Process Control Model for Growth Rate of Molecular Beam Epitaxy of MgO (111) Nanoscale Thin Films on 6H-SiC (0001) Substrates
Yung-Tsun T. Lee
Magnesium oxide (MgO) is a good candidate for an interface layer in multifunctional metal-oxide nanoscale thin-film heterostructures due to its high breakdown field and compatibility with complex oxides through O-bonding. In this research molecular beam epitaxy (MBE) is used to deposit 10 to 15 nm MgO single-crystal films on 6H-SiC (Silicon carbide with hexagonal polytype 6H) to serve as an interface layer for effective integration of functional oxides. We investigate the effect of MBE process control variables on the growth rate of the MgO film measured in nanometers per minutes. We conducted experiments at various process conditions and measured the resulting MgO film growth rate. The process control variables studied are the substrate temperature (100° C - 300° C), magnesium source temperature (328° C - 350° C), plasma intensity (0 mV 550 mV) and percentage oxygen on the starting surface of 6H-SiC substrate (9 % - 13 %) after the substrate is prepared by high temperature hydrogen etching. The film thickness is used to compute using the effective attenuation length (EAL) of silicon photoelectron peak intensity changes as measured by x-ray photoelectron spectroscopy (XPS). The film thickness is converted to growth rate by dividing it with the duration of film growth. Using the experimental data, a neural network model is developed to estimate growth rate for any given process variable combination. The study reveals that the plasma intensity has the most significant influence on growth rate. The results indicate that growth rate is relatively low on high quality substrates with (square root 3 x square root 3)-R30 degrees ((√3 x √3) R30°) lattice reconstructed 6H-SiC (0001) surface with optimum oxygen content (approximately 10%); in contrast, the growth rate is relatively high on substrates with high surface roughness and excessive oxygen on the starting substrate surface.
International Journal of Advanced Manufacturing Technology