Investigation Of Geometrically Asymmetric Capacitively Coupled Plasma Based On A Global Model Coupled With External Circuit

Radio frequency capacitively coupled plasmas(RF CCPs)are widely used in semiconductor integrated circuit manufacturing processes such as etching and thin film deposition.Most of the CCP sources used in industry are geometrically asymmetric and the RF source is connected with the electrode plate through the matching network.The finite geometry asymmetry effect in low pressure discharges would lead to the strong nonlinearity,like high-order harmonics of plasma current.And different dynamic processes of the two sheaths may have a very important impact on the heating process of charged particles.Therefore,making a real and complete electrical analysis of CCP source,the plasma circuit model should also include the matching box and other components of the real circuit system.In the current research works,the electron density and electron temperature used in the nonlinear global model are fixed input parameters,so the simulation model is not self-consistent.A external circuit coupled with plasma model can predict and analyze the high-order harmonics within a certain density range of the current in the plasma which can be used as a diagnostic method to judge whether the plasma density increases or decreases.Through the study of it,we can deepen the understanding of the basic physical phenomena,such as heating mechanism of CCP.Therefore,it is necessary to make a depth research on these issues.In addition,considering the impedance characteristics of plasma discharge from the perspective of the circuit is an effective auxiliary method for understanding the capacitive or inductive properties of plasma.In this thesis,the plasma equivalent circuit model based on external circuit impedance matching coupled with self consistent nonlinear global model is used to study the influence of different external control parameters on plasma energy deposition,heating mechanism and related electrical physical quantities in geometrically asymmetric chamber configuration.In the first chapter,corresponding basic theory of low temperature plasma,and research progresses of geometric asymmetry effect in RF capacitively coupled plasma source,based on equivalent circuit model and impedance matching of external circuit,are introduced.In the second chapter,the simulation methods,including plasma equivalent circuit model,nonlinear global model,external circuit impedance matching module and the two-way coupling processes of internal loop and external loop,are introduced.In Chapter 3,simulation results based on above models are discussed.The effects of different control parameters on the dynamic behavior of geometrically asymmetric CCP,including discharge pressure,electrode gap,voltage source amplitude and discharge frequency on plasma current,plasma density,plasma absorbed power,plasma current induced higher harmonic,sheath thickness and sheath voltage drop,are studied.Based on different physical simulation conditions which satisfy impedance matching,the mechanism of current of each branch,dissipation power distribution of each part of load,the trend for the stochastic heating power and ohmic heating power variation trend are studied.The results show that at low pressure,when the area ratio of the power and ground electrode plates is small,the series resonance phenomenon coupled by the nonlinear sheath capacitance under the geometric asymmetry will enhance the electronic heating process.However,when the area ratio of the ground electrode is large and under high pressure conditions,this enhancement effect is reduced.The power deposited in the sheath at low pressure is much greater than the heating powers of plasma resistance.As the discharge gap increases under low pressure,the plasma current intensity increases,and the high-frequency oscillation of the current becomes obvious,while the frequency of series resonance decreases,but the amplitude at resonance accordingly increases.Secondly,in the discharge chamber with low pressure and narrow gap,the stochastic heating power is higher than the ohmic heating power in the plasma.Meanwhile,it has the stronger dependence on voltage.Finally,as the discharge frequency increases,the harmonic order of series resonance decreases,and the phenomenon of series resonance is more likely to occur at high frequencies.