Glow discharge-optical emission spectroscopy for in situ analysis of surfaces in plasmas

In situ, real-time characterization of surfaces exposed to plasmas is of great interest. Common chemical analysis methods such as x-ray photoelectron spectroscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy cannot be used. Here, we discuss the use of glow discharge-optical emission spectroscopy for this purpose. A small coupon piece (aluminum coated with yttria in this study) was mounted on an rf-biased electrode and inserted into an opening in the reactor wall. Silicon or SiO₂ substrates on a separately rf-biased electrode were etched in an inductively coupled plasma (ICP) of Cl₂/Ar/O₂ or C₄F₈/O₂, respectively. Pulsed bias was applied to sputter the surface of the coupon piece in the wall at the edge of the ICP, either after etching in an Ar ICP or during etching in the Cl₂/Ar/O₂ ICP. Optical emission from the region above the coupon surface was collected and spectrally resolved. The difference in intensity between the coupon bias on and off conditions was used to determine what species were present on the surface. A quantification method for converting emission intensities into atomic composition depth profiles is presented.