Identification of halogen containing radicals in silicon etching plasmas and density measurement by UV broad band absorption spectroscopy

Silicon etching by-products play a major role in silicon gate etching processes because they are the precursors to SiOClX passivation layer formation on feature sidewalls and on reactor walls. As a result, the understanding and modelling of these processes relies on the knowledge of the absolute value of SiClX (SiBrX) fluxes to the surfaces exposed to the plasma. However, only a few experimental data on the absolute concentration of SiClX etch byproducts are available in the literature. In this work, we show that broad band UV absorption spectroscopy can be used to measure the absolute densities of SiClX (X = 0-2), SiFX (X = 1-2) and SiO species, as well as to detect SiBr molecules. In addition, a new absorption spectrum has been observed and attributed to the SiClF radical. We have used a state of the art silicon gate etching process operating in a low pressure high density HBr/Cl2/O2/CF4 plasma etching a 200 mm diameter silicon wafer to produce the different radicals. The absorption bands of these species are all located in the 200-400 nm spectral region. Absorbances of 10-4 could be detected with a good signal to noise ratio in a few seconds exposure time using a Xe arc light source and a photodiode array detector. Details of the experimental procedure used to measure absorption spectra and to extract absolute concentrations from these spectra are presented, including a discussion concerning the influence of the monochromator spectral resolution on the absolute density determination for atomic species