Surface Modification and Behavior of Ions and Radicals in Plasma Immersion Ion Implantation

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Plasma immersion ion implantation (PIII) has been focused as a novel technique for large-area and/or three-dimensional surface modification. However, there are various problems such as process repeatability and so on. In the present study, surface modification and its in-process monitoring were investigated to solve the problems of the PIII process. The process monitoring was based on measurements of secondary electron emission coefficient (SEEC) of the ion-implanted surface. The SEEC were measured by comparing the total target current to the secondary electron current obtained with a semiconductor detector directly immersed into the plasma. This technique enabled us to measure the SEEC with a displacement current, discriminated.In argon-diluted oxygen plasma, the SEEC of silicon and copper increased with the processing time in proportion to amount of the implanted oxygen, however the SEEC gradually saturated because the oxygen implantation balanced with ion sputtering of the target surface. On the other hand, in helium-diluted BF3 plasma, the SEEC of silicon decreased with the processing time proportionally to amount of the implanted boron. The results revealed that the SEEC measurements could be applied to in-process monitoring of implanted element existing the target surface.Optical emission from the plasma had a significant influence on the SEEC since it included vacuum-ultra-violet (VUV) emission whose photon energy is large enough to induce photo electron emission at the irradiated surface. In the present experiments, the VUV emission made the SEEC approximately twice, and the SEEC was sometimes larger than 10. Therefore most of energies supplied to implant ions were consumed for the secondary electron current. To solve the problem, pulse modulation of the discharge was proposed because the optical emission intensity could be reduced with the ion flux kept.