Probe Diagnosis Of Pulse-modulated 27.12MHz Capacitively Coupled Ar/O2 Plasma

Low-temperature electronegative plasmas have wide application prospects in integrated circuits,solar cells,optical devices and other fields due to their wide electron temperature and high chemical activity.Among them,capacitively coupled plasma(CCP)has become an important choice for industrial applications because of its large-area,high-density and uniform characteristics.Low-temperature plasmas are required to have less etching damage and higher etching accuracy in the nano linewidth scale etching in semiconductor technology.Therefore,plasmas applied needs not only independent control of ion flux and ion energy,but also smaller ion bombardment damage and less charge accumulation.The pulse-modulated capacitively coupled plasmas are gradually attracting people's attention.Compared with continuous wave-modulated capacitively coupled plasmas,plasmas operating in a pulsed mode not only have greater flexibility in controlling discharge parameters,but also can effectively reduce the dielectric damage caused by the charge accumulation during the processing of devices,thus significantly improve the etching quality.The periodic interruption of the driving frequency during the pulse modulation also means that the plasma characteristics show strong temporal changes,which affects the physical and chemical properties of the plasma.Based on this,this thesis focuses on the study of physical characteristics of pulse-modulated plasmas by using Langmuir probe,emissive probe and laser induced photo-detachment(LIPD)technique,especially on how the electronegative gas oxygen affects the physical process of pulsed plasmasOn one hand,Langmuir probe combined with LIPD technique is used to study the characteristics of electron energy probability function(EEPF),electron temperature and electronegativity at different oxygen content in capacitively coupled Ar/O2 plasmas driven by 27.12MHz;on the other hand,an emissive probe operated in floating point mode is used to study the temporal evolution of plasma potential as well as electron temperature in Ar/O2 CCPs modulated by three pulse frequencies(100Hz,500Hz and 1KHz).The discharge parameters include power,pressure,oxygen content and duty cycle.Diagnosis results of plasmas operating in a continuous mode show that the introduction of oxygen causes obvious dissipation in the low energy region of EEPFs and even a 'concave'shape distribution is found under high pressures,which just corresponds to the decrease of electron density with oxygen content.Plasma potential and electron temperature show different or even opposite trends with oxygen content at low and high pressures.With the introduction of oxygen,electronegativity at center of the plasma increases greatly,while positive and negative ion density change almost identically with oxygen content.Measurements of plasma potential and electron temperature in pulse-modulated plasmas show that the potential tends to be stable within 200-300?s after the pulse is set on,and presents a 'ladder' shape distribution after the pulse is set off.The 'ladder' shape distribution is not found in oxygen-containing discharges and high pulse frequency(too short'pulse off time' duration)modulated discharges.Electron temperature is found to experience an overshoot as the pulse is set on,which is more obvious at conditions of high power and Ar discharge.After the pulse is set off,electron temperature decreases to the lowest level within 200-300?s.The effects of discharge power,pressure,oxygen content and duty cycle on the plasma potential in each phase of the pulse cycle are almost linear,while these factors have little effect on the process of electron cooling after the pulse is set off.