The Role of Ultrafine Crystalline Behavior and Trace Impurities in Copper on Intermetallic Void Formation
Journal article, 2019

In the microelectronic component industry, because of the miniaturization of functional units, the interaction of materials and interfaces play a much more significant role in their performance. The result of this is that ultrafine crystalline and trace impurity behavior impact a device's operation to a much greater extent. This is the case with micro-connects for 3D integration, such as micro-bumps. Any unwanted crystalline behavior or interfacial segregated impurities can drastically alter a micro-connect's performance, with a particular issue being intermetallic void formation, often known as Kirkendall voiding. Currently, it is unclear under what conditions voids form and how to prevent them. This work studies the microstructural and compositional differences between samples with different voiding densities. Results show that samples that exhibit an ultrafine crystalline have a higher propensity to exhibit voiding. Also, there is a high concentration of trace impurities located in the electrochemically deposited Cu layer. After isothermal annealing, high concentrations of impurities are located at the interface between Cu and the Cu-Sn intermetallic compound of Cu3Sn. An alternative explanation to the traditional Kirkendall void formation theory is presented. The explanation is based on the interaction of trace impurities from the electroplating process and the microstructural evolution.

X-ray diffraction

residual stress

scanning transmission electron microscopy


time-of-flight secondary ion mass spectroscopy

Kirkendall voids

intermetallic voids



Glenn Ross

Aalto University

Per Malmberg

Chalmers, Chemistry and Chemical Engineering, Chemistry and Biochemistry

Vesa Vuorinen

Aalto University

Mervi Paulasto-Krockel

Aalto University

ACS Applied Electronic Materials

2637-6113 (eISSN)

Vol. 1 1 88-95

Subject Categories

Materials Chemistry

Other Materials Engineering


Chemical Imaging Infrastructure



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