Glass Slurry Applied Research In The Mems Wafer-level Hermetic Package

Wafer bonding is an essential technological step for wafer encapsulation of sensitive structures like freely moveable MEMS. In the last years,different wafer bonding technology were established in research and in industrial production processes. The wafer bonding steps have to be adapted to the special application or the technology environment. Therefore we were looking for a bonding technology, which is universally useable for a wide range of applications,independent on preceding process steps and design variations. Glass frit wafer bonding fulfils these requirements and provides furthermore a safe process with high bonding yield,very well suitable for industrial production.This paper demonstrated on the package process, from screen printing, glass frit firing to wafer bonding. To improve glass frit printing uniformity,detail process characterization of glass frit printing by using precision screen printing machine and firing were carried on and discussed in this work. To reach high accuracy of screen printing, a diameter of 2mm of circle mark, which is etched by dry etching,was fabricated.And to improve glass frit uniformity and smoothness,printing speed of 8mm/s and two times printing was used ,and the firing process of 15-20min holding time at 450°C in vacuum atomphere was adopted. In the bonding step,450°C of bonding temperature and 300mbar of bonding pressure were selected .After bonding, no void but few organic solvents were observed through polished cross-section of bonding area and the strength of bonding area was high. But the width of glass frit after bonding was increased excessively. To limit the width of glass frit after bonding,etched channels were fabricated before printing to improve process yield of glass frit of wafer bonding.Shear test results of improved samples fulfiled the corresponding MIL-STD standard. In the leakage test, the qualification rate reached to as high as 95%.The quality factor Q of device measured after vacuum packaging reached to 577.41, compared to 301.9 of no vacuum packaging. And glass frit wafer bonding allows hermetic sealing and a high process yield.