(629d) Photodefineable Epoxycyclohexyl Polyhedral Oligomeric Silsesquioxane

Epoxy based polymers are widely used as dielectric materials in microelectronics and microfluidics due to their photo-definability and mechanical characteristics. However, polymer overcoats may deform during thermal cycling and have processing limitations. The use of a hybrid inorganic/organic dielectric may add chemical, thermal, plasma, and mechanical resiliency to the overcoat and overall device. Polyhedral oligomeric silsesquioxanes (POSS) has shown promise for its strong silicon oxide cage and functionalized organic arms, and it has also been studied as a polymer additive, imprint material, underfill, and coating material.

In this study, a novel photo-definable dielectric utilizes an epoxycyclohexyl POSS monomer. The POSS dielectric was studied to utilize its hybrid organic/inorganic characteristics in improving mechanical strength and stability for microfabrication applications. Films were characterized for optical, mechanical, chemical stability, and thermal stability properties. The POSS dielectric was photo-defined into crisp, high-resolution features as small as 10 µm and showed a 0.66 contrast as a negative-tone resist. The polymer film showed thermal stability up to 350° C and chemical stability in a variety of solvents and oxidants. Mechanical properties were tested and showed a relative modulus of 5.3 GPa that compares well to other dielectrics. POSS films have also shown high resiliency in oxygen plasma compared to organic polymers and has been used as a high selectivity permanent mask for patterning sacrificial polymers in a reactive ion etch (RIE). The POSS dielectric is under investigation as an overcoat material in microelectromechanical systems (MEMS) packaging and support in coaxial transmission lines.