Patent ID: 8671879

Claim:
A system for processing a microfeature workpiece, comprising: a plasma chamber coupleable to a source of gas; a workpiece support positioned within the plasma chamber and configured to carry the microfeature workpiece; an energy source positioned to generate a plasma within the plasma chamber; a detector positioned external to the plasma chamber for measuring optical emissions from the plasma in the plasma chamber; and a controller operably coupled to the detector and the energy source, the controller containing a non-transitory computer-readable medium having instructions to perform a method comprising: measuring intensities of optical emissions at discrete wavelengths from a first region of the plasma spaced apart from the microfeature workpiece by a first distance; selectively adding only some intensities of the optical emissions at discrete wavelengths from the first region; measuring intensities of optical emissions at discrete wavelengths from a second region of the plasma spaced apart from the microfeature workpiece by a second distance different than the first distance; selectively adding only some intensities of the optical emissions at discrete wavelengths from the second region; and estimating a dimension of a sheath of the plasma based on (a) the selectively added intensities from the first region, and (b) the selectively added intensities from the second region, wherein the dimension of the sheath is estimated by determining a distance from the microfeature workpiece at which the intensity of the optical emissions is a predetermined percentage of a maximum of the selectively added intensities.