In this contribution we present a method to prepare a mixed material composed of a positive electron-beam resist (ZEP520A) and C60 fullerene. The addition of C60 to the ZEP resist changes the material properties under electron beam exposure significantly. This mixed material has shown an increased clearance dose as well as an increased reflow temperature. An improvement of the mixed material on the thermal resistance has been demonstrated by fabricating multimode interference couplers and coupling regions of micro-ring resonators. This shows improvement with respect to the same structures fabricated with normal ZEP resist. An improvement on the propagation loss of the InP membrane waveguides from 6 to 3 dB/cm using this mixed material is shown.