The effects of ultra-smooth surface atomic step morphology on CMP performances of sapphire and SiC wafers
Whether sapphire or SiC wafer, clear and regular atomic step morphology could be observed all over the ultra-smooth wafer surface via atomic force microscopy (AFM) using our CMP technology. However, towards sapphire and SiC wafers, the variations of atomic step widths and step directions on the whole of wafer surface are different. The step widths and step directions on the different positions of sapphire wafer are uniform, while that on SiC wafer are distinct. Thus, the effects of atomic step width on CMP removal rate of sapphire and SiC wafers were studied. On the other side, the CMP removal model of super-hard hexagonal crystalline wafer to realize atomically ultra-smooth surface is proposed. The variations of atomic step morphology towards different defects on sapphire and SiC wafers surface are analyzed, and the formation mechanism of the defects is discussed.
XPS, UV-vis spectroscopy and AFM studies on removal mechanisms of Si-face SiC wafer chemical mechanical polishing (CMP)
Abstract Chemical mechanical polishing (CMP) removal mechanisms of on-axis Si-face SiC wafer have been investigated through X-ray photoelectron spectroscopy (XPS), UV–visible (UV–vis) spectroscopy and atomic force microscopy (AFM). XPS results indicate that silicon oxide is formed on Si-face surface polished by the slurry including oxidant H2O2, but not that after immersing in H2O2 solution. UV–vis spectroscopy curves prove that •OH hydroxyl radical could be generated only under CMP polishing by the slurry including H2O2 and abrasive, so as to promote oxidation of Si-face to realize the effective removal; meanwhile, alkali KOH during CMP could induce the production of more radicals to improve the removal. On the other side, ultra-smooth polished surface with atomic step structure morphology and extremely low Ra of about 0.06 nm (through AFM) is obtained using the developed slurry with silica nanoparticle abrasive. Through investigating the variations of the atomic step morphology on the surface polished by different slurries, it's reveals that CMP removal mechanism involves a simultaneous process of surface chemical reaction and nanoparticle atomic scale abrasion.
Impact of surface step heights of 6H–SiC (0 0 0 1) vicinal substrates in heteroepitaxial growth of 2H–AlN
Abstract Impact of step height of silicon carbide (SiC) substrates on heteroepitaxial growth of aluminum nitride (AlN) was investigated. Step-and-terrace structures with various step heights, 6 monolayer (ML), 3ML and 1ML, were formed on 6H–SiC (0 0 0 1) vicinal substrates by high-temperature gas etching. 2H–AlN layers were grown on the substrate by plasma-assisted molecular-beam epitaxy (MBE) and then these layers were characterized by atomic-force microscopy (AFM) and X-ray diffraction (XRD). High-quality AlN can be grown on SiC substrates with 6ML- and 3ML-height step, while AlN grown on SiC substrates with 1ML-height step exhibited inferior crystalline quality. A model for high-quality AlN growth on SiC substrates with 3ML-height step is proposed.