A. F. Saavedra

Modeling extended defect ({311} and dislocation) nucleation and evolution in silicon

End of range (EOR) defects are the most commonly observed defects in ultrashallow junction devices. They nucleate at the amorphous-crystalline interface upon annealing after amorphization due to ion implantation. EOR defects range from small interstitial clusters of a few atoms to {311} defects and dislocation loops. They are extrinsic defects and evolve during annealing. Li and Jones [Appl. Phys. Lett., 73, 3748 (1998)] showed that {311} defects are the source of the projected range dislocation loops. In this article, the same theory is applied to EOR dislocation loops to model the nucleation and evolution of the loops. The model is verified with experimental data and accurately represents the nucleation, growth, and Ostwald ripening stages of dislocation loop evolution. The density and the number of interstitials trapped by dislocation loops are compared with the experimental results for several annealing times and temperatures.

Electrical activation in silicon-on-insulator after low energy boron implantation

We have investigated the electrical activation of implanted boron in silicon-on-insulator (SOI) material using Hall effect, four-point probe, and secondary ion mass spectrometry. Boron was implanted at energies ranging from 1keVto6.5keV with a dose of 3×1014cm−2 into bonded SOI wafers with surface silicon thickness ranging from 300Ato1600A. In one sample set, furnace anneals at 750°C were performed in a nitrogen ambient for times ranging from 5minto48h. A second sample consisted of isochronal furnace anneals performed from 450°Cto1050°C for 30min. Significantly less activation of boron is observed in SOI at temperatures below 750°C, regardless of the implant energy and surface silicon thickness. Between 750°C and 900°C, the active dose of boron in SOI is similar to that of bulk Si. As the implant energy increases, the fractional activation in thin SOI increases, due to a reduction in boron interstitial clusters (BIC) in the surface Si layer. It is concluded that an increase in the BIC population is the li...

Influence of the surface Si/buried oxide interface on extended defect evolution in silicon-on-insulator scaled to 300 Å

As device dimensions continue to be scaled, incorporation of silicon-on-insulator (SOI) as mainstream complementary metal–oxide–semiconductor technology also increases. This experiment set out to further investigate the effect of the surface Si/buried oxide (BOX) interface on the formation and dissolution of extended defects in SOI. UNIBOND® wafers were thinned to 300, 700, and 1600 A. Si+ ion implantation was performed from 5 to 40 keV with a constant, nonamorphizing dose of 2×1014 cm−2. Inert ambient furnace anneals were performed at 750 °C for times of 5 min up to 8 h. Transmission electron microscopy was used to study the evolution of extended defects, as well as to quantify the number of trapped interstitials. It is observed that the surface Si/BOX interface does not enhance the dissolution rate of extended defects unless ⩾15% of the dose is truncated by the BOX. Further, no reduction in the trapped interstitial concentration is seen unless ⩾6% of the dose is truncated. It is concluded that the surfa...

Secondary defect formation in bonded silicon-on-insulator after boron implantation

Silicon-on-insulator (SOI) has proven to be a viable alternative to traditional bulk silicon for fabrication of complementary metal–oxide–semiconductor devices. However, a number of unusual phenomena with regards to diffusion and segregation of dopants in SOI have yet to be explained. In the present study, SOITEC wafers were thinned to 700 and 1600 A using oxidation and etching. Ion implantation was performed into SOI and bulk silicon wafers using 11B+ ions at 6.5 and 19 keV with a dose of 3×1014 cm−2. Thermal processing occurred in a furnace at 750 °C for times ranging from 5 min to 8 h under an inert ambient. Using quantitative transmission electron microscopy it was observed that the concentration of trapped interstitials and density of {311} defects was significantly reduced in SOI compared to the bulk. Hall effect was used to monitor the activation process of boron in SOI and bulk silicon. Significantly less activation was observed in SOI compared to the bulk and was dependent on the surface silicon ...

Defect evolution of low energy, amorphizing germanium implants in silicon

The defect evolution upon annealing of low energy, amorphizing germanium implants into silicon was studied using plan-view transmission electron microscopy. Implants with energies of 5–30 keV at an amorphizing dose of 1×1015 Ge+ cm−2 were annealed at 750 °C from 10 s to 360 min. For the implant energies of 10 and 30 keV, the defects form clusters which evolve to {311} defects that subsequently dissolve or form stable dislocation loops. However, as implant energy drops to 5 keV, the interstitials evolve from clusters to small, unstable loops which dissolve within a small time window and do not form {311}’s. To determine the effect of the free surface as an interstitial recombination sink for 5 keV implants, the amorphous layer of a 10 keV implant was lapped to less than the thickness of a 5 keV amorphous layer and then annealed. We found that the defect dissolution observed for the 5 keV implant energy was dependent on the implant energy and not the proximity of the end-of-range damage to the surface. The ...

Comparison of { 311 } Defect Evolution in SIMOX and Bonded SOI Materials

The effect of silicon-on-insulator (SOI) substrate type and surface silicon thickness on extended defect evolution due to silicon ion implantation has been investigated. Nonamorphizing silicon implants ranging from 15 to 48.5 keV, I × 10 14 cm -2 , were performed into SOITEC and separation by implantation of oxygen (SIMOX) wafers. Subsequently, furnace anneals were performed at 750°C in an inert ambient. Quantitative transmission electron microscopy was used to measure the trapped interstitial concentration, defect density, and defect size. The type of surface silicon/buried oxide interface (e.g., SIMOX or SOITEC) does not appear to affect the decay of the trapped interstitial population or the evolution of the defect microstructure. However, the thickness of the surface silicon/BOX interface strongly affects the evolution of {311} defects, as well as the decay of trapped interstitials. The interface appears to promote formation of dislocation loops as the trapped interstitial population evolves.

Silicon Self-Interstitial Cluster Formation and Dissolution in SOI

Silicon-on-insulator (SOI) is a promising alternative to bulk silicon as ultra shallow junction depths have begun to shrink below 50 nm. This study examined the effect of the SOI surface silicon/buried oxide interface on {311} defect evolution after Si + ion implantation. SOI wafers were produced such that the surface silicon thickness varied from 300A to 1600A. Non-amorphizing Si+ implants at 5 and 20 keV with a dose of 2x10 14 cm -2 were performed into SOITEC SOI wafers. Furnace anneals were done at 750°C from 5 minutes to 4 hours and quantitative transmission electron microscopy (QTEM) was used to study the implant damage evolution. At 5 keV, the dissolution behavior of the SOI was very similar to that of the bulk. However, the extended defects in the 300 A SOI did not nucleate the same as those observed in the bulk or thicker SOI. Similar results were seen at 20 keV for the 700 A SOI, but a slight decrease in the concentration of trapped interstitials was observed due to interface recombination as a result of the increased projected range of the implant. It is concluded that the surface Si/BOX interface does not significantly affect recombination of interstitials trapped in extended defects unless the interstitial profile is close to or truncates the interface. However, the interface does appear to affect the stability of zig-zag {311} defects and dislocation loops in thin SOI at lower implant energies.

Modeling of B diffusion in the presence of Ge

In order to investigate the B and Ge interaction in silicon, an implant/anneal experiment is performed. The initial Si pre-amorphization step defines the amorphous layer depth and the end-of-range point defect distributions for all samples. The following Ge implant provides a low Ge content, thus minimizing the strain and the band gap narrowing effects on the diffusion of the subsequent B implant. The control sample received Si and B implants. The annealed profiles of the control samples show B profile broadening consistent with the transient enhanced diffusion. The B tail diffusion in the Ge implanted samples is almost identical to that of the control samples, indicating that Ge does not act as a trap for the BI pair. The GeB complex, suggested in literature, was used to explain the higher profile peak magnitude in Ge implanted samples.

Modeling B Uphill Diffusion in the Presence of Ge

Several models for B diffusion in Si1-x Gex have been proposed [1, 2]. In order to help discriminate between the models, an experiment was performed. Preamorphized Si wafers were implanted with varying doses of Ge, followed by a B implant. Samples were annealed at several temperatures. Ge implanted samples showed an increase in the B profile peak magnitude with anneal time, as well as its shift towards the surface. Control samples, receiving two Si implants, showed the expected enhanced B diffusion and none of the uphill diffusion behavior. Simulations accounting for the formation of GeB complex show qualitative fit to the measured profiles.