9 December 2004 Laser direct write patterned indium tin oxide films for photomasks and anisotropic resist applications
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Abstract
A laser direct write process has been developed for turning patterned bimetallic Sn/In film into a indium tin oxide layer. Sn over In films (15-120nm thick) with a 1:10 thickness ratio were deposited by DC sputtering. An argon laser beam (0.1 - 0.9 W, spot size: 2 micron, scan speed: 1 cm/s) exposes the film into patterns. These Sn/In films' optical absorption changed from 3 OD at deposition to 0.24 OD after exposure (at 356 nm). XRD, SEM, EDX, and Auger have been used to investigate the film's microstructure and composition suggesting ITO like characteristics. XRD indicated a preferred In2O3 (222) orientation which is similar to ITO films deposited by other methods. Four-point probe tests showed a converted film resistivity of 0.26x10-3 to 9.7x10-3 ohm-cm depending on the laser power and Sn concentration. Hall tests indicated that the bulk carrier concentration was in the range of 1018 to 1020 cm-3. Developed in a wet HCl: H2O2: H2O =1:1:48 solution removes unexposed Sn/In leaving patterned ITO films created at much lower laser power levels than needed for ablative patterning of ITO. Developed films are also resistant to KOH anisotropic etching at a 1:700 ratio producing <111> trenches in Si (100). The large change in optical density means Sn/In films can be used as a material of the direct write photomasks.
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Jun Peng, Glenn H. Chapman, Yuqiang Tu, "Laser direct write patterned indium tin oxide films for photomasks and anisotropic resist applications", Proc. SPIE 5578, Photonics North 2004: Photonic Applications in Astronomy, Biomedicine, Imaging, Materials Processing, and Education, (9 December 2004); doi: 10.1117/12.567642; https://doi.org/10.1117/12.567642
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