The measurement of boron at silicon wafer surfaces by neutron depth profiling

The thermal neutron reaction n+10B→4He+7Li is utilized to measure the boron concentration on the surface of silicon wafers. This neutron depth profiling measurement technique requires no sample preparation. Boron is determined on the as-received wafers at a level of 1012 to 1013 atoms/cm2. A boron level of about 2×1012 atoms/cm2 is found at the wafer surface after oxidation or epitaxial or polycrystalline silicon deposition. Ambient air appears to be one source of the boron. Secondary-ion mass spectroscopy performed on wafers with polysilicon provides additional support for an atmospheric source of boron.