Experimental Study Of Radio-frequency And Pulse-modulated Radio-frequency O₂/Ar Inductively Coupled Plasmas

Inductively coupled plasmas（ICPs）have been widely used in the semiconductor manufacturing industry based on its high density,large uniform processing area and good manipulation performance.Due to the continuous shrinkage in the dimension of integrated circuits,there are many new challenges come up,e.g.,the bowl etching,the differential charge on the material surface,high energy ions bombardment damage,etc.On the other hand,the new designed devices which are envisioned for sub-10 nm technology are FinFET and FDSOI transistors.These devices will be built on an ultra-thin SiO₂ layer（less than a few nanometers）.This thin layer is vulnerable during the etch processes in Radio-frequency（RF）discharge plasmas.Pulse-modulated（pulsed）plasma has been proposed as a powerful tool to meet these challenges,since it does not only provide two additional flexible knobs（pulse frequency and pulse duty cycle）to precisely control plasrmas,but also owns the capability of solving the aforementioned problems.The most noticeable benefit from pulsed plasma is that during the afterglow period,when the sheath collapses,the charged particles can flow to the material surface and even arrive at the bottom of the trench to neutralize the charges,which are accumulated during the etching processes during glow period.Another important merit for pulsed plasma is to improve the radial uniformity of the etching rate.This is suitable for the increasing demand of larger waferin semiconductor manufacturing.Hence,it is important to explore the discharge conditions,under which a uniform pulsed plasma is achieved.In this dissertation,the RF/pulsed O₂/Ar ICPs have been studied by means of Langmuir probe,Hairpin probe and Optical emission probe.Combined with the Global Model and Fluid Model,the plasmas have been simulated under the same discharge conditions as in experiment.By comparing the results from experiment and simulations,the underlying mechanisms of some physical phenomena have been revealed.In 1^st chapter,a brief description of the low temperature plasma,brief descriptions of serval types of plasma sources,the developments and existing problems related to the pulsed plasma have been demonstrated.At last,the schedule of this dissertation and the research plan have also been stated.In 2^nd chapter,the experimental setups and some diagnostic tools,e.g.time resolved Langmuir probe,Hairpin probe,Optical emission probe and the Z-Scan,have been described in detail.In 3^rd chapter,the characteristics of O₂/Ar plasmas have been studied by means of a Langmuir probe and a Hairpin probe under different gas ratios,discharge pressures and applied powers.The simulated results obtained from Global Model have a good qualitative agreement with experimental results.By means of simulated results,the underlying mechinisms of the non-monotonic variation of the electron density have been revealed.In 4^th chapter,the pulsed O₂/Ar ICPs have been studied with a time resolved Langmuir probe and an Optical emission probe.It has been found that the pulse-on period has a strong relationship to the variation of ne during the active glow period.Moreover,the ignition of the plasma depends on the electron energy after the power turned on.In 5^th chapter,the radial uniformity of the RF/pulsed RF O₂/Ar plasma have been well studied with a time resolved Langmuir probe,which is placed 3 cm above the substrate table.It is clear that the increase of O₂ content and gas pressure is important to increase the radial uniformity of the electron density in CW discharge.But the increase of the applied power won’t have an obvious effect on the radial uniformity of the electron density.In pulsed O₂/Ar ICP,the electron density exhibits the similar radial distribution as in CW discharge when the plasma arrives at the stable state.While the E to H mode transition will strongly affect the radial distribution of electron density at the beginning of active glow period.After the power is turned off,the electron density gradually exhibits a better uniform radial distribution firstly then becomes worse next.According to the results calculated by the Fluid Model,the density of O-starts to decrease after the power turned off,and then increases again after a little while.Due to the higher increase rate of O-in the reactor center,the electron density shows a hollow radial distribution at the same time.In 6^th chapter,the major results,innovations and prospects of this dissertation have been stated.