Papers by Author: Joon Ho An

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.

Abstract: 2inch 6H-SiC (0001) wafers were sliced from the ingot grown by a conventional physical vapor transport (PVT) method using an abrasive multi-wire saw. While sliced SiC wafers lapped by a slurry with 1~9㎛ diamond particles had a mean height (Ra) value of 40nm, wafers after the final mechanical polishing using the slurry of 0.1㎛ diamond particles exhibited Ra of 4Å. In this study, we focused on investigation into the effect of the slurry type of chemical mechanical polishing (CMP) on the material removal rate of SiC materials and the change in surface roughness by adding abrasives and oxidizer to conventional KOH-based colloidal silica slurry. The nano-sized diamond slurry (average grain size of 25nm) added in KOH-based colloidal silica slurry resulted in a material removal rate (MRR) of 0.07mg/hr and the Ra of 1.811Å. The addition of oxidizer (NaOCl) in the nano-size diamond and KOH based colloidal silica slurry was proven to improve the CMP characteristics for SiC wafer, having a MRR of 0.3mg/hr and Ra of 1.087Å.

Abstract: We investigated the effects of hydrogen addition to the growth process of SiC single crystal using sublimation physical vapor transport (PVT) techniques. Hydrogen was periodically added to an inert gas for the growth ambient during the SiC bulk growth. Grown 2”-SiC single crystals were proven to be the polytype of 6H-SiC and carrier concentration levels of about 1017/cm3 was determined from Hall measurements. As compared to the characteristics of SiC crystal grown without using hydrogen addition, the SiC crystal grown with periodically modulated hydrogen addition definitely exhibited lower carrier concentration and lower micropipe density as well as reduced growth rate.

Abstract: SiC single crystal ingots were prepared onto different seed material using sublimation PVT techniques and then their crystal quality was systematically compared. In this study, the conventional SiC seed material and the new SiC seed material with an inserted SiC epitaxial layer on a seed surface were used as a seed for SiC bulk growth. The inserted epitaxial layer was grown by a sublimation epitaxy method called the CST with a low growth rate of 2μm/h. N-type 2”-SiC single crystals exhibiting the polytype of 6H-SiC were successfully fabricated and carrier concentration levels of below 1017/cm3 were determined from the absorption spectrum and Hall measurements. The slightly higher growth rate and carrier concentration were obtained in SiC single crystal ingot grown on new SiC seed materials with the inserted epitaxial layer on the seed surface, maintaining the high quality.

Abstract: A sublimation epitaxial method, referred to as the Closed Space Technique (CST) was adopted to produce thick SiC epitaxial layers for power device applications. We aimed to systematically investigate the dependence of SiC epilayer quality and growth rate during the sublimation growth using the CST method on various process parameters such as the growth temperature and working pressure. The etched surface of a SiC epitaxial layer grown with low growth rate (30 μm/h) exhibited a low etch pit density (EPD) of ~2000 /cm2 and a low micropipe density (MPD) of 2 /cm2. The etched surface of a SiC epitaxial layer grown with a high growth rate (above 100 μm/h) contained a high EPD of ~3500 /cm2 and a high MPD of ~500 /cm2, which indicates that high growth rate aids the formation of dislocations and micropipes in the epitaxial layer.