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

Abstract

Using trace rare gases-optical emission spectroscopy (TRG-OES) and Langmuir probe measurements, electron temperatures (Te) were obtained in Cl2/BCl3/N2 plasmas in an inductively coupled plasma system, under typical processing conditions for metal etching. A small amount (1.7% each) of the five rare gases was added to the plasma and emission spectra were recorded. TRG-OES Tes 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. Te was determined as a function of total pressure, source power, fraction of BCl3 added to Cl2 and substrate material (SiO2, 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 Tes in Cl2/BCl3/N2/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. Reduced plasma induced damage to the gate oxide at higher pressures (18 vs 10 mTorr) correlates with a drop in both Te (1.7 vs 1.9 eV) and plasma density (1.0×1011 vs 1.3×1011 cm−3), but is due mostly to the lower Te.