Nanoparticle bombardment -GCIB-

1. Meeting report 11.1.2007 Nanoparticle bombardment-GCIB- Inkyu Eu Univ.of Michigan Ann Arbor Mechanical Engineering

2. 1.What is the GCIB? -GCIB: Gas cluster ion beam -Using electrically charged cluster ions consisting of a few hundreds to a few thousands of atoms or molecules of gas-eous materials. -When an cluster ion impacts upon a surface, it interacts nearly simultaneously with many target atoms and deposits high energy density into a very small volume of the target material. Fig.1.Illustration of monomer and cluster ion beam concept

3. 1.What is the GCIB? -Result in highly non-linear sputtering and implantation effects which are fundamentally different from monomer ion impacts. Fig.2.Characteristics ofGCIB-solid surface interaction and their industrial application fields.

4. 2.The GCIB Experiment -Ethanol (organic liquid material) -The size separation of the ethanol cluster ions by a retarding potential method -The surface etching for several kinds of metal films irradiated by the ethanol cluster ion beams is investigated (To clarify the spe- cific characteristics of the cluster ion beam process for surface treatment.) Fig.4.Schematic of liquid cluster ion beam system.

5. 2.The GCIB Experiment -A cluster ion beam contains many monomer ions -Decreases rapidly at a retarding voltage of 0 V -The cluster ion current measured at positive retarding voltages increases with the increase in vapor pressure -An ion current of a few hundreds of nano Ampere is obtained Fig.5.Retarding spectrum for an ethanol ion beam

6. 2.The GCIB Experiment -The distributedcluster size and the intensity of ethanol clusters increases with the increase in vapor pressure. -Although the mass resolution is quite low in this method, ethanol cluster ions with a size larger than a few hundreds are obtained. Fig.6.Ethanol cluster size distribution measured at ionization conditions of Ve = 200 V and Ie = 200 mA as a parameter of ethanol vapor pressure.

7. 2.The GCIB Experiment -The surface etching by irradiation of ethanol cluster ion beams for the metal films consid- ering the etched depth and the ion dose, the sputtering yield was calculated by estimating the density of the metal films. -The sputtering yield for Al, Cu, Ag and Au films at an acceleration voltage of 9 kV. The cluster size was larger than 95 molecules per cluster. -The Al films, which have the small sputtering yield for the case of physical sputtering by Ar ion beams, are sputtered more effectively than the Cu, Ag and Au films.(due to the enhancement of chemical sputtering) Fig. 7. Sputtering yield for Al, Cu, Ag and Au films irradiated by ethanol cluster ions and Ar monomer ions.

8. 2.The GCIB Experiment -The surface roughness was measured. -This is due to the lateral sputtering effect of cluster ion irradiation as well as the inherent fluid property of liquid materials. -The high rate sputtering and very flat sur- face formation can be achieved by the ethanol cluster ion irradiation. Fig.8.AFM images of Au film surfaces unirradiated by ethanol cluster ions at an acceleration voltage of 9 kV and an ion dose of 1 · 1015 ions/cm2.

9. 2.The GCIB Experiment -These results are explained by the uni- que characteristics of the cluster ion irradiation effects such as the high den- sity irradiation effect and multiple coll- ision effect, which are not achieved by the conventional ion beam technology. Fig.7.AFM images of Au film surfaces that irradiated by ethanol cluster ions at an acceleration voltage of 9 kV and an ion dose of 1 · 1015 ions/cm2.