Fundamental study on powder-scattering in positive- and negative-ion implantation into powder materials

The scattering of powder particles is caused by charging in the ion implantation of positive ions into dielectric powders without a charge compensation, this makes dose control difficult. We have studied the particle-scattering phenomenon in ion implantation into spherical powders both theoretically and experimentally. Taking into account Coulomb force, Van der Waals force and a gravity working on a sphere, the force balance equation was driven to give the threshold charging voltage above which the charged sphere begins to be scattered. In positive-argon-ion implantation into three oxide powders at an average size of 5, 115 and 425 μm, particle-scattering was observed above each ion-acceleration voltage (i.e., charging voltage) of 6.5, 1.0 and 2.7 kV, respectively. These voltages were in good agreement with the predicted threshold charging voltages. Conversely, in the negative-carbon-ion implantation, on the contrary, there was no scattering for all samples even at an ion acceleration voltage of 20 kV. The negative-ion implantation technique was found to be a non-scattering implantation method for powders.