Diffusion in silicon of elements from columns III and V of the Periodic Table is reviewed in theory and experiment. The emphasis is on the interactions of these substitutional dopants with point defects (vacancies and interstitials) as part of their diffusion mechanisms. The goal of this paper is to unify available experimental observations within the framework of a set of physical models that can be utilized in computer simulations to predict diffusion processes in silicon. The authors assess the present state of experimental data for basic parameters such as point-defect diffusivities and equilibrium concentrations and address a number of questions regarding the mechanisms of dopant diffusion. They offer illustrative examples of ways that diffusion may be modeled in one and two dimensions by solving continuity equations for point defects and dopants. Outstanding questions and inadequacies in existing formulations are identified by comparing computer simulations with experimental results. A summary of the progress made in this field in recent years and of directions future research may take is presented.

Point defects and dopant diffusion in silicon

A numerical solution of the problem of diffusion via a dual mechanism is obtained for P, As, and B diffusion in Si by solving the full system of impurity, vacancy, and self‐interstitial continuity equations. The suitable constants are derived by fitting on experimental results for diffusions in both inert and oxidizing ambients, and lead to interesting information on silicon point defects at high temperature. In particular, it is found that dopant diffusion is essentially vacancy assisted, whereas self‐diffusion proceeds primarily via self‐interstitials.

Dopant diffusion in silicon: A consistent view involving nonequilibrium defects

Oxidation‐enhanced diffusion of phosphorus, arsenic, and boron and oxidation‐reduced diffusion of antimony in silicon have been studied as a function of oxidation time. Data for the early phase of oxidation in dry oxygen from 5 to 60 min have been obtained. Oxidation‐enhanced diffusivities show a steady decrease with decreasing oxidation rate for phosphorus, arsenic, and boron, with enhancements at long oxidation times in agreement with previously reported results. Antimony shows a reduction in diffusivity during oxidation. A model allowing calculation of diffusivity enhancement or reduction for all elements and oxidation times has been developed. The present data support the theory of a dual vacancy‐interstitialcy diffusion mechanism for all the elements studied. The fraction of interstitialcy diffusion fI has been calculated, yielding fI=0.38 for phosphorus at 1000 °C, fI=0.30 for boron at 1000 °C, fI=0.35 for arsenic at 1090 °C, and fI=0.015 for antimony at 1100 °C. It has also been shown that the oxid...

Diffusion of substitutional impurities in silicon at short oxidation times: An insight into point defect kinetics

This paper describes an experimental investigation on the infrared radiative properties of heavily doped Si at room temperature. Lightly doped Si wafers were ion-implanted with either boron or phosphorus atoms, with dosages corresponding to as-implanted peak doping concentrations of 10 20 and 10 21 cm -3 ; the peak doping concentrations after annealing are 3.1 × 10 19 and 2.8 × 10 20 cm -3 , respectively. Rapid thermal annealing was performed to activate the implanted dopants. A Fourier-transform infrared spectrometer was employed to measure the transmittance and reflectance of the samples in the wavelength range from 2 μm to 20 μm. Accurate carrier mobility and ionization models were identified after carefully reviewing the available literature, and then incorporated into the Drude model to predict the dielectric function of doped Si. The radiative properties of doped Si samples were calculated by treating the doped region as multilayer thin films of different doping concentrations on a thick lightly doped Si substrate. The measured spectral transmittance and reflectance agree well with the model predictions. The knowledge gained from this study will aid future design and fabrication of doped Si microstructures as wavelength selective emitters and absorbers in the midinfrared region.

Infrared Radiative Properties of Heavily Doped Silicon at Room Temperature

Photonic technologies lack non-invasive monitoring tools to inspect the light inside optical waveguides. This is one of the main barriers to large scale integration, even though photonic platforms are potentially ready to host thousands of elements on a single chip. Here, we demonstrate non-invasive light observation in silicon photonics devices by exploiting photon interaction with intra-gap energy states localized at the waveguide surface. Light intensity is monitored by measuring the electric conductance of the silicon core through a capacitive access to the waveguide. The electric contacts are located at suitable distance from the waveguide core, thus introducing no measurable extra-photon absorption and a phase perturbation as low as 0.2 mrad, comparable to thermal fluctuations below 3 mK. Light monitoring with a sensitivity of -30 dBm and a dynamic range of 40 dB is demonstrated in waveguides and high-Q resonators, and for the tuning of coupled-resonator optical filters. This approach realizes a ContactLess Integrated Photonic Probe (CLIPP), that is simple, inherently CMOS compatible, non-invasive and scalable to hundreds of probing points per chip. The CLIPP concept provides a viable route to real-time conditioning and feedback control of densely-integrated photonic systems.

Non-Invasive On-Chip Light Observation by Contactless Waveguide Conductivity Monitoring

The diffusivity of boron in and silicon is experimentally determined under both inert and oxidizing (dry ) ambient conditions in the range of temperatures 850°–1200°C The boron is implanted at moderate dose and energy (70 keV) and subsequently activated by a moderate temperature anneal The resulting profile ensures near‐intrinsic silicon at the processing temperatures and serves as initial condition for subsequent processing Diffusivities and segregation coefficients are calculated as fitting parameters in numerical solution of the experiments A systematic fitting procedure is used and the target experimental parameters are sheet resistances and junction depths Inert ambient diffusivities agree well with previous measurements, thus demonstrating the integrity of newly published mobility data used in the simulations Diffusivities in oxidizing ambient are enhanced, more so in than in silicon The enhancement increases with decreasing temperature, being about 10 for at 850°C It is demonstrated that there is good agreement between the observed diffusivity enhancement and growth of oxidation stacking faults if an interstitialcy mechanism is invoked to explain both phenomena Observed segregation coefficients are different for the two silicon orientations but they obey the same activation energy over the temperature range

https://iopscience.iop.org/article/10.1149/1.2131554/pdf

Adalberto G. Gonzalez

Papers

Boron in Near‐Intrinsic and Silicon under Inert and Oxidizing Ambients—Diffusion and Segregation