Laser-Induced Polymer Removal and Transmittance Enhancement of an Indium-Tin-Oxide (ITO) Film by Reduction of Surface Roughness

The stripping of the photoresist (PR) layer on a silicon wafer and transmittance enhancement of an indium-tin-oxide (ITO) film was investigated by irradiation with the line beam of a KrF excimer laser with a wavelength of 248 nm. A 0.82-μm-thick PR layer was removed perfectly at an energy density of 300 mJ/cm2 after a 6-pulse irradiation with the line beam without the aid of any chemical or solvent. The ablation rates were 0.06 μm/pulse for 100 mJ/cm2, 0.10 μm/pulse for 200 mJ/cm2 and 0.13 μm/pulse for 300 mJ/cm2. Many application fields require materials with optically smooth surfaces. A non-contact optical polishing method with a line beam technology is introduced and discussed for reducing the ITO surface roughness with angstrom (°A) precision without any pre- or post-treatment with chemicals. The transmission spectra of the ITO film before and after line beam irradiation showed an enhanced transmittance of over 8 % in the visible region (400 800 nm). The effects of the excimer laser’s fluence and the number of pulses applied to the ITO surface on reducing the surface roughness were investigated. The root-mean-square (RMS) roughness of the ITO film was decreased by 30 37 % compared to the initial laser-untreated ITO surface roughness. The main reason for the enhanced transmittance of the ITO film is the reduction of the ITO surface roughness, which reduces light scattering at the surface of the ITO. Non-contact laser technology has shown the ability to strip the PR without any pre- or post-chemical process and without any substrate damage. KCI Citation Count: 5