S. Mack et al., GAS DEVELOPMENT AT THE INTERFACE OF DIRECTLY BONDED SILICON-WAFERS - INVESTIGATION ON SILICON-BASED PRESSURE SENSORS, Sensors and actuators. A, Physical, 56(3), 1996, pp. 273-277
Hydrophobic and hydrophilic silicon direct bonding (SDB) under vacuum
conditions are compared with respect to the capability to form hermeti
cally sealed cavities with minimal enclosed residual gas pressure, The
quality of the enclosed vacuum inside the cavities of pressure-sensor
test structures is monitored for different cavity layouts and anneali
ng processes. The observed pressure increase during annealing is found
to be strongly dependent on annealing temperature, subsequent storage
time and on the bonded area surrounding each cavity. Trapped gaseous
reaction products originating at the bonding interface are responsible
for this effect. There is a significant difference in annealing-relat
ed gas evolution for hydrophobic and hydrophilic bonding surfaces, whi
ch can be explained by the existing theories of the bonding mechanism,
Hydrophobic bonding leads to about 50% lower residual gas pressures c
ompared with hydrophilic bonding. For hydrophilically bonded wafers a
slow saturation of the gas pressure after annealing is observed.