Influence Of Convection In The Background Gas In Radio Frequency Inductively Coupled Plasma On Discharge Mechanism

Radio Frequency Inductively Coupled Plasma Source?RF-ICP?can produce high-density plasma in low gas pressure,and its structure is simple.RF-ICP sources is widely used in semiconductor fabrication,microelectronics photo-voltaic industry and aerospace field for thin film deposition,etching,ion implantation,doping,plasma photo-resist,cleaning and so on.The plasma is a complex physical and chemical process,the transport process is an important basic process.The transport process causes the heating,diffusion,convection and viscosity of the neutral particles,then changes the spatial characteristics of the plasma for electron density,electron temperature,charged particles,and neutral particles.In this paper,a two dimensional axis-symmetric fluid mechanics model is established for the ICP device.Plasma model includes electron equation,electromagnetic field equation,Maxwell-Stefan equation in COMSOL software calculated by the finite element algorithm.We researched the characteristics of the plasma and the spatial distribution of particles with Ar/O₂ plasma that couples background gas convection fields.At first,the reliability of the model is verified under pure oxygen condition.We calculated the spatial distribution of the charged particles?e,O-,O+,O₂+,Ar+?and neutral particles?O,O*,O₂*,Ar*?with the condition of pressure 30 m Torr and power 300 w.We explain the electron density,electron temperature,spatial distribution of the charged particles?e,O-,O+,O₂+,Ar+?and neutral particles?O,O*,O₂*,Ar*?by analyzing the particle equation and the chemical reaction process.The results show that the electron density exhibits a parabola uniform distribution in the body region.The electron temperature reaches the maximum near the coils and decreases in the body region.O-is mainly localized in a small area like its reaction rate.The spatial distribution of O+and O₂+is mainly a parabola in the body region with a little collapse below the quartz window,which is affected by the spatial distribution of O-.The spatial distribution of Ar+ number density is similar to electron.But there is a small tip in the central region,which is caused by the loss reactions,mainly the collision loss reaction between O-and Ar+,so Ar+is affected by the spatial distribution of O-.O and O* have similar spatial distribution,both are parabola.Ar* is not completely parabola,and the spatial distribution of O₂* is scattered in the whole space with the number density is higher at the edge than bulk region.We also research Ar/O₂ coupled background gas convective field.Main researches include the changes of neutral particles?O,O*,O₂,O₂*,Ar*,Ar?space distribution,electronnumber density and temperature and charged particles density peak value?O-,O₂+,O+,Ar+?with increasing flow velocity.The results show that:?1?The effect on neutral particles,when the inlet velocity is 150 m/s,the spatial distributions of O,O*,O₂*,O₂ are obviously collapsed in the inlet compared with pure plasma,and stretched outward at the outlet.The number density peaks of those particles all slightly increase,due to the fact that convection reduces the loss of O,O*,O₂*and O₂ at the boundary.The spatial distribution of Ar* number density did not change obviously,but the number density peak value slightly reduces.Actually,the effect of convection on Ar* is very small,Ar* is mainly caused by collision ionization between electrons and Ar,and the number density peak value of Ar decreases with increasing flow velocity,so the number density of Ar* are decreased by decreasing Ar density.In particular,the evolution of the Ar number density spatial distribution with increasing flow velocity is very different with other particles.Ar number density minimum gradually moves towards the inlet,and decreased with increasing flow velocity.This is mainly due to the fact that the sum of number density peak value of other particles increases with increasing flow velocity,and gradually moves towards the inlet,thus affecting the spatial distribution and number density of Ar.?2?The effect on electron number density and temperature,the number density peak value of electron is gradually reduced with increasing flow velocity,because Ar is the main reactive gas,the collision ionization between electron and Ar is the main way to produce electrons,and the number density peak value of Ar decreases with increasing flow velocity,so the number density peak value of electron decreases.The electron temperature peak value increases with increase of flow velocity,due to the dissociation attachment reactions increase and the ionization energy loss decreases.?3?The effect on charged particles,number density peak value of O-gradually increased with increasing flow velocity,O-is main produced by the collision dissociation and attachment between electrons and O₂,O₂*,the number density peak value of O₂ and O₂* increase with increasing flow velocity,which makes the number density peak value of O-increases.The O+number density peak value gradually decreases with increasing flow velocity,because O is produced by main reaction between O+and O-,but O-density peak value gradually increases with increasing flow velocity,so O+number density peak value decreases.The O₂+density peak value gradually increased with increasing flow velocity,O₂+is mainly produced by collision ionization between electrons and O₂,so O₂+increases with increasing O₂.Ar+number density peak value reduces slowly with increasing flow velocity,because Ar+is mainly produced by collision ionization between electrons and Ar,the number density peak value of Ar decreases with increasing flow velocity,and the collision ionization reaction decreases,so the Ar+number density reduces slowly.