Extended Defects Formation in Nanosecond Laser-Annealed Ion Implanted Silicon

Abstract

Damage evolution and dopant distribution during nanosecond laser thermal annealing of ion implanted silicon have been investigated by means of transmission electron microscopy, secondary ion mass spectrometry, and atom probe tomography. Different melting front positions were realized and studied: nonmelt, partial melt, and full melt with respect to the as-implanted dopant profile. In both boron and silicon implanted silicon samples, the most stable form among the observed defects is that of dislocation loops lying close to (001) and with Burgers vector parallel to the [001] direction, instead of conventional {111} dislocation loops or {311} rod-like defects, which are known to be more energetically favorable and are typically observed in ion implanted silicon. The observed results are explained in terms of a possible modification of the defect formation energy induced by the compressive stress developed in the nonmelted regions during laser annealing.

Ultrafast Generation of Unconventional{001}Loops in Si

“…1. It is worth noting that higher temperatures produce fewer but larger {001} loops, in agreement with experiments [20]. However, at the highest simulated temperature T* = 0.92 no loops are observed, just one large disordered cluster that encompasses all the Is formerly introduced in the lattice (see Fig.…”

“…[20]). In order to further support these findings we have performed dedicated LA experiments in which Si on insulator (SOI) substrates were used in order to modify the thermal biaxial strain with respect to conventional Si bulk substrates, and bring it below the theoretical level for the inversion of stability between {111} and {001} loops. )…”

“…However, in recent ultrafast laser annealing (LA) experiments, where the Si substrate region is heated close to the melting temperature at the nanosecond timescale, new physical effects are revealed since: (a) large I-clusters form in a time scale (few tens of nanoseconds) incompatible with the OR mechanism, and (b) planar {001} I-loops instead of conventional {111} dislocations are observed by transmission electron microscopy (TEM) [20]. {001} loops had not been found in 3 Si before and indeed were not expected from an energetic point of view.…”

“…{001} loops had not been found in 3 Si before and indeed were not expected from an energetic point of view. To justify their presence, it was hypothesized that the generation of {001} loops in Si could be due to the reduction of the defect formation energy relative to {111} defects as a consequence of the compressive biaxial stress developed in non-melted regions of the substrate during LA [20]. Anyhow, this stability argument cannot explain the kinetic mechanism underlying the ultrafast gathering of Is in such large aggregates.…”

Improved physical models for advanced silicon device processing

“…Nevertheless, existing understanding is still improving, some issues remain unsolved and new challenges are appearing. For instance, just recently unexpected {001} dislocation loops have been observed in laser annealed implanted Si [33]. Defect growth models based on coalescence instead of conventional Ostwald ripening have been proposed to account for such defects [30].…”