Investigation of the ablation of fluorine-doped tin oxide thin films by square top-hat ultraviolet laser beams

Abstract

This paper presents a square top-hat beam shaper in an ultraviolet (UV) laser processing system for electrode patterning and investigates the interaction between square laser beams and fluorine-doped tin oxide (FTO) thin films deposited on glass substrates. The various patterning parameters to ablate the FTO films used in this experiment are included laser fluences, pulse repetition frequencies, and feeding rates of a motorized platform. The laser pulse repetition frequency and the feeding rate of the motorized platform were used to calculate the overlapping rate of laser spot and to determine the patterning quality. The line width and depth, edge quality, three-dimensional topography, and electrical conductivity properties of the patterned FTO films were measured and analyzed using a confocal laser scanning microscope and a four-point probe instrument. Experimental results indicated that the ablated line width and depth increased with increasing laser fluence. After electrode patterning with laser fluence of 2.07J/cm2 and 80% overlapping rate, no damages were observed in the patterned lines on the glass substrate. Moreover, the patterned line paths were narrow, smooth, clear, and flat in response to uniform laser energy distribution interacted in FTO films. The measured values of sheet resistance ranged from 109.7±3.8Ω/□ to 139.3±4.9Ω/□ at 2.07J/cm2 to 9.37J/cm2 laser fluences, respectively. The proposed process can reduce the fabrication steps and improve the removal efficiency of transparent conductive oxide materials and no waste etching chemical solution is produced.