Concentration Profiling of Boron in Solids by Neutron Time-of-Flight

Boron concentrations as a function of depth below the surface of a solid of otherwise-known composition may be determined from neutron spectra resulting from the 11B(p,n)11C reaction. Pulsed-beam, time-of-flight techniques have been used to study this reaction from threshold to 4.5 MeV. Differential cross sections have been measured at 11 angles between 0° and 155°. Magnitudes of 0° cross sections indicate that sensitivities of 3.0 ± 0.3 atomic ppm of boron in silicon at a depth resolution of 1 ¿m can be obtained. Front surface depth resolutions of 0.3 ¿m in silicon can be achieved with a klystron-bunched, pulsed beam and depths of several tens of microns can be probed nondestructively.