Vapor phase decomposition is a method by which trace elements on the
surface of a silicon wafer are collected into a liquid sample. The
silicon wafer is exposed to hydrofluoric acid vapor in a sealed
chilling chamber. The hydrofluoric acid vapor forms a condensate on top
of the chilled wafer that etches the oxide layer off the surface of the
wafer along with any trace metals that might be present. The condensate
is then collected by rolling a drop of scan solution (93% ultrapure
water, 5% hydrogen peroxide, 1% nitric acid, and 1% hydrofluoric acid)
across the surface of the wafer.
The drop is transferred from the surface of the wafer into a clean vial with a pipette. The liquid sample is then analyzed for trace metals using HR-ICP-MS. The VPD technique is capable of measuring metallic contaminants at concentrations of 1E6 to 1E7 atoms per square centimeter. It is particularly useful in measuring light elements (e.g., lithium, beryllium, boron, sodium, magnesium and aluminum) on bare silicon or in HF soluble thin films.
The drop is transferred from the surface of the wafer into a clean vial with a pipette. The liquid sample is then analyzed for trace metals using HR-ICP-MS. The VPD technique is capable of measuring metallic contaminants at concentrations of 1E6 to 1E7 atoms per square centimeter. It is particularly useful in measuring light elements (e.g., lithium, beryllium, boron, sodium, magnesium and aluminum) on bare silicon or in HF soluble thin films.