SiC homoepitaxial layers grown on substrates with vicinal off-angle (epi-layers with vicinal off-angle) are effective for suppressing anisotropy of SiC trench devices. Step bunching, however, is easily generated on the substrates with vicinal off-angle during increase in temperature at H₂ atmosphere prior to the growth of the epi-layers. It is indispensable to suppress the generation of step bunching during increase in temperature in order to improve the surface morphology of the epi-layers with vicinal off-angle. It is thought that the etching reactions between the surface of the substrates and H₂ gas should be suppressed in order to suppress the generation of step bunching. In this study, we have investigated the process for suppressing the etching reactions during increase in temperature prior to the growth of the epi-layers.

We used the 4H-SiC Si-face substrates with vicinal off-angle (0.9 deg.). The etching process was conducted in a horizontal hot-wall CVD reactor at a temperature of 1660 °C and a pressure of 10.3 kPa for 1 min. It has been reported that the etching rate is lowered by adding a source gas such as SiH₄ and C₃H₈ and by reducing the flow rate of H₂ [1,2]. Therefore, we investigated the effects of adding SiH₄ and C₃H₈ and of reducing the flow rate of H₂ on the etching depth and the generation of step bunching.

Firstly, we observed a substrate etched by using H₂ of 100 slm. The etching depth was estimated at 7 nm. It has been reported that basal plane dislocations generate giant step bunching with finite length which is called short step bunching (SSB) [3]. We found that SSB, whose height and length was over 5 nm and about 1 mm, respectively, was generated on the substrate. The density of SSB generated on the substrate was about 200 cm^-2. Secondly, we investigated substrates etched by adding each of SiH₄ and C₃H₈. The etching depth of the substrate was decreased to 3-4 nm by adding each of SiH₄ and C₃H₈. The density of SSB was not reduced by adding C₃H₈ but reduced by adding SiH₄. It is thought that both the reduction of the etching depth and the etching in an Si-rich environment are important for suppressing the generation of SSB. Finally, we tried to suppress the etching reactions by reducing the flow rate of H₂ added by SiH₄. The etching depth was decreased to 1 nm by reducing the flow rate of H₂ to 30 slm. As a result, the density of SSB was decreased to 16 cm^-2 as shown in the Figure.

We have found that the etching reactions between the SiC substrates with vicinal off-angle and H₂ gas were suppressed by adding SiH₄ and reducing the flow rate of H₂ at once. As a result, we have succeeded in drastically decreasing the density of SSB. We will present the detail of the differences between the addition of SiH₄ and that of C₃H₈, and the growth of epitaxial layers using this process at the conference.

Acknowledgement

This work is supported by Novel Semiconductor Power Electronics Project Realizing Low Carbon Emission Society under New Energy and Industrial Technology Development Organization (NEDO).

References

[1] K. Kojima et.al., Mater. Sci. Forum 556-557 (2007) 85.

[2] J. Zhang et.al., Mater. Sci. Forum 389-393 (2002) 239.

[3] K. Tamura et.al., Ext. Abstr. 21^st Meeting on SiC and Related Wide Bandgap Semiconductors (2012) 6 [in Japanese].

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