| Radio frequency(RF)inductively coupled plasmas(ICPs)have been extensively employed in the semiconductor industries,therefore,it is of great significance to study the physical processes of ICP discharge for optimizing the plasma processing technology.There are two typical discharge modes(i.e.,electrostatic mode(E mode)operating at low RF power and electromagnetic mode(H mode)operating at high RF power)in an ICP reactor.In this work,by a combination of experimental diagnostics and numerical simulations,we have studied the two discharge modes and the E-H mode transition in Ar and Ar/O2 ICP discharges.In chapter 1,the applications of the ICP source and recent research progress of the E-H mode transition are introduced.Besides,the shortcomings of existing researches are analyzed.Finally,the detailed arrangement of this thesis is presented.In chapter 2,the experimental setup and diagnostic methods used in this work are introduced.The basic principle and construction of each diagnostic method are described in detail.In chapter 3,by using a VI probe,a Langmuir probe,and a two-dimensional electromagnetic analytical model,the power transfer efficiency and threshold power during the E-H mode transition in Ar and Ar/O2 ICP are studied.In the E-mode,the power transfer efficiency is less than 30%.When the E-H mode transition occurs,the power transfer efficiency increases significantly by a factor of 2-4 times due to the increase of plasma density.In addition,it is found that the power transfer efficiency increases first and then decreases with the increase of pressure in Ar/O2 discharge,which is related to plasma density and electron collision frequency.The experimental result of the threshold power shows that influenced by the threshold electron density,the threshold power also exhibits a non-monotonic change behavior with the pressure,i.e.,the threshold power decreases first and then increases with the pressure.In chapter 4,the negative ion density and electronegativity during E-H mode transition in Ar/O2 ICP are studied by the laser photo-detachment technique.Although the negative ion density is lower in E-mode,the electronegativity in E-mode is much higher than that in H-mode.During the E-H mode transition,the negative ion density shows a monotonic increase,however,because of the larger increase of electron density,the electronegativity shows a monotonic decrease.Besides,it is found that in E-mode discharge the negative ion density decreases monotonically with the pressure,but in H-mode discharge it increases monotonically with the pressure.In chapter 5,the neutral gas temperature of Ar and Ar/O2 ICP is measured by the FBG temperature sensor.It is found that the neutral gas is mainly heated by the high-energy ions and electrons.In E-mode discharge,the neutral gas temperature is close to the room temperature.During the E-H mode transition,the neutral gas temperature increases greatly.When the discharge is operated in the H-mode,the heating effect of neutral gas is very obvious,e.g.,the neutral gas can be heated up to about 1000 °C in Ar discharge with 9 Pa and700 W.In addition,it is found that the increase of O2 content will lead to a significant decrease in plasma density which,in turn,effectively reduces the neutral gas temperature and improves the radial uniformity of the neutral gas temperature.In chapter 6,the spatial distribution of the magnetic field in Ar ICP is studied by a magnetic probe.It is found that in a planar ICP,the radial component of the magnetic field shows a bimodal distribution in the whole radial direction,and the peaks are below the RF coil.The axial component of the magnetic field shows a maximum at the radial center.The azimuthal component of the magnetic field is roughly concave throughout the radial direction.It is also found that the spatial attenuation of the magnetic field in E mode is much lower than that in H mode.Finally,the main conclusions and innovations of the this work are summarized,meanwhile,related future works are prospected. |
