Transient Enhanced Diffusion Research Articles

Simulation of Transient Enhanced Diffusion in Silicon Taking into Account Ostwald Ripening of Defects

AbstractThe transient enhanced diffusion (TED) of high-dose implanted P is simulated taking into account Ostwald ripening of end-of-range (EOR) defects. First, we integrated a basic diffusion model based on the simulation of in-diffusion, where no implanted damages are involved. Second, from low-dose implantation, we developed a model for TED due to {311} self-interstitial (I) clusters involving Ostwald ripening and the dissolution of {311} clusters. Third, from medium-dose implantation, we showed that P-I clusters should be taken into account, and during the diffusion, the clusters are dissolved to emit self-interstitials that also contribute to TED. Finally, from high-dose implantation, EOR defects are modeled and we derived a formula to describe the time-dependence for Ostwald ripening of EOR defects, which is more significant at higher temperatures and longer annealing times. The simulation satisfactorily predicts the TED for annealing conditions, where the calculations overestimate the diffusion without taking Ostwald ripening into account.

Complete Suppression of the Transient Enhanced Diffusion of B Implanted in Preamorphized Si by Interstitial Trapping in a Spatially Separated C-Rich Layer

AbstractA method for completely suppressing the transient enhanced diffusion (TED) of boron implanted in preamorphized silicon is demonstrated. Boron is implanted in a molecular beam epitaxy (MBE) grown silicon sample that has been previously amorphized by silicon implantation. The sample is then annealed in order to epitaxially regrow the amorphous layer and electrically activate the dopant. The back-flow of silicon interstitials released by the preamorphization end-of-range (EOR) damage is completely trapped by a carbon-rich silicon layer interposed by MBE between the damage and the implanted boron. No appreciable TED is observed in the samples up to complete dissolution of the EOR damage, and complete electrical activation is obtained. The method might be considered for the realization of ultra shallow junctions for the far future complementary metal-oxide semiconductor technology nodes.

Influence of in situ ultrasound treatment during ion implantation on amorphization and junction formation in silicon

We report the first study of the effect of in situ ultrasound treatment during ion implantation on amorphization and transient enhanced diffusion (TED) in silicon. Rutherford backscattering spectroscopy, ion channeling, and Raman spectroscopy measurements show that amorphization of Si during Ar ion implantation is increased by ultrasound treatment, especially at ultrasound frequencies around 2 MHz. By secondary ion mass spectroscopy we investigate the influence of ultrasound treatment on TED of B atoms. Our data show that TED is reduced due to the influence of ultrasound treatment. The results are discussed in terms of the interaction of ultrasound waves with point defects and the ultrasound stimulated enhanced diffusion of interstitials.

Influences of Point and Extended Defects on As Diffusion in Si

The influences of point and extended defects introduced by ion implantation on the transient enhanced diffusion (TED) of As have been examined. The implantation of a subamorphizing dose of Si into Si wafers with nearly uniform As background doping results in the slight segregation of As into {311} defects after annealing at 670°C, whereas an amorphizing dose of Si is found to induce significant segregation of As into end-of-range (EOR) dislocation loops after annealing at 820°C, regardless of the background As concentration. In the second experiment, As ions were implanted into Si wafers at 30 keV to low and medium doses. Some of the wafers were preannealed in order to recrystallize the amorphous layer and subsequently implanted with subamorphizing doses of Si at 50 keV. The resulting profiles reveal that the TED of As increases with Si implantation dose, indicating that transient As diffusion occurs via Si self-interstitials in the same way as for B and P. A suppression of the TED of As in the early stages of annealing at higher As and Si implantation doses is also observed. This is considered to originate from the formation of immobile arsenic-vacancy clusters.

Effect of Fluorine on the Diffusion of Boron in Amorphous Silicon

AbstractFluorine and boron co-implantation within amorphous silicon has been studied in order to meet the process challenges regarding p+ ultra-shallow junction formation. Previous experiments have shown that fluorine can reduce boron TED (Transient Enhanced Diffusion), enhance boron solubility and reduce sheet resistance. In this study, boron diffusion characteristics prior to solid phase epitaxial regrowth (SPER) of the amorphous layer in the presence of fluorine are addressed. Samples were pre-amorphized with Si+ at a dose of 1x1015 ions/cm2 and energy of 70 keV, leading to a deep continuous amorphous surface of approximately 1500 Å. After pre-amorphization, B+ was implanted at a dose of 1x1015 ions/cm2 and energy of 500 eV, while F+ was implanted at a dose of 2x1015 ions/cm2 and energies ranging from 3 keV to 9 keV. Subsequent furnace anneals for the F+ implant energy of 6 keV were conducted at 550°C, for times ranging from 5 minutes to 260 minutes. During annealing, the boron in samples co-implanted with fluorine exhibited significant enhanced diffusion within amorphous silicon. After recrystallization, the boron diffusivity was dramatically reduced. Boron in samples with no fluorine did not diffuse during SPER. Prior to annealing, SIMS profiles demonstrated that boron concentration tails broadened with increasing fluorine implant energy. Enhanced dopant motion in as-implanted samples is presumably attributed to implant knock-on or recoil effects.

Damage and Dopant Profiles Produced by Ultra-Shallow Boron And Arsenic Ion Implants into Silicon at Different Temperatures Characterised by Medium Energy Ion Scattering.

AbstractMedium energy ion scattering (MEIS), operated at sub-nm depth resolution in the double alignment configuration, has been used to examine implant and damage depth profiles formed in Si(100) substrates irradiated with 2.5 keV As+ and 1 keV B+ ions. Samples were implanted at temperatures varying between 150°C, and 300°C to doses ranging from 3X1014 to 2X1016 cm-2. For the As implants the MEIS studies demonstrate the occurrence of effects such as a dopant accommodation linked to the growth in depth of the damage layer, dopant clustering, as well as damage and dopant movement upon annealing. Following epitaxial regrowth at 600°C, approximately half of the As was observed to be in substitutional sites, consistent with the reported formation of AsnV complexes (n≤4), while the remainder became segregated and became trapped within a narrow, 1.1 nm wide layer at the Si/oxide interfaceMEIS measurements of the B implants indicate the formation of two distinct damage regions each with a different dependence on implant dose, the importance of dynamic annealing for implants at room temperature and above, and a competing point defect trapping effect at the Si/oxide interface. B+ implantation at low temperature resulted in the formation of an amorphous layer due to the drastic reduction of dynamic annealing processes.Notably different dopant distributions were measured by SIMS in the samples implanted with As at different temperatures following rapid thermal annealing (RTA) up to 1100°C in an oxidising environment. Implant temperature dependent interactions between defects and dopants are reflected in the transient enhanced diffusion (TED) behaviour of As.

Self- and Dopant Diffusion in Extrinsic Boron Doped Isotopically Controlled Silicon Multilayer Structures

AbstractIsotopically controlled silicon multilayer structures were used to measure the enhancement of self- and dopant diffusion in extrinsic boron doped silicon. 30Si was used as a tracer through a multilayer structure of alternating natural Si and enriched 28Si layers. Low energy, high resolution secondary ion mass spectrometry (SIMS) allowed for simultaneous measurement of self- and dopant diffusion profiles of samples annealed at temperatures between 850°C and 1100°C. A specially designed ion-implanted amorphous Si surface layer was used as a dopant source to suppress excess defects in the multilayer structure, thereby eliminating transient enhanced diffusion (TED) behavior. Self- and dopant diffusion coefficients, diffusion mechanisms, and native defect charge states were determined from computer-aided modeling, based on differential equations describing the diffusion processes. We present a quantitative description of B diffusion enhanced self-diffusion in silicon and conclude that the diffusion of both B and Si is mainly mediated by neutral and singly positively charged self-interstitials under p-type doping. No significant contribution of vacancies to either B or Si diffusion is observed.

Complete suppression of the transient enhanced diffusion of B implanted in preamorphized Si by interstitial trapping in a spatially separated C-rich layer

A method for completely suppressing the transient enhanced diffusion (TED) of boron implanted in preamorphized silicon is demonstrated. Boron is implanted in a molecular beam epitaxy (MBE) grown silicon sample that has been previously amorphized by silicon implantation. The sample is then annealed in order to epitaxially regrow the amorphous layer and electrically activate the dopant. The backflow of silicon interstitials released by the preamorphization end-of-range (EOR) damage is completely trapped by a carbon-rich silicon layer interposed by MBE between the damage and the implanted boron. No appreciable TED is observed in the samples up to complete dissolution of the EOR damage, and complete electrical activation is obtained. The method might be considered for the realization of ultrashallow junctions for the far future complementary metal–oxide–semiconductor technology nodes.

A reduced approach for modeling the influence of nanoclusters and {113} defects on transient enhanced diffusion

To simulate transient enhanced diffusion (TED) of dopants after ion implantation, a very accurate model for the interaction of self–interstitials with extended defects is indispensable. Recently, such a model has been published by Cowern including the formation of {113} defects via small self–interstitial clusters. Extracted from experimental results, this continuum model consists of a large set of coupled differential equations and, consequently, simulation times are rather high. In this letter, we present a model based on only seven differential equations leading to almost identical results in comparison to those of the original model. The reduction obtained will allow the application of the clustering model for the simulation of TED in commercial software tools.

Effect of the Ge preamorphization dose on boron diffusion and defect evolution in silicon

In this paper, we study the effect of the Ge + preamorphization dose on boron diffusion and on the thermal evolution of end of range (EOR) defects during annealing. Amorphizations were carried out by implanting Ge + at 150 keV to doses ranging from 1×10 15 to 8×10 15 ions/cm 2 . Boron was subsequently implanted at 3 keV with a dose of 1×10 14 ions/cm 2 . Rapid thermal annealing (RTA) was performed for various time/temperature combinations in nitrogen ambient. Secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) were used to study boron diffusion and defect evolution, respectively. We have found that after a given annealing, both the defect size and boron diffusivity are independent on the Ge ion dose. Increasing this dose only results in an increase of the defect density. These results are discussed and definitely show that EOR defects are involved in a quasi-conservative Ostwald ripening process during annealing. The diffusive behavior of boron suggests that the coupling of boron atoms with the “mean field” of Si interstitial atoms in dynamical equilibrium with the defects is responsible for transient enhanced diffusion (TED).

Issues on boron electrical activation in silicon: Experiments on boron clusters and shallow junctions formation

A comprehensive understanding of dopant activation mechanisms in crystalline Si is required in order to form shallow junctions. In this paper, we will review several experimental assessments on boron clustering and novel methods to form shallow junctions. Boron marker-layer structures have been used to investigate the fundamental aspects of formation and ripening boron-interstitial clusters (BICs) and their influence on the associated transient enhanced diffusion (TED). The samples were damaged by Si implants at different doses in the sub-amorphizing range and annealed at high temperatures. We found that BICs act as a sink for interstitials at supersaturations values S( t)>10 4. This implies that silicon self-interstitial defects are the primary source of interstitials driving TED, and that BICs act as a secondary “buffer” for the interstitial supersaturation. These clusters are less sensitive to the ripening process than pure interstitial clusters do, so that their size remain below 2 nm regardless of the annealing time. Moreover, we found that BICs formed in the early stage of the annealing reduce considerably the active amount of B. An extensive characterization of the electrical activation of ultra-low energy implanted boron in silicon is also reported. The spreading resistance profiling (SRP) technique has been used, in a suitable configuration, for measuring doped layers shallower than 100 nm, in order to extract the carrier concentration profiles. High ramp rates are certainly useful in order to form shallow and highly active layers. Laser annealing represents the most promising approach to match the requirements for the needs of fabrication of the future devices. The feasibility of laser annealed ultra-shallow junctions, with depths below 100 nm and high electrical activation, is demonstrated.

Influence of fluorine on the simulation of the transient enhanced diffusion of 15 keV BF 2+ ion implantation into silicon

We have simulated the transient enhanced diffusion (TED) of boron fluoride (BF 2 +) implanted in crystalline and germanium amorphized silicon. Based on recently published models, the effect of fluorine on boron diffusion in silicon has been introduced and a modelling has been suggested. In order to simulate the boron experimental profiles, we have assumed that fluorine forms clusters involving interstitial boron which reduces the junction depth. Experimental results indicate that fluorine behaviour depends on amorphization energy. Moreover, even no germanium preamorphization is performed, silicon is still amorphized by fluorine species. Hence, BF 2 + implantation leads to an amorphous/crystalline (a/c) interface near the surface. An improvement of published models is suggested taking into account fluorine effects. The simulations satisfactory reproduce the SIMS experimental profiles for a large scale of experimental conditions.

Effect of nitrogen segregation on TED and loss of phosphorus in CZ-Si

Transient enhanced diffusion (TED) and dose loss (pile-up) are investigated for phosphorus-implanted samples covered with both oxide and nitride films. P ions were implanted into p-type (1 0 0) CZ-Si (dose 5×10 13 cm −3 , 100 keV) through a chemical vapor deposition (CVD) Si 3N 4 film. For a half of samples, Si 3N 4 was etched off and SiO 2 films were grown by CVD. Both samples were annealed for 20–360 min at 700 °C. Diffusivity of P and the dose loss were estimated based on the secondary-ion mass spectrometry (SIMS) P profiles. Both Si/Si 3N 4 and Si/SiO 2 interfaces were investigated with transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). There is no significant difference in P diffusivity between the SiO 2 and Si 3N 4 films for the present annealing condition of 700 °C for 20–360 min. Regarding dose loss, a distinct different behavior was observed. In case of the SiO 2 cover film, amount of dose decreases with the annealing time. On the other hand, amount of dose decrease with annealing time up to 180 min, but is recovered for more than 180 min in case of the Si 3N 4 cover film. From TEM and EELS analyses, it is found that nitrogen segregates at the Si/Si 3N 4 interface, resulting in recovery of dose loss.

Initial anomalous diffusion of boron atoms at low‐temperature annealing

AbstractExperiments on the transient enhanced diffusion (TED) of boron in superlattice silicon wafers, for the first time demonstrated the existence of the anomalous enhanced diffusion of boron at the very early stage of low‐temperature annealing at locations situated deeper than the implantation damage zone. It was confirmed that this phenomenon is caused by free self‐interstitial silicon atoms present in the implantation tail region. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(10): 59–64, 2001

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.

Atomistic modeling of the effects of dose and implant temperature on dopant diffusion and amorphization in Si

We discuss atomistic simulations of ion implantation and annealing of Si over a wide range of ion dose and substrate temperatures. The DADOS Monte Carlo model has been extended to include the formation of amorphous regions, and this allows simulations of dopant diffusion at high doses. As the dose of ions increases, the amorphous regions formed by cascades eventually overlap, and a continuous amorphous layer is formed. In that case, most of the excess interstitials generated by the implantation are swept to the surface as the amorphous layer regrows, and do not diffuse in the crystalline region. This process reduces the amount of transient enhanced diffusion (TED) during annealing. This model also reproduces the dynamic annealing during high temperature implants. In this case, the local amorphous regions regrow as the implant proceeds, without the formation of a continuous amorphous layer. For sufficiently high temperatures, each cascade is annealed out independently; interstitials and vacancies can escape from the cascade and thus increase dopant diffusion.

Modeling of the transient enhanced diffusion of boron implanted into preamorphized silicon: the case of BF 2+ implantation

We have simulated transient enhanced diffusion (TED) in the presence of end-of-range (EOR) defects produced by Ge amorphization followed by BF 2 + implantation. Ostwald ripening of EOR defects has been taken into account. A comparison of annealed profiles with equivalent B + implantation shows that the existing models are not sufficient to simulate the BF 2 + experimental profiles where the boron diffusion depth is very low. We have proposed that the presence of fluorine can act as sinks for interstial boron and, hence, reduces the boron diffusion depth in order to obtain a good approximation of experimental profiles.

Identification of stable boron clusters in c-Si using tight-binding statics

As a particularly important p-type dopant, boron exhibits some problematical phenomena during the fabrication of microelectronic devices, especially transient enhanced diffusion (TED) following ion implantation and annealing. TED is due, in large part, to the formation of boron-defect clusters. This article describes a search for particularly stable boron-defect clusters (up to B4I4). A tight-binding method, in conjunction with atomic-scale statics calculations, is used to study boron and boron-defect clusters containing up to four boron atoms and four self-interstitials within a matrix of crystalline silicon. Formation and binding energies are reported for these species. There is a tendency to form a four-atom ring containing two Si self-interstitials and two boron atoms. One guiding principle for the stability of the geometry of the clusters is to maximize the number of unstrained bonds (i.e. with Si-like bond lengths); the higher the extent of unstrained bonds, the lower the formation energy. Symmetry is found to play a smaller role in determining preferred structures.

Interface induced uphill diffusion of boron: an effective approach for ultrashallow junction

This paper investigates anomalous diffusion behavior for ultra low energy implants in the extension or tip of PMOS devices. Transient enhanced diffusion (TED) is minimal at these low energies, since excess interstitials are very close to the surface. Instead, interface induced uphill diffusion is found, for the first time, to dominate during low temperature thermal cycles. The interface pile-up dynamics can be taken advantage of to produce shallower junctions and improve short channel effect control in PMOS devices. Attempts to minimize TED before spacer deposition by inclusion of extra RTA anneals are shown to be detrimental to forming boron ultra shallow junctions.

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.