Both Langmuir probe and spatial optical emission spectroscopy (OES) measurements have been used to characterize the Tetra™ chrome etch chamber. Langmuir data was measured over a range of process pressures between 1.5mT and 10mT and source powers between 150W and 500W. At 350W, the data show electron and ion densities near 1 × 109 cm-3 for Ar and for Cl2/O2 etch plasmas. Ion density trends with pressure were observed to be opposite for the two plasmas. The effect of the third electrode designed in the chamber was demonstrated to reduce ion density by more than an order of magnitude for Ar plasma and still lower for Cl 2/O2 plasma. Electron temperature and plasma potential are also reduced. Radial OES measurements are reported with a new apparatus that yields direct spatial emission data. Spatial scans of infrared emission from atomic Cl were measured under a range of several chamber conditions already measured with the Langmuir probe. The scans showed that the emission uniformity above the mask can be adjusted to a flat profile by selection of the process condition.