Study of the fabrication technology on tapered structure in quartz

Zero-mode waveguides (ZMWs) are nanostructures that drastically reduce the effective optical observation volume beyond the diffraction limit, thereby permitting the use of higher concentrations of fluorescently tagged molecules for single-molecule studies. This work presents the fabrication technology of quartz plasma etching to create tapered sidewalls for the application in ZMWs, utilizing an inductively coupled plasma (ICP) reactive ion etching tool. This method involves a meticulously designed two-step etching process to achieve quartz cavities with a minimum sidewall angle of approximately 60 deg. Initially, the process involves altering the photoresist pattern from a vertical to a tapered form, facilitated by the use of CF4/O2/Ar plasma at elevated radio frequency power settings. Subsequently, the quartz material is etched utilizing CF4 based plasma, with the tapered photoresist serving as a mask. This innovative approach allows for the successful transference of the tapered photoresist structure onto the quartz material, culminating in the formation of uniform and symmetrical tapered quartz cavities. Most importantly, the surface roughness (Rq) of the tapered quartz, measured to be around 3 nm, is extremely low and meets the stringent requirements for optical devices.