Papers by Author: Hyun Hee Hwang

Abstract: We adopted HMDS(Hexamethyledisilane) as a SiC(Silicon carbide) source material for epitaxial growth of 3C-SiC on Si substrate. Various growth profiles were investigated to optimize hetero-epitaxial growth of 3C-SiC layers. We also focused on the homogeneous film deposition of 3C-SiC on Si by employing two susceptor shapes, flat and tilted susceptors, to control a thickness of the boundary layer formed on the Si substrate. Fringe color patterns were observed on 3C-SiC layer on Si and hence it was easy to characterize the film uniformity by analyzing this color. 3C-SiC epitaxial layers were systematically analyzed by an optical microscope, a Raman spectroscopy, a SEM and an XRD.

Abstract: GaN epitaxial layers were grown on sapphire substrate deposited an aluminum (Al) buffer layer using a hydride vapor phase epitaxy (HVPE) system with a two-zone resistance furnace. A 10nm-thick Al buffer layer was prepared by an e-beam evaporation in order to reduce the stress resulted from thermal mismatch between the GaN layer and the substrate. The growth temperature and growth rate for GaN epitaxial layer were 1050oC and 40 m/hr, respectively. GaN epitaxial layer grown on substrate with Al buffer layer exhibited uniform and smooth morphology on 2-inch whole substrate and a bow value of 33.5 m. The addition of Al-buffer layer apparently reduced the full width at half maximum (FWHM) value of GaN layer, which indicated the improvement of crystal quality.

Abstract: The effect of slurry composition and wafer flatness on a material removal rate (MRR) and resulting surface roughness which are evaluation parameters to determine the CMP characteristics of the on-axis 6H-SiC substrate were systematically investigated. 10 x 10 mm2 6H-SiC substrates and 2-inch SiC wafers fabricated from the ingot grown by a conventional physical vapor transport (PVT) method are used for this study. The SiC substrate after the CMP process using slurry added oxidizers into slurry consisted of KOH-based colloidal silica and nano-size diamond particle exhibited the significant MRR value and a fine surface without any surface damages. SiC wafers having high bow value after the CMP process exhibited large variation in surface roughness value compared to wafer with low bow value. The CMP-processed SiC wafer having a low bow value of 10m was observed to result in the MRR value of 0.15 m/h and the mean height (Ra) value of 0.772Ǻ.

Abstract: A sublimation epitaxial method, referred to as the Closed Space Technique (CST) was adopted to produce AlN epitaxial layers. In this study, we report the surface morphology of AlN epitaxial layer grown on various substrates such as 3C-SiC (100), 4H-SiC (0001) with 8o off-axis (0001) plane tilted toward the <11 2 0> direction and on-axis 4H-SiC (0001). An average growth rate of AlN layer at 2350oC in 500 Torr of N2 was measured to be about 6μm/hr. While AlN layer grown on the 3C-SiC (100) substrate at 2350oC exhibited polycrystalline structure, AlN epitaxial layer grown on on-axis and off-axis 4H-SiC (0001) substrates had highly c-axis oriented epitaxial structure. In particular, the stacked structure of hexagonal plates was observed on off-axis substrate and the size of the hexagonal plates increased with growth time. Hexagonal plates were observed to be coalesced and the step-bunching was finally disappeared.