a method of etching a wafer using resonant infrared energy and a filter to control non - uniformities during plasma etch processing . the filter includes a predetermined array or stacked arrangement of variable transmission regions that mirror the spatial etch distortions caused by the plasma etching process . by spatially attenuating the levels of ir energy that reach the wafer , the filter improves uniformity in the etching process . filters may be designed to compensate for edge fast etching due to macro - loading , asymmetric pumping in a plasma chamber , and magnetic field cusping .