SiOH Concentration Research Articles

Vacuum-ultraviolet absorption of amorphousSiO2: Intrinsic contribution and role of silanol groups

We present a study on the vacuum-ultraviolet (VUV) absorption properties of amorphous ${\text{SiO}}_{2}$ $(a{\text{-SiO}}_{2})$ with high concentrations of silanol groups (Si-OH). We found that the absorption spectra are made up of a couple of exponential profiles. The first, in the range from $\ensuremath{\sim}7.5$ to $\ensuremath{\sim}8.1\text{ }\text{eV}$, was attributed to Si-OH group absorption, while the second, in the range from $\ensuremath{\sim}8.1$ to $\ensuremath{\sim}8.25\text{ }\text{eV}$, was ascribed to the intrinsic absorption. The VUV absorption cross section of Si-OH groups in $a{\text{-SiO}}_{2}$ was determined as well. The intrinsic absorption was found to be affected by the Si-OH concentration: high silanol group contents allow lower values of the Urbach energy. This result is interpreted in terms of a reduction in the degree of disorder in wet materials.

High-Temperature Resistance Fiber Bragg Grating Temperature Sensor Fabrication

Fiber Bragg grating (FBG) temperature sensor and sensor arrays were applied widespread particularly in harsh environments. Although FBGs are often referring to permanent refractive index modulation in the fiber core, exposure to high-temperature environments usually results in the bleach of the refractive index modulation. The maximum temperature reported for the conventional FBG temperature sensor is around 600 degC due to its weak bonds of germanium and oxygen. In this paper, we report design and development of a novel high-temperature resistance FBG temperature sensor, based on the hydrogen-loaded germanium-doped FBG. The refractive index modulation in the FBG is induced by the molecular water. The results of our experiments have shown that the stability of the device is substantially increased at high temperature range. Due to the high bonds energy of hydroxyl and the low diffusivity of the molecular water, the thermal testing results of this temperature sensor show the thermal stability of hydrogen-loaded FBG can be increased by using annealing treatment; moreover, the highest erasing temperature for the device could reach to 1100 degC or more. The reflectivity of this new FBG depends on the concentration of Si-OH and indirectly related to the reflectivity of hydrogen-loaded FBG. Furthermore, the experimental results have provided a better understanding of the formation of the hydrogen-loaded FBGs and the chemical transfers at elevated temperatures in the fiber core

Influence of Si—OH groups on properties and avoidance for SiCOH films prepared by decamethylcyclopentasiloxane electron cyclotron resonance plasma

This paper investigates the effect of Si—OH groups on dielectric property and leakage current of the SiCOH low dielectric constant films deposited by decamethylcyclopentasioxane (D5) electron cyclotron resonance plasma. The results show that the increasing of Si—OH content in the films can lead to the increasing of dielectric constant k, decreasing of leakage current and rise in dielectric dispersion. The increasing of k value is the result of compensation of the decreasing of k value originated from cage by the strong polarization of Si—OH groups. The decreasing of leakage current at high Si—OH content is due to the low connecting probability p of networks because the networks break at the terminal Si—OH groups. In the case of high ionization degree of D5 plasma, more Si—OH groups break and form Si—O—Si linkages by chemical condensation occurring between proximal Si—OH groups. As a result, the k value of SiCOH films can be further reduced.

Effect of Si–OH group on characteristics of SiCOH films prepared by decamethylcyclopentasiloxane electron cyclotron resonance plasma

This paper investigates the effect of Si–OH group on dielectric property and leakage current of the SiCOH low dielectric constant films deposited by decamethylcyclopentasiloxane electron cyclotron resonance plasma. The results show that the increasing of Si–OH content in the films can lead to the increasing of dielectric constant k, decreasing of leakage current and stronger dielectric dispersion. Due to the strong polarization of Si–OH group, it leads to the increase of k value of the SiCOH films. The decreasing of leakage current at high Si–OH content is due to the low connecting probability p of networks because the networks break at the terminal Si–OH groups. At the case of high ionization degree of precursor, more Si–OH groups break and form Si–O–Si linkages by condensation chemistry occurring between proximal Si–OH groups. As a result, the k value of SiCOH films can be further reduced.

Interstitial oxygen molecules in amorphous SiO2. II. The influence of common dopants (SiOH, SiF, and SiCl groups) and fictive temperature on the decay of singlet photoluminescence

Time decay of photoluminescence due to interstitial oxygen molecules (O2) in synthetic amorphous SiO2(a-SiO2) was studied by varying the fictive temperature and the concentrations of common dopants (SiOH, SiCl, and SiF groups). The decay constant is insensitive to the fictive temperature, but strongly depends on the type of dopants: it is reduced by the nonradiative decay via an energy transfer from O2 to the vibrational modes of the dopants. The increases in the nonradiative decay rate due to SiOH, SiF, and SiCl groups are strong, slight, and negligible, respectively, which correlates with their vibrational energies. The quantum yield decreases by ∼20% as the SiOH content increases from 1017 to 1020cm−3. The deviation from the single exponential decay is due to the shape variation in the a-SiO2 network cages that surround O2, and to the distance distribution between O2 and SiOH groups.

Chemical and dielectrical characteristics of ultrathin oxides grown by atomic force microscopy and scanning electron beam

We report a comparative study on the chemical and dielectrical properties of ultrathin oxides grown by atomic force microscopy (AFM) and scanning electron beam (SEB) techniques. Oxide grown by AFM (AFM oxide) shows preferential etching as compared to oxide grown by SEB (SEB oxide). The structural and chemical features of these oxides were probed using time-of-flight secondary ion mass spectrometry (TOF-SIMS) time profiling. It was found that AFM oxide is richer in Si–H and Si–OH content, while SEB oxide is oxygen rich and relatively dense in structure. The dielectric strength of AFM and SEB oxides were further evaluated by conducting AFM (c-AFM). The current–voltage characteristics and dielectric breakdown probability of these oxides were compared. The correlation between Si–H and Si–OH site formation and its impact on the chemical and dielectrical stability of AFM and SEB oxides was discussed.

Thin-film transformations and volatile products in the formation of nanoporous low-k polymethylsilsesquioxane-based dielectric

The thermal transformation of spin-cast thin films to produce nanoporous low-k dielectric layers has been investigated using polymethysilsesquioxane (PMSSQ) for the low-k matrix and polymethylmethacrylate-co-dimethylaminoethylacrylate (PMMA-co-DMAEMA) as the porogen which is volatilized to leave nanopores in the matrix. Surface analysis methods, including time of flight-secondary ion mass spectrometry and x-ray photoelectron spectroscopy, and thin film analysis by small-angle neutron scattering revealed the kinetics of matrix crosslinking, while thermal desorption mass spectrometry showed the evolution of gaseous reaction products from porogen and matrix during the complex chemical transformations which occur with thermal cycling from 100°Cto450°C. Matrix crosslinking occurs primarily at lower temperatures (100–225°C), while porogen diffusion and decomposition begins somewhat above 200°C, leading to phase separation which creates the final nanoporous structure. Since matrix and porogen reaction kinetics have some overlap, relative kinetics can be important: e.g., matrix crosslinking proceeds more rapidly for PMSSQ precursors with high Si–OH content cf. low SiOH content, with implications for the morphology of porogen-derived nanostructure. As surface species transform (matrix crosslinking) and disappear (porogen volatilization), their complements are seen in the gas phase as reaction and decomposition products. Porogen decomposition is ligand selective, in that the N-containing ligand of DMAEMA is volatilized at considerably lower temperatures (∼200°C) than that (∼400°C) for the remaining species (the PMMA ligand and the common backbone for both PMMA and DMAEMA).

Synthesis and characterization of polyimide/oligomeric methylsilsesquioxane hybrid films

AbstractIn this study, polyimide/silsesquioxane hybrid materials were synthesized from aminoalkoxysilane‐capped poly(pyromellitic dianhydride‐co‐4,4′‐oxydianiline) (PMDA‐ODA) and oligomeric methylsilsesquioxane (O‐MSSQ) precursors. The O‐MSSQ moiety was used to obtain well characterized nano‐inorganic cage and network structures in the hybrid materials. The effects of molecular structures and composition on the morphologies and properties of the prepared hybrid materials were studied. The phase separation of the prepared hybrid materials could be controlled by varying the molecular weight of the polyimide moiety, the SiOH end group content of the O‐MSSQ or the coupling agent. Homogeneous and transparent hybrid thin films were obtained from the low molecular weight polyimide moiety with a coupling agent, 3‐aminopropyltrimethoxysilane (APrTMS). However, microphase separation occurred if the molecular weight of the polyimide moiety was enhanced or was prepared without a coupling agent, as evidenced by atomic force microscopy (AFM), field emission scanning electron microscopy (FE‐SEM), and electron spectroscopy for chemical analysis (ESCA). The high SiOH content of the O‐MSSQ could enhance the bonding density between the organic and inorganic moiety and thus retard phase separation. The thermal and mechanical properties of the prepared hybrid materials were largely improved compared with the parent polyimide, PMDA‐ODA, and were demonstrated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and thermal‐stress analysis. The hybrid materials showed adjustable refractive index and dielectric constant by varying the O‐MSSQ content. The birefringence of the PMDA‐ODA was reduced by incorporating the O‐MSSQ moiety. This work revealed that the polyimide/O‐MSSQ hybrid materials could have potential applications as optical films or low dielectric constant materials. Copyright © 2004 Society of Chemical Industry

Structural control and properties of low‐dielectric‐constant poly(hydrogen silsesquioxane) precursors and their thin films

AbstractThe precursors of poly(hydrogen silsesquioxane) (PHSSQ) were synthesized from triethoxysilane (TES) through variations in the pH and molar ratio of water to TES (R1). The molecular structures of the prepared PHSSQ precursors were controlled by the reaction conditions, including the molecular weight, the content of SiOH end groups, and the cage/network ratio. The effect of the reaction conditions on the PHSSQ structure was quite different from that previously reported for poly(methyl silsesquioxane) (PMSSQ). The SiOH content and cage/network ratio of the prepared PHSSQ precursors increased with increasing R1 and pH. The molecular weight of the prepared PHSSQ precursors first increased with increasing R1 or pH and then decreased at high values of R1. These results were explained by the effects of R1 and pH on the hydrolysis and condensation reactions. The cage/network ratio of the prepared PHSSQ films decreased with increasing curing temperatures and resulted in an increasing refractive index or dielectric constant. The steric effect from the side groups yielded PMSSQ films that had a smaller refractive index or dielectric constant than the PHSSQ precursors. PHSSQ films have potential applications as low‐dielectric‐constant materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2653–2660, 2004

Growth and characterization of SiON thin films by using thermal-CVD machine

Silicon oxynitride (SiON) films have been deposited by thermal-CVD system and characterized by the ellipsometry, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The present paper reports the effect of deposition temperature on the properties of deposited SiON films. The stress of the film has been observed to be tensile in nature and it is found to be increased by increasing the deposition temperature through ellipsometric study. The decrease in refractive index of the film has been observed with increasing deposition temperature. The Si–O–Si and Si–N stretching characteristic peaks of SiON films have been observed with significant intensities by using FTIR spectroscopy. The peak positions of Si–O–Si stretching and the corresponding full width at half maxima (FWHM) have also been analyzed. The FWHM observed to be increasing on corresponding increase in the deposition temperature, which indicates the improvement in the quality of the deposited films. However, these films deposited in the temperature range of 780 to 850 °C, have more Si–H and less Si–OH contents. The SEM has been used to carry the morphological study of the films.

Structure and mechanical properties of thin films deposited from 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane and water

Pulsed-plasma chemical vapor deposition of 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane (V3D3) and water produced thin films with significant Si–OH content. Subsequent annealing of the films resulted in condensation of proximal Si–OH groups, further generating a Si–O–Si network and strengthening the film. Fourier-transform infrared spectroscopy analysis showed increasing OH content with increasing plasma duty cycle, and nanoindentation results confirmed increasing hardness with duty cycle, with the 10–40 duty cycle annealed sample having a hardness value of 0.527 GPa. These results were explained within the context of the continuous random network theory and percolation of rigidity arguments. Thermal stability was excellent, with a best-case thickness retention of 99.25% after a 2 h anneal at 400 °C under N2. Dielectric constants for the annealed films ranged between 2.55 and 2.9. The moderate power involved (200 W peak) is amenable to inclusion of a porogen species, opening the possibility of using this methodology to generate a porous thin film with adequate mechanical properties via chemical vapor deposition.

Nanoporous Silica Films Derived from Structural Controllable Poly(silsesquioxane) Oligomers by Templating

AbstractIn this study, nanoporous silica films were prepared from the poly(hydrogen silsesquioxane)(HSSQ) and a templating agent. Three different kinds of the HSSQ with different molecular weight and Si-OH end group content were prepared through the variation of the water/triethoxysilane ratio or pH. The templaing agent for generating nanopore was triphenylsilanol (TPS). The experimental results of refractive index, dielectric constant, and FE-SEM supported the formation of the nano-size pores in the prepared silica films. The dielectric constant of the prepared nanoporous thin films could be reduced form 2.89 (porosity: 12%) to 1.85 (porosity: 58%) by increasing the added TPS. The surface roughness of the prepared nanoporous silica film in comparison with the film thickness was less than 1%. For successful generating small and uniform nanopore in the film, low molecular weight or high Si-OH content of the prepared HSSQ would be required. The current approach is useful for preparing new kinds of low dielectric constant materials.

Characterization of Deposition Process, Microstructure and Interfacial States of Silicon Dioxide Film Using Tetraethylorthosilicate/ O 2 with Various Dilution Gases

We investigate gas-phase chemistry, and the properties of films and the interface formed by plasma chemical vapor deposition with tetraethylorthosilicate and various dilution gases. The dilution gas produced a faster deposition rate than either He or Ar dilution gases. Excited nitrogen gas reacts with TEOS to form NH radicals, which enhance the dissociation of TEOS. Compared with He, the dilution gas suppressed the formation of OH radicals in the gas phase and reduced the concentration of SiH and SiOH in the film. As a result, characteristics of the interface were improved. At the same deposition condition, the interface roughness was almost identical at approximately two to three atomic layers regardless of dilution gas. However, the increase in plasma power enhanced the interface roughness to three to five atomic layers, which possibly increased the interface traps density. The center decreased abruptly down to and the interface characteristic improved when using the dilution gas. © 2001 The Electrochemical Society. All rights reserved.

Characterization of Surface Structure of Silica Thin Films by Auger Parameter

Abstract Si Auger parameter of silica films obtained under different hydrolysis conditions was calculated in order to determine SiOH concentration. It was found that the Auger parameter increased with increasing silicate molecular. Silica films with a large Auger parameter were observed by transmission electron microscope (TEM) to consists of a large diameter particle than films with a small Auger parameter. Increased silica particle diameter demonstrates that the condensation reaction proceeds to an extent that the concentration of OH groups has decreased. It has been concluded that silica film surfaces with a large Auger parameter had few OH groups per Si atom.

Controlled Synthesis of Perfluoroaryl Functionalized Hybrid Materials for Optical Applications based on NMR Spectroscopy and Molecular Modeling

ABSTRACTThe synthesis of ORMOCER®*s (inorganic-organic polymers) for optical applications is studied in detail. Producing waveguide materials with the desired low optical losses at wavelengths of 1310 and 1550 nm requires a thorough control of the initial inorganic network formation, because absorption losses are particularly due to Si-OH bonds beside aliphatic C-H bonds. Therefore, the synthesis of UV- or thermally curable organopolysiloxane resins with minimized Si-OH content is crucial. The investigation of the sol-gel reaction of organoalkoxysilanes by 29Si-NMR spectroscopy provides a detailed insight into the influence of reaction conditions on the species and networks formed. Reaction parameters were optimized towards the formation of ORMOCER® resins suitable for waveguide applications. Finally, the material synthesis is completed by crosslinking organically polymerizable units present in the ORMOCER® resin to establish the inorganic-organic hybrid network. The experimental work is accompanied by computational chemistry. Calculating electronic properties is of value in predicting silane reactivities as well as spectroscopic data of intermediates. Molecular modeling is a convenient tool for the visualization of structural details on the molecular level.

Low Si-OH ORMOCER®s for Dielectrical and Optical Interconnection Technology

ABSTRACTORMOCER®*s (inorganic-organic hybrid polymers) with low Si-OH content were synthesized by a new sol-gel route. Optimization of the sol-gel process parameters (catalyst, temperature etc.) was performed in order to achieve reproducible low cost materials which are photo-patternable even in higher layer thicknesses up to 150 μm within one step without cracking or delamination. The materials combine low losses in the NIR region (0.2 dB/cm at 1310 nm and 0.5 dB/cm at 1550 nm without fluorination!) with low dielectric constants (3.3 at 10 kHz).Beside the dielectric and optical properties the materials have a variety of additional advantages for interconnection technology: good wetting and adhesion on various substrates (e.g. glass, silicon and several polymers), low processing temperatures (postbake below 160 °C), high thermal stability (up to 270 °C) and a tunable refractive index.Details of chemical synthesis and characterization as well as photo-lithographic processing of ORMOCER® materials are presented.

Changes in Orientational Polarization and Structure of Silicon Dioxide Film by Fluorine Addition

Use of F‐doped silicon dioxide film as a low dielectric constant intermetal film for ultralarge scale integrated circuits (ULSI) is useful from the viewpoint of product cost and compatibility with present processing technologies. By adding to plasma‐enhanced chemical vapor deposition, we obtained F‐doped films with a dielectric constant as low as 2.6. The mechanism behind this decrease was investigated by estimating the dielectric constants due to the polarization components using capacitance‐voltage measurements, Kramers‐Kronig transformation, and spectroscopic ellipsometry. Fluorine addition lowers the orientational polarization by decreasing the number of ‒OH bonds, and this decrease in Si‒OH concentration is a key factor which is responsible for the lower dielectric constant in the F‐doped film. Orientational polarization due to the Si‒OH bond disappears in the far infrared with increasing frequency, thus the dielectric constant is composed only of ionic and electronic polarization components in the frequency range beyond the far infrared. The quantitative analysis of fluorine and OH shows that excess Si‒F bonds replace Si‒O and form . We suggest that the water absorption for F‐doped film can be minimized by suppressing fluorine addition at the time that the Si‒OH bonds vanish in order to avoid forming and destroying the threefold rings. © 1999 The Electrochemical Society. All rights reserved.

Effects of O2- and N2O-Plasma Treatments on Properties of Plasma-Enhanced-Chemical-Vapor-Deposition Tetraethylorthosilicate Oxide

The high quality silicon oxide films were prepared by plasma-enhanced chemical vapor deposition (PECVD) using tetraethylorthosilicate (TEOS)-oxygen based chemistry. The O2- or N2O-plasma treatments were performed on the as-deposited films as an attempt to improve the properties of the TEOS oxide films. TEOS oxide film deposited at lower pressure had lower Si–OH content, less carbon impurity, and flatter surface, and hence had better electrical properties. Both O2- and N2O-plasma would decrease the oxygen content of the oxide film, which led the composition of the film to deviate from the stoichiometric SiO2. The O2-plasma treatment did not show the encouraging effect on the chemical structure and electrical properties of the TEOS oxide films. In contrast, the N2O-plasma treatment could be a promising means to improve the breakdown field and leakage current density of the TEOS oxide films, which was accomplished by the N2O-plasma effect to facilitate the passivation of dangling bonds, linking reaction of Si–OH bonds, nitridation reaction and densification of the amorphous silicon oxide network.

Silanol Concentration Depth Profiling during Plasma Deposition of SiO2 Using Multiple Internal Reflection Infrared Spectroscopy

The SiOH concentration profiles as a function of depth within films deposited from , and Ar containing plasmas were measured using real‐time attenuated total reflection Fourier transform infrared spectroscopy. The effective thickness approximation in conjunction with mathematical deconvolution of the temporal evolution of the spatially averaged SiOH concentration during deposition allowed the conversion of integrated SiOH absorbance to local SiOH concentration as a function of distance normal to the substrate surface. Thus, depth profiling of SiOH species in growing films was realized. As an example, SiOH concentration profiles in deposited on Si substrates cleaned with plasma was studied as a function of ‐to‐ gas flow rate ratio. For the depositions performed after plasma cleaning, the local concentration profiles revealed strong evidence of high SiOH density at the interface. This method can be applied to measuring concentration depth profiles of Si‐H, Si‐F, or any other infrared active species in plasma‐deposited films in real time.

Plasma and surface diagnostics during plasma-enhanced chemical vapor deposition of SiO 2 from SiH 4/O 2/Ar discharges

Factors affecting the SiOH incorporation into SiO 2 films during plasma-enhanced chemical vapor deposition were studied using in-situ attenuated total reflection Fourier transform infrared spectroscopy, optical emission actinometry, and Langmuir probe measurements. The silane-to-oxygen ratio, R, in the process gas mixture determines the chemical nature of the substrate surface and the incorporation rate of SiOH and SiH into the film. The oxide surface and the film are hydroxyl rich during deposition with SiH 4-to-O 2 ratio below 0.7. Silicon hydrides are observed on the surface and in the film when R exceeds 0.7. The SiOH concentration in the film correlated well with SiH concentration above the substrate surface, which is representative of the silane fragment (SiH x ) flux arriving at the surface of the growing film. High O flux compared to SiH x flux results in immediate oxidation of the silane fragments adsorbed onto the surface which leads to OH rich surface and SiOH incorporation. As the SiH x flux relative to O flux increases, the reaction of silane fragments with surface. SiOH reduces the SiOH coverage on the surface and the SiOH incorporation rate into the film.