Depth profiling of a Co-implanted silicon wafer by total-reflection X-ray fluorescence analysis after repeated oxidation and HF-etching

A new method of depth profiling has been developed and applied to a Co-implanted Si-wafer. A square section of only some cm2 was chosen, a thin near-surface sublayer oxidized by an oxygen plasma and the oxidized sublayer precisely etched by a solution of hydrofluoric acid. The mass of Si within the sublayer was determined via differential weighing of the wafer piece and the mass of Co determined by TXRF (total reflection X-ray fluorescence) of the loaded acidic solution. These steps were repeated time and again in order to record a total depth profile showing the relative concentration of Co dependent on the depth within the wafer. The integration of this profile gave a total dose of 1.13 × 1017 ions cm–2 with high accuracy. The depth resolution of the new method might be in the order of a few nm, the detection limit about 0.01% or 5 × 1018 atoms cm–3 of Co.