Ultrasonic and dip resist development processes for 50 nm device fabrication

A comparison between the conventional dip development process and resist development with ultrasonic agitation at 40 kHz has been conducted for the development of high-resolution resist nanostructures with dimension down to 50 nm. High-resolution commercially available ZEP520 positive electron resist and an in-house epoxy-based negative resist were used in the study. For large area exposure with ultrasonic agitation for resist development, improved resist sensitivity (≈4%) over a dip development process was observed for positive resist and no sensitivity improvement was seen with negative resist. There was also no observable improvement in the measured resist contrast for both positive and negative resist with and without ultrasonic agitation. For resist development in dense arrays or isolated nanostructures, ultrasonic agitation for positive and negative resist development offered faster development rate, more uniformity in resist development and a larger window for exposure dose variation in resist nanostructures. For negative resist, it was also observed that the descum rate with ultrasonic agitation was more than a factor of 3 faster than for dip development. Experiments on the relative merits of ultrasonic agitation for resist development with cavitation at 25 kHz and a narrowly focused acoustic beam at 400 kHz indicated that faster development rate and resist contrast were obtained with cavitation for the experimental conditions used.