Faculty Sponsor's Department:
Imaging of nanoscale devices often proves challenging. The device substrate significantly affects how images develop. A substrate must be robust, chemically inert, and high-temperature stable in order for devices to be reliable fabricated. Silicon nitride membranes are good candidates because of their mechanical stability, electrical insulation, and transparency to common imaging technologies like TEM and X-Ray. Using high-stress nitride wafers and common industrial micromachining techniques, we are able to create arrays of windows that serve as a physical foundation for devices, without affecting the electrical and mechanical properties of the device. Processing these wafers involves photolithography, anisotropic reactive ion etching, potassium hydroxide (KOH) wet etching, and isotropic HF oxide etching. The main consideration in design is the etch profile of silicon created by the KOH. This silicon etch has a well-studied crystal plane rate selectivity. Throughout this process, common etch rates and nuanced behavior of these materials have been characterized for the group. By optimizing the process flow, we have created micron-scale imaging windows with exceptional yield and reproducibility.