Microfluidic chip designs process optimization and dimensional quality control

Abstract

The challenge of fabricating geometries with critical dimensions ranging from few microns down to 10 nm with high production rate is delaying the development of nanotechnology based products. Diverse research works have shown the capability of technologies such as UV lithography, nano imprint lithography and e-beam lithography to produce micro and nano features. However, their application for tooling purposes is relatively new and the potential to produce nanometer features with high volume and low cost is enormous. Considering possible implementation in a mass production environment the precision of measuring results and the accuracy of measurement relocation are very relevant. In this paper, the capability of producing with high volume Lab-on-chip devices through injection molding is evaluated. Preparation of master geometries was made in a Si wafer using e-beam lithography and reactive ion etching. Subsequent nickel electroplating was employed to replicate the obtained geometries on the tool, which was used to mold on transparent polymer substrates the functional structures. To assess the critical factors affecting the replication quality throughout the different steps of the proposed process chain, test geometries were designed and produced on the side of the functional features. The so-called "Finger Print" of the lithography and molding processes was qualitatively and quantitatively evaluated through scanning electron microscopy and atomic force microscopy respectively. The entire process chain is therefore characterized and the degree of replication among the different replication steps quantified with precise measurements using a high accuracy relocation technique on the produced key test geometries. Influence of injection molding process parameters, feature dimensions and orientation relative to the polymer flow direction have been assessed in respect of the replication fidelity of the produced micro/sub-μm channels. Finally the paper addresses product compliance with specifications, focusing on tolerances of vertical dimensions using a metrological approach: sub-μm features on silicon, nickel stampers and injection molded substrates are measured. Results of measurement uncertainty calculation, quantitative replication fidelity assessment, and dimensional tolerances at the nanometer scale verification are reported.