Improving Insulation Methods in New and Existing Fabrication Processes

Silicon dioxide is widely used as a deposited insulator in a variety of fabrication processes for microelectronic devices and circuits. SiO2 has a relatively low dielectric constant (3.9), is the native oxide of silicon and a natural choice for the silicon integrated circuit industry, and can be conveniently deposited with a variety of techniques. For this thesis, issues of insulator pinholes, edge/topology coverage, repeatable material parameters, and compatibility with liftoff processes are of particular importance. In this work, we focus primarily on the sputter deposition of silicon dioxide thin films, given the potential advantages typically offered by sputtering over the commonly used technique of evaporation for liftoff. An important additional thermal constraint in our work rules out PECVD or thermally grown silicon dioxide. The electrical and material properties of these films are in some cases essential to the intended devices, so the characterization of these thin films is an important aspect of this thesis. The optimization of the deposition method is also constrained by the fabrication process associated with the devices involved. A discussion of accompanying device processing improvements, including the resist etch- mask and liftoff processes for superconducting-insulator-superconducting (SIS) junctions, and the development of aerogel microelectrical-mechanical systems (MEMS) base devices with silicon dioxide capping layers will also be discussed. We find diode sputtered SiO2 films to be superior to evaporated and magnetron films, where reduced pinhole density, superior edge coverage, low optical extinction coefficient, and a more repeatable dielectric constant is obtained with the diode deposited technique. With careful attention and adjustment of our fabrication processes, these diode sputtered SiO2 films have been successfully incorporated into our existing superconducting circuits, replacing the SiOx evaporation technique used in our devices for the past 25 years. The diode sputtered films were also successfully introduced into a newly developed single resist method for fabricating SIS junctions as well as for physical protection for aerogel thin film device insulation.