一种MEMS陀螺晶圆级真空封装工艺
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摘要
为了提高MEMS陀螺的品质因数(Q值),提出了一种晶圆级真空封装工艺。先在陀螺盖帽晶圆上刻蚀出浅腔,然后在浅腔结构上制备钨(W)金属引线,再通过PECVD工艺淀积介质层,在介质层上制备钛/金(Ti/Au)键合环,最后将盖帽晶圆与制备好的结构晶圆完成金硅共晶键合,并利用吸气剂实现晶圆的长久真空封装。经测试,采用本方案的封装的气密性与金属层厚度紧密相关,调整合适的金属层厚度后可使真空泄漏速率小于2.0×10-12 Pa·m~3·s-1。此外,设计了一种特殊的浅腔阵列结构,该结构将金硅键合强度从小于20 MPa提升至大于26 MPa,同时可防止键合时液相合金向外溢流。对陀螺芯片的性能测试表明,该真空封装工艺简单有效,封装气密性良好,Q值高达168 540,满足设计指标要求。
In order to improve the quality factor(Q value)of the MEMS gyro,a wafer level vacuum packaging process was proposed.Firstly,the shallow cavities were etched on the gyro cap wafer.Then,tungsten(W)metal leads were fabricated on the shallow cavities,and a dielectric layer was deposited by the PECVD process.After that,the titanium/gold(Ti/Au)bonding rings were prepared on the dielectric layer.Finally,the cap wafer was bonded with the prepared structural wafer by the Au/Si eutectic bonding process,and the getters were used to realize the wafer long-term vacuum packaging.The test results show that the hermeticity of the package is closely related to the thickness of the metal layer.By adjusting the appropriate thickness of the metal layer,the vacuum leak rate can be reduced to less than 2.0×10-12 Pa·m~3·s-1.In addition,a special shallow cavity array structure was designed to increase the Au/Si bonding strength from less than20 MPa to more than26 MPa,preventing the overflowing of the liquid alloy during bonding process simultaneously.The performance test results of the gyro chip demonstrate that the vacuum packaging process is simple and effective,and an excellent hermetic sealing is obtained,the Qvalue is as high as 168 540,satisfying the design specifications.
In order to improve the quality factor(Q value)of the MEMS gyro,a wafer level vacuum packaging process was proposed.Firstly,the shallow cavities were etched on the gyro cap wafer.Then,tungsten(W)metal leads were fabricated on the shallow cavities,and a dielectric layer was deposited by the PECVD process.After that,the titanium/gold(Ti/Au)bonding rings were prepared on the dielectric layer.Finally,the cap wafer was bonded with the prepared structural wafer by the Au/Si eutectic bonding process,and the getters were used to realize the wafer long-term vacuum packaging.The test results show that the hermeticity of the package is closely related to the thickness of the metal layer.By adjusting the appropriate thickness of the metal layer,the vacuum leak rate can be reduced to less than 2.0×10-12 Pa·m~3·s-1.In addition,a special shallow cavity array structure was designed to increase the Au/Si bonding strength from less than20 MPa to more than26 MPa,preventing the overflowing of the liquid alloy during bonding process simultaneously.The performance test results of the gyro chip demonstrate that the vacuum packaging process is simple and effective,and an excellent hermetic sealing is obtained,the Qvalue is as high as 168 540,satisfying the design specifications.
引文
[1]杨静,张富强.圆片级真空封装技术在MEMS陀螺中的应用[J].微纳电子技术,2012,49(5):69-73.
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[5] MITCHELL J,LAHIJI G R,NAJAFI K.Encapsulation of vacuum sensors in a wafer level package using agold-silicon eutectic[C]//Proceedings of the 13th International Conference on Solid-State Sensors,Actuators and Microsystems.Seoul,South Korea,2005:928-931.
[6] TISONE T C,DROBEK J.Diffusion in thin film Ti-Au,TiPd,and Ti-Pt couples[J].Journal of Vacuum Science and Technology,1972,9(1):271-275.
[7]王翔,张大成,李婷,等.压阻加速度计的Au-Si共晶键合[J].半导体学报,2003,24(3):332-336.
[8]张卓,汪学方,王宇哲,等.MEMS圆片级真空封装金硅键合工艺研究[J].电子与封装,2011,11(1):1-4.
[9]陈颖慧,施志贵,郑英彬,等.金-硅共晶键合技术及其应用[J].纳米技术与精密工程,2015,13(1):69-73.
[10]王玉朝,滕霖,孙香政,等.真空封装硅微陀螺品质因数的标定[J].光学精密工程,2014,22(10):2708-2714.
[2]胥超,徐永青,杨拥军,等.Au/Sn共晶键合技术在MEMS封装中的应用[J].微纳电子技术,2014,51(2):131-135.
[3] ESASHI M.Wafer level packaging of MEMS[J].Journal of Micromechanics and Microengineering, 2009, 18(7):073001-1-073001-13.
[4] MITCHELL J S,NAJAFI K.A detailed study of yield and reliability for vacuum packages fabricated in a wafer-level Au-Si eutectic bonding process[C]//Proceedings of International Solid-State Sensors,Actuators and Microsystems Conference.Denver,CO,USA,2009:841-844.
[5] MITCHELL J,LAHIJI G R,NAJAFI K.Encapsulation of vacuum sensors in a wafer level package using agold-silicon eutectic[C]//Proceedings of the 13th International Conference on Solid-State Sensors,Actuators and Microsystems.Seoul,South Korea,2005:928-931.
[6] TISONE T C,DROBEK J.Diffusion in thin film Ti-Au,TiPd,and Ti-Pt couples[J].Journal of Vacuum Science and Technology,1972,9(1):271-275.
[7]王翔,张大成,李婷,等.压阻加速度计的Au-Si共晶键合[J].半导体学报,2003,24(3):332-336.
[8]张卓,汪学方,王宇哲,等.MEMS圆片级真空封装金硅键合工艺研究[J].电子与封装,2011,11(1):1-4.
[9]陈颖慧,施志贵,郑英彬,等.金-硅共晶键合技术及其应用[J].纳米技术与精密工程,2015,13(1):69-73.
[10]王玉朝,滕霖,孙香政,等.真空封装硅微陀螺品质因数的标定[J].光学精密工程,2014,22(10):2708-2714.