Agglomeration Of Self-interstitials Research Articles

Diffusion and activation of dopants in silicon and advanced silicon-based materials**Invited paper.

A quantitative description of the transient diffusion and activation of boron during post-implantation annealing steps is one of the most challenging tasks in the simulation of silicon doping processes. In industrially relevant situations, simulations needs to address diffusion at extrinsic concentrations, the agglomeration of self-interstitials, and the formation of boron-interstitial clusters. This paper describes the experimental work performed or used to calibrate model parameters as independently as possible. The combined model is then applied to ultra-shallow junction formation by annealing boron implanted into crystalline or preamorphized silicon. In comparison to bulk silicon, much less is known about diffusion of dopants in SiGe and germanium which are considered as technological options for future technology nodes. Therefore, dedicated experiments were performed to clarify open points in the diffusion behaviour of dopants in these materials.

Boron-Interstitial Cluster Kinetics: Extraction of Binding Energies from Dedicated Experiments

ABSTRACTA description of the transient diffusion and activation of boron during post-implantation an- nealing steps is one of the most challenging tasks. In industrially relevant situation, it needs to address diffusion at extrinsic concentrations, the agglomeration of self-interstitials, and the formation of boron-interstitial clusters. This article describes the experimental work performed or used to calibrate model parameters as independently as possible. In particular, the experiments used to extract information about the energetics of boron-interstitial clusters are described.

Difference of secondary defect formation by high energy B+ and Al+ implantation into 4H–SiC

The difference of secondary defect formation between high-energy B+ and Al+ implanted layers was investigated by transmission electron microscopy. At the same volume concentration of implanted ions, the density of secondary defects in the Al+ implanted layers is higher than that in the B+ implanted layers and the mean defect size in the B+ implanted layers is larger than that in the Al+ implanted layers. These secondary defects are formed by agglomeration of self-interstitials and the amount of interstitials stored in the defects roughly coincides with that of implanted ions. This correlation does not depend on the ion species. The activation energies of secondary defect formation are not significantly different for B+ and Al+ implanted layers. B+ and Al+ implanted layers have different agglomerations of interstitials, which cause the differences of defect size and density. The difference does not originate from the self-diffusion of interstitials in implanted layers but is probably due to the initial nucleation of defects.

Agglomeration of self-interstitials in Si observed at 450 degreesC by high-resolution transmission electron microscopy.

We have observed an early stage of agglomeration of self-interstitial atoms in a Czochralski-Si crystal by high-resolution transmission electron microscopy at 450 \ifmmode^\circ\else\textdegree\fi{}C. Based on analyses of the experimental data, it has been suggested that self-interstititals, introduced by electron (300 keV) irradiation, are first arranged along the 〈110〉 direction, forming a linear interstitial defect structure that has no dangling bond in the {110} cross section. After the nucleation, the defect is extended on the {113}-type plane.

HREM Investigations of the Agglomeration of Self-Interstitials in Silicon

The initial stages of the formation of rod-like defects (RLD) in FZ silicon (n-type as well as p-type Si) are investigated by high-resolution electron microscopy (HREM). These defect represent a special type of agglomeration of self-interstitials on {113} planes. As possible sites of their nucleation, interstitial-type clusters are generated by ion implantation (B+, Si+). For their further growth self-interstitials are created by electron irradiation (400 keV) at room temperature. The HREM investigations show that the early stages of RLDs and their further growth are influenced by point defect and impurity clusters existing in the Si bulk. Die Bildung der Anfangsstadien von sogenannten, rod-like' Defekten (RLD) in FZ Silizium (sowohl n- als auch p-dotiertes Material) wird mittels hochauflosender Elektronenmikroskopie (HREM) untersucht. Diese Defekte stellen eine spezielle Form der Agglomeration von eigen-interstitiellen Atomen auf {113} Ebenen dar. Mogliche Stellen fur eine bevorzugte Agglomeration sind Punktdefektcluster, die in den vorliegenden Kristallen durch Ionenimplantation (B+, Si+) erzeugt werden. Die fur das weitere Defektwachstum benotigten Eigen-Zwischengitteratome werden durch Elektronen-Bestrahlung (400 keV) generiert. Die HREM Untersuchungen zeigen, das die fruhen Stadien der RLD's und ihr weiteres Wachstum durch die im Si Kristall vorhandenen Punktdefektcluster beeinflust werden.

Annealing behavior of dislocation loops near the projected ion range in high-dose As +- and P +-implanted (001) Si

The annealing behavior of dislocation loops near the projected range ( R p loops) in (001) Si implanted by 150 keV As + and 65 keV P + to a dose of 5 × 10 15 cm −2 has been studied by both plane-view and cross-sectional transmission electron microscopy and Rutherford-backscattering spectrometry. The annealing behavior of R p loops in single- and two-step annealed samples and in sample with an oxide capping layer were found to be consistent with the suggestion that their formation is related to the agglomeration of self-interstitials mediated by the presence of a high concentration of electrically inactive arsenic or phosphorous atoms. However, the R p loops were found to be more prone to be annealed out in P +-implanted than in As +-implanted (001) Si.

Annealing behaviors of dislocation loops near the projected range in high-dose As+- implanted (001)Si

Annealing behaviors of dislocation loops formed near the projected range (Rp loops) in 150 keV, 5×1015/cm2 As+- implanted (001)Si have been studied by both planview and cross-sectional transmission electron microscopy and Rutherford backscattering spectrometry. Factors influencing the formation and growth of the Rp loops, such as annealing temperature and time, as well as single- and two-step annealings have been investigated. The Rp loops were observed in samples annealed at 550–900 °C for 0.5 h. The loops were also found in samples annealed at 800 °C for a time as short as 1 s and as long as 8 h. However, they were not seen in samples annealed at 470 °C for 4 h, 500 °C for 2 h, or 550 °C for 15 min. The annealing behaviors of Rp loops in single- and two-step annealed samples and in samples with an oxide capping layer were found to be consistent with the suggestion that their formation is related to the agglomeration of self-interstitials mediated by the presence of a high concentration of electrically inactive arsenic atoms.

U- and W-shaped diffusion profiles of gold in silicon

The diffusion of Au in dislocation-free Si was investigated at 1473K by means of neutron-activation analysis combined with mechanical sectioning. In most wafers the diffusion profiled were U-shaped, as known from previous studies of this kind performed at lower temperatures. In these wafers the Au concentration in the profile centres measured after 45 min diffusion anneals decrease inversely proportional to the wafer thicknesses in accordance with the so-called kick-out diffusion model. This model is confirmed further by the good agreement of the contribution by self-interstitials to the self-diffusion coefficient at 1473K calculated from the present Au-diffusion data with directly measured values of the Si self-diffusion coefficient. In some Au-diffused Si wafers W-shaped penetration profiles were found. From spreading-resistance, preferential-etching, and X-ray topography studies it is concluded that the Au-concentration peaks occurring in the interior of these specimens are located at faulted dislocation loops formed during the in-diffusion of Au. An electron-microscopy analysis showed that the stacking faults are of extrinsic nature. Presumably they were formed by agglomeration of self-interstitials produced in supersaturation via the kick-out diffusion mechanism.

The formation of swirl defects in silicon by agglomeration of self-interstitials

Through recent electron microscope investigations it is now well established that A-swirl defects in float-zone grown silicon crystals are dislocation loops of interstitial type which are formed by the agglomeration of silicon self-interstitials. In the first part the origin of the silicon self-interstitials is discussed: the “non-equilibrium interstitial model” invoked by Petroff and De Kock and the “equilibrium interstitial model” proposed by Föll et al. are contrasted. It is shown that only the “equilibrium interstitial model” is compatible to all the experimental facts of swirl defects known up to now. In the second part a general model for the formation of swirl defects is presented. The basic idea of this model is the assumption that A-swirl defects are generated by the collapse of B-swirl defects. B-swirl defects are assumed to be droplet-like agglomerates of silicon self-interstitials and some impurity atoms, particularly carbon, which govern the growth kinetics and stability of B-swirl defects. Thermodynamic considerations are presented, which in the case of A-swirl defects are relatively simple and straightforward, whereas those for the B-swirl defects are more sophisticated and include several speculative assumptions. This model is able to interpret all swirl data known so far, especially the dependence of the occurence of swirl defects on the growth rate and the dependence of the swirl properties on the carbon concentration.

Formation and nature of swirl defects in silicon

Point defect agglomerates in dislocation-free silicon crystals, usually called “swirls”, have been investigated by means of high-voltage electron microscopy. It was found that a single swirl defect consists of a dislocation loop or a cluster of dislocation loops. By contrast experiments it could be shown that these loops are formed by agglomeration of self-interstitial atoms. Generally the loops have a/2〈110〉 Burgers vectors, but in specimens with high concentrations of carbon (∼1017 cm−3) and oxygen (∼1016 cm−3) also dislocation loops including a stacking fault were observed. In crystals grown at growth rates higher thanv=4 mm/min no swirls are observed; lower growth rates do not markedly affect the size and shape of the dislocation loops. With decreasing impurity content (particulary of oxygen and carbon) the swirl density decreases, whereas the dislocation loop clusters become larger and more complex. A model is presented which describes the formation of swirls in terms of agglomeration of silicon self-interstitials and impurity atoms.