Dynamics Of Energetic Electrons In A Pulsed RF Capacitively Coupled Plasma

Capacitively coupled plasma?CCP?source have been widely used in material processing such as plasma etching or plasma enhanced chemical vapor deposition?PECVD?in semiconductor manufacture and flat panel display industries due to its simple structure,and the ability of generating large area plasma.The energetic electron dynamics in these plasmas can directly determine various complex chemical reaction rates and the concentrations of the reactive species,affecting properties of plasma.Therefore,the study on the dynamic behavior of energetic electrons in a plasma is of practical and fundamental importance.With the development of semiconductor and microelectronics technology,the feature size shrinks,the charging effect of etching grooves is inevitable,as a results,plasma could damage the wafer,so people proposed the pulse-modulation capacitively coupled plasma to alleviate charge accumulation effect at the bottom of etching grooves and to reduce the damage of the wafer.In this work,the dynamics of energetic electrons in the pulse-modulation capacitively coupled Ar and Ar/CF₄ mixed gas discharges were studied by phase resolved optical emission spectroscopy.Particularly,we studied the effects of rf power,working pressure and pulse duty cycle on the electronic excitation dynamics.The experimental results show that,during the pulse-on stage,by increasing the rf power or working pressure in Ar discharge,electron excitation rate reaches the maximum in a shorter time,and the plasma emission intensity peak at the igniting phase becomes sharp.At a higher pressure or a higher power,secondary electrons emitted from the surface of the powered electrode due to ion bombarding the electrode,can excite/ionize background gas,We found that in the early stage of the phase-on period of electropositive Ar discharge,due to the low plasma density,the electric field could permeate the bulk plasma region,leading to enhanced bulk heating mode.As time advances,the plasma gradually switches from bulk heating mode to the sheath heating mode.In Ar/CF₄ gas mixture discharge,with the increase of CF₄ content,electrons are more intensively consumed,due to dissociative attachment reaction,leading an increase in negative ions density,and a decrease in the electron density.To keep a certain current flowing through the plasma region,the bulk electric field is enhanced,so that electrons can acquire substantially energy from the high electric field in the bulk region,lead to the enhancement of the electron excitation rate.Different from Ar pulsed CCP,the CF₄ plasma is generally operated in bulk heating mode at different time within the pulse-on stage.