Distribution and segregation of arsenic at theSiO2/Si interface

Abstract

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.

Role of Defects in the Dopant Diffusion in Si

“…However, it was reported soon that phosphorus ( Johannessen et al, 1978;Schwarz et al, 1981) as well as arsenic and antimony (Sai-Halasz et al, 1985) pile-up even during inert annealing in a thin layer at the interface with a concentration that exceeds the bulk concentration by an order of magnitude. The current knowledge about such effects (see Dabrowski et al, 2002;Pei et al, 2008;Steen et al, 2008, and the references therein) is that the pile-up occurs within about one to few nm at the silicon side of the interface to silicon dioxide. There, they can be removed by a dip in HF or by an SC1/SC2 clean.…”

Ab-Initio Modeling of Arsenic Pile-Up and Deactivation at the Si/SiO2 Interface

“…However, recent measurements involving anneals in oxidizing and inert ambients found negligible influence of the ambient on the segregated dose under near-equilibrium conditions, indicating that point defects may not play a dominating role in the segregation process [3]. Reference [3] also reported that the segregated arsenic atoms were deep donors with an electrical activity that increased eventually to full electrical activation for high sheet concentrations of the segregated atoms. Initially, it was believed that As piles up in a narrow region on the oxide side of the interface [5].…”

“…Since it has been found experimentally that As diffuses in Si with the help of both interstitials and vacancies [1], it has been speculated that this trapping of As at the interface is due to a local supersaturation of point defects generated during the implantation process [2]. However, recent measurements involving anneals in oxidizing and inert ambients found negligible influence of the ambient on the segregated dose under near-equilibrium conditions, indicating that point defects may not play a dominating role in the segregation process [3]. Reference [3] also reported that the segregated arsenic atoms were deep donors with an electrical activity that increased eventually to full electrical activation for high sheet concentrations of the segregated atoms.…”

A first-principles study of As doping at a disordered Si–SiO2interface

“…Several experimental studies have reported the uphill thermal diffusion and segregation of arsenic atoms to the Si-SiO 2 interface region during the hightemperature anneal following implantation [3][4][5][6][7][8][9][10][11][12]. Up to a monolayer of dopant atoms can be collected in this region [3,13].…”