Si-B Bond Research Articles

Evaluation of the chemical states and electrical activation of ultra-highly B-doped Si1-xGex by ion implantation and subsequent nanosecond laser annealing

Given that transistordimensions are approaching atomic scale in metal–oxide–semiconductor field-effect-transistors (MOSFETs), attaining low-contact resistivity (ρc) between contact-metal and Si is a primary challenge for source/drain (S/D) fabrications. To reduce ρc, it is necessary to increase active dopant concentration in the semiconductor region underneath the contact-metal. High-dose ion-implantation and nanosecond laser-annealing (NLA) have been intensively investigated to produce highly activated layers in S/D regions. Particularly for the B-doped SiGe layers, which are used as S/D stressor for p-MOSFETs, non-substitutional B species are generated in the highly doped films at concentrations exceeding ∼ 1021 cm−3. These non-substitutional B are electrically non-activated and thus should be minimized to reduce ρc. In this study, we investigated the chemical states and electrical activation in highly B-doped SiGe layer. Using X-ray photoelectron spectroscopy (XPS), we examined the substitutionality of B-atoms and identified new chemical states of Si-B and Ge-B bonds in Si 2p and Ge 3d peaks. In the B 1s spectra, electrical activation states are determined by quantifying relative area ratios of the active/inactive B peaks, which are well matched with activation rates calculated by Hall measurements. Our findings systematically explained the activation behavior of NLA-treated B-doped SiGe films in high B-concentration ranges.

First-principles study of effect of impurity compensation on optical properties of Si

Presently, impurity-compensated silicon (Si) has no clear potential applications due to high resistance and few carriers. Thus, it has received little attention from researchers. In this study, we find that impurity compensation can make localized state energy levels form in Si bandgap, which can improve the light absorption of Si in the near infrared region. In this work, in order to comprehensively and deeply understand the photoelectric properties of impurity-compensated Si, the localized state energy levels composed of P<sup>+</sup>/B<sup>–</sup> ions are constructed in Si bandgap through the co-doping of phosphorus (P) and boron (B), thereby forming impurity-compensated Si. The first-principles based on a density functional theory framework is used to study the photoelectric properties of the impurity-compensated Si (n/p-Sic) such as the density of states (DOS), dielectric function and refractive index. The DOS study reveals the following results: after the n- and p-Si with the same concentration of P and B (12.5%) are fully compensated for by impurities, the Fermi energy levels of their compensated counterparts are at the valley bottom formed by the two adjacent DOS peaks, and the DOS is not zero at the valley bottom. In the study of dielectric function and refractive index, it is found that when the doping ratio is <i>C</i><sub>B</sub>/<i>C</i><sub>P0</sub> = 0.25, n-Sic has the largest dielectric function and refractive index in the low energy region. In addition, comparing intrinsic Si with its doped counterparts in the real part (Re) of their dielectric constant, the following regularity is found: in the high energy region of <i>E</i> > 4 eV, the Re values of the intrinsic Si, n/p-Si and p-Sic are negative. In the low energy region of 0.64 eV< <i>E</i> < 1.50 eV, the Re value of n-Sic is negative for the doping ratio of <i>C</i><sub>B</sub>/<i>C</i><sub>P0</sub> = 0.25. The above comparison indicates that the n-Sic with <i>C</i><sub>B</sub>/<i>C</i><sub>P0</sub> = 0.25 can achieve good metallicity in the low energy region, indicating that the electrons in valence band are easily excited by low-energy long-wavelength light. Theoretical studies show that the good photoelectric properties of n-Sic with <i>C</i><sub>B</sub>/<i>C</i><sub>P0</sub> = 0.25 may be related to Si dangling bonds and localized state energy levels in Si bandgap. The Si dangling bonds are caused by the impurity compensation of B dopant for n-Si, leading part of Si-Si bonds to change into Si-B bonds. This study provides theoretical guidance for the application of impurity-compensated Si in the field of photodetectors such as CMOS image sensors and infrared photodetectors.

Advances in disilylation reactions to access cis/trans-1,2-disilylated and gem-disilylated alkenes.

Organosilane compounds are widely used in both organic synthesis and materials science. Particularly, 1,2-disilylated and gem-disilylated alkenes, characterized by a carbon-carbon double bond and multiple silyl groups, exhibit significant potential for subsequently diverse transformations. The versatility of these compounds renders them highly promising for applications in materials, enabling them to be valuable and versatile building blocks in organic synthesis. This review provides a comprehensive summary of methods for the preparation of cis/trans-1,2-disilylated and gem-disilylated alkenes. Despite notable advancements in this field, certain limitations persist, including challenges related to regioselectivity in the incorporation and chemoselectivity in the transformation of two nearly identical silyl groups. The primary objective of this review is to outline synthetic methodologies for the generation of these alkenes through disilylation reactions, employing silicon reagents, specifically disilanes, hydrosilanes, and silylborane reagents. The review places particular emphasis on investigating the practical applications of the C-Si bond of disilylalkenes and delves into an in-depth discussion of reaction mechanisms, particularly those reactions involving the activation of Si-Si, Si-H, and Si-B bonds, as well as the C-Si bond formation.

Cleavage anisotropy of boron doped cracks in crystalline silicon

We demonstrate a density functional theory (DFT) research on the modified cleavage anisotropy in crystalline silicon (c-Si) by impurity boron (B). Three representative cracks, (1 1 1)[1 1¯ 0], (1 1 0)[0 0 1] and (1 1 0)[1 1¯ 0] with B atoms located at the crack front, are investigated. The anisotropic behaviors are characterized by the stability (or lattice trapping) of the cracks subjected to Mode I load. Results show that B performs rather inconsistently in different cracks. The upper lattice trapping limit of the B implanted (1 1 1)[1 1¯ 0] crack is largely increased, indicating that it is more difficult to propagate. This is principally because B promotes the transition of the fracture surface from Haneman reconstruction to Pandey reconstruction which is structurally more stable. In comparison, the B-doped (1 1 0) [0 0 1] crack propagates more easily because B is energetically favored at the valley site of the reconstructed (1 1 0) fracture surface, thus making the SiB bond at the crack front easier to break. As for the (1 1 0) [1 1¯ 0] crack, B weakens the neighboring SiSi bonds, consequently inclines the propagation from (1 1 0) plane to adjacent (1 1 1) plane.

Reaction of BCl3 with H- and Cl-terminated Si(1 0 0) as a pathway for selective, monolayer doping through wet chemistry

The reaction of boron trichloride with the H- and Cl-terminated Si(100) surfaces was investigated to understand the interaction of this molecule with the surface for designing wet chemistry-based silicon surface doping processes using a carbon- and oxygen-free precursor. The process was followed with X-ray photoelectron spectroscopy (XPS). Within the reaction conditions investigated, the reaction is highly effective on Cl-Si(100) for temperatures below 70 °C, at which point both surfaces react with BCl3. The XPS investigation followed the formation of a B 1s peak at 193.5 eV corresponding to (B-O)x species. Even the briefest exposure to ambient conditions lead to hydroxylation of surface borochloride species. However, the Si 2p signature at 102 eV allowed for a confirmation of the formation of a direct Si-B bond. Density functional theory was utilized to supplement the analysis and identify possible major surface species resulting from these reactions. This work provides a new pathway to obtain a functionalized silicon surface with a direct Si-B bond that can potentially be exploited as a means of selective, ultra-shallow, and supersaturated doping.

Structural evolution of in situ boron-doped SiGe ultrathin film analyzed by multi-optical methods

In situ boron (B)-doped SiGe (BSG) layer is extensively used in the source (S)/(D) drain of metal-oxide-semiconductor field-effect transistors. An unexpected structural evolution occurs in BSG during metallization and activation annealing during actual fabrication, which involves a correlated interaction between B and SiGe. Herein, the complicated phenomena of the structural evolution of BSG were analyzed by 325 nm micro-Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), reflective second harmonic generation (RSHG), and synchrotron x-ray diffraction (XRD). Optical inspection was integrated into these processes to establish a multi-optical method. 325 nm micro-Raman spectroscopy was used to determine variations in Si–Si, Si–Ge, and Ge–Ge bonds in BSG. XPS exhibited the binding energy evolution of Ge3d during different annealing processes at varied Ge ratios and B concentrations. RSHG revealed the polar Si-B and Ge-B bonds formed during annealing. Synchrotron XRD provided the structure and strain changes of BSG. Secondary-ion mass spectrometer profiles provided the species distribution, which was used to examine the results of multi-optical method. Furthermore, double-layered BSG (DBSG) with different B concentrations were analyzed using the multi-optical method. Results revealed that Ge aggregated in the homogeneous interface of DBSG, and that B dopants in BSG served as carrier providers that strongly influenced the BSG structure. However, BSG with excessive B concentration was unstable and increased the B content (SiB3) through metallization. For BSG with a suitable B concentration, the formation of Si–B and Ge–B bonds suppressed the diffusion of Ge from SiGe, thereby reducing the possibility of Ge loss and further B pipe-up in the heavily doped S/D region.

In Situ Generation of Silyl Anion Species through Si-B Bond Activation for the Concerted Nucleophilic Aromatic Substitution of Fluoroarenes.

In situ generated silyl anion species enable the concerted nucleophilic aromatic substitution of fluoroarenes. Model DFT calculations indicated that addition of a base to a silylborane would thermodynamically form a silyl borate complex and then kinetically release a silyl anion species through Si-B bond cleavage, and that the in situ generated silyl anion equivalent would further react with a fluoroarene through a concerted nucleophilic aromatic substitution pathway with an activation barrier of ca. 20 kcal/mol to afford the silylated product with a large energy gain. Experiments confirmed that the defluorosilylation reaction took place smoothly at room temperature simply upon mixing fluoroarenes with commercially available silylborane and NaOt Bu. Radical scavenger and radical clock reaction experiments provide further evidence for the in situ generation of the silyl anion.

Reduction of Carbon Oxides by an Acyclic Silylene: Reductive Coupling of CO.

Reactions of a boryl-substituted acyclic silylene with carbon dioxide and monoxide are reported. The former proceeds through oxygen atom abstraction, generating CO (with rearrangement of the putative silanone product through silyl-group transfer). The latter is characterized by reductive coupling of CO to give an ethynediolate fragment, which undergoes formal insertion into the Si-B bond. The net conversion of carbon dioxide with two equivalents of silylene offers a route for the three-electron reduction of CO2 to [C2 O2 ]2- .

Cr5Si3B and Hf5Si3B: New MAB phases with anisotropic electrical, mechanical properties and damage tolerance

Through a combination of electronic structure, chemical bonding and mechanical property investigations, anisotropic electrical and mechanical properties, and damage tolerant ability of MAB phases Cr5Si3B and Hf5Si3B are predicted. The anisotropic electrical conductivity is due to the anisotropic distribution of Cr in Cr5Si3B and Hf in Hf5Si3B, which mainly contribute to the electrical conductivity. The anisotropic mechanical properties are underpinned by the anisotropic chemical bonding within the crystal structures of Cr5Si3B and Hf5Si3B. The high stiffness is determined by the strong covalent-ionic Cr1BCr1 and Cr1Si bonds in Cr5Si3B and the ionic-covalent Hf1BHf1 and SiB bonds in Hf5Si3B; while the low shear deformation resistance is attributed to the presence of metallic CrCr, HfHf and SiSi bond. Based on the low Pugh’s ratio, Cr5Si3B and Hf5Si3B are predicted tolerant to damage. The possible cleavage plane is (0001) and the possible slip systems are <1 1¯00>|{11 2¯0} and <11 2¯0>|{0001} for both Cr5Si3B and Hf5Si3B.

Damage and annealing recovery of boron-implanted ultra-shallow junction: The correlation between beam current and surface configuration

Abstract The condition of the beam current in the implantation process is a key issue in the damage rate and structural evolution in the sequent annealing process, especially for ultra-shallow layers. In this work, we develop a compensative optical method combined with UV Raman, X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge spectroscopy (XANES) to inspect the influence of the beam current in the implantation process. The optima condition of the beam current in the implantation process is determined by higher effective Si-B bond portion in UV Raman spectra and less the peak of B–B bond in XPS spectra which is caused by B cluster defects. Results of XANES indicate that the B oxide layer is formed on the surface of the ultra-shallow junction. The defects in the ultra-shallow junction after annealing are analyzed by novel optical analyses, which cannot be inspected by a traditional thermal wave and resistance measurement. This work exhibits the structural variation of the ultra-shallow junction via a variant beam current and provides a valuable metrology in examining the chemical states and the effective activation in the implantation technology.

The chemical states and atomic structure evolution of ultralow-energy high-dose Boron implanted Si(110) via laser annealing

Further scale down the dimension of silicon-based integrated circuit is a crucial trend in semiconductor fabrication. One of the most critical issues in the nano-device fabrication is to confirm the atomic structure evolution of the ultrathin shallow junction. In this report, UV Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and reflective second harmonic generation (RSHG) are utilized to monitor the pulse laser induced atomic structure evolution of ultralow-energy high-dose Boron implanted Si(110) at room and cold substrate temperature. A peak feature around 480 cm−1 resolved in UV Raman spectra indicates the formation of Si-B bond after the laser irradiation. The red shift of binding energy of Si element (~99 eV) in XPS and the evolution of absorption peak (~196.2 eV) in XANES reveal that the changes in the chemical states of ultra shallow junction strongly correlate to the activation process of Boron implantation, which is confirmed by RSHG measurement. The substrate temperature effect in the recrystallization of Boron implanted region is also realized by cross-section high-resolution TEM (HRTEM). The phenomena of Si-B bond formation and ultra-shallow junction recrystallization can be traced and applied to improve the reliability of Si ultra shallow junction in the future.

Mn@B3N3Si8 +: a stable singlet manganese-doped hetero-atom-mixed silicon fullerene

A B3N3Si8 cage is formed upon substitution of Si sites of rhombus faces of the pure Si14 cluster by B and N atoms. Doping by the ion Mn+ leads to the hetero-silicon fullerene B3N3Si8Mn+ which comprises three rhombi (BNBN, Si3B and Si3N) and four pentagons (two Si2B2N and two Si2BN2). Hetero-atoms form polarized Si-N and Si-B bonds as indicated by electron localization function (ELF) maps and NBO charges. The Mn center connects the B3N3Si8 cage by ionic interactions. Valence electrons of B3N3Si8Mn+ occupy a shell configuration of [1S2 1P6 1D10 1F14 1G12 2S2 2P6 2D10] and induce a certain thermodynamic stability. The high spin of the Mn+ metal cation is completely quenched within the hetero-Si fullerene.

Trapping Experiments on a Trichlorosilanide Anion: a Key Intermediate of Halogenosilane Chemistry.

Treatment of Si2Cl6 with [Et4N][BCl4] in CH2Cl2 furnished the known products of a chloride-induced disproportionation reaction of the disilane, such as SiCl4, [Si(SiCl3)3]-, and [Si6Cl12·2Cl]2-. No Si-B-bonded products were detectable. In contrast, the addition of Si2Cl6 to [Et4N][BI3Cl] afforded the Si-B adduct [Et4N][I3SiBI3]. Thus, a quantitative Cl/I exchange at the silicon atom accompanies the trihalogenosilanide formation. [Et4N][I3SiBI3] was also accessible from a mixture of Si2I6, [Et4N]I, and BI3. According to X-ray crystallography, the anion [I3SiBI3]- adopts a staggered conformation with an Si-B bond length of 1.977(6) Å. Quantum-chemical calculations revealed a polar covalent Si-B bond with significant contributions from intramolecular I···I dispersion interactions.

Formation of the Si-B bond: insertion reactions of silylenes into B-X(X = F, Cl, Br, O, and N) bonds.

The insertion reactions of the silylene H2Si with H2BXHn-1 (X = F, Cl, Br, O, N; n = 1, 1, 1, 2, 3) have been studied by DFT and MP2 methods. The calculations show that the insertions occur in a concerted manner, forming H2Si(BH2)(XHn-1). The essences of H2Si insertions with H2BXHn-1 are the transfers of the σ electrons on the Si atom to the positive BH2 group and the electrons of X into the empty p orbital on the Si atom in H2Si. The order of reactivity in vacuum shows the barrier heights increase for the same-family element X from up to down and the same-row element X from right to left in the periodic table. The energies relating to the B-X bond in H2BXHn-1, and the bond energies of Si-X and Si-B in H2Si(BH2)(XHn-1) may determine the preference of insertions of H2Si into B-X bonds for the same-column element X or for the same-row element X. The insertion reactions in vacuum are similar to those in solvents, acetone, ether, and THF. The barriers in vacuum are lower than those in solvents and the larger polarities of solvents make the insertions more difficult to take place. Both in vacuum and in solvents, the silylene insertions are thermodynamically exothermic. Graphical Abstract The insertion process of H2Si and H2BXHn-1(X = F, Cl, Br, O, and N; n = 1, 1 , 1, 2, 3).

Boron Oxygen Pair Effect in p+ Emitter and Nanosized Boron Rich Layer by Fold Coordination Analysis for Crystalline Silicon Solar Cell Applications.

N-type substrates possess better material characteristics than p-type substrates for high efficiency mass producible Si solar cells with HIT, IBC structures. The major drawbacks of these structures are a complicated fabrication process and an expensive unit cost. In this paper, the boron emitter doping profile of a nanosized boron rich layer (BRL), for which the boron and oxygen concentrations are correlated, is optimized to fabricate high efficiency solar cells on an n-type substrate. Boron doping was carried out using a BBr3 furnace with varying oxygen gas ratios and the surface was treated with acid etching. The effect of the oxygen on the nanosized BRL was analyzed using both FTIR spectroscopy and XPS, where by conductivity and the Si-B bond were observed for the three-fold and four-fold coordinated borons, respectively. The results showed that the oxygen quantities in the boron doped emitter and the nanosized BRL affected the characteristics of the solar cell. Regarding the solar cells that were fabricated using the boron emitter and shallow emitter (90 ohm/sq) processes, the open-circuit voltage increased by 54 mV and the short circuit current (J(sc)) increased by 3.7 mA/cm2. The J(sc) increase was due to an increased quantum efficiency in the short wavelength range. The shallow emitter etch back process minimized the boron-oxygen defects in the doping profile.

Cu(II)-Catalyzed Allylic Silylation of Morita–Baylis–Hillman Alcohols via Dual Activation of Si–B Bond and Hydroxyl Group

The reaction of Morita-Baylis-Hillman (MBH) alcohols with Me2PhSiBpin under the catalysis of Cu(OTf)2/pyridine in methanol has been developed. The direct silylation of allylic alcohols via dual activation of the Si-B bond and the hydroxyl group of the MBH alcohol provides an efficient and convenient method for the synthesis of functionalized allylsilanes.

ChemInform Abstract: Asymmetric Synthesis of α‐Chiral Allylic Silanes by Enantioconvergent γ‐Selective Copper(I)‐Catalyzed Allylic Silylation.

Gamma way: Regio- and enantioselective allylic substitution with a silicon nucleophile generated by copper(I)-catalyzed Si-B bond activation provides direct access to α-chiral allylic silanes from linear acceptors. The enantioconvergent catalysis employing McQuade's six-membered N-heterocyclic-carbene-copper(I) catalyst is applicable to aryl- and alkyl-substituted allylic phosphates (see scheme).

Asymmetric Synthesis of α‐Chiral Allylic Silanes by Enantioconvergent γ‐Selective Copper(I)‐Catalyzed Allylic Silylation

Gamma way: Regio- and enantioselective allylic substitution with a silicon nucleophile generated by copper(I)-catalyzed Si-B bond activation provides direct access to α-chiral allylic silanes from linear acceptors. The enantioconvergent catalysis employing McQuade's six-membered N-heterocyclic-carbene-copper(I) catalyst is applicable to aryl- and alkyl-substituted allylic phosphates (see scheme).

The [formula omitted] surface reconstruction of alkali/Si(1 1 1):B semiconducting surfaces

The surface structure of alkali doped Si(111):B ultra-thin films has been studied by low-energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). A comparative study of K/Si(111)-3×1 and K/Si(111):B-23×23R30 interfaces allowed us to determine the saturation coverage to be 0.5 monolayer in the later case. The 23-surface reconstruction is shown to be a common property of pure K, Rb, Cs materials and K0.4Rb0.6 alloys but progressively disappears if Rb is replaced by Ca. Taking into account the existence of two distinct boron sites in the ratio 1/3 as seen from B-1s core levels spectra, LAPW-DFT calculations have been carried out in order to optimize the atomic structure. As a result, alkali adatoms are shown to form trimers leading to a large modulation of the SiB bonds accompanied by an inhomogeneous doping of the dangling bonds in agreement with voltage dependent STM images.

Copper(I)-Catalyzed Regioselective Propargylic Substitution Involving Si–B Bond Activation

The silicon nucleophile generated by copper(I)-catalyzed Si-B bond activation allows several γ-selective propargylic substitutions. The regioselectivity (γ:α ratio) is strongly dependent on the propargylic leaving group. Chloride is superior to oxygen leaving groups in linear substrates (γ:α > 99:1), and it is only the phosphate group that also shows promising regiocontrol (γ:α = 90:10). That leaving group produces superb γ-selectivity (γ:α > 99:1) in α-branched propargylic systems, and enantioenriched substrates react with excellent central-to-axial chirality transfer.