Search

The properties of boron-doped silicon layers obtained by ion implantation using BF/sub 2//sup +/ molecular ions are studied with Rutherford backscattering spectrometry, transmission electron microscopy, secondary ion mass spectrometry, and with incremental sheet resistance and sheet Hall coefficient measurements by the anodic sectioning method. The implantation step is responsible for the formation of interstitial aggregates at the amorphous/crystal interface. The size of these aggregates, and hence the total number of defects involved, depends on the implant conditions, and is different for samples implanted in the two systems used (a medium current and a high current implanter). During a high temperature (900-1000/sup 0/C) diffusion step in an inert atmosphere, the aggregates anneal out and induce an interstitial oversaturation. As a consequence diffusion enhancement is observed which was modeled simulating the creation of the excess of interstitials with a thermal treatment in a partially oxidizing atmosphere (oxidation-enhanced diffusion). The carrier concentration profiles are nearly identical for samples implanted in the two systems and show an incomplete dopant activation in the diffusion tail.

The equilibrium solid solubility of antimony in silicon was determined in the range 850°–1300°C by carrier density measurements on polysilicon films doped by ion implantation. Up to 1150°C this property follows very tightly the exponential dependence with and . The values at higher temperatures show a smaller increase, the figures at 1200°, 1250°, and 1300°C being , respectively. The attainment of the two‐phase equilibrium was confirmed by carrier profile measurements on isothermally annealed single‐crystal specimens doped in a wide range of concentrations, as well as by TEM examinations which detected a high density of particles having the hexagonal structure of antimony. It is shown that the new solubility values, unlike the previous ones, fully comply with the conditions for phase equilibrium. According to this treatment, the values of 0.58 eV and of are deduced for the partial molar enthalpy and, respectively, for the excess partial molar entropy of the dopant in silicon relative to the standard liquid state of antimony.