Improving the wet chemical patterning of nichrome film by inserting an ultrathin titanium layer

We studied how to improve the quality of nichrome (NiCr) films patterned with wet chemical etching by inserting an ultrathin titanium film. The experimental results showed that inserting a 20-nm Ti layer between the photoresist (PR) and NiCr greatly improved the quality of the resultant pattern, which had minimal undercut and smooth edges. We attributed this improvement to the improved mask/NiCr interface, which we confirmed by scanning electron microscopy (SEM). In addition, we found that the undercutting of NiCr comprised two stages—an initial, relatively slow undercut stage and a second, faster stage—separated by the critical time point, the time at which the unmasked NiCr film etched away completely.