Formation energies and relative stability of perfect and faulted dislocation loops in silicon

Abstract

A study of the relative thermal stability of perfect and faulted dislocation loops formed during annealing of preamorphized silicon wafers has been carried out. A series of transmission electron microscopy experiments has been designed to study the influence of the ion dose, the annealing ambient and the proximity of a free surface on the evolution of both types of loops. Samples were implanted with either 150 keV Ge+ or 50 keV Si+ ions to a dose of 2×1015 cm−2 and annealed at 900 °C in N2, N2O, and O2. The calculations of formation energy of both types of dislocation loops show that, for defects of the same size, faulted dislocation loops (FDLs) are more energetically stable than perfect dislocation loops (PDLs) if their diameter is smaller than 80 nm and vice versa. The experimental results have been analyzed within the framework of the Ostwald ripening of two existing populations of interstitial defects. It is found that the defect ripening is nonconservative if the surface is close to the end of range defect layer or if the sample is oxidized during annealing. In both cases, the knowledge of the formation energy of both types of dislocation loops allows a realistic estimate of the interstitial flux towards and from the surface, respectively, during annealing, in agreement with the experimental results. During a conservative ripening process, a direct correspondence exists between the formation energy of the two defect families and the number of atoms bound to them. In this case, the relative stability of FDLs and PDLs depends on the initial supersaturation of Si interstitial atoms created during implantation.

Si interstitial contribution of F+ implants in crystalline Si

“…The coimplantation of Si + and the lower F + fluence causes a higher B TED for longer annealings because more Si I's ͑those generated by both Si + and F + implants͒ have contributed to it. The samples implanted with a higher F + fluence ͑5 ϫ 10 14 cm −2 ͒ do not show more B diffusion than that implanted only with Si + , even for the longest analyzed annealing ͑1800 s͒, in spite of the much larger effective Si interstitial fluence contribution for the F + implant ͓ϳ2 ϫ 10 14 cm −2 for F + ͑0.4ϫ implant fluence͒ versus ϳ6.5ϫ 10 13 cm −2 for Si + ͑1.3ϫ implant fluence͔͒ because many I's still remain stored in stable dislocation loops 21 and have not effectively contributed to enhance B diffusion. FIG.…”

Correlation between Copper Precipitation and Grown-In Oxygen Precipitates in 300~mm Czochralski Silicon Wafer

“…Like the case of oxygen precipitation, Cu precipitation is usually accompanied with ejection of interstitial silicon (Si i ) atoms due to the volume expansion. In certain regions, the supersaturated Si i atoms may aggregate into dislocations [14]. Then, Cu precipitate colonies form through the repeated aggregation of Cu i atoms on the climbing dislocations [15,16].…”

Anisotropy of strain relaxation in (100) and (110) Si/SiGe heterostructures

“…In contrast, for the Si þ ion implantation method, the dislocation loops are directly formed in the SiGe layer by transformation from {311} planar defects. 35,36 The strain relaxation is constrained only by the formation of loops of a critical size and their extension through the SiGe layer to the surface and SiGe/Si substrate interface. 37 The localization and homogenization of dislocation loop sources for the He þ ion implantation method, by introducing the d-Si:C interlayer, the relaxation strongly increases, reducing the quality factor to 1.7, the closest to ideal experimental value for planar layer relaxation.…”