Anodic bonding for Pyrex 7740 and nitride silicon for wafer level vacuum packaging

In this paper, some 4-in. glass wafers are bonded to silicon wafers covered with a silicon nitride layer of about 1 um thickness. The leakage rate is measured by Helium mass spectrometer. A set of 27 different anodic bonding conditions have been considered and three different conditions have been included for each of three process parameters: bonding temperature, anodic voltage and voltage supply time. Taguchi method has been used to reduce the number of experiments required for the leakage rate evaluation, thus obtaining nine independent cases out of the 27 possible combinations. Among the three process parameters, the bonding temperature has been found to cause the most dominant influence to the leakage rate. Time presents the second greatest response, and voltage presents the third greatest response. The minimum leakage rate of 0.4×10^-9 Pa. m³/sec can be achieved at the bonding temperature of 400 °C with the bonding pressure of 2000 mbar, the applied voltage of 800 V and the voltage supply time of 60 min.