Si Samples Research Articles

Effectiveness of tungsten addition on the performance of electroplated nickel diffusion barriers for copper metallization on textured silicon

In this work, the nickel-tungsten alloy is used as the diffusion barrier for copper metallization on textured silicon. Nickel silicides formed as the seed layer for the nickel-tungsten alloy. Then, copper metallization was performed by an electroplating method to create the Cu/NiW/NiSiy/Si structure. The Cu/NiW/NiSiy/Si samples were annealed at various temperatures for 10 minutes in an annealing furnace under Ar/H2 atmospheres. The annealed Cu/NiW/NiSiy/Si samples were characterized by X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy. For the Cu/NiW/NiSiy/Si samples with NiW thicknesses of 300 nm and 350 nm, the Cu3Si phase developed at annealing temperatures of 500 °C and 600 °C, respectively. The NiW layer is a better diffusion barrier against copper than the Ni layer.

Reducing the uncertainty caused by the laser spot radius in frequency-domain thermoreflectance measurements of thermal properties.

In a frequency-domain thermoreflectance (FDTR) experiment, the phase lag between the surface temperature response and the applied heat flux is fit with an analytical solution to the heat diffusion equation to extract an unknown thermal property (e.g., thermal conductivity) of a test sample. A method is proposed to reduce the impact of uncertainty in the laser spot radius on the resulting uncertainty in the fitted property that is based on fitting to the quotient of the test sample phase and that of a reference sample. The reduction is proven analytically for a semi-infinite solid and was confirmed using numerical and real experiments on realistic samples. When the spot radius and its uncertainty are well known, the reference phase can be generated numerically. In this situation, FDTR experiments performed on Au-SiO2-Si and PbS nanocrystal test samples demonstrate 32% and 82% reductions in the overall uncertainty in thermal conductivity. When the spot radius used in the test sample measurement is not well known, a real reference sample, measured under conditions that lead to the same unknown spot radius, is required. Although the real reference sample introduces its own uncertainties, the total uncertainty in the fitted thermal conductivity can still be reduced. A reference sample can also be used to reduce uncertainty due to other sources, such as the transducer properties. Because frequency-domain solutions to the heat diffusion equation are the basis for time-domain thermoreflectance (TDTR) analysis, the approach can be extended to TDTR experiments.

Study of high–low KPFM on a pn-patterned Si surface

Comparative measurements between frequency modulation Kelvin probe force microscopy (FM-KPFM) using low frequency bias voltage and heterodyne FM-KPFM using high frequency bias voltage were performed on the surface potential measurement. A silicon substrate patterned with p- and n-type impurities was used as a quantitative sample. The multi-pass scanning method in the measurements of FM-KPFM and heterodyne FM-KPFM was used to eliminate the effect of the tip–sample distance dependence. The measured surface potentials become lower in the order of the p-type region, n-type region and n+-type region by both FM-KPFM and heterodyne FM-KPFM, which are in good agreement with the order of the work functions of the pn-patterned Si sample. We observed the difference in the surface potentials due to the surface band bending measured by FM-KPFM and heterodyne FM-KPFM. The difference is due to the fact that the charge transfer between the surface and bulk levels may or may not respond to AC bias voltage.

Microstructure and morphology of Si crystals grown in pure Si and Al–Si melts

Microstructure of Al-40 wt%Si samples solidified in electromagnetic levitation furnace is studied at high melt undercooling. Primary Si with feathery and dendritic structures is observed. As this takes place, single Si crystals either contain secondary dendrite arms or represent faceted structures. Our experiments show that at a certain undercooling, there exists the microstructural transition zone of faceted to non-faceted growth. Also, we analyze the shape of dendritic crystals solidifying from liquid Si as well as from hypereutectic Al–Si melts at high growth undercoolings. The shapes of dendrite tips grown at undercoolings >100 K along the surface of levitated Al-40 wt%Si droplets are compared with pure Si dendrite tips from the literature. The dendrite tips are digitized and superimposed with theoretical shape function recently derived by stitching the Ivantsov and Brener solutions. We show that experimental and theoretical dendrite tips are in good agreement for Si and Al–Si samples.

Integrative RNA-Seq analysis of Capsicum annuum L.-Phytophthora capsici L. pathosystem reveals molecular cross-talk and activation of host defence response.

The online version contains supplementary material available at 10.1007/s12298-021-01122-y.

Magnetic Phase Diagram of the MnxFe2-xP1-ySiy System.

The phase diagram of the magnetocaloric MnxFe2−xP1−ySiy quaternary compounds was established by characterising the structure, thermal and magnetic properties in a wide range of compositions (for a Mn fraction of 0.3 ≤ x < 2.0 and a Si fraction of 0.33 ≤ y ≤ 0.60). The highest ferromagnetic transition temperature (Mn0.3Fe1.7P0.6Si0.4, TC = 470 K) is found for low Mn and high Si contents, while the lowest is found for low Fe and Si contents (Mn1.7Fe0.3P0.6Si0.4, TC = 65 K) in the MnxFe2−xP1−ySiy phase diagram. The largest hysteresis (91 K) was observed for a metal ratio close to Fe:Mn = 1:1 (corresponding to x = 0.9, y = 0.33). Both Mn-rich with high Si and Fe-rich samples with low Si concentration were found to show low hysteresis (≤2 K). These compositions with a low hysteresis form promising candidate materials for thermomagnetic applications.

Effects of interfacial oxide layer formed by annealing process on WORM characteristics of Ag/CuxO/SiOx/n+–Si devices

In this paper, we investigate the effects of a SiOx interfacial layer on ON/OFF current ratios, endurance characteristics and read-disturb immunities of Ag/CuxO/SiOx/n+-Si write-once-read-many-times (WORM) memories. The CuxO active layers were prepared using a sol-gel process. After coating CuxO films on n+-Si substrates, the CuxO/n+-Si samples were annealed in air at 400 ℃ and 600 ℃, respectively, to obtain a SiOx interfacial layer at the CuxO/n + -Si interfaces. The 400 ℃-annealed CuxO device shows an ON/OFF current ratio of 104. However, degradation of OFF state current (IOFF) with increasing read-pulse cycles and stress time is observed. For the 600 ℃-annealed CuxO device, stable ON and OFF state currents can be observed both in an endurance test for over 1.2 × 104 read cycles and in a read-disturb test for 2 × 104 s. Moreover, a higher ON/OFF current ratio of 107 is obtained. A rigorous retention test executed at an elevated temperature of 85 ℃ indicates that the data retention time is expected to last for 10 years. The performance improvement of the 600 ℃-annealed CuxO device is due to an increase in the thickness of the SiOx interfacial oxide layer. The mechanism for the influence of the interfacial layer on memory performance is investigated and illustrated. The OFF state current of the memory is limited by hopping and trap-assisted tunneling transport in the SiOx interfacial layer. In the ON state, conductive paths in the device cause that the carriers can easily migrate by Ohmic and space charge limited conduction.

Evaluation of the accuracy of stopping and range of ions in matter simulations through secondary ion mass spectrometry and Rutherford backscattering spectrometry for low energy heavy ion implantation

The freely available “Stopping and Range of Ions in Matter” (SRIM) code is used for evaluating ion beam ranges and depth profiles. We present secondary ion mass spectrometry and Rutherford backscattering experimental results of Si samples implanted with low energy Sb ions to evaluate the accuracy of SRIM simulations. We show that the SRIM simulation systematically overestimates the range by 2–6 nm and this overestimation increases for larger ion implantation energy. For the lowest energy implantation investigated, here we find up to a 25% error between the SRIM simulation and the measured range. The ion straggle shows excellent agreement between simulation and experimental results.

Optimization of tungsten-doped high density carbon target in inertial confinement fusion

A tungsten (W)-doped high density carbon (HDC) target is a promising design for an ignition target in inertial confinement fusion (ICF). The influence of silicon (Si) and W on the transmission of M-band x-ray has been studied by experiment. With a radiation temperature of ∼200 eV, the transmitted M-band x-ray (1.6–4.4 keV) flux and spectrum of Si or W-buried HDC sample were measured by M-XRDs and TGS, respectively. The thin layer of Si or W was buried at two different depths (2.1 μm and 11 μm). Results show that M-band transmission flux of Si-buried HDC sample decreases with buried depth (bd). However, bd does not influence that of the W-buried HDC sample. The one-dimensional simulation result is consistent with the experimental result. In the 1D simulation, the Au M-band (2–5 keV) transmission flux of Si-buried HDC also decreases with bd. However, the Au M-band transmission flux of W-buried HDC increases at first and then decreases. This is mainly due to the different characteristics of Si and W opacity. Especially as the peak radiation temperature reaches 260 eV, W can still absorb the M-band x-ray efficiently as it is buried near the radiation source. Based on these studies, an optimized W-doped HDC target with low doped fraction and mass has been proposed in this paper.

Drift of two-dimensional vacancy islands on the Si(100) surface under electromigration conditions

The paper presents an experimental study of morphological changes of the Si(100) surface under electromigration conditions that was carried out using the in situ method involving ultrahigh vacuum reflection electron microscopy. The study aims to determine the temperature dependence of the effective electric charge of an adsorbed atom on the Si(100) surface. A system of concentric two-dimensional vacancy islands was formed on the surface of Si(100) samples by low-energy argon ion sputtering and subsequent high-temperature annealing. Quasi-equilibrium conditions were created on the sample surface by compensating the sublimating flow from the surface from an external silicon source. The video images of the drift of vacancy islands were recorded under the conditions of electromigration with the compensation of sublimation. Based on the processing and analysis of video images, the authors described the dependence of the velocity of motion of vacancy islands on the Si(100) surface for various temperatures and the direction of the electric current along and across the dimer rows with the (2 × 1) superstructure inside the island. It is shown that the drift rate of vacancy islands does not depend on their size under quasi-equilibrium conditions. A simplified one-dimensional theoretical model has been constructed. It includes one atomic step moving by a detachment of atoms from the step and their drift under the force of electromigration in the absence of desorption and deposition of atoms on the surface. Based on the proposed model, the effective electric charge is estimated, and the temperature dependence of the effective charge in the temperature range of 1010 to 1120 °C is obtained. The absolute value of the effective charge decreases linearly with increasing temperature. The sign of the effective charge is negative, and its average value is Z = –0.5 ± 0.3 elementary charges. The obtained results can be used for creating structures with a countable number of atomic steps and act as secondary measures of height with reference to the silicon crystal lattice.

Abnormal diffusion profile of adatoms on extremely wide terraces of the Si(111) surface

The authors experimentally studied the distribution of the adatom concentration on extremely wide terraces of the Si(111) surface whose dimensions are comparable with the diffusion length of adatoms. The extremely wide terraces were created during in situ experiments carried out by ultrahigh vacuum reflection electron microscopy by high-temperature annealing of Si(111) samples (more than 1000 °C) followed by rapid cooling to 750 °C to form 7 × 7 superstructure domains. A detailed analysis of the surface morphology of the terraces was carried out by ex situ atomic force microscopy under ambient conditions. Based on high-resolution (1.2 nm/pixel) atomic force microscopy images, panoramic topographic images of the terraces were formed. Digital processing of the panoramic images visualized the distribution of the adatom concentration n. For a terrace cooled from 1070 °C, central terrace regions show minimum n values around 0.13 BL (1 bilayer (BL) = 1.56×1015 cm−2); close to the monatomic step bordering the terrace, n increases to about 0.14 BL. The authors determined that this radial distribution n(r) at 1070 °C corresponds to the adatom diffusion coefficient D = 59 ± 12 μm2/s. It was found that, for a terrace cooled from 1090 °C, the approach assuming the same adatom diffusion length over the entire terrace does not describe the experimental n(r) distribution. For its analysis, the authors used the solution of the stationary diffusion equation under the assumption that D is not constant. Based on a numerical solution, the dependence of D on the experimentally measured n values was obtained. Under the assumption that adatom lifetime does not depend on n at 1090 °C, the adatom diffusion coefficient was found to decrease from 140 μm2/s at n = 0.093 BL (in the central terrace regions) to 5 μm2/s at n = 0.118 BL (near the step). The results of this work experimentally demonstrated that the control over adatom concentration can be used to significantly vary the diffusion properties of the adsorption layer on the crystal surface.

Mechanically activated zero-valent silicon by coating silica to decolorize Acid Red 73 dye

For the treatment of various contaminants involving the reduction action, utilization of zero-valent silicon (ZVS) may be expected due to its higher reactivity than zero-valent iron (ZVI) which has been predominantly investigated. However, the higher reactivity also means the easier passivation of ZVS, to which new approaches are required to prepare an active ZVS sample. In this study, a novel composite material consisting of microscale ZVS and silica was prepared by one-step mechanical ball milling. Such an easy operation of co-grinding allowed the generation of active ZVS sample through coating silica layer on the newly-generated surface of ZVS particles, which could prevent the easy passivation to lose reactivity when exposed to air. Typical experimental conditions for preparing active ZVS were: the mass ratio of ZVS to silica of 50 wt%, milling parameters with speed at 600 rpm and time for 60 min. A nearly complete decolorization of AR73 at a concentration of 100 mg/L was achieved by using the sample dosage at 2 g/L and stirring for 120 min. Results from this study suggest that tremendous amounts of Si sample from the solar cell after the termination of service life could serve as raw sample for preparing active reductive agents to deal with various contaminants, offering alternative to ZVI with high potentials for environmental remediation.

Spurious grain formation due to Marangoni convection during directional solidification of alloys in µ-g environment of International Space Station

During directional solidification of alloys in the microgravity environment of the International Space Station (ISS), growth of dendritic array is expected to be under purely diffusive transport conditions. The resulting microstructure is expected to make up uniformly arranged primary dendrites on sample cross-sections without any defects, such as macrosegregation and spurious (misoriented) grains. However, spurious grains have been seen in recently directionally solidified Al-7 wt% Si samples under the joint NASA-ESA project (MICAST) and also in SCN-0.24 wt% H2O samples grown under the NASA-PFMI project. Careful examination of both these experiments shows the presence of voids at the melt-crucible interface which are the likely source of the convective flows responsible for the fragmentation of dendrite-side arms, and their rotation which creates the nucleus for the spurious grains. In this paper, we assume that side-arm of a primary dendrite has gotten detached from the primary trunk during remelting and isothermal hold, prior to the onset of directional solidification on the Space Station, in the vicinity of a pore at the melt-crucible interface. We numerically simulate the influence of the Marangoni convection on the trajectory of such a dendrite fragment in the alloy melt and compare with the experimental observations. The experimentally observed rotation behavior of the fragmented side-arm in transparent SCN-0.24 wt% H2O, observed from the PFMI video, shows a good agreement with simulation results. The predicted rotational speeds of broken-off secondary arm in the Al-7 wt% Si (MICAST) samples is significantly higher than those in the SCN-0.24 wt% H2O (PFMI). The strength of the convection is dependent on the Marangoni Number and location of the surface pore relative to the Mushy zone. Marangoni convection is strong enough to force the rotation of broken-off side arms and should be considered an important source of microstructural inhomogeneity during terrestrial solidification processing applications.

Electroluminescence in plasmonic actuator based on Au/SiO2/n-Si tunnel junction

AbstractA compact electrical source capable of generating surface plasmon polaritons would represent a crucial step for on-chip plasmonic circuitry. The device fabrication of plasmonic actuator based on Au/SiO2/n++Si tunnel junction and performance have been reported in [ACS photonics, 2021, 8, 7, 1951–1960]. This work focuses on the underlying mechanisms of electroluminescence. The n-type Si samples were doped with concentrations ranging from 1.6 × 1015 cm−3to 1.0 × 1020 cm−3. A low voltage of 1.4 V for intense light emission was achieved at the highest concentration. The electrical/spectral characteristics and energy band diagrams calculation show two distinct behaviors indicating two distinct mechanisms of light emission are at work in the heavily doped versus the lightly doped Si. In the heavily doped case, the light output is correlated to tunneling current and the subsequent conversion of surface plasmons to photons, while that for the lightly doped case is due to indirect band-to-band recombination in silicon. The results are validated by numerical simulation which indicates that the heavy doping of the n++-Si is necessary to achieve surface plasmon generation via electron tunneling due to the presence of band tail states and their effect on lowering the barrier height.

Protein Adsorption onto Modified Porous Silica by Single and Binary Human Serum Protein Solutions.

Typical porous silica (SBA-15) has been modified with pore expander agent (1,3,5-trimethylbenzene) and fluoride-species to diminish the length of the channels to obtain materials with different textural properties, varying the Si/Zr molar ratio between 20 and 5. These porous materials were characterized by X-ray Diffraction (XRD), N2 adsorption/desorption isotherms at −196 °C and X-ray Photoelectron Spectroscopy (XPS), obtaining adsorbent with a surface area between 420–337 m2 g−1 and an average pore diameter with a maximum between 20–25 nm. These materials were studied in the adsorption of human blood serum proteins (human serum albumin—HSA and immunoglobulin G—IgG). Generally, the incorporation of small proportions was favorable for proteins adsorption. The adsorption data revealed that the maximum adsorption capacity was reached close to the pI. The batch purification experiments in binary human serum solutions showed that Si sample has considerable adsorption for IgG while HSA adsorption is relatively low, so it is possible its separation.

The stability of Cl-, Br-, and I-passivated Si(100)-(2 × 1) in ambient environments for atomically-precise pattern preservation

Atomic precision advanced manufacturing (APAM) leverages the highly reactive nature of Si dangling bonds relative to H- or Cl-passivated Si to selectively adsorb precursor molecules into lithographically defined areas with sub-nanometer resolution. Due to the high reactivity of dangling bonds, this process is confined to ultra-high vacuum (UHV) environments, which currently limits its commercialization and broad-based appeal. In this work, we explore the use of halogen adatoms to preserve APAM-derived lithographic patterns outside of UHV to enable facile transfer into real-world commercial processes. Specifically, we examine the stability of H-, Cl-, Br-, and I-passivated Si(100) in inert N2 and ambient environments. Characterization with scanning tunneling microscopy and x-ray photoelectron spectroscopy (XPS) confirmed that each of the fully passivated surfaces were resistant to oxidation in 1 atm of N2 for up to 44 h. Varying levels of surface degradation and contamination were observed upon exposure to the laboratory ambient environment. Characterization by ex situ XPS after ambient exposures ranging from 15 min to 8 h indicated the Br– and I–passivated Si surfaces were highly resistant to degradation, while Cl–passivated Si showed signs of oxidation within minutes of ambient exposure. As a proof-of-principle demonstration of pattern preservation, a H–passivated Si sample patterned and passivated with independent Cl, Br, I, and bare Si regions was shown to maintain its integrity in all but the bare Si region post-exposure to an N2 environment. The successful demonstration of the preservation of APAM patterns outside of UHV environments opens new possibilities for transporting atomically-precise devices outside of UHV for integrating with non-UHV processes, such as other chemistries and commercial semiconductor device processes.

Evaluation of Crystalline Volume Fraction of Laser-Annealed Polysilicon Thin Films Using Raman Spectroscopy and Spectroscopic Ellipsometry.

We investigated the crystallinities of poly silicon (poly Si) annealed via green laser annealing (GLA) with a 532-nm pulsed laser and blue laser annealing (BLA) with 450-nm continuous-wave lasers. Three-dimensional heat transfer simulations were performed to obtain the temperature distributions in an amorphous silicon (a-Si) thin film, and GLA and BLA experiments were conducted based on the thermal simulation results. The crystallinity of annealed poly Si samples was analyzed using Raman spectroscopy and spectroscopic ellipsometry. To evaluate the degree of crystallization for the annealed samples quantitatively, the measured spectra of laser-annealed poly Si were fitted to those of crystalline Si and a-Si, and the crystal volume fraction (fc) of the annealed poly Si sample was determined. Both the Raman spectroscopy and ellipsometry showed consistent results on fc. The fc values were found to reach >85% for optimum laser power of GLA and BLA, showing good crystallinity of the laser-annealed poly Si thin films comparable to thermal furnace annealing.

Molecular dynamics study of the mechanical properties of reinforced silicon structure with iron nanoparticles

In this computational work, the mechanical behavior of silicon (Si) samples in the presence of iron (Fe) nanoparticles is investigated by using the Molecular Dynamics (MD) method. Technically, in our simulations, Si sample and Fe nanoparticles are represented by Embedded Atom Model (EAM) for atomic interaction parameter. The MD simulation results on atomic structure’s mechanical behavior have been reported by calculating some physical parameters such as potential energy (per atom), temperature, Young’s modulus, and ultimate strength. The results indicate the atomic stability of the Si-Fe structure just after 5 ns. By inserting the Fe nanoparticles into the pristine Si sample, Young’s modulus of the structure reaches 155.18 GPa, and its ultimate strength increases to 40.30 GPa. On the other hand, as the cross-sectional area of ​​the simulated nanostructure increases, the atomic interaction between the Si sample and the Fe nanoparticles decreases. Therefore, the values of Young’s modulus and the ultimate strength of the structure are decreased. Generally, the results of this simulation show Fe nanoparticles’ significant effect on the pristine Si sample’s mechanical properties, which can be used for industrial applications.

Two-dimensional lateral photovoltaic effect in MOS structure of Ti–SiO2–Si

Previous works on lateral photovoltaic effect (LPE) were mostly limited to one dimension, but this paper explored two-dimensional characteristics of metal-oxide-semiconductor (MOS) sensor by preparing Ti–SiO2–Si samples with high sensitivity. The experiment shows that the lateral photovoltage (LPV) sensitivity decreases gradually when the laser scanning direction deviates from the line between two electrodes. However, there is nonlinear between the LPV and laser point position but it has symmetry when the scanning direction is perpendicular to the line between the two electrodes. Meanwhile, the mechanism of LPE is explained by carrier diffusion theory, further experiments and calculation of difference between laser point position and the two electrodes, the results prove that the difference and LPV are the same variation trend with the laser point position. Based on this phenomenon, the mathematical equation between the difference and LPV is clarified, this can be a new choice for two-dimensional displacement detection of MOS sensor.

Hydrophobisation of electrospun nanofiber membranes by plasma deposited CF coating

Electrospun nanofiber membranes for filtration and medical applications are still under rapid development. The common example of membranes - polyamide 6 (PA6) with hydrophilic properties was selected for the conversion to hydrophobic membranes. The fiber diameter in the membrane is about 100 nm. To reach the hydrophobic properties, the hydrophilic PA6 membrane was plasma coated by CF film from Argon/C4F8 = 2:1 gas mixture in radio frequency (RF) 20 W plasma in total pressure about 0.7 Pa for 5 min. The membranes are by this process coated deeply inside the structure up to underlying spunbond substrate used for the membrane production as a collector substrate. The contact angle measured on CF functionalized membrane is about 120° and it is higher than the contact angle measured on the reference flat CF coating on Si sample with same chemical bonding. Chemical structure was studied by XPS where identical CFx components were identified on flat samples and on the top of functionalized membrane. The zeta potential decreased significantly if PA6 membrane is functionalized by CF groups. The coating process did not damage the nanofibers in the membrane and the diameters of the fibers were not significantly increased.