Lithographic fabrication of soda-lime glass based microfluidics

Abstract Glass is an important material for chemical processing and analysis because of its relatively low cost, mechanical strength, chemical inertness, optical transparency, and electrical insulation and temperature resistance far beyond that of most polymeric materials. We have investigated techniques for direct writing with MeV ions on soda-lime glass as well as capping procedures to form closed buried channels suitable for high-pressure driven flow. Exposure and development of open-channel structures was studied using a combination of programmable proximity aperture lithography and different developers. Unlike our previous work on MeV ion beam lithography of natural silica where an 8% w/v HF in aqueous solution was used as a developer, it was found that 6% w/v HF + 0.5% w/v HCl was an effective developer. Addition of HCl to the developer was necessary, presumably to dissolve oxide residues that were insoluble in HF solution. Different capping and bonding procedures to create closed channels that are strong enough to withstand high hydrostatic pressure have also been tested. It was found that capping to create a closed channel could be achieved after thorough cleaning. This was followed by activation in ∼32% w/v NH 4 OH or ∼30% w/v H 2 O 2 solution, drying on a hot plate and bonded under uniaxial pressure in a furnace ramped up and down at 1 °C/min to 575 °C. Activation in H 2 O 2 was found to give better bonding. Other methods using HF lead to poor bonding due to oxide precipitation.