Hot-embossing performance of silicon micromold coated with self-assembled n-octadecyltrichlorosilane

Self-assembled monolayer (SAM) coatings of n-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] were deposited on Si micromolds for micro hot-embossing by dipping the Si molds into an anhydrous toluene solvent containing OTS. The coated samples were designated as OTS20, OTS40, OTS60 and OTS80 with respect to deposition time of 20, 40, 60 and 80 min to study the effect of deposition time on the coating quality. The composition, surface roughness, friction coefficient, thermal stability and surface energy were measured using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), nanotribological test and contact angle test, respectively. The thermal stability of the OTS coatings was determined by measuring water contact angle after heating at various temperatures. The XPS and AFM results showed that a prolonged deposition induced a denser and thicker coating structure and more aggregation of OTS, which also increased the surface roughness. A comparative study of the uncoated and OTS60 coated Si micromolds depicted that the OTS coatings had a good potential to improve the surface quality and efficiency of the molds. The OTS60 coating was evaluated after heat treatment at embossing temperature of 130 °C for a better understanding of the failure mechanism of the micromolds, which showed that the surface properties of the molds remained unchanged at the embossing temperature. Further characterization of the damaged Si micromolds showed that the peel-off of the coatings after a number of replications was the main reason for the failure of the molds. It was found that periodic re-cleaning of the micromolds and re-deposition of the OTS coatings on the coated Si micromolds could extend the lifetime of the molds up to about 112 embossing operations per mold.