Laser Direct Write Patterned Indium Tin Oxide Films for Photomasks and Anisotropic Resist Applications

摘要

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 In_2O_3 (222) orientation which is similar to ITO films deposited by other methods. Four-point probe tests showed a converted film resistivity of 0.26 x 10~(-3) to 9.7 x 10~(-3) ohm-cm depending on the laser power and Sn concentration. Hall tests indicated that the bulk carrier concentration was in the range of 10~(18) to 10~(20) cm~(-3). Developed in a wet HCl: H_2O_2: H_2O =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.