Oxidation Resistive, CMOS Compatible Copper-Based Alloy Ultrathin Films as a Superior Passivation Mechanism for Achieving 150 degrees C Cu-Cu Wafer on Wafer Thermocompression Bonding

Panigrahi, A K and Ghosh, T and Vanjari, S R K and Singh, S G (2017) Oxidation Resistive, CMOS Compatible Copper-Based Alloy Ultrathin Films as a Superior Passivation Mechanism for Achieving 150 degrees C Cu-Cu Wafer on Wafer Thermocompression Bonding. IEEE Transactions on Electron Devices, 64 (3). pp. 1239-1245. ISSN 0018-9383

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Abstract

Surface passivation plays a dual role of protecting copper (Cu) from getting oxidized and reducing the surface roughness of Cu thin film and thus enables low-temperature Cu-Cu bonding. In this paper, we utilized an oxidation resistive, CMOS compatible copper-nickel-based alloy, constantan as a passivation layer, as it does not get oxidized at room temperature and is also CMOS damascene process compatible. Systematically optimized ultrathin, constantan (2 nm) on Cu surface not only protected Cu from oxidation but also reduced the surface roughness to about 0.7 nm, which led to Cu-Cu bonding at a temperature as low as 150 degrees C at 4 bar pressure. Cross-sectional TEM of bonded Cu layer reveals very significant interdiffusion and grain growth between the Cu films resulting in a zigzag bonding interface and the presence of Cu grains that extend across the entire bonding layer. Furthermore, reliability investigation of passivated Cu bonded structure was demonstrated using current stressing, temperature cycling test, and relative humidity test, which suggest excellent stable bonding without electrical performance degradation. This method of alloy-based passivation is confirmed to be effective and enable low temperature, low-pressure Cu-Cu wafer on wafer bonding for 3-D integration applications.

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IITH Creators:
IITH CreatorsORCiD
Vanjari, S R KUNSPECIFIED
Singh, S Ghttp://orcid.org/0000-0001-7319-879X
Item Type: Article
Uncontrolled Keywords: 3-D integration; alloy passivation; Cu-Cu bonding; low temperature; ultrathin constantan
Subjects: Others > Electricity
Physics > Astronomy Astrophysics
Divisions: Department of Electrical Engineering
Depositing User: Team Library
Date Deposited: 23 Mar 2017 10:25
Last Modified: 18 Jul 2017 11:28
URI: http://raiith.iith.ac.in/id/eprint/3110
Publisher URL: https://doi.org/10.1109/TED.2017.2653188
OA policy: http://www.sherpa.ac.uk/romeo/issn/0018-9383/
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