Pre-amorphized Si Research Articles

Xenon-ion irradiation of Co/Si bilayers: Magnetic and structural properties

Evolution of the structure of cobalt-silicon films during Xe ions irradiation has been studied and the same is correlated with magnetic properties. The polycrystalline cobalt films were deposited by electron beam evaporation method to a thickness of 50 nm on crystalline silicon (c-Si) and silicon with pre-amorphized surface (a-Si). After deposition the layers were irradiated with 400 keV Xe ions to the fluences in the range of 2–30 × 1015 ions/cm2. Structural analysis was done by means of transmission electron microscopy, atomic force microscopy (AFM) and X-ray diffraction (XRD), while the magnetic properties were analyzed by using magneto-optical Kerr effect (MOKE) technique. For the both types of substrate the AFM and XRD results show that after Xe ions irradiation the layers become more rough and the grain size of the crystallites increases; the effects being more evidenced for all fluences for the layers deposited on pre-amorphized Si. The MOKE measurements provided the in-plane azimuthal angular dependence of the hysteresis loops and the change of magnetization with the structural parameters. Although the coercive field is influenced by the surface roughness, in the case of c-Si substrate we found it is much more determined by the size of the crystallites. Additionally, independently on the substrate used the magnetic anisotropy in the Co films disappeared as the Xe ion fluence increased, indicating that the changes of magnetization in both systems occur for similar reasons.

Optimization of Ni(Pt)/Si-cap/SiGe Silicidation for pMOS Source/Drain Contact

The Ni(Pt)/Si-cap/SiGe silicidation process has been optimized by modulating the Si-cap layer thickness and a cold Si preamorphization implantation (PAI), which effectively reduces the sheet resistance (Rs). In addition, it is revealed that PAI can obviously increase the Ni(Pt)Si grain size for a lower Rs.

Comparative computational study of the energetics of Li, Na, and Mg storage in amorphous and crystalline silicon

To assess the potential of amorphous Si (a-Si) as an anode for Li, Na, and Mg-ion batteries, the energetics of Li, Na, and Mg atoms in a-Si are computed from first-principles and compared to those in crystalline Si (c-Si). It is shown that Si preamorphization increases the average anode voltage and slightly reduces the volume expansion of the anode during the insertion of the metal atoms. Analysis of computed formation energies of Li, Na, and Mg defects in a-Si and c-Si suggests that the insertion energetics of single atoms into a-Si are thermodynamically more favorable. For instance, the lowest defect formation energies of Li, Na, and Mg defects in a-Si are respectively 0.43, 1.42, and 1.52eV lower compared to those in c-Si. Moreover, the defect formation energies of Li, Na, and Mg defects (vs. vacuum reference states) in a-Si are comparable with the metal cohesive energies and consequently the insertion of the metal atoms might be possible with appropriate control of charging process. This is in contrast to c-Si, where the storage of Na and Mg atoms is limited due to high energy cost of Na and Mg insertion into c-Si.

Xenon-ion-induced and thermal mixing of Co/Si bilayers and their interplay

Studies on ion-irradiated transition-metal/silicon bilayers demonstrate that interface mixing and silicide phase formation depend sensitively on the ion and film parameters, including the structure of the metal/Si interface. Thin Co layers e-gun evaporated to a thickness of 50 nm on Si(1 0 0) wafers were bombarded at room temperature with 400-keV Xe + ions at fluences of up to 3 × 10 16 cm −2. We used either crystalline or pre-amorphized Si wafers the latter ones prepared by 1.0-keV Ar-ion implantation. The as-deposited or Xe-ion-irradiated samples were then isochronally annealed at temperatures up to 700 °C. Changes of the bilayer structures induced by ion irradiation and/or annealing were investigated with RBS, XRD and HRTEM. The mixing rate for the Co/c-Si couples, Δ σ 2/ Φ = 3.0(4) nm 4, is higher than the value expected for ballistic mixing and about half the value typical for spike mixing. Mixing of pre-amorphized Si is much weaker relative to crystalline Si wafers, contrary to previous results obtained for Fe/Si bilayers. Annealing of irradiated samples produces very similar interdiffusion and phase formation patterns above 400 °C as in the non-irradiated Co/Si bilayers: the phase evolution follows the sequence Co 2Si → CoSi → CoSi 2.

Formation and incorporation of SiF4 molecules in F-implanted preamorphized Si

The local structure of fluorine incorporated in crystalline silicon following solid phase epitaxial regrowth was investigated by means of x-ray absorption spectroscopy at the F K-edge. We clearly demonstrate that most F is found in SiF4 molecules in the crystalline matrix. A kinetic pathway, which explains our observation and which is also able to rationalize previous results in a common and coherent framework, is proposed.

A low-cost method of forming epitaxy SiGe on Si substrate by laser annealing

In this letter, a low-cost alternative for forming high grade silicon germanium (SiGe) by a laser-induced crystallization of an amorphous Ge layer deposited directly on Si+ preamorphized implantation Si substrate is demonstrated. The results show that a fully strained epitaxial SiGe layer on the Si (100) substrate can be obtained at laser fluence above the epitaxial threshold. This is due to a liquid-phase epitaxial regrowth process of the laser annealing induced melted layer. Below the epitaxial threshold, polycrystalline SiGe is formed due to explosive recrystallization process. Simultaneous boron activation is achieved with the SiGe formation, a result due to the high temperature induced by the laser annealing.

Role of the strain in the epitaxial regrowth rate of heavily doped amorphous Si films

Solid phase epitaxial regrowth (SPER) of p-doped preamorphized Si was studied by time resolved reflectivity. Strain and dopant concentration were opportunely varied by implanting neutral (Ge) and isovalent (B, Ga) impurities in order to disentangle the two different effects on SPER. Larger SPER rate variations occurred in strained doped Si with respect to undoped samples. The generalized Fermi level shifting model was implemented to include the role of the strain and to fit the experimental data over a large range of temperature for p- and n-type doping. We introduced a charged defect, whose energy level is independent of the dopant species.

N-Channel MOSFETs With Embedded Silicon–Carbon Source/Drain Stressors Formed Using Cluster-Carbon Implant and Excimer-Laser-Induced Solid Phase Epitaxy

In this letter, we report the use of a novel cluster-carbon (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) implant and pulsed-excimer-laser-induced solid-phase-epitaxy technique to form embedded silicon-carbon (Si:C) source/drain (S/D) stressors. A substitutional carbon concentration C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sub</sub> of ~ 1.1% was obtained in this letter. N-channel MOSFETs (n-FETs) integrated with embedded silicon-carbon (Si:C) S/D stressors formed using the novel cluster-carbon implant and pulsed-laser-anneal technique demonstrate improvement in current drive of 14% over control n-FETs formed with Si preamorphization implant. I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DSAT</sub> comparison shows a 15% I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DSAT</sub> enhancement for n-FETs with embedded Si:C S/D at an I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> = 1 nA/mum despite a slightly higher series resistance.

Effects of the Ar ions pre‐amorphization of Si substrateon interface mixing of Fe/Si bilayers

Ion beam mixing of Fe/Si bilayers, induced by 100 keV (40)Ar ions at room temperature was investigated. Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for structural characterization. The main focus of this study was on the influence of the substrate structure on interface mixing. The influence of the substrate structure is due to the two classes of irradiated bilayers, Fe thin films deposited on crystalline or pre-amorphized Si substrates. An about 76% higher efficiency of atomic transport across the pre-amorphized Fe/a-Si interface as compared to that of Fe/c-Si bilayers was observed.

Atomistic modeling of F nV m complexes in pre-amorphized Si

The co-implantation of F and B in pre-amorphized Si has been proved to be beneficial for the fabrication of ultrashallow junctions due to a remarkable reduction of B diffusion. This is attributed to the presence of fluorine-vacancy (F–V) complexes after regrowth, acting as annihilation centers for Si interstitials. Whereas the resulting F profile in the recrystallized layer can be easily determined by chemical profiling, the vacancy distribution, which has a strong influence on B diffusion, can only be indirectly estimated. In this work, atomistic simulations have been used to analyze several aspects that can affect the efficiency of F–V complexes on Si interstitials annihilation, by considering the effects on B diffusion and the evolution of F profiles. The vacancy content of the complexes, determined by the F/V ratio, and the complex size play an important role on B redistribution. The existence of a recombination barrier for the interaction of a Si interstitial and some F–V complexes, as proposed by theoretical calculations, and its influence on the Si interstitial annihilation efficiency of the complexes are also analyzed.

He implantation to control B diffusion in crystalline and preamorphized Si

We demonstrate that He can be a powerful tool to control B diffusion both in crystalline (c-Si) and preamorphized Si (PA-Si). By means of positron annihilation spectroscopy (PAS), we showed in He-implanted c-Si the formation after annealing of large open-volume defects at the implant projected range Rp of He (voids) and of smaller vacancy-type defects toward the surface (nanovoids). In particular, these nanovoids locally suppress the amount of self-interstitials (Is) generated by B implantation, as verified by PAS, eventually reducing B diffusion and leading to a boxlike shape of the B-implanted profile. On the other hand, for B implantation in PA-Si, the authors demonstrated that if He-induced voids are formed between the end-of-range (EOR) defects and the surface, they act as a diffusion barrier for Is coming from the EOR defects. Indeed, this barrier strongly reduces diffusion of B placed in proximity of the surface.

Substitutional B in Si: Accurate lattice parameter determination

In this work the lattice deformation induced by substitutional B in Si is carefully determined by using different experimental techniques. The investigated Si1−xBx∕Si layers x=(0.0012÷0.005) are grown by solid phase epitaxy of B-implanted preamorphized Si and by molecular beam epitaxy. Nuclear reaction analysis both in random and in channeling geometry, secondary ion mass spectrometry and high resolution x-ray diffraction allow to quantify the total amount of B and its lattice location, the B depth profile and the B-doped Si lattice parameter, respectively. The reasons for the large spread present in the data reported so far in literature are discussed. Our results, thanks to the synergy of the earlier techniques, lead to a significantly more accurate strain determination, that is in agreement with very recent ab initio theoretical calculations.

Boron diffusion and activation in SOI and bulk Si: The role of the buried interface

We investigate the influence of the buried Si/SiO2 interface in Silicon-on-insulator (SOI) substrates on B electrical activation by comparing experimental data and atomistic simulations in bulk Si and SOI materials. In crystalline Si, the effect of the Si/SiO2 interface on the formation of B clusters is practically negligible because they are formed rapidly and locally in the region with high B and Si interstitial concentrations. Only during post-implant anneal a slight acceleration of B activation occurs, as the Si/SiO2 interface increases the removal of Si interstitials and facilitates B cluster dissolution. In pre-amorphized Si, B clusters form during the regrowth. Therefore, the effect of the Si/SiO2 interface is mainly related to its influence on end of range defect (EOR) evolution after regrowth which in turn affects B deactivation and reactivation. Thus, slightly less B deactivation occurs in SOI compared to bulk Si samples as the Si/SiO2 interface accelerates EOR defect dissolution. The effect is more significant as EOR damage is closer to the Si/SiO2 interface.

B diffusion and activation phenomena during post-annealing of C co-implanted ultra-shallow junctions

In order to meet the technological requirements for the next generations of p–n junctions, highly promising methods consist of B and C ultra-low energy co-implantation in Ge pre-amorphized Si. We investigated the B diffusion and the activation phenomena occurring during post-annealing of ultra-shallow junctions (USJ) obtained by spike annealing Si samples pre-amorphized by 20keV Ge and co-implanted with C at 4keV and B at 500eV. Isochronal (60s) post-annealing processes were performed in inert atmosphere (N2) by rapid thermal annealing (RTA) in the 500–1050°C temperature range. We show that, contrary to what reported in the literature about C-free USJ, no B diffusion occurs up to 900°C, and further B clustering is completely suppressed over the whole investigated temperature range. Moreover we observed an increase of the sheet resistance by increasing the temperature up to 900°C followed by a subsequent decrease, that can be easily interpreted on the basis of B diffusion and segregation in native SiO2 and B cluster dissolution. Finally, we show that C significantly reduces up to two orders of magnitude the diffusion coefficient of B, that in our experiments is present in highly extrinsic conditions.

Fluorine incorporation in preamorphized silicon

We studied the effect of implanted fluorine on B-doped silicon formed by Si preamorphization, solid phase epitaxy (SPE) regrowth and post-SPE thermal treatments. We showed that the fluorine is an efficient diffusion inhibitor for boron, revealing the crucial importance of F implementation in the future generation devices. In samples doped with B we observed an anomalous F accumulation at the dopant implantation peak. Since the physical mechanisms driving these phenomena are not yet well understood, we investigated the effect of the presence of B and/or As on the F incorporation during the SPE process at 580°C. By using As coimplantation (thus modifying the SPE rate) we demonstrated that the above mentioned increased F incorporation is due to a kinetic effect, related to the SPE rate modification by doping, while a F–B chemical bonding is refused. These data shade new light upon the mechanism responsible for B diffusion reduction by F.

Modeling of B diffusion in the presence of Ge

In order to investigate the B and Ge interaction in silicon, an implant/anneal experiment is performed. The initial Si pre-amorphization step defines the amorphous layer depth and the end-of-range point defect distributions for all samples. The following Ge implant provides a low Ge content, thus minimizing the strain and the band gap narrowing effects on the diffusion of the subsequent B implant. The control sample received Si and B implants. The annealed profiles of the control samples show B profile broadening consistent with the transient enhanced diffusion. The B tail diffusion in the Ge implanted samples is almost identical to that of the control samples, indicating that Ge does not act as a trap for the BI pair. The GeB complex, suggested in literature, was used to explain the higher profile peak magnitude in Ge implanted samples.

Group III impurities – Si interstitials interaction caused by ion irradiation

The off-lattice displacement of substitutional impurities (B, Ga) in Si caused by irradiation with energetic light ion beams has been investigated. Samples have been prepared by solid phase epitaxy (SPE) of pre-amorphized Si subsequently implanted with B and Ga at a concentration of about 1×1020at/cm3 confined in a 300nm thick surface region. The off-lattice displacement of the impurities was induced at room temperature (RT) by irradiation with high energy (>600keV) light ion beams (H, He) and detected by the channelling technique along different axes, using the 11B(p,α)8Be reaction and standard RBS, for B and Ga, respectively. The normalized channelling yield χ of the impurity signal increases with the ion fluence, indicating a progressive off-lattice displacement of the dopant during irradiation, until it saturates at χF<1 suggesting a non-random displacement of the dopant. Although the precise value of χF depends on the channelling direction and dopant species, the off-lattice displacement rate, deduced from the χ versus interstitial fluence curve, only depends on the excess of Si self-interstitials (SiI) generated by the irradiating beam through a parameter σ that can be interpreted as an effective cross-section for the impurity–SiI interaction.

Effects of Si(001) surface amorphization on ErSi 2 thin film

In a materials study of ErSi 2/Si(001) as a potential candidate for Schottky source/drain NMOS application, the properties of ErSi 2 thin film were investigated with varying degrees of Si(001) surface amorphization. The amorphization was carried out by in situ Ar plasma cleaning and Si pre-amorphization implant. It was found that the ErSi 2 thin film becomes smoother but less textured and less epitaxial with Si(001) with increasing degree of the Si surface amorphization. In addition, an increased oxygen penetration during rapid thermal annealing occurs with increasing substrate amorphization.

Impurities–Si interstitials interaction in Si doped with B or Ga during ion irradiation

Substitutional impurities (B, Ga) in Si experienced an off-lattice displacement during ion-irradiationusing a H+ or He+ beam at room temperature in random incidence. Samples were prepared by solid phase epitaxy(SPE) of pre-amorphized Si subsequently implanted with B and Ga at a concentration of about1 × 1020 at. cm−3 confined in a 300 nm thick surface region. The lattice location of impurities wasperformed by a channelling technique along different axes (, ) using the 11B(p,α)8Be reaction and standard RBS for B and Ga, respectively. The normalized channelling yieldχ of the impurity signal increases with the ion fluence, indicating a progressive off-latticedisplacement of the dopant during irradiation in random incidence, until it saturates atχF<1, suggesting a non-random displacement of the dopant. In particular, atsaturation the off-lattice displacement of B and Ga was investigated byangular scanning, revealing different positions for each dopant. This effecthas been related to the interaction of impurities with the Si self-interstitials(SiI) generated by the impinging beam in the doped region.

Ultra-Shallow Junction Formation by a Non-Melting Process; Double-Pulsed Green Laser Annealing

AbstractIn order to investigate the possibility of nanosecond activation in the non-melting state, we adopted the method of double-pulsed green laser annealing (DPSS), controlling effectively the combined pulse width with two pulsed lasers (pulse duration: ˜100ns, frequency: 1kHz). We investigated the formation of ultra-shallow junctions (USJ) less than 10nm in spite of the deep penetration depth of the green wavelength in crystalline Si (˜1000nm). In order to limit the depth of B implant, a Ge pre-amorphization implant was performed at an energy of 3keV to a dose of 3E+14/cm2. After the pre-amorphization implant, a B implant was performed at 0.2kev and doses of 5E+14/cm2 and 1E+15/cm2. The implanted B dopants remain within the pre-amorphized Si layer. The double-pulsed laser irradiation was performed with a homogenized line beam of 0.1mm x 17mm, scanning a sample stage at a constant velocity of 10mm/s, that is, at an overlap ratio of 90%. The non-melting state was found to be in the pulse energy density range of E ≤ 780mJ/cm2 at a delay time of 300ns. Overcoming the issues of the short annealing time (˜&lt;1μs) and the deep penetration depth (˜1000nm), we succeeded in the ultra-shallow junction formation beyond the 45nm CMOS node: maximum junction depth of 6nm, minimum sheet resistance of 0.65kohm/sq at a B dose of 1E+15/cm2, an abruptness of 1.4nm/dec.