X-Ray Diffraction Method

Several of the patented methods included in this suite of technologies enable super-hetero-epitaxy of rhombohedral/cubic compound semiconductors on specially oriented trigonal (e.g. sapphire) or hexagonal (e.g. quartz) crystal wafer substrates. This includes alignment of the growth crystal lattice with the underlying substrate lattice to minimize misfit strain-induced dislocation defects in the growing crystal. Thus thicker, defect-free crystal layers can be made. Rhombohedral/Cubic crystal twin defects which is 60 degree rotated on [111] orientation in a rhombohedral/cubic SiGe layer structure can be reduced to well less than 1% by volume, essentially providing a defect-free semiconductor material. Alternately, engineered lattice structures with a high degree of twinning can provide SiGe with improved thermoelectric properties due to the phonon scattering that inhibits thermal conduction without compromising electrical conductivity. Additional patented technologies in this suite provide for physical vapor deposition (PVD) growth methods utilizing molten sputtering targets and thermal control of heated substrates, including electron beam heating, in order to give the atoms in the sputtered vapor or on the substrate surface the energy needed for the desired crystal growth. The remaining patented technologies enable x-ray diffraction methods for detecting and mapping crystal twin defects across the entire as-grown semiconductor layer. These defects are critical to the performance of any semiconductor device manufactured from such compound semiconductor materials.

III-nitride devices are commonly made on sapphire substrates today for various commercial electronic and optoelectronic applications. Thus, this innovation relates directly to the combination of devices on opposite sides of the sapphire substrate. One possible device combination is to have LEDs one side and solar cells on the other, such as for displays.

This technology is a method of using x-ray diffraction (XRD) to evaluate the concentration of crystal structure defects, and thus the quality, of cubic (100)-oriented semiconductor wafers. Developed to enhance NASA's capabilities in fabricating chips for aeronautics applications, the method supplants existing methods that not only destroy the wafer in question, but can take as long as a day to determine the quality of a single wafer. The approach can be used with any commonly used semiconductor, including silicon, SiGe, GaAs and others, in a cubic (100) orientation, which covers at least 90% of commercial wafers. It can also be used to evaluate the quality of epi layers deposited on wafer substrates, and of ingots before they are sliced into wafers.

Performance of solar cells and other electronic devices such as transistors can be improved greatly if carrier mobility is increased. Si and Ge have Type-II bandgap alignment in cubically strained and relaxed layers. Quantum well and super lattice with Si, Ge, and SiGe have been good noble structures to build high electron mobility layer and high hole mobility layers. However, the atomic lattice constant of Ge is bigger than that of Si and direct epitaxial growth generates large density of misfit dislocations which decrease carrier mobility and shorten device life time. So it required special buffer layers such as super lattice or gradient indexed layers to grow Ge on Si wafers or Si on Ge wafers. The growth of these buffer layers takes extra effort and time such as post-annealing process to remove dislocations by dislocation gliding inside buffer layer. This invention is a fabrication method for high mobility layer structures of rhombohedrally aligned SiGe on a trigonal substrate. The invention utilizes C-plane (0001) Sapphire which has a triangle plane, and a Si (Ge) (C) (111) crystal or an alloy of group TV semiconductor (111) crystal grown on the Sapphire.

The Molten Target Sputtering (MTS) method can increase the kinetic energy, the energy latency, and the flux density of sputtered atoms by combining the benefits of both magnetron sputtering and evaporation systems. It does this by a clever, but simple mechanical modification to the magnetron sputtering gun. For the MTS method, only a 1~2mm (depth and width) ring-shape groove is cut between the magnets in order to keep a gap between the copper plate and the sputtering target, as below. This effectively increases the efficiency of magnetron based sputtering machines. The ring enhances the magnetic field intensity and increases the temperature of the target material. A key difference in design between a conventional sputtering gun and the MTS gun seems very minor, but the ring-shape groove between magnets allows for trapping a portion of magnetic field within the groove. A trapped field creates an additive force to expel the ionized particles (atoms and molecules combined within plasma) by increasing their kinetic energy. The ring groove also serves to increase the target material temperature because the conduction passage of thermal energy to the water-cooled copper sink is interrupted by the empty space of a ring groove below the target. Accordingly, the target surface material is heated to a higher temperature, which in turn increases the flux density by more easily liberating the atoms from the target.