A study of 2 MeV helium-irradiated phosphorus-diffused silicon

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Abstract
2 MeV He+ ions have been used for the location of phosphorus atoms in P-diffused silicon using the Rutherford back-scattering technique. Back-scattered signals from the 〈110〉 and 〈111〉 directions indicated a very high non-substitutional phosphorus content in the diffusion profile. This was subsequently shown to be produced by the irradiating He+ ions, which also increased the sheet resistivity correspondingly. Isochronal annealing experiments on the irradiated samples over the temperature range 500 to 1100 K using sheet resistivity and Hall measurements to detect changes in conductivity showed that the conductivity of both high and low phosphorus concentration specimens recovered by a first order process with activation energies of ∼ 0·45 eV and rate constants of ∼ 0·2 sec−1. Examination of the annealed specimens by transmission electron microscopy revealed large triangular pits or voids and prismatic dislocation structures coincident with the projected range of the He+ ions. Jet etching experiments showed that these voids produced a preferential etch rate which was accurately described by a Gaussian distribution, enabling values of both projected range Rp and projected standard deviation op for 2 MeV He+ ions in silicon to be obtained. The annealing characteristics and the activation energies and rate constants have been discussed and shown to be consistent with values which could be produced if the process were a vacancy-controlled mechanism.