Numerical Simulation Of Ion Energy And Angular Distributions In Inductively Coupled Discharges

The planar radio frequency?rf?inductively coupled plasma?ICP?source has been widely employed in semiconductor chip processing technology due to many benefits,for instance,it can produce a high plasma density at relatively low pressure in the absence of an external magnetic field.In addition,by applying a bias source to the electrode,it is possible to control the ion energy/angular distributions?IEDs/IADs?and the ion flux independently.In general,the bias source is used to control IEDs and IADs,whereas the coil source is used to control the ion flux on the surface of the electrode.These plasma properties determine not only the etching efficiency but also the etching profile,thus play a quite important role in the plasma processing,especially in the etching process.It is expected that IEDs/IADs and the ion flux can be modulated by external discharge parameters?e.g.,bias power,bias frequency,mixed gas ratio,rf coil power,pressure,etc?.Therefore,it is of utmost importance to study the dependence of these plasma properties on the external discharge parameters.In this paper,a hybrid model is developed to study the effect of external discharge parameters on IEDs/IADs in ICP discharges.In chapter 1,the application background of low temperature cold plasmas is introduced.Then,recent research progress with regard to IEDs and IADs in inductively coupled plasmas are overviewed.Finally,the purpose and significance of this dissertation are put forward.In chapter 2,we give a detailed description of the hybrid model employed in this work,which includes a two-dimensional fluid model,a sheath mode and an ion Monte Carlo model.Details of the numerical methods and boundary conditions in the model are also presented.In chapter 3,by using the hybrid model introduced in chapter 2,we investigate the effect of external discharge parameters on IEDs and IADs in Ar discharges.The results indicate that the bimodal distribution appears as bias power increases or bias frequency decreases.Moreover,the low and high energy peaks of IEDs move to lower energy with the increase of coil power and pressure.The ion angular distribution on the surface of the electrode is approximately characterized by a Gaussian distribution,and a larger percentage of ions incident on the electrode with a smaller deflection angle by increasing bias power.However,an increase in the bias frequency or pressure can cause an increase in the large-angle deflection ratio in IADs,and the width of IADs becomes wider,while the coil power only has little influence on IADs.In chapter 4,the hybrid model has been extended to Ar/O₂ plasmas to investigate the effect of external discharge parameters on the electron density,as well as on the density and IEDs/IADs of three important ions?O⁺,O₂⁺and Ar⁺?adjacent to the electrode.Our simulation results show that the density of each particle decreases with bias power but increases with bias frequency or coil power.As pressure or O₂ content increases,the electron density decreases,whereas,O₂⁺density gradually increases.Besides,with pressure or O₂ content increases,O⁺density first increases gradually and then decreases.For IEDs and IADs,the influence of rf bias power,bias frequency,coil power and pressure is similar to that in Ar discharges,except for different ion energy peak separation width.In addition,we have also investigated the influence of O₂ content in Ar/O₂ plasmas.By increasing O₂ content,both low and high energy peaks of Ar⁺,O₂⁺and O⁺move towards a higher energy,and the peak of the ion angular distributions becomes more pronounced.In order to validate the model,a retarding field energy analyzer was employed to measure the ion energy distributions,and a good agreement between simulation predictions and experimental results was obtained for different bias powers and O₂ contents.The results presented in this work not only allow us to gain a deeper insight into the dependence of IEDs and IADs on external discharge parameters,but it is also of significant importance for increasing the etching rate and anisotropy in plasma etching processes.