Multiscale Studies Of Influences Of Reactant Transport On Profile Evolution In Plasma Etching

Plasma etching is widely used in semiconductor manufacturing,in combination with film deposition,photo lithography and other process steps,micro structures of electronic devices are fabricated on the wafer surface.As the sub-10 nm technology is coming in industry,the shrinkage of critical dimension(CD)and more complex micro structues bring challenges on plasma etching,the precision demand for pattern control has shrinked to atom/molecule scale.In plasma etching,the generation of reactants,and their transport to material surface in the sheath and the feature determine reactant fluxes and energies at the feature surface,thus influence the pattern control,selectivity and damage,etc.In this thesis,a multiscale model considering processes in the reactor,sheath,trench and surface is constructed,it can simulate feature profile evolution with conditions used in industry applications,this can help to understand the complex multiscale and multiphysics progresses with smaller Try-and-Error costs during equipment design and process development.In chapter ?,the low temperature plasma and their applications in semiconductor manufacturing are first described,then the challenges and prospects for plasma etching are given.In chapter ?,the multiscale model for plasma etching is described.First,a global model is used to calculate ion and radical densities,as well as the electron temperature which can influence sheath properties.Then the hybrid sheath model is used to describe sheath properties and ion transport through the sheath,and finally,ion energy and angular distributions(IEADs)are calculated.These results are used as initial conditions in the feature scale model,where ion and radical movements in feature and their distributions at the surface are calculated,the charging effect and ion reflection at sidewall are also considered in the feature scale model.At last,the reactant fluxes and their energy and angular distributions are coupled with the surface reaction algorithm to simulate the surface reactions including passivation,sputtering and deposition,realizing the simulation of feature profile evolution.In chapter ?.first,the reactant generation under different discharge conditions,as well as the reactant transport in the sheath and the trench are simulated in the feature model,where the ion reflection and charging effect are considered.Then by coupling the reactant distribution at the trench surface with the surface reaction algorithm,Si etching in C12 plasmas is simulated,influence of macroscopic discharge conditions and microscopic transport mechanisms on profile evolution are studied.Results show that ions focus at the corners of the trench bottom when they're reflected at the trench sidewall,results in microtrenches,when the trench depth increases,more ions are reflected at the larger sidewall,making the micro trenches more serious.When the pressure increases,more ions arrive at the top of trench sidewall,so the sidewall etch is more serious there,moreover,the reflected ions tend to arrive at bottom center when pressure is larger,so the microtrenches move toward to center,furthermore,more low energy ions exist under higher pressure,they're more easily influenced by the local electric field near mask opening and are reflected at trench sidewall,contributing to microtrenches.For radicals,the surface coverage is related to the discharge parameters and the feature topography,when the trench depth increases,coverage,and thus the etch rate decreases,this is called the aspect ratio dependent etching(ARDE).In chapter ?,the Monte Carlo surface model is coupled in the cellular model to simulate SiO2 etching in Ar/C4F8 plasmas,the complex surface passivation,etching and deposition are considered.Influence of discharge conditions,as well as microscopic reactant transport in sheath and trench on feature profile evolution are studied.Results show that microtrenches and ARDE are more serious when pressure increases,when bias voltage increases,the etch rate increases,and the taper appears more quickly at trench bottom.Besides,by applying the tailored waveform,proportion of high and low energy ions,and the positions of energy peaks in IEDs can be controlled to realize better profile control.In chapter ?,atomic layer etching(ALE)of Si and SiO2 are studied.Results show that in ALE of Si,compared to conventional etching,the bottom is flatter and the sidewall is more vertical.When the etching depth increases,the chemical etching at top of sidewall increases.Besides,by applying a long-pulsed bias power to control ion energy distributions,the surface passivation and etching processes can be separated to some extent,better profile control can be achieved with decrease of microtrench and ARDE.In ALE of SiO2,the non-ideal factor,ion sputtering of the bare SiO2 makes the profile influenced by non-uniform distributions of reactant at the surface.Microtrenches exist at the trench bottom,and the bottom becomes sharp when etching goes on,as radical fluxes decrease when the depth increases.With appropriate etch duration,bettern profile can be achieved due to the compromise between ion sputtering and radical surface coverage.