Highlights

Role of the Induced Defects under Ion Beam on CoSi₂ Nucleation in Si

Scientific Achievement

Predicting and controlling the formation of low dimensionality precipitates requires adequate knowledge of the mechanisms involved in nucleation and growth processes under ion irradiation.  This is particularly important for systems in which 2 nanostructure populations coexist in a matrix such as CoSi₂ in a Si host where Co implantation in Si largely favors (90%) the formation of  semi-coherent platelets (B-type) in spite of the fact that they are thermodynamically less stable than A-type nanoprecipitates (i.e. octahedral in perfect epitaxy).  Kinetic Monte Carlo simulations evidenced a nucleation mechanism related to the presence of defects (specifically vacancies) created during  implantation.

A first series of experiments at the EMC facility of ANL allowed us to study the role of defects during Co implantation.  Independent control of the defect rate production and of the implanted Co concentration was obtained using the Argonne 300 kV IVEM and simultaneous in situ Co implantation.  Synergy effects are obtained in the dual beam area: both the nature and density of defects are modified in the co-irradiated area.  We observed the formation of a high concentration of large dislocations (some hundred nanometers to micron) and faulted defects (hundred nm in size) in the dual beam region.  Whereas classical small perfect dislocation loops are observed in areas where only Co implantation was acting.

Also, in the co-irradiation area, the increase of Frenkel pair density (electron beam effect) increased nucleation-growth rate of CoSi₂ nanoprecipitate (2 times greater for the nanoprecipitate concentration and 2 times lower in size ). 

Significance

First evidence of synergy effects was observed during dual beam experiments. Those effects lead to the observed faulted dislocation loop network and to the modification of the nucleation-growth rate.  This preliminary results are the first steps in defect engineering control for the selection of nanoprecipitate nature.

Performers

F. Fortuna, B. Décamps, E. Oliviero, M.-O. Ruault (CSNSM/CNRS/Univ. P-Sud, Orsay, France); M. Kirk, P. Baldo (Argonne-MSD)