The laser exposure requirements of liquid crystal polymer thin films for photomasking applications

Abstract

Thin solid films of a cyanobiphenyl based polymethacrylate liquid crystal polymer (LCP) coated onto quartz substrates have been thermally processed to give a UV light scattering texture for use as a photomask opaque layer. UV transparent line patterns in the scattering layer may subsequently be written by scanning a focused laser beam across the LCP surface. The exposed linewidths are found to be strongly dependent upon the thickness of the LCP film, the incident power of the laser, and the overall residence time of the focused beam waist at a given location on the film surface. Successful exposure of the LCP films demands that the absorbed laser energy and beam waist residence time should exceed minimum threshold magnitudes however, and it is demonstrated that the smallest feature size which may be defined in the scattering layer is effectively limited by heat conduction from the LCP to the quartz substrate. Possible approaches towards improving the exposure requirements of the LCP are considered, and the compatibility of the proposed LCP photomask with current industrial direct-write laser systems is appraised.