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Micromachines 2016, 7(12), 234; doi:10.3390/mi7120234

Investigation of Surface Pre-Treatment Methods for Wafer-Level Cu-Cu Thermo-Compression Bonding

1
Department of Robotics, Tohoku University, 6-6-01, Aza Aoba, Aramaki Aoba-ku, Sendai 980-8579, Japan
2
Fraunhofer Institute for Electronic Nano Systems (ENAS), Technology Campus 3, Chemnitz 09126, Germany
3
World Premier International Research Center Initiative-Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
4
Micro System Integration Center (µSIC), Tohoku University, 6-6-01, Aza Aoba, Aramaki Aoba-ku, Sendai 980-8579, Japan
5
Center for Microtechnologies (ZfM), Technische Universität Chemnitz, Reichenhainer Str. 70, Chemnitz 09126, Germany
*
Author to whom correspondence should be addressed.
Academic Editors: Frank Niklaus and Roy Knechtel
Received: 20 October 2016 / Revised: 25 November 2016 / Accepted: 7 December 2016 / Published: 15 December 2016
(This article belongs to the Special Issue 3D Integration Technologies for MEMS)
View Full-Text   |   Download PDF [1239 KB, uploaded 15 December 2016]   |  

Abstract

To increase the yield of the wafer-level Cu-Cu thermo-compression bonding method, certain surface pre-treatment methods for Cu are studied which can be exposed to the atmosphere before bonding. To inhibit re-oxidation under atmospheric conditions, the reduced pure Cu surface is treated by H2/Ar plasma, NH3 plasma and thiol solution, respectively, and is covered by Cu hydride, Cu nitride and a self-assembled monolayer (SAM) accordingly. A pair of the treated wafers is then bonded by the thermo-compression bonding method, and evaluated by the tensile test. Results show that the bond strengths of the wafers treated by NH3 plasma and SAM are not sufficient due to the remaining surface protection layers such as Cu nitride and SAMs resulting from the pre-treatment. In contrast, the H2/Ar plasma–treated wafer showed the same strength as the one with formic acid vapor treatment, even when exposed to the atmosphere for 30 min. In the thermal desorption spectroscopy (TDS) measurement of the H2/Ar plasma–treated Cu sample, the total number of the detected H2 was 3.1 times more than the citric acid–treated one. Results of the TDS measurement indicate that the modified Cu surface is terminated by chemisorbed hydrogen atoms, which leads to high bonding strength. View Full-Text
Keywords: wafer bonding; thermo-compression bonding; pre-treatment; Cu-Cu bonding; 3D integration wafer bonding; thermo-compression bonding; pre-treatment; Cu-Cu bonding; 3D integration
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Tanaka, K.; Wang, W.-S.; Baum, M.; Froemel, J.; Hirano, H.; Tanaka, S.; Wiemer, M.; Otto, T. Investigation of Surface Pre-Treatment Methods for Wafer-Level Cu-Cu Thermo-Compression Bonding. Micromachines 2016, 7, 234.

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