Stress reduction in silicon/oxidized silicon–Pyrex glass anodic bonding for MEMS device packaging: RF switches and pressure sensors

Standard temperature for anodic bonding process (usually 450 °C) degrade the MEMS device performance due to stress generated on mechanical components during wafer level packaging. The traditional perspective of bonding at medium temperatures (280–350 °C) by various research communities were pertaining to lesser efficiency and un-reliability. Partial bonding and increased number of voids were the results of medium temperature bonding. Here we introduce a new method that reduced the bonding temperature well below to 280 °C for silicon–Pyrex bond and to 320 °C for oxidized silicon–Pyrex bond. This article reports the study of stress reduction (by reducing the bow) in bonding material by decreasing bonding temperature through a modified electrode (cathode) in anodic bonding process. Dropping the temperature from 450 to 280 °C has reduced the bowing effect up to 51 times. Also the effect of glass thickness (2 and 1 mm) on bonding has been studied. It was found that there was a decrease of 49 and 53 % in bow height (at 400 and 450 °C) when used 1 mm thick Pyrex glass instead of 2 mm thick glass. The amount of gas trapped to form voids while bonding by means of the new load, has reduced to a great level. Extensive characterization of the surfaces and interfaces have been made with AFM, OM, SEM and laser bow measurement equipment which defines the surface roughness, cleanliness, bubble formation, interface integrity and surface bow.