A new masking technology for deep glass etching and its microfluidic application

A new masking technology for wet etching of glass, to a depth of more than 300 mum, is reported. Various mask materials, which can be patterned by standard photolithography and metal etching processes, were investigated for glass etching in concentrated hydrofluoric acid (HF). A multilayer of metal, Cr/Au/Cr/Au, in combination with thick SPR220-7 photoresist, was found to be ideal for this purpose. Through holes etched from both sides of a 500 mum thick Pyrex glass wafer were obtained. Pinholes, created in the glass by failure of simple metal masking when subjected to HF etching, were successfully eliminated using the new masking technology. In addition, the lateral undercutting of glass caused by the underetching of the Cr mask was minimized to 27% of the etching depth. With these advantages, this newly developed masking method was successfully applied to fabricate microfluidic components for a micro-peristaltic pump to be integrated in a micro polymerase chain reaction (PCR) device. These components include through holes for liquid accessing and electrical contacting and a 200 mum thick pump diaphragm. This new masking technology also adds to the methods available to fabricate the microfluidic devices in glass substrates. (C) 2004 Elsevier B.V. All rights reserved.