Oriented Silicon Wafers Research Articles

Study of the Vacuum Pressure Sensing from the Electrical Resistance Response of Porous Silicon Fabricated via Photo-Electrochemical Technique

The manufacturing of vacuum sensors is critical to several vacuum-based applications. Porous silicon (PSi) was chosen as the vacuum sensor due to the possibility of moving air particles settled inside the pores while being put in the vacuum. The characteristics of porous silicon sensing to the evacuation of gases during vacuum was inferred by changing in the electrical resistivity. This work depends on the change in the electrical resistance of the PSi layers that was prepared via photo-electrochemical technique on the n-type (100) oriented silicon wafer. The surface topography of porous silicon is necessary to understand the morphological properties. Therefore, structural and morphological characterization of PSi samples were studied and analyzed using the scanning electron microscope (SEM) and X-Ray Diffraction (XRD) pattern. The etching process was carried out with various etching times, hydrofluoric acid (HF) concentration, and constant current density. The results showed that the pore size is increased as the etching time increased. The etching time produced pores of different sizes. The electrical resistance values were calculated after placing the sample in the vacuum system, starting from atmospheric pressure down to torr. The electrical properties of PSi indicate that electrical resistance gradually decreases with increasing vacuum pressure.

Selective electrochemical deposition of indium in-between silicon nanowire arrays fabricated by metal-assisted chemical etching

Indium electrodeposition in-between silicon nanowire arrays fabricated by silver-assisted chemical etching of lightly-doped (100)-oriented silicon wafers is evaluated. It is concluded based on SEM and EDX analysis of indium's distribution that, by utilizing pulsed-mode electrodeposition and maintaining a sufficiently low duty cycle value, indium particles can be formed exclusively at the very bottom of each consecutive pore on the residual silver particles left over from metal-assisted etching. This result differs significantly from irregular pore filling along with surface and subsurface deposition observed in the cases of continuous galvanostatic deposition regimes at prolonged durations or in the absence of residual silver particles. Bottommost fusible metal deposit localization, which is unattainable on porous silicon fabricated by electrochemical anodization, is presumed to be optimal for the growth of germanium crystallites inside the pores via the electrochemical liquid-liquid-solid approach and subsequent silicon-germanium alloy formation through thermal annealing.

Design, fabrication, and characterisation of a silicon microneedle array for transdermal therapeutic delivery using a single step wet etch process

The fabrication of silicon in-plane microneedle arrays from a simple single wet etch step is presented. The characteristic 54.7° sidewall etch angle obtained via KOH etching of (100) orientation silicon wafers has been used to create a novel microneedle design. The KOH simultaneously etches both the front and back sides of the wafer to produce V shaped grooves, that intersect to form a sharp pyramidal six-sided microneedle tip. This method allows fabrication of solid microneedles with different geometries to determine the optimal microneedle length and width for effective penetration and minimally invasive drug delivery. A modified grooved microneedle design can also be used to create a hollow microneedle, via bonding of two grooved microneedles together, creating an enclosed hollow channel. The microneedle arrays developed, effectively penetrate the skin without significant indentation, thereby enabling effective delivery of active ingredients via either a poke and patch application using solid microneedles or direct injection using hollow microneedles. This simple, scalable and cost effective method utilises KOH to etch the silicon wafer in-plane, allowing microneedles with variable length of several mm to be fabricated, as opposed to out-of-plane MNs, which are geometrically restricted to dimensions less than the thickness of the wafer. These microneedle arrays have been used to demonstrate effective delivery of insulin and hyaluronic acid into the skin.

A novel method to fabricate on-chip ultra-high-Q microtoroid resonators

Fabricating an optical microtoroid with ultra-high quality factor is an indispensable procedure both for scientific research and engineering. Here, HF/HNO3 wet etching is specially tailored to form silicon pillars for ultra-high quality factor microtoroids instead of xenon difluoride (XeF2) or reactive ion etching (RIE) methods. This is a low-cost, easily maintained and time-saving method. The method uses a very simple etching device and is robust to temperature variations and humidity changes at room temperature(20–25 °C). Anisotropy in isotropic HF/HNO3 etching, which may limit the quality factor, is minimized in the experiment. Quality factor dependence on silicon orientation is experimentally investigated and theoretically explained with group theory, which shows that [111] oriented silicon wafers are superior to [100] and [110] in the wet etching method. The maximum quality factor observed at 1550 nm waveband in the experiment is 1.05 × 108. We believe this technique will have great influence both on laboratory and future production use.

Method for Manufacturing Silicon X-Ray Masks Via Plasma Chemical Etching

A simple method for manufacturing silicon masks for deep X-ray lithography, conducted with the application of exposure radiation of the spectral range (0.5–7 A), is described. This method is based on planar silicon technology, which is widely used in the production of semiconductor devices. A significant difference between this method and previously known analogues is that it does not apply the creation of a stop layer by doping during formation of the support membrane of the mask. As the initial blank, a standard (100) oriented silicon wafer is used. The silicon support membrane of the mask is formed in the final stage of its manufacture by plasma-chemical etching of the rear-side of the wafer to a predetermined depth. The thus obtained X-ray masks on a silicon wafer are characterized by relative ease of manufacture, radiation and chemical resistance, geometric stability, and relatively high levels of mechanical strength and X-ray transparency of the support membrane, depending on its thickness, which can be manufactured with good accuracy and within a fairly wide range of ~2.5–50 μm, depending on the purpose of the mask.

INFLUENCE OF SILICON WAFER CRYSTALLOGRAPHIC ORIENTATION ON ANODIZATION MECHANISM

The influence of silicon wafer crystallographic orientation on the formation of porous silicon during anodization in an HF solution is studied. Cross-section SEM image comparison of samples with different crystallographic orientations has shown that (111) Si samples exhibit a more branching, tree-like pore structure with a higher porosity value compared to (100) Si samples. This phenomenon is explained by pointing out differences in crystal structure and numbers of Si-Si chemical bonds in different crystallographic directions. Namely, in (100)-oriented silicon crystals every surface Si atom has two bonds connecting it to atoms underneath it, as well as two broken bonds able to interact with Fions. Through electron injection into silicon, enough energy is applied to break the underlying bonds, forming SiF as a result. The presence of two Fions bonded with every surface silicon atom leads to weakening the bonds of surface silicon atoms with the underlying atoms, thus making the process of breaking the Si-Si bonds more energy efficient. As for (111)-oriented crystals, silicon atoms only have one broken surface bond, and breaking backbonds with underlying silicon atoms requires a higher value of activation energy due to their larger amount (three as opposed to two for (100) silicon). It is concluded that this very reason leads to slower etching speeds of (111)-oriented silicon wafers. The results help evaluate the way the silicon crystal structure affects the etching process, including its speed and direction, which is an especially important factor to consider when forming (111)-oriented porous silicon.

Enhancement of Responsivity and Sensitivity of p-Silicon/n-Zinc Oxide-Based Photodetector Using Titanium Dioxide Nanoparticles

Here we report band structure design, fabrication and characterization of a novel ultraviolet photodetector which functions based on the heterostructure between silicon, zinc Oxide, and titanium dioxide nanostructures. For this purpose, Zinc Oxide nanowires were grown on p-type (100) oriented silicon wafer by hydrothermal method and covered by a ∼20nm film of titanium dioxide which were deposited by chemical vapor deposition (CVD) method. Results reveal that in forward bias, the shell titanium dioxide layer reduces the dark current and enhances the sensitivity of photodetector, while in reverse bias titanium dioxide layer increases the responsivity. Responsivity and sensitivity as high as 2.5 A/W and 0.95 are obtained in this work, respectively. In our structure, photocurrent showed a linear dependence to illumination intensity. This linearity together with short response time demonstrate that the titanium dioxide nanostructure lowered the effect of trap states on the photo-response of the device, therefore, the dominant role in photocurrent generation was found to be related to the band structure design of the device.

Multi-staged deposition of trench-gate oxides for power MOSFETs

Here, silicon oxide was formed in a U-shaped trench of a power metal-oxide semiconductor field-effect transistor device by various processes. One SiO2 formation process was performed in multiple steps to create a low-defect Si-SiO2 interface, where first a thin initial oxide was grown by thermal oxidation followed by the deposition of a much thicker oxide layer by chemical vapor deposition (CVD). In a second novel approach, silicon nitride CVD was combined with radical oxidation to form silicon oxide in a stepwise sequence. The resulting stack of silicon oxide films was then annealed at temperatures between 1000 and 1100 °C. All processes were executed in an industrial environment using 200 mm-diameter (100)-oriented silicon wafers. The goal was to optimize the trade-off between wafer uniformity and conformality of the trenches. The thickness of the resulting silicon oxide films was determined by ellipsometry of the wafer surface and by scanning electron microscopy of the trench cross sections. The insulation properties such as gate leakage and electrical breakdown were characterized by current–voltage profiling. The electrical breakdown was found to be highest for films treated with rapid thermal processing. The films fabricated via the introduced sequential process exhibited a breakdown behavior comparable to films deposited by the common low-pressure CVD technique, while the leakage current at electric fields higher than 5 MV/cm was significantly lower.

Influence of Annealing Temperature and Time on the Photoluminescence and the Structure of Y2O3:Eu Thin Films

Y2O3:Eu thin films were deposited on p-type (100)-oriented silicon wafers by using the radiofrequency (RF) magnetron sputter deposition technique and then post-annealed in an air ambient at various temperatures and holding times. X-ray diffraction data showed that the as-deposited films had a cubic Y2O3 structure textured with the (222) plane. The as-deposited films were found to be under internal compressive stress, and the annealing treatment led to relaxation of the stress in the films. Photoluminescence (PL) was observed from the films annealed at temperatures ≥ 400°C, and the strongest peak occurred at 613 nm in the red range. The PL intensity increased as the annealing temperature was increased, resulting from the improved crystalline quality of the Y2O3:Eu films annealed at higher temperatures. The PL intensity reached a maximum at 1200°C and then decreased due to the formation of the Y2SiO5 phase. The Y2O3:Eu films were also annealed at 1200°C for different periods of time from 1 to 10 h. The PL intensity of the 1200°C-annealed films was decreased for longer holding time resulting from the formation of the Y2SiO5 phase.

Tvrdoća i procena adhezije jednoslojnih i višeslojnih tankih filmova nikla elektrohemijski deponovanih na silicijumskim podlogama sa i bez ultrazvučnog mešanja

Composite systems of monolayer and multilayer nickel films electrochemically deposited on single crystal (100)-oriented silicon wafers were fabricated with and without the ultrasonic agitation. The hardness and adhesion behaviour of these composite structures were characterized by Vickers microindentation test. The dependence of composite microhardness and film adhesion on the structure of the film and mixing conditions of electrolyte were analysed. Mathematical models of Chicot-Lesage and Chen-Gao were applied to experimental data in order to obtain the film hardness and adhesion parameter respectively. It is confirmed that the mechanical properties of composite systems of nickel thin films on silicon substrate can be enhanced by formation of multilayer film structure by ultrasound-assisted electro-deposition and by reducing the layer thickness in the multilayer film.

Fabrication Technology and Characteristics Research of a Monolithically-Integrated 2D Magnetic Field Sensor Based on Silicon Magnetic Sensitive Transistors

A monolithically-integrated two-dimensional (2D) magnetic field sensor consisting of two difference structures (DSІ and DSII) is proposed in this paper. The DSІ and DSII are composed of four silicon magnetic sensitive transistors (SMST1, SMST2, SMST3 and SMST4) and four collector load resistors (RL1, RL2, RL3 and RL4). Based on the magnetic sensitive principle of SMST, the integrated difference structure can detect magnetic fields’ component (Bx and By) along the x-axis and y-axis, respectively. By adopting micro-electromechanical systems (MEMS) and packaging technology, the chips were fabricated on a p-type <100> orientation silicon wafer with high resistivity and were packaged on printed circuit boards (PCBs). At room temperature, when the VCE = 5.0 V and IB = 8.0 mA, the magnetic sensitivities (Sxx and Syy) along the x-axis and the y-axis were 223 mV/T and 218 mV/T, respectively. The results show that the proposed sensor can not only detect the 2D magnetic field vector (B) in the xy plane, but also that Sxx and Syy exhibit good uniformity.

Corrosion Behavior of Highly As-Doped Oriented Si-Wafer Anodes in Alkaline Si–Air Batteries

One line of development to establish resource-efficient metal–air batteries is focusing on silicon materials as anode electrodes. While operation of primary Si–air batteries with ionic liquid electrolytes is one possible approach [1], employing conventional alkaline electrolyte is also considered by the recent investigations [2]. At the current state of development, the alkaline Si–air batteries suffer from high corrosion rates that reduce the theoretical specific capacity of 3820 mAh/g to 120 mAh/g [3]. Thereby, corrosion as being the major challenge has to be overcome in order to establish practical application of primary alkaline Si–air batteries. The objective of the present work is to investigate the corrosion behavior of highly As-doped <100> oriented silicon wafer anodes in alkaline solutions for a scope of conditions that may arise in battery operation. Firstly, the influence of the immersion times on the open-circuit corrosion rates are discussed in combination with the surface morphology development in 72 h. Secondly, the impact of KOH electrolyte concentration on the open-circuit corrosion rates is investigated and three ranges of KOH concentrations are identified with different limiting mechanisms. Moreover, basing on the electrochemical corrosion rates obtained from potentiodynamic polarization method, the comparison between the chemical and electrochemical corrosion mechanisms are pointed out. Further investigations are carried out on the corrosion behavior of Si wafers under anodic voltages as present during the discharge of batteries. The dependency of the discharge characteristics as the discharge voltage, corrosion rates, and mass conversion efficiencies on the KOH concentrations and current densities are analyzed and accordingly, optimum conditions for the battery application are discussed.

Laser Source Influence on the Preferential Growth and the Inversion Degree in Pulsed Laser CoFe2O4 Films

A comparative study between cobalt ferrite films deposited by pulsed laser deposition as a function of the laser sources, 355 nm (Nd:YAG) and 248 nm (KrF excimer), on amorphous quartz (AQ) and -oriented silicon wafer (SW) at different temperatures (650–800 ∘C) is presented. Also, a quantitative estimation of the preferential crystalline growth orientation as laser source function was made by means of Lotgering factor and Harris texture coefficient, which were obtained from XRD patterns. The inversion degree in spinel-type structure for cobalt ferrite films was calculated through a deconvolution in Raman spectra, where the band A1g vibrating modes in tetrahedral sites were associated with Fe and Co sites (687 and 611 cm−1, respectively). Additionally, saturation magnetization was also calculated from the inversion degree obtained from deconvolution of the Raman spectra in CoFe2O4 films, being compared with experimental results, which is in a good agreement with cobalt ferrite bulk, and we also correlated the preferential growth and the particle size with increment of the coercive field.

Investigation of the corrosion behavior of highly As-doped crystalline Si in alkaline Si–air batteries

High corrosion rate is one of the major obstacles that have to be overcome in order to establish practical application of primary alkaline Si–air batteries. At the current state of development the theoretical specific capacity of 3820 mAh/g is reduced to 120 mAh/g in long term operable alkaline Si–air batteries, with most of the capacity losses being due to corrosion reactions. In the present work the corrosion behavior of highly As-doped <100> oriented silicon wafers, that have proved stable performance as anode materials is summarized for a scope of conditions that may arise in battery operation. More specific, corrosion rates are presented and discussed with respect to (i) time dependence, (ii) influence of KOH electrolyte concentration, (iii) chemical vs. electrochemical corrosion, and (iv) corrosion under anodic potentials as present during the discharge of batteries. Corrosion rates were found to exhibit stable time profiles for immersion times longer than 8 h. With respect to concentration dependence, three ranges of KOH concentrations were identified. Within each range, the corrosion behavior is governed by similar mechanisms, but different limiting factors. Potentiodynamic measurements show that large part of the corrosion is chemical in nature. Under discharge conditions corrosion increases whereby the discharge potential, corrosion rates, and mass conversion efficiencies depend on KOH concentrations and discharge current densities.

Experimental and Simulation Study of Nanometric Cutting of Silicon by Diamond Turning

Diamond turning is an ultra-precision manufacturing method which is employed to fabricate components requiring submicron geometric accuracy and atomically smooth surface finish, such as those utilized in the x-ray optics, IR optics and semiconductors industries. This study represents the experimental investigation as well as MD Simulation to elucidate the strong dependence of cutting parameters (tool feed rate, depth of cut and spindle speed) in influencing the ductile-regime machining conditions during cutting of silicon. Precitech Nanoform 200 diamond turning machine is used to perform experiments on 50 mm diameter (111) oriented silicon wafers. To enhance the understanding of actual cutting mechanism, Molecular Dynamic Simulation is being incorporated to mimic the nanometric cutting of silicon. The simulation study encompasses the investigation of phase transformation, cutting force, thrust force and temperature exerted at the cutting zone. The actual cutting mechanism involved during the nanometric cutting of silicon is clearly visualized from MD simulation.

Characteristics research of pressure sensor based on nanopolysilicon thin films resistors

To further improve the sensitivity temperature characteristics of pressure sensor, a kind of pressure sensor taking nanopolysilicon thin films as piezoresistors is proposed in this paper. On the basis of the microstructure analysis by X-ray diffraction (XRD) and scanning electron microscope (SEM) tests, the preparing process of nanopolysilicon thin films is optimized. The effects of film thickness and annealing temperature on the micro-structure of nanopolysilicon thin films were studied, respectively. In order to realize the measurement of external pressure, four nanopolysilicon thin films resistors were arranged at the edges of square silicon diaphragm connected to a Wheatstone bridge, and the chip of the sensor was designed and fabricated on a [Formula: see text] orientation silicon wafer by microelectromechanical system (MEMS) technology. Experimental result shows that when [Formula: see text] = 6.80 mA, the sensitivity of the sensor PS-1 is 0.308 mV/kPa, and the temperature coefficient of sensitivity (TCS) is about −1742 ppm/[Formula: see text]C in the range of −40–140[Formula: see text]C. It is possible to obviously improve the sensitivity temperature characteristics of pressure sensor by the proposed sensors.

Comparison of cross-sectional transmission electron microscope studies of thin germanium epilayers grown on differently oriented silicon wafers.

We compare transmission electron microscopical analyses of the onset of islanding in the germanium-on-silicon (Ge/Si) system for three different Si substrate orientations: (001), (11¯0) and (11¯1)Si. The Ge was deposited by reduced pressure chemical vapour deposition and forms islands on the surface of all Si wafers; however, the morphology (aspect ratio) of the deposited islands is different for each type of wafer. Moreover, the mechanism for strain relaxation is different for each type of wafer owing to the different orientation of the (111) slip planes with the growth surface. Ge grown on (001)Si is initially pseudomorphically strained, yielding small, almost symmetrical islands of high aspect ratio (clusters or domes) on top interdiffused SiGe pedestals, without any evidence of plastic relaxation by dislocations, which would nucleate later-on when the islands might have coalesced and then the Matthews-Blakeslee limit is reached. For (11¯0)Si, islands are flatter and more asymmetric, and this is correlated with plastic relaxation of some islands by dislocations. In the case of growth on (11¯1)Si wafers, there is evidence of immediate strain relaxation taking place by numerous dislocations and also twinning. In the case of untwined film/substrate interfaces, Burgers circuits drawn around certain (amorphous-like) regions show a nonclosure with an edge-type a/4[1¯12] Burgers vector component visible in projection along [110]. Microtwins of multiples of half unit cells in thickness have been observed which occur at the growth interface between the Si(11¯1) buffer layer and the overlying Ge material. Models of the growth mechanisms to explain the interfacial configurations of each type of wafer are suggested.

Apatitic Deposition in Osteoblasts Cultured on Micropatterned Silicon

In this study, the osteogenic differentiation of murine pre-osteoblasts cultured on patterned silicon was investigated. Specifically, micropatterns were fabricated in orientation silicon wafers to create linear gratings with a width of either 2 μm (2 μm depth, 10 μm pitch) or 20 μm (2 μm depth, 30 μm pitch). Two subclones (4, 24) of the MC3T3-E1 osteoblast-like cell line were seeded on the micropatterns and cultured in osteogenic induction medium for 28 days. Cells cultured on planar silicon served as the controls. Apatite formation was examined using synchrotron X-ray diffraction. Deposition of [002] and [211]/[112] apatite-like material was clearly observed in subclone 4 (strongly mineralizing) osteoblasts cultured on both micro patterns.

Design, fabrication and characterization of a high-sensitivity pressure sensor based on nano-polysilicon thin film transistors

Based on the nano-polysilicon thin film transistors (TFTs), a high-sensitivity pressure sensor was designed and fabricated in this paper. The pressure sensing element is composed of a Wheatstone bridge with four nano-polysilicon TFTs designed on different positions of the square silicon diaphragm. Via taking the four channel resistors of the TFTs as piezoresistors, the measurement to the external pressure can be realized according to the piezoresistive effects of channel layer. Through adopting complementary metal oxide semiconductor (CMOS) technology and micro-electromechanical system (MEMS) technology, the chips of sensor were fabricated on &amp;lt;100 &amp;gt; orientation silicon wafer with a high resistivity. At room temperature, when applying a voltage 5.0 V to the Wheatstone bridge, the full scale (100 kPa) output voltage and the sensitivity of the sensor with 35 μm-thick silicon diaphragm are 267 mV and 2.58 mV/kPa, respectively. The experimental results show that the pressure sensors can achieve a much higher sensitivity.

Dynamic Wet Etching of Silicon through Isopropanol Alcohol Evaporation

In this paper, Isopropanol (IPA) availability during the anisotropic etching of silicon in Potassium Hydroxide (KOH) solutions was investigated. Squares of 8 to 40 µm were patterned to (100) oriented silicon wafers through DWL (Direct Writing Laser) photolithography. The wet etching process was performed inside an open HDPE (High Density Polyethylene) flask with ultrasonic agitation. IPA volume and evaporation was studied in a dynamic etching process, and subsequent influence on the silicon etching was inspected. For the tested conditions, evaporation rates for water vapor and IPA were determined as approximately 0.0417 mL/min and 0.175 mL/min, respectively. Results demonstrate that IPA availability, and not concentration, plays an important role in the definition of the final structure. Transversal SEM (Scanning Electron Microscopy) analysis demonstrates a correlation between microloading effects (as a consequence of structure spacing) and the angle formed towards the (100) plane.