Direct write patterning of ito film by femtosecond laser ablation

Abstract

Indium tin oxide (ITO) is a commonly used conducting transparent oxide film (CTO) used in flat panel display applications. The ITO needs to be patterned during panel fabrication to form pixels and to repair defects. Direct write laser ablation is sometimes employed for this purpose and it is important that the substrate material and remaining ITO be affected as little as possible by the laser ablation. In this investigation, femtosecond laser ablation of ITO was studied to identify laser processing parameters which cleanly ablated ITO with a minimum of damage to a glass substrate and surrounding ITO. The material used for the experiments was glass with a deposited ITO film thickness of approximately 150 nm. The Ti:Sapphire chirp pulse amplified femtosecond laser used for the experiments had a wavelength of 775nm and produced pulses with a duration of 150 fs at a rate of 2 kHz. The pulse energy was attenuated with thin film polarizers and was focused by a 10x microscope objective with NA=0.6 and 25.4 mm focal length achromatic lens, producing a calculated minimum spot sizes of 2.5 µm and 6.5 µm respectively. The fiber-based femtosecond laser used for experiments had a wavelength of 1045 nm and pulses with a duration of 500 fs at a rate of 100 kHz. It was focused with a 20x microscope objective to spot sizes of 3.6 µm and 6.3 µm. Ablation was carried out at a sufficiently high panel scanning speed that single ablation spots could be studied. The pulse energy was adjusted to determine feasible spot diameters and depths which could be ablated into the ITO without damaging the glass substrate. Ablation of lines without glass damage was also demonstrated. The beam from the Ti:Sapphire laser was also used focused at the tip of an atomic force microscope (AFM) and the feasibility of nanomachining was demonstrated with this apparatus.Indium tin oxide (ITO) is a commonly used conducting transparent oxide film (CTO) used in flat panel display applications. The ITO needs to be patterned during panel fabrication to form pixels and to repair defects. Direct write laser ablation is sometimes employed for this purpose and it is important that the substrate material and remaining ITO be affected as little as possible by the laser ablation. In this investigation, femtosecond laser ablation of ITO was studied to identify laser processing parameters which cleanly ablated ITO with a minimum of damage to a glass substrate and surrounding ITO. The material used for the experiments was glass with a deposited ITO film thickness of approximately 150 nm. The Ti:Sapphire chirp pulse amplified femtosecond laser used for the experiments had a wavelength of 775nm and produced pulses with a duration of 150 fs at a rate of 2 kHz. The pulse energy was attenuated with thin film polarizers and was focused by a 10x microscope objective with NA=0.6 and 25.4 mm fo...