Diagnostics of inductively coupled chlorine plasmas: Measurements of the neutral gas temperature

We report measurements of the bulk, neutral gas temperature in a chlorine transformer-coupled plasma. A trace amount (2%-5%) of N-2 was added to the discharge and the rotational temperature of the C(3)Pi(u) state was determined from the C(3)Pi(u)--> B(3)Pi(g) emission in the ultraviolet. This temperature has been shown by others to be equal to the rotational temperature of ground-state N-2, which is the thermally equilibrated (translational and rotational) gas temperature (T-g). The gas temperature 3 cm above the wafer is equal to, or only slightly above the wall temperature (300 K) throughout the low-power, capacitively coupled regime (< 60 W, 0.024 W/cm(3)). Between the lowest (130 W, 0.053 W/cm(3)) and highest (900 W, 0.36 W/cm(3)) inductively coupled mode powers investigated, T-g increases sublinearly with power (and electron density). The high-power (900 W) T-g increases with increasing pressure (650, 750, 900, and 1250 K at 2, 5, 10, and 20 mTorr, respectively). Mechanisms of neutral gas heating are discussed. The energy released in dissociation of Cl-2 appears to be the dominant heating mechanism. (C) 2000 American Institute of Physics. [S0003-6951(00)02642-5].