Nanoscale superconducting THz hot electron bolometers fabricated with UV lithography on ultra-thin Si beam lead chips

While focused E-beam and Focused Ion Beam patterning tools have been shown to be successful methods for defining nanoscale features of superconducting hot electron bolometers (HEBs), there are some drawbacks to these techniques. These serial processes are not widely available and are slow for producing large numbers of HEBs. Although device throughput has not been traditionally emphasized for typical HEB and microwave circuits, HEBs are very vulnerable to ESD damage and low circuit yield. Also, there is growing interest in building high density HEB receiver arrays. As an alternative to high-end nanolithography techniques, we have developed a novel "Suspended Sidewall Nano Patterned Stencil" (SSNaPS) process, which requires conventional I-line contact lithography, sputtering, and RIE tools, which are all commonly available. This method involves a conformal sputtering of Titanium over patterned polyimide steps and a subsequent anisotropic etch of Titanium on the horizontal surfaces. Thin lines of Ti remain on the sidewalls of the polyimide features whose width is determined by the thickness of the initial sputtered layer. These nanoscale Ti-lines, combined with micrometer scale Ti patterns, can be used for the accurate patterning required for superconducting HEB fabrication. This method allows for simplified parallel fabrication of large numbers of HEBs or other nanoscale devices and is available to most fabrication facilities.