Fundamental characteristics of liquid cluster ion source for surface modification

We have developed a cluster ion source using liquid organic materials, which has several advantages for surface modification based on the different properties of liquid cluster ions. When vapors of liquid materials such as ethanol were ejected through a nozzle into a high-vacuum region, clusters were produced by an adiabatic expansion phenomenon. The clusters produced were ionized by an electron bombardment method, and the cluster ion current increased with increase of an electron current for ionization. In order to achieve the effective transport of cluster ion beams, a unipotential or einzel lens was used. The current density was much larger than that without using the lens. Furthermore, the beam diameter could be controlled by adjusting the lens voltage, and it was changed between 5 mm and 20 mm. In addition, several kinds of substrates such as Si, SiO₂, PC substrates were irradiated at different acceleration voltages with ethanol cluster ion beams, and chemical and physical sputtering with a high sputtering yield was achieved. The sputtered surfaces were very smooth at an atomic level. The liquid cluster ion beams have a high potential for surface etching with the atomic level flatness, which is not obtained by a conventional wet process.