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

等离子体浸没离子注入（PIII）是一种用于大面积和/或三维表面改性的新技术。但是，存在着工艺可重复性等各种问题。为了解决PIII工艺中存在的问题，本文对表面改性及其过程监控进行了研究。过程监测是基于离子注入表面二次电子发射系数（SEEC）的测量。SEEC是通过将总目标电流与直接浸入等离子体中的半导体探测器获得的二次电子电流进行比较来测量的。该技术使我们能够测量具有位移电流的SEEC。在氩气稀释的氧等离子体中，硅和铜的SEEC随处理时间的增加而成比例地增加，但由于氧注入与靶表面的离子溅射平衡，SEEC逐渐饱和。另一方面，在氦稀释的BF3等离子体中，硅的SEEC随处理时间的延长而降低，且与硼注入量成正比。结果表明，SEEC测量可以应用于靶表面植入元素的过程监测。等离子体的光发射对SEEC有重要的影响，因为它包括真空紫外线（VUV）发射，其光子能量大到足以在被照射表面诱导光电子发射。在本实验中，紫外辐射使SEEC约为2倍，有时SEEC大于10。因此，提供给植入离子的大部分能量都被二次电子电流消耗掉了。为了解决这一问题，在保持离子通量的情况下，可以降低光发射强度，提出了脉冲调制放电的方法。

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.