Hot Filament CVD epitaxy of 3C-SiC on 6H and 3C-SiC substrates
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Hot Filament CVD epitaxy of 3C-SiC on 6H and 3C-SiC substrates Philip Hens1, Ryan Brow2, Hannah Robinson2, Bart Van Zeghbroeck1,2 1 University of Colorado Boulder, ECEE Department, CB 425, Boulder, CO 80309, USA 2 BASiC 3C, Inc., 1830 Boston Avenue, Longmont, CO 80501, USA ABSTRACT For the first time, we are reporting the growth of high quality single crystalline 3C-SiC epitaxially on hexagonal silicon carbide substrates using Hot Filament Chemical Vapor Deposition (HF-CVD) on full 4” wafers. Rocking curve X-Ray diffraction (XRD) measurements resulted in a full width at half maximum (FWHM) as low as 88 arcsec for a 40 µm thick layer. We achieved this quality using a carefully optimized process making use of the additional degrees of freedom the hot filaments create. The filaments allow for precursor pre-cracking and a tuning of the vertical thermal gradient, which creates an improved thermal field compared to conventional Chemical Vapor Deposition. Growth rates of up to 8 µm/h were achieved with standard silane and propane chemistry, and further increased to 20 µm/h with chlorinated chemistry. The use of silicon carbide substrates promises superior layer quality compared to silicon substrates due to their better match in lattice parameters and thermal expansion coefficients. High resolution scanning electron microscopy, X-Ray rocking measurements, and micro-Raman allow us to assess the crystalline quality of our material and to compare it to layers grown on low-cost silicon substrates. Hall measurements reveal a linear increase of the charge carrier density in the material with the flow of nitrogen gas as a dopant. Electron densities above 10-18 cm-3 have been reached. INTRODUCTION Cubic silicon carbide (3C-SiC) is a promising new material for switching devices in the medium voltage range (600V-1200V) because of its superior channel mobility compared to hexagonal silicon carbides (4H and 6H-SiC). Due to the lack of 3C-SiC bulk material as substrates for epitaxy, 3C-SiC is typically grown on either silicon or hexagonal SiC. Growth on silicon substrates reduces cost, but also leads to a large number of defects in the grown layer [1]. These defects are caused by the mismatch in the lattice constant, thermal expansion coefficient, and the basic lattice structure (polar vs. unipolar). These defects include anti-phase boundaries, dislocations, stacking faults, and twins. Anti-phase boundaries still exist in layers grown on hexagonal silicon carbide but due to a better matching of lattice and expansion constants, the number of planar defects is significantly reduced, making this material more suitable for power electronic devices. This effect is visible in the reduced FWHM width of XRD rocking curves and using SEM imaging on as grown surfaces. While conventional CVD has been extensively used to grow 3C-SiC, there are only a limited number of reports of hot filament CVD (HF-CVD) growth of 3C-SiC [2] and even fewer reporting the FWHM of the double rocking curve [3]. HF-CVD has previously been used for the deposition of polyc
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