EFFECTS OF WALL RECOMBINATION ON THE ETCH RATE AND PLASMA COMPOSITIONOF AN ETCH REACTOR

A helicon plasma etch reactor is simulated using direct simulation Mon te Carlo and particle-in-cell methods for a chlorine (Cl-2) feed gas f low. Computations for the gas discharge are carried out by modeling th e ions and neutrals as particles and by imposing the electrons as a ba ckground condition conforming to experimental measurements. The neutra ls and ions are then allowed to interact with the background electrons and to relax to a steady state. The effects on the reactor flow field and etch rate of chlorine atom recombination into chlorine molecules at the walls is investigated. Results show that recombination at the w alls results in the depletion of the amount of chlorine atoms (Cl) in the reactor. The depleted chlorine atom population leads to lower ioni zation levels and a diminished ion (Cl+) flux to the wafer. Consequent ly, the etch rate is decreased by as much as 15% when compared to simu lations without recombination. The creation of chlorine (Cl-2) molecul es at the walls through recombination also provides a new source for n egative ions (Cl-) which increases the electronegativity of the plasma . In addition, the results of the simulation are compared with ion cur rent and optical emission spectroscopy (OES) measurements. The Cl-Ar r atio (measured by the OES technique) increases less than 20% from the centerline to the wall of the reactor. An inspection of absolute densi ties, however, reveals that the individual near-wall densities are as much as a factor of 2 greater than the centerline densities. The trace species, Ar, therefore, does not become distributed evenly throughout the reactor. (C) 1998 American Vacuum Society. [S0734-2101(98)04604-1 ].