Investigation of Eutectic and Solid State Wafer Bonding of Silicon with Gold

• Author / Creator

  Abouie, Maryam

• Permanent wafer bonding technology is a very important process for different types of applications such as MEMS (microelectromechanical systems), LED (light-emitting diode) devices, advanced packaging, 3D stack and SOI (silicon on isolator) substrate applications. Depending on the type of application, several bonding technologies exist. The MEMS market road map suggests the market for MEMS will be close to $21B in 2017.
  The driving force for development of different wafer bonding processes is the large applications that need to be addressed. The wafer bonding market generated almost 5 million 8-inch wafers bonded for BSI (back-illuminated sensor), CIS (CMOS image sensor) and MEMS device applications and it is expected to reach 16 million 8-inch bonded wafers in 2019. The growing demand is mainly driven by the miniaturization required for 3D Stack TSV (through- silicon via) applications.
  Among different wafer bonding techniques, eutectic bonding is more appealing due to its good hermeticity, ability to create electrical connection, good mechanical strength and low temperature processing.
  In this study, Au-Si eutectic bonding was applied due to its high bonding strength, excellent hermeticity and good tolerance to surface topology prior to bonding. Au/a-Si wafer bonding was introduced in order to reduce the risk of possible damage to active devices in Au/c-Si wafer bonding due to formation of large craters in c-Si. Solid state bonding was introduced in order to reduce the process temperature, which is desirable in the manufacturing industry. Bonding parameters were optimized as much as possible. The microstructure of bonded pairs was imaged using SEM (scanning electron microscopy) and TEM (transmission electron microscopy) for both Au/a-Si and Au/c-Si samples and for both eutectic and solid state methods. In-situ TEM imaging of the Au/a-Si diffusion couple during annealing was performed in an attempt to understand and explain the reason for the layer exchange mechanism in Au/a-Si wafer bonding. The diffusion coefficient for Au in a-Si was also calculated using in-situ TEM results. The mechanical strength of bonded wafers was measured using shear testing on eutectic and solid state bonded Au/a-Si and Au/c-Si samples.

• Subjects / Keywords

  • Eutectic bonding
  • Au
  • Wafer bonding
  • C-Si
  • Solid state bonding
  • A-Si

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R32D5H

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.