Materials Science Forum Vol. 924

Abstract: Si_0.56Cr_0.4M_0.04 (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Rh, and Pd) solvents were investigated to identify new multi-component materials in which carbon is highly soluble, because solubility is a key parameter in solution growth of SiC. The solubility of carbon in Si_0.56Cr_0.4Co_0.04 was 8.37 at%, the highest value among the tested multi-component materials. This is about 2.5 times the solubility of carbon in Si_0.6Cr_0.4. These results show that addition of a small amount of a transition metal enhanced the solubility of carbon in Si_0.6Cr_0.4. This technique for determining carbon solubility is effective for investigating crystal growth using solvents with several components, for which complex thermodynamic calculations are necessary.

Abstract: The modified crucible in the top seeded solution growth (TSSG) method was proposed to get the stable growth condition and the enhanced growth rate. The temperature gradient and the distribution of dissolved carbon in the solvent were obtained by numerical approaches. Compared simulation results and experiment, we investigated the region where is the most of dissolved carbon and it is supplied to the seed through what path. The cross-sectional samples of crucibles and grown SiC crystals were systematically analyzed to investigate the effect of the crucible modification on SiC crystal growth.

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 investigated the dependence of the macrostep height on various additives in solution growth of n-type 4H-SiC. Surface modification by adding transition elements in periods 4‒6 (Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Y, Nb, Mo, Ce, and W) and group 13‒14 elements (B, Al, Ga, Ge, Sn) was systematically studied to find additives improving smoothness of the growth surface. We found that Sc, Co, Mo, and Ge improved surface smoothness in addition to the already-known additives, such as Al, B, and Sn. Besides, these additives (Sc, Co, Mo, Ge) give no measurable influence on the conductivity of n-type grown crystals. These results demonstrated that Sc, Co, Mo, Ge and Sn are useful additives for solution growth of n-type 4H-SiC.

Abstract: We achieved the growth of extremely-high quality SiC crystal with two-step solution method with specially-designed seed crystals. The two-step growth consists of 1^st step growth on Si-face for the reduction of threading dislocations and 2^nd step growth on C-face for the reduction of basal plane dislocations and thickening. In this method, we can make the dislocation density extremely low, while the polytype easily changes during growth due to the absence of spiral hillocks originating from threading screw dislocation (TSD). In this study, we prepared specially designed seed crystals for both 1^st and 2^nd growth steps to provide steps continuously. In the seeds, a few TSDs exist at the upper-side of the step structure. Consequently, we demonstrated the suppression of the polytype transformation during the C-face growth with extremely low-dislocation-density crystal. Accordingly, we successfully obtained extremely low-dislocation density 4H-SiC with TSD, TED and BPD density of 11, 385 and 28 cm^-2.

Abstract: SiC-powered devices which reduce the power loss, size, and weight of power converters are gradually appearing in the power electronics market. From now on, cost reduction and quality improvement of SiC epitaxial wafers is required to further increase their popularity. This paper describes the state of development of mass production of the epi-wafer at Showa Denko K. K.

Abstract: Epitaxial growth of 4H-SiC on 150 mm wafers has been investigated using experimental results and numerical simulations toward the goal of BPDs reduction and doping uniformity control in the epitaxial layer. We have reported analyses of the temperature distribution dependence of the doping uniformity and BPDs propagations on the 3 x 150 mm multi-wafer CVD epitaxial growth. By optimizing epitaxial growth conditions, we have demonstrated an excellent doping and thickness uniformity and a 99.9% BPD free region, simultaneously.

Abstract: In this work we report the latest epitaxial growth of 150 mm 4H-SiC on 4° off-axis substrates by a commercial hot-wall reactor. A statistical analysis of more than 300 runs with an epi thickness range of 6μm~15μm shows that the average uniformities of the thickness and the doping concentration are 1.34% (sigma/mean) and 3.90% (sigma/mean), respectively, and the average 2 mm x 2 mm projected device yield is 97.79%. The growths of ~60 μm-thick 150 mm 4H-SiC epitaxial layers have also been carried out. The repeatability of this system for thick epitaxial layer growth has been verified, showing a run-to-run uniformity similar to that of the thin wafers. These results of 150 mm 4H-SiC epitaxial growths indicate that this comercial hot-wall reactor has the potential for mass production of large diameter 4H-SiC epitaxial wafers.

Abstract: The glide of basal plane dislocations (BPDs) during 150 mm 4H-SiC epitaxial growth by a hot-wall reactor is characterized, and its formation mechanisms are discussed. The reason for the glide of BPDs during 150 mm 4H-SiC epitaxial growth is believed to be due to the strain related to the strain originally in the 150 mm substrate and the strain generated during the epitaxial growth. After the epitaxial growth process is optimized, it is possible to suppress the glide of BPDs, as a result of the effective relaxation of the strain.

Abstract: In this work the deposition of buffer layer has been studied in order to increase the quality of the epitaxial layer and improve the performance of device. The comparison between two different thicknesses of buffer layer reveals a decrease of crystallographic defects and an improvement of electrical parameters of MOSFET device as leakage current and breakdown voltage.