Showing papers on "Silicon published in 1991"

Porous silicon formation: A quantum wire effect

Abstract: Porous silicon layers grown on nondegenerated p‐type silicon electrodes in hydrofluoric acid electrolytes are translucent for visible light, which is equivalent to an increased band gap compared to bulk silicon. It will be shown that a two‐dimensional quantum confinement (quantum wire) in the very narrow walls between the pores not only explains the change in band‐gap energy but may also be the key to better understanding the dissolution mechanism that leads to porous silicon formation.

Visible light emission due to quantum size effects in highly porous crystalline silicon

Abstract: LIGHT-emitting devices based on silicon would find many applications in both VLSI and display technologies, but silicon normally emits only extremely weak infrared photoluminescence because of its relatively small and indirect band gap1. The recent demonstration of very efficient and multicolour (red, orange, yellow and green) visible light emission from highly porous, electrochemically etched silicon2,3 has therefore generated much interest. On the basis of strong but indirect evidence, this phenomenon was initially attributed to quantum size effects within crystalline material2, but this interpretation has subsequently been extensively debated. Here we report results from a transmission electron microscopy study which reveals the structure of the porous layers that emit red light under photoexcitation. Our results constitute direct evidence that highly porous silicon contains quantum-size crystalline structures responsible for the visible emission. We show that arrays of linear quantum wires are present and obtain images of individual quantum wires of width <3 nm.

A silicon-based, three-dimensional neural interface: manufacturing processes for an intracortical electrode array

Abstract: A method is described for the manufacture of a three-dimensional electrode array geometry for chronic intracortical stimulation. This silicon based array consists of a 4.2*4.2*0.12 mm thick monocrystalline substrate, from which project 100 conductive, silicon needles sharpened to facilitate cortical penetration. Each needle is electrically isolated from the other needles, and is about 0.09 mm thick at its base and 1.5 mm long. The sharpened end of each needle is coated with platinum to facilitate charge transfer into neural tissue. The following manufacturing processes were used to create this array: thermomigration of 100 aluminum pads through an n-type silicon block, creating trails of highly conductive p/sup +/ silicon isolated from each other by opposing pn junctions; a combination of mechanical and chemical micromachining which creates individual penetrating needles of the p/sup +/ silicon trails; metal deposition to create active electrode areas and electrical contact pads; and array encapsulation with polyimide. >

Compressive-stress-induced formation of thin-film tetrahedral amorphous carbon

Abstract: Thin tetrahedrally coordinated amorphous carbon (ta-C) films have been grown using a filtered vacuum arc. ta-C is a new allotrope of carbon whose existence was previously thought to be unlikely. A model is proposed which accounts for the formation and structure of these films on the basis of the compressive stress generated by the shallow implantation of carbon ions. An optimal range of beam energies between 15 and 70 eV, a high film stress, and a graphitic surface are predicted and confirmed by experimental evidence. Computer simulation of the growth confirms that high compressive stress is generated by impact energies in this range.

Generation of diamond nuclei by electric field in plasma chemical vapor deposition

Abstract: Generation of diamond nuclei has been realized on a silicon mirror surface in plasma chemical vapor deposition. Prior to the normal diamond growth process, a predeposition process of several minutes duration was introduced in which a high methane fraction in the feed gas was used and in which a negative bias voltage was applied to the substrate. This resulted in an enormous enhancement of the generation of diamond nuclei. For the onset of diamond nucleation the minimum voltage was −70 V and the minimum methane fraction in the methane‐hydrogen feed gas was 5%. Density of a diamond nuclei as high as 1010/cm2 was attained with this method.

A silicon neuron.

Abstract: By combining neurophysiological principles with silicon engineering, we have produced an analog integrated circuit with the functional characteristics of real nerve cells. Because the physics underlying the conductivity of silicon devices and biological membranes is similar, the 'silicon neuron' is able to emulate efficiently the ion currents that cause nerve impulses and control the dynamics of their discharge. It operates in real-time and consumes little power, and many 'neurons' can be fabricated on a single silicon chip. The silicon neuron represents a step towards constructing artificial nervous systems that use more realistic principles of neural computation than do existing electronic neural networks.

Stress‐related problems in silicon technology

Abstract: The silicon integrated‐circuits chip is built by contiguously embedding, butting, and overlaying structural elements of a large variety of materials of different elastic and thermal properties. Stress develops in the thermal cycling of the chip. Furthermore, many structural elements such as CVD (chemical vapor deposition) silicon nitride, silicon dioxide, polycrystalline silicon, etc., by virtue of their formation processes, exhibit intrinsic stresses. Large localized stresses are induced in the silicon substrate near the edges and corners of such structural elements. Oxidation of nonplanar silicon surfaces produces another kind of stress that can be very damaging, especially at low oxidation temperatures. Mismatch of atomic sizes between dopants and the silicon, and heteroepitaxy produce another class of strain that can lead to the formation of misfit dislocations. Here we review the achievements to date in understanding and modeling these diverse stress problems.

Field-Induced Nanometer- to Atomic-Scale Manipulation of Silicon Surfaces with the STM

Abstract: The controlled manipulation of silicon at the nanometer scale will facilitate the fabrication of new types of electronic devices. The scanning tunneling microscope (STM) can be used to manipulate strongly bound silicon atoms or clusters at room temperature. Specifically, by using a combination of electrostatic and chemical forces, surface atoms can be removed and deposited on the STM tip. The tip can then move to a predetermined surface site, and the atom or cluster can be redeposited. The magnitude of such forces and the amount of material removed can be controlled by applying voltage pulses at different tip-surface separations.

Deposition of device quality, low H content amorphous silicon

Abstract: Device‐quality hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device‐quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament. These low H content films show an Urbach edge width of 50 mV and a spin density of ∼1/100 as large as that of glow discharge films containing comparable amounts of H. High substrate temperatures, deposition in a high flux of atomic H, and lack of energetic particle bombardment are suggested as reasons for this behavior.

Hydrogen in semiconductors

Abstract: :N. H. Nickel, Introduction to Hydrogen in Semiconductors II. Noble M. Johnson and Chris G. Van de Walle, Isolated Monatomic Hydrogen in Silicon. Yu. V. Gorelkinskii, Electron Paramagnetic Resonance of Hydrogen and Hydrogen-Related Defects in Crystalline Silicon. N. H. Nickel, Hydrogen in Polycrystalline Silicon. W. Beyer, Hydrogen Phenomena in Hydrogenated Amorphous Silicon. Chris G. Van de Walle, Hydrogen Interactions with Polycrystalline and Amorphous Silicon-Theory. K. M. McNamara Rutledge, Hydrogen in Polycrystalline CVD Diamond. R. L. Lichti, Dynamics of Muonium Diffusion, Site Changes and Charge-State Transitions. Matthew D. McCluskey and Eugene E. Haller, Hydrogen in III-V and II-VI Semiconductors. S. J. Pearton and J. W. Lee, The Properties of Hydrogen in GaN and Related Alloys. Jorg Neugebauer and Chris G. Van de Walle, Theory of Hydrogen in Ga N.

Optimized antireflection coatings for high-efficiency silicon solar cells

Abstract: Antireflection coatings for silicon solar cells have been optimized both theoretically and experimentally for a range of possible situations, such as single-layer and double-layer coatings, and on planar and microgrooved surfaces. The effect of a thin passivating silicon dioxide layer under the coating was also considered. A critical passivating oxide thickness of about 300 AA was found to be important for the design of these coatings. A new half-quarter-wavelength double layer antireflection coating can be achieved with very low reflection if the passivating oxide has to be thicker than this critical thickness. >

Electroluminescence in the visible range during anodic oxidation of porous silicon films

Abstract: Porous silicon/silicon structures under anodic oxidation conditions give rise to an electroluminescence phenomenon in the visible range. Using an optical multichannel analyzer the spectral distribution of the emitted light was measured−in situ−during the anodic oxidation step. Recorded spectra show a maximum which shifts continuously from red‐orange at the beginning of the process towards the yellow range. The visible emission well above the band gap of bulk silicon is attributed to a quantum size effect in the very small size (5–20 A) silicon island which constitutes the porous silicon skeleton. The light emission is interrupted when the current flow stops due to the formation of a continuous oxide layer at the porous silicon/silicon interface.

Impurity enhancement of the 1.54‐μm Er3+ luminescence in silicon

Abstract: The effect of impurity coimplantation in MeV erbium‐implanted silicon is studied. A significant increase in the intensity of the 1.54‐μm Er3+ emission was observed for different coimplants. This study shows that the Er3+ emission is observed if erbium can form an impurity complex in silicon. The influence of these impurities on the Er3+ photoluminescence spectrum is demonstrated. Furthermore we show the first room‐temperature photoluminescence spectrum of erbium in crystalline silicon.

Silicon oxycarbide glasses: Part II. Structure and properties

Abstract: Silicon oxycarbide glass is formed by the pyrolysis of silicone resins and contains only silicon, oxygen, and carbon. The glass remains amorphous in x-ray diffraction to 1400 °C and shows no features in transmission electron micrographs (TEM) after heating to this temperature. After heating at higher temperature (1500–1650 °C) silicon carbide lines develop in x-ray diffraction, and fine crystalline regions of silicon carbide and graphite are found in TEM and electron diffraction. XPS shows that silicon-oxygen bonds in the glass are similar to those in amorphous and crystalline silicates; some silicons are bonded to both oxygen and carbon. Carbon is bonded to either silicon or carbon; there are no carbon-oxygen bonds in the glass. Infrared spectra are consistent with these conclusions and show silicon-oxygen and silicon-carbon vibrations, but none from carbon-oxygen bonds. 29Si-NMR shows evidence for four different bonding groups around silicon. The silicon oxycarbide structure deduced from these results is a random network of silicon-oxygen tetrahedra, with some silicons bonded to one or two carbons substituted for oxygen; these carbons are in turn tetrahedrally bonded to other silicon atoms. There are very small regions of carbon-carbon bonds only, which are not bonded in the network. This “free” carbon colors the glass black. When the glass is heated above 1400 °C this network composite rearranges in tiny regions to graphite and silicon carbide crystals. The density, coefficient of thermal expansion, hardness, elastic modulus, index of refraction, and viscosity of the silicon oxycarbide glasses are all somewhat higher than these properties in vitreous silica, probably because the silicon-carbide bonds in the network of the oxycarbide lead to a tighter, more closely packed structure. The oxycarbide glass is highly stable to temperatures up to 1600 °C and higher, because oxygen and water diffuse slowly in it.

Atmospheric impregnation of porous silicon at room temperature

Abstract: Microporous and mesoporous Si layers contain a very large surface area that affects both their optical and electrical properties. Secondary ion mass spectroscopy (SIMS) analysis is used for the first time to simultaneously monitor all the major impurities on that surface. SIMS data on a microporous layer demonstrate that its chemical composition changes dramatically with time during ambient air exposure. Similar trends are observed for mesoporous layers. Extended storage in air at room temperature converts the hydride surface of freshly anodized layers to that of a contaminated native oxide. Characterization techniques need to take the metastability of the hydride surface into account since the structural, optical, and electrical properties of porous Si can consequently change with time upon exposure to ambient air. Low‐temperature photoluminescence and spectroscopic ellipsometry data on freshly anodized and ‘‘aged’’ microporous and mesoporous layers are chosen to illustrate typical changes in optical pro...

Structural relaxation and defect annihilation in pure amorphous silicon

Abstract: Thick amorphous Si layers have been prepared by MeV self-ion-implantation and the thermodynamic and structural properties examined by calorimetry, Raman-spectroscopy, and x-ray-diffraction techniques. Defects have been introduced into well-annealed amorphous and single-crystal Si by He, C, Si, and Ge bombardment. The defect structures are examined by these techniques and by transmission electron microscopy. The structure of amorphous Si in intermediate states of relaxation or annealing have been determined. It is shown that amorphous Si formed by either implantation or deposition contains a large population of point defects and point-defect clusters. Amorphous Si formed by laser quenching cannot be distinguished from well-annealed amorphous Si. Structural relaxation, also known as short-range ordering, can be understood as annihilation of a large fraction of these defects. Both structural relaxation in amorphous Si and defect annihilation in crystalline Si obey bimolecular reaction kinetics. The defect-formation and -annihilation processes are similar in amorphous and crystalline Si. Defect saturation occurs in amorphous Si at estimated defect concentrations of about 1 at. %. These formation and annihilation properties are intrinsic to pure amorphous Si. For hydrogenated amorphous Si, it is pointed out that the metastable-defect-creation and -annealing processes are essentially different from the annihilation processes in pure amorphous Si.

Current-induced light emission from a porous silicon device

Abstract: Experiments with light-emitting porous silicon (LEPOS) are described. The porous silicon was made from n-type silicon by anodization in an electrolytic cell by HF with an applied electrical current. Visible light emission was achieved by irradiation with ultraviolet light. Visible electroluminescence (EL) was achieved by applying a DC or AC voltage to a solid-state contact on top of the porous layer. Optical spectra from both experiments are shown. >

Nanosurface Chemistry on Size-Selected Silicon Clusters

Abstract: Studies of the chemistry that occurs on the nanosurfaces of size-selected silicon clusters reveal a number of fascinating qualitative similarities to the behavior of bulk surfaces. However, silicon clusters containing up to 70 atoms appear to be much less reactive than bulk silicon surfaces. This unexpected result suggests that these large silicon clusters are not just small crystals of bulk silicon, but have much more compact geometric structures

Transport properties of silicon

Abstract: Electrical conductivity, thermal conductivity, and thermoelectric power of single-crystalline silicon are investigated at temperatures between 2 and 300 K. From the measured data we calculate the mean free path of electrons and phonons and separate diffusion part and phonon-drag part of the thermoelectric power. Using a new method, we evaluate the mean free path of those phonons which are responsible for the phonon drag effect.

Pressure-induced silicon coordination and tetrahedral structural changes in alkali oxide-silica melts up to 12 GPa: NMR, Raman, and infrared spectroscopy

Abstract: The 29 Si and 23 Na NMR, Raman, and infrared spectra of glasses quenched from liquids at pressures up to 12 GPa for three alkali silicate compositions (Na 2 Si 2 O 5 , Na 2 Si 4 O 9 , K 2 Si 4 O 9 ) and silica (SiO 2 ) reveal systematic changes in the melt structure with pressure. The most novel change is the occurrence of [5] Si and [6] Si species at high pressures identified by peaks in the 29 Si MAS NMR spectra of the alkali silicate glasses. -from Authors

Chemical etching of vicinal Si(111): Dependence of the surface structure and the hydrogen termination on the pH of the etching solutions

Abstract: Infrared spectroscopy is used to study the etching process of stepped Si(111)9° surfaces as a function of the pH of the etching HF solutions. This process results in complete H termination of the silicon surface, including terraces, steps, and defects; the surface structure can therefore be well studied using infrared (IR) spectroscopy. Polarized IR absorption spectra of the Si–H stretching vibrations (i.e., in the region 2060–2150 cm−1) vary dramatically as the pH of the etching solutions increases from 2.0 to 7.8. In general, higher pH solutions yield sharper bands and more easily assigned spectra, making it possible to identify the step and terrace species and thus to infer the surface structure and step morphology (i.e., to investigate the etching process). The data are explained by a model involving different etching rates for each individual surface species: The highest rate of removal is for isolated adatom defects located on (111) planes and the lowest is for the ideally H‐terminated (111) planes ...

Method for forming a thin layer on a semiconductor substrate and apparatus therefor

Abstract: A method and apparatus for manufacturing a semiconductor device having a thin layer of material formed on a semiconductor substrate with a much improved interface between them are disclosed. A silicon substrate is heated up to a temperature around 300° C. in the presence of ozone gas under exposure to UV light. Through this process, organic contaminants that might be present on the surface of the silicon substrate are dissipated by oxidation, and a thin oxide film is formed on the substrate surface on the other. The silicon substrate with the thin oxide film coated thereon is then heated up to temperatures of 200°-700° C. in the presence of HCl gas under illumination to UV light to strip the oxide film off the substrate surface, thereby exposing the cleaned substrate surface. Finally, HCl cleaned surface of the silicon substrate is coated with a thin layer of material such as monocrystalline silicon without exposing the cleaned substrate surface. The method provides a semiconductor with the thin layer of material formed thereon having a well-controlled, well organized interface between them.

Mechanism of negative‐bias‐temperature instability

Abstract: Although negative‐bias‐temperature instability in metal‐oxide‐semiconductor integrated circuits has been minimized empirically, the exact mechanism is unknown. We argue in this paper that the mechanism of negative‐bias‐temperature instability can be modeled by a first‐order electrochemical reaction between hydrogenated trivalent silicon, a neutral water‐related species located in the oxide near the Si‐SiO2 interface, and holes at the silicon surface to form neutral trivalent silicon and a positively charged water‐related species. To show that such a reaction describes the phenomenon, we show that (1) water must be present in the oxide near the Si‐SiO2 interface, (2) induced interface and oxide‐fixed charge densities are equal, (3) the saturation interface‐trap and oxide‐fixed charge densities depend on the initial hole concentration at the silicon surface or aging field, (4) the buildup of these charge densities follows first‐order reaction kinetics, and (5) time constants for this charge buildup are inde...

Silicon oxycarbide glasses: Part I. Preparation and chemistry

Abstract: Silicone polymers were pyrolyzed to form silicon oxycarbides that contained only silicon, oxygen, and carbon. The starting polymers were mainly methyl trichlorosilane with a small amount of dimethyl dichlorosilane. NMR showed that the polymers had a silicon-oxygen backbone with branching and ring units. When the polymer was heated in hydrogen, toluene and isopropyl alcohol, used in production of the polymer, were given off in the temperature range 150 °C to 500 °C. Substantial decomposition of the polymer itself began only above about 700°by evolution of methane. The network of silicon-oxygen bonds and silicon-carbon bonds did not react and was preserved; the silicon-carbon bonds were linked into the silicon-oxygen network. The silicon oxycarbide was stable above 1000 °C, showing no dimensional changes above this temperature. The interior of the silicon oxycarbide was at very low effective oxygen pressure because oxygen diffused slowly in it. There was also a protective layer of silicon dioxide on the surface of the silicon oxycarbide.

Efficient pulsed laser removal of 0.2 μm sized particles from a solid surface

Abstract: Laser cleaning with pulsed ultraviolet and infrared lasers is successfully employed to remove particulate contamination from silicon wafer surfaces and from delicate lithography membrane masks. Particulate material investigated include latex, alumina, silicon, and gold. Gold particles as small as 0.2 μm can be effectively removed. This new and highly efficient laser cleaning is achieved by choosing a pulsed laser with short pulse duration (without causing substrate damage), and a wavelength that is strongly absorbed by the surface; the removal efficiency is further enhanced by depositing a liquid film of thickness on the order of micron on the surface just before the pulsed laser irradiation.

The brittle-ductile transition in silicon

Abstract: Experimental and theoretical studies of the brittle-ductile transition (BDT) of precracked single crystals of silicon are discussed. For a given strain-rate the temperature T c at which the BDT occ...

Silicon‐On‐Insulator by Wafer Bonding: A Review

Abstract: Various approaches to wafer bonding technology are reviewed. Bonding kinetics are discussed as well as different mechanical and chemical thinning techniques. The structural and electrical qualities of state‐of‐the‐art bonded SOI silicon films and devices built in them are detailed. Problems faced by this technology are evaluated.

Molded circuit package having heat dissipating post

Abstract: A major issue in the semiconductor industry is the amount of power that a silicon device dissipates. As the density of silicon integrated circuits increases with improvements in wafer processing, so does the amount of heat which must be evacuated. If the power of the silicon devices exceeds one watt, the plastic encapsulating material normally yields to the more expensive ceramic or metal packages which can dissipate thermal energy more efficiently. The conventional molded package is a silicon device such as a chip mounted onto a copper paddle which spreads the heat radially in the material and is bonded to leads via thin wires. The three major paths for the heat to escape are by conduction through the molding compound to the surface of the package where removal is by convection, and by conduction from the silicon device through the thin wires to the leads of the package and then to the printed circuit board, and by a heat conducting paddle which radially spreads the heat through the molding compound. In each instance, the heat dissipating path is through a relatively poor thermal conductor. In accordance with the principles of the invention, there is provided an improved thermal path for conducting heat from the silicon device to the surface of the plastic package. The improved thermal path comprises a post of heat conducting material positioned to extend from the silicon device to a surface of the plastic package. One end of the post is positioned to receive heat generated by the silicon device and the other end is exposed to air at the surface of the plastic package. A waist section of the post located between the ends of the post has a dimension which is different than that of the end. Additionally the ends can have dimensions which are either equal or unequal. The post configuration enables the molded package to capture the post without creating cracks in the molded package.