Irradiation effects of liquid cluster ion beams on silicon surfaces

We have developed a liquid cluster ion source, and produced liquid clusters such as ethanol and water clusters by an adiabatic expansion phenomenon. The average size was about 500 to 1000 molecules for the ethanol and about 2500 molecules for the water, respectively. The intensity of the cluster ion beams increased with increase of the vapor pressures. The irradiation effects of the liquid cluster ion beams on Si(100) surfaces were investigated. The sputtered depth increased with increase of an acceleration voltage for the ethanol and water cluster ions. In particular, the ethanol cluster ion irradiation sputtered the Si surface with the sputtering yield of approximately 100 times larger than that for Ar monomer ion irradiation. In addition, the Si surfaces after sputtering had an average roughness of less than 1 nm. Furthermore, the RBS channeling measurement showed that the irradiation damage of the Si surfaces by the ethanol and water cluster ions was smaller than that by the Ar monomer ion irradiation. This indicates that the low energy ion irradiation effect is predominant for the liquid cluster ion beams. As an engineering application of the liquid cluster ion beam process, the etching and patterning process were performed on the Si surfaces using metal masks. The mask patterns were formed very swiftly and finely by irradiation of the ethanol cluster ion beams.