Dislocation Loops In Silicon Research Articles

On continuum simulations of the evolution of faulted and perfect dislocation loops in silicon during post-implantation annealing

Predictive models of the damage evolution during post-implantation annealing are important for predicting the performance of final devices. An existing model of the thermal evolution of dislocation loops in silicon during post-implantation annealing has been recalibrated to better capture the distinction between faulted and perfect dislocation loops. The calibration was based on experimental findings from the literature on the simultaneous presence of both faulted and perfect dislocation loops after post-implantation annealing.Graphical abstract

Three-dimensional X-ray diffraction imaging of process-induced dislocation loops in silicon

In the semiconductor industry, wafer handling introduces micro-cracks at the wafer edge and the causal relationship of these cracks to wafer breakage is a difficult task. By way of understanding the wafer breakage process, a series of nano-indents were introduced both into 20 × 20 mm (100) wafer pieces and into whole wafers as a means of introducing controlled strain. Visualization of the three-dimensional structure of crystal defects has been demonstrated. The silicon samples were then treated by various thermal anneal processes to initiate the formation of dislocation loops around the indents. This article reports the three-dimensional X-ray diffraction imaging and visualization of the structure of these dislocations. A series of X-ray section topographs of both the indents and the dislocation loops were taken at the ANKA Synchrotron, Karlsruhe, Germany. The topographs were recorded on a CCD system combined with a high-resolution scintillator crystal and were measured by repeated cycles of exposure and sample translation along a direction perpendicular to the beam. The resulting images were then rendered into three dimensions utilizing open-source three-dimensional medical tomography algorithms that show the dislocation loops formed. Furthermore this technique allows for the production of a video (avi) file showing the rotation of the rendered topographs around any defined axis. The software also has the capability of splitting the image along a segmentation line and viewing the internal structure of the strain fields.

Atomistic study of the effect of crack tip ledges on the nucleation of dislocations in silicon single crystals at elevated temperature

We model a single crystal of silicon approaching dimensions of 20 nm × 20 nm × 10 nm with up to 200,000 atoms based on the ReaxFF first principles based reactive force field, applied here to examine the influence of crack tip heterogeneities on the nucleation of dislocations from crack tips as the temperature is increased well beyond 1000 K. Our study aims at generating insight into mechanisms of the brittle-to-ductile transition (BDT) observed in silicon, which is known to change the behavior of silicon crystals from predominantly brittle at low temperatures to ductile at higher temperatures, likely involving a competition between brittle bond-breaking and emission of dislocations. We first examine the crystallographic orientations most widely known to exhibit fracture, for example failure on the {1 1 1} and {1 1 0} planes. We find that even at very high temperatures considered here (around 1500 K), the material behaved in a completely brittle manner for systems with cracks oriented in the {1 1 1} and {1 1 0} planes. In contrast, when the crack plane is changed to the {1 0 0} orientation, the formation of complete dislocation loops is observed. The results reported in our paper is the first direct observation of dislocation loops in silicon driven by an increase in the temperature, and extends earlier studies that were focused solely on extremely thin quasi-two-dimensional models. We demonstrate here that the formation of these loops can be linked to the geometrical ledges at the crack tip with favorable orientations for slip on the {1 1 1} planes. The detailed mechanisms leading to the nucleation of dislocations involve changes at the crack tip with bond rotations and formation of ledges, and we find that the emergence of dislocations causes the crack to arrest, but re-initiation takes place and no conclusive nucleation of dislocations and complete arrest of the crack is observed. The thickness effect is discussed together with other sources for formation of ledges along the crack front. Our findings provide important insight towards the development of models for the brittle–ductile-transition in silicon and potentially other materials, and emphasize on the significance of thickness effects in simulations of fracture in crystal slabs.

Arsenic Segregation to Dislocation Loops in Silicon

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Formation of dislocation loops in silicon by ion irradiation for silicon light emitting diodes

We have studied the influence of the ion species, ion energy, fluence, irradiation temperature and post-implantation annealing on the formation of shallow dislocation loops in silicon, for fabrication of silicon light emitting diodes. The substrates used were (100) Si, implanted with 20–80keV boron at room temperature and 75–175keV silicon at 100 and 200°C. The implanted fluences were from 5×1014 to 1×1015 ions/cm2. After irradiation the samples were processed for 15s to 20min at 950°C by rapid thermal annealing. Structural analysis of the samples was done by transmission electron microscopy and Rutherford backscattering spectrometry. In all irradiations the silicon substrates were not amorphized, and that resulted in the formation of extrinsic perfect and faulted dislocation loops with Burgers vectors a/2〈110〉 and a/3〈111〉, respectively, sitting in {111} habit planes. It was demonstrated that by varying the ion implantation parameters and post-irradiation annealing, it is possible to form various shapes, concentration and distribution of dislocation loops in silicon.

Very shallow boron junctions in Si by implantation and SOD diffusion obtained by RTP

Because of their very large integration capabilities and continuous scaling, the CMOS devices are the basic element in the current-integrated circuits. Their scaling up to sub-micrometric scale presents advantages like diminution of power consumption, faster devices and a larger level of integration. But the physics limitations begin to be important at these dimensions, anomalous effects like hot electrons, leakage currents and punch through, among others, appear. These effects can be reduced if, at the source/drain region, shallow junctions are obtained with junction depth (xj) less than 200nm. To achieve this goal, new junction fabrication methods, which include pre-amorphization [S.D. Kim, C.M. Park, J.C.S. Woo, Formation and control of box-shaped ultra-shallow junction using laser annealing and pre-amorphization implantation, Solid State Electron. 49 (2005) 131–135] are required. Other alternative techniques that do not require ion implantation [T. Uchino, P. Ashburn, Y. Kiyota, T. Shiba, A CMOS-compatible rapid vapor-phase doping process for CMOS scaling, IEEE Trans. Electron Devices 51(1) (2004) 14–19.], in order to prevent surface crystal damage and as a consequence the inhibition of boron interstitial clusters and {311} defects [R.T. Crosby, K.S. Jones, M.E. Law, L. Radic, Dislocation loops in silicon–germanium alloys: the source of interstitials, Appl. Phys. Lett. 87 (192111) (2005) 1–3.], which are the trigger of the “transient enhanced diffusion” (TED) process are used. In this essay, it is shown that rapid thermal process, allow the fabrication of very shallow junctions with a xj less than 300nm by using with high energies and high doses of boron/BF2 ions implantation. By this way the slow dissolution of the dislocation loops, present at the end of range (EOR) of the implanted boron, allow this process. These obtained junctions are compared with those prepared by using the spin on doping (SOD) technique. The diffusion profiles obtained by both processes and their electrical properties are measured and compared for their application as S–D regions in a current CMOS process.

Efficient TCAD Model for the Evolution of Interstitial Clusters, {311} Defects, and Dislocation Loops in Silicon

AbstractThe simulation of deep-submicron silicon-device manufacturing processes relies on predictive models for extended defect clusters. For submicroscopic interstitial clusters and {311} defects, an efficient and highly accurate model for process simulation has been developed and calibrated recently [1]. This model combines equations for three small interstitial clusters and two moments for {311} defects. In this work, we extend this model to include dislocation loops and to reproduce a greatly increased range of experimental data, including thermal annealing of end-of-range defects after amorphizing implants.

Generation of dislocation loops in silicon near local heat sources

The thermal conditions created in an aluminum metallization layer on a silicon wafer by a rectangular current pulse are analyzed at pulse heights of up to 6 × 1010 A/m2 and pulse durations from 50 to 103 μs. The thermoelastic stress developing in silicon substrates as a result of unsteady-state heating of the metallization layer is calculated. The theoretically predicted formation of linear defects near thermal shock sources in silicon is confirmed by experimental data.

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

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.

The Influence of the Initial Supersaturation of Si Interstitial Atoms on the Relative Thermal Stability of Dislocation Loops in Silicon

AbstractIn this work, we have studied the relative stability of perfect (PDLs) and faulted (FDLs) dislocation loops formed during annealing of preamorphised silicon. In particular, we have investigated the effect of the initial supersaturation of Si interstitial atoms (Si(int)s) created by the implantation process on their thermal evolution. Transmission Electron Microscopy analysis shows that in samples with a low Si interstitial supersaturation, FDLs are the dominant defects while PDLs appear as the most stable defects in highly supersaturated samples. We have calculated the formation energies of both types of dislocation loops and found that, for defects of the same size, FDLs are more energetically stable than PDLs, if their diameter is smaller than 80 nm and viceversa. The application of these calculations to the samples studied in this work indicates that a direct correspondence exists between the formation energy of the two defect families and the number of atoms bound to them. Moreover, we have shown that the relative stability of FDLs and PDLs depends on the initial supersaturation of Si(int)s created during the implantation process.

Effect of surface proximity on end-of-range loop dissolution in silicon

The effect of surface proximity on the dissolution of end-of-range dislocation loops in silicon was investigated by transmission electron microscopy (TEM). A layer of dislocation loops was formed at a depth of 2600 Å by annealing a Si wafer amorphized by a 1015 cm−2, 120 keV, and a 1015 cm−2, 30 keV dual Si+ implant for 30 min at 850 °C. The wafer was diced into 1 cm×1 cm pieces and polished by a chemical–mechanical polishing technique to decrease the loop depth to 1800 and 1000 Å. The samples were then furnace annealed at 900 and 1000 °C in N2 gas. Quantitative TEM analysis revealed that the density of small loops decreases as the loop band is brought closer to the surface. The flux of interstitials to the surface varied inversely with loop depth, indicating that the loop dissolution is diffusion limited. Assuming that the loops maintain a supersaturation of interstitials (CIL) around them, and by integrating the measured interstitial flux from the loop layer to the surface, the relative supersaturation of interstitials near the loop layer (CIL/CI*) was extracted 900 and 1000 °C.

Simulation of metallic impurity gettering in silicon by MeV ion implantation

A simple model for metallic impurity gettering by buried layers created by MeV ion implantation in silicon is presented. For our experimental conditions, the precipitation of supersaturated Fe at dislocation loops in silicon is not diffusion limited. Furthermore, a non-zero silicide-matrix interfacial energy density was required to fit our experimental data. In samples containing dislocations and boron-implanted layers, the dislocations trap more Fe than the boron, but the latter is more effective at reducing the concentration of ungettered Fe. Although we were able to simulate impurity distributions fairly well in many cases, the model is not free from adjustable parameters due to a lack of knowledge of detailed impurity–defect interactions and the silicide-matrix interfacial energy density.

Relative Stability of Perfect and Faulted Dislocation Loops in Silicon

ABSTRACTWe have studied by TEM the thermal evolution of a population of extrinsic defects composed of a mixture of both perfect and faulted dislocation loops (PDL's and FDL's respectively). It is shown that, when isolated from an external sink, the FDL's trap the Si interstitial atoms emitted by PDL's. When a highly recombining surface is located close to the defects, it preferably « pumps » the PDL's. On the contrary, injecting Si(int)'s from the surface helps stabilizing the PDL's while the FDL's grow. These experiments clearly show that FDL's are more stable, i.e. have higher binding energies than PDL's.

Nonconservative Ostwald ripening of dislocation loops in silicon

We have investigated the effects of the proximity of the surface on the ripening behavior of dislocation loops in preamorphized silicon. Starting from well-defined initial conditions, we have varied the location depth of the loops by successive chemical removal of surface layers and measured changes of the size–distribution function during subsequent annealing by means of transmission electron microscopy. Our results show that the amount of Si atoms bound in the loops is not conserved during annealing and that the loop location depth has a prominent effect on the ripening kinetics. Both these observations prove the nonconservative nature of Ostwald ripening of dislocation loops near wafer surfaces. In addition, we observed different ripening kinetics for annealing in vacuum and in Ar which show that different boundary conditions at the surface are established during annealing in these two ambients.

Capture of vacancies by extrinsic dislocation loops in silicon

The capture of a flux of vacancies in Si by a band of extrinsic dislocation loops has been observed in Sb doping superlattices. Annealing Sb doping superlattices containing a band of dislocation loops in NH3 results in an injection of vacancies, which enhances the diffusion of Sb spikes located between the surface and loop band. By extracting the diffusivity in the Sb spikes on either side of the loop band, we conclude that over 90% of the injected vacancies are captured by the loops.

Transmission electron microscopy on {113} rodlike defects and {111} dislocation loops in silicon-implanted silicon

Plan-view and cross-sectional transmission electron microscopy have been used to study the microstructural evolution of {113} rodlike defects as well as their correlation with the formation of {111} dislocation loops in silicon implanted with 50 keV 3.6×1014 Si+/cm2 8.0 mA and rapid thermally annealed at temperatures ranging from 500 °C to 1100 °C for various times. It was determined that the size distribution of {113} defects is a log-normal Gaussian probability function. The nucleation, growth and dissolution of both {113} defects and {111} dislocation loops were observed. The nuclei of {113} defects form first and are circular interstitial clusters. The nucleation is homogeneous in the matrix at the crystalline side of the amorphous/crystalline interface and occurs at a temperature as low as 600 °C for 1 s. These circular nuclei grow into rods along the 〈110〉 direction in a {113} habit plane. It was found that the growth of {113} defects inclined to wafer surface is more preferable than that parallel to the surface. Similarly their dissolution is also faster. The dissolution strongly depends on annealing temperature. Most of them can last for more than 240 s at 800 °C but only 15 s at 900 °C. It was found that the formation of {111} faulted Frank dislocation loops is an independent event of nucleation and growth. This nucleation of {111} Frank dislocation loops does not occur until the {113} defects begin to grow along a 〈110〉 direction and/or dissolve into the matrix. This means that there is a period when {113} defects release interstitial point defects before the {111} dislocation loops nucleate from the matrix. The growth of {111} dislocation loops, together with {113} defects, is a nonconservative Ostwald ripening process. The {113} defects were found to disappear completely at 900 °C for 120 s, but the {111} dislocation loops disappear at 1100 °C for 60 s.

Nucleation barrier of voids and dislocation loops in silicon

We have calculated the nucleation energy barrier of voids and vacancy (V) type dislocation loops in Si under V-supersaturation conditions. The barrier of V-type dislocation loops is higher than that of voids by more than one order of magnitude, with the former exceeding 35 eV at attainable V-supersaturation levels. Thus, voids can be nucleated, but not dislocation loops. This provides an explanation for the observations that, in Si crystals grown under V-supersaturation conditions, voids exist but V-type dislocation loops do not. Voids seriously degrade the Si device gate oxide integrity. It is highly probable that the D-type swirl defects in Si are nanoscopic voids. Our calculated results have also provided information for limiting the formation temperature range of the D-swirl defects to be lower than ∼1050 °C, and the Si V formation enthalpy to be above ∼3.0 eV.

Size-distribution and annealing behavior of end-of-range dislocation loops in silicon-implanted silicon

A study of end-of-range (EOR) dislocation loops in silicon implanted with 50 keV 1016 Si/cm2 was carried out by using transmission electron microscopy. Two kinds of post-implantation anneals were performed, furnace anneals at 850 °C and rapid thermal anneals at 1000 °C. We observed the ripening for two types of EOR dislocation loops. They were faulted Frank dislocation loops and perfect prismatic dislocation loops. By separating their size distribution profiles, we found that their distribution profiles are different from that of conventional Ostwald ripening for precipitates. A long tail distribution profile was formed for perfect prismatic dislocation loops. We analyzed the distribution profiles and found that the size distribution profile of faulted Frank dislocation loops could be well fitted by a normal Gaussian probability function and that of perfect prismatic dislocation loops by a log-normal Gaussian probability function. Measurement of the total number of interstitials within both types of loops shows that the ripening of EOR dislocation loops is conservative. Knowing the size-distribution profiles of the EOR dislocation loops, it was possible to perform an analysis of the ripening behavior of the two types of dislocation loops.

Nucleation and Growth of {113} Defects and {111} Dislocation Loops Insilicon-Implanted Selicon

ABSTRACTPlan-view and cross-sectional transmission electron microscopy have been used to study the microstructural characterization of the nucleation and growth behavior of {113} rodlike defects, as well as their correlation with {111} dislocation loops in silicon amorphized with 50 keV, 36×1014 Si/cm2, 8.0 mAand annealed by rapid thermal anneals at temperatures from 500 °C to 1100 °C for various times. We found that the nucleations of the {113} rodlike defects and {111} dislocation loops are two separate processes. At the beginning of anneals, excess interstitials accumulate and form circular interstitial clusters at the preamorphous/crystalline interface at as low as 600 °C for 1 s. Then these interstitial clusters grow along the <110> direction to form {113} rodlike defects. Later, while the {113} defects have begun to grow and/or dissolve into matrix, the {111} faulted Frank dislocation loops start to form. We also found that the initial interstitial clusters prefer to grow along the <110>directions inclined to the implantation surface.

Size distribution of end-of-range dislocation loops in silicon-implanted silicon

The size and distribution of end-of-range dislocation loops in silicon implanted with 50 keV 1016 Si/cm2 and annealed at 750 °C for various times have been studied by transmission electron microscropy. The normalized distribution profile of the dislocation loops has been found to be invariant with time, based on density and size measurement. The profile is quite different from the conventional distribution profile of Oswald ripening in grain growth and precipitate coarsening. Measurement of the total number of interstitials bound in the extrinsic loops shows that the ripening is a conservative process. An explanation for the particular distribution profile is attributed to the stress field associated with the dislocation loops.