筒形高功率脉冲磁控溅射源的开发与放电特性

Cylindric high power impulse magnetron sputtering source and its discharge characteristics

高功率脉冲磁控溅射以较高的溅射材料离化率及其所带来的高致密度、高结合力和高综合性能成为物理气相沉积领域的新宠,然而其沉积速率低、放电不稳定、溅射材料离化率不一等缺点阻碍了其在工业界的推广和应用.针对高功率脉冲磁控溅射技术固有的缺陷,我们从靶源出发,设计了一种筒形溅射源,将放电限制在筒形溅射源内部,放电不稳定喷溅出的"金属液滴"和溅射出来但并未离化的溅射材料无法被负电位的引出栅引出而影响薄膜沉积,只有离化的溅射材料可以引出并沉积形成薄膜,而电子将在筒形溅射源内部反复振荡,和未离化的溅射原子剧烈碰撞,带动进一步离化.本文通过磁场和放电的模拟发现筒形溅射源内部电子、离子呈花瓣状分布,8条磁铁均匀分布的结构具有最优的靶材利用率.据此开发的筒形溅射源可在高功率脉冲磁控溅射条件下正常放电,其放电靶电流随靶电压变化呈现出高功率脉冲磁控溅射典型的伏安特性特征,复合电流施加后,有明显的预离化作用.溅射"跑道"面积占靶材表面的60%以上,筒形溅射源中心的离子电流波形与靶电流波形类似,但相对靶电流延迟约40μs,数值约为靶电流的1/10.结果证明,筒形溅射源可有效地应用到高功率脉冲磁控溅射放电中,并成为促进其推广和应用的一种新路径.

High power impulse magnetron sputtering（Hi PIMS） is a popular physical vapor deposition（PVD） technology because of the high ionization of the sputtering materials,large coating density,good adhesion,and other favorable properties.However,this technique suffers some disadvantages such as the small deposition rate induced by the high target potential,the ＂metallic droplets＂ produced by the unstable discharge,and different ionizations for different sputtering materials,thereby hampering wider acceptance by the industry.A cylindric Hi PIMS source in which the discharge is restricted in the cylinder is described in this paper.By using this source,coatings can be deposited with 100% ions without ＂metallic droplets＂ arising from the unstable discharge,and the unionized sputtered atoms cannot be extracted by the extraction grid with negative potential.Electron oscillation and repetitive sputtering of the unionized atoms occur in the cylinder to enhance collision and ionization.Due to the enlarged discharge area by the cylinder internal surface comparing with the area of the ion outlet（end face of the cylinder）,the sputtering ions converge from the inwall to the center of the cylinder target and form an enhanced flow to spray out from the source,which will improve the deposition rate.The structure and discharge characteristics of the novel Hi PIMS source are investigated by simulation and experiments.Our results indicate that 8 magnets can provide the reasonable magnetic field and the highest target utilization rate.The distributions of electrons and ions in the target each consist of 8 petals in the optimized magnetic structure,and the highest plasma density happens near the target,which is above 1.3×10^17m^-3.The discharge characteristics confirm that the cylindric sputtering source can be operated under Hi PIMS conditions and the evolution of the target currents with target voltage exhibits I-V characteristics typical of Hi PIMS.An obvious pre-ionization is observed on the discharge glow and discharge current curves when the extra direct current（DC） is added.The ＂racetrack＂ area is about 60.0% of the target surface.The ion current curves are similar to those of the target currents,but a 40 μs delay and about one-tenth current value are observed compared with the target currents.The sputtering is improved by the extra DC,inducing the increased metallic ions and the opposite evolution of gas ions.The results suggest that the cylindric sputtering source can be effectively used to conduct Hi PIMS and is a novel way to improve and promote the application of Hi PIMS.