A Compact Low-Cost Low-Maintenance Open Architecture Mask Aligner for Fabrication of Multilayer Microfluidics Devices
A custom-built mask aligner (CBMA), which fundamentally covers all the key features of a commercial mask aligner, while being low cost, light weight, and having low power consumption and high accuracy is constructed. The CBMA is comprised of a custom high fidelity LED light source, vacuum chuck and mask holder, high-precision translation and rotation stages, and high resolution digital microscopes. The total cost of the system is under $7,500, which is over ten times cheaper than a comparable commercial system. It produces a collimated ultraviolet illumination of 1.8-2.0 mW cm-2 over an area of a standard 4-inch wafer, at the plane of the photoresist exposure; and the alignment accuracy is characterized to be < 3 microns, which is sufficient for most microfluidic applications. Moreover, this manuscript provides detailed descriptions of the procedures needed to fabricate multilayered master molds using our CBMA. Finally, the capabilities of the CBMA are demonstrated by fabricating two and three-layer masters for micro-scale devices, commonly encountered in biomicrofluidics applications. The former is a flow-free chemical gradient generator and the latter is an addressable microfluidic stencil. Scanning electron microscopy is used to confirm that the master molds contain the intended features of different heights.