Investigation Of Mode Transition In Ar-Hg Inductively Coupled Plasma And Experimental Study Of A Microwave Plasma

"There is a widely use of high density plasma source in both industry and sci-ence investigation.Several ways have been used for making high density plasma source,like radio frequency inductively coupled plasma(ICP)or electron cyclotron resonance plasma.ICP has drawn a lot of attention since it was discovered,and is widely applied in electrical light and semiconductor industry nowadays,due to its useful properties,e.g.,relatively high electron density,less ion damage,inde-pendently controllable ion energy,and simplicity of source configuration.There are two operational modes in ICP reactors.At low power,a low density plasma coupled capacitively is observed(E mode),as power rises,a fast transition oc-curs to the H mode characterized by much higher density and brightness of the plasma.The mode transition has long been known to researchers,as one of the characteristic features of ICP.It is a possible method to control ICP discharge mode transition by mixing discharge matter.In our work,the characteristics of E·(?)H mode transition in argon-mercury mixture ICP were investigated.The addition of mercury resulted in the decline of the E to H mode transition powers and the rise of the H to E mode transition powers for low mercury content.In the E mode,the electron densities increased faster with input power due to the contribution of mercury atoms.Consequently,the electron densities approached a specific density region faster with the rising of the power,and the E to H mode transition subsequently occurred at a relatively low input power.The E-H mode transition process in an inductively coupled argon-mercury mixture discharge plasma was investigated by an interferometer and a spectrometer.The transition powers upon different natural pressures and mercury content were studied.The electron density ver-sus input power under several discharge conditions in the E mode and H mode were measured detailedly by the interferometer.These results suggested that the nonlinear effects of power absorption and dissipation play significant role in the mode transition process.In addition,the optical emission system was employed to measure the spectrum of argon-mercury discharge.The 750 nm line inten?sity and the 811.5 nm line intensity are characteristic lines of argon discharge,the ratio of them means the metastable argon atoms density of plasma,which shed light on the mechanism of stepwise ionization and the variability of H to E mode transition powers in the argon-mercury mixture discharge.In this work,the transition powers from the E to H and H to E mode were measured macroscop-ically at different argon pressures and mercury contents,which would be helpful in controlling of the argon-mercury mixture discharge.Within the power range near the transition point,the relationships between electron density ne and input power P in both E and H mode were displayed and discussed according to the nonlinearity of power transfer and dissipation.The results demonstrate that the electron densities change significantly in Ar-Hg mixture discharge.Additionally,the OES was applied and several spectrum line intensity ratios were obtained.At last the oddity of mode transition powers and the electron densities in the H mode were discussed with multistep ionization effect.The stepwise effect of ionization became more significant.Therefore,with the addition of mercury,the metastable argon atoms were consumed a lot by mercury atoms,which were suggested by the ratios of spectral lines intensity.With the decrease of metastable atoms,the H mode could not be sustained anymore and then it was transformed into the E mode at a relatively high power.Meanwhile,there is many configuration of electron cyclotron resonance plasma,like the high length-width ratio and low length-width ratio plasma,slot-antenna ECR and uniform distribution ECR,which have been widely used in the semicon?ductor industry like etching,ion input and new configuration of electric propul-sion.In this work,a new configuration of ECR plasma is introduced.It use the combination of a resonance cavity and a single antenna to transfer microwave energy,and the coils to create a resonance magnetic field.Besides the traditional vacuum cavity,a quartz glass hemi-sphere was used to make the vacuum,which has extremely increased the contacting area of plasma and EM wave,making the ECR plasma source a good platform of investigating principle of plasma with EM wave.In this work,we have measured the plasma parameters in the resonance cav-ity first,like the electron density and electron temperature.While controlling the discharge pressure vary from 1 Pa to 16 Pa.electron density in the cavity could go up to 5 × 1012 cm-3,and the density distribution in the cavity is not uniform,elec-tron density decreased with the increase of radius,and the electron temperature is vary from 0.8 eV to 3.5 eV,approximately decreased while increasing the dis-charge pressure.In order to make the resonance cavity ECR source behave better.xenon has been considered as an alternate discharge matter in our work.Because of the high mass of xenon atom,xenon ions reflect more advantage in the electron propulsion field,like the non-electrode thruster made by OREAN and a thruster of JAXA.Also the xenon atoms are the no radioactivity inert gas that have least first ionization energy.In the regime of low discharge pressure from 1 Pa to 2 Pa,xenon plasma behaves better than argon plasma.The electron density of xenon plasma could be up to 5 x 1011 cm-3 at 1 Pa discharge,approximately twice of that in argon plasma.Besides,at the center of the resonance cavity,about 5 cm in diameter the density is almost uniform,which is much more uniform than ar-gon plasma too.When the electron density in xenon plasma is higher,the optical emission of plasma is stronger especially the characteristic spectrum at 882 nm,while the electron density is lower,the optical emission is weaker,reversely.On the experiment of plasma covered with a semi-sphere quartz glass shield,the electron density in the cavity and shield was also measured by probe and microwave interferometer.Besides,we measured the amplitude of microwave through at a wave length from 9 GHz to 12 GHz,the results suggested that microwave amplitude damped a lot when go through a dense plasma.While the microwave reflected from plasma on the front side,the amplitude of 9 GHz to 12 GHz microwave also attenuate at a specific plasma status.The convenient use of quartz glass shield plasma reactor makes it a good platform of investigating the mechanize plasma interact with EM wave.