Characteristics of a cluster-ion beam of Os₃(CO) _n⁺ (n = 7 or 8) for low-damage sputtering

A cluster-ion source has been developed to produce stable ion beams of metal-cluster-complex ions. As a metal cluster complex, triosmium dodecacarbonyl, Os₃(CO)₁₂, was used, which has a molecular weight of 906.7. Using the ion source, energy dependence of beam current and sputtering yield of silicon bombarded with Os₃(CO)_n ⁺ (n = 7-8) were investigated at beam energies from 2 to 10 keV under the normal incidence condition. By high-resolution Rutherford backscattering spectrometry (HR-RBS), a silicon target bombarded with the normally incident Os₃(CO)_7-8⁺ ions at 10 keV with oxygen flooding at 5 × 10^-4 Pa was analyzed. The experimental results showed that the ion-beam current increased almost linearly with the acceleration voltage. It was found that the sputtering yields of silicon with Os ₃(CO)_7-8⁺ ions varied substantially with beam energy. The sputtering yield with Os₃(CO)_7-8⁺ at 10 keV was higher than that with SF₅⁺ or Ar⁺ by a factor of 3-20, whereas the yield at 3 keV was lower than that with Ar⁺. In the case of 2 keV, deposition was found to occur on the silicon surface. The substantial variation in the sputtering yield with beam energy would arise from the lower kinetic energy of each atom constituting the metal-cluster-complex ions. From HR-RBS results, it was confirmed that the constituent atoms of the Os₃(CO)_7-8⁺ ions, Os, C, and O, were implanted into the silicon target. The observed depth profiles of Os and C atoms were in good agreement with results of TRIM simulation, while that of the O atom was significantly different from the simulation results. The depth profile of the O atom was examined in terms of oxygen diffusion and implantation.