut angles (in the range 2° to 12° degrees) and different growth rates, finding that substrates with miscut of 3-4° degrees towards the <1-100> direction should be the best choice for the growth of high quality cubic epitaxial films, being able to promote, given a suitable pre-growth treatment to induce step bunching, the nucleation of single domain 3C-SiC films.

Abstract: We have investigated key factors for controlling the polytype and surface morphology of 4H-SiC homoepitaxial growth on less than 4^o off-axis substrates. In addition, we characterized the crystal quality and surface quality of the epitaxial layer of an entire 3-inch vicinal off angled substrate. The results suggested that the control of surface free energy, control of the vicinal off angle itself, and high temperature growth, is highly important in controlling the surface morphology and polytype stability of the epitaxial layer grown on a vicinal off angled substrate. We also obtained a high-quality epitaxial layer grown on a 3-inch vicinal off angle substrate, which was comparable to those on 4^o off-axis substrates.

Abstract: The study compared the influences of silicon materials from different sources on the crystal growth process and geometry of silicon carbide (SiC). As revealed by the results of the study, although the purity of commercial silicon material was as high as 11N, the rate of crystal growth was slow. However, if the silicon material made by electron beam refining metallurgical silicon was utilized for the SiC crystal growth experiment, the morphology of SiC crystal was better and the rate of crystal growth was faster despite its purity being only about 4.5N.