arXiv subjects

O. I. Velichko

Publications and source records attributed to O. I. Velichko.

25 records · Page 2Linked to original sources

arXiv2007

Set of equations for transient enhanced diffusion in shallow ion-implanted layers

To simulate the transient enhanced diffusion near the surface or interface, a set of equations describing the impurity diffusion and quasichemical reactions of dopant atoms and point defects in ion-implanted layers is proposed and analyzed. The diffusion equations obtained take into account different charge states of mobile or immobile species and drift the mobile species in the built-in electric field and field of elastic stresses. The absorption of self-interstitials on the surface and drift of the defects due to elastic stresses result in the nonuniform distributions of point defects. It was shown analytically and by means of numerical calculations that consideration of the nonuniform defect distributions enables one to explain the phenomenon of "uphill" impurity diffusion near the surface during annealing of ion-implanted layers. The performed calculations of the boron concentration profile after annealing of a shallow implanted layer agree well with the experimental data confirming the efficiency of the proposed equations.

cond-mat.mtrl-sci↗

arXiv2006

Mechanisms of arsenic clustering in silicon

A model of arsenic clustering in silicon is proposed and analyzed. The main feature of the proposed model is the assumption that negatively charged arsenic complexes play a dominant role in the clustering process. To confirm this assumption, electron density and concentration of impurity atoms incorporated into the clusters are calculated as functions of the total arsenic concentration. A number of the negatively charged clusters incorporating a point defect and one or more arsenic atoms are investigated. It is shown that for the doubly negatively charged clusters or for clusters incorporating more than one arsenic atom the electron density reaches a maximum value and then monotonically and slowly decreases as total arsenic concentration increases. In the case of doubly negatively charged cluster incorporating two arsenic atoms, the calculated electron density agrees well with the experimental data. Agreement with the experiment confirms the conclusion that two arsenic atoms participate in the cluster formation. Among all present models, the proposed model of clustering by formation of doubly negatively charged cluster incorporating two arsenic atoms gives the best fit to the experimental data and can be used in simulation of high concentration arsenic diffusion.

cond-mat.mtrl-sci↗

arXiv2006

Analytical solutions for the interstitial diffusion of impurity atoms

The analytical solutions of the equations describing impurity diffusion due to migration of nonequilibrium impurity interstitials were obtained for the impurity redistribution during ion implantation at elevated temperatures and for diffusion from a doped epitaxial layer. The reflecting boundary condition at the surface of a semiconductor and the conditions of constant concentrations at the surface and in the bulk of it were used in the first and second cases, respectively. On the basis of these solutions hydrogen diffusion in silicon during high-fluence low-energy deuterium implantation and beryllium diffusion from a doped epi-layer during rapid thermal annealing of InP/InGaAs heterostructures were investigated. The calculated impurity concentration profiles agree well with experimental data. The fitting to the experimental profiles allowed us to derive the values of the parameters that describe interstitial impurity diffusion.

cond-mat.mtrl-sci↗

arXiv2006

Simulation of Arsenic Diffusion During Rapid Thermal Annealing of Silicon Layers Doped with Low-Energy High-Dose Ion Implantation

The model of transient enhanced diffusion of ion-implanted As is formulated and the finite-difference method for numerical solution of the system of equations obtained is developed. The nonuniform distribution of point defects near the interface and more accurate description of arsenic clustering are simultaneously taking into account. Simulation of As diffusion during rapid annealing gives a reasonable agreement with the experimental data. Keywords: diffusion; clusters; ion implantation; arsenic; silicon PACS: 66.30.Jt

cond-mat.mtrl-sci↗

arXiv2006

Simulation of point defect diffusion in structures with local elastic stresses

The stress-mediated diffusion of nonequilibrium point defects from the surface to the bulk of the semiconductor is investigated by computer simulation. It is supposed that point defects are generated in the surface region by ion implantation and during diffusion pass over the local region of elastic stresses because the average defect migration length is greater than the thickness and depth of the strained layer. Within the strained layer point defect segregation or heavily defect depletion occur if defect drift under stresses is directed respectively in or out of the layer. On the other hand, the calculations show that, in contrast to the case of local defect sink, the local region of elastic stresses practically does not change the distribution of defects beyond this region if there is no generation/absorption of point defects within the strained layer.

cond-mat.mtrl-sci↗

arXiv2006

Clustering of phosphorus atoms in silicon

To explain the effect of electron density saturation at high phosphorus concentrations the model of negatively charged phosphorus clusters was compared with the experimental data. A number of negatively charged clusters incorporating a point defect and phosphorus atoms were investigated at temperatures of 920 and 1000 Celsius degrees. It was established that for clusters incorporating more than one phosphorus atom calculated electron density reached a maximum value and then monotonically and slowly decreased with increasing the total dopant concentration. If the cluster incorporates 3-4 phosphorus atoms the calculated dependencies of carrier concentration agree well with the experimental data for both temperatures regardless of the negative charge state of the cluster (- or 2-). Moreover, for all investigated doubly negatively charged clusters the fitting parameter is independent on the temperature. It means that formation of doubly negatively charged clusters is most likely but it is difficult to choose between clusters incorporating two, three or four phosphorus atoms. From a good agreement of the calculated curves with the experiments it follows that the model based on the formation of negatively charged clusters can be used in simulation of high concentration phosphorus diffusion.

cond-mat.mtrl-sci↗

arXiv2006

Macroscopic description of the diffusion of interstitial impurity atoms considering the influence of elastic stress on the drift of interstitial species

The diffusion equation for nonequilibrium interstitial impurity atoms taking into account their charge states and drift of all mobile interstitial species in the built-in electric field and in the field of elastic stress was obtained. The obtained generalized equation is equivalent to the set of diffusion equations written for the interstitial impurity atoms in each individual charge state. Due to a number of the characteristic features the generalized equation is more convenient for numerical solution than the original system of separate diffusion equations. On this basis, the macroscopic description of stress-mediated impurity diffusion due to a kick-out mechanism was obtained. It is supposed that the interstitial impurity atom makes a number of jumps before conversion to the substitutional position. At the same time, a local equilibrium prevails between substitutionally dissolved impurity atoms, nonequilibrium self-interstitials, and interstitial impurity atoms. Also, the derived equation for impurity diffusion due to the kick-out mechanism takes into account all charge states of interstitial impurity atoms as well as drift of interstitial species in the electric field and in the field of elastic stress. Moreover, this equation exactly matches the equation of stress-mediated impurity diffusion due to generation, migration, and dissociation of the equilibrium pairs "impurity atom - self-interstitial".

cond-mat.mtrl-sci↗