Creation of embedded structures in SU-8

Abstract

Two methods were investigated for the creation of encapsulated micro-fluidic channels and bridges in negative tone SU-8 photoresist. The first uses two exposures at different wavelengths to create the channel sidewalls and microchannel encapsulation layer; the other method creates both using a single I-line (365 nm) exposure and a grayscale photomask. These methods can define structures with vertical dimensions ranging to hundreds of microns and introduces very little extra processing complexity. For the dual wavelength method, an I-line light source is used to define the channel walls while a non-collimated deep-UV (254 nm) light source provides a large energy dose to the top surface of the SU-8 to produce a membrane over all the channels. Using the dual wavelength method allows SU-8 to be used as the material for the channels and the encapsulation method is self-limiting avoiding the requirement for precise control over the exposure dose. The rate of UV dose and the post-exposure baking parameters are critical to the quality and strength of the micro-channels. Properly designed channels have been successfully developed in lengths up to 1 cm. Alternatively using a grayscale Zn/Al bimetallic photomask and a single I-line exposure, 3D bridge micro-structures were successfully made on SU-8. The use of grayscale masks for both techniques also provides the possibility of shaping the channel. With the ability to create micro-bridges, further research will be performed to investigate how well the single exposure technique can be used to produce micro-channels of various sizes and dimensions.