Effects of vacuum ultraviolet surface treatment on the bonding interconnections for flip chip and 3-D integration

Katsuyuki Sakuma*, Jun Mizuno, Noriyasu Nagai, Naoko Unami, Shuichi Shoji

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


This paper focuses on the effects of a vacuum ultraviolet (VUV) surface treatment process on the interconnections for flip chip and 3-D integration. Organic contaminants that hinder reliable bonding are broken down and eliminated from the bumps and pad surfaces by irradiation with UV light at a wavelength of 172 nm at room temperature. There is no charge buildup, no temperature increase, and no ion bombardment damage during the process. Two different VUV cleaning conditions, with N2 or O2 gas in the vacuum chamber, were compared and evaluated. Samples of flip chip with Cu/Sn bumps and Au surface substrate were examined by measurement of contact angle, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) before and after VUV surface treatment. Cleaning times and ambient conditions have dramatic effects on the surface contact angles. The photoelectron spectra of C 1s were obtained by XPS analysis for information on the chemical species and the XPS results showed a reduction in surface carbon for both Au and Cu/Sn after the cleaning. The evidence indicates cleavage of the carboncarbon bonds in the organic molecules occurs during the cleaning process. From the shear test results, it appears that VUV treatment improves the Cu/Sn-bump bonding strength, making it two times larger than for untreated samples. No delamination or obvious voids were detected on the bonding interface by Scanning acoustic microscopy (SAM) and cross-sectional SEM analysis. The experiments show that the VUV cleaning can effectively remove the organic contaminants on the surface of the bonding pads and improve the bonding strength.

Original languageEnglish
Article number5471123
Pages (from-to)212-220
Number of pages9
JournalIEEE Transactions on Electronics Packaging Manufacturing
Issue number3
Publication statusPublished - 2010 Jul


  • Bonding
  • Cu/Sn
  • VUV (vacuum ultraviolet)
  • flip chip
  • micro-bump
  • three-dimensional (3-D) integration

ASJC Scopus subject areas

  • Industrial and Manufacturing Engineering
  • Electrical and Electronic Engineering


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