Impurities In Silicon Research Articles

Ab initio Computer Simulation of the Energy Parameters and the Magnetic Effects in Ternary Fe–X–C (X = Si, P, S, Cr, Mn) Systems

The equilibrium structure and the properties of ternary Fe–X–C (X = Si, P, S, Cr, Mn) systems are studied by ab initio simulation using the WIEN2k software package. The calculations are performed by the full-potential linearized augmented plane wave method (FLAPW) with allowance for the generalized gradient approximation (PBE-GGA). These methods are most accurate in terms of the density functional theory. The magnetic structure of Fe–X–C alloys and the interaction between carbon and impurity atoms at various distances are analyzed. Repulsion is detected between impurity silicon, phosphorus, and chromium atoms and carbon atoms in all three coordination shells, which significantly increases the dissolution energies of these impurities. Analogous repulsion for the first two coordination shells is also observed for the interaction of sulfur and carbon atoms, and weak attraction between these atoms appears in the third coordination shell. The interaction of carbon with manganese is characterized by attraction in the first two coordination shells, and the dissolution energies of both manganese and carbon decrease.

Mechanically Strengthened Amorphous Silicon by Phosphorus: A Molecular Dynamics Simulation and Experimental Study

The effects of phosphorus (P), one of the most common impurities in silicon(Si), on the mechanical responses of amorphous Si (a-Si) have been investigated numerically and experimentally. Tensile behaviors of P doped a-Si films were investigated using classical Molecular Dynamics(MD) simulations prescribed by Modified Embedded Atom Method(MEAM) formalism. The validity of this potential was verified by comparing our simulation results with accessible higher level calculations and experimental data. By conducting uniaxial tension simulations, it was revealed that the stiffness, yield strength and flow stress of bulk P-doped a-Si are increased, and that the ductibility of a-Si film is evidently enhanced by P. Two factors account for this observation. One goes to larger bond strength of P-Si than that of Si-Si, and the other is the higher compactness of a-Si after introducing P impurities, both of which are in good agreement with experiments. Nanoindentation technology was applied to acquire the knowledge about how P impurities influence the indentation responses of a-Si. We observed a larger stiffness and stronger resistance to nanoindentation destruction as the concentration of P grew, consistent with MD conclusions though the enhanced ductibility from MD calculations needs further work to verify.

Molecular Dynamics Investigation on the Phosphorus Doping Effects on the Mechanical Properties of Crystal Silicon

The effects of phosphorus (P), one of the most common impurities in silicon (Si), on the mechanical responses of crystal Si (c-Si) under tension are investigated using molecular dynamics with a Modified Embedded Atom Method (MEAM) potential. Tensile tests at 300K are applied for bulk c-Si with uniformly distributed and aggregated P impurities, notched c-Si films with P doping on the crack tip or at the middle of the crack propagation path. For bulk c-Si, local defects come into being around P, then rapidly nucleate and propagate, finally lead to brittle fracture. The fracture threshold decreases as the concentration increases, no matter P atoms are uniformly distributed or regionally aggregated. However, for notched c-Si film, P can evidently enhance its fracture strength by blocking the origin and propagation of cracks. With regard to Si-based micro/nano structures, fracture usually starts from the surface, indicating that P impurities play a critical role on the surface.

Electronic Raman scattering as a probe for investigating interactions between impurities in silicon

AbstractElectronic Raman scattering (ERS) is investigated as a probe for interactions between impurities in silicon. We report ERS measurements of donors (P, Sb, and As) and acceptors (B) at various concentrations and measurements at various illumination wavelengths. The difference between above and below indirect band gap measurement is discussed in terms of the difficulties of using ERS as a localised probe. We extend the previous literature on impurity interactions of Si:P in the bulk to include Sb and B and demonstrate that the perturbation of the observed ERS transition energy resulting from wavefunction overlap of nearest neighbours is opposite for donors and acceptors. Finally, we model the magnitude of the shift to the first order as a function of the mean impurity atom separation.

Влияние образования силицидов на удельное сопротивление кремния

AbstractThe effect of the formation of thin films of nickel silicides on the migration of intrinsic p -type impurities in silicon was studied for the first time. It was found that bulk resistance $${{\rho }_{{v}}}$$ of a single Si crystal increases by a factor of 3–4 if a NiSi_2 film with thickness θ ≥ 50–100 Å forms on its surface. This is attributable to the migration of boron atoms toward the silicide film. The Si layer thickness enabling measurable boron migration was estimated at 800–1000 Å.

The Influence of Sulfur, Phosphorus, and Silicon Impurities on Structure and Properties of Single Crystals of Nickel Heat-Resistant Alloys

Structural modifications in single crystals of nickel heat-resistant alloys with increased content of sulfur, phosphorous, and silicon are described. A negative influence of these impurities on long-term and fatigue strength at operating temperatures has been demonstrated using large test bases.

High-Temperature Synthesis of Al–Zr–W Aluminum-Matrix Alloys

This paper reports the preparation of Al–Zr–W aluminum-matrix alloys containing reinforcing inclusions of various phases. The alloys have been produced by the aluminothermic reduction of starting mixtures consisting of zirconium and tungsten oxides in the first stage and of baddeleyite and scheelite mineral concentrates in a second stage. According to our experimental data, the use of baddeleyite and scheelite instead of zirconium and tungsten oxides in the starting mixture produces no significant changes in the elemental composition of the alloy: the total zirconium and tungsten content of the alloy is 31–32 wt %. Characterization of the alloy prepared using the mineral concentrates has shown that the aluminum matrix contains inclusions of the Al3Zr and Al4W intermetallic phases and a small amount of the ZrN nitride. The volume fraction of the inclusions in the alloy is 32–38%. Most of the structural constituents of the alloy contain a small amount of unwanted silicon and iron impurities (~3%), which originate from the mineral concentrates. In the future, to reduce the impurity concentration we plan to use technological approaches that will ensure preliminary purification of mineral concentrates.

Obtaining of Alumino-Matrix Alloys Al-Zr, Al-Zr-W by SHS-Metallurgy Method

The paper considers conditions for the synthesis of Al-Zr and Al-Zr-W alloys under aluminothermic reduction of zirconium oxide or mineral zirconium concentrate, baddeleyite. The alloys obtained are identified as aluminomatrix basing on the results of element and X-ray phase analysis. It is shown that the alloy synthesized from baddeleyite concentrate contains small amounts of impurities of silicon and oxygen (0,5 % by weight). It is established that the alloys have a composite structure: inclusions of intermetallides Al 3 Zr and Al 4 W are distributed in the aluminum matrix, and they have the increased microhardness (7.9 and 4.5 GPa).

Interaction Between Hydrogen and Vacancy Defects in Crystalline Silicon

Hydrogen is one of the most important impurities in silicon. It is a mobile and highly reactive species that can passivate dangling bonds at dislocations, surfaces, and interfaces, which has been widely used in the microelectronics and solar cell industry for improving device performance. Vacancy defects are elementary complexes containing dangling bonds, and the study of their interaction with hydrogen is of significant importance. In this work, the interactions of hydrogen with the vacancy‐oxygen complex (VO) and the divacancy (V2) are discussed, which are the most dominant and fundamental vacancy defects stable at room temperature. It is shown that VO and V2 can interact with both atomic and diatomic hydrogen species. This complicates the interpretation of experimental data and results in different reaction paths in differently prepared samples. Besides, some of important electronic properties, particularly electronic levels for V2Hn with n > 1, are not experimentally established.

Studying the Effect of Electrically Active Impurities Coming from Trimethylgallium Synthesized by Different Means on the Electrophysical Characteristics of Gallium Arsenide Epitaxial Layers

Chemical deposition from vapors of metalorganic compounds and volatile hydrides (metalorganic vapor phase epitaxy) is the main way of growing devices’ heteroepitaxial structures based on gallium arsenide (GaAs) and solid solutions of it (AlxGa1 – xAs and InyGa1 – yAs) on an industrial scale. Electrically active impurities deposited uncontrollably on epitaxial layers during growth worsen the electrophysical parameters of devices’ structures. Sources of deposited background impurities include the initial material. In this work, ways of synthesizing trimethylgallium (TMG) are compared from the viewpoint of impurities, especially electrically active GaAs, being incorporated into the final product. Ways of preparing TMG that include the exchange reaction between gallium trichloride and trimethylaluminum (TMA) and magnesium–organic syntheses in which metallic magnesium is used as the initial reagent are selected as the objects of study. The behavior of electrically active impurities during the purification of TMG via rectification is studied. The investigations are performed by means of spectral analysis and functional control over the growth of electrophysical parameters of GaAs epitaxial layers from TMG and arsine. It is established that the qualitative and quantitative composition of impurities in TMG depends on their content in the initial reagents. TMG prepared using the exchange reaction between gallium trichloride and TMA is the source of n-type impurities in GaAs. These are mainly Group IV elements (silicon, tin, and lead), with silicon impurities predominating. TMG fabricated using metallic magnesium is a source of both p- (preferentially zinc) and n-type (preferentially silicon) impurities. Irrespective of the quality of the initial raw TMG, the use of reduced-pressure rectification allows the fabrication of TMG with low impurity contents. Epitaxial GaAs layers grown using purified TMG (TMG rectificate) have n-type conduction with a low level of background doping (0.7–4) × 1014 cm–3 and high carrier mobilities of 7300–8500 cm2/(V s) at 300 K and 90 000–156 000 cm2/(V s) at 77 K. These values correspond to purest samples made with TMG and arsine using MOC-hydride epitaxy. Based on the data on functional control, the content of impurities that display electrical activity in GaAs is on the level of 10−7–10−6 at % in fabricated TMG-rectificate samples.

Conditions for the Production of Active Aluminum Oxide Meeting the Requirements of Prospective Chloride Technology

The features of the dehydration and recrystallization processes were studied on samples of aluminum hydroxide obtained by carbonization of an aluminate solution at 40°C and isolated by Bayer’s decomposition. The main differences in the structural transformations of these samples consist in the individual sequence of the formation of polymorphic modifications of oxides in the dehydration of each aluminum hydroxide. The structural transformations of these types of hydroxide and the dynamics of the polymorphism of the decomposition products were studied in the temperature range of 100–1000°С. Data from crystallooptical, X-ray phase, and thermogravimetric methods of analysis showed that the recrystallization of the structure occurs more slowly when calcining the carbonized aluminum hydroxide than in the decomposition method. It is determined that, with the dehydration of the hydroxide, sodium aluminosilicate and carbon reduce the rate of formation of high-temperature modifications of alumina. The reactivity of aluminum oxide obtained by thermal decomposition of chemically pure sulfuric, hydrochloric, and nitric acid crystalline salts of aluminum salts is determined not only by the phase composition but also by the nature of the starting material. Despite the general morphology of the process of formation of aluminum oxide during the decomposition of the investigated crystalline hydrates, the formation of the phase composition of Al2O3 occurs at different temperatures and at different rates. Structural rearrangements during the decomposition of salts occur in the solid phase, which determines the total porosity and the specific surface area of each type of aluminum oxide. A study of the polymorphism of black alumina containing iron and silicon impurities was also carried out on samples obtained after leaching of the mineral part of the carbonaceous rocks with sulfuric, hydrochloric, and nitric acids in the temperature range of 100–1000°C. An inhibitory effect of impurities and a reducing agent on the formation of high-temperature structural modifications of aluminum oxide in the process of heat treatment of sulfuric, hydrochloric, and nitric acid crystalline hydrates of aluminum salts was revealed.

Hydrogen resist lithography and electron beam lithography for fabricating silicon targets for studying donor orbital states

Recently, phosphorous structures in silicon have been of interest theoretically and experimentally due to their relevance in the field of quantum computing. Coherent control of the orbital states of shallow donors in silicon has been demonstrated in bulk doped samples. Here we discuss the fabrication techniques required to 1) obtain patterned two dimensional dilute sheets of impurities in silicon of controlled doping densities 2) get them to act as targets for a terahertz laser. Scanning tunnelling microscope hydrogen lithography enables patterning of impurity features in silicon with a resolution from 1nm to tens of nm. Molecular beam epitaxy is used for a protective thin-film crystalline silicon growth over the impurity sheet. Electron beam lithography coupled with reactive ion etching allows features from tens to hundreds of microns to be etched into the silicon with 10 to 20nm resolution. The experimental readout is achieved via illumination of the silicon target by terahertz light and subsequent electrical detection. The electrical signal comes from coherent and non-linear excitations of the impurity electrons. This detection technique enables the precision condensed matter samples to remain intact after exposure to the free electron laser pulse.

Further investigations of the deep double donor magnesium in silicon

The deep double donor levels of substitutional chalcogen impurities in silicon have unique optical properties which may enable a spin/photonic quantum technology. The interstitial magnesium impurity (Mg$_i$) in silicon is also a deep double donor but has not yet been studied in the same detail as have the chalcogens. In this study we look at the neutral and singly ionized Mg$_i$ absorption spectra in natural silicon and isotopically enriched 28-silicon in more detail. The 1s(A$_1$) to 1s(T$_2$) transitions, which are very strong for the chalcogens and are central to the proposed spin/photonic quantum technology, could not be detected. We observe the presence of another double donor (Mg$_{i*}$) that may result from Mg$_i$ in a reduced symmetry configuration, most likely due to complexing with another impurity. The neutral species of Mg$_{i*}$ reveal unusual low lying ground state levels detected through temperature dependence studies. We also observe a shallow donor which we identify as a magnesium-boron pair.

(Invited) Deep-Level Analysis of Passivation of Transition Metal Impurities in Silicon

Experimental results on the interactions of transition metal (TM) impurities with hydrogen and on passivation by the displacement of the metals from interstitial to substitutional sites in crystalline silicon will be presented in this talk. Iron, titanium and vanadium from the 3d series, and Zr and Mo from the 4d series have been studied. The results have been obtained by means of deep level transient spectroscopy (DLTS), high resolution Laplace DLTS, minority carrier transient spectroscopy and secondary ion mass spectroscopy. The 3d metals are the most important TM series in relation to recombination in silicon. The most recombination active site is with the 3d metal in an interstitial position. It is found that in the presence of excess vacancies 3d TMs tend to move to substitutional sites and are quite stable in this position with no or much reduced recombination activity and much reduced diffusion. The experimental results on passivation of TMs with hydrogen show that in general the reactions of H atoms with TM impurities are much more effective in n-type material than in p-type Si. These findings can be easily explained considering charge states of the interacting species. Essentially the initial H-TM reaction is driven coulombically at equilibrium conditions. We have managed to promote reactions of hydrogen atoms with Fe, Mo and V impurities in p-type silicon by changing charge states of the interacting defects either by shifting the Fermi level upon the application of reverse bias to Schottky barrier diodes or by illumination of the contaminated and hydrogenated Si samples with the use of light emitting diodes with photon energies above the Si band gap energy. It has been found that the binding of hydrogen to the metal atoms, in all cases we have examined, is rather weak … of the order of 2 eV. This implies that the passivated fraction of the TMs resulting from the reaction of hydrogen with metals in bulk silicon is diminishingly small at device processing temperatures. Based on the results obtained we try to understand some of the previously published data on lifetime improvement in Si crystals by hydrogenation. In some of the commercially important cases, particularly those reporting on multi-crystalline slices, this is far from simple as other important effects such as enhanced diffusion, precipitation and gettering can take place during hydrogenation simultaneously with hydrogen-metal reactions. It appears that in some cases hydrogen-metal reactions does not seem to be the most important processes in enhancing the minority carrier lifetime of the silicon.

(Invited) Metallic Contamination Issues in Advanced Semiconductor Processing

As semiconductor devices continue to shrink, metallic contamination on silicon surfaces become to have a detrimental impact on VLSI device performance and yield. Surface metal impurities degrade gate oxide integrity [1] and cause the whisker growth in film deposition [2], while metal impurities dissolved in silicon cause recombination centers, junction leakage [3] and dark current in image sensors [4]. In this article, we have extensively reviewed metallic contamination issues including the analysis, prevention, removal, and gettering in advanced semiconductor processing. Trace metallic contamination on the silicon surfaces can be detected with VPD- or LPD-TXRF, AAS, and ICP-MS and these methods have been widely used. These analyses provide average metal concentration on the whole wafer surface with high detection sensitivity, while they do not give in-wafer distribution of metal concentration. However, metal impurities accidentally deposited in wafer processing are often localized. Direct TXRF provides in-wafer distribution of metal concentration, while its sensitivity is insufficient. Therefore, the methods to detect localized metal atoms with high sensitivity are required. TXRF following vapor phase treatment (VPT) has been developed to enhance the detection sensitivity without droplet collection [5] and the influence of VPT-induced trace particles on the detection sensitivity has been studied [6]. When III-V compound semiconductor materials are introduced for high mobility channels, the detection sensitivity on the III-V semiconductor surface by TXRF [7] and the metal collection efficiency [8] becomes critical issues. In order to control metal impurities in silicon, understanding of their penetration and diffusion behaviors is valuable. The amount of metals penetrating the silicon substrate depends on metal species, underlying films, their thickness, and annealing temperature. Cr and W penetrate the silicon substrate through the Si3N4 film more easily than through the thermally-grown SiO2 [9]. These metals on Si3N4 films must be strictly controlled before ion implantation. In-wafer distribution of recombination centers should be detected with high sensitivity and visualized with high detection sensitivity for advanced contamination control [10]. The deep energy levels, their depth profiles, and dark currents induced by metal impurities are varied with metal species [10-12]. The sensitivity of the deep level measurements should be improved. Gettering is effective to mitigate the influence of metal impurities on device characteristics. When extrinsic gettering such as ion implantation defects is used, the gettering design based on physical properties of metal species is required [13]. One of the intrinsic gettering techniques is gettering using oxide precipitates in silicon. For effective gettering by the oxide precipitates, the sufficient total surface area of the oxide precipitates should be close to the DZ [14]. Reference [1] P. S. D. Lin, J. Electrochem. Soc., 131, 1878 (1983). [2] G. M. Choi, ECS transactions, vol. 11, no. 2, p.133. [3] T. Kuroi, et. al, Tech. Digest of SSDM ’92 (1992). [4] W. C. McColgin, et.al, Mat. Res. Soc. Symp., Proc. Vol. 262, 1992 Material Research Society. [5] H. Takahara, et. al., Spectrochimica Acta Part B, 65, 1022 (2010). [6] R. Ohno and K. Saga, to be presented in 14th Symposium on Ultra Clean Processing of Semiconductor Surfaces, 2-5, Sept.2018, Leuven, Belgium. [7] K. Saga and R. Ohno, Solid State Phenomena, Vol. 255, pp 319-322 [8] H .Fontaine, T. Lardin, ECS transactions, 58 (6) 327-335 (2013). [9] K. Saga, et.al, ECS Journal of Solid State Science and Technology, 4 (5) P131-P136 (2015). [10] P. W. Mertens, et. al, Solid State Phenomena, Vol. 255, pp 309-312 [11] F. Russo, et. al, ECS J. Solid State Sci. Technol,. 6 (5), P217-P226 (2017). [12] E. Simoen, et.al, ECS Journal of Solid State Science and Technology, 5 (4) P3001-P3007 (2016). [13] K. Saga, Solid State Phenomena Vol. 187 (2012) 283-286 [14] K. Saga, et. al, ECS Journal of Solid State Science and Technology, 6 (5) P231-P234 (2017). [14] K. Saga, et. al, ECS Journal of Solid State Science and Technology, 6 (5) P231-P234 (2017).

(Invited) Deep-Level Analysis of Passivation of Transition Metal Impurities in Silicon

The transition metals (TMs) from 3d and 4d series are very effective recombination centers in silicon. They are harmful for some electronic devices and Si solar cells and should be either neutralized or removed from active areas of the devices. Some of the TMs have low diffusivities, so their gettering is difficult. In this paper we present experimental results on the interactions of transition metals with hydrogen atoms in silicon and on passivation by the displacement of the metals from the interstitial to the substitutional site. The results have been obtained by means of deep level transient spectroscopy. We have studied iron, titanium and vanadium from the 3d series, and Mo from the 4d series. It is found that in the presence of excess vacancies 3d TMs tend to move to substitutional sites and are quite stable in this position with no or much reduced recombination activity and reduced diffusion. Hydrogen reactions with TMs are found to be dependent on the charge states of the reacting species. It is shown that H-TM reactions in p-type Si can be facilitated by manipulating charge states of the reacting species using several techniques.

Addressable electron spin resonance using donors and donor molecules in silicon.

Phosphorus donor impurities in silicon are a promising candidate for solid-state quantum computing due to their exceptionally long coherence times and high fidelities. However, individual addressability of exchange coupled donors with separations ~15 nm is challenging. We show that by using atomic precision lithography, we can place a single P donor next to a 2P molecule 16 ± 1 nm apart and use their distinctive hyperfine coupling strengths to address qubits at vastly different resonance frequencies. In particular, the single donor yields two hyperfine peaks separated by 97 ± 2.5 MHz, in contrast to the donor molecule that exhibits three peaks separated by 262 ± 10 MHz. Atomistic tight-binding simulations confirm the large hyperfine interaction strength in the 2P molecule with an interdonor separation of ~0.7 nm, consistent with lithographic scanning tunneling microscopy images of the 2P site during device fabrication. We discuss the viability of using donor molecules for built-in addressability of electron spin qubits in silicon.

Dislocation etching of diamond crystals grown in Mg-C system with the addition of silicon

The dislocation structure of diamond crystals grown in the Mg-Si-C system at pressure of 7.0–7.5 GPa and temperature of 1800 °C was studied by selective etching. We determined the dislocation density and identified individual features of etching for the growth sectors of {111} and {100} faces. On the {111} faces, all etch pits formed at the outcrops of different dislocations were found to be identical. The feature of grown diamond crystals is the presence of numerous large dislocation loops in the {100} growth sectors. The identified patterns of crystals etching and the internal crystal structure features are associated with the presence of a silicon impurity in the grown diamonds.

Electron-Beam Manipulation of Silicon Dopants in Graphene.

The direct manipulation of individual atoms in materials using scanning probe microscopy has been a seminal achievement of nanotechnology. Recent advances in imaging resolution and sample stability have made scanning transmission electron microscopy a promising alternative for single-atom manipulation of covalently bound materials. Pioneering experiments using an atomically focused electron beam have demonstrated the directed movement of silicon atoms over a handful of sites within the graphene lattice. Here, we achieve a much greater degree of control, allowing us to precisely move silicon impurities along an extended path, circulating a single hexagon, or back and forth between the two graphene sublattices. Even with manual operation, our manipulation rate is already comparable to the state-of-the-art in any atomically precise technique. We further explore the influence of electron energy on the manipulation rate, supported by improved theoretical modeling taking into account the vibrations of atoms near the impurities, and implement feedback to detect manipulation events in real time. In addition to atomic-level engineering of its structure and properties, graphene also provides an excellent platform for refining the accuracy of quantitative models and for the development of automated manipulation.

Influence of a silicon impurity on growth of diamond crystals in the Mg-C system

This article reports a study of the morphology of diamond crystals grown at 7.0 GPa and 1800 °C in the Mg-C system with the addition of silicon in an amount of 0.5 wt%. Step patterns on {111} and {100} faces were studied in a wide range of magnifications using optical microscopy (DIC), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Morphological studies revealed that a reduction in the growth rate and a change in the morphological significance of the {100} and {111} faces were associated with adsorption of a mobile impurity (silicon) leading to poisoning of kinks and (or) steps. This leads to roughing of the faces and formation of macrosteps as well as 2D and 3D nucleation islands. At a silicon concentration of 1.0 wt% or more, immobile impurity particles are apparently formed on macrostep terraces, and growth inhibition occurs according to the Cabrera-Vermilyea model.