Solid Phase Epitaxial Regrowth Research Articles

Enhanced n-type dopant solubility in tensile-strained Si

The creation of highly conductive ultrashallow-doped regions in strained Si is a key requirement for future Si based devices. It is shown that in the presence of tensile strain, Sb becomes a contender to replace As in strain-engineered CMOS devices due to advantages in sheet resistance. While strain reduces resistance for both As and Sb; a result of enhanced electron mobility, the reduction is significantly larger for Sb due to an increase in donor activation. Differential Hall measurements suggest this is a consequence of a strain-induced Sb solubility enhancement following solid-phase epitaxial regrowth, increasing Sb solubility in Si to levels approaching 10 21 cm − 3 . Experiments highlight the importance of maintaining substrate strain during thermal annealing to maintain this high Sb activation.

Stressed solid-phase epitaxial growth of ion-implanted amorphous silicon

The kinetics of stressed solid-phase epitaxial growth (SPEG), also referred to as solid-phase epitaxy, solid-phase epitaxial regrowth, solid-phase epitaxial recrystallization, and solid-phase epitaxial crystallization, of amorphous (α) silicon (Si) created via ion-implantation are reviewed. The effects of hydrostatic, in-plane uniaxial, and normal uniaxial compressive stress on SPEG kinetics are examined in intrinsic (0 0 1)Si. Particular emphasis is placed on unifying the results of different experiments in a single-stress-dependent SPEG model. SPEG kinetics are observed to suffer similar exponentially enhanced growth rates in hydrostatic and normal uniaxial compressive stress. However, there are discrepancies between researchers in terms of the influence of in-plane stress on growth rates. Two different stress-dependent SPEG models are thus advanced, each with different physical bases. The model advanced by Aziz et al. proposes SPEG can be modeled as a single-atomistic process while the model advanced by Rudawski et al. suggests that stress influences the nucleation and migration processes of growth differently and that SPEG cannot be modeled as a single step. The basis for the Rudawski et al. model is based on the crystal island and ledge migration model of SPEG advanced by others. Morphological instabilities of the growing α/crystalline interface with in-plane compression are also addressed within the context of both the Aziz et al. and Rudawski et al. models. Finally, using the Rudawski et al. model, it is possible to examine, characterize, and isolate the different atomistic processes during growth. Calculation of the activation energies for nucleation and migrations processes suggests that the activation energy of 2.7 eV observed for the growth rate in stress-free SPEG by Olsen and Roth is representative of the activation energy for the single-atomistic process of crystal island nucleation. Thus, the study of stressed SPEG provides a new atomistic picture of the nature of growth.

Characterization of the low temperature activated N +/P junction formed by implant into silicide method

Shallow junction formation and low thermal budget control are important for advanced device manufacturing. Implant into silicide (IIS) method is a candidate to achieve both requirements. In this work we show that the high activation ability of the implant into nickel silicide method at low activated temperature is strongly related to the solid phase epitaxial regrowth (SPER) process. The SIMS, capacitance–voltage ( C– V), four points probe (FPP), and current–voltage ( I– V) measurements are combined to demonstrate that the SPER process of the IIS method is starting from the silicide/silicon (M/S) interface. The best N +/P interface is formed when SPER is complete. After SPER process finished, additional thermal budget may cause junction performance degradation at the temperature higher than 550 °C.

A Comprehensive Atomistic Kinetic Monte Carlo Model for Amorphization/Recrystallization and its Effects on Dopants

ABSTRACTThis work shows a comprehensive atomistic model to describe amorphization and recrystallization, and its different effects on dopants in silicon. We begin by describing the physical basis of the model used, based on the transformation of ion-implanted dopants and generated point defects into amorphous pockets of different sizes. The growth and dissolution of amorphous pockets is simulated by the capture and recombination of point defects with different activation energies. In some cases, this growth leads to the formation of amorphous layers. These layers, composed of a set of amorphous elements, have an activation energy to be recrystallized. The recrystallization velocity is modeled not only depending on temperature, but also on dopant concentration. During the recrystallization, dopants move with the recrystallization front to simulate the dopant redistribution during solid phase epitaxial regrowth (SPER). At the edge of the amorphous-crystalline interface, the remaining damage forms end-of-range (EOR) defects.Once the model is explained, we discuss the calibration methodology used to reproduce several amorphous/crystalline (A/C) experiments, including the dependencies of the A/C transition temperature on dose rate and ion mass, and the A/C depth on ion implant energy.This calibrated model allows us to explore the redistribution of several dopants, including B, As, F, and In, during SPER. Experimental results for all these dopants are compared with relevant simulations.

Level set modeling of the orientation dependence of solid phase epitaxial regrowth

Level set methods have previously been successfully implemented in interface propagation for etching and deposition processes. In this article, the authors show that level set methods can be used to model solid phase epitaxial regrowth. The model incorporates orientation dependence of regrowth as found by Csepregi et al. [J. Appl. Phys. 49, 3906 (1978)]. The orientation dependent velocity data are taken from Csepregi’s paper and fitted to a polynomial function to give the growth velocity for level set methods. Simulations show the capability of our model in predicting the pinching of the corners in ⟨111⟩ direction and humplike shape in ⟨100⟩ direction. This is confirmed by the transmission electron microscope pictures from recent papers. This modeling holds special interest because of the different diffusivities of boron in amorphous and crystalline silicon (approximately five orders of magnitude difference) and because of the various defects forming at the pinching corners which could lead to higher leakage current in scaled devices. The level set model is implemented in FLOOPS.

P implantation into preamorphized germanium and subsequent annealing: Solid phase epitaxial regrowth, P diffusion, and activation

Phosphorus implantation (30 keV, 3×1015 cm−2) into preamorphized Ge and subsequent rapid thermal or flash lamp annealing is investigated. During annealing a significant P diffusion in amorphous Ge is not observed. However, the fast solid phase epitaxial regrowth causes a rapid redistribution of P. After completion of the regrowth and at temperatures above 500 °C, a concentration-dependent diffusion of P in crystalline Ge takes place and leads to considerable loss of P toward the surface. An appreciable influence of implantation defects on the diffusion coefficient of P is not detected. For 60 s rapid thermal annealing at 600 °C and for 20 ms flash lamp annealing at 900 °C, the junction depth and the sheet resistance vary between 140 and 200 nm and between 50 and 100 Ω, respectively, and the maximum electrical activation of P is about 3–7×1019 cm−3.

Effect of low Ge content on B diffusion in amorphous SiGe alloys

Diffusion of B in amorphous Si is known to be four orders of magnitude higher than in crystalline Si. The effect of Ge at low concentrations on B diffusion in the amorphous phase is unknown. 1.5μm thick relaxed layers of varying SiGe alloys (0, 6, 12, and 100at.% Ge) were grown on Si. After growth the layer was amorphized to a depth of 0.8μm using a 500keV, 5×1015ion∕cm2 Si+ implant at 77K. Next a 500eV, 1×1015ions∕cm2 B+ implant was introduced. The amorphous SiGe was recrystallized at temperatures between 300 and 600°C and the B diffusion during solid phase epitaxial regrowth was studied using dynamic secondary ion mass spectrometry. Comparison of B diffusivities for amorphous Si and amorphous Si0.88Ge0.12 revealed similar activation energies (2.7 and 2.8eV, respectively) and preexponential factors (0.8 and 4.8cm2∕s, respectively). The negligible change in B diffusion in amorphous SiGe at low Ge concentrations is similar to reports on B diffusivity for strain-relaxed crystalline SiGe alloys with Ge content. These results suggest that Ge is not an effective trap for B in the amorphous phase.

Optimization of Stressor Layers Created by ClusterCarbon™ Implantation

ABSTRACTSi:C layers are interesting candidates as stressor layers for NMOS transistors. Growth of such a Si:C layer has been realized by an expensive epitaxial growth process for devices to produce tensile strain in the channel, leading to enhanced mobility and device performance. Use of a monomer carbon ion implant in conjunction with a Ge pre-amorphizing implant (Ge-PAI) in Si is an alternative, lower cost approach to obtaining such SiC layers. This approach has not yielded desired device performance owing to low carbon substitutionality [C]sub, and also the presence of end-of-range (EOR) defects and large leakage currents due to the Ge-PAI implant. In this study we will show the formation of a Si:C layer using a ClusterCarbon approach that creates self-amorphization in Si thus avoiding an extra Ge-PAI implant step. We show that more than 2% substitutional carbon can be realized by using solid-phase-epitaxial-regrowth (SPER) and millisecond anneal. Si:C layers are characterized by using High Resolution X-ray Diffraction (HRXRD) and SIMS techniques.

Improved Boron Activation with Reduced Preheating Temperature during Flash Annealing of Preamorphized Silicon

In flash lamp annealing, the entire wafer is uniformly preheated to an intermediate temperature before a millisecond duration flash of intense light is applied. This interaction of the preheating condition and final flash energy density on the properties of preamorphized boron-implanted silicon was studied. It was found that for a fixed flash energy density, an increase in sheet resistance was observed with higher preheating temperature. This sheet resistance degradation is attributed to the occurrence of solid-phase epitaxial regrowth (SPER) during preheating instead of during the high temperature flash step. When the preheating temperature is reduced, occurrence of SPER of the amorphous silicon during preheating is not possible due to the low temperature. As such, SPER has to take place during the high temperature flash anneal step. Since the solid solubilities attainable using SPER is higher than flash, by introducing SPER at a higher temperature, the amount of activated boron atoms that can be incorporated into the silicon lattice is increased and a sheet resistance improvement is observed.

Properties of Si:Cr Annealed under Enhanced Stress Conditions

The effect of hydrostatic argon pressure equal to 105 Pa and 1.1 GPa applied to processing at up to 1270 K (HT) of Si:Cr samples prepared by Cr+ implantation (dose 1x1015 cm-2, 200 keV) into (001) oriented Czochralski silicon, has been investigated by Secondary Ion Mass Spectrometry, photoluminescence, X-ray and SQUID methods. Cr+ implantation at this energy and dosage produces amorphous silicon (a-Si) near the implanted ions range. Solid phase epitaxial re-growth (SPER) of a-Si takes place at HT. The Cr profile does not depend markedly on HP applied during processing at 723 K. Si:Cr processed at up to 723 K indicates magnetic ordering. Annealing under 105 Pa at 873 K, 1070 K and 1270 K results in a marked diffusion of Cr toward the sample surface. In the case of processing under 1.1 GPa this diffusion is less pronounced, SPER of a-Si is retarded and the a-Si/Si interface becomes enriched with Cr. The Cr concentration in Si:Cr sample processed at 1270 K under 1.1 GPa forms two distinct maxima, the deeper one at 0.35 μm depth.

Solid phase epitaxy in uniaxially stressed (001) Si

The effect of [110] uniaxial stresses up to 1.5GPa on defect nucleation during solid phase epitaxy of amorphous (001) Si created via ion implantation was examined. The solid phase epitaxial regrowth velocity was slowed in compression. However, in tension, the velocity was unaffected. Both compression and tension resulted in an increase in regrowth defects compared to the stress-free case. The defects in compression appear to arise from roughening of the crystallizing interface whereas in tension it is proposed that reorientation of crystallites near the initial amorphous/crystalline interface is responsible for defect formation.

Increase of Carbon Substitutionality and Silicon Strain by Molecular Ion Implantation

We have shown that molecular carbon ion implantation instead of the atomic species enhances the substitutional fraction of carbon upon solid phase epitaxial regrowth. Ultra-high temperature annealing by a laser was used for the first time, to produce the regrowth.

Interface roughening and defect nucleation during solid phase epitaxy regrowth of doped and intrinsic Si0.83Ge0.17 alloys

Metastable pseudomorphic Si0.83Ge0.17 with thickness of 135nm was deposited on (001) Si substrate by molecular beam epitaxy and amorphized to a depth of ∼360nm, using 3×1015cm−2 Ge ions at 270keV. Samples were regrown by solid phase epitaxy in the 500–600°C temperature range. The regrowth rate was measured in situ by time resolved reflectivity, while the structure of the epilayers was investigated by transmission electron microscopy. Three regions can be distinguished in SiGe after solid phase epitaxy, independent of the annealing temperature: (1) a 20nm defect-free layer close to the original crystal-amorphous interface, (2) a middle region with a high density of planar defects, and (3) a layer with dislocations and stacking faults extending up to the surface. The activation energy of the SiGe solid phase epitaxy is equal to the activation energy of Si except in the middle region. The amorphous-crystal interface evolution was studied by transmission electron microscopy of partially regrown samples. In order to study the effects of dopants, some samples were also implanted with B+ and Sb+ ions. At the ion projected range (125nm for both implants) the regrowth rate increases by a factor of 3 with respect to the unimplanted SiGe, but the defect-free layer again is found to be about 20nm in all cases. Moreover, the activation energy of the solid phase epitaxy regrowth process does not depend on dopant introduction, while the only observable effect of B or Sb incorporation is a smoothness of the amorphous-crystal interface during solid phase epitaxy.

High-$\kappa$ Metal Gate MOSFETs: Impact of Extrinsic Process Condition on the Gate-Stack Quality—A Mobility Study

The effects of source/drain activation thermal budget and premetallization degas conditions on interfacial regrowth, carrier mobility, and defect densities are examined for SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TaN stacks. We observe a correlation between the mobility degradation and the interfacial re-growth possible with the thermal budget employed. The mobility degradation arises from an increase of defects, both within the interface layer (IL) and the high-kappa bulk, as detected by both pulsed current-voltage and charge-pumping measurements. Two junction activation processes have been applied: a conventional process (peak temperature of 1000 degC spike for t=1 s) and a Solid Phase Epitaxial Re-growth (SPER) (peak temperature of 650 degC for t=60 s). For 1000 degC spike-annealed films, where the highest SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /IL defect density is observed, the consequent mobility degradation is explained by a transition region between HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and the IL which increases for high-temperature processing

Arsenic Junction Thermal Stability and High-Dose Boron-Pocket Activation During SPER in nMOS Transistors

In this letter, thermal stability of arsenic (As) junctions formed by solid-phase epitaxial regrowth and their impact on device performance are investigated. If the temperature does not exceed 800 degC, a 35% junction sheet-resistance improvement over the conventional rapid thermal anneal is observed. The overlap junction resistance is not degraded and transistors, processed exclusively with lowly doped drain junctions, show a significant performance gain. High boron (B)-pocket dose leads to good transistor short-channel effect control, overcoming the B deactivation issue. The impact of B-pocket-related counterdoping and channel-mobility degradation on device characteristics are investigated. In the presence of heavily doped substrates, band-to-band tunneling is the dominant mechanism driving the reverse-bias junction leakage and is higher than the trap-assisted tunneling contribution related to the end-of-range defects

Formation of germanium shallow junction by flash annealing

We have investigated flash-lamp annealing (FLA) of germanium wafers doped with phosphorous and boron introduced in the crystal by ion implantation. Annealing was performed by using pre-heating at 400–450°C in a conventional rapid thermal processing (RTP) unit and a fast (3–20ms) FLA annealing at 800°C or 900°C. Diffusion of P is suppressed during the 800°C–20ms FLA annealing, while concentration-enhanced diffusion occurs upon 900°C FLA anneals. Importantly, in both cases P activation seems to be enhanced by the FLA process. However, junction stability following the FLA process and possible deactivation are a concern.In contrast, the FLA process applied to B-doped pre-amorphized Ge layers does not show advantages as compared to a RTP conventional annealing combined with a solid phase epitaxial regrowth, in terms of B activation level.

Amorphous–crystalline interface evolution during Solid Phase Epitaxy Regrowth of SiGe films amorphized by ion implantation

Transmission Electron Microscopy was combined with Time Resolved Reflectivity to study the amorphous–crystalline (a–c) interface evolution during Solid Phase Epitaxy Regrowth (SPER) of Si0.83Ge0.17 films deposited on Si by Molecular Beam Epitaxy and amorphized with Ge+ ion implantation. Starting from the Si/SiGe interface, a 20nm thick layer regrows free of defects with the same SPER rate of pure Si. The remaining SiGe regrows with planar defects and dislocations, accompanied by a decrease of the SPER velocity. The sample was also studied after implantation with B or P. In these cases, the SPER rate raises following the doping concentration profile, but no difference in the defect-free layer thickness was observed compared to the un-implanted sample. On the other hand, B or P introduction reduces the a–c interface roughness, while B–P co-implantation produces roughness comparable to the un-implanted sample.

Electroluminescence of nanopatterned silicon with carbon implantation and solid phase epitaxial regrowth

Electroluminescence at 1.28mum is observed in a nanopatterned silicon test structure that has been subjected to carbon implantation followed by solid-phase epitaxial regrowth for recrystalization. The sub-bandgap luminescence comes from a di-carbon complex known as 'G center'. Enrichment of silicon with carbon atoms has been achieved in a procedure consisting of two implantations and solid-phase epitaxial regrowth. Nanopatterning was done using an anodized aluminum oxide membrane as a mask for reactive ion etching. Along with the electroluminescence, an enhanced photoluminescence was measured.

Microwave Activation of Dopants &amp; Solid Phase Epitaxy in Silicon

AbstractMicrowave heating is used to activate solid phase epitaxial re-growth of amorphous silicon layers on single crystal silicon substrates. Layers of single crystal silicon were made amorphous through ion implantation with varying doses of boron or arsenic. Microwave processing occurred inside a 2.45 GHz, 1300 W cavity applicator microwave system for time-durations of 1-120 minutes. Sample temperatures were monitored using optical pyrometery. Rutherford backscattering spectrometry, and cross-sectional transmission electron microscopy were used to monitor crystalline quality in as-implanted and annealed samples. Sheet resistance readings show dopant activation occurring in both boron and arsenic implanted samples. In samples with large doses of arsenic, the defects resulting from vacancies and/or micro cluster precipitates are seen in transmission electron micrographs. Materials properties are used to explain microwave heating of silicon and demonstrate that the damage created in the implantation process serves to enhance microwave absorption.

An EXAFS investigation of arsenic shallow implant activation in silicon after laser sub-melt annealing

It is well known that arsenic deactivates easily in silicon at moderate temperature (500–800°C), supposedly by clustering around vacancies. The deactivation hinders the preservation of the high level of activation reached by processes such as solid phase epitaxial regrowth (SPER) or laser sub-melt annealing. This paper presents results obtained on 2keV arsenic implants in silicon subsequently annealed by either laser sub-melt or spike processes. In particular, we investigated the local order around arsenic atoms by extended X-ray absorption fine structure (EXAFS) measurements. A sample preparation consisting of removal of some atomic layers was carried out to eliminate inactive dopant segregated at the surface oxide. The chemical depth profiles were measured by secondary ion mass spectrometry (SIMS) whereas the electrical activation was investigated by four point probe and Hall effect measurements. The EXAFS results show that the spike annealing produces a surface accumulation with a local order around As atoms similar to the amorphous structure observed in the as implanted sample. After removal of the surface accumulation, EXAFS spectra are typical of a sample with a high level of activation. This was also observed for samples processed with laser sub-melt annealing before the spike anneal. Samples treated with the only laser process show an intermediate level of crystal order. Electrical data are in agreement with the qualitative EXAFS observations.