ION ENERGY-DISTRIBUTION FUNCTIONS IN INDUCTIVELY-COUPLED RADIOFREQUENCY DISCHARGES - MIXTURES OF CL-2 BCL3/AR/

We have used a gridded energy analyzer to measure positive ion energy distributions and fluxes at the grounded electrode of a high-density r f discharge. We present details of ion energies and fluxes in discharg es containing mixtures of chlorine, boron trichloride and argon. These feedstock mixtures have been used extensively in the patterning of me tal films for semiconductor interconnects. Our experiments were carrie d out in a Gaseous Electronics Conference Reference Cell which had bee n modified to produce inductively coupled discharges. The 15-cm-diam b ottom electrode was grounded for these experiments. Stainless steel, a nodized aluminum, and silicon were used as bottom electrode materials to understand the effects of various chamber boundary conditions on th e ion energy parameters. In most cases, the ion energy distributions h ad-a single peak, well separated from zero energy with a 1.0-3.0 eV fu ll width at half maximum. These peaks were typically centered at 12-16 eV, with ion energy increasing as pressure decreased. Addition of BCI 3 to a CI2 discharge resulted in a reduction of total ion flux of more than a factor of 2, e.g., from 5 to 2.5 mA/cm(2) (20 mTorr, 200 W). T he ion fluxes decreased with increasing pressures in BCI3/CI2 mixtures , while increasing with pressure in pure CI2 discharges. Addition of A r to several mixtures of BCI3/CI2 changed the ion fluxes and mean ion energies by less than 15%. At high pressures or low inductive rf power s, the distributions can split into two overlapping peaks separated by as much as 8 eV. This splitting is indicative of capacitive coupling between the rf coil and the discharge. Insertion of a Faraday shield b etween the coil and the discharge removed most of the splitting. (C) 1 998 American Vacuum Society. [S0734-2101(98)01806-5].