The segregation and pile-up of arsenic atoms at the Si/SiO2 interface in steady state was investigated in detail by a combination of gracing incidence x-ray fluorescence spectroscopy (GI-XRF) measurements, electrical measurements, etching on the nanometer scale, and measurements of the step heights by interferometry. Using GI-XRF measurements and removal of the highly doped segregation layer by a sensitive etching process it was possible to distinguish clearly between the piled-up atoms and the arsenic atoms in the bulk over a large range of implantation doses, from 3×1012 to 1×1016 cm−2. The samples were annealed at different temperatures from 900 °C to 1200 °C for time periods long enough to make sure that the segregation reflects an equilibrium state. With additional step height measurements at line-space structures, the thickness of the layer with the piled-up arsenic and the shape of the segregation profile was determined. Electrical measurements indicated that the segregated arsenic atoms are deep donors with an electrical activity that increases eventually to full electrical activation for high sheet concentrations of the segregated atoms. The measured data can be modeled as a steady state of neutral arsenic atoms in the segregation layer with positively charged substitutional arsenic atoms and free electrons. For the highest concentration, a saturation of the sheet concentration of segregated arsenic atoms was observed that correlates with the increase in electrical activation. For the use in process simulation programs, a three-phase segregation model was adapted and calibrated.

We have developed a diffusion and activation model for implanted arsenic in silicon. The model includes the dynamic formation of arsenic-vacancy complexes (As4V) as well as the precipitation of a SiAs phase. The latter is mandatory to correctly describe concentrations above solid solubility while the former are needed to describe the reduced electrical activity as well as the generation of self-interstitials during deactivation. In addition, the activation state after solid-phase epitaxy and the segregation at the interface to SiO2 are taken into account. After implementation using the Alagator language in the latest version of the Sentaurus Process Simulator of Synopsys, the parameters of the model were optimized using reported series of diffusion coefficients for temperatures between 700 °C and 1200 °C, and using several SIMS profiles covering annealing processes from spike to very long times with temperatures between 700 °C and 1050 °C and a wide distribution of implantation energies and doses. The model was validated using data from flash-assisted RTP and spike annealing of ultra-low energy arsenic implants.

The pile-up of arsenic at the Si/SiO(2) interface after As implantation and annealing was investigated by high resolution Z-contrast imaging, electron energy-loss spectroscopy (EELS), grazing incidence x-ray fluorescence spectroscopy (GI-XRF), secondary ion mass spectrometry, x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, as well as Hall mobility and four-point probe resistivity measurements. After properly taking into account their respective artifacts, the results of all methods are compatible with each other, with EELS and GI-XRF combined with etching providing similar spatial resolution on the nanometer scale for the dopant profile. The sheet concentration of the piled-up As at the interface was found to be similar to 1 x 10(15) cm(-2) for an implanted dose of I X 1016 cm-2 with a maximum concentration of similar to 10 at. %. The strain observed in the Z-contrast images also suggests a significant concentration of local distortions within 3 nm from the interface, which, however, do not seem to involve intrinsic point defects

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