Determination of ultra-trace germanium on a silicon wafer by hydrofluoric acid vapor-decomposition/microconcentric nebulizer-ICP-MS

Abstract

Silicon/germanium (SiGe) compound semiconductor devices have attracted much attention as high-frequency devices. However, there is some possibility that germanium (Ge) contaminates silicon (Si) devices, because both SiGe and Si devices can be made on the same Si wafer, using the same process. We therefore need a technique to determine an ultra-trace amount of Ge on a Si wafer. We have adopted a conventional hydrofluoric acid (HF) vapor-decomposition method as a pretreatment technique. The recovery was more than 95% when using oxidizer, such as a nitric acid, as a recovery solution. On the other hand, we used a microconcentric nebulizer (MCN)-ICP-MS as a measurement technique to enhance the analytical sensitivity and precision, because the sample volume required for the analysis should be minimized to determine trace elements on a Si wafer. The detection limit (3σ) was 13 pg ml-1 for a 0.5 ml recovery solution and 3 × 108 atoms cm-2 for a 6-inch wafer, RSD(%) was less than 3% for a 5 ng ml-1 Ge standard solution. We confirmed that this technique made it possible to determine ultra-trace Ge with high sensitivity and precision.