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Title: Physical mechanisms of copper-copper wafer bonding

The study of the physical mechanisms driving Cu-Cu wafer bonding allowed for reducing the bonding temperatures below 200 °C. Metal thermo-compression Cu-Cu wafer bonding results obtained at such low temperatures are very encouraging and suggest that the process is possible even at room temperature if some boundary conditions are fulfilled. Sputtered (PVD) and electroplated Cu thin layers were investigated, and the analysis of both metallization techniques demonstrated the importance of decreasing Cu surface roughness. For an equal surface roughness, the bonding temperature of PVD Cu wafers could be even further reduced due to the favorable microstructure. Their smaller grain size enhances the length of the grain boundaries (observed on the surface prior bonding), acting as efficient mass transfer channels across the interface, and hence the grains are able to grow over the initial bonding interface. Due to the higher concentration of random high-angle grain boundaries, this effect is intensified. The model presented is explaining the microstructural changes based on atomic migration, taking into account that the reduction of the grain boundary area is the major driving force to reduce the Gibbs free energy, and predicts the subsequent microstructure evolution (grain growth) during thermal annealing.
Authors:
 [1] ;  [2] ;  [3]
  1. EV Group, DI E. Thallner Straße 1, 4782 St. Florian/Inn (Austria)
  2. (Austria)
  3. Center for Surface- and Nano Analytics, Johannes Kepler University, 4040 Linz (Austria)
Publication Date:
OSTI Identifier:
22492786
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 13; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANNEALING; COMPRESSION; COPPER; FREE ENTHALPY; GRAIN BOUNDARIES; GRAIN GROWTH; GRAIN SIZE; INTERFACES; MASS TRANSFER; PHYSICAL VAPOR DEPOSITION; RANDOMNESS; ROUGHNESS; SPUTTERING; THIN FILMS