TXRF capability of metallic contamination analysis on rough silicon wafers

Total X-Ray Fluorescence (TXRF) is a non-destructive technique for the characterization of metallic contaminants on bare silicon wafers. TXRF is sensible to roughness leading to a diffraction phenomenon. In this study, the effects of roughness on TXRF analysis were evaluated with various rough silicon wafers produced by microelectronic processes of grinding, wet cleaning and chemical mechanical polishing. TXRF parameters rise as roughness increases, starting from 3 nm RMS (Root Mean Square) roughness. On spectra, characteristic Si (silicon wafer) and W (TXRF anode) peaks widen. Secondary peaks, sum/escape peaks appear, inducing interferences with Al, Cu, Zn and background noise increases as well. Through intentionally contaminated grinded wafers (RMS 12 nm) by spin-coating at selected concentrations, it was observed that most of the elements are quantified at 1 x 1012 at/cm2. At concentrations of 1 x 1010 at/cm2 and 1 x 1011 at/cm2, only few elements are quantified due to the elevated background noise and interferences.