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

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%.