Effect of substrate absorption on the efficiency of laser patterning of indium tin oxide thin films

Maskless laser patterning of indium tin oxide thin films for flat panel display applications was studied as a function of wavelength using different harmonics of a diode-pumped Q-switched Nd:YLF laser. Electrically isolating lines could be written at all wavelengths used. However, while lines written at the infrared and the visible wavelengths exhibited a ripplelike morphology due to incomplete material removal, ultraviolet laser irradiation produced residue-free etch lines with superior smoothness even at higher scan speeds. The threshold fluences for material removal at different wavelengths were found to correlate with the optical properties of the indium tin oxide film. In addition, numerical simulations of laser-induced temperature rise yielded peak surface temperatures well above the vaporization temperature of the indium tin oxide film, indicating that, at all wavelengths studied, material removal occurs via thermal vaporization. The calculations also revealed that the absorption of the ultraviolet laser light by the glass substrate is the key factor for the residue-free removal of the indium tin oxide film. Moreover, using a flashlamp-pumped Nd:yttrium-aluminum-garnet laser and a galvanometric scanning system, high process speeds in excess of 1 m/s could be achieved. (C) 1999 American Institute of Physics. [S0021-8979(99)03608-7].