Diagnostic studies of aluminum etching in an inductively coupled plasma system: Determination of electron temperatures and connections to plasma-induced damage

Using trace rare gases-optical emission spectroscopy (TRG-OES) and Langmuir probe measurements, electron temperatures (T-e) were obtained in Cl-2/BCl3 /N-2 plasmas in an inductively coupled plasma system, under typical process ing conditions for metal etching. A small amount (1.7% each) of the five ra re gases was added to the plasma and emission spectra were recorded. TRG-OE S T(e)s corresponding to the high-energy tail of the electron energy distri bution function were derived from the best match between the observed and c omputed rare gas emission intensities. T-e was determined as a function of total pressure, source power, fraction of BCl3 added to Cl-2 and substrate material (SiO2, Al, and photoresist). Positive ion densities and relative e lectron densities were also measured for some of these conditions. At sourc e and bias powers of 1000 and 100 W, TRG-OES T(e)s in Cl-2/Cl-3/N-2/rare ga s 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 similar to 1.4 times lo wer than those measured with a Langmuir probe. Reduced plasma induced damag e to the gate oxide at higher pressures (18 vs 10 mTorr) correlates with a drop in both T-e (1.7 vs 1.9 eV) and plasma density (1.0 x 10(11) vs 1.3 x 10(11) cm(-3)), but is due mostly to the lower T-e. (C) 2000 American Vacuu m Society. [S0734-2101(00)00303-1].