SMOOTHING OF ULTRASONICALLY DRILLED HOLES IN BOROSILICATE GLASS BY WET CHEMICAL ETCHING

Besides silicon various types of glass play an important role in micro system technology. One requirement of the glasses is that they have to be microstructurable. In many applications for microsensors and micro structures the glass must be suitable for anodic bonding. Usually boro silicate glass (e.g. Coming Pyrex code 7740 glass) is used, which has a thermal expansion coefficient that is almost equal to the thermal ex pansion coefficient of silicon and which has the necessary electrical conductivity at the temperature at which the bonding process occurs. F or many applications, e.g., microfluidic systems, it is necessary to h ave fluids flown through ultrasonically drilled holes in the Pyrex gla ss to the silicon chip. The main objective of the investigation was to obtain smooth walls of ultrasonically drilled holes because every con tamination influences the performance of the microsystem. In this pape r the ultrasonic drilling method is compared with two other procedures for machining holes (sand blasting and laser machining). Other ways o f structuring glass have been presented previously. A process was deve loped to smooth the walls of the drilled holes with different concentr ations of hydrofluoric acid.