Analysis of polycrystalline silicon diffusion sources by secondary ion mass spectrometry

Abstract

Polycrystalline silicon diffusion sources have been analyzed using secondary ion mass spectrometry. Polysilicon films were grown by standard low-pressure chemical vapor deposition and doped with As, P, or B by ion implantation. Although dopant segregation at the poly-Si/single-crystal-silicon interface occurred and has been analyzed quantitatively, no diffusion barrier has been observed at this interface. Diffusion profiles in the single-crystal substrate have been measured for diffusion temperatures between 800 and 1000 °C. It is shown by comparison to numerical simulations that these profiles obey standard diffusion theory. Proper boundary conditions to be used for such calculations are deduced for the different dopant species. Furthermore, the saturation concentration of boron in silicon over the temperature range given above has been reliably determined.

Indium penetration through thermally grown silicon oxide

“…The indium tail profile increased slightly toward the thin oxide. Similar phenomenon was observed for boron diffusion in polycrystalline silicon [11]. This was explained by the change of grain structure along the depth of polycrystalline silicon.…”

Diffusion and segregation of arsenic and boron in polysilicon/silicon systems during rapid thermal annealing

“…It is important to compare the results obtained in this work and those obtained by Josquin et al [6]. These authors have noticed that 6% of the implanted dose have been segregated to the interface in polysilicon layers implanted with arsenic, after an anneal for 95 min at 1000 • C. Schaber et al [5] mention that 4% of arsenic atoms and 1% of boron atoms segregate to the interface (the doses used: 2 × 10 16 and 5 × 10 15 atoms/cm 3 for arsenic and boron, respectively). The comparison between diffusion and co-diffusion of arsenic diffused in silicon shows a decrease of about 50% of the arsenic dose in the case of co-diffusion with respect to diffusion.…”

“…Knowing that the dose/thickness ratio is 2.5 × 10 20 atoms/cm 3 , the nearly total conservation of the implanted dose within the polysilicon is easily explainable. This fast diffusion of arsenic in the polysilicon layer, creating a flat concentration profile up to the interface, characterizes the absence of epitaxial realignment [5]. The latter would induce, starting from the interface on the polysilicon side, the appearance of monocrystalline silicon, thus stopping diffusion.…”

“…The junctions created in the underneath silicon can also present non ideal electrical characteristics [8]. Moreover the RCA cleaning minimizes diffusion barrier effects at the interface [5]. According to Batra et al [9], the thickness of the oxide layer is estimated to be 1.4 and 0.8 nm for RCA cleaning and that one in HF, respectively.…”

“…This cleaning procedure makes it possible to avoid the epitaxial realignment of the polysilicon layer starting from the polycrystalline silicon/single crystal silicon interface [3,[5][6][7]. This realignment can modify the diffusion process in the polysilicon and makes its control more complicated.…”