Advances in broadband radio-frequency sensing for real-time control of plasma-based semiconductor processing

A novel sensing system based on plasma impedance spectroscopy is compared t o standard radio-frequency (rf) metrology. The new system uses an antenna i n the glow discharge to excite the bulk plasma over a frequency range of 27 .5 MHz to 2.75 GHz. The standard method of rf metrology is implemented by m easuring 1000 points of the rf power signal using a digital oscilloscope sa mpling at 1 GHz. An experiment varying power, pressure, Ar and O-2 is const ructed. Using. a subset of the data to regress a linear model, standard rf sensing reconstructs the experimental variables with a best average R-2 of 0.49, whereas the novel sensing system results in a best average R-2 of 0.8 76. A nearest neighbor algorithm is used which results in 70% correct ident ification of process conditions for standard rf sensing, and 99.5% correct identification of process conditions for the novel sensing system. (C) 1999 American Vacuum Society. [S0734-2101(99)19004-3].