Investigation of surface pre-treatment methods for wafer-level Cu-Cu thermo-compression bonding

Koki Tanaka, Wei Shan Wang, Mario Baum, Joerg Froemel, Hideki Hirano, Shuji Tanaka, Maik Wiemer, Thomas Otto

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

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.

Original languageEnglish
Article number234
JournalMicromachines
Volume7
Issue number12
DOIs
Publication statusPublished - 2016

Keywords

  • 3D integration
  • Cu-Cu bonding
  • Pre-treatment
  • Thermo-compression bonding
  • Wafer bonding

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Mechanical Engineering
  • Electrical and Electronic Engineering

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