Diagnostic Studies of Aluminum Etching in an Inductively-Coupled Plasma System: Determination of Electron Temperatures and Connections to Plasma-Induced Damage

Electron temperatures (T sub e) were obtained in Cl sub 2/BCl sub 3/N sub 2 plasmas in an Applied Materials decoupled plasma source (DPS) metal etcher under typical processing conditions, using trace rare gases optical emission spectroscopy (TRG-OES) and Langmuir probe measurements. A small amount (1.7% each) of the five rare gases was added to the plasma and emission spectra were recorded. TRG-OES T sub e s corresponding to the high energy tail of the electron energy distribution function were derived from the best match between the observed and computed rare gas emission intensities. T sub e was determined as a function of total pressure, source power, fraction of BCl sub 3 added to Cl sub 2 and substrate material (SiO sub 2, Al, and photoresist). Positive ion densities and relative electron densities were also measured for some of these conditions. At source and bias powers of 1000 and 100 W, TRG-OES T sub 3 s in Cl sub 2/BCl sub 3/N sub 2/rare gas plasmas increased from 1.4 eV at 40 mTorr to 2.3 eV at 3 mTorr, about 15% lower than values computed from a global model and ~1.4 times lower than those measured with a Langmuir probe.