Design and preparation of porous polybenzoxazole films using the tert-butoxycarbonyl group as a pore generator and their application for patternable low-k materials

The continuous advance of the device performance in microelectronics requires the development of the lower dielectric constant (low-k) materials. We target the development of a next generation low-k material based on poly(p-phenylene benzobisoxazole) (PPBO) films due to their low k value, remarkable mechanical toughness, excellent thermal stability, extremely low coefficient of thermal expansion and chemical inertness. In order to overcome the poor processability caused by the insolubility in organic solvents, the tert-butoxycarbonyl (t-Boc) group was introduced into the PPBO precursor (t-Boc-prePBO). The obtained t-Boc-prePBO shows excellent solubility in common organic solvents and fine films were successfully prepared. The thermal treatment of the t-Boc-prePBO film produces the PPBO film, which was completely characterized using IR. The low dielectric constant (k) value of 2.37 was achieved in the PPBO film. Scanning electron microscopy revealed the formation of a pore structure that plays an important role in the low k value of the film. The porous PPBO film also showed a good mechanical strength (16.0 MPa) and remarkably high thermal conductivity (0.445 W m^-1 K^-1). Furthermore, the t-Boc functionalization enabled micropatterning using a photolithographic technique. Such a patternable film with a low k value, mechanical toughness, and high thermal conductivity is a promising candidate for the next generation low-k materials. Our calculation revealed that a k value could be lowered to 1.98 by controlling the film morphology, the value that satisfies the requirement of the International Technology Roadmap for Semiconductors (ITRS 2009).