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SIMS21, Poland 2017 - Stefan Schwab abstract

Stefan Schwab oral presentation (OB2-Mon2-2-1)

Measurement of Ion Diffusion in Polymers used for Semiconductor Packaging

Stefan Schwab1,2, Julia Appenroth2, Sabine Holzer3, Stefan Miethaner4, Michael Bauer4, Holger Doepke4, Michael Nelhiebel3, Herbert Hutter2

1 Kompetenzzentrum Automobil und Industrieelektronik - TU Wien, Europastraße 8, 9524 Villach, Austria
2 TU Wien, Getreidemarkt 9, 1060 Wien, Austria
3 Infineon Technologies Austria AG, Siemensstraße 2, 9500 Villach, Austria
4 Infineon Technologies Germany AG, Wernerwerkstraße 2, 93049 Regensburg, Germany

Diffusion of mobile ions is a prominent reliability risk for high voltage transistors. Small amounts of contamination in the gate oxide can provoke a shift in the threshold voltage of these devices [1]. Therefore, it is of utmost importance to prevent mobile ions from reaching these sensitive areas. To protect the chip from environmental influences, various materials such as polymers and mold compounds are used for dielectric passivation and encapsulation [2]. Modern high voltage transistors are often operated under harsh conditions, such as high temperatures, high humidity and high ion contamination risk (e.g. in offshore wind farms). In order to evaluate the risk of ion diffusion through these materials, it is important to understand the fundamental diffusion properties of these materials, e.g. activation energies EA, under similar conditions.

Within this work, sodium, potassium and chlorine ion diffusion in three different polymers used for dielectric passivation are investigated. For that purpose, polymer samples are stored in aqueous salt solutions for several days at different temperatures from 90 °C to 150 °C. After that, depth profiles of the samples are acquired by means of time of flight secondary ion mass spectrometry. Implant standards are used for concentration calibration. The achieved depth profiles are fitted using an error function in order to determine the temperature dependent diffusion coefficients. The activation energies as well as the pre-exponential factors of the diffusion will be evaluated for each material by means of Arrhenius fitting. The results as well as additional influences on the diffusion properties (e.g. curing temperature) will be discussed.

This work was jointly funded by the Austrian Research Promotion Agency (FFG, Project No. 854247) and the Carinthian Economic Promotion Fund (KWF, contract KWF-1521/ 28101/40388).

[1] E. H. Snow, A. S. Grove, B. E. Deal, C. T. Sah, Journal of Applied Physics, 36 (1664), 1965

[2] W. Greig, Integrated Circuit Packaging, Assembly and Interconnections, 2007