Research on the Glow Discharge Cleaning Method by Use of Glow Mode Plasma Source

虽然辉光放电清洗方法具有设备简单、不使用磁场等优点，但由于阴极落差大(通常为300伏)，存在等离子体离子轰击真空壁、真空腔捕获放电气体、清洗过程中气体压力过高导致抽气系统抽气速度慢等问题。为了解决这些问题，改进辉光放电清洗方法，我们引入了一种利用热阴极的辉光模式等离子体源的辅助等离子体源，并演示了这些问题的解决方案。实验研究结果表明，放电气体的工作压力可以降低到0.2Pa，大约降低两个数量级。阴极落差和等离子体与真空室之间的电势差减小到10伏。我们还研究了放电清洗过程中杂质气体的脱附机理。用Ar、H_2、H_4气体作为放电气体，测量了这些气体的分压随时间的变化。研究结果表明，杂质气体在短时间内的主要脱附机制是由于离子的轰击这一物理过程。另一方面，在较长的操作时间内，化学过程是主要的脱附机制，从以上结果可以看出，GMPS放电清洗方法是一种非常有效的方法，它改善了常规辉光放电清洗方法的缺点，可以说这种使用GMPS的放电清洗方法在短时间内获得超高真空是相当有效的。

Although there are many merits in the glow discharge cleaning method to have ultra-high vacuum within a short time, such as use of simple equipment and without usage of the magnetic field, because of large cathode fall (typically 300 volt), it has some problems, such as the sputtering of the vacuum wall by the bombardment of the plasma ions, trapping of the discharge gas in the vacuum chamber, and slow pumping speed of the pumping system due to the high gas pressure during cleaning discharge. To solve those problems and to improve the glow discharge cleaning method, we introduced an auxiliary plasma source of glow mode plasma source (GMPS) by use of hot cathode, and we demonstrated the solution of those problems.As results of the experimental investigation, the working pressure of the discharge gas could be reduced to 0.2 Pa, which is about two order of magnitudes smaller. The cathode fall and the difference of the potential between the plasma and the vacuum chamber are reduced to several 10 volts.We have also investigated the mechanism of the desorption of the impurity gases during the discharge cleaning. The argon, hydrogen, deuterium gases are used as the discharge gases, and temporal variation of the partial pressure of those gases have been measured. As the results from this study, the dominant desorption mechanism of the impurity gases within a short time is due to the physical process, which is bombardment of the ions. On the other hand, in a longer time of the operation, the chemical process is the dominant desorption mechanism.From those results mentioned above, we concluded that the discharge cleaning method with use of GMPS is quite effective method by improving the demerit of the normal glow discharge cleaning methods.It can be said that this discharge cleaning method with use of GMPS is quite effective to obtain ultra-high vacuum within a short time.