Plasma etch optimization of a photo-sensitive benzocyclobutene (BCB) planarisation layer for photonic integrated circuit manufacturing

Abstract

Benzocyclobutene (BCB) polymers have demonstrated excellent planarization capabilities. They are procesed using photo patterning or dry etching. A combination process involving both these methods has been developed and optimized for photonic integrated circuits (PICs). Inductively Coupled Plasma (ICP) and Reactive Ion Etching (RIE) are compared as well as soft and hard mask processes. An orthogonal design experiment is demonstrated as an excellent method for evaluating the parameter space of an etch process with variables of table power, ICP power, pressure, and O2/(O2+CF4) ratio. The sensitivities of these variables on etch rate, selectivity and etch profile are discussed. Etch rates of over 1.0 μm/min were achieved with the ICP source, which was in order of magnitude improvement to that of RIE and vertical to positive sloped BCB profiles with excellent mask selelctivity were established.