Highlights

Free Surfaces Influence on Induced Defects and Disilicide Growth During Ion Implantation in Si

Scientific Achievement

We have in-situ observed the structural evolution of inhomogeneous Si samples.  The latter consist of a 3 nm nanocavity zone (~300 nm width) followed by a 10-20 nm cavity zone (~100 nm layer) and then a cavity free zone.  Nanocavities in Si were synthetized by 50keV He implantation at room temperature following by rapid annealing at 800°C. Then, cross sections were prepared for TEM microscopy.  The latter were in situ implanted with Co and Ni ions at 650°C using the Argonne IVEM in line (the electron voltage was set to 150 kV to avoid a simultaneous electron irradiation).

For both ions, we observed interactions of the induced defects with the 3 nm nanocavities.  The latter are sink for induced defects leading to a free defect zone in the nanocavity region up to a dose as high as 3x10¹⁴ ions/cm².

According to the high mobility and the solubility of Ni in Si as a preliminary result, we observed the formation of NiSi₂ precipitates in the region of the 10-20 nm cavitiy layer.  The free surfaces of the cavities seem to play a barrier role for the Ni diffusion and allow the nucleation and growth of the disilicide all along the cavity layer.  The elongation of those disilicides in the direction of the nanocavity layer  could reach a micron length.

Significance

This work adresses defect engineering in silicon.  A first important result is a demonstration that nanocavities (<4 nm)  are tools to control defect density related to ion implantation.

As an original result, nickel disilicide nucleation-growth oriented along the cavity layer was observed during implantation.  Since no precipitation occured elsewhere in the sample, this preliminary result is an indication of the preponderant role of the free surfaces for the control of disilicide formation.

Performers