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 to standard radio-frequency (rf) metrology. The new system uses an antenna in 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 measuring 1000 points of the rf power signal using a digital oscilloscope sampling at 1 GHz. An experiment varying power, pressure, Ar and O2 is constructed. Using a subset of the data to regress a linear model, standard rf sensing reconstructs the experimental variables with a best average R2 of 0.49, whereas the novel sensing system results in a best average R2 of 0.876. A nearest neighbor algorithm is used which results in 70% correct identification of process conditions for standard rf sensing, and 99.5% correct identification of process conditions for the novel sensing system.