Using imprinting technology to fabricate three-dimensional devices from moulds of thermosetting polymer patterns

Abstract

The fabrication of moulds for imprinting can be simplified significantly by using specialized cross-linking polymers to define the pattern on a silicon wafer. Thermosetting polymers (SU-8) can be used to pattern silicon moulds for imprinting technologies because ( 1) silicon oxide moulds bearing a thermosetting polymer pattern can be obtained using conventional semiconductor technologies and ( 2) thermosetting polymers have no obvious glass transition temperature (T-g) because of their cross-linked structure, but the hardness decreases significantly when the temperature is above the Tg. In this study, we used Su-8 resist as the thermosetting polymer pattern to obtain moulds on a silicon wafer. We have tested the thermal properties of thermosetting (SU-8) and thermoplastic polymers (22A4) for use as imprinting patterns and imprinted resists. We fabricated a hill-like structure by applying an electron beam strategy and used this thick film to increase the adhesion between the pattern and the silicon wafer. We used scanning electron microscopy to investigate the resolution of the thermoplastic polymer resist ( 22A4) pattern that we imprinted using the thermosetting polymer (SU-8) pattern. To define the feature size after imprinting, we determined the feature size shrink factor after separation of the thermosetting polymer pattern (SU-8) from the thermoplastic polymer ( 22A4) resist. In addition, we have fabricated a microlens of polydimethylsiloxane ( PDMS) through replication using the thermoplastic polymer resist ( 22A4) obtained after imprinting the mould with the microlens structure of the thermosetting polymer ( SU- 8).