Reducing warpage of thick 4H-SiC epitaxial layers by grinding the back of the substrate

Abstract

We grew 3 inch thick 4H-SiC epitaxial layers on the substrate Si-face, and attempted warpage reduction. The substrates were coved by grinding their C-face before the epitaxial growth to cancel out the increase in convex warpage due to the epitaxial growth. We found that the amount of convex warpage change was approximately 26 μm, when the thickness of the epitaxial layer was 200 μm. To reduce warpage, we prepared the substrate with concave warpage of about 27 μm by grinding the C-face, whose roughness was 60 nm. Then, we grew an epitaxial layer of 200 μm thickness on this and we succeeded in reducing the warpage to 5 μm. We concluded that the warpage of thick epitaxial layers on the substrates can be reduced by controlling the roughness of the ground back side, in accordance with the estimated amount of warpage change from the objective thickness of the epitaxial layers.