Satoshi Kuroda

Epitaxial growth of high-quality 4H-SiC carbon-face by low-pressure hot-wall chemical vapor deposition

High-quality 4H-SiC Carbon-face (C-face) epitaxial layers have been grown by a low-pressure, horizontal hot-wall type chemical vapor deposition system. A specular surface morphology was obtained at a substrate temperature of about 1600°C and a C/Si ratio of 1.5 or less. The site-competition behavior is observed in the doping process of C-face epitaxial growth at a low pressure of 250 mbar and C/Si ratios between 0.6 and 3. The lowest residual donor concentration of 7 ×1014 cm-3 is obtained at a C/Si ratio of 3. The optimal conditions for growing a C-face epitaxial layer having both a good surface morphology and reduced residual impurity concentration are discussed.

Effect of Additional Silane on In Situ H2 Etching prior to 4H-SiC Homoepitaxial Growth

We have investigated the influence of in-situ H2 etching on the surface morphology of the 4H-SiC substrate prior to homoepitaxial growth. In this study, we varied the types of gas atmosphere during in-situ H2 etching; namely, hydrogen (H2) alone, hydrogen-propane (H2+C3H8), and hydrogen-silane (H2+SiH4). We found that in-situ H2 etching using H2 + SiH4 significantly improved the surface morphology of 4H-SiC substrate just after in-situ H2 etching. By adding SiH4, formation of bunched step structure during in-situ H2 etching could be significantly suppressed. In addition, H2 etching using H2 + SiH4 was able to remove scratches by etching a thinner layer than that using H2 alone. We also discussed the in-situ H2 etching mechanism under the additional SiH4 condition.

Nitrogen incorporation characteristics on a 4H-SiC epitaxial layer

The N incorporation characteristics on a 4H-SiC epitaxial layer were reinvestigated. It was found that the desorption process and thermally activated process are aspects of the N incorporation mechanism of 4H-SiC to which attention should be paid. This mechanism depends on both the rate-limiting condition and lattice polarity. The N desorption process dominates the N incorporation of the Si-face under the C-supply-limiting condition and that of the C-face without recourse to the rate-limiting condition. On the other hand, the thermally activated process dominates only the N incorporation of the Si-face under the Si-supply-limiting condition. The site-competition phenomenon was also found to depend on the rate-limiting condition.

2-Inch 4H-SiC Homoepitaxial Layer Grown on On-Axis C-Face Substrate by CVD Method

Homoepitaxial growth was carried out on 4H-SiC on-axis substrate by horizontal hot wall chemical vapor deposition. By using carbon face substrate, specular surface morphology of a wide area of up to 80% of a 2-inch epitaxial wafer was obtained at a low C/Si ratio growth condition of 0.6. The Micropipe in on-axis substrate was indicated to be filled with spiral growth and to be dissociated into screw dislocations during epitaxial growth. It was found that the appearance of basal plane dislocations on the epitaxial layer surface can be prevented by using an on-axis substrate.

4H-SiC Carbon-Face Epitaxial Layers Grown by Low-Pressure Hot-Wall Chemical Vapor Deposition

4H-SiC Carbon-face (C-face) epitaxial layers have been grown by a low-pressure, horizontal hot-wall type chemical vapor deposition system. The site-competition behavior is observed in the doping process of the C-face epitaxial growth. This site-competition behavior depends on the growth pressure. Specular surface was obtained at a substrate temperature of 1600C and C/Si ratios less than 3 with a buffer layer grown by the C/Si ratioof 0.6. The residual donor concentration decreases with lowering the growth pressure. The lowest residual donor concentration of 2x10 14 cm -3 was obtained on an epitaxial layer grown at a C/Si ratio of 3 and a growth pressure of 60 mbar. Hall effect measurement indicates grown C-face epitaxial layers have the crystalline quality as high as that of the Si-face epitaxial layer. The electron mobility of the obtained C-face epitaxial layer with Nd-Na = 1 x10 15 cm -3 was 956 cm 2 /Vs at 293 K and 41700 cm 2 /Vs at 40 K.

Investigation of In-Grown Dislocations in 4H-SiC Epitaxial Layers

We have investigated the generation of new dislocations during the epitaxial growth of 4H-SiC layers. Dislocations were mainly propagated from the substrate into the epitaxial layer. However, it was found that some amount of new threading edge dislocations (TEDs) and basal plane dislocations (BPDs) were generated during the epitaxial growth. The generation of those dislocations appeared to depend on the in-situ H2 etching conditions, not the epitaxial growth conditions. By optimizing in-situ H2 etching condition, we were able to effectively suppress the generation of new dislocations during epitaxial growth, and obtain 4H-SiC epitaxial layers which have the equivalent etch pit density (EPD) to the substrates. Our additional investigation of the conversion of BPDs to TEDs revealed that its efficiency similarly depends on in-situ H2 etching. We were able to obtain a high conversion efficiency of 97 % by optimizing the in-situ H2 etching conditions before epitaxial growth.