Wafer-Level Low-Temperature Solid-Liquid Inter-Diffusion Bonding With Thin Au-Sn Layers for MEMS Encapsulation

Temel O., KALAY Y. E., AKIN T.

JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, vol.30, no.1, pp.64-71, 2021 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 30 Issue: 1
  • Publication Date: 2021
  • Doi Number: 10.1109/jmems.2020.3040039
  • Journal Name: JOURNAL OF MICROELECTROMECHANICAL SYSTEMS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, PASCAL, Aerospace Database, Applied Science & Technology Source, Communication Abstracts, Compendex, Computer & Applied Sciences, INSPEC, Metadex, Civil Engineering Abstracts
  • Page Numbers: pp.64-71
  • Keywords: Au-Sn, MEMS encapsulation, solid-liquid inter-diffusion bonding, SLID, transient liquid phase, TLP, wafer-level, wafer bonding
  • Middle East Technical University Affiliated: Yes

Abstract

A novel solid-liquid inter-diffusion ( SLID) bonding process is developed allowing to use thin layers of the Au-Sn material in wafer-level microelectromechanical systems (MEMS) packaging while providing a good bonding strength. The bond material layers are designed to have a robust bond material configuration and a metallic bond with a high re-melting temperature, which is an important advantage of SLID bonding or with its alternative name, transient liquid phase (TLP) bonding. The liquid phase in SLID bonding is the gold-rich eutectic liquid of the Au-Sn material system, where the bonding temperature is selected to be 320 degrees C for a reliable bonding. The average shear strength of the bonds is measured to be 38 +/- 1.8 MPa. The hermeticity of the package is tested with the He-Leak test according to MIL-STD 883, which yields a leak value lower than 0.1x10(-9) atm.cm(3)/s. The vacuum inside the package without a getter is calculated as 2.5 mbar after cap wafer thinning. The vacuum level is well preserved after post-processes such as annealing at 400 degrees C and the dicing process. These results verify that thin layers of Au-Sn materials can be used reliably with the SLID or TLP bonding technique using the new approach proposed in this study.