The use of glasses in low-temperature wafer bonding processes

Abstract In wafer bonding technologies used for micro-electro-mechanical systems (MEMS) capping, sealing and system integration, the bonding temperature is becoming an increasingly critical parameter with respect to very different aspects such as device functionality and for the process itself, especially in terms of overall process time, which directly defines both the bonding process cost and the bonding tool capacity. This paper shows that even for classical bonding processes, such as anodic and glass frit bonding, temperatures can be reduced, resulting in functional benefits such as avoiding outgassing of plasma-enhanced chemical vapour deposition layers into the sealed cavities and allowing the use of temperature sensitive materials in wafer bonded MEMS. For the standard glass Schott Borofloat ® 33 it has been shown that anodic wafer bonding can be performed at 200 °C if the thermomechanical stress between glass and silicon, which is higher at this process condition, is not critical for the realted application. Using a newly available material, AGC TNS-062, glass frit bonding can be done at temperatures as low as 310 °C. These significantly lower bonding temperatures, demonstrated in two different wafer bonding processes, enable more economical processing with about 1/3 shorter bonding times, reduced energy requirements and increased wafer bonding tool capacity.