Numeric Investigations On The Influence Of Input Power On Electron Temperature In Argon Radio-frequency Inductively Coupled Plasmas

Radio-Frequency Inductively Coupled Plasma Source,which has a simple device to generate high-density plasma under low pressure conditions,is widely used in industrial production.In the manufacture of microelectronic integrated circuits,as the size of the wafer increases and the feature size of the microstructure decreases,there are increasingly strict demands on the uniformity and Etching selectivity of different materials of plasma sources.In order to meet these demands,it is necessary to figure out the role of various plasma parameters in the production process and the discharge mechanism behind these parameters.Among them,electron temperature is one of the most important plasma parameters.In plasma processing,electron temperature is one of the key parameters that affect the etching and deposition processes.In experimental research,the electron temperature is the basic plasma parameter which contains information on the electron heating mechanism and discharge mechanism of the Inductively Coupled Plasma source.Such as Ohm's and stochastic heating mechanisms,depletion scheme of input power,the collision and reaction between particles and so on.The main research topics in this paper is aimed at explaining the experimental phenomenon,i.e.,the electron temperature non-monotonic behavior with the increase of input power in the argon ICP.The predecessors have done a lot of work on this experimental phenomenon and found out that the multi-step ionization reaction between electrons and metastable argon atoms grows faster at low input power,accounts for a large proportion of the total reaction,which decrease the electron temperature;As the input power increases,the skin effect increases which enlarge electron temperature value.However,when the pressure is 50 mTorr,there is still some differences between the electron temperature curves in the experiment and the simulation work.As a result of the experiment,the input power value of electron temperature transition region is about 500 W,while the input power value is around 100 W in the simulation work.Considering the reason for this difference is that the previous simulation work did not consider the neutral gas heating effect,this paper explores the effect of neutral gas heating through two-dimensional pure fluid model and hybrid model of fluid and Monte Carlo.This paper also discusses the influence of factors such as gas convection and pressure,chamber height on the electron temperature in argon ICP.By analyzing the calculation results of the pure fluid model and the hybrid model,the influence of different factors on the electron temperature is discussed in this thesis.Due to various limitations in the PEGASUS software,it is difficult to reflect the effect of neutral gas heating on the electron temperature in the fluid model.so the neutral gas heating needs to be further explored by the Monte Carlo model.In the simulation results given by the pure fluid model,the larger excitation cross section of metastable argon atoms will increase the number density of metastable argon atoms,which promote the collision process of electrons with metastable argon atoms,resulting in the decrease of the electron temperature value and slowing down the trend of electron temperature in the high input power region;As the skin effect is weakened at the center of the chamber,the electron temperature at the center of the chamber has larger input power value of electron temperature transition region and the electron temperature rising trend is slower compared with the maximum electron temperature;The convection effect will increase the number density of argon atoms,which also promotes the collision process of electrons and argon atoms,resulting in decreasing the electron temperature value;The increase in gas pressure leads to a decrease in the excitation ratio of argon atoms to metastable argon atoms,which suppresses the multi-step ionization reaction of metastable argon atoms.That will decrease the electron temperature down trend and increase the electron temperature rising trend.At the same time,the increase in air pressure will also make the gas viscous,which reduces the effect of gas convection on the electron temperature;In the larger chamber,because of the increase of the transport process of plasma,the electron energy consumption per unit length increases,which causes the electron temperature decreasing.At the same time,the effect of gas convection on the electron temperature in a larger chamber will also be reduced;Because the higher pressure and the larger chamber have similar effects on the electron temperature,in the case of the high pressure and large chamber,the gas convection effect is very weak.It is difficult to affect the plasma at the center of the chamber.Gas convection directly blows argon atoms away from the chamber,which causes the number density of argon atoms in the chamber decreases,resulting in the disappearance of the electron temperature down trend and the increase of the electron temperature value.The neutral gas heating is calculated by the Monte Carlo method.The temperature of the neutral gas has been improved compared to the fluid model.There has been a phenomenon that the electron temperature increases and the electron density decreases.This is because the neutral gas follows the description of the gas equation.Neutral gas heating will decrease the density of the neutral gas,resulting in decreasing collisions between neutral atoms and electrons.Since the ion temperature in Monte Carlo is still room temperature,the temperature of the neutral gas calculated by the Monte Carlo model is still far lower than the measured temperature in the experiment,and the input power value of electron temperature transition region keeps unchanged.When the temperature of the neutral gas is set to a value equivalent to the experiment,it is found that the higher temperature of the neutral gas decreases the number density of argon atoms and the skin effect that is closely related to the number density of argon atoms is also decreased.It is equivalent to enhance the multi-step ionization reaction of electrons and metastable argon atoms,which increases the input power value of electron temperature transition region.This result shows that the neutral gas heating effect will move the electron temperature trend toward high input power and confirms the previous conjecture about the effect of neutral gas heating on electron temperature in argon ICP in the simulation work.