Ultraviolet curable branched siloxanes as low-k dielectrics for imprint lithography

Abstract

A methacrylate-based, UV curable branched siloxane (MA-Si-12) was designed for use as a low-k dielectric that can be directly patterned by step and flash imprint lithography. MA-Si-12 has the properties of low viscosity (20 cP) and low vapor pressure (1.3 Torr), which make the material suitable for imprint processes based on an inkjet dispensing system. However, the mechanical strength of UV cured MA-Si-12 is too low (0.4 GPa Young's modulus by nanoindentation) for use with chemical mechanical polishing. Therefore, a methacrylate-based, UV curable cyclic siloxane (8-ring) was synthesized to be blended with the siloxane and improve the modulus. A formulation consisting of a mixture of MA-Si-12 and 8-ring (50 wt. % respectively) provides patterned structures with a modulus of 2.0 GPa. This formulation still has a viscosity (19 cP) and vapor pressure (1.3 Torr) low enough for inkjet dispensing. The UV cured resin has a dielectric constant of 2.8 at 1 MHz, low water absorption (0.7 wt. % after 24 h), and low UV cure shrinkage (5.6%). It provides high resolution, high fidelity imprint patterns. Mixing or blending of branched and cyclic siloxanes is a valuable approach to the design of imprint resist formulations with low dielectric constants.