Kevin J. Coakley
Statistical Engineering Division, ITL
Analytical Chemistry Division, CSTL
David S. Simons
Surface and Microanalysis Science Division, CSTL
Neutron Depth Profiling (NDP) is a nondestructive method for analysis of the concentration profile of an element in material. Inferences about the concentration depth profile are based on the observed energy spectrum of charged particles emitted due to specific nuclear reactions. The detector response function (DRF) is a probability transition matrix which relates the depth of emission to the expected energy spectrum of the detected particles. The DRF depends on the geometries of the emitter and detector, and assumed models for the stopping power of the material, energy straggling, multiple scattering and random detector measurement error and detector calibration. In previous work, we developed a computer code to predict the DRF.
We check the consistency and validity of the NDP method as follows. The depth profile of boron in a silicon sample was measured by Secondary Ion Mass Spectrometry (SIMS). In a separate experiment, the NDP energy spectrum was measured for the same sample. Based on the measured SIMS profile and the modeled DRF, we predict the NDP energy spectrum.
differences in the
predicted and observed NDP spectra
to imperfect knowledge in one or more of
stopping power of silicon,
density of silicon, calibration of NDP detector,
energy resolution of the detector,
straggling in silicon,
calibration the SIMS instrument.
Based on the current data,
we can not
which of the factors
is responsible for
To better explain
a new experimental study is underway.
Figure 15: Top: The concentration profile of boron in silicon measured by SIMS. This profile is fit with a smoothing spline. We convolve the fitted concentration profile with the modeled detector response function to get a predicted energy spectrum. Bottom: Predicted and observed NDP energy spectra.
Date created: 7/20/2001