Homoepitaxial growth on 4H-SiC Substrates by Chemical Vapor Deposition
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0911-B09-05
Homoepitaxial growth on 4H-SiC Substrates by Chemical Vapor Deposition Christer Hallin, Igor Khlebnikov, Yuri Khlebnikov, Peter Muzykov, Elif Berkman, Monica Sharma, George Stratiy, Murat Silan, Cem Basceri, and Cengiz Balkas Intrinsic Semiconductor, Dulles, Virginia, 20166 ABSTRACT Results presented here indicate a strong dependence between the surface roughness and its uniformity of epitaxial layers grown by chemical vapor deposition (CVD) and the underlying substrate dislocations and its domain structure. The substrates used were cut from boules grown by physical vapor deposition (PVT). The facet area and its borders were found to impact the CVD grown epitaxial layers. Epitaxial layers, 50 µm thick, were grown on 8o off-axis substrates. Substrates with and without micropipes were selected in order to investigate their impact on the epitaxy. Both wafers indicate a correlation between etch pit dislocation (EPD) density and surface roughness. However, the in general lower EPD density in the micropipe free wafer enhances the variation in surface roughness between different regions. The micropipe free substrate has an EPD equal to 1.3x104 cm-2 in the facet region, and the surface roughness, Ra, is 1.0 nm (2.98x2.32 mm2 area), while there is an increase both in EPD density and surface roughness in the close proximity corresponding to the border around the facet. Also thick epitaxial layers, 30 µm thick, were grown on near on-axis substrates, both Cface and Si-face, in order to investigate how the surface morphology develops with less influence from the step-flow growth mechanism. Both crystal directions are characterized by a three dimensional growth front surface similar as for PVT grown crystals in the facet region. The mix between step-flow and dislocation driven growth on near on-axis C-face chemical vapor deposition (CVD) grown epi-layers is resulting in a as smooth, and measured surface roughness is as low as for growth on 8o off-axis substrates.
INTRODUCTION The steady improvements in growth and processing of SiC over the past decade have led to a level of maturity where commercial quality SiC devices are now being demonstrated in high power and high frequency applications. The open core screw dislocations, or more commonly called micropipes, has for many years been the main obstacle for realizing large area devices and high yield. However, now both low density (105 cm-2 and micropipe density around 14 cm-2. Near on-axis C-face epitaxial layers should therefore offer less ingrown BPD. The same should yield for the Si-face, however, step-bunching and three dimensional growth is more pronounced increasing the surface roughness.
SUMMARY The 4H-SiC substrate dislocations and their density, and therefore also domain structure, have a strong impact on the epitaxial layers surface roughness. This is valid even though the substrates are cut 8o off-axis from the -direction, and step-flow growth is predominant. The three dimensional growth at the facet, and the mixed step-flow and dislocation driven growth
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