Comparison of Conventional and Variable Frequency Microwave Curing of SU8 Photoresist: Effects on the Dielectric, Thermal, and Morphological Properties

Abstract

Abstract. Variable Frequency Microwave (VFM) is known to be a rapid, volumetric, and selective form of heating which has shown potential as an alternative technique for the processing of negative-tone SU8 photoresist in the Micro-Electro-Mechanical System (MEMS) industry. A comparison of thermal properties of the films cured during the softbake and post exposure bake process using different techniques, i.e. conventional thermal curing, VFM curing, and a combination of both (referred to as hybrid, HY), was investigated using a Differential Scanning Calorimeter (DSC) and Thermogravimetric Analysis (TGA). A significant increase on the degree of cure (between 13-23%) was observed using the VFM over the hybrid and hotplate curing which means that SU8 curing at lower temperatures or rapid curing is possible. The increase in cure rates can be attributed to a combination of heat transfer and the unique capability of microwave to couple with the sample (selective heating). The improvement in curing at the same processing temperatures has important implications for processing thick films. It was found that regardless of curing methods, crosslink densities increased as the baking temperature increased, resulting in lower dielectric properties. Despite higher crosslinking contents, VFM cured samples decomposed at 2-4°C lower temperatures. In addition to better thermal properties, VFM offered satisfactory microstructure at lower curing temperatures; however, high processing temperatures could result in film cracking.

Fabrication of Functional Microdevices in SU-8 by Multi-Photon Lithography

“…Kuebler et al showed that pre-exposure solvent content as low as 1 wt.-% causes features in woodpile structures to become rounded and less well resolved, whereas reducing solvent content down to 0.68 wt.-% yielded higher resolution structures with more sharply defined features [ 50 , 55 ]. While hot-plate heating is typically employed, alternative heating methods like IR and frequency variable microwave heating can also be used to reduce heating times and achieve lower solvent contents [ 56 , 57 ]. Convection oven heating is not recommended, because a skin of dry resin will form at the interface with air, which limits the vaporization of the solvent.…”

Comparative study on the properties of cross‐linked cellulose nanocrystals/chitosan film composites with conventional heating and microwave curing

“…Furthermore, microwave curing has also been known as an environmental-friendly technology due to its characteristics such as higher cross-linking rate, shorter reaction time, the reduction of hazards and pollution, better heat uniformity and higher product yield compared to conventional thermal curing. [16,17] According to the literature, a number of studies have reported the cross-linking of chitosan film using different cross-linkers and curing methods. [11,[18][19][20] However, to the best of our knowledge, there are no studies comparing of the influence of different cross-linking methods on the properties of CNC/chitosan film composites.…”