Injection Of Self-interstitials Research Articles

Theory of Carbon-Vacancy Diffusion at the SiO<sub>2</sub>/4H-SiC Interface

Experimental data indicate that carbon vacancies incorporated in active regions of SiC devices are important electrical defects, responsible for device limiting effects such as carrier lifetime reduction. For field-effect transistors that include a 4H-SiC/SiO2 interface, such as at the gate, the oxidation pro- cess is understood to introduce native defects to the SiC, including injection of carbon self-interstitials and vacancies, that diffuse into the active layer and interact with other defects and impurities. It is therefore important to understand the migration behaviour of primary native defects such as VC in the vicinity of 4H-SiC/SiO2 interfaces. We report here the results of a density-functional theory investi- gation into the diffusion of the carbon vacancy in such a region. We conclude that the migration of VC is significantly hindered in the immediate vicinity of the interface, with the energy of diffusion barrier being approximately 15% greater than the corresponding diffusion in bulk 4H-SiC.

(Invited) Strain Assisted Band Gap Engineering of SiGe Core–Shell Nanowires using Low-Temperature Condensation Process

Selective oxidation of the silicon element of silicon germanium (SiGe) alloys during thermal oxidation is a very important and technologically relevant mechanism used to fabricate a variety of microelectronic devices. We show a two-step epitaxy/condensation process at low temperature to produce atomically flat Ge rich layer fully strained and free of defects. We demonstrate that the condensation based process enables the total inhibition of the classical ATG morphological instability, together with the hindering of dislocations for critical thickness much greater than those commonly obtained by direct deposition. Those behaviors could be explained by the injection of self-interstitials in the Ge-rich layers during condensation. An integrative approach involving vapor–liquid–solid (VLS) growth followed by selective oxidation steps to the construction of core–shell nanowires and higher-level ordered systems with scalable configurations is used. We contrast this strategy that uses reaction-diffusion-segregation mechanisms to produce coherently strained structures with highly configurable geometry and abrupt interfaces with growth-based processes which lead to low strained systems with non uniform composition, three-dimensional morphology, and broad core–shell interface. We specially focus on SiGe small core–shell nanowires and demonstrate that they can have up to 70% Ge-rich shell and 2% homogeneous strain with core diameter as small as 14 nm. Key elements of the building process associated with this approach are identified with regard to existing theoretical models. Moreover, starting from results of ab initio calculations, we discuss the electronic structure of these novel nanostructures as well as their wide potential for advanced device applications. Similar core-shell structures can be formed around small nanocrystals for photonic applications.

Quantification of germanium-induced suppression of interstitial injection during oxidation of silicon

The oxidation of silicon is known to inject interstitials, and the presence of silicon–germanium (SiGe) alloys at the Si/SiO2 interface during oxidation is known to suppress the injection of silicon self-interstitials. This study uses a layer of implantation-induced dislocation loops to measure interstitial injection as a function of SiGe layer thickness. The loops were introduced by a 50 keV 2 × 1014 cm−2 P+ room-temperature implantation and thermal annealing. Germanium was subsequently introduced via a second implant at 3 keV Ge+ over a range of doses between 1.7 × 1014 cm−2 and 1.4 × 1015 cm−2. Results show that upon oxidizing at 850 °C for 3 h or 900 °C for 70 min to condense the germanium at the Si/SiO2 interface, where if forms a Si0.5Ge0.5 alloy. Upon subsequent oxidations of 850 °C for 6 h or 900 °C for 2 h, partial suppression of interstitial injection can be observed for sub-monolayer doses of germanium, and more than three monolayers of Si0.5Ge0.5 (1.4 × 1015 cm−2) are necessary to suppress interstitial injection below the detection limit during oxidation. These results show that low-energy implantation of germanium can be used to eliminate or modulate injection of oxidation-induced interstitials.

Elimination and Quantification of Oxidation Induced Interstitial Injection via Ge Implants

The presence of Silicon-Germanium (SiGe) alloys at the Si/SiO2 interface during oxidation is known to suppress the injection of silicon self-interstitials that normally accompanies silicon oxidation and lead to observed effects such as Oxidation Enhanced Diffusion (OED) and stacking fault growth. This study uses a layer of implantation induced dislocation loops to measure interstitial injection as a function of SiGe layer thickness. The loops were introduced by implanting phosphorus and thermal annealing, and Germanium was subsequently introduced via a second implant at 3 keV over a range of doses between 1.7 x1014 cm-2 and 1.4 x1015 cm-2. Results show that partial suppression of interstitial injection can be observed for sub-monolayer doses of germanium, and that more than three monolayers of SiGe are necessary to fully suppress interstitial injection below our detection limit during oxidation. They further show that low energy implantation of germanium opens up possibilities to eliminate or modulate injection of interstitials during thermal processing of future devices.

Elimination and Quantification of Oxidation Induced Interstitial Injection via Ge Implants

The presence of Silicon-Germanium (SiGe) alloys at the Si/SiO2 interface during an oxidation is known to suppress the injection of silicon self interstitials that normally accompanies silicon oxidation and leads to observed effects such as Oxidation Enhanced Diffusion (OED) and stacking fault growth. To measure interstitial injection, a layer of implantation induced dislocation loops was introduced and the interstitial fluxes measured via quantitative plan-view TEM. Germanium was introduced via a second implant at 3keV over a range of doses between 1.7 x1014 cm-2 and 1.4 x1015 cm-2. We show that partial suppression can be observed for sub-monolayer quantities of germanium, and that more than three monolayers of SiGe are necessary to suppress interstitial injection below the detection limit during oxidation. This study shows that low energy implantation of germanium can be used to eliminate or modulate injection of interstitials. Additional results suggest the mechanism is related to stopping interstitial formation, not migration. Figure 1

Remarkable Strength Characteristics of Defect-Free SiGe/Si Heterostructures Obtained by Ge Condensation

We compare the morphological and structural features of SiGe membranes fabricated by three different processes: direct deposition of Si0.5Ge0.5 on Si(001) nominal substrate, direct deposition of Si0.5Ge0.5 on silicon on insulator, and deposition of SiGe with low Ge concentration on silicon on insulator followed by Ge enrichment by condensation. We show that the formation of fully strained Ge-rich layers free of defects with a flat surface is possible only by the two-step epitaxy–condensation process. We demonstrate that the condensation-based process enables the total inhibition of the morphological instability, together with the hindering of dislocations for critical thickness much greater than those commonly obtained by direct deposition. Those behaviors could be explained by the injection of self-interstitials in the Ge-rich layers during condensation. Such remarkable properties could be generalized to many other systems using a similar condensation process.

Observation of point defect injection from electrical deactivation of arsenic ultra‐shallow distributions formed by ultra‐low energy ion implantation and laser sub‐melt annealing

AbstractThe stability and the evolution of electrical properties of high concentration arsenic ultra‐shallow junctions in silicon have been studied with regard to their effect on the evolution of point defects. The activation of 2 keV 1 × 1015 cm‐2 As implants was performed using millisecond sub‐melt laser annealing at two different temperatures, 1100 and 1300 °C. The electrical deactivation upon subsequent thermal treatment at 700 °C was indirectly monitored through the diffusion of five 10 nm‐wide boron layers aimed to detect the injection of self‐interstitials coming from dopant clustering. Thermal treatments were repeated on samples implanted with Ge at condition similar to the As ones. The comparison helped to discriminate between interstitials coming from lattice damage evolution and dopant clustering. The results show the relevance of the laser annealing temperature in order to ensure junction stability in terms of active carrier concentration and junction depth. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Self-interstitials injection in crystalline Ge induced by GeO2nanoclusters

The effect of O implantation in crystalline Ge on the density of native point defects has been investigated through transmission electron microscopy and B diffusion experiments. Annealing at 650 \ifmmode^\circ\else\textdegree\fi{}C following O implants produces a band of defects (\ensuremath{\sim}5--10 nm), compatible with GeO${}_{2}$ nanoclusters (NCs). A clear shape transformation from elongated to spherical forms occurs within 2 h, concomitant with a transient enhanced diffusion of B. A large injection of self-interstitials from GeO${}_{2}$ NCs, giving a vacancy undersaturation, and a long-range migration of self-interstitials are evidenced and discussed.

Room temperature migration of boron in crystalline silicon during secondary ion mass spectrometry profiling

Recently we have demonstrated that substitutional boron in crystalline silicon can migrate for long distances even at room temperature (RT) and below during secondary ion mass spectrometry (SIMS) profiling. The phenomenon is suppressed after amorphization or by cooling the sample. The above data force to reconsider the observations obtained in the last decades by SIMS in light of possible long-range migration artifacts. Here we show that the use of oxygen flooding (OF) during the analysis enhances the injection of self-interstitials (I) responsible for the migration of B, producing profiles that are more broadened and less accurate than in ultrahigh vacuum. On the other hand, by properly controlling OF, we have obtained new insights on the mechanisms of B diffusion and interaction with intrinsic traps at RT. Moreover, by cooling the sample the migration of B is suppressed even while using OF, allowing measurements of boron deltas in c-Si of unprecedented level of accuracy and sensitivity. Finally, we have clarified the role of the migration phenomena on the profiling of ultra low energy B implants for ultra shallow junctions.

Fractal Self-Assembled Nanostructures on Monocrystalline Silicon Surface

We present ultra-shallow diffusion profiles performed by short-time diffusion of boron from the gas phase using controlled surface injection of self-interstitials and vacancies into the ntype Si(100) wafers. The diffusion profiles of this kind are found to consist of both longitudinal and lateral silicon quantum wells of the p-type that are self-assembled between the layers of microdefects, which are produced by previous oxidation. These layers appear to be passivated during short-time diffusion of boron thereby forming neutral d - barriers. The fractal type selfassembly of microdefects is found to be created by varying the thickness of the oxide overlayer, which represents the system of microcavities embedded in the quantum well plane.

Diffusion of phosphorus in relaxed Si1−xGex films and strained Si/Si1−xGex heterostructures

Phosphorus diffusion has been studied in relaxed Si1−xGex samples (x=0.11 and 0.19) and strained Si/Si1−xGex/Si heterostructures (x=0.08, 0.13, and 0.18). The diffusivity of P is found to increase with increasing Ge content, while the influence of compressive strain results in a decrease in diffusivity as compared to that in relaxed material. The effect of strain is found to be equivalent to an apparent activation energy of −13 eV per unit strain, where the negative sign indicates that the P diffusion is mediated by interstitials in Si1−xGex (x<0.20). This conclusion is also supported by an experiment utilizing injection of Si self-interstitials, which results in an enhanced P diffusion in strained Si1−xGex. Further, P is found to segregate into Si across Si/Si1−xGex interfaces and the segregation coefficient increases with increasing Ge concentration.

Self-Assembled Impurity Superlattices and Microcavities in Silicon

We present ultra-shallow (5-30 nm) diffusion profiles performed by short-time boron diffusion from the gas phase into the n-type Si(100) wafer using controlled surface injection of selfinterstitials and vacancies. The diffusion profiles of this art are found to consist of both self-assembled longitudinal and lateral quantum wells formed naturally between the δ barriers heavily doped with boron. The deformed potential fluctuations created by self-interstitials microdefects embedded into the p-diffusion profile are shown to cause the formation of self-assembled microcavities that are revealed by the light transmission spectra.

Self-interstitial migration during ion irradiation of boron delta-doped silicon

Boron delta layers in silicon, grown by molecular beam epitaxy and characterized by the secondary ion mass spectrometry, have been employed to investigate the migration of silicon self-interstitials during irradiation with MeV protons in the 500–850°C temperature range. After growth, the samples were thinned from the backside to a thickness that made them transparent for the proton energies used. As a result, the generation rate of point defects can be considered as essentially uniform throughout the samples. However, the evolution of the boron profiles is almost identical to that observed after injection of self-interstitials caused by thermal oxidation of the samples at elevated temperature. This strongly indicates that the surface acts as a reflective boundary for the migrating self-interstitials or/and an efficient sink for mobile vacancies. Furthermore, higher value of interstitial supersaturation in the near-surface region in proton-irradiated samples is consistent with experimentally detected depth dependence for immobile fraction in boron clusters. Then, activation energy of boron mobilization, (0.9±0.4) eV, was attributed to the dissociation of boron clusters.

Sb-precipitation-induced injection of Si self-interstitials in Si

The issue of point-defect injection during antimony precipitation in silicon is addressed in the present investigation. By studying the effect of Sb precipitation in an Sb-box distribution on the diffusion of B or Sb in deeper-lying spikes it is unambiguously concluded that Si self-interstitials are injected during the precipitation process. Possible causes of the self-interstitial injection are discussed.

Diffusion of Phosphorus in Strained Si/SiGe/Si Heterostructures

ABSTRACTPhosphorus diffusion in a biaxially compressed Si0.87Ge0.13 film has been investigated in the temperature range of 810–900°C. A significant enhancement of the P diffusion in the biaxially compressed Si0.87Ge0.13 in comparison with P diffusion in Si is observed. Injection of Si self-interstitials (I) during oxidation of a Si-cap in Si/Si0.87Ge0.13/Si heterostructures is used to characterize the atomic mechanism of P diffusion in Si0.87Ge0.13. It is found that the upper limit of the interstitial fraction of the P diffusion in Si0.87Ge0.13 is 0.87 of that in Si. A comparison between B and P diffusivities in SiGe supports the hypothesis of the pairing-controlled mechanism for the diffusion of B in SiGe.

Injection of self-interstitials during sputter depth profiling of Si at room temperature

Samples consisting of multi B delta layers and a single Sb delta layer, grown using molecular beam epitaxy, have been sputter depth profiled using O2+ ions with incidence energy of 8.2 or 3.2 keV. The leading and the trailing edge of the B distributions show an anomalous broadening induced by the sputtering, which apparently increases with ion energy. Similar feature is not observed for the Sb distribution. Incorporation of substitutional C to concentrations ∼1019 cm−3 suppresses the broadening feature almost completely. This anomalous broadening is interpreted as a consequence of injection of Si self-interstitials from the region damaged by the ion bombardment. These interstitials may migrate far beyond the mixing depth and interact with the B dopants, which yields a mixing of the B atoms before the distribution is within the “ordinary” mixing depth.

Infrared induced emission from silicon quantum wires

Studies of infrared induced emission from the silicon quantum wires, which is due to the formation of a correlation gap in the DOS of degenerate hole gas, are presented. The quantum wires of this art are created by electrostatic confining potential inside ultra-shallow p +n junctions which are realized using controlled surface injection of self-interstitials and vacancies in the process of non-equilibrium boron diffusion.

Infrared-induced emission from silicon quantum wires

We present the first findings of a study of infrared-induced emission from silicon quantum wires, which is due to the formation of a correlation gap in the DOS of the degenerate hole gas. The quantum wires in this case are created by an electrostatic confining potential inside ultra-shallow p–n junctions which are realized using controlled surface injection of self-interstitials and vacancies in the process of non-equilibrium boron diffusion.

Control of The Sb Redistribution in Strained SiGe Layers Using Point Defect Injection

AbstractSb diffusion in strained Si1−xGex (x = 0.1 and 0.2) layers during nitridation (in NH3, 810 °C) and oxidation (in dry O2, 825 and 900 °C) of Si/Si1−xGex/Si heterostructures is measured and, subsequently, compared with that obtained for treatments in vacuum. An enhancement (ν) or retardation (η) of Sb diffusion in strained Si1−xGex after nitridation/oxidation anneals is detected. For example, 810 (NH3) and 900 °C (O2) anneals results in ν ∼ 2 and η ∼ 0.15 in strained Si0.9Ge0.1, respectively. The retardation of Sb diffusion is attributed to the injection of excess self-interstitials (I) and strongly indicating low interstitialcy fraction of Sb diffusion in strained Si1−xGex. The enhancement of Sb diffusion may be due to direct injection of vacancies (V), but only if the V diffusivities are significantly different in Si and Si1−xGex, or depletion of I in the strained Si1−xGex layers caused by the excess V concentration at the top surface of silicon layer

Infrared Induced Emission From Silicon Quantum Wires

Abstract Studies of infrared induced emission from the silicon quantum wires, which is due to the formation of a correlation gap in the DOS of degenerate hole gas, are presented. The quantum wires of this art are created by electrostatic confining potential inside ultra-shallow p + n junctions which are realized using controlled surface injection of self-interstitials and vacancies in the process of non-equilibrium boron diffusion.