SEMICONDUCTOR DEVICE COATINGS, MATERIALS & PROCESSES

Past Coating Materials News & More (CMN) discussions have examined optical materials and their deposition processes in terms of applicability to regions of the electromagnetic spectrum from deep ultraviolet (DUV) to infrared (IR). The thin film industry applies PVD and epitaxy processes and combinations of materials to achieve control of light and energy in specific applications. In this issue, we will connect the materials and processes as they are applied to increasingly complex solutions in the fields of manufacturing, communications, and energy efficiency.

Optical and semiconductor applications based on thin film layers involve mature process and materials engineering. Manufacturing principles for growing single-crystal Silicon (Si) and Germanium (Ge), as well as condensing Zinc Sulfide (ZnS) and Zinc Selenide (ZnSe) for use as substrates are central to advanced solid state device structures. Specialized epitaxy and CVD technologies that allow the deposition of single or multi-element compound species with precise control of crystal structure, band structure, and intricate composition are critical to the industry. In an oversimplification, during Molecular Beam Epitaxy (MBE) film growth, multiple effusion cells are used to direct impinging beams of thermally induced flux onto the substrate. The combination of high-vacuum condensation of the sublimed material and the substate temperature allow the formation of single-crystal films of complex high purity composition with controlled microstructure. The lower population of defects produced in MBE deposition results in longer free carrier lifetimes, and therefore higher emitter and sensor device efficiencies. Analogous to optical designs based on stacking of oxides or fluoride layers, this technique creates multi-layer structures like Quantum Wells, distributed Bragg Reflectors, and other critical elements for industry. These are the foundation of light-emitting diodes (LEDs), laser diodes, and multijunction solar cells that are used to power infotainment, laser machining, and energy harvesting technologies. MBE enables better control of deposition parameters than metalorganic chemical vapor deposition (CVD).