Accurate determinations of Ge atom fractions in SiGe semiconductor chips using high performance ICP-OES

Abstract

The Ge atom fractions in SiGe chips with nominal values in the range 3.5% to 14% were accurately determined using high performance inductively coupled plasma optical emission spectroscopy (HP-ICP-OES). For each chip, Si and Ge were determined in separate HP-ICP-OES experiments, and the Ge atom fraction was calculated from the data. This approach eliminated the need to measure the mass of the chip, thereby avoiding a potentially significant source of uncertainty. Digestion of the chips occurred in the presence of HF–HNO₃ at room temperature in closed vessels to prevent the loss of Si as volatile SiF₄. Recoveries of both Si and Ge in these digests were observed to be effectively 100%. For the Si determinations, NaOH was introduced to reduce Si background and memory. Expanded uncertainties (95% confidence) associated with the Ge atom fractions determined, accounting for all significant components of uncertainty, were observed to be ∼0.2%.