Atom Redistribution during co-Doped Amorphous Silicon Crystallization

Abstract

Atom redistribution during crystallization of a B and P co-doped amorphous Si layer produced by Si and P chemical vapor co-deposition and B implantation has been investigated. The crystallization of the entire layer is quasi-instantaneous for annealing temperature greater than 650 °C. The crystallization rate is well reproduced by the Avrami-Johnson-Mehl-Kolmogorov model of transformation. The Avrami n is found equal to 4, which is corresponding to 3D bulk crystallization. Crystallization promotes a non-Fickian redistribution of B atoms, allowing for an abrupt interface between B-doped and B-undoped regions. After crystallization, B diffuses in the polycrystalline Si layer for concentrations lower than 1.5  1020 at cm3 via the type B kinetic regime. Crystallization has no significant (or detectable) influence on the P profile. For temperatures higher than 750 °C, P diffuses in the poly-Si layer towards the region of highest B concentration via the type B kinetic regime, leading to P uphill diffusion. This phenomenon can be simulated considering chemical interactions between B and P atoms in both grains and grain boundaries.

A Study of Parameters Affecting Atom Probe Tomography Specimen Survivability

“…The surface was then implanted with boron (B) at 7 keV and a dose of 3.5×10 15 /cm 2 . Subsequent annealing at 755°C for 4 h resulted in poly-recrystallization of the amorphous-Si layer and some activation and redistribution of the P and B within the layer (Portavoce et al, 2007, 2009). This process is similar to the process generally used for fabrication of semiconductor memory floating gates.…”

Dopant diffusivity and solubility in nickel silicides

“…In a second scenario, the top part of the profile could be due to the presence of dissolving precipitates. Precipitates are known to give an immobile contribution to the concentration profile [13] and, when they dissolve, act as a source of mobile species which diffuse below the solubility limit giving such profile shapes [14,15]. Thus, the bottom part of the profile would be due to a type A diffusion in the volume and the GBs.…”

B diffusion in implanted Ni2Si and NiSi layers

“…The first two samples consisted of either a 250 nmthick polycrystalline Ni 2 Si layer or a 180 nm-thick polycrystalline NiSi layer located between two Si oxide layers, the thickness of the surface oxide being 20 nm and the thickness of the oxide separating the silicides from the Si͑001͒ substrate being 30 nm. [19][20][21] If part of B atoms would have formed clusters, part of the B SIMS profiles would not change despite annealing. 17 for the description of sample fabrication and of silicide grain size stabilization procedures͒.…”

“…Doping conditions were targeted in order to confine the entire boron dose within the top half of the silicide layer. [19][20][21] The fact that the B cluster distribution follows a Gaussian distribution suggests that B cluster formation may result from heterogeneous nucleation on implantation-induced defects. Before Ni deposition, the B-implanted Si substrate was annealed at 1050°C for 30 s in order to activate the dopant.…”

“…Pieces of these three samples were annealed all together either at 400, 450, 500, or 550°C for 1 h under vacuum ͑ϳ10 −7 Torr͒. [19][20][21] We notice that, at that temperature, the B GB diffusivity is high as the profile is flat in GBs. B concentration profiles were measured in the samples by secondary ion mass spectrometry ͑SIMS͒ using a 3 kV Cs + ion primary beam.…”