Organosilicon Precursors Research Articles

Direct-write deposition with a focused electron beam

The fabrication of nanostructured dielectrics of high purity produced by electron beam induced deposition (EBID) was investigated. Additionally, the process parameters were optimized towards high deposition rate. Silicon oxide was chosen as exemplary dielectric. The deposition was performed with an electron microscope with a self-designed nozzle system. An organo-silicon precursor was used to deposit silicon oxide. The increase of the oxygen content and the reduction of carbon contaminations of the depositions were preformed by adding molecular oxygen. Patterns of large areas as well as nm-scale arrays were fabricated. To optimize the deposition rate the correlation between beam parameters and deposition rate was studied. It has been shown that this direct-write method allows obtaining arbitrary structures with superior material quality.

Silicon Oxide Thin Film Deposition on Alumina in a Circulating Fluidized Bed Reactor

Silicon oxide deposition on fine alumina powders by plasma-enhanced chemical vapor deposition (PECVD) at atmospheric pressure was carried out in a circulating fluidized bed reactor. To deposit silicon oxide on alumina powders, the organo-silicon source precursors (tetraethoxysilane (TEOS) and hexamethyldisiloxane (HMDSO)) and oxygen were used as the reactant gases while helium and argon were used as the dilute gases. The surface property of plasma-treated alumina powder varies from hydrophobic to hydrophilic in the surface composition with variation of the discharge power. In oxygen-containing atmospheres, chemical composition of the deposited film is more inorganic with increasing the discharge power and the flow ratio of O2/precursor for both organo-silicon precursors.

NMR Spectroscopy and Atomic Force Microscopy Characterization of Hybrid Organic – Inorganic Coatings

AbstractHybrid organic–inorganic (O‐I) epoxide‐based products made from functionalized organosilicon precursors, oligomeric di‐ and triamines and in some cases colloidal silica particles were characterized by NMR spectroscopy and atomic force microscopy (AFM). The kinetics and reaction mechanism of condensation reactions, structure and segmental dynamics of final films, as well as homogeneity and partial ordering were studied by solid‐state NMR spectroscopy (2D CRAMPS, 2D 1H‐13C WISE, relaxation experiments); the surface morphology and other surface characteristics were determined by AFM.

Cyclopentadienyl-functionalised polyhedral silsesquioxanes as building blocks for new nanostructured materials

This work is to design new organosilicon precursors, which contain both siloxane and cyclopentadienyl functionalities and use these compounds as building blocks for new nanomaterials. Polyhedral silsesquioxanes, (RSiO 1.5) n ( n = 8 and 10) with cyclopentadienyl (R = –C 5H 5 or –(CH 2) 3–C 5H 5) functionalities have been prepared by hydrolytic condensation of the correspondent silicon organic precursors RSiCl 3 or RSi(OC 2H 5) 3. The products with cyclopentadienyl groups have been used to prepare new cross-linked 3D polymeric materials by Diels–Alder reaction. The compounds have been characterised by multinuclear ( 1H and 29Si) NMR, ESI MS and IR spectroscopy, UV/Vis spectrometry, gel permeation chromatography and scanning electron microscopy. The approach above seems to be very promising for the preparation of new nanostructured materials.

Stereoselective histidine sensor based on molecularly imprinted sol-gel films

A piezoelectric sensor coated with a thin molecularly imprinted sol-gel film has been developed for the determination of l-histidine in the liquid phase. Without preprotection, l-histidine was imprinted directly into silica sol-gel films that consisted of a hybrid mixture of functionalized organosilicon precursors (phenyltrimethoxysilane and methyltrimethoxysolane). The viscoelasticity of the film in the air and in buffer solution has been studied by the piezoelectric quartz crystal impedance technique. The binding of l-histidine to the imprinted film in the liquid phase was investigated by the piezoelectric microgravimetry and electrochemical impedance technique. Scatchard analysis showed that the maximum binding site ( Q max) of the l-histidine imprinted sol-gel film is about 23.7 μmol/g. A linear range from 5.0 × 10 −8 to 1.0 × 10 −4 M for a detection of l-histidine has been observed with a detection limit of 2.5 × 10 −8 M for S/N = 3. The proposed imprinted sol-gel sensor exhibits good stability, high specificity, and excellent stereoselectivity.

Reduction of semiconductor process emissions by reactive gas optimization

Tailoring the chemical environment in plasmas by addition of reactive gases to affect byproduct formation has been demonstrated to reduce perfluorocompound (PFC) emissions. Perfluorocompound emissions from dielectric etch processes are reduced by oxygen addition, which reduces polymerization and increases etch rates, primarily by affecting the fluorine or carbon in the plasma, and secondarily, by affecting resist erosion. Oxygen or water vapor introduced upstream of plasma abatement devices reduces PFC reformation by preferentially combining with carbon and fluorine-containing radicals to form thermodynamically favorable byproducts that are non- or low-global warming. Introducing oxygen to low-k chemical vapor deposition (CVD) chamber clean processes also reduces PFC emissions, primarily by reducing CF/sub 4/ by forming thermodynamically stable CO and CO/sub 2/. Analogously, adjusting the fuel or the oxidizer flow in fuel-fired abatement devices provides a higher flame temperature where thermal cracking of higher molecular weight low-k CVD organosilicon precursors can more readily occur, allowing the carbon-rich precursors to more completely oxidize.

Fluoride-promoted cross-coupling reactions of alkenylsilanols. Elucidation of the mechanism through spectroscopic and kinetic analysis.

The mechanism of the palladium-catalyzed cross-coupling reaction of (E)-dimethyl-(1-heptenyl)silanol ((E)-1) and of (E)-diisopropyl-(1-heptenyl)silanol ((E)-2) with 2-iodothiophene has been investigated through spectroscopic and kinetic analysis. A common intermediate in cross-coupling reactions of several types of organosilicon precursors has been identified as a hydrogen-bonded complex between tetrabutylammonium fluoride (TBAF) and a silanol. The order in each component has been determined by plotting the initial rates of the cross-coupling reaction at varying concentrations. These data provide a mechanistic picture that involves a fast and irreversible oxidative insertion of palladium into the aryl iodide and a subsequent turnover-limiting transmetalation step achieved through a fluoride-activated disiloxane derived from the particular silanol employed. The inverse order dependence of TBAF at high concentration is consistent with a pathway that proceeds through a hydrogen-bonded complex which is the lowest energy silicon species in solution.

Organosilicon Thin Films Deposited from Cyclic and Acyclic Precursors Using Water as an Oxidant

Pulsed-plasma chemical vapor deposition was used to deposit thin films from four different organosilicon precursors using water as the oxidant. The precursors varied in structure, chemical composition, and type of organic substituent. Differences in film structure were observed based on precursor structure and type of organic substituents. More reactive substituents, such as vinyl groups, facilitated cross-linking. At low power (200 W), film structure was dictated by precursor identity. At high power (400 W) film structure became more uniform and precursor identity was less important. Mechanical and thermal properties correlated with plasma power and could be explained by the continuous random network theory and percolation of rigidity arguments. Low-power samples are relatively soft, with hardness values between 0.13 and 0.54 GPa. High-power samples are more extensively cross-linked and oxidized, resulting in enhanced mechanical properties, and had hardness values between 0.68 and 3.2 GPa, depending upon precursor identity. Thermal stability was strongly correlated to the degree of cross-linking, with non-cross-linked films showing up to 30% thickness loss upon annealing. Cross-linked films exhibited less than 8% thickness loss. Dielectric constants for the films ranged between 2.4 and 4.3 and were primarily dependent upon the extent of oxidation and organic content remaining in the films. © 2004 The Electrochemical Society. All rights reserved.

Preparation and characterization of hybrid organic–inorganic epoxide‐based films and coatings prepared by the sol–gel process

AbstractHybrid organic–inorganic coatings and free‐standing films were prepared and characterized. The hybrids were prepared from [3‐(glycidyloxy)propyl]trimethoxysilane, diethoxy[3‐(glycidyloxy)propyl]methylsilane, poly(oxypropylene)s of different molecular weights end‐capped with primary amino groups (Jeffamines D230, D400, and T403), and colloidal silica particles with hydrochloric acid as a catalyst for the sol–gel process and water/propan‐2‐ol mixtures as solvents. The structure evolution during the network formation was followed by NMR spectroscopy and small‐angle X‐ray scattering; the surface morphology was tested by atomic force microscopy. The influence of the reaction conditions (the organosilicon precursor, oligomeric amine, ratio of functional groups, and method of preparation) on the network buildup and product properties was studied and examined. The mechanical testing, based on stress–strain experiments, in combination with dynamic mechanical thermal analysis served as an effective instrument for the optimization of the reaction conditions for the preparation of products with desired properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 937–950, 2004

Fluorescent response of sol–gel derived ormosils for optical ammonia sensing film

Optical sensing films for ammonia have been investigated based on a fluorescent indicator aminofluorescein (AF). AF was immobilized in diverse organically modified silicates (ORMOSILSs) obtained by copolymerizing various proportions of methyltrimethoxysilane (Me–TriMOS), phenyltrimethoxysilane (Ph–TriMOS), dimethyldimethoxysilane (DiMe–DiMOS), and diphenyldimethoxysilane (DiPh–DiMOS) with tetramethoxysilane (TMOS). The effective polarities of ormosils were probed by using the solvatochromic dye E T (30) [2,6-diphenyl-4-(2,4,6-triphenyl- N-pyridino)]phenolate. Compared with the fluorescent responses of fluorescein and fluorescein isothiocyanate, the fluorescent intensity enhancement of AF for ammonia was caused by the reaction between ammonia and the NH 2 group on AF. The reaction may cause the reduction of the intermolecular self-quenching of AF to make a fluorescence enhancement of sensing film in NH 3 solution. The ammonia sensing range and rate of response were found to highly depend on the type and content of organosilicon precursors employed. Films prepared with a 1:3, 1:1.5, 1:1.2, or 1:1 mole ratio (TMOS:Me–TriMOS, TMOS:Ph–TriMOS, TMOS:DiMe–DiMOS, or TMOS:DiPh–DiMOS) was found to be the best in terms of stability and response. Their detection limits for ammonia in water was 0.01, 0.5, 0.2, and 0.5 μg ml −1, respectively.

Temperature-resolved Fourier transform infrared study of condensation reactions and porogen decomposition in hybrid organosilicon-porogen films

Composite organosilicon/porogen thin films were deposited via pulsed-plasma chemical vapor deposition. The organosilicon monomer was polymerized using water as the oxidant, allowing incorporation of silanol (Si–OH) moieties for subsequent condensation reactions and crosslinking for enhanced mechanical properties. The porogen monomer [methylmethacrylate (MMA)] was codeposited in the same step, and the degree of MMA incorporation was shown to scale with both the peak plasma power and porogen flow rate. Fourier transform infrared (FTIR) spectroscopy spectra of the composite material show features from both the organosilicon precursor and the porogen species, indicating that both materials are successfully incorporated into the thin film. The kinetics of both the condensation reaction and porogen removal were determined by a temperature/time-resolved FTIR method. The condensation reaction and crosslinking events occur between 100 and 425 °C. Porogen decomposition occurs simultaneously between approximately 325 and 400 °C, which is consistent with the decomposition of poly(methylmethacrylate). Using these data, the activation energy for the primary decomposition mode was found to be approximately 53.6 kJ/mol (12.8 kcal/mol). Both the index of refraction and the dielectric constant scale with the degree of porogen removal, suggesting the formation of free volume in the films. The lowest index of refraction and dielectric constant obtained was 1.404 and 2.3, respectively, for a 1 h anneal at 425 °C. Worst-case thickness loss for the films was approximately 36% of the as-deposit thickness.

Pulse-modulated plasma-enhanced chemical vapor deposition of SiO 2 coatings from octamethylcyclotetrasiloxane

Silicon dioxide coatings can be grown at low substrate temperatures in a pulse-modulated microwave electron cyclotron resonance (ECR) oxygen plasma with octamethylcyclotetrasiloxane (OMCTS) as the organosilicon precursor. The 2.45 GHz microwave power was pulse-modulated with repetition frequencies of 20 Hz–20 kHz, duty ratios (pulse on-time/pulse period) from 25 to 100%, and peak microwave power from 800 to 2400 W. The coatings are SiO 2-like with Si:O ratios of approximately 3:4 and carbon percentages of 20–25%. Pulsed plasma deposition significantly lowers the deposition substrate temperature as the peak power and duty ratio decrease. With 1600 W input continuous microwave power, substrate temperatures were 140–150 °C after 10 min of deposition, while with a 50% pulse duty cycle and 1600 W peak power the temperature decreased to 90 °C. The coating hardness decreased with pulsed operation compared to continuous operation, unless the average microwave power levels were made equivalent. Deposition growth rates depended only weakly on the pulse repetition frequency and duty ratio, but increased strongly as the pulse peak power was raised. Pulsed deposition at 800 W peak power and 50% duty ratio gave a growth rate of 0.5–0.6 μm/min for all frequencies between 20 Hz and 20 kHz, increasing to 0.8–0.9 μm/min at 1600 W peak power.

Organosilsesquioxane Particles Prepared by Controlled Sol-Gel Process or Heterocondensation with Colloidal Silica Particles: A Novel Route Towards Nanoporous Silica Particles by a Templating Effect

Hybrid organic-inorganic particles containing labile organic templates have been prepared by either controlled Sol-Gel processing or co-condensation of colloidal silica particles with organosilicon precursors. Chemical removal of the templating organic spacer led to monomodal, microstructured porous silica particles exhibiting up to 50% porosity. Particle size and distribution, and porosity varied depending upon the process and the chemistry used to remove the porogen organic groups.

Mechanical Properties of Organosilicon Thin Films Deposited from Cyclic and Acyclic Precursors using Water as an Oxidant.

AbstractPulsed-plasma chemical vapor deposition was used to deposit thin films from four different organosilicon (OSG) precursors, using water as the oxidant. The OSG precursors varied in structure (cyclic or acyclic), chemical composition (siloxane or silane), and type of organic substituent. Significant differences in final film structure were observed based on precursor identity, with the primary result being that cyclic siloxane precursors yielded films with a greater degree of crosslinking. The identity of the organic substituents was shown to affect the crosslinking potential, in that more reactive side groups, such as vinyl groups, facilitated the formation of crosslinking groups. At low power (200 W), film structure was dictated by precursor identity, whereas at high power (400 W), film structure became more uniform and precursor identity was less important. Mechanical properties tracked with plasma power, with low power samples being relatively soft, with hardness values between 0.126 GPa and 0.536 GPa. Samples produced at higher powers are more extensively crosslinked, resulting in enhanced mechanical properties. Samples produced at high powers had hardness values between 0.679 and 3.22 GPa, depending upon precursor identity. Dielectric constants ranged between 2.3 and 4.0.

Optimized Materials Properties for Organosilicate Glasses Produced by Plasma-Enhanced Chemical Vapor Deposition

AbstractIn this paper we examine the relationship between precursor structure and material properties for films produced from several leading organosilicon precursors on a common processing platform. Results from our study indicate that for the precursors tested the nature of the precursor has little effect upon film composition but significant impact on film structure and properties.

Fabrication of titanium carbonitride based cermets with graded structure : I. Konyashin. (Max-Planck Inst. for Metallforschung, Stattgart, Germany.) Int. J. Refract. Metals/Hard Mater., Vol 19, No 4–6, 2001, 523–526

Si3N4/SiC nanocomposite materials are of great interest for structural applications at high temperature. In silicon nitride based ceramics, the small size and the spherical shape of the grains constituting the material are two important parameters in favour of high temperature deformation. Therefore, SiCN nano-sized powders are real candidates as starting materials to elaborate dense Si3N4/SiC nanocomposites exhibiting the microstructure required for ductility at high temperature. SiCN nanopowders with different chemical compositions and characteristics can be prepared by CO2 laser pyrolysis of organosilicon precursors. Laser pyrolysis of gaseous precursors is able to produce partly crystallised SiCN nanoparticles exhibiting a reasonable thermal stability and suitable for elaboration of ceramic materials. In order to reduce the cost and to improve the safety of the process, an aerosol generated from a liquid precursor, hexamethyldisilazane (HMDS), has also been used to synthesised SiCN nanopowders. However, in this latter case the powders obtained exhibit a high weight loss during heat treatment at high temperature. Therefore, in this study the effects of various synthesis parameters (chemical nature of the precursor and laser power) on the degree of crystallisation and on the thermal stability of nanopowders are investigated. Characteristics of powders such as chemical composition, morphology, structure and thermal stability are reported. A correlation between the synthesis conditions of powders and their thermal stability is established, and the synthesis parameters enabling improvement of thermal stability are determined.

Comparative performance of various plasma polysiloxane films for the pervaporative recovery of organics from aqueous streams

Thin SiO x C y H z film membranes were deposited from two different organosilicon precursors, one cyclic and one linear, in a low-frequency plasma polymerisation process. The ability of the films for effective recovery of various organic contaminants from aqueous waste was tested using the process of pervaporation. Four separate organic components, phenol, chloroform, pyridine and methylisobutylketone (MIBK), each representative of an industrially significant family of chemicals, were chosen for evaluation. Trends between the pervaporation performances of plasma polysiloxane membranes and the composite plasma parameter V/ FM ( V: input voltage; F: monomer flow rate; M: monomer molecular weight) were found. Pervaporation measurements reveal that polysiloxane membranes synthesised by the plasma deposition process are sufficiently permeable for the mass transfer boundary layer above the membrane to be dominant. The permeability of plasma membranes formed from cyclic octamethylcyclotetrasiloxane were up to an order of magnitude more permeable than those formed from linear hexamethyldisiloxane. Future work should involve vapour permeation.

Nanoporous silica particles prepared by chemical reactivity of ORMOSILs

Hybrid organic–inorganic particles containing labile organic templates have been prepared by either controlled sol–gel processing or co-condensation of colloidal silica particles with organosilicon precursors. Chemical removal of the templating organic spacer led to monomodal, porous microstructured silica particles exhibiting up to 50% porosity. Particle size and distribution, and porosity varied depending upon the process and the chemistry used to remove the porogen organic groups.

Laser synthesis of silicon carbonitride nanopowders; structure and thermal stability

Si3N4/SiC nanocomposite materials are of great interest for structural applications at high temperature. In silicon nitride based ceramics, the small size and the spherical shape of the grains constituting the material are two important parameters in favour of high temperature deformation. Therefore, SiCN nano-sized powders are real candidates as starting materials to elaborate dense Si3N4/SiC nanocomposites exhibiting the microstructure required for ductility at high temperature. SiCN nanopowders with different chemical compositions and characteristics can be prepared by CO2 laser pyrolysis of organosilicon precursors. Laser pyrolysis of gaseous precursors is able to produce partly crystallised SiCN nanoparticles exhibiting a reasonable thermal stability and suitable for elaboration of ceramic materials. In order to reduce the cost and to improve the safety of the process, an aerosol generated from a liquid precursor, hexamethyldisilazane (HMDS), has also been used to synthesised SiCN nanopowders. However, in this latter case the powders obtained exhibit a high weight loss during heat treatment at high temperature. Therefore, in this study the effects of various synthesis parameters (chemical nature of the precursor and laser power) on the degree of crystallisation and on the thermal stability of nanopowders are investigated. Characteristics of powders such as chemical composition, morphology, structure and thermal stability are reported. A correlation between the synthesis conditions of powders and their thermal stability is established, and the synthesis parameters enabling improvement of thermal stability are determined.

Gas diffusion and sorption properties of polysiloxane membranes prepared by PECVD

Thin a-SiO x C y H z film membranes were deposited from two different cyclic and linear organosilicon precursors in a low-frequency plasma polymerization process. The qualification of the films for effective gas permeation membranes was tested on the ester of cellulose substrates using N 2, H 2, CO 2 and CH 4. The gas permeability and diffusion coefficients were determined by using the constant-volume pressure-increase method. The solubility coefficients ( S) were obtained by using a gravimetric method with a quartz microbalance. Correlations between the composite plasma parameter ( V/ FM) ( V: input voltage, F: monomer flow rate and M: monomer molecular weight), which describes the energetic character of the plasma and the permeation performances of plasma polysiloxane membranes were established. Permeation measurements reveal that a wide range of gas transport properties can be obtained according to the applied plasma energy. The global mass transfer could be controlled by diffusion or sorption mechanism according to the relative influence of the different structural factors (chain packing density, chain flexibility and chemical composition) of plasma polysiloxane films directly related to deposition parameters.