Improved electron-beam lithography with C60 fullerene for InP membrane waveguides

We present a method to prepare a mixed resist material composed of a positive electron-beam resist (ZEP520A) and C 60 fullerene. The method is modified from previous methods in literatures to achieve an optimized mixing. An improvement of the mixed material on the thermal resistance respect to the same structures fabricated with normal ZEP resist has been demonstrated by fabricating multimode interference couplers and coupling regions of micro-ring resonators. An improvement on the propagation loss of the InP membrane waveguides from 6.6 to 3.3 dB/cm using this mixed material is also shown.