Kinetic Simulation Of Electron-beam-driven Low Temperature Plasma Sources

With the size of semiconductor devices tends to be nanometer-scale,atomic layer etching process has become an essential technical means for the further development of microelectronics industry.The particles used for atomic layer etching must satisfy three basic requirements,i.e.,the particle energy should be low,the particle energy distribution should be concentrated,and the particle flux should be easy to regulate,which takes a big challenge for the LTP source.Due to the high electron temperature then easy to damage the substrate,conventional low temperature plasma?LTP?source such as radio frequency?RF?capacitively coupled plasma?CCP?is challenging to meet the basic requirements of atomic layer etching currently.In contrast,the electron-beam-driven LTP source can provide large flux ion with low energy to the substrate surface,making it suitable for use in atomic layer etching.Therefore,studying the electron beam-driven LTP source is of great significance for the development of atomic layer etching process.Three kinds of electron-beam-driven LTP source,i.e.,electron-beam-driven?EB?plasma,electron-beam-driven RF CCP,and electron beam/direct current source driven?EB/DC?plasma discharge are studied in this thesis by using improved implicit PIC/MCC kinetic method.The evolution of physical characteristics of electron beam driven LTP source with the plasma discharge operating parameters is not fully understood yet.Therefore,we study the modulation of discharge parameters?electron beam current/energy and gas pressure?on the plasma density,electron energy distribution,ion flux,and the ion energy distribution of electron-beam-driven LTP source,expecting to provide a theoretical reference for the application of electron beam driven LTP source to the atomic layer etching process.The main research contents and results of this thesis are as follows:1.The modulation of beam current/energy and gas pressure on the characteristics of EB plasma is studied in chapter III.The results show that:?I?the EB plasma has excellent plasma uniformity with a plasma density on the order of 10¹⁶ m^-33 at least.The electron energy distribution function?EEDF?is a Druyvesteyn-like distribution with high energy tail,and the concentration of low-energy???27?1eV?electron is extremely high.The ion flux can reach the order of 10²⁶ m^-2s^-1.The ratio of the low-energy???27?5eV?ion bombarding the electrodes is above 99%.?II?The plasma density and electron temperature of EB plasma increase with the injected beam current or energy.?III?Increasing the gas pressure,the heating mode convertes from?mode to?-like mode due to the localized enhancement of the injected electrons.?IV?Increasing the injected beam current,the EEDF tends to Druyvesteyn distribution.Reducing the injected beam energy,the EEDF tends to Maxwell distribution.Increasing the gas pressure,the EEDF tends to B-Maxwell distribution.?V?Reducing the beam current/energy,the ion energy distribution function?IEDF?is more compact and moves to the low energy region,the proportion of ions with ultra-low energy???27?0.5 eV?further increases,indicating that modulation of IEDF is feasible.The ion flux changes several orders of magnitude while the corresponding ion energy changes several times only by adjusting the beam current and gas pressure,indicating the modulation of ion flux is more sensitive.2.The modulation of electron beam injected from the opposite electrode of the RF source on the RF CCP is studied in chapter IV.The results show that the separate modulation of plasma density and electron temperature of RF CCP can be achieved by injecting electron beam from the opposite electrode of RF source.The plasma density increased by several times and to¹0¹⁷ m^-3 while the electron temperature reduced from³eV to lower than 1 eV.It is found that:?I?The electron energy probability function can be control and moved to the low energy region by injecting electron beam.?II?The electron flux and ion flux at the electrode increase significantly by injecting electron beam.The total electron flux increase by one order of magnitude,the total ion flux increase by a factor of five,and the time-averaged percentage of the low-energy???27?1eV?electron flux increase by a factor of eight.These low-energy electrons improve the applicability of RF CCP to the atomic layer etching process.3.The characteristics of EB/DC plasma discharge are studied in chapter V.The results show that the EB/DC plasma discharge has good plasma uniformity.Its ions take the advantages of low energy,large flux,and easy to regulate,which is very suitable for atomic layer etching.It is found that:?I?For the discharge mode of electron beam injected from cathode,the plasma density,electron temperature,and the ion flux increase with the beam current increasing but decrease with the beam energy increasing.?II?For the discharge mode of electron beam injected from ground electrode,the plasma density,electron temperature,and the ion flux increase then decrease with the beam energy increasing.When the energy of injected beam is lower than the confinement energy,the cross-section is the major factor to affect the effective ionization,thus the parameters of the plasma increase with the beam energy increasing.When the energy of injected beam is larger than the confinement energy,the number of electrons participating in ionization collision is the major factor to affect the effective ionization,thus the parameters of the plasma decrease with the beam energy increasing.