Phosphorus diffusion in silicon; influence of annealing conditions
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Phosphorus diffusion in silicon; influence of annealing conditions J. S. Christensen1, A. Yu. Kuznetsov1, H. H. Radamson1, and B. G. Svensson1,2 1 Royal Institute of Technology (KTH), Department of Electronics, Electrum 229, SE-164 40 Kista-Stockholm, Sweden 2 University of Oslo, Physics Department/Physical Electronics, P. B. 1048 Blindern, N-0316 Oslo, Norway ABSTRACT Phosphorus diffusion has been studied in both pure epitaxially grown silicon and Cz silicon, with a substantial amount of impurities like oxygen and carbon. Anneals have been performed in different atmospheres, N2 and dry O2, as well as in vacuum, at temperatures between 810 – 1100 °C. Diffusion coefficients extracted from these anneals show no difference for the P diffusion in the epitaxially grown or the Cz silicon. The diffusion coefficients follow an Arrhenius dependence with the activation energy Ea=2.74±0.07 eV and a prefactor D0 = (8±5)×10-4 cm2/s. These parameters differ considerably from the previously reported and widely accepted values (3.66 eV and 3.84 cm2/s, respectively). However, vacuum anneals of the same samples result in values close to this 3.6 eV diffusion mode. Furthermore, control anneals of boron doped samples, with similar design as the phosphorus samples, suggest the same trend for boron diffusion in silicon – lower versus higher values of activation energies for nitrogen and vacuum anneals, respectively. These results are discussed in terms of the concentration of Si self-interstitials mediating the diffusion of phosphorus and boron. INTRODUCTION The scaling of electronic devices down to nanometer-technology modes makes it important to control how the dopant atoms redistribute with an accuracy of a few monolayers during device manufacturing. Phosphorus is one of the most commonly used impurities, and its diffusion in silicon has been extensively studied. A lot of experiments concerning phosphorus diffusion have been performed during the 70’s and 80’s [1-5], and these experiments showed that the diffusion of phosphorus in Si, at concentrations lower than 1019 P/cm3, is well described by a diffusion P coefficient with an activation energy Eold ~ 3.6 eV[1-5]. However, more recent results for P P P diffusion in Si yield an activation energy E new ~ 2.8 eV [6,7]. The difference between Eold and P E new is huge (~0.8 eV) and should be studied and interpreted accordingly. There can of course be several sources for this discrepancy. For example: (i) experimental errors during either “new” or “old” measurements. (ii) different types of silicon used for the different measurements (orientation, phosphorus and other impurity concentrations , etc.), (iii) different or uncontrollable atmospheres during anneals. In the present paper we have addressed a part of the issues above and the intrinsic phosphorus diffusion have been studied in both pure epitaxially grown silicon and ordinary Cz silicon with oxygen and carbon concentrations in the 1017 and 1016 cm-3 range, respectively. Anneals have been performed in different atmospheres, N2 and dr
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