Development of Cu Etching Using O₂ Cluster Ion Beam under Acetic Acid Gas Atmosphere

Abstract

Cu etching was carried out at a low substrate temperature using a gas cluster ion beam (GCIB) under an acetic acid gas atmosphere. A very shallow Cu surface was oxidized by O2-GCIB irradiation. Reactions between copper oxide and acetic acid occurred, and the reaction products were desorbed by local heating owing to the O2-GCIB irradiation. Thus, Cu etching at a low substrate temperature (<60 °C) was achieved. By introducing acetic acid gas during O2-GCIB irradiation, the etching depth of Cu became almost 29 times higher than the depth achieved when the etching was carried out using O2-GCIB alone at an acceleration voltage of 5 kV. In addition to the etching of Cu, there was no surface roughening after O2-GCIB irradiation under acetic acid atmosphere.

The new mechanism of sputtering with cluster ion beams

“…According to the authors [3,4] just lateral sputtering is the dominating process in surface smoothing. Up to now, extensive information on this smoothing effect for various materials under irradiation by cluster ions of inert and chemically active gases has been accumulated [5,6]. At the same time, it should be noted that insufficient attention was paid to investigations of angular distributions of sputtered particles.…”

Gas Cluster Ion Beam Etching under Acetic Acid Vapor for Etch-Resistant Material

“…However, it reached saturation at around 5:3 Â 10 À3 Pa, which indicates that the surface coverage of acetic acid is sufficient. 19) If the partial pressure of acetic acid becomes too high, a decrease of etching would occur due to collisions of GCIB with residual gases. 23) The thicknesses of Pt, Ru, Ta, CoFe, Si 3 N 4 , and SiO 2 films were 100, 100, 300, 300, 150, and 500 nm respectively.…”

“…In order to overcome this problem, introduction of reactive gas as a background gas was performed during GCIB irradiation. 19) Enhancement of chemical reactions between background gas and the target surface is expected by GCIB irradiation. 20) In addition, etching products desorb from the surface by the heating effects of GCIB irradiation.…”

“…Recently, we have reported Cu etching with O 2 -GCIB irradiation under acetic acid vapor at room temperature without halogen gas. 19) In this study, by extending this method, we examined etching effects of Pt, Ru, Ta, CoFe, Si 3 N 4 , and SiO 2 by Ar-or O 2 -GCIB irradiation under acetic acid vapor. In addition, surface morphology, angular distribution of sputtered materials, and surface composition analysis with XPS were carried out for Pt after O 2 -GCIB irradiation with or without acetic acid in order to understand the etching process.…”