Production of Liquid Cluster Ions for Surface Treatment

Abstract

We have developed a cluster ion beam system using organic liquid materials, which has several advantages for surface etching and chemical modification based on the different properties of liquid cluster ions. By utilizing the system, ethanol vapor was ejected through a nozzle into a high-vacuum region, and ethanol clusters were produced by an adiabatic expansion phenomenon. The clusters were ionized by an electron bombardment method, and cluster ions were accelerated toward a substrate by applying an acceleration voltage. Silicon substrates were irradiated at different acceleration voltages with ethanol cluster ion beams, and chemical sputtering of the substrate surface was achieved even at an acceleration voltage of a few kV. In addition, the sputtering yield at an acceleration voltage of 9 kV was approximately 100 times larger than that by argon ion beams, and the sputtered surface had an average roughness of less than 1 nm. Thus, ethanol cluster ion beams have unique characteristics suitable for surface treatment, such as high sputtering yield and smooth surface at an atomic level.