Development of the large current cluster ion beam technology

A cluster is an aggregate of a few to several thousands atoms. Because many atoms constituting a cluster ion bombard a local area, high-density energy deposition and multiple-collision processes are realized. Because of the interactions, cluster ion beam processes can produce unusual new surface modification effects, such as surface smoothing, high rate sputtering and very shallow implantation. High ion dose is needed to realize the nano-level smoothing and etching of hard materials. It is necessary to develop the technology of large current cluster ion beam for the purpose of increasing the productivity of processing using cluster ion beam. In order to achieve large current cluster ion beam, the cluster generation, ionization and ion transportation were studied. The efficient cluster generation was realized by increase of source gas pressure. The mass distributions of Ar cluster beams generated from a Laval nozzle were measured with a Time-of-Flight (TOF). The distributions prove that the neutral beams include clusters with the size up to 160000 atoms. The efficient ionization and extraction were realized by structural improvement of the ionizer. The ionization efficiency increases with the emission current. When the emission current is 100mA, the ionization efficiency reaches about 80 %. The structural improvements of ionizer suppressed the loss of ions by coulomb repulsion and realized the extraction of large current cluster ion beams. As a result, when the gas pressure was 15000 Torr and the electron emission current is 300 mA, the beam current reached 500 μA. The cluster ion dose of more than 1×10¹⁶ ions/cm² is needed to realize the nano-level smoothing. With this beam current, 6 inches wafers can be treated for about 10 minutes.