Abstract
A thin, chemically inert 3C-SiC layer between GaN and Si helps not only to avoid the “melt-back” effect, but also to inhibit the crack generation in the grown GaN layers. The quality of GaN layer is heavily dependent on the unique properties of the available 3C-SiC/Si templates. In this paper, the parameters influencing the roughness, crystalline quality, and wafer bow are investigated and engineered to obtain high quality, low roughness 3C-SiC/Si templates suitable for subsequent GaN growth and device processing. Kinetic surface roughening and SiC growth mechanisms, which depend on both deposition temperature and off-cut angle, are reported for heteroepitaxial growth of 3C-SiC on Si substrates. The narrower terrace width on 4° off-axis Si enhances the step-flow growth at 1200 °C, with the roughness of 3C-SiC remaining constant with increasing thickness, corresponding to a scaling exponent of zero. Crack-free 3C-SiC grown on 150-mm Si substrate with a wafer bow of less than 20 μm was achieved. Both concave and convex wafer bow can be obtained by in situ tuning of the deposited SiC layer thicknesses. The 3C-SiC grown on off-axis Si, compared to that grown on on-axis Si, has lower surface roughness, better crystallinity, and smaller bow magnitude.
Highlights
GaN grown on 3C-SiC/Si templates, the thickness, roughness, off-cut angle, and wafer bow of the SiC/Si template need to be carefully selected
For SiC grown on on-axis Si, the SiC surface roughness is found to increase with thickness
Due to the mismatch in lattice constant and thermal expansion coefficients, the grown SiC layer has a tensile residual stress after cooling the samples to room temperature, which is more pronounced for the thicker SiC layer, resulting in the wafer always bending towards the thicker SiC coated side. These results demonstrate that the wafer bow shape can be tuned by adjusting the SiC layer thickness deposited at the both sides of the Si substrate
Summary
GaN grown on 3C-SiC/Si templates, the thickness, roughness, off-cut angle, and wafer bow of the SiC/Si template need to be carefully selected. For SiC grown on on-axis Si, the SiC surface roughness is found to increase with thickness. SiC deposited on off-axis Si has a constant surface roughness, being independent of film thickness, consistent with what is expected for a step-flow growth mode. The growth and roughening mechanisms for 3C-SiC are proposed, based on the surface morphology and roughness evolution characteristics. Both concave and convex wafer bow can be obtained by adjusting SiC thickness deposited on both sides of a Si wafer
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