| AVS 60th International Symposium and Exhibition | |
| Applied Surface Science | Monday Sessions |
| Session AS-MoA |
| Session: | Analyses Using Novel Ion Beams |
| Presenter: | K. Mochiji, University of Hyogo, Japan |
| Authors: | K. Mochiji, University of Hyogo, Japan N. Inui, University of Hyogo, Japan K. Moritani, University of Hyogo, Japan |
| Correspondent: | Click to Email |
Argon cluster ions, typically consisting of hundreds to thousands of argon atoms, have been used in nanometer-scale fabrications such as thin film deposition or primary ion source for SIMS. The average kinetic energy per atom in the cluster ion is equal to the energy used to accelerate the cluster ion divided by the number of atoms in the cluster ion (called the cluster size). For example, when a cluster of 1000 atoms is accelerated to 5 kV, the average kinetic energy per atom of the cluster ions is only as low as 5 eV. Furthermore, when a cluster ion collides with a surface, chemical reactions such as sputtering or etching of target materials can be occurred within a very thin layer by multiple collisions among the numerous atoms constituting the cluster ion. Such the characteristics of the argon cluster ion are strongly effective to low damage and high throughput processing.
In this study, we have investigated the dissociation of an argon cluster ion by the impact on material surfaces. The ion emission from the target material by the bombardment of the argon cluster ions (cluster size: 1000-5000 atoms) was analyzed by a time of flight mass analyzer. Smaller sizes of argon cluster ions were observed in the mass spectra by lowering the kinetic energy per atom of the incident cluster ion below 10 eV/atom. The prominent ions were dimer (Ar2+) and trimer ions(Ar3+), but monomer ions (Ar+) were not observed. This can be explained as follows. It was reported that the charge of an argon cluster ion is localized on the central three atoms, which forms trimeric ion core and the ion core is much more stable as compared with the shell of neutral argon atoms surrounding the ion core. Consequently, an argon cluster ion dissociates into many neutral argon atoms and a small argon cluster ion whose size could depend on the impulsive force at the impact. We measured the mass spectra of the dissociated cluster ions by the impact on several kinds of metals. As a result, the mass spectra changed by the metal even at the same bombardment condition. As a degree of dissociation, the ion-yield ratio of Ar2+ /(Ar2+ + Ar3+) was plotted as a function of the stress acting on the contact area between the incident cluster ion and the metal surface, which can be calculated by using the values of elastic coefficient and density of the argon cluster and the metals. The result clearly showed that the ion-yield ratio is linearly increased with the stress. Such the correlation could be used as a new method for measuring the mechanical strength such as elastic coefficient or hardness of metals.