Improved copper detection in hydrofluoric acid by recombination lifetime measurements on dedicated silicon substrates

Copper (Cu) adsorption from diluted hydrofluoric acid (DHF) onto bare silicon surfaces strongly depends on the substrate doping. On highly phosphorus-doped silicon, the adsorption rate is up to three orders of magnitude larger than on moderately doped silicon. This may open a gap between Cu-induced semiconductor device degradation and the detection of Cu contaminations in DHF by minority carrier lifetime measurements. Using dedicated copper monitor wafers where a highly phosphorus-doped backsurface ensures strong Cu adsorption while a moderately doped frontsurface enables minority carrier lifetime measurements, we are able to improve the limit of detection for Cu in DHF by two orders of magnitude.