Accelerated thermo-mechanical fatigue of copper metallizations studied by pulsed laser heating

- Laser setup for fast thermal cycling and reliability checks of metallizations on silicon substrates
- Tracking microstructure and topography site-specifically with electron backscatter diffraction and atomic force microscopy
- Detailed microstructural and topographical information throughout the entire experiment
- Four probe resistance measurements demonstrate changes in sheet resistance

Fatigue is an important reliability issue for microelectronics. In this work, a technique for fast thermal cycling of thin films on substrates is introduced using an infrared laser beam. The advantages of this method are the significantly increased heating and cooling rates compared to conventional slow furnace processes, and the use of readily available small pieces of metallized wafers, which avoid complicated sample preparation. To demonstrate the applicability of the new experimental setup two copper metallization films, differing in their content of additives used for film deposition, on silicon substrates were investigated with respect to microstructural, topographical and electrical changes due to pulsed thermo-mechanical loading. The results, such as grain growth and roughness evolution, are compared to results from specimens which experienced slow infrared furnace cycling. Furthermore, changes in electrical sheet resistance are shown. When analyzing the outcomes from processes of different heating/cooling rates, it can be stated that accelerated laser heating leads to faster changes in these properties which enables fast screening of metallization materials under development.

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