Interstitial Supersaturation Research Articles

Electron irradiation enhanced precipitation in a Mg-6 wt% Sn alloy in TEM

The precipitation in a Mg-6 wt% Sn alloy under electron irradiation has been investigated by in-situ heat treatment at 200 °C in a transmission electron microscope. Electron irradiation produced a high number density (9.78 ± 1.27 × 1021 m−3) of fine β-Mg2Sn precipitates with the average length close to 15 nm whereas the β-Mg2Sn precipitates formed in the region without electron irradiation have a low number density of 2.55 ± 0.68 × 1019 m−3 and a coarse size averaging around 200 nm. The β-Mg2Sn precipitates formed with and without electron irradiation have the same orientation relationship with the Mg matrix:11¯00Mg//112β,0002Mg//22¯0β with the habit planes parallel to the basal (0001)Mg plane. Experimental results clearly demonstrate that electron irradiation is effective in refining the precipitate distribution in the Mg-6 wt% Sn alloy and the possible underlying mechanisms are discussed in relation to the supersaturation of vacancies and interstitials produced by electron irradiation.

Current concepts on the pathogenesis of urinary stones

The process of kidney stone formation is complex and still not completely understood. Supersaturation and crystallization are the main drivers for the etiopathogenesis of uric acid, xanthine and cystine stones but this physicochemical concept fails to adequately explain the formation of calcium-based nephrolithiasis, which represents the majority of kidney stones. Contemporary concepts of the pathogenesis of calcium-based nephrolithiasis focus on a nidus-associated stone formation of calcium-based nephrolithiasis on Randall's plaques or on plugs of Bellini's duct. Randall's plaques originate from the interaction of interstitial calcium supersaturation in the renal papilla, vascular and interstitial inflammatory processes and mineral deposits of calcifying nanoparticles on the basal membrane of the thin ascending branch of the loop of Henle; however, plugs of Bellini's duct are assumed to be caused by mineral deposits on the wall of the collecting ducts. Aggregation and overgrowth are influenced by the interaction of matrix proteins with calcium supersaturated urine, by an imbalance between promoters and inhibitors of stone formation in the calyceal urine. Current research has elucidated many factors contributing to stone formation by revealing novel insights into the physiology of nephron and papilla, by analyzing vascular, inflammatory and calcifying processes in the renal medulla, by examining the proteome, the microbiome, promoters and inhibitors of stone formation in the urine and by conducting the first genome-wide association studies; however, more future research is mandatory to fill the gap of knowledge and hopefully, to obtain novel prophylactic, therapeutic and metaphylactic tools beyond the current state of knowledge.

“Colossal” interstitial supersaturation in delta ferrite in stainless steels: (II) low-temperature nitridation of the 17-7 PH alloy

Low-temperature gas-phase nitridation has been studied in interstitially-hardened 17-7 precipitation-hardening stainless steel. After nitridation, conventional transmission electron microscopy reveals that delta ferrite grains in such alloys show a uniform weak diffraction contrast. Chemical analysis reveals that the weak-contrast ferrite grains contain an enormous interstitial nitrogen supersaturation (>20 at.%). Surprisingly, there is no significant tetragonality in these weak-contrast ferrite grains. Such weak diffraction contrast is attributed to a nanometer-scale nitridation-induced spinodal decomposition of delta ferrite grains. In addition, nitride nanoparticles are observed in the steel, and were identified as rocksalt-structured MN nitride (M: Fe, Cr, Ni, and Al). Further, platelets of hexagonal M2N1-x are observed at low nitriding temperatures (623 and 653 K), but were absent during nitridation at a higher temperature (713 K).

“Colossal” Interstitial Supersaturation in Delta Ferrite in 17-7 PH Stainless Steels After Low-temperature Nitridation

“Colossal” Interstitial Supersaturation in Delta Ferrite in 17-7 PH Stainless Steels After Low-temperature Nitridation

Silicon germanium interdiffusion in SiGe device fabrication: A calibrated TCAD model

SiGe alloys are used in many types of electronic devices. For upcoming FinFET technologies, there is interest in the use of SiGe heterostructures in the complete mole fraction range (0–100% Ge atoms). For high Ge mole fraction and small device dimensions, interdiffusion of Si and Ge atoms can lead to critical changes in the distribution of Si and Ge atoms, impacting channel strain and carrier mobility. A process model for Si–Ge interdiffusion has been developed which covers the needs for actual device fabrication processes. Interdiffusion is understood to be correlated with the diffusion of vacancies, self-interstitials, and dopant-defect pairs. We consider the impact of non-equilibrium point defect concentrations (such as interstitial super-saturation after ion implantation), the impact of compressive or tensile strain, and a twofold impact of doping: first, doping determines the local electron concentration and thereby the abundance of charged point defects, and second, the diffusion of dopant-defect pairs can contribute to the interdiffusion of Si and Ge atoms. The model covers the full range of possible Ge mole fractions (0–100%). For undoped SiGe, it has been calibrated against a broad range of published experimental data for radio-tracer diffusion in SiGe and for interdiffusion in biaxially strained SiGe heterostructures grown on Si, stress-relaxed SiGe, or Ge. The extensions for doped SiGe are presented with a reference to few interdiffusion data for heavily doped SiGe heterostructures. Finally, the model has been consistently integrated into a set of models for the continuum process simulation of point defects and dopants in pure Si, SiGe, and pure Ge, in Sentaurus Process.

“Colossal” interstitial supersaturation in delta ferrite in stainless steels—I. Low-temperature carburization

Low-temperature carburization has been successfully used to surface harden 17-7 precipitation-hardening (PH) and 2205 duplex stainless steels. After carburization, the delta ferrite grains in both alloys near the free surface show a uniform weak contrast under conventional transmission electron microscopy (TEM). Spatially resolved compositional analysis shows that these delta ferrite grains possess enormous carbon contents (as high as 18at.%) in solid solution, but structurally there is no detectable tetragonality (<5%) or evidence of carbide formation. Near the interface between the interstitially hardened layer and bulk material, weak-contrast plates with significant carbon concentrations were observed in ferrite grains in 17-7 PH stainless steel. A carbon-induced spinodal-like decomposition of delta ferrite to the nanometer-scale Cr-rich and Fe-rich alpha ferrite phases is observed. Carbon is enriched in Cr-rich ferrite due to the high affinity between C and Cr, which introduces lattice mismatch between the Cr-rich and Fe-rich regions. The weak contrast is believed to be the result of overlapping strain fields of these Cr-rich and Fe-rich phases. As the binding energies of carbon interstitials to dislocations in body-centered cubic Fe-based alloys are greater than the binding energy of C to Fe in possible carbides, segregation to dislocation cores is expected. The extremely high dislocation density we observe in high-resolution scanning TEM is consistent with the hypothesis that carbon segregation to dislocation cores effectively delays carbide precipitation and makes possible the “colossal” carbon supersaturation.

Lithium implantation at low temperature in silicon for sharp buried amorphous layer formation and defect engineering

The crystalline-to-amorphous transformation induced by lithium ion implantation at low temperature has been investigated. The resulting damage structure and its thermal evolution have been studied by a combination of Rutherford backscattering spectroscopy channelling (RBS/C) and cross sectional transmission electron microscopy (XTEM). Lithium low-fluence implantation at liquid nitrogen temperature is shown to produce a three layers structure: an amorphous layer surrounded by two highly damaged layers. A thermal treatment at 400 °C leads to the formation of a sharp amorphous/crystalline interfacial transition and defect annihilation of the front heavily damaged layer. After 600 °C annealing, complete recrystallization takes place and no extended defects are left. Anomalous recrystallization rate is observed with different motion velocities of the a/c interfaces and is ascribed to lithium acting as a surfactant. Moreover, the sharp buried amorphous layer is shown to be an efficient sink for interstitials impeding interstitial supersaturation and {311} defect formation in case of subsequent neon implantation. This study shows that lithium implantation at liquid nitrogen temperature can be suitable to form a sharp buried amorphous layer with a well-defined crystalline front layer, thus having potential applications for defects engineering in the improvement of post-implantation layers quality and for shallow junction formation.

Defect engineering via ion implantation to control B diffusion in Si

The processes which are currently studied in the fabrication of B-doped ultra shallow junctions (USJ) usually involve a preamorphization step to reduce B channelling effect during implantation and to improve B electrical activation. At this stage a high amount of Si interstitial atoms (Is), which dramatically increases the B diffusivity, is introduced. The introduction of voids in Si is a promising tool to control B transient enhanced diffusion (TED), because of their ability to capture Is. In this work the efficiency of a cavity band to reduce B TED is checked in silicon interstitial supersaturation conditions, obtained by high dose Si implantation. He is implanted either at 10 keV or at 50 keV with a fluence of 5 × 10 16 cm −2. Conventional techniques to introduce and activate the B (conventional ion implantation and rapid thermal annealing (RTA)) are applied in order to have a better control of the technological process to focus on the benefit of the cavity layer. The samples were characterized by cross section transmission electron microscopy (XTEM), secondary ion mass spectroscopy (SIMS) and Hall Effect (HE). The latter shows that good activation of the B is achieved only after 1000 °C RTA, though a 900 °C RTA is sufficient for implantation-damage recovery, as it is confirmed by XTEM observations. B SIMS profiles show that the band of cavities plays its best effect in reducing B TED when it is located near the surface.

Si interstitial contribution of F+ implants in crystalline Si

The F effect in crystalline Si is quantified by monitoring defects and B diffusion in samples implanted with 25 keV F+ and/or 40 keV Si+. We estimate that about +0.4 Si interstitials are generated per implanted F+ ion, in agreement with the value resulting from the net separation of Frenkel pairs. For short annealings, B diffusion is lower when F+ is coimplanted with Si+ than when only Si+ is implanted, while for longer annealings, B diffusion is higher. This is consistent with a lower but longer-lasting Si interstitial supersaturation set by the additional defects generated by the F+ implant.

Suppression of boron deactivation and diffusion in preamorphized silicon after nonmelt laser annealing by carbon co-implantation

For preamorphized boron-implanted samples subjected to nonmelt laser spike annealing (LSA), increasing the LSA temperature at temperatures below 1250 °C results in negligible sheet resistance changes due to the formation of inactive boron-interstitial clusters (BICs). These clusters, which are evidenced as a kink in the boron profile beyond the amorphous/crystalline interface, result chiefly from the inadequate removal of end-of-range (EOR) defects. When the LSA temperature is elevated beyond 1250 °C, sheet resistance improvement takes place due to the increase in active boron dose from the dissolution of the BIC at higher temperatures. Cluster dissolution also gives rise to a supersaturation of silicon interstitials that deepen the junctions as a result of transient enhanced diffusion (TED). With an additional post-LSA treatment, severe deactivation, especially at lower LSA temperatures, and further TED is observed. Two concurrent mechanisms, namely, boron clustering (which gives rise to deactivation and sheet resistance degradation) and dissolution of the BIC (which gives rise to TED) formed during the LSA step, are believed to take place during the post-LSA thermal budget. As the LSA temperature increases, TED from the as-LSA profile upon rapid thermal annealing (RTA) is significantly reduced as a result of the improved effectiveness of the EOR defect dissolution during the higher temperature LSA step. When carbon co-implantation is performed, deactivation and TED is successfully suppressed with the reduction in free silicon interstitial concentration due to the formation of complexes of carbon and silicon interstitials. The amount of deactivation upon RTA becomes independent of LSA temperature for the carbon-implanted samples, largely because boron clustering becomes limited by the small concentration of free silicon interstitials present instead of the LSA temperatures used.

Evolution of fluorine and boron profiles during annealing in crystalline Si

In this work the authors study the interaction of F with point defects and the influence of F on B diffusion in crystalline Si. The authors perform 25 and 100 keV F+ implants and combine them with a 40 keV Si+ implant. The appearance of peaks in the F profile during annealing supports the idea of the formation of F complexes with vacancies and Si interstitials. In all samples implanted with F+ analyzed in this work, B diffusion is higher than in equilibrium conditions indicating that F+ implants in crystalline Si produce a Si interstitial supersaturation. However, B diffusion is reduced when F+ is coimplanted with Si, compared to only Si implants. This effect is more evident when B is located in the region where the F+ implant generates an excess of vacancies, but it also appears in the Si interstitial-rich region. The results indicate that the effect of F on B diffusion in crystalline Si is time dependent.

Modeling of Effect of Stress on C Diffusion/Clustering in Si

ABSTRACTExtensive ab-initio calculations were performed to find formation energies of stable C complex configurations in silicon as function of stress. The results indicate that substitutional C is the lowest energy state, while the &lt;100&gt; split interstitial is the dominant mobile species. Investigation of small carbon/interstitial clustering suggests that these clusters are only significant under a substantial interstitial supersaturation. We studied the diffusion path for neutral C including the impact of stress. Through KLMC analysis of stress effect on diffusivity, we found that tensile biaxial strain enhances the effective C diffusivity, with a stronger stress dependence for C diffusivity in the out-of-plane direction.

F+ implants in crystalline Si: the Si interstitial contribution

ABSTRACTIn this work the Si interstitial contribution of F+ implants in crystalline Si is quantified by the analysis of extended defects and B diffusion in samples implanted with 25 keV F+ and/or 40 keV Si+. We estimate that approximately 0.4-0.5 Si interstitials are generated per implanted F+ ion, which is in good agreement with the value resulting from the net separation of Frenkel pairs obtained from MARLOWE simulations. The damage created by F+ implants in crystalline Si may explain the presence of extended defects in F-enriched samples and the evolution of B profiles during annealing. For short anneals, B diffusion is reduced when F+ is co-implanted with Si+ compared to the sample only implanted with Si+, due to the formation of more stable defects that set a lower Si interstitial supersaturation. For longer anneals, when defects have dissolved and TED is complete, B diffusion is higher because the additional damage created by the F+ implant has contributed to enhance B diffusion.

Physical insight into ultra-shallow junction formation through atomistic modeling

We use atomistic simulations to gain physical understanding of relevant dopant–defect interactions involved in junction formation. The analysis of the energetics of B–Si interstitial clusters (BICs) indicates that a high Si interstitial supersaturation is necessary to nucleate BICs in crystalline Si, but only a Si interstitial supersaturation slightly larger than that set by BICs is enough to cause the stabilization and growth of preexisting BICs. We have analyzed the mechanisms associated to B uphill diffusion and deactivation in preamorphized Si upon subsequent annealing. Both phenomena occur simultaneously and they are the result of the trapping of B atoms by preexisting B clusters in the high concentration region.

In-situ TEM observation of transformation of dislocations from shuffle to glide sets in Si under supersaturation of interstitials

Dislocations of the shuffle set were introduced into an Si single crystal by indentation at room temperature. Foil specimens for transmission electron microscope (TEM) observation were fabricated using a focused ion beam (FIB) apparatus. The foil specimens were heated in the temperature range between room temperature and 800°C in the TEM. The shuffle set of dislocations were transformed into a glide set of dislocations at around 400°C. At higher temperatures, screw dislocations in the glide set were transformed into helices. Contrast experiment and stereomicroscopy revealed that the screw dislocation interacted with interstitials. These interstitials must have been introduced during either FIB fabrication of the TEM specimens or during TEM observation at lower temperatures.

Atomistic modeling of dopant implantation, diffusion, and activation

Atomistic kinetic Monte Carlo simulations have been performed to illustrate the correlation between the Si interstitial defects generated by ion implantation, and B diffusion and activation in Si. The amount of residual damage is not very affected by moderate dynamic anneal during subamorphizing implants. However, dynamic anneal even at room temperature significantly influences the residual damage in amorphizing implants. The efficiency of the surface as a sink for point defects affects the evolution of Si interstitial defects. They set the Si interstitial supersaturation that is responsible for transient enhanced diffusion of B and also control the formation and dissolution of B–Si interstitial clusters.

Physical insight into boron activation and redistribution during annealing after low-temperature solid phase epitaxial regrowth

Kinetic Monte Carlo simulations of B diffusion and activation in preamorphized Si during annealing after solid phase epitaxial regrowth have been used to provide insight into the mechanisms that drive these phenomena. Simulations show that the presence of an initially high active B concentration along with a Si interstitial supersaturation set by end of range defects leads to simultaneous B deactivation and uphill diffusion through the capture of mobile interstitial B in the high concentration region during subsequent anneal treatments. Once the Si interstitial supersaturation decays close to equilibrium values, B clusters dissolve and emitted B diffuses downhill, following the B concentration gradient. The active B concentration at the minimum state of activation becomes higher as the annealing temperature increases as a consequence of a faster increase of the B cluster dissolution rate compared with the formation rate.

Injection of point defects during annealing of low energy As implanted silicon

In this work, we investigate the interstitial injection into the silicon lattice due to high-dose, low energy arsenic implantation. The diffusion of the implanted arsenic as well as of boron, existing in buried δ-layers below the silicon surface, is monitored while successive amounts of the arsenic profile are removed by low temperature wet silicon etching. From the analysis of the diffusion profiles of both dopants, consistent values for the interstitial supersaturation ratio can be obtained. Moreover, the experimental results indicate that the contribution of the implantation damage to the TED of boron, and thus the interstitial injection, is not the main one. On the contrary, interstitial generation due to arsenic clustering seems to be more important for the present conditions.

The agglomeration dynamics of self-interstitials in growing Czochralski silicon crystals

Silicon single crystals grown by the Czochralski process can contain various defects known as microdefects, formed by the agglomeration of vacancies and self-interstitials (or interstitials). The dynamics of the formation of interstitial-type microdefects is studied. Interstitials form globular clusters called B defects, which, upon sufficient growth, transform into the large dislocation loops known as A defects. A growing crystal exhibits a nucleation and growth zone, in which, at any given time, interstitials agglomerate to form B defects, B defects grow and transform into A defects, and A defects grow in size. The growth of the formed microdefects decreases the interstitial supersaturation and suppresses the formation of new microdefects. By suddenly decreasing the temperature of the active nucleation and growth zone, the linear sizes of the relatively larger agglomerated A defects can be frozen, and smaller B and A defects in higher densities can be formed, facilitated by a rapid increase in the interstitial supersaturation. The co-existence of both B and A defects was experimentally verified, and the width of the nucleation and growth zone was characterized. The quantification of the rapid-cooled nucleation and growth zone provides insights into the formation and the growth of the interstitial microdefects in particular and defect dynamics in general.

Oxidation-enhanced diffusion of boron in very low-energy N2+-implanted silicon

In this article we study the interstitial injection during oxidation of very low-energy nitrogen-implanted silicon. Buried boron δ layers are used to monitor the interstitial supersaturation during the oxidation of nitrogen-implanted silicon. No difference in boron diffusivity enhancement was observed compared to dry oxidation of nonimplanted samples. This result is different from our experience from N2O oxynitridation study, during which a boron diffusivity enhancement of the order of 20% was observed, revealing the influence of interfacial nitrogen on interstitial kinetics. A possible explanation may be that implanted nitrogen acts as an excess interstitial sink in order to diffuse towards the surface via a non-Fickian mechanism. This work completes a wide study of oxidation of very low-energy nitrogen-implanted silicon related phenomena we performed within the last two years [D. Skarlatos, C. Tsamis, and D. Tsoukalas, J. Appl. Phys. 93, 1832 (2003); D. Skarlatos, E. Kapetanakis, P. Normand, C. Tsamis, M. Perego, S. Ferrari, M. Fanciulli, and D. Tsoukalas, J. Appl. Phys. 96, 300 (2004)].