| Radio frequency inductively coupled plasma(ICP)sources have been the subject of interest in both industrial plasma processes and fundamental laboratory research,due to the high plasma density at low pressure,and simple reactor geometry.The most challenging issue of ICP sources is to generate a high density plasma with a high degree of uniformity at low pressure.In this dissertation,the single and dual frequency Ar ICP are studied in detail by using Langmuir double probe diagnostics combined with the optical emission spectra method.The internal physical mechanism is discussed in particular.In Chapter 1,the main structure and principles of ICP sources are introduced.Then,the common methods of plasma uniformity modulation are introduced in detail.The progress of the dual frequency ICP sources and the problems in the current research are reviewed.Finally,main research contents in this dissertation are presented.In chapter 2,the experimental setup is introduced in detail.The diagnostic methods used in the experiment are also introduced,such as the Langmuir double probe,spectrograph,current probe and oscilloscope.The global model used in this dissertation is also presented.In Chapter 3,the effects of driving frequency on plasma density and electron temperature are studied in single frequency Ar ICP.The effect of driving frequency in the scaling relation between plasma density and discharge parameters is verified by comparing the plasma density in high frequency and low frequency ICP at different pressures.When the pressure is relatively low,the driving frequency has little impact on the plasma density and plasma uniformity.With the increase of gas pressure,higher plasma density with a worse uniformity are observed in high frequency discharge.In addition,with the increase in gas pressure,the radial profile of electron temperature would change from ‘concave’ to ‘convex’ distribution in low frequency discharge,while the electron temperature remains a ‘concave’ distribution in high frequency discharge.This is mainly caused by the difference in electron heating mechanisms at different driving frequencies and pressures.The discharge chamber is a core component of ICP Source.The chamber design should be improved after selecting driving frequency in single frequency ICP source.In Chapter 4,an attempt is made to improve the performance of ICP source by chamber design improvement.The influence of chamber height on plasma parameters and plasma uniformity is studied by using Langmuir probe and a global model.On the one hand,the power density is determined by the chamber height,which could influence the plasma parameters.In the small chamber,the plasma density and electron temperature are high due to the high power deposition density.On the other hand,the axial movement of electrons could be affected by chamber height.In the small chamber,electrons could move along the axial direction easily at a low pressure,which would lead to the weakening of plasma density at chamber center,and a more uniform plasma.Therefore,the plasma uniformity could be improved by reducing the electron accumulation at chamber center through chamber height selection.The results in Chapter 3 and Chapter 4 is the basis of the improved design of dual frequency ICP Source.In Chapter 5,the power coupling effect,plasma parameters and plasma uniformity of dual frequency ICP source are studied with interleaved coils on the basis of experimental results above.Firstly,based on the transformer mode,a circuit model suitable for interleaved ICP is proposed,and the absorbed powers are calculated along with the power coupling efficiency.In dual frequency discharge,the input powers are distributed between the two groups of coils,which could result in the reduction of the coil current and an effective improvement of the power coupling efficiency.Secondly,under the same input power,the plasma parameters of single and dual frequency discharge are compared.It is found that the low frequency discharge could be enhanced by selecting the appropriate combination of input powers.The plasma density could be effectively improved by a small amount of high frequency power.Finally,the radial distribution of plasma parameters in dual frequency discharge is compared by changing the high frequency power with fixed low frequency power.The improvement of plasma uniformity by high frequency power depends on the selection of gas pressure and chamber height.In Chapter 6,the main conclusions,innovations and prospects of this dissertation are presented. |
