Simulations of low field Helicon discharges using a two dimensional hybrid plasma equipment model

Abstract

Summary form only given. As the semiconductor industry moves towards larger wafers, a greater degree of process uniformity than is currently available with conventional inductively coupled plasma reactors will be necessary. Due to their high ionization efficiency, high flux density and their ability to deposit power within the volume of the plasma, helicon reactors are being developed for downstream etching and deposition. The power coupling of the antenna radiation to the plasma is of concern due to issues related to process uniformity. Furthermore, operation of helicon discharges at low magnetic fields (5-20 G) is not only economically attractive, but lower fields provide greater ion flux uniformity to the substrate. At low magnetic fields, it has been observed that there is a resonant peak in the power deposition and plasma density (Chen et al., 1996). This has been attributed to the occurrence of an electron cyclotron wave, or Trivelpiece-Gould (TG) mode, when /spl omega///spl omega//sub c/, is of order unity. To investigate these issues, we have improved the electromagnetics module of the WPEM (Rauf and Kushner, 1997) to resolve the helicon wave structure of a m=0 mode. The electrostatic component of the wave equation has been neglected, so this work focuses on the effects of the Helicon mode. Plasma dynamics are coupled to the electromagnetic fields through a tensor form of Ohm's law and an effective collision frequency for Landau damping has been incorporated. Using a solenoidal magnetic field and an antenna operating at 13.65 MHz, studies show a shift in the power deposition towards the center of the reactor as the magnetic field is decreased below 30 G. Furthermore, peak values and wave structure is sensitive to the magnetic field configuration. Results for process relevant gas mixtures are examined and the dependence on magnetic field strength, field configuration and power are discussed.