Oxide Coated Silicon Wafers Research Articles

Effect of silicon nitride coating thickness on silicon wafer substrates for signal enhancement in laser-induced breakdown spectroscopic analysis of liquids

It has been shown by previous studies of our group that the use of nitride-coated silicon wafer surfaces as a sample loading substrate in dried-droplet LIBS analysis provided enhancement in plasma emission signal and better detection limits compared to uncoated or oxide-coated silicon wafer surfaces. To further investigate the effect of coating thickness for enhanced sensitivity in dried nano-droplet analysis of liquids, silicon-wafer substrates of different nitride coating thicknesses; 75, 300, 450, and 1000 nm, were comparatively studied. With 75 nm silicon nitride coating, the thin-film effect due to the anti-reflective behavior of the silicon nitride film is observed, and plasma emission signal is enhanced up to three times compared to 300 nm coated substrates. With coating thicknesses of 450 nm and 1000 nm, on the other hand, thermophysical and mechanical properties of the silicon nitride material, like thermal conductivity and hardness, become more dominant factors, leading to higher emission signals for all the elements studied. With 1000 nm coating thickness, enhancement factors of 4.8, 6.4, and 3.7 were obtained for the elements of Pb, Cu, and Cr, respectively. Optimization of the experimental LIBS parameters was conducted, calibration curves were constructed, and analytical figures of merits were determined. Sub-picogram amounts absolute detection limits; 0.7 pg Pb, 0.6 pg Cr, and 0.4 pg Cu, in 500 nanoliter droplets were obtained from the slopes of the calibration curves. The nitride-coated substrates' analytical performance was tested using certified reference solutions, standard water, and real water samples. The materials and the methodology developed can be used for waste-water monitoring of environmental samples by LIBS.

Influence of substrate-induced thermal stress on the superconducting properties of V3Si thin films

Thin films of superconducting V3Si were prepared by means of RF sputtering from a compound V3Si target at room temperature onto sapphire and oxide-coated silicon wafers, followed by rapid thermal processing under secondary vacuum. The superconducting properties of the films thus produced are found to improve with annealing temperature, which is ascribed to a reduction in defects in the polycrystalline layer. Critical temperatures (Tc) up to 15.3 K were demonstrated after thermal processing, compared to less than 1 K after deposition. The Tc was always found to be lower on the silicon wafers, by on average 1.9±0.3K for the annealed samples. This difference, as well as a broadening of the superconducting transitions, is nearly independent of the annealing conditions. In situ XRD measurements reveal that the silicide layer becomes strained upon heating due to a mismatch between the thermal expansion of the substrate and that of V3Si. Taking into account the volume reduction due to crystallization, this mismatch is initially larger on sapphire, though stress relaxation allows the silicide layer to be in a relatively unstrained state after cooling. On oxidized silicon, however, no clear evidence of relaxation upon cooling is observed, and V3Si ends up with an out-of-plane strain of 0.3% at room temperature. This strain increases as the sample is cooled down to cryogenic temperatures, though the deformation of the polycrystalline layer is expected to be highly inhomogeneous. Taking into account also the reported occurrence of a Martensitic transition just above the critical temperature, this extrapolated strain distribution is found to closely match an existing model of the strain dependence of A-15 superconducting compounds.

Optical and electrical properties of H2 plasma-treated ZnO films prepared by atomic layer deposition using supercycles

High mobility H-doped ZnO (ZnO:H) thin films are prepared on thermal oxide coated silicon wafers by a novel supercycle approach of thermal atomic layer deposition (ALD) technique. The influence of H2 plasma treatment and substrate composition on optical and electrical properties of ZnO films are studied using spectroscopic ellipsometry (SE) and direct electrical measurements. This work significantly expands the measured range of ZnO:H optical properties into the far infrared to obtain the complex dielectric function (ε = ε1 + iε2) spectra from 0.4 meV to 5.89 eV compared to what has been previously investigated by using SE. A blue shift in the optical band gap energy is observed with decreasing cycle ratio (n) or more frequent H2 plasma treatments during deposition. The amplitude of phonon absorption is increased with decreasing n. Free carrier transport characteristics are determined by applying the Drude model in modeling ε, and the result indicates lower n improves material conductivity as confirmed by direct electrical measurements. Regarding the effect of substrate composition, the samples prepared using the same n but on bare thermal oxide, a 5 nm ZnO:H film, or a 5 nm intrinsic ZnO film each have differences in ε and free carrier transport characteristics resulting from substrate composition, demonstrating an additional method of tailoring material properties. Effective carrier mass (m*) for the ZnO films are determined by combining results from Hall effect measurements with UV to THz spectra in ε. Thus, variation of n and substrate composition are demonstrated as an effective mean of controlling the resultant opto-electronic film properties.

Stripping and Transforming Alloyed Semiconductor Quantum Dots via Atomic Interdiffusion

We report the transformation of near-infrared CdSeTe/ZnS quantum dots (QDs) that are exposed to water. When the colloidal QDs with 840 nm emission wavelength and 75 nm spectral line width are self-assembled on water surface and transferred to an oxide-coated silicon wafer using a Langmuir–Blodgett (LB) procedure, two prominent relatively sharp photoluminescence (PL) bands are observed at ∼630 and ∼660 nm peak wavelengths with line width of ∼23 and ∼39 nm, respectively. On the other hand, the PL spectrum of the QDs as they are assembled on the water surface is essentially the same as that of the solution phase. Structural analysis of the LB films shows that the QDs are stripped off the stabilizing excess surfactant molecules by the preferential interaction at the water–air interface. After the film is transferred, the QDs are interfaced with each other and with the substrate directly, while covered with the stack of surfactant molecules from the top. Based on analysis of the chemical composition using X-ra...

Development and validation of a laser-induced breakdown spectroscopic method for ultra-trace determination of Cu, Mn, Cd and Pb metals in aqueous droplets after drying

The present study reports a fast and accurate methodology for laser-induced breakdown spectroscopic, LIBS, analysis of aqueous samples for environmental monitoring purposes. This methodology has two important attributes: one is the use of a 300nm oxide coated silicon wafer substrate (Si+SiO2) for the first time for manual injection of 0.5 microliter aqueous metal solutions, and two is the use of high energy laser pulses focused outside the minimum focus position of a plano convex lens at which relatively large laser beam spot covers the entire droplet area for plasma formation. Optimization of instrumental LIBS parameters like detector delay time, gate width and laser energy has been performed to maximize atomic emission signal of target analytes; Cu, Mn, Cd and Pb. Under the optimal conditions, calibration curves were constructed and enhancements in the LIBS emission signal were obtained compared to the results of similar studies given in the literature. The analytical capability of the LIBS technique in liquid analysis has been improved. Absolute detection limits of 1.3pg Cu, 3.3pg Mn, 79pg Cd and 48pg Pb in 0.5 microliter volume of droplets were obtained from single shot analysis of five sequential droplets. The applicability of the proposed methodology to real water samples was tested on the Certified Reference Material, Trace Metals in Drinking Water, CRM-TMDW and on ICP multi-element standard samples. The accuracy of the method was found at a level of minimum 92% with relative standard deviations of at most 20%. Results suggest that 300nm oxide coated silicon wafer has an excellent potential to be used as a substrate for direct analysis of contaminants in water supplies by LIBS and further research, development and engineering will increase the performance and applicability of the methodology.

Study of die break strength and heat-affected zone for laser processing of thin silicon wafers

As semiconductor based devices are manufactured on ever thinner silicon substrates, the required associated die break strength has to increase commensurately to maintain pick yields. In this study, the influence of laser processing parameters on the die break strength in laser dicing of silicon oxide-coated silicon wafers and silicon-based memory devices is investigated experimentally using ultraviolet lasers spanning a wide range of pulse width, from 400 fs to 150 ns. It is found that the net fluence, an accumulated pulse energy per surface area, is a meaningful process metric for damage induced by heat-affect zone to compare lasers processes with a large variety of pulse widths, laser scan speed, average powers, and repetition rates. Optimized process conditions for both nanosecond and femtosecond pulse widths are identified for achieving the highest die break strength in the target devices. The dependence of heat-affected zone on pulse width and net fluence during nanosecond laser processing is further demonstrated using multiphysical simulations. Simulations suggest that the thickest heat-affected zone section during laser scribing is typically located at the boundary of the laser incident surface. Simulation results also show that for a given repetition rate the heat-affected zone becomes larger as the net fluence increases due to smaller interpulse separation, consistent with the experimental observation.

Atomic layer deposition of MoS2 thin films

Atomic layer deposition (ALD) was used to grow thin films of MoS2 over 5 × 5 cm areas of silicon oxide coated silicon wafers. Smooth, uniform, and continuous films were produced over a temperature range of 350 °C–450 °C. The as-grown films were analyzed using x-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence, and x-ray diffraction. Electrical characteristics of the films were evaluated by fabricating a back gated field effect transistor. These analyses indicate that ALD technique can produce large area, high quality MoS2 films.

Direct Near-Field Observation of Orientation-Dependent Optical Response of Gold Nanorods

The orientation-dependent optical response of short gold nanorods (length less than 100 nm) has been directly observed in the near-field, mapping the in-plane and out-of-plane vector components selectively using interferometric apertureless near-field scanning optical microscope. For the gold nanorods dispersed randomly on oxide-coated silicon wafer, the optical amplitude and phase contrast that are characteristic of the longitudinal and transverse mode dipolar plasmon resonances have been clearly resolved when the long axes of the nanorods are aligned parallel and perpendicular to the electric field of the laser, respectively. The near-field amplitude ratio of the longitudinal to the transverse plasmon mode is much smaller than the corresponding ratio of the scattering cross section, indicating the more efficient coupling of the longitudinal mode to the far-field than the transverse mode. This near-field amplitude ratio increases with the length-to-width aspect ratio of the nanorods, and electromagnetic ...

Curing Temperature Effects on Network Structure and Chemistry of Silane Coupling Agent Layers and Their Influence on Water-Assisted Crack Growth

Interfaces between ∼10 nm thick 3-glycidoxypropyltrimethoxysilane (GPS) layers on silicon oxide-coated silicon wafers and amine cured epoxy were investigated. Before applying the epoxy the direct effect of the precuring temperature, Tpre, on the chemistry of the GPS layers was probed using Fourier-transformed infrared (FT-IR) spectroscopy. Swelling of the GPS layers when exposed to water or solvent vapor was measured by X-ray reflectometry. As expected, higher curing temperatures promote the siloxane formation process leading to near-completion of cross-linking around 250°C. On the other hand, the epoxy groups of the GPS layer already disappear at a precuring temperature of 90°C. Both the fracture energy (Gc) of dry Si/SiOx/GPS/epoxy interfaces at room temperature and the threshold (wet) fracture energy (Gth) of the interface in water at 80°C were found to decrease progressively as the GPS layer was precured at increasing Tpre above 90°C. At Tpre below 90°C, Gc increased with decreasing Tpre while the Gth (at 80°C) showed a peak for Tpre ≈ 80°C. There is a strong correlation between swelling of the GPS layer in deuterated nitrobenzene vapor (reflecting the cross-link density of the GPS as well as the thermodynamic compatibility with polar organic molecules such as epoxy and amines) and Gth. On the other hand, the epoxy functionality of GPS appears to play only a minor role in creating an interface with epoxy that is resistant to water-assisted crack growth since a Gth that is close to the maximum is achieved at a Tpre (90°C) at which the epoxy groups of the GPS have mostly disappeared. We conclude that for these GPS layers the interfaces with epoxy most resistant to water attack result under conditions where the mobile epoxy and amine species can interpenetrate a swellable precured GPS layer and that the reactive functionality of the GPS is relatively unimportant. The decrease in C and increase in Si on both sides of the fracture after curing at higher temperatures also supports this conclusion.

ChemInform Abstract: Studies of the Possible Reaction of WF6 with SiO2 and Si3N4 at Several Temperatures

Chemical vapor deposition (CVD) of tungsten by the hydrogen reduction of WF6 is increasingly important in very large scale integration technology. There is, however, a concern about possible interference of this CVD process by the reaction of WF 6 with the SiO 2 mask material. Because of disagreement between thermodynamic calculations and some experimental evidence concerning this reaction, the reaction was examined by several techniques not previously employed. Oxide coated silicon wafers were exposed to the hexafluoride in argon, with and without hydrogen present, at several temperatures from room temperature to 400 o C

DNA-mediated site-specific deposition of gold nanoparticles on silicon wafers

We report a method for the site-specific deposition of gold nanoparticles, as programmed by DNA sequences immobilized on the surface of silicon oxide-coated silicon wafers. After optimization of surface chemistries, selectivities of between 8:1 and 118:1 were achieved for the DNA-based sorting of populations of gold nanoparticle of 15 nm and 60 nm diameter from a common suspension via oligonucleotide duplex formation.

Direct write of optical waveguides on chalcogenide thin films using electron beams

Electron beam induced reliefs in Ge0.2Se0.8 thin films deposited by pulsed laser deposition on oxide coated silicon wafers are fabricated for the direct write of rib optical waveguides at telecommunication wavelengths. The physical dimensions of the reliefs are experimentally determined as a function of electron beam exposure conditions. Relief heights in excess of three times the initial film thickness are achieved. The lateral translation of the thin film material is observed to be of the order of tens of microns for relatively slow beam scan rates. Numerical simulations based on a full-wave finite element eigenmode analysis support the existence of single mode guided waves. The surface roughness of the optical waveguides, dominated by the pulse laser deposition process, is reduced to approximately 1nm by planarization of the thin film, via thermal embossing, prior to electron beam exposure. A bidirectional writing scheme is implemented to remove variations in relief heights observed at waveguide terminations. Nonuniform electron beam exposures are used to demonstrate three-dimensional waveguide tapers useful for the realization of fiber-to-waveguide optical transitions.

Room temperature photoluminescence in the visible range from silicon nanowires grown by a solid-state reaction

The solid-liquid-solid method (also known as the solid-state method) is used to produce silicon nanowires at the core of silica nanowires with a support catalyst layer structure of nickel and titanium layers sputtered on oxide-coated silicon wafers. This silane-free process is low cost and large-area compatible. Using electron microscopy and Raman spectroscopy we deduce that the wires have crystalline silicon cores. The nanowires show photoluminescence in the visible range (orange), and we investigate the origin of this band. We further show that the nanowires form a random mesh that acts as an efficient optical trap, giving rise to an optically absorbing medium.

Yield and Deformation in Biaxially Stressed Multilayer Metallic Thin Films

Multilayer thin films of CuNb, CuNi, and CuNbNi with 20 nm individual layer thicknesses were fabricated by magnetron sputtering on oxide coated silicon wafers. The mechanical properties of the films were measured using bulge testing and nanoindentation. Elastic and plastic properties were determined for freestanding films in both square and rectangular window geometries. A finite element model of the window was used to determine the yielding behavior to account for stress concentrations in the membranes. The initial yield in a pressurized membrane, on the order of 400–500 MPa, is approximately one-half of the flow stress inferred from nanoindentation hardness results between 1.9 GPa and 3.4 GPa, and is a result of microscale yielding prior to uniform deformation in these high strength systems.

Surface blistering of low-temperature annealed hydrogen and helium co-implanted silicon and its application to splitting of bonded wafer substrates

Applications involving transfer of pre-processed silicon layers to substrates of different material often requires a restricted thermal budget. In the case of thermal splitting of hydrogen and helium implanted bonded wafer substrates this can mean restricting temperatures within the range 250–400 °C depending on application. The present study investigates the phenomenon of blistering of implanted substrates as a precursor to thermal splitting following annealing over this temperature range. Optical microscopy was used to detect blister initiation temperature and TEM to show details of sub-surface processes. Results showed that plots of Ln(time) v. blister initiation temperature consisted of several straight-line regions yielding an activation energy for each region. TEM showed strain lines extending to the surface and the development of voiding at the platelet line and between the platelet line and sample surface. The results suggest that the movement of He and its interaction with vacancy complexes plays an important role during annealing. Hydrogen and helium co-implanted silicon wafers bonded to oxide-coated silicon wafers were thermally split at a temperatures between 280 and 300 °C yielding a pinhole-free silicon-on-oxide (SOI), layer of about 460 nm with an RMS roughness measured by AFM in the range 3–6 nm rms.

Nanocrystalline Diamond as a Dielectric for SOD Applications

AbstractNanocrystalline diamond (NCD) has been grown on oxide coated silicon wafers by microwave plasma assisted chemical vapour deposition using a novel seeding technique followed by optimised growth conditions, and leads to a highly-dense form of this material with grain sizes around 100nm for films approximately 1.5 microns thick. The electrical properties of these films have been investigated using Impedance Spectroscopy, which enables the contributions from sources characterised by differing capacitances, such as grain boundaries and grain interiors, to be isolated. After an initial acid clean the electrical properties of the film are not stable, and both grain boundaries and grains themselves contribute to the frequency dependant impedance values recorded. However, following mild oxidation grain boundary conduction is completely removed and the films become highly resistive (>1013 ohm/sq). This is most unusual, as conduction through NCD material is more normally dominated by grain boundary effects. Interestingly, the AC properties of these films are also excellent with a dielectric loss value (tan δ) as low as 0.002 for frequencies up to 10MHz. The dielectric properties of these NCD films are therefore as good as high quality free-standing (large grain) polycrystalline diamond films, and not too dissimilar to single crystal diamond, and are therefore ideally suited to future ‘silicon-on-diamond’ applications.

Fabrication and testing of planar chalcogenide waveguide integrated microfluidic sensor

We have fabricated and tested, to the best of our knowledge, the first microfluidic device monolithically integrated with planar chalcogenide glass waveguides on a silicon substrate. High-quality Ge(23)Sb(7)S(70) glass films have been deposited onto oxide coated silicon wafers using thermal evaporation, and high-index-contrast channel waveguides have been defined using SF(6) plasma etching. Microfluidic channel patterning in photocurable resin (SU8) and channel sealing by a polydimethylsiloxane (PDMS) cover completed the device fabrication. The chalcogenide waveguides yield a transmission loss of 2.3 dB/cm at 1550 nm. We show in this letter that using this device, N-methylaniline can be detected using its well-defined absorption fingerprint of the N-H bond near 1496 nm. Our measurements indicate linear response of the sensor to varying N-methylaniline concentrations. From our experiments, a sensitivity of this sensor down to a N-methylaniline concentration 0.7 vol. % is expected. Given the low-cost fabrication process used, and robust device configuration, our integration scheme provides a promising device platform for chemical sensing applications.

The electrical behavior of nitro oligo(phenylene ethynylene)’s in pure and mixed monolayers

In order to realize molecular electronic devices, molecules with electrically interesting behavior must be identified. One molecule that has potential for use in devices is an oligo(phenylene ethynylene) (OPE) molecule with nitro sidegroup(s). These “nitro” molecules have been reported to show electrical switching with memory behavior, as well as negative differential resistance (NDR). However, different research groups testing the nitro molecules in different test beds have observed different electrical behaviors. In this work, we assembled two different nitro monolayers: one completely composed of nitro molecules and the second a mixed matrix where nitro molecules were separated by dodecanethiol molecules. We used scanning tunneling microscopy to image each of the monolayers and observed that the nitro molecules were effectively inserted into the ordered dodecanethiol monolayer. We tested the electrical behavior of the pure monolayer, as well as the mixed monolayer, in our nanowell test device. The nanowell devices were fabricated on micron-size gold lines patterned on oxide-coated silicon wafers. The gold lines were covered with a silicon dioxide layer, through which a nanometer size well was milled. This nanowell device was filled with a self-assembling monolayer of organic molecules, and capped with titanium and gold. The nanowell electrical results showed switching with memory for the pure nitro monolayer, but not for the mixed monolayer. This switching behavior consisted of a molecule starting in a high conductivity state and switching to a low conductivity state upon application of a threshold voltage. The high conductivity state could only be returned by application of an opposite threshold voltage.

Particle‐Laden Drop Impacting on Solid Surfaces

This paper presents an experimental study of the effects of particles on spreading and retracting of a single drop impacting on a smooth surface. The results are reported for particle concentrations from 0 to 0.30, different liquids (mixtures of water and glycerin), Reynolds number from 6.1 to 2700 Weber number from 0.0084 to 180, and four different surfaces (thermal oxide coated silicon wafer, silicon wafer, 1,1,1,3,3,3, hexamethyl disilazane (HMDS) coated silicon wafer, and Teflon® film). Drops laden with polystyrene particles coated with calcium phosphate are observed to behave differently from pure liquids, especially on thermal oxide coated silicon wafer, which is the most hydrophilic surface studied. It was found that pure fluid viscosity is more important than apparent viscosity of the particle‐laden fluid in setting the spreading and retraction. At an impact speed of 2 m/sec, the rebound behavior on the Teflon® surface depends on particle volume fraction.

Lead Titanate Thin Films Prepared by Metallorganic Chemical Vapor Deposion (MOCVD) on Sapphire, Pt, and RuOx Substrates

AbstractTransparent and highly specular PbTiO3 thin films were deposited on sapphire, platinum and ruthenium oxide-coated silicon wafers by hot-wall metallorganic chemical vapor deposition (MOCVD). Lead bis-tetramethylheptadionate and titanium ethoxide were used as chemical precursors. Films were deposited over a range of experimental conditions. X-ray diffraction (XRD) was used to determine the phases present in the films; Scanning Electron Microscopy (SEM) was used to examine the surface morphology and Energy Dispersive Spectroscopy (EDS) was used to determine the composition. Optical spectra were obtained to confirm the highly dense and transparent nature of the films. The chemical stability of the ruthenium oxide substrates in the MOCVD environment as well as the existence of a high-temperature deposition regime for composition control are also discussed.