Particle-in-cell Monte Carlo collision simulation and experimental measurement of Ar plasma in a fast atom beam source for surface-activated bonding

Ar plasma in a fast atom beam (FAB) source with magnetic fields, which was previously developed [Precis. Eng. 62, 106 (2020)] to achieve high-performance surface activated bonding, was analyzed by particle-in-cell-Monte Carlo collision simulation and experimental measurements. Simulation in the proposed FAB source with magnetic fields shows that higher electron density accumulation occurs near the irradiation port by E × B drift, and the potential gradient near the irradiation port steepens, which results in an increase in Ar+ flux to the irradiation port. The variation in the plasma distribution due to the effect of the magnetic field contributes to an increase in the amount of Ar-FAB irradiation, which reduces erosion of the carbon electrodes and suppresses the formation of carbon agglomerates. These simulation results were verified experimentally with Langmuir probe measurements and FAB irradiation experiments with oxide layer removal. The analysis results explain why high performance is achieved with the proposed FAB source.