FUNDAMENTAL-STUDY ON POWDER-SCATTERING IN POSITIVE-ION AND NEGATIVE-ION IMPLANTATION INTO POWDER MATERIALS

The scattering of powder particles is caused by charging in the ion im plantation of positive ions into dielectric powders without a charge c ompensation, this makes dose control difficult. We have studied the pa rticle-scattering phenomenon in ion implantation into spherical powder s both theoretically and experimentally. Taking into account Coulomb f orce, Van der Waals force and a gravity working on a sphere, the force balance equation was driven to give the threshold charging voltage ab ove which the charged sphere begins to be scattered. In positive-argon -ion implantation into three oxide powders at an average size of 5, 11 5 and 425 mu m, particle-scattering was observed above each ion-accele ration voltage (i.e., charging voltage) of 6.5, 1.0 and 2.7 kV, respec tively. These voltages were in good agreement with the predicted thres hold charging voltages. Conversely, in the negative-carbon-ion implant ation, on the contrary, there was no scattering for all samples even a t an ion acceleration voltage of 20 kV. The negative-ion implantation technique was found to be a non-scattering implantation method for pow ders.