Experimental Characterization Of Femtosecond Laser Micromachining For Silicon Mold Fabrication And Hot Embossing For Polymer Microreplication

Abstract

Hot embossing is a fabrication technique employed for replicating microfeatures on a polymer surface that was primarily developed to fabricate MEMS devices for microfluidic applications. This manuscript deals with characterization of the femtosecond laser micromachining (FLM) and hot embossing (HEMM) processes for master mold fabrication on silicon and polymer replication respectively. Given the required size of the features to be fabricated or replicated, process parameters for FLM can be determined using the derived empirical equations, process parameters for the HEMM process can be established using the characteristic plots. A novel two-stage embossing process is developed and introduced that employs polymer molds during the second stage. Validation experiments along with results focusing on mold quality with respect to the embossing cycles of the secondary polymer mold and the embossing quality of the substrate as compared to the primary silicon mold have been presented. Micromachining of a biodegradable polymer, PLLA, with potential drug delivery applications have been performed using hot embossing and laser micromachining. The comparison of flow rate of PLLA into the mold during single and two stage embossing has been studied. Threshold fluence values of different number of pulses for PLLA during femtosecond laser micromachining have been determined. Finally, process parameters for thermal bonding using the HEMM system of two PMMA substrates are established along with their effects on feature quality after bonding.