Ion Property And Electrical Characteristics Of ICP Pre-ionized Very-high-frequency Magnetron Discharge

Magnetron sputtering is a famous physical vapor deposition method.Technological developments of magnetron sputtering system have made it widely used in the film deposition.The ion energy and ion fluxes to the substrate can make strong influence on the growth of the film.In order to improve the film properties,the ionized sputtered particles are needed.Therefore,the ionized physical vapor deposition,such as the high power impulse magnetron sputtering(HiPIMS)discharge,is paid more attentions and is developed rapidly.Except for the HiPIMS,the ionized physical vapor deposition can also be achieved by very-high-frequency(VHF)magnetron sputtering.The recent works showed that the ions with higher energy can be produced using the VHF magnetron sputtering.However,the ion flux density to the substrate is found very low,leading to a lower growth rate of films,limiting the wide application of VHF magnetron sputtering.In order to raise the ion flux density,the discharge should be generated at low pressure or very low pressure,to reduce the collision loss of ions.However,due to the limit of discharge pressure,the magnetron discharge at low pressure is very difficult and unstable.Thus,the pre-ionized magnetron discharge,that is the magnetron discharge assisted by low-pressure discharge plasma,has been developed.But for the VHF magnetron sputtering,the pre-ionized magnetron discharge is seldom reported.Recent works showed that inductively coupled plasma(ICP)discharge can excite low-pressure discharge and ionize the species to a higher degree.Thus,if the ICP discharge is used as pre-ionized discharge to assist the VHF magnetron discharge,the VHF magnetron sputtering at low pressure may be achieved.Therefore,in this thesis,a 13.56 MHz RF ICP-assisted pre-ionized 60 MHz VHF magnetron discharge at low pressure was developed.The ion property and the electric characteristics of this pre-ionized VHF magnetron sputtering were investigated.It was found that using a 13.56 MHz RF ICP-assisted discharge,a pre-ionized 60 MHz VHF magnetron discharge at low pressure of 1 Pa can be achieved.By a retarding field energy measurement,it was found that as the discharge pressure reduced from 5 Pa to 1 Pa,the ion flux density to the substrate increased about four times,meanwhile the ion energy also increased doubly.The maximum ion energy(40.2 eV)and ion flux density(7.2×10-2 Am-2)to the substrate were obtained at operating pressure of 1 Pa and sputtering power of 66.0 W.Therefore,the ion properties of 60 MHz VHF magnetron sputtering can be well improved.By a voltage-current(I-V)probe measurement on electric characteristics of discharge,it was found that the VHF power was dissipated mainly in the ions in the sheath,and a little improvement of sputtering effectiveness was achieved by reducing discharge pressure.However,the enhanced electron inertia at 60 MHz VHF discharge led to a reactance impedance characteristic and the increase of discharge impedance with the discharge current.It was also found that during the pre-ionized 60 MHz VHF magnetron discharge,the ICP discharge had some influence on the electric characteristics of VHF magnetron discharge and the ion property.The ICP discharge led to the increase of PSputtering/Pinput at lower sputtering power and the decrease of Psputtering/Pinput at higher sputtering power,the increase of power factor(cos?)at lower discharge current and the decrease of power factor(cos?)at higher discharge current,as well as the electron dissipation in the bulk plasma at lower discharge current and the ion dissipation in the sheath at higher discharge current.The ICP discharge also led to the decrease of ion flux density at lower ICP power and the increase of ion flux density at higher ICP power,the decrease of maximum ion energy.In conclusion,a pre-ionized 60 MHz VHF magnetron discharge at low pressure of 1 Pa can be achieved by using a 13.56 MHz RF ICP-assisted discharge.The maximum ion energy and ion flux density can be increased largely by this pre-ionized 60 MHz VHF magnetron discharge.During the pre-ionized 60 MHz VHF magnetron discharge,the ICP assisted discharge can lead to the increase of the ion flux density,but the decrease of maximum ion energy.