Diagnostics of Inductively Coupled Chlorine Plasmas: Measurement of the Neutral Gas Temperature

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