Experimental Research On The Electron Beam Driven And Modulated Capacitively Coupled Plasma

The high-density,low-energy plasma is required for fabricating nanometer scale semiconductor devices.At present,electron beam plasma is considered an effective means of producing such plasma.The electron beam is primarily generated within a hollow cathode,and due to the small size of the hollow cathode,external power sources can effectively deposit energy into the plasma,heating the electrons effectively.High-energy electrons oscillate back and forth within the cathode,promoting ionization and producing high-energy electrons.Subsequently,a direct current(DC)bias is applied between the grid and slotted anode to extract electrons from the hollow cathode,forming a high-energy electron beam.Such electron beams possess high energy and density characteristics and can be applied in various fields,including surface treatment of materials,evaporation of refractory materials and their deposition onto surfaces to form thin films,and etching,among others.The electron beam is of great research value.In the present study,we have developed an integrated electrode system that is capable of generating an electron beam for use in a capacitively coupled plasma(CCP)chamber.The hollow cathode located within the integrated electrode is driven by a radio frequency source,thereby producing an electron beam that is injected into the chamber.This process induces breakdown within the chamber,leading to the formation of a CCP.This novel system is referred to as an electron beam CCP(EBCCP).Used the Langmuir probe,Optical Emission Spectroscopy with the Collisional-Radiative Model(OES-CRM)method to investigate the characteristics of EBCCP:(1)electron beam driven CCP;(2)electron beam modulated CCP;(3)Using a CCD camera and a set of filters,a two-dimensional distribution of the EB modulated CCP was obtained by capturing discharge images with the CCD camera and calibrating them with the spectral data obtained from the spectrometer.In Chapter I,the generation and applications of low temperature plasma were introduced,along with a discussion of the experimental and simulation studies on electron beam plasma.In Chapter II,the experimental setup and diagnostic methods were presented.In Chapter III,the discharge characteristics of EBCCP were investigated.The plasma parameters at the center of the discharge in the chamber were measured using a Langmuir probe and compared with those obtained from OES-CRM.The results showed that the trends in electron temperature and electron density obtained by both methods were consistent.the effect of different RF frequencies on EBCCP was investigated using a Langmuir probe.The results showed that,as the frequency increased,the self-bias decreased and the injection of electrons decreased,resulting in a decrease in both electron density and electron temperature.Then the effect of work pressure on EBCCP was investigated,the result demonstrated that as the pressure increase,electron density increased,so did the collision increased,which cause electron temperature decreased.Additionally,we can observe from the electron energy probability function,the concentration of high-energy electron decreased and the concentration of low-energy electron increased,as the pressure increased.This indicates that high-energy electrons mainly undergo ionization collisions with neutral particles,generating more low-energy electrons.Finally,the effect of DC bias voltage was investigated,the results indicated that the electron density gradually increased with the influence of bias voltage,while the electron temperature was almost unaffected by the bias voltage.This is because the bias voltage forms an acceleration electric field between the grid and the solotted anode,but due to the small electrode spacing,the energy gained by the electrons is limited.Therefore,the main role of the bias voltage is to affect the extraction of electrons from the hollow cathode,further increasing the electron density in the chamber.In Chapter Ⅳ,the discharge characteristics of EB modulated CCP were studied,focusing on the modification of the electron beam characteristics through external parameters,which can result in different modulation effects on the CCP.Firstly,the effects of the RF power on the hollow cathode and bottom electrode of the chamber were compared,and then compared with the single-frequency CCP.The results indicate that power variation on the lower electrode side mainly affects electron temperature,while power variation on the hollow cathode side mainly affects electron density.Compared with the single-frequency CCP,injection of electron beams promotes the mode transition from α-γ and only requires lower power to achieve higher electron density.When exploring the effect of frequency on discharge parameters on the hollow cathode side,it was found that both electron temperature and density have a high dependence on the RF frequency.With the increase of frequency,the electron temperature gradually decreases,while the electron density slightly decreases.However,this does not apply to the case of low RF frequency(2 MHz),as the decrease in self-bias voltage results in a decrease in injected electron density.At 2 MHz,the sheath layer inside the hollow cathode is thick,and the electrons gain higher energy,but the ionization decreases due to the compression of the body region,leading to lower electron density.The effect of working pressure on discharge is similar to that in Chapter Ⅲ,where the increase in pressure promotes collisions between neutral particles and electrons,leading to more low-energy electrons generated by ionization.Similarly,the effect of bias voltage on discharge mainly increases electron density and has little effect on electron temperature.In addition,with the increase of bias voltage,the increase in electron density at higher frequencies is greater than that at lower frequencies.This indicates that electron density in the hollow cathode still increases significantly with the increase of driving frequency.In Chapter V,the two-dimensional distribution of EBCCP and EB modulated CCP was studied as a function of external parameter,RF power.In the EBCCP,an increase in power leads to an increased influx of electrons entering the cavity from the injection port,while maintaining a "beam" shape extending downwards.In contrast,the electron temperature exhibits an opposite trend.By comparing the changes in the two-dimensional distribution when changing the RF frequency on the hollow cathode side and the lower electrode side,it can be observed that changing the RF frequency on the hollow cathode side primarily affects the characteristics of the electron beam.With increasing power,both the electron density and high-energy electrons increase,leading to more high-energy electrons ionizing neutral particles after injection,thereby having a greater impact on electron density.On the other hand,changing the power on the lower electrode side leads to electrons acquiring higher energy and a more uniform distribution of discharge.