Experimental Investigations Of Pulse Modulated Radio Frequency Inductively Coupled Ar/O₂ And Ar Plasmas

With the rapid development of the semiconductor technology,the device feature size shrinks,and the structure of the integrated circuit becomes more and more complicated.To achieve the device critical dimension under 5 nm,the plasma etching technique,which plays a pivotal role in etching process,needs to be controlled accurately.On the other hand,the challenges met in plasma etching also needs to be solved,such as notching caused by the charge building-up.Therefore,pulse modulated radio frequency(rf)inductively coupled plasma is proposed.This is because during the pulse-off stage in pulse modulated rf inductively coupled plasma,the sheath will collapse.Thus,the negative ions can move to the wafer and neutralize the positive ions in the trench,in which way the charge building-up can be reduced.As a consequence,the etching profile can be improved.In addition,the pulse modulated rf inductively coupled plasma can provide two additional tunable parameters,i.e.,pulse frequency and duty cycle.Moreover,the plasma parameters,i.e.,the electron density,electron temperature,active radical densities,ion energy and ion flux,can also be controlled flexibly,which will improve the etching selectivity,etching rate and etching uniformity.However,although the pulse modulated rf inductively coupled plasma exhibits many advantages,its inherent physical mechanisms become much more complex at the same time,especially for the discharges in electronegative gases for the etching processes,such as O2,C,Fy,SF6,Cl2 and HBr,etc.In industry,in order to control the etching property precisely,the characteristics of pulse modulated rf inductively coupled plasma need to be understood comprehensively.Therefore,in this dissertation,by using a Langmuir probe,a VI probe,a phase-resolved optical emission spectrum and a retarding field energy analyzer,the pulse modulated rf inductively coupled Ar/O2 and Ar plasmas are investigated in detail.Particularly,the experimental results as well as their inherent physical mechanisms are discussed.In chapter 1,the rf inductively coupled plasma is described in general at first,and then the pulse modulated rf inductively coupled plasma is introduced in detail.After that,the research works of the pulse modulated rf inductively coupled plasma and the shortages are reviewed.Finally,the content of this dissertation and its schedule are presented.In chapter 2,first of all,the experimental apparatus is described in detail.Then,it is focused on the introduction of experimental diagnostics,including a Langmuir probe,a retarding field energy analyzer,a phase-resolved optical emission spectrum,a VI probe,and a high-voltage probe.Meanwhile,the corresponding diagnostic theories are introduced.In chapter 3,by applying the Langmuir probe and a global model,the temporal evolutions of the electron density and the effective electron temperature under different discharge conditions are investigated systematically in pulse modulated rf inductively coupled Ar/O2 plasma.Both of the experimental and simulated results show that when the pulse is turned off,both of the electron density and the effective electron temperature exhibit a peak,which mainly caused by the energy release of the matching network.In chapter 4,in rf inductively coupled molecule gases discharges,the temporal evolutions of the energetic electron excitation rate/the plasma emission intensity exhibit different peak numbers within a rf cycle under E mode(single peak)and H mode(bimodal).Through this phenomenon,in this chapter,by employing the phase-resolved optical emission spectrum,the E-H mode transition moment during the initial pulse stage are investigated at first in pulse modulated rf inductively coupled Ar/O2 plasma.It is found that as the pulse duty cycle/discharge pressure increases,the mode transition moment appears earlier.However,when the source power increases,the mode transition moment appears later.In addition,the spatial-temporal evolution of the energetic electron excitation rate is investigated during the whole pulse period,especially during the steady state.It is found that during the steady state(H mode),when the pressure increases,the energetic electron excitation rate first increases and then decreases,its bimodal structure becomes more obvious and the axial distribution localizes near the quartz window.In chapter 5,by using the retarding field energy analyzer,the effects of the phase shift,which means the phase shift of the rf signals between the rf source power and the rf bias voltage,on the ion energy distribution at the biased electrode are explored in continuous wave and pulse modulated rf inductively coupled Ar plasma.It is found that when the phase shift 0 increases from 0 to ?,the ion energy distribution moves to low energy side,and its energy width shrinks.In chapter 6,the conclusions are summarized,and the innovation points as well as several future outlook are put forward.