Contrast tuning, image reversal, and automated track developing

An experiment was conducted to determine if contrast tuning could be performed on an automated track developer using a standard spray versus an ultrasonic nozzle. GaAs wafers were patterned with a linear variable neutral density filter (LVNDF) and developed by spray and an ultrasonic nozzle. The ultrasonic nozzle produced a lower chemical contrast than the standard spray development. This lower chemical contrast used in conjunction with image reversal makes photoresist sidewalls more retrograde, which is advantageous in GaAs processing for metal liftoff. In addition to contrast tuning, the LVNDF technique is described that was used to quickly and easily compare the contrasts of the two development systems. With the LVNDF mask, chemical contrast as well as process uniformity could be quickly measured