Thick Silicon Research Articles

Investigation of Strongly Hydrophobic and Thick Porous Silicon Stain Films Properties

Porous silicon (PSi) structures with strong hydrophobicity have been achieved by chemical etching of p-type silicon substrates in a solution based on hydrofluoric acid solution (HF) and vanadium oxide (V2O5). The surface morphology and microstructure of the elaborated structured silicon surfaces were investigated using Scanning Electron Microscope (SEM), contact angle and Fourier Transform Infrared spectroscopy (FTIR). The results show that the obtained structures exhibit hierarchically porous surfaces with porous pillars of silicon (PPSi) and an important hydrophobicity of the surface. The electrical properties of those PPSi structures were investigated in presence of 10 ppm of NO2 gas. The response time was about 30s at room temperature. Our results demonstrate that PPSi/Si are highly hydrophobic for long time and suitable for applications in the field of self-cleaning and may be a good candidate in elaborating practical NO2 sensors.

Advanced barrier and seed layer deposition enabling multiple type of TSVs integration

TSV integration is a key technology allowing heterogeneous devices 3D integration. However, depending on the targeted application, various TSV sizes and integration schemes exist, all requesting very high aspect ratio. The most common integration is the Mid-process TSV for which aspect ratio is required to be higher than 10:1 whatever application. In the case of large interposers, silicon thickness has to be increased to limit the deformation of the substrate due to highly stressed devices. Same requirements are made by photonic interposers which use thick SOI substrate leading to high warpage during integration. In the opposite, imagers requires to save silicon surface thus reduce TSV size and keep out zone. Silicon thickness has to be kept in the 100 μm range leading then the aspect ratio of the TSV to increase. Recently, Hybrid bonding progresses allowed a new type of TSV to be introduced : High Density TSVs for imagers. In this application, micrometer range TSV have to be filled with a Silicon thickness reduction limited to 10 μm by grinding process control. In order to allow the metal filling of all those type of structures, we have developed a highly conformal barrier and seed layer processes using standard materials for easier integration. The process is based on the use of MOCVD TiN as a barrier. This material is deposited using TDMAT precursor which allows low temperature deposition (200 °C)[1] which extends also the polyvalence of the process toward polymer bonded integrations. The very high step coverage of this process, reported at more than 30% in 20:1 aspect ratio coupled to high resistance to copper diffusion allows as thin as 20 nm barrier thickness which appears relevant economically (for deposition and CMP) and for stress consideration, compared to the well known but thicker PVD TaN process. Considering seed layer, the eG3D process[2] was brought to a high maturity allowing it to be integrated in an applied material raider tool coupled to TSV filling reactors. This process, based on electrografting of copper has already proved a step coverage of more than 50% in 12:1 aspect ratio structures. The presented work shows that the same process requires only deposition parameters change to be able to fully cover 10×150 μm Mid-process TSV as well as 1×10 μm High density ones. The excellent step coverage of this process allowed as thin as 200 nm (for 10×120 μm TSVs) and 100 nm (for (1×10 μm ones) deposited thicknesses to ensure perfect coverage of the structures. eG3D process also has the ability to be used as a repair process for non-continuous widely used PVD Cu seed layers but also be deposited directly on the barrier material. These 2 layers were evaluated together in a 300mm TSV integration schemes of both 10×120 mid process and 1×10 μm High Density structures and qualified electrically. The paper will discuss the deposition process development leading to simultaneously allow copper filling of the very wide range of TSVs on the same process equipment and using the same chemicals. We will then present integration results as well as electrical test of TSV daisy chains of both mid and High density TSVs showing excellent yield for all TSV size and integration schemes.

Fabrication and verification of a glass-silicon-glass micro-/nanofluidic model for investigating multi-phase flow in shale-like unconventional dual-porosity tight porous media.

Unconventional shale or tight oil/gas reservoirs that have micro-/nano-sized dual-scale matrix pore throats with micro-fractures may result in different fluid flow mechanisms compared with conventional oil/gas reservoirs. Microfluidic models, as a potential powerful tool, have been used for decades for investigating fluid flow at the pore-scale in the energy field. However, almost all microfluidic models were fabricated by using etching methods and very few had dual-scale micro-/nanofluidic channels. Herein, we developed a lab-based, quick-processing and cost-effective fabrication method using a lift-off process combined with the anodic bonding method, which avoids the use of any etching methods. A dual-porosity matrix/micro-fracture pattern, which can mimic the topology of shale with random irregular grain shapes, was designed with the Voronoi algorithm. The pore channel width range is 3 μm to 10 μm for matrices and 100-200 μm for micro-fractures. Silicon is used as the material evaporated and deposited onto a glass wafer and then bonded with another glass wafer. The channel depth is the same (250 nm) as the deposited silicon thickness. By using an advanced confocal laser scanning microscopy (CLSM) system, we directly visualized the pore level flow within micro/nano dual-scale channels with fluorescent-dyed water and oil phases. We found a serious fingering phenomenon when water displaced oil in the conduits even if water has higher viscosity and the residual oil was distributed as different forms in the matrices, micro-fractures and conduits. We demonstrated that different matrix/micro-fracture/macro-fracture geometries would cause different flow patterns that affect the oil recovery consequently. Taking advantage of such a micro/nano dual-scale 'shale-like' microfluidic model fabricated by a much simpler and lower-cost method, studies on complex fluid flow behavior within shale or other tight heterogeneous porous media would be significantly beneficial.

Process Dependence of Soft Errors Induced by Alpha Particles, Heavy Ions, and High Energy Neutrons on Flip Flops in FDSOI

Soft-error tolerance depending on threshold voltage of transistors was evaluated by $\alpha $ -particle, heavy-ion, and neutron irradiation. Three chips were fabricated, one embeds low-threshold general-purpose (GP) transistors and the others embed high-threshold low-power (LP) transistors in a 65 nm fully depleted silicon on insulator (FDSOI) process. There were a few errors on LPDFFs (DFFs with LP transistors). Error probability (EP) of LPDFFs was 99.88% smaller than that of GPDFFs (DFFs with GP transistors) by $\alpha $ particles. Average cross sections (CSs) of LPDFFs by heavy ions were 50% smaller than those of GPDFFs. Average soft-error rates (SERs) of LPDFFs by neutrons were 68% smaller than those of GPDFFs. 3-D device simulations revealed that CSs of the LP and GP transistors are changed by fitting methods using the work function of the gate material and doping concentration of the substrate under the BOX layer. The difference is due to the number of carriers in diffusion and silicon thickness of the raised layer above drain and source terminals.

Feasibility study of a Ge2Sb2Te5-clad silicon waveguide as a non-volatile optical on-off switch

This paper reports on the design optimization of compact optical ON-OFF switches based on a GST-clad silicon rib waveguide and compares it to a GST-clad silicon nanowire at the telecommunication wavelength 1.55 µm. Effective index and modal loss of the quasi-TE modes are calculated by a full-vectorial H-field finite element method. It shows that the electro-refraction effect-based switch may not be viable because of the higher modal loss in the GST crystalline state. On the other hand, the larger modal loss difference between GST amorphous and crystalline states would be more suitable for an electro-absorption type switch design. The effect of silicon slab thickness, silicon core width, and GST layer thickness for both the waveguides are presented. As the presence of the GST layer modifies the mode field profiles, so the incurring coupling loss at the butt-coupled junctions between the input/output silicon waveguide and Si-GST waveguide are also calculated by using the least squares boundary residual method. These results show that the GST-clad silicon rib waveguide with a 500-nm-wide silicon core, 60-90 nm thick silicon slab, and 15-25 nm thick GST layer is the optimal self-sustained switch design. In this case, a very compact, 2-5 µm long device is expected to show an extinction ratio of more than 20 dB with the total insertion loss of only 0.36 dB.

Free-carrier detection in a silicon slab via absorption measurement in 2D integrating cells.

2D integrating cells provide long optical path lengths on a chip by multiple reflections at highly reflective mirrors similar to integrating spheres in free space. Therefore, they build a promising platform for integrated optical absorption sensing. Here, we present first absorption measurements of free carriers generated by a modulated pump laser inside a 2D integrating cell in a silicon slab. The results can be used to evaluate the lifetimes of free carriers in silicon slabs for integrated optics. Employing a silicon-on-insulator platform with a silicon thickness of 220nm, we demonstrate measurements of the access free-carrier concentration on the order of 1-8·1015 cm-3 with lifetimes on the order of 0.1-1μs governed by surface recombination at the silicon interfaces. The measured lifetimes are dependent on free-carrier concentration, which confirms previous observations. The presented free-carrier absorption experiment verifies the sensitivity of 2D integrating cells to changes in the absorption coefficient and thus demonstrates the potential of 2D integrating cells for absorption sensing.

Experimental investigations of heat transfer mechanisms of a pulsating heat pipe

Experimental work was carried out to clarify the heat transfer mechanism of a pulsating heat pipe (PHP). A micro pulsating heat pipe (MPHP) with five turns was fabricated by engraving an interconnected micro-channel on a 1.1 mm thick transparent glass wafer. The engraved glass wafer and a 500 μm thick silicon wafer were anodically bonded to form a closed-loop MPHP. Ethanol was charged into the MPHP as the working fluid. The MPHP was vertically oriented with a bottom-heating mode. Using infrared (IR) thermometry, the distributions of temperature and heat flux were measured at the fluid-wall interface for the first time over the entire MPHP with high spatial and temporal resolution. High-speed flow visualization, which was synchronized to heat transfer measurements, was utilized to identify the local flow patterns corresponding to the local temperature and heat flux. The heat transfer at the fluid–silicon interface in the channels could be divided into the two parts: sensible heat transfer and latent heat transfer, and quantitative analysis of the data clarified the contributions of sensible/latent heat transfer to overall heat transfer. The overall contribution of latent heat transfer was estimated to be between 66% and 74%. Latent heat transfer not only induces the oscillating flow but also contributes significantly to overall heat transfer, whereas sensible heat transfer is a byproduct of the oscillating flow.

The Variation of Crystalline Structure Induced by Gas Dilution and Thermal Annealing in Silicon Layers Deposited by PECVD Technique

We prepared hydrogenated thick silicon film by plasma enhanced chemical vapor deposition (PECVD) method using SiH4 and H2 gas mixture and we investigated the effect of the hydrogen dilution ratio defined as $$ R=\frac{\left[{H}_2\right]}{\left[{SiH}_4\right]} $$ on the as-deposited and annealed films. With increase in hydrogen dilution ratio, amorphous to microcrystalline transition has been observed. The crystallization has been confirmed from Raman spectroscopy, UV reflectance, low angle X-ray diffraction (XRD), spectroscopic ellipsometry and atomic force microscopy (AFM) analysis. Tauc band gap shows a decreasing trend with increasing H2 dilution of silane. It decreases from 1.8 to 1.57 eV. It has been concluded that H2 dilution of silane in PECVD enhances the crystallinity of the film and affects its optical and structural properties.

Preparation of flat surfaces on silicon carbide substrate using electron beam processing

Electron beam processing of 6H-SiC{0001} surfaces is studied. Initial substrates contain polishing scratches on (0001) face and rough surface of (000-1) face specially developed by KOH etching which are eliminated by electron beam processing. Processing is carried out in vacuum of 0.1 mTorr, energy about of 69 kJ, and background temperature of 1100 K in presence of 1-30 µm thick silicon film on the substrates. Atomic force microscopy images show near atomically flat surfaces which roughness decreases in 22-23 times for (000-1) and 1.5-2.0 times for (0001), respectively. Root-mean square value of processed surfaces are 0.27-0.30 nm for 5×5 μm2 scan area. The steps (height of 0.5-1.0 nm) between the terraces (length of 500 nm) correspond to a height of 2-4 Si-C bilayers. The obtained changing of roughness factor also indicates a decrease of real surface area of the faces during electron beam processing.

Study of the radiation fields in LEO with the Space Application of Timepix Radiation Monitor (SATRAM)

We present the analysis of data taken by the Space Application of Timepix Radiation Monitor (SATRAM). It is centred on a Timepix detector (300 μm thick silicon sensor, pixel pitch 55 μm, 256 × 256 pixels). It was flown on Proba-V, an Earth observing satellite of the European Space Agency (ESA) from an altitude of 820 km on a sun-synchronous orbit, launched on May 7, 2013. A Monte Carlo simulation was conducted to determine the detector response to electrons (0.5–7 MeV) and protons (10–400 MeV) in an omnidirectional field taking into account the shielding of the detector housing and the satellite. With the help of the simulation, a strategy was developed to separate electrons, protons and ions in the data. The measured dose rate and stopping power distribution are presented as well as SATRAM’s capability to measure some of the stronger events in Earth’s magnetosphere. The stopping power, the cluster height and the shape of the particle tracks in the sensor were used to separate electrons, protons and ions. The results are presented as well. Finally, the pitch angles for a short period of time were extracted from the data and corrected with the angular response determined by the simulation.

Compact silicon TE-pass polarizer using adiabatically-bent fully-etched waveguides.

A high-performance integrated silicon TE-pass polarizer is proposed and demonstrated. The polarizer uses a series of adiabatic waveguide bends that yield high extinction ratio for the TM polarization and low insertion loss for the TE polarization, and does not require special materials or complex fabrication steps. The polarizer, implemented on a silicon-on-insulator platform with a 220 nm silicon thickness, is measured to have insertion loss ≤ 0.37 dB (average 0.12 dB) and extinction ratio ≥ 27.6 dB (average 36.0 dB) over a 1.5 μm to 1.6 μm wavelength range, with a footprint of 63 μm × 9.5 μm. The trade-off between the footprint of the polarizer and its performance is established. While the analysis was done for a silicon-on-insulator platform, the concept is applicable to other waveguide geometries and integrated photonic platforms.

First measurements of the spectral and angular distribution of transition radiation using a silicon pixel sensor on a Timepix3 chip

Abstract X-ray Transition radiation detectors (TRDs) are used for particle identification in both high energy physics and astroparticle physics . Particle identification is often achieved based on a threshold effect of the X-ray transition radiation (TR). In most of the detectors, TR emission starts at γ factors above ∼ 500 and reaches saturation at γ ∼ 2 − 3 ⋅ 1 0 3 . However, many experiments require particle identification up to γ ∼ 1 0 5 , which is difficult to achieve with current detectors, based only on the measurement of the photon energy together with the particle ionization losses. Additional information on the Lorentz factor can be extracted from the angular distribution of TR photons. TRDs based on pixel detectors give a unique opportunity for precise measurements of spectral and angular distributions of TR at the same time. A 500 μ m thick silicon sensor bump bonded to a Timepix3 chip was used in a test beam measurement at the CERN SPS. A beam telescope was employed to separate clusters produced by the primary beam particles from the potential TR clusters. Spectral and angular distributions of TR were studied with high precision for the first time using beams of pions , electrons and muons at different momenta. In this paper, the measurement and analysis techniques are described, and first results are presented.

Silicone-coated polyimide films deposited by surface dielectric barrier discharges

Hybrid dielectric barrier discharges are investigated for plasma generated on the surface of a dielectric layer, where two conducting electrodes of high voltage and ground are formulated on the upper and bottom surfaces. Using a flexible thin polyimide-film of a thickness ranging from 25 to 125 μm, a plasma is generated with a voltage of about 1 kV and a frequency of 40 kHz. However, the surface of the dielectric layer was etched through a chemical reaction involving plasma oxygen radical species, and thus the polyimide films failed readily, resulting in dielectric breakdown within short operating time ranging from a few minutes to several tens of minutes, based on the film thicknesses of 25 μm and 125 μm, respectively. These plasma erosions were prevented by coating the polyimide surface with a 25 μm thick silicone paste. The silicone-coated film surface was then reinforced remarkably against plasma erosion as the organic polymer was vulnerable to chemical reaction of the plasma species, while the inorganic silicone exhibited a high chemical resistance against plasma erosion.

Analytical Drain Current Model for Fully Depleted Surrounding Gate TFET

In this paper, we propose the analytical modeling for fully depleted surrounding gate TFET surrounding gate tunneling field effect transistor with single metal gate. This model comprises the surface potential using 2-D Poisson’s equation and drain current with the effects of oxide thickness, silicon thickness as radius, drain voltage, gate metal work function, and assuming channel is fully depleted. The model is tested using TCAD Simulation Tool.

Operation and performance of the JUNGFRAU photon detector during first FEL and synchrotron experiments

JUNGFRAU is a hybrid pixel photon detector developed at the Paul Scherrer Institut for free electron laser (FEL) and synchrotron applications. A charge integrating detector, JUNGFRAU features three automatically switching gains per pixel which adjust the amplification factor to the amount of deposited charge. This enables single photon sensitivity, while ensuring a dynamic range over four orders of magnitude. Each detector module consists of eight 256×256 pixel ASICs bump-bonded to a single 320 μm thick silicon sensor, resulting in half a million pixels of 75 μm pitch arranged in 1024×512 arrays for a sensitive area of approximately 8×4 cm2. Modules can be combined in various configurations to produce larger systems. These proceedings present the required steps, both operational and in terms of data processing, necessary to perform experiments with the JUNGFRAU detector. This includes the calculation and application of pedestal and gain corrections and the geometric arrangement of the recorded image. Examples of these techniques in action will be presented from the first experiments performed with JUNGFRAU detectors; the pilot experiment of the SwissFEL Bernina beamline and proof-of-principle macromolecular crystallography measurements from the X06SA beamline of the Swiss Light Source. Successful operation and data processing methods from FEL and synchrotron facilities will be compared and contrasted, and experience of overcoming challenges in the two scenarios will be shared. Finally, the capability of JUNGFRAU for FEL and synchrotron applications will be demonstrated.

Selective Oxidation and Carbonization by Laser Writing into Porous Silicon

AbstractThe selective formation of either oxidized or carbonized features into 2.5 µm thick porous silicon (PS) films using laser writing at a wavelength of 405 nm is demonstrated. Oxidized features are formed in air while carbonized features are achieved during the flow of propane at 600 sccm. Voids which have been previously associated with the use of propane are not observed, largely due to the rapid heating and high flow rates achieved in the experiment. Carbonized regions with feature widths down to 1.8 µm are achieved and chemical resistance to both hydrofluoric acid and potassium hydroxide is demonstrated. Once carbonized regions are formed, the surrounding areas can be overwritten in air to convert the surrounding regions into oxidized PS allowing films to be created with as‐fabricated, oxidized and carbonized regions. Energy dispersive X‐ray and Raman analysis confirms the presence of carbon within the written structures. At high optical powers, cracking around the carbonized features is observed which is attributed to a contraction of the film. Such cracking is not observed during selective oxidation of features. This work significantly enhances the ability to engineer and pattern the composition of PS films enabling selective control of the material's properties and functionality.

On-chip unidirectional dual-band fiber-chip grating coupler in silicon nitride

We report, for the first time, a single state polarization (TE) dual-band grating fiber-chip coupler on a 700 nm thick silicon nitride platform that couples to both O and C band channels. Dual-band coupling with a single grating coupler is achieved using cross mode k-space equalization. By phase matching the first-order vertical TE01 mode and the fundamental TE00 mode in two distinct bands, we observe simultaneous co-directional dual-band coupling to a single waveguide. Experimental peak efficiency per coupler is measured to be −7.3 dB in the O-band and −8.2 dB in the C-band and the combined 1 dB bandwidth is observed to be 82 nm.

Formation of thicker silicon wires on a sufficiently cooled substrate during the gas phase zinc reduction reaction of SiCl4

In this study, we demonstrate that thick silicon whiskers (wires) formed on a sufficiently cooled substrate. We used the gas phase zinc reduction reaction of SiCl4 at a gas reaction temperature of 910 °C. Wires formed via the tip-growth mode in the vapor–liquid–solid mechanism. When the substrate was the same temperature as the gas phase, the formation of multiple wires from a single point was observed. Conversely, this multiple formation was not observed, and thicker wires formed, on the sufficiently cooled substrate. We propose that splitting of a zinc catalytic droplet into several smaller ones is one of the main reasons for the formation of multiple wires. Suppression of this splitting on the cooled substrate was considered to be a main reason for the formation of thicker wires. We conducted a numerical approach to predict temperature profiles along a growing wire, because the growth rate of wires was about 5 mm min−1 and heating owing to the release of the latent heat for solidification was not negligible. Three processes, the conduction in a wire, the convection to the surrounding gas and the radiation via the surface of wire, were considered. We also considered the heating of the growing tip due to solidification as well. Our simulation revealed that the tip temperature of a rapidly growing wire increased and was higher than that of the substrate. The effect of substrate temperature and subsequent temperature profile for a growing wire was discussed.

Modeling Deformations in Multichip Packages of NAND Memory

Deformation of NAND memory multichip packages (MCPs) with various thicknesses of substrate and silicon dies have been numerically simulated. The results of calculations are consistent with experimental data and show equivalence of the deformation in single- and multichip packages with the same total thickness of silicon. Analytical relationship between the values of MCP deformation, substrate core thickness, and total thickness of silicon dies is proposed, which agrees quite well with the data of modeling and can be used for preliminary estimation of MCP deformations.

Design and implementation of a Thomson parabola for fluence dependent energy-loss measurements at the Neutralized Drift Compression eXperiment.

The interaction of ion beams with matter includes the investigation of the basic principles of ion stopping in heated materials. An unsolved question is the effect of different, especially higher, ion beam fluences on ion stopping in solid targets. This is relevant in applications such as in fusion sciences. To address this question, a Thomson parabola was built for the Neutralized Drift Compression eXperiment (NDCX-II) for ion energy-loss measurements at different ion beam fluences. The linear induction accelerator NDCX-II delivers 2 ns short, intense ion pulses, up to several tens of nC/pulse, or 1010-1011 ions, with a peak kinetic energy of ∼1.1 MeV and a minimal spot size of 2 mm FWHM. For this particular accelerator, the energy determination with conventional beam diagnostics, for example, time of flight measurements, is imprecise due to the non-trivial longitudinal phase space of the beam. In contrast, a Thomson parabola is well suited to reliably determine the beam energy distribution. The Thomson parabola differentiates charged particles by energy and charge-to-mass ratio, through deflection of charged particles by electric and magnetic fields. During first proof-of-principle experiments, we achieved to reproduce the average initial helium beam energy as predicted by computer simulations with a deviation of only 1.4%. Successful energy-loss measurements with 1 μm thick silicon nitride foils show the suitability of the accelerator for such experiments. The initial ion energy was determined during a primary measurement without a target, while a second measurement, incorporating the target, was used to determine the transmitted energy. The energy-loss was then determined as the difference between the two energies.