Metastable chlorine ion transport in a diverging field electron cyclotron resonance plasma

Abstract

For applications in ultralarge scale integration, low pressure, high density plasmas are being developed for etching and deposition of thin films. To control critical parameters such as the flux and energy distribution of ions impacting surfaces, it is necessary to understand how these parameters are influenced by physical and electromagnetic design. In this work, we extend previous measurements of ion velocity distributions in Ar/He electron cyclotron resonance plasmas to Cl2/He plasmas. Using Doppler-shifted laser-induced fluorescence spectroscopy, we measure metastable Cl ion velocity distributions parallel and perpendicular to the magnetic field as a function of magnetic field amplitude, pressure, and microwave power. We also examine the effects of the wafer platen on the distribution functions by repeating the measurements after removing the platen. Surprisingly, little qualitative difference is seen when chlorine and argon discharges are compared; this is most likely a result of the low pressures employed (≲0.15 Pa). As in Ar, we find nearly isotropic ion velocity distributions when the source is operated as a magnetic mirror. Downstream, we consistently observe bimodal ion velocity distributions: the fast component, created in the source, appears to follow magnetic flux lines into the reactor; the slow component, created mostly where the plasma expands from the source into the reaction chamber, is more isotropic. Despite the localized input of energy by cyclotron resonance heating, the spread in ion velocities is largely determined by distributed ionization and spatial variations in the plasma potential. Show more