Processing and Characterization of Dry-Etch Benzocyclobutene as Substrate and Packaging Material for Neural Sensors

Electrode substrate is one of the most important factors affecting the recording or stimulation efficiency and long-term stability of chronically implanted neural sensors for laboratory research. Various biocompatible polymers have been investigated as potential substrate and packaging material for neural sensors in neuroscience research applications. Dry-etch benzocyclobutene (BCB) is one candidate due to its desirable combination of electrical, mechanical, and thermal properties and its biocompatibility. In this paper, processing techniques were investigated to control the uniformity and pin-pole density of dry-etch BCB film. Dry-etch BCB film as thick as 25 mum with a surface roughness less than 1000 A and a pinhole density less than 1.5 x 10^-3 mm^-2 has been acquired using an optimized coating and curing recipe. A traditional surface micro-machining technique was used to form the metallization and etch masks during the fabrication of the neural electrode based on dry-etch BCB substrate. Special consideration was given to the study of dry-etch BCB thin film patterning using plasma reactive ion etching dry etching. The optimized plasma etch condition shows that greater than 1 mum etch rate and 65deg via angle are the most suitable for the packaging and patterning of the neural probes. The results show that this fabrication process is optimal for chronically implantable neural sensors based on dry-etch BCB thin film as substrate. The process may find applications in other devices using BCB as substrate.