Removal of copper from silicon surfaces using hexafluoroacetylacetone (hfacH) dissolved in supercritical carbon dioxide

Bo Xie, Casey C. Finstad, Anthony J. Muscat

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37 Scopus citations


Copper was etched from a silicon surface using the chelator hexafluoroacetylacetone (hfacH) dissolved in supercritical carbon dioxide (scCO 2) at 40-60°C and 100-250 atm. Copper was deposited on Si(100) using doped HF solutions in the form of 10-90 nm Cu islands, as shown by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) indicated the islands were composed of Cu(I) 2O due to air exposure before etching was attempted. Oxidation of the Cu(I) was performed using aqueous 30% H 2O 2 or a UV-Cl 2 gas phase, forming shells of Cu(II)O or Cu(II)Cl 2, respectively, surrounding cores of Cu(I) 2O. SEM images showed that the Cu(II)O had a flake morphology. The Cu(II) shells were removed selectively to the Cu(I) 2O cores by processing with pure scCO 2 and rapidly releasing the system pressure (300 atm/min). Mechanical failure of the Cu(II)O and Cu(II)Cl 2 when CO 2 in stress corrosion cracks quickly expanded delaminated these layers, leaving only Cu(I) 2O on the surface. Etching of both Cu(II) and Cu(I) was achieved when oxidized samples were processed in scCO 2 containing approximately 120 ppm of hfacH for 2 min. Nucleophilic attack of Cu(II) centers by hfacH formed copper(bis-hexafluoroacetylacetonate), Cu(hfac) 2 and water, or the monohydrate Cu(hfac) 2· H 2O, which was soluble in scCO 2. The Cu(hfac) 2·H 2O byproduct is proposed to oxidize Cu(I) 2O to Cu(II), allowing attack and etching by hfacH.

Original languageEnglish (US)
Pages (from-to)1753-1764
Number of pages12
JournalChemistry of Materials
Issue number7
StatePublished - Apr 5 2005
Externally publishedYes

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering
  • Materials Chemistry


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