Spatial profile monitoring of etch products of silicon in HBr/Cl2/O2/Ar plasma

The authors have developed a radical-distribution monitoring system for obtaining the spatial profiles of etching products. This system combines Abel inversion and actinometry to estimate the local densities of radicals. The profiles of Si, SiCl, and SiCl2 in HBr/Cl-2/O-2/Ar plasma are captured with this monitoring system. From the gradient analysis of silicon-containing etch products, they found that the source of SiCl2 is the wafer surface and Si and SiCl are produced in the plasma. In other words, SiCl2 is produced by the etching reactions on the wafer and diffuses into the plasma to be the source of Si or SiCl through dissociation. In the etcher used for this experiment, etching gases are supplied from a top plate inducing downward flows. At a pressure as low as 0.4 Pa, the effect of convection on etch products is also observed. Increasing total gas flow rate intensifies convection and changes the spatial profile of SiCl2. However, on the wafer surface, the convective effect saturated at a total flow rate of 200 SCCM (SCCM denotes cubic centimeter per minute at STP). The ratio of the emission intensities of SiCl2 and supplied etching gases was found to be a convenient index for visualizing the effect of gas flow. The shapes of the gas jet from both 170- and 50-mm-diameter gas inlets were drawn in contour plots. The jet from the narrow inlet swept away the etch products in the center of the wafer. (c) 2007 American Vacuum Society.