Substrate-assisted laser patterning of indium tin oxide thin films

Maskless laser patterning of indium tin oxide (ITO) thin films was studied by the use of a diode-pumped Q-switched Nd:YLF laser. The ITO films were sputter-deposited either on lime glass, the standard substrate material for hat panel display applications, or fused quartz so that the efficiency of laser patterning as a function of substrate absorption could be studied. The laser wavelength was varied among infrared (lambda = 1047 nm), visible (lambda = 523 nm), and ultraviolet (lambda = 349 nm and lambda = 262 nm). It is observed that strong light absorption by the substrate is a crucial requirement for a residue-free patterning of the ITO film. Observations and numerical calculations of the laser-induced surface temperature indicate that material removal occurs via thermal vaporization and that other mechanisms such as photochemical decomposition or spallation can be neglected.