Boron-interstitial Clusters Research Articles

Modeling the suppression of boron transient enhanced diffusion in silicon by substitutional carbon incorporation

Recent work has indicated that the suppression of boron transient enhanced diffusion (TED) in carbon-rich Si is caused by nonequilibrium Si point defect concentrations, specifically the undersaturation of Si self-interstitials, that result from the coupled out-diffusion of carbon interstitials via the kick-out and Frank–Turnbull reactions. This study of boron TED reduction in Si1−x−yGexCy during 750 °C inert anneals has revealed that the use of an additional reaction that further reduces the Si self-interstitial concentration is necessary to describe accurately the time evolved diffusion behavior of boron. In this article, we present a comprehensive model which includes {311} defects, boron-interstitial clusters, a carbon kick-out reaction, a carbon Frank–Turnbull reaction, and a carbon interstitial-carbon substitutional (CiCs) pairing reaction that successfully simulates carbon suppression of boron TED at 750 °C for anneal times ranging from 10 s to 60 min.

Ab initio modeling study of boron diffusion in silicon

We present investigations of boron diffusion in crystalline silicon using ab initio calculations (W. Windl et al., Phys. Rev. Lett. 83 (1999) 4345). Based on these results, a new mechanism for B diffusion mediated by Si self-interstitials was proposed. Rather than kick-out of B into a mobile channel-interstitial, one- or two-step diffusion mechanisms have been found for the different charge states. The predicted activation energy of 3.5–3.8 eV, migration barrier of 0.4–0.7 eV, and diffusion-length exponent of −0.6 to −0.2 eV are in excellent agreement with experiment. We also present results of ab initio calculations for the structure and energetics of boron-interstitial clusters in Si. We show how these first-principles results can be used to create a physical B diffusion model within a continuum simulator which has strongly enhanced predictive power in comparison to traditional diffusion models.

First-Principles Modeling of Boron Clustering in Silicon

We present results of ab initio calculations for the structure and energetics of boron–interstitial clusters in Si and a respective continuum model for the nucleation, growth, and dissolution of such clusters. The structure of the clusters and their possible relationship to boron precipitates and interstitial-cluster formation are discussed. Our continuum model suggests that inclusion of the fractional activation of charged clusters into the overall carrier count can make a substantial difference, if a sample contains a large fraction of B clustered in B3I— clusters, which might present a way to probe these clusters experimentally.

A simple continuum model for boron clustering based on atomistic calculations

Boron exhibits anomalous diffusion during the initial phases of ion implant annealing. Boron transient enhanced diffusion is characterized by enhanced tail diffusion coupled with an electrically inactive immobile peak. The immobile peak is due to clustering of boron in the presence of excess interstitials which also enhance boron diffusion in the tail region. We present a simple model for the formation of immobile boron interstitial clusters and associated point defect interactions derived based on atomistic calculations.

A Comprehensive Model for Carbon Suppression of Boron Transient Enhanced Diffusion

ABSTRACTIn this work, the time evolution of B transient enhanced diffusion (TED) suppression due to the incorporation of 0.018% substitutional carbon in silicon was studied. The combination of having low C concentrations, which reduce B TED without completely eliminating it, and having diffused B profiles for several times at a single temperature provides much data upon which various models for the suppression of B TED can be tested. Recent work in the literature has indicated that the suppression of B TED in C-rich Si is caused by non-equilibrium Si point defect concentrations, specifically the undersaturation of Si self-interstitials, that result from the coupled out-diffusion of carbon interstitials via the kick-out and Frank-Turnbull reactions. Attempts to model our data with these two reactions revealed that the time evolved diffusion behavior of B was not accurately simulated and that an additional reaction that further reduces the Si self-inter- stitial concentration was necessary. In this work, we incorporate a carbon interstitial, carbon substitutional (CiCs) pairing mechanism into a comprehensive model that includes the C kick-out reaction, C Frank-Turnbull reaction, {311} defects, and boron interstitial clusters (BICs) and demonstrate that this model successfully simulates C suppression of B TED at 750 °C for anneal times ranging from 10 s to 60 min.

Boron-interstitial silicon clusters and their effects on transient enhanced diffusion of boron in silicon

The nature of ion-implantation induced clusters of boron and silicon-self interstitials (BICs), and their effects on transient enhanced diffusion (TED) of B in Si have been investigated in samples predoped with B at different concentrations. Excess Si interstitials have been introduced by Si+ implantation at 60 keV with doses of 1 and 5×1014 cm−2. The B diffusivity and the amount of B trapped in the clusters have been evaluated from the best fits of simulation-prediction profiles to experimental B profiles, after annealing at 740 and 800 °C for different times. Our results show that the BICs in the beginning act as a sink for interstitials, strongly reducing the TED in the early phases of the annealing. However, being more stable than the Si-interstitial clusters and the {113} defects, they dissolve slowly and can, therefore, sustain a moderate Si-interstitial supersaturation for longer annealing times, even when the Si-interstitial defects are completely dissolved. The data show that the amount of B in the BICs is higher than that of the interstitials; we estimate an average ratio between the B and interstitial concentrations to be about 1.5.

Ab initio modeling of boron clustering in silicon

We present results of ab initio calculations for the structure and energetics of boron-interstitial clusters in Si and a respective continuum model for the nucleation, growth, and dissolution of such clusters. The structure of the clusters and their possible relationship to boron precipitates and interstitial-cluster formation are discussed. We find that neither the local-density approximation nor the generalized-gradient approximation to the density-functional theory result in energetics that predict annealing and activation experiments perfectly well. However, gentle refitting of the numbers results in a model with good predictive qualities.

Role of self- and boron-interstitial clusters in transient enhanced diffusion in silicon

We investigate the nucleation and evolution of boron-interstitial clusters (BIC), driven by high interstitial supersaturations, S(t), during Si implant damage annealing. The BICs are “fabricated” in a narrow band by overlapping the Si implant damage tail with a lightly doped B buried layer. The BIC band is found to be a net sink for interstitials at supersaturations S(t)>104. Our results suggest that silicon self-interstitial defects are the primary source of interstitials driving transient enhanced diffusion, and that BICs act as a secondary “buffer” for the interstitial supersaturation.

A Comparative Study of Dose Loss and Diffusion for B11 and BF2 Implants

AbstractWe have studied dose loss for B11 and BF2 implants with energies ranging from 10 keV to 1keV for B11 and 45 keV to 2keV for BF2. We found that B11 implants during a 1050C-10s RTA anneal segregate mainly to the bulk of the oxide. High dose BF2 implants on the other hand, show significantly larger amounts of dose loss after stripping the oxide, due to a pile-up of boron at the Si/SiO2 interface. In order to simulate B11 diffusion we have introduced a simple average cluster size model to simulate Boron-Interstitial-Cluster (BIC) evolution. For BF2 implants, we have simulated the effect of F by reducing the damage and we have used interface traps to account for the dose loss observed experimentally. Using these models, we have been able to fit the SIMS profiles across the whole matrix of implant conditions for both B11 and BF2 implants.

Evolution of {311} type defects in boron-doped structures: Experimental evidence of boron–interstitial cluster formation

Boron-doped well structures formed in Czochralski silicon are subjected to a self-implant and various anneals to form a population of type {311} defects. Quantitative transmission electron microscopy is then used to measure the residual interstitials trapped in the {311} defects as a function of boron concentration and anneal temperature. We have found a strong tendency for increased dissolution rates of {311} type defects at boron concentrations above 1018 cm−3, providing direct evidence for the formation of boron–interstitial clusters. By profiling the samples with secondary ion mass steptroscopy and comparing the results to spreading resistance measurements the degree of deactivation can be determined.

Fundamental Modeling of Transient Enhanced Diffusion through Extended Defect Evolution

Prediction of transient enhanced diffusion (TED) requires modeling of extended defects of many types, such as {311} defects, dislocation loops, boron-interstitial clusters, arsenic precipitates, etc. These extended defects not only form individually, but they also interact with each other through changes in point defect and solute concentrations. We have developed a fundamental model which can account for the behavior of a broad range of extended defects, as well as their interactions with each other. We have successfully applied and parameterized our model to a range of systems and conditions, some of which are presented in this paper.