In device manufacturing sites, plasma states are conventionally monitored by measuring the etch rate. A means for plasma monitoring is presented. This was accomplished by characterizing profile variations by means of a discrete wavelet transformation (DWT). The sensitivity of wavelet coefficients was evaluated as a function of plasma faults, which were simulated with the variations in the process parameters, including radio frequency source power, bias power, and SF6 flow rate. For each plasma fault, wavelet sensitivity was conducted separately for vertical, lateral, and overall profiles. Wavelet coefficients demonstrated high sensitivity to detecting plasma faults. Improved sensitivity was obtained as they were monitored individually. Compared to conventional etch rate-or profile anisotropy-based sensitivity, the wavelet-based one was considerably enhanced. By the demonstrated high sensitivity, the proposed DWT-based profile monitoring can be effectively used to monitor and diagnose plasma processes. (C) 2003 American Vacuum Society.