Analysis and depth profiling of deuterium with the D( 3He, p) 4He reaction by detecting the protons at backward angles

Abstract

Detection at backward angles of protons from D( 3He, p) 4He presents distinct advantages with respect to the associated α particle detection used until now for depth profiling deuterium. This geometry does not require glancing incidence for good depth resolution so that rough samples may be analyzed, while the flux and energy of the elastically scattered beam particles is reduced, their pile-up problems minimized, their filtering, when necessary, with mylar absorbers or electrostatic deflectors more favourable, etc. The various contributions to the depth resolution have been calculated taking into account detector acceptance angle, size of the probing beam, energy straggling, multiple scattering and lateral spread contributions and the way to combine them discussed in detail. The 13 MeV protons emitted at 165° for E 3He=700 keV were detected using a 1500 μ deep silicon surface barrier detector with a measured overall resolution of 17 keV (fwhm). The probing beam was produced with a 350 kV HVEE accelerator using 3He 2+ ions thus demonstrating the feasibility of such measurements with low energy ion implantation machines. Depth resolutions were measured and found to be in good agreement with theory. Typically, surface resolutions of 500 Å were reached for incident beams normal to the target surface. This resolution could be reduced below 200 Å by tilting the target with respect to the beam. The method has been applied to deuterium depth profiling in amorphous silicon hydrogenated by implantation or plasma diffusion of deuterium. A comparison with SIMS measurements is reported.