Taro Nishiguchi

Heteroepitaxial growth of (111) 3C–SiC on well-lattice-matched (110) Si substrates by chemical vapor deposition

Heteroepitaxial growth of 3C–SiC on (110) Si substrates by chemical vapor deposition was carried out, and the grown epitaxial layers were investigated by high resolution transmission electron microscopic (HRTEM) analysis. The interface structure between 3C–SiC and Si substrates depended on the flow rate of C3H8 during the carbonization process. In the case of the growth under C3H8=0.4 sccm, the interface was flat and 3C–SiC layer was grown epitaxially on (110) Si substrate in a well-lattice-matched relationship of (110) Si//(111) 3C–SiC and [110] Si//[110] 3C–SiC. In contrast, the interface was rough under C3H8=1.2 sccm and polycrystalline 3C–SiC grew without epitaxial relationship to the substrate. HRTEM observations revealed that an atomically flat (110) Si substrate surface is significant in order to grow high quality 3C–SiC with suppressing the generation of stacking faults.

Nondestructive Analysis of Propagation of Stacking Faults in SiC Bulk Substrate and Epitaxial Layer by Photoluminescence Mapping

The effectiveness of room-temperature photoluminescence (PL) mapping was demonstrated for nondestructive detection of in-grown stacking faults in off-axis 4H-SiC bulk substrates and epitaxial layers. The use of a deep-UV light excitation is essential to detect the stacking fault related intensity pattern in the bulk substrates because of its shallow penetration depth. A bar-shaped PL intensity pattern agreed well with the etch-pit pattern due to the stacking faults in the bulk substrate. The expansion length of the bar pattern from a bulk substrate to an epitaxial layer corresponded to the projected width of basal plane in the epitaxial layer. These results allowed us to analyze the stacking faults propagated from the bulk substrate to the epitaxial layer.

Structural Analysis of (211) 3C-SiC on (211) Si Substrates Grown by Chemical Vapor Deposition

CVD of 3C-SiC on (211), (100) and (111) Si substrates was carried out with the source gases of HCDS and C3H8. The C/Si ratio for single crystal growth was established for each substrate orientation. Crystallographic orientation between 3C-SiC and Si on (211), (100) and (111) substrates respectively was identical. Surface morphology of as-grown (211) 3C-SiC exhibited stepbunching, which suggests that the step-flow growth is dominating. (100) and (111) nano-facets were generated alternately on (211) substrates, which is named as “nano-undulation” structure. It is a selfarranged structure, and it enabled the crystals to grow in step-flow growth on (211) substrates. Stacking faults on (211) substrates canceled more effectively than that on (100) and/or (111) substrates, which is also due to the nano-undulation structure on (211) substrates. It is suggested that CVD growth on (211) substrates with vicinal off-angles toward [011, ] or [01, 1] is effective to reduce stacking fault density.

Suppression Mechanism of Double Positioning Growth in 3C-SiC(111) Crystal by Using an Off-Axis Si(110) Substrate

Hetero-epitaxial CVD growth of 3C-SiC on a Si(110) substrate gives a (111) crystal with low defects density. However, double positioning growth often disturbs growth of a single crystal. The growth on an off-axis Si(110) substrate suppressed propagation of the double positioning defects in the grown layer effectively. Cross-sectional transmission electron microscopy revealed the details of the suppression process on the off-axis substrate. The suppression mechanism and the origin of the defects formation at double positioning boundaries were interpreted by the growth model based on an anisotropic growth rate on (111) plane of 3C-SiC.

Thermal Etching of 6H–SiC Substrate Surface

Thermal etching was investigated as one of the methods of obtaining atomically flat surfaces of SiC substrates. The formation of a graphite layer on substrate surface was suppressed by reducing the C/Si ratio in the vapor phase. Although (1120) substrates etched in argon atmosphere had round pits on their surface, such pits were not observed and an atomically flat surface with an RMS roughness of approximately 0.3 nm was obtained in nitrogen atmosphere even at the high etching rate of 250 µm/h. The substrates with higher nitrogen concentrations had both higher surface flatness and higher etching rate. The thermal etching method was found to be an effective technique for obtaining the flat surface of SiC substrates that is suitable for crystal growth and/or device fabrication. The etching mechanisms of (0001) and (1120) surfaces were compared, and the result was discussed by taking into consideration the bond configuration on the surface.

Growth of Micropipe Free Crystals on 4H-SiC {03-38} Seeds

Growth of 4H-SiC bulk crystals on 4H-SiC {03-38} seeds was done. 4H-SiC {03-38} is obtained by inclining the c-plane toward <01-10> at a 54.7 degrees angle. Growth on the 4H-SiC {03-38} seed has the potential to achieve high quality crystals without micropipes and stacking faults. Micropipe-free c-plane 4H-SiC wafers were achieved by growth on the 4H-SiC {03-38} seed. A transmission X-ray topograph image of the micropipe free c-plane wafer revealed that there are no macroscopic defects with displacements.

Suppression of the Twin Formation in CVD Growth of (111) 3C-SiC on (110) Si Substrate

Chemical vapor deposition of (111) 3C-SiC on (110) Si substrate was carried out, and the effect of the substrate off-axis introduced on (110) Si substrate for suppressing the twin formation in 3C-SiC hetero-epitaxial layers was investigated. From the growth on hemispherically polished (110) Si substrate, it was found that the off-axis toward the [001] Si axis had a noble effect for suppressing the twin formation, while the off-axis toward the [110] Si axis was ineffective. The growth of single 3C-SiC crystal containing few double positioning boundaries, which are related with the twin formation, was demonstrated on the (110) Si substrate 3° off-axis toward the [001] Si axis. Transmission electron microscopic observation revealed that double positioning boundaries on the (110) Si substrate off-axis toward the [001] Si axis were nearly eliminated within the initial a few hundreds nano meter in thickness.

A proposal for CVD growth of 15R-SiC by observing the etch pits on 15R-SiC C-face

Abstract As grown Acheson crystals of 15R-SiC and 6H-SiC were etched by molten KOH. Etch pits peculiar to each polytype were observed both on C-face and Si-face of etched crystals. The inside of etch pit on the C-face was flat. Etch pits on 6H-SiC showed six-fold symmetry, and etching rate toward six equivalent 〈1 1 2 0〉 was the fastest. In case of 15R-SiC, etching rate toward [1 1 0 0] was faster than that of [ 1 1 0 0] , and etch pits showed three-fold symmetry. Etching rate anisotropy between [1 1 0 0] and [ 1 1 0 0] of 15R-SiC was explained by the number of dangling bonds per edge atom. Though the chemical vapor deposition (CVD) growth of 15R-SiC has been conducted on Si-face 8.0° off-oriented toward 〈1 1 2 0〉 , [1 1 2 0] and [ 11 2 0] might not be equivalent in 15R-SiC. If the crystal grew at near-equilibrium condition, the difference between off-orientation toward [1 1 2 0] and [ 11 2 0] might become obvious. Further research is necessary for the CVD growth of 15R-SiC to achieve high quality crystals.

Lateral Epitaxial Overgrowth of 3C-SiC on Si Substrates by CVD Method

Lateral epitaxial overgrowth (LEO) is known as method of defects reduction for GaN. LEO is expected to reduce crystal defects on hetero-epitaxial growth of 3C-SiC. (100) Si substrate patterned with SiO2 mask was used as the substrate. Before CVD process, V shape crater was made on Si surface by HCl etching. And growth condition of CVD was optimized. Single crystal of 3C-SiC was grown laterally on SiO2 layer. Cross-sectional transmission electron microscopic observation indicated that crystal quality of LEO region was single and no defect crystal.

Influence of Substrate Roughness on the Formation of Defects in 3C-SiC Grown on Si(110) Substrate by Hetero-Epitaxial CVD Method

Interfaces between a Si(110) substrate and 3C-SiC crystals grown hetero-epitaxially by CVD were investigated by cross-sectional transmission electron microscopy. Gas flow condition during the carbonization process affects the roughness of the substrate surface and there is an optimum condition to preserve the flat surface. High quality 3C-SiC crystals grew only on the flat substrate, with crystallographic relationship of Si[1-10]//SiC[1-10] and Si[001]//SiC[1-1 - 2], because the well-lattice-match relationship was limited in a two-dimensional region at the SiC(111)/Si(110) interface. Using the optimum condition, some kinds of roughness at an atomic scale remained on the surface of the substrate. Nanoscopic observation of the crystals grown on an off-axis substrate revealed the influence of the roughness on the epitaxial growth and the defects generation at the interface.