Annealing of electron-, proton-, and ion-produced vacancies in Si

Abstract

Positron lifetime and Doppler measurements were performed on float-zone-refined and variously doped Czochralski-grown Si. The samples were irradiated by various particles ͑e − , p, Kr͒ with energies between 2 MeV and 245 MeV. Electron or proton irradiation gave rise to divacancies, whereas the damage from ion implantation ͑Kr͒ was mainly in the form of four-vacancy clusters, with only a small fraction of vacancies in the form of divacancies. In the case of impurity-lean Si, detailed isothermal annealing at various temperatures between 125°C and 500°C showed that after an initial fast decrease in divacancy concentration, a much slower process of vacancy agglomeration took place. At 450°C agglomeration steadily progressed even after 30 h of annealing at which point the average cluster size corresponded to ten monovacancies. In impurity-rich Si, containing oxygen and dopants, there is nearly no initial decrease in vacancy concentration, and isothermal and isochronal annealings showed that vacancy agglomeration was also nearly absent. Doppler data showed that vacancy-dopant complexes slowly acquired oxygen as annealing progressed, and these complexes survived annealing at 500°C for many hours. Measurements between 8 K and 530 K on samples containing divacancies, or larger clusters, showed a temperature dependence of the positron trapping rate that cannot be explained by the clusters being negatively charged, but can be explained if neutral clusters have a weakly bound positron state which at low temperatures makes trapping more efficient. Generally, the present positron experiments have given an indication for the type of defects that survive annealing at temperatures where electron paramagnetic resonance and infrared spectroscopy yield little useful information.

Activation Energies for the Formation and Evaporation of Vacancy Clusters in Silicon

“…This discrepancy was attributed to vacancy aggregation at the temperature at which the V 2 become mobile, the resulting clusters being positron detectable but not optically active. A similar discrepancy was reported by Dannefaer et al [3][4][5], who explained it in terms of V 2 associating loosely with each other without clustering. However, Makhov and Lewis later suggested that vacancy clustering may well not lead to a clear change in PAS parameters, while the IR response is destroyed [6].…”

“…Pinning of V 2 by impurities has been invoked to explain the survival of vacancy defects in Cz-Si to temperatures of 500 C [3,8].…”

Effects of Fluences of Irradiation with 107 MeV Krypton Ions on the Recovery Charge of Silicon p+n-Diodes

“…Although an increase in leakage currents at the given irradiation fluences may be considerable (by more than an order of magnitude), it can likely be minimized by annealing. It is known that in the case of large local concentrations of irradiation-induced defects annealing can cause formation of vacancy and interstitial clusters [12,13]. Because of issues indicated above, annealing experiments on optimization of leakage currents and reverse resistance recovery time of diodes irradiated with high-energy heavy ions require careful preparation and electron microscope studies which are beyond the scope of the current work.…”

In SituProbing of Fast Defect Annealing in Cu and Ni with a High-Intensity Positron Beam

“…The beam intensity is hence at least 2 orders of magnitude higher than at conventional laboratory beam setups and still higher than comparable large scale facilities [9,10]. Using the remoderated beam with 5 Â 10 7 positrons=second in situ positron-electron annihilation parameters can now be measured and analyzed on a time scale of a minute, and hence roughly at least 10 times faster than with conventional laboratory based positron annihilation facilities [11]. It allows for specific studies of fast defect-annealing kinetics.…”