Doped Silicon Wafers Research Articles

Frequency shifts in two-level ultra-deep reactive ion etched slow-wave structures for 0.1 THz backward-wave oscillations

We present microfabricated slow-wave structures for millimeter- or terahertz-wave vacuum electronic sources. A two-level ultra-deep reactive ion etching (u-DRIE) on highly doped silicon wafers has been employed and allowed for complicated 3-dimensional structures with high aspect ratio. The measured spectra of return loss, however, show 1.2% and 6.8% upshifts in both cutoff and resonant frequencies, respectively. We found the suppression of two-level u-DRIE at the narrow channel between resonant cavities has caused the change of aspect ratios, i.e., saddle-shaped bottom surfaces, which is proved to be associated with the difference in frequency shifts as well as RF attenuation by comparison with theoretical prediction.

Copper-selective electrochemical filling of macropore arrays for through-silicon via applications

In this article, the physico-chemical and electrochemical conditions of through-silicon via formation were studied. First, macropore arrays were etched through a low doped n-type silicon wafer by anodization under illumination into a hydrofluoric acid-based electrolyte. After electrochemical etching, ‘almost’ through-silicon macropores were locally opened by a backside photolithographic process followed by anisotropic etching. The 450 × 450-μm² opened areas were then selectively filled with copper by a potentiostatic electrochemical deposition. Using this process, high density conductive via (4.5 × 105 cm−²) was carried out. The conductive paths were then electrically characterized, and a resistance equal to 32 mΩ/copper-filled macropore was determined.

Microlens Arrays: Fabrication of Microlens Arrays with Well‐controlled Curvature by Liquid Trapping and Electrohydrodynamic Deformation in Microholes (Adv. Mater. 23/2012)

Y. C. Ding, J. Y. Shao, and co-workers demonstrate a creative and economic method for manufacturing large-area microlens arrays (MLAs) with controllable curvature and supersmooth surfaces. On page OP 165, the production of a concave MLA is achieved by electrohydrodynamically deforming the surface of a photocurable prepolymer trapped in microhole array which has been etched onto a doped silicon wafer. The concave MLA is then used as a master to generate the convex MLA via vacuum micromoulding.

Studies of influence of high temperature preannealing on oxygen precipitation in CZ Si wafers

We have investigated Czochralski grown low boron doped silicon wafers after oxygen precipitation using high temperature preannealing. Wafers originating from the part of the silicon ingot close to head and close to tail were used for the experiments representing different temperature history of the wafers. The loss of interstitial oxygen, precipitate morphology and stoichiometry at various stages of precipitation were determined by infrared absorption spectroscopy at liquid nitrogen and at room temperature. The impact of a high temperature preannealing at various temperatures on the parameters of precipitates including also their concentration determined from chemical etching was observed during the growth of oxygen precipitates. The obtained results were compared with transmission electron microscopy.

Comparison of carbon nanotube modified electrodes for photovoltaic devices

Substrates with four different nanotube modifications have been prepared and their electron transport properties measured. Two modification techniques were compared; covalent chemical attachment of both single and multi-walled carbon nanotubes to transparent conductive (fluorine doped tin oxide) glass surfaces and chemical vapour deposition (CVD) growth of both single and multi-walled carbon nanotubes on highly doped conductive silicon wafers. These carbon nanotube modified substrates were investigated using scanning electron microscopy and substrates with nanotubes grown via CVD have a much higher density of nanotubes than substrates prepared using chemical attachment. Raman spectroscopy was used to verify that nanotube growth or attachment was successful. The covalent chemical attachment of nanotubes was found to increase substrate electron transfer substantially compared to that observed for the bare substrate. Nanotube growth also enhanced substrate conductivity but the effect is smaller than that observed for covalent attachment, despite a lower nanotube density in the attachment case. In both modification techniques, attachment and growth, single-walled carbon nanotubes were found to have superior electron transfer properties. Finally, solar cells were constructed from the nanotube modified substrates and the photoresponse from the different substrates was compared showing that chemically attached single-walled nanotubes led to the highest power generation.

Photovoltaic properties of black silicon microstructured by femtosecond pulsed laser

Prototype devices based on black silicon have been fabricated by microstructuring 250μm thick multicrystalline n doped silicon wafers using femtosecond pulsed laser in ambient gas of SF6 to measure its photovoltaic properties. The enhanced optical absorption of black silicon extends across the visible region and all the black silicons prepared in this work exhibit enhanced optical absorption close to 90% from 300nm to 800nm. The highest open-circuit voltage (Voc) and short-circuit current (Isc) under the illumination of He–Ne continuous laser at 632.8nm were measured to be 53.3mV and 0.11mA, respectively at a maximum power conversion efficiency of 1.44%. Upon excitation with He–Ne continuous laser at 632.8nm, external quantum efficiency (EQE) of black silicon as high as 112.9% has also been observed. Development of black silicon for photovoltaic purposes could open up a new perspective in achieving high efficient silicon-based solar cell by means of the enhanced optical absorption in the visible region. The current–voltage characteristic and photo responsivity of these prototype devices fabricated with microstructured silicon were also investigated.

Bistable behavior of silicon wafer in rapid thermal processing setup

The bistable behavior of a silicon wafer in the thermal reactor of the rapid thermal processing (RTP) setup has been theoretically predicted and for the first time detected experimentally. It is shown that the effect of the temperature and optical bistability depends on a doping degree of the wafer. It has been found experimentally that the lightly doped silicon wafer with resistivity [email protected] has the bistable behavior being heated by the radiation of tungsten-halogen quartz lamps, in argon atmosphere, with 0.2mm between the wafer and the water-cooled pedestal. At the same heating conditions, the heavily doped silicon wafer with resistivity [email protected] has not exhibited the bistable behavior. As a part of the study, an analytical expression is proposed to approximate the temperature dependence of the spectral emissivity of the lightly doped silicon wafer.

Ignition of a Microcavity Plasma Array

Microcavity plasma arrays are regular arrays of inverse pyramidal cavities created on positively doped silicon wafers. Each cavity acts as a microscopic dielectric barrier discharge. It has an opening of 50 μm × 50 μm and a depth of 45 μm. The separation of the cavities is 50 μm. Operated at atmospheric pressure in argon and excited with a 100-kHz RF voltage, each cavity develops a localized microplasma. Experiments show a strong interaction of the individual cavities, leading, for example, to the propagation of ionization waves along the array surface. This paper studies the ignition of a microcavity plasma array by means of a numerical simulation. The propagation of an ionization wave is observed. Its propagation speed matches experimental findings.

Nanoveneers: An Electrochemical Approach to Synthesizing Conductive Layered Nanostructures

We report herein a facile electrochemical approach to synthesizing various layered composite films of nanomaterials and conducting polymers, called nanoveneers. Layered structures of polypyrrole film with single-walled carbon nanotubes (SWNTs), graphene, and Au nanoparticles have been obtained by electropolymerization of pyrrole molecules on a heavily doped silicon wafer preloaded with target conductive nanomaterials. A free-standing, transparent, and highly conductive composite film was achieved after peeling off from a silicon wafer. Different from traditional homogeneous composite materials, such kinds of nanoveneers combined to the best extent the structural continuity and processability of conducting polymers with the high conductivity and functionality of discontinuous SWNTs, graphene, and other nanomaterials. The layered electrochemical deposition provides a great freedom for constructing various nanostructures with well-controlled geometry and thus physicochemical properties, as demonstrated by SWNT/polypyrrole nanoveneers. These nanoveneers are particularly attractive in areas of chemical sensors, labels, transparent electronics, and optoelectronics.

A Porous Silicon/Iron Oxide Nanocomposite with Superparamagnetic and Ferromagnetic Behavior

The infiltration of iron oxide nanoparticles into mesoporous silicon is performed to investigate the influence of different arrangements of the particles on the magnetic behaviour of the achieved nanocomposite consisting of a semiconductor and a magnetic material. The porous silicon is fabricated from a highly doped n-type silicon wafer by anodization. The Fe3O4 particles fabricated by high temperature decomposition offer a size of 5 and 8 nm, respectively. In the present work the influence of the porous silicon matrix on the magnetic behaviour of such hybrid materials is figured out. In general iron oxide particles of a few nanometer in size are superparamagnetic but due to dipolar coupling between them the blocking temperature can be shifted, which is demonstrated by modification of the particle size and the distance between the particles.

Design and Fabrication of a Planar Three-DOFs MEMS-Based Manipulator

Abstract-This paper presents the design, modeling, and fabrication of a planar three-degrees-of-freedom parallel kinematic manipulator, fabricated with a simple two-mask process in conventional highly doped single-crystalline silicon (SCS) wafers (100). The manipulator's purpose is to provide accurate and stable positioning of a small sample (10 × 20 × 0.2 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ), e.g., within a transmission electron microscope. The manipulator design is based on the principles of exact constraint design, resulting in a high actuation-compliance combined with a relatively high suspension stiffness. A modal analysis shows that the fourth vibration mode frequency is at least a factor 11 higher than the first three actuation-related mode frequencies. The comb-drive actuators are modeled in combination with the shuttle suspensions gaining insight into the side and rotational pull-in stability conditions. The two-mask fabrication process enables high-aspect-ratio structures, combined with electrical trench insulation. Trench insulation allows structures in conventional wafers to be mechanically connected while being electrically insulated from each other. Device characterization shows high linearity of displacement wrt voltage squared over ±10 μm stroke in the xand y-directions and ±2° rotation at a maximum of 50 V driving voltage. Out-of-plane displacement crosstalk due to in-plane actuation in resonance is measured to be less than 20 pm. The hysteresis in SCS, measured using white light interferometry, is shown to be extremely small.

Roughness of silicon nanowire sidewalls and room temperature photoluminescence

Strong room temperature visible (red-orange) photoluminescence (PL) has been observed in silicon nanowires (SiNWs) that were realized by wet chemical etching of heavily (arsenic, As: ${10}^{20}\text{ }{\text{cm}}^{\ensuremath{-}3}$) and lowly doped (boron, B: ${10}^{15}\text{ }{\text{cm}}^{\ensuremath{-}3}$) single crystalline silicon (Si) wafers. Optical characterization of these SiNWs by PL combined with structural characterization by transmission and scanning electron microscopy strongly suggest that the visible PL at room temperature results from the rough SiNW sidewall structure that is composed of nanoscale features in which quantum confinement effects may occur.

Investigation of state retention in metal–ferroelectric–insulator–semiconductor structures based on Langmuir–Blodgett copolymer films

Among the ferroelectric thin films considered for use in nonvolatile memory devices, the ferroelectric copolymer of polyvinylidene fluoride, PVDF (C2H2F2), with trifluoroethylene, TrFE (C2HF3), has distinct advantages, including low dielectric constant, low processing temperature, relative low cost compared with epitaxial ferroelectric oxides, and compatibility with organic semiconductors. We report the operation and polarization retention properties of a metal–ferroelectric–insulator–semiconductor bistable capacitor memory element consisting of an aluminum gate, a P(VDF-TrFE) Langmuir–Blodgett film, a 30 nm cerium oxide buffer layer, and a moderately doped silicon wafer. The device exhibited a 1.9 V wide hysteresis window obtained with a ±7 V operating range with a state retention time of 10 min. The mechanisms contributing to loss of state retention are discussed.

The effect of dopants on the brittle-to-ductile transition in silicon single crystals

The brittle-to-ductile transition (BDT) in boron, antimony and arsenic doped Cz silicon crystals has been experimentally studied, respectively. The BDT temperatures in antimony and arsenic doped silicon wafers are lower than that in a non-doped wafer while the BDT temperature in a boron doped wafer is almost the same as that in the non-doped wafer. The activation energy was obtained from the strain rate dependence of the BDT temperature. It was found that the values of the activation energy in the antimony and arsenic doped wafers are lower than that in the non-doped and boron doped wafers, indicating that the dislocation velocity in the antimony and arsenic doped silicon is faster than that in the non-doped while the dislocation velocity in the boron doped is the same as that in the non-doped. The effect of increasing in dislocation velocity on the BDT temperature was calculated by two-dimensional discrete dislocation dynamics simulations, indicating that the increasing in dislocation velocity decreases the BDT temperature in silicon single crystals.

Reduced pore diameter fluctuations of macroporous silicon fabricated from neutron‐transmutation‐doped material

AbstractThe precision of photo‐electrochemical etching of perfectly‐ordered macropores in single‐crystalline silicon is limited by pore diameter fluctuations due to doping variations of the starting wafer (striations). The doping variation originates from the rotation during crystal growth in the float‐zone or Czochralski process, respectively. Experimentally, variations of the pore diameter up to 7% can occur. These so‐called striations limit performance of possible applications of macroporous silicon. As doping inhomogeneities are the reason for the striations, uniformly doped silicon wafers by neutron transmutation doping were used for the first time. Photoelectrochemical etching of neutron transmutated silicon has been carried out and the pore diameter fluctuation has been reduced by about 40% compared to standard doped float‐zone wafers. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Quantitative depth profile analysis of boron implanted silicon by pulsed radiofrequency glow discharge time-of-flight mass spectrometry

The analytical potential of pulsed radiofrequency glow discharge time-of-flight mass spectrometry (pulsed-rf-GD-TOFMS) is investigated for fast quantitative analysis of major and dopant elements in bulk and thin film layers. This technique does not require sampling at ultra-high vacuum conditions and so it facilitates high sample throughput compared to reference techniques as secondary ionization mass spectrometry (SIMS). In this paper, bulk and boron implanted silicon samples are analyzed. Boron concentration in Si samples is calculated from calibration curves obtained using solar grade silicon and B doped silicon wafers as calibrating materials, and using 29Si + ion signal as internal standard. Qualitative depth profiles of 10B implanted silicon are determined in a few seconds using the low-pressure pulsed-rf-GD-TOFMS system. Additionally, quantitative depth profiles are easily determined making use of the calibration curves. A good agreement with the depth profiles measured using SIMS was obtained, demonstrating the analytical potential of the pulsed-GD-TOFMS system for fast, sensitive and high depth resolution analysis of implanted silicon samples.

Ultimate quality factor of silica microtoroid resonant cavities

Silica optical microcavities with quality (Q factors above 1×108 have applications throughout science and engineering. While both the microtoroid and microsphere resonant cavity have demonstrated Q&amp;gt;1×108, only the microsphere has surpassed 1×109. Surprisingly, the reason for this performance disparity is directly related to type of silicon substrate used in the fabrication process. In the present work, the theoretical Q of planar toroidal silica resonant cavities is calculated and compared to experimental results from a series of devices fabricated from oxide on doped silicon wafers. As predicted, the Q depends on the substrate dopant concentration.

Study and development of non-aqueous silicon-air battery

Silicon-air battery utilizing a single-crystal heavily doped n-type silicon wafer anode and an air cathode is reported in this paper. The battery employs hydrophilic 1-ethyl-3-methylimidazolium oligofluorohydrogenate [EMI·(HF) 2.3F] room temperature ionic liquid electrolyte. Electrochemical studies, including polarization and galvanostatic experiments, performed on various silicon types reveal the predominance performance of heavily doped n-type. Cell discharging at constant current densities of 10, 50, 100 and 300 μA cm −2 in ambient atmosphere, shows working voltages of 1.1–0.8 V. The study shows that as discharge advances, the moist interface of the air electrode is covered by discharge products, which prevent a continuous diffusion of oxygen to the electrode–electrolyte interface. The oxygen suffocation, governed by the settlement of the cell reaction products, is the main factor for an early failure of the cells. Based on the results obtained from scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy studies, we propose a series of reactions governing the discharge process in silicon-air batteries, as well as a detailed mechanism for silicon oxide deposition on the air electrode porous carbon.

Detection of arsenic dopant atoms in a silicon crystal using a spherical aberration corrected scanning transmission electron microscope

In recent silicon transistors, fluctuation of the gate threshold voltage due to statistical variation in the number of dopant atoms has been pointed out to be a serious problem. For this reason, characterization methods are required which can detect individual dopant atoms within the transistor. In this paper, we present a technique for visualizing individual arsenic (As) atoms in a doped silicon crystal using our developed spherical aberration corrected scanning transmission electron microscope (STEM) with a convergent electron probe with a half angle of 30 mrad to view very thin doped silicon crystals from the [001] direction. The STEM images show the distribution of As dopant atoms within a 2.7 nm defocusing range around the focal position. It was found that in a highly doped silicon wafer following rapid thermal annealing, clustering of As atoms was extremely rare.

Ferromagnetic nanostructure arrays self-assembled in mesoporous silicon

The investigated nanocomposite system is composed of a porosified silicon wafer and embedded ferromagnetic nanostructures. Porous silicon achieved by anodization of a highly doped (100) silicon wafer offers straight pores grown in (001)-direction which are clearly separated from each other. Within the pores of the porous silicon matrix ferromagnetic nanostructures are precipitated. The obtained self-assembled hybrid system combines the electronic properties of silicon with the magnetic properties of the incorporated ferromagnetic metal. Such a magnetic system can be achieved by electrochemical deposition of a transition metal from a metal salt solution into the pores of the nanostructured silicon skeleton. The porous silicon/metal nanocomposites are characterized by electron microscopy (SEM, TEM) to get information about the interior interface and SQUID-magnetometry. Furthermore the structural analyzed regions are investigated by MFM to gain more local information about the magnetic state of the embedded nanostructures.