Polymer-like Films Research Articles

Surface plasmon-induced luminescence: a probe to study electrical aging and dielectric breakdown in polymer-like thin films

Electroluminescence was observed in sandwich structures composed of a thick layer of plasma-deposited hydrogenated carbon and two metallic electrodes. Luminescence experiments combined with transport analysis show that the light comes from the radiative decay of electrode surface plasmons excited by hot electrons produced in the films. The precise nature of the dielectric is unimportant since the emission process involves the electrode parameters. The optical response is governed by the nature and thickness of the positively biased electrode: (i) when a thick electrode is used, the only excited surface plasmon mode is located at the dielectric-electrode interface which acts as a probe for the low energy end of the electron energy distribution function; (ii) when a semi-transparent electrode is used, electrons with an energy of a few eV can cross the metallic layer. These hot carriers are able to excite a surface plasmon mode located at the outer interface. Depending on the temperature and metal thickness, hot carriers of different kinetic energies can excite this surface plasmon mode. The interface acts as a probe for the high energy end of the electron energy distribution function. Detection of luminescence due to electrode surface plasmon decay gives access to carrier energy which is the main aging and breakdown controlling factor of the dielectric layer.

Role of hydrogen ions in plasma-enhanced chemical vapor deposition of hydrocarbon films, investigated by in situ ellipsometry

Ion bombardment during plasma-enhanced chemical vapor deposition of hydrocarbon films mainly governs the properties of the films. The range of this ion-induced modification of the optical properties of hydrocarbon films was determined in situ by monochromatic ellipsometry. The hydrocarbon films were deposited by an electron cyclotron resonance methane plasma onto silicon substrates and additional rf bias was applied to vary the kinetic energy of the impinging ions. The ion-induced modification of the film properties was investigated by means of a double layer consisting of a polymerlike film with low optical absorption and a hard carbon film with high absorption on top. The deposition of this double layer was monitored in situ by ellipsometry during the growth and during the erosion of this film system in an oxygen plasma at floating potential. From these data it is possible to determine with high accuracy the range of the ion-induced modification of the optical properties. This layer ranges from 6 Å at 30 V dc self-bias to 40 Å at 100 V dc self-bias, which is consistent with TRIM.SP calculations for the bombardment of polymerlike films by hydrogen ions.

The Role of Ions for the Deposition of Hydrocarbon Films, investigated by In-Situ Ellipsometry

AbstractThe growth mechanisms for the deposition of hydrocarbon films (C:H-films) from a methane electron cyclotron resonance (ECR) plasma are investigated by means of in-situ ellipsometry. Ion bombardment during plasma-enhanced chemical vapor deposition of hydrocarbon films mainly governs the properties of the films and the total growth rate. the role of ions for the growth rate and the film properties is discussed in this paper. Films were deposited with varying RF-bias, resulting in a DC self-bias ranging from floating potential up to 100 V. the ion-induced modification of the film properties was investigated by a new technique using a double layer consisting of a polymer-like film with low optical absorption and a hard carbon film with high absorption on top. the interface between these layers was analysed after deposition by a layer-by-layer etching in an oxygen plasma at floating potential. From these data it is possible to determine with high accuracy the range of the ion-induced modification of the optical properties in the underlying polymer-like film. the thickness of this modified layer ranges from 6 Å at 30 V self-bias to 40 Å at 100 V self-bias, which is consistent with the range of hydrogen ions in polymerlike films as calculated by the computer code TRIM.SP.Based on the presented results, the growth of C:H-films and the resulting film properties can be modelled by the growth at activated sites at the film surface. these activated sites are represented by dangling bonds, induced by the ion bombardment. they also show up in the ellipsometric results during the deposition of C:H-films by a change of the optical response of the film surface.

Structure and Tribological Characteristics of DC-Magnetron Sputtered DLC Overlayer Films

We investigated the structure xand tribological properties of diamond-like carbon (DLC) overcoat films for rigid magnetic disks. DLC films were produced by DC magnetron sputtering, introducing CH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> gas into Ar gas in various quantities. Drag tests and CSS tests were performed, and the electrical resistivity, Raman spectra and film hydrogen contents were measured. A more polymer-like DLC film appeared to have good tribological properties, making it suitable as a hard-head slider material (Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> -TiC).

XPS and XAES studies of the amorphous hydrogenated carbon/silicon interface

Low-pressure multipolar-plasma assisted deposition on c-Si substrates has been used to grow carbon films. Angle-resolved XPS and XAES were used to analyze the initial stages of the growth as a function of the ion deposition energy. A good signal-to-noise ratio allowed us to study simultaneously the film and the relatively deep inteface without any damage to the samples. Channeling RBS, NRA and ERDA were also used to complete the analysis. The same as in the a-C: H film, the physical and chemical nature of the film/substrate interface also varies with the ionic energy impinging on the substrate. After deposition, the original native silicon oxide, 10 Å thick, is either left practically unmodified for polymer-like films or an oxicarbide SiO 1.3C 0.3 + 20%SiC about 50 Å thick is formed for “diamond-like” films.

X-ray photoelectron spectroscopy and X-ray-excited Auger electron spectroscopy studies of the initial deposition of hydrogenated amorphous carbon

The initial layers and the film-substrate interface of hydrogenated amorphous carbon films obtained by low pressure multipolar methane-plasma-assisted deposition on crystalline Si have been studied by angle-resolved X-ray photoelectron spectroscopy and X-ray-excited Auger electron spectroscopy as a function of the ion deposition energy. Nuclear reaction analysis and elastic recoil detection analysis were also used to complete the analysis. The rate of growth, the H content and the sp 3 concentration decrese with increasing energy of ions impinging on the substrate, producing from polymer-like films (less than 400 eV) to “diamond-like” films (above 400 eV). The H and sp 3 concentrations decrease also during deposition. The film-substrate interface also varies with the energy of the ions. Either the original native oxide, 10 Å thick, is left almost unmodified for polymer-like films or an oxicarbide SiO 1.2C 0.4 about 50 Å thick is formed for “diamond-like” films.

Deposition of dense hydrocarbon films from a nonbiased microwave plasma

An electron cyclotron resonance plasma was used to prepare C:H layers from methane. The temperature dependence of the deposition rate was investigated at substrate temperatures ranging from room temperature to 700 K, at a gas pressure of 1.6 Pa. Despite low ion energies corresponding to the plasma potential, transparent hard coatings were obtained at elevated temperature with a density up to 2 g cm−3. A deposition model is proposed which describes the growth from an adsorbed layer, including surface reactions with radicals and atomic hydrogen as well as the direct incorporation of ions. Two different deposition processes can be identified, yielding polymerlike films in the temperature range up to 450 K and dense hydrocarbons above this temperature. The observed temperature dependence of the film properties such as H/C ratio, index of refraction, and density is consistent with the predictions of the model.

Deposition mechanism of hydrogenated hard-carbon films in a CH4 rf discharge plasma

To examine the mechanism of film deposition in a planar rf CH4 discharge plasma, measurements were made of the spatial distributions of the deposition rate and optical emission intensity along the discharge axis between parallel electrodes. Optical-absorption properties of the deposited carbon films were also measured over both the infrared and visible regions. To measure the spatial deposition rates, the substrate surface was elevated from the cathode electrode with the use of quartz glass plates. It was found that the spatial properties of films, which were deposited in both the ion-sheath and bulk-plasma regions, differ markedly from each other. The carbon films obtained from within the ion-sheath region were found to be extremely hard, while those obtained in the bulk-plasma region were polymerlike soft films. This disparity was thought to be due to the difference in the kinetic energy of the ions bombarding the substrate surface; that is, the substrate surface potential could be changed by elevating the substrate surface. These results were incorporated in the discussion of the deposition mechanism, with emphasis on the contribution of ion bombardment to the film-deposition process. It was tentatively concluded that the film-deposition rate was predominantly dependent on the product of the ion kinetic energy and ion flux density that reached the substrate surface.

RF-plasma deposited polymerlike thin films: preparation, properties and applications

RF-plasma deposited polymerlike thin films: preparation, properties and applications

Polymer-like and hard amorphous hydrogenated carbon films prepared in an inductively coupled R.F. glow discharge

An inductively coupled r.f. discharge was used to prepare amorphous hydrogenated carbon (a-C:H) films in a wide pressure range, at different ion energies, and at different substrate temperatures. Because of the inductive coupling the substrate bias and the r.f. power can be varied independently. The gas pressure ranged from 3 × 10 −2 to 5 × 10 −4 mbar and rather high deposition rates of 30 Å s −1 at 8 × 10 −4 mbar have been obtained. Depending on the plasma parameters and the substrate temperature, polymer-like or hard a-C:H films were prepared. Their properties were analysed by IR and visible spectrometry, and measuring the electrical conductivity, the hydrogen content, the Knoop hardness, the adhesion to different substrates, and the internal stress. Strong correlations exist between the optical gap, the relative IR absorption coefficients for the CC vibrational mode, for the integrated CH x ( x = 1,2,3) stretching modes, and the conductivity of the polymer-like films. Measurements of the temperature dependence of the conductivity indicate a superposition of activated conductivity and hopping conductivity at the Fermi level. The hard a-C:H films were prepared with average ion energies between 80 and 330 eV. The films exhibited significant enhancement of the Knoop hardness from 700 kgf mm −2 (7 GPa) to 2000 kgf mm −2 (20 GPa) and density up to 2.0 g cm −3 with increasing ion energy from 80 to 160 eV. A further increase in the ion energy up to about 300 eV does not influence the film properties. Films deposited on silicon wafers had a stress of 1–6 GPa, and the critical load in scratch tests was between 20 and 30 N, being equivalent to an adhesion of about 300 MPa. The influence of the r.f. power (for constant ion energy) on the film properties was also examined.

Analysis of the interface of hydrogenated amorphous carbon films on silicon by angle-resolved x-ray photoelectron spectroscopy

Thin amorphous hydrogenated carbon films were deposited from a methane rf plasma (13.56 MHz) at 68 mTorr on Si(100) substrates both on the powered (negatively self biased) and on the nonpowered (grounded) electrode. The interface was analyzed with angle-resolved X-ray photoelectron spectroscopy. An approximately stoichiometric silicon carbide layer was found at the interface of a hard carbon film produced on the powered electrode. The thickness of the interfacial carbide as estimated from the angle resolved spectra was approximately 7 A, which is much thinner than previously reported by other workers. There was no interfacial silicon carbide formation evident for a soft polymer-like film produced on the grounded electrode. Instead, a submonolayer amount of oxide was detected at the interface of the soft carbon film which showed poor adhesion. Our results indicate that the high energy ions incident on the powered electrode in the rf plasma are responsible for the production of the interfacial silicon carbide and are also likely to be responsible for the good adhesion of the film to the silicon substrate.

The deposition and study of hard carbon films

Carbon films have been deposited by rf plasma decomposition of methane at 50–1400 V negative bias and 1.3×10−3–1.3×10−1 mbar pressure. Hardness, internal stress, density, hydrogen content, and infrared absorption depending on the preparation parameters have been measured. From the IR measurements the ratio of sp3 to sp2 bonds was calculated and the total amount of hydrogen in the films was determined by elastic recoil detection (0.5&amp;gt;H/C&amp;gt;0.15). We found in the range of bias voltages 0&amp;lt;‖−VB ‖&amp;lt;100 V polymerlike films, in the range 100 V&amp;lt;‖−VB ‖&amp;lt;600 V diamondlike hard carbon films with high internal stress, and in the range 600&amp;lt;‖−VB ‖&amp;lt;1400 V graphitelike soft films with low stress. The density of the diamondlike films was about 2 g/cm3 and of the graphitelike films about 1.4 g/cm3. The microhardness seems to be correlated to the internal mechanical stress.

Thin films prepared from tetramethyltin

Thin metallic tin films are obtained by plasma deposition from tetramethyltin. It can be shown that extraneous depolymerization gas (O 2) must not be added to get films with metallic properties. Careful control of the discharge conditions is necessary to prevent the deposition of polymer-like films. The main parameters seems to be the power density, substrate temperature and monomer flow or partial pressure of the alkyl compound. By variation of these parameters it is possible to deposit either metallic films or metal-polymer films of different compositions.

Properties of polymeric layers of amorphous hydrogenated carbon produced by a plasma- activated chemical vapour deposition process I: Spectroscopic investigations

In the literature it has been reported that graphite- and diamond-like carbon layers have been produced from hydrocarbons by a plasma-activated chemical vapour deposition (CVD) process. In this study we re-investigated this process and we analysed the structure by spectroscopic methods. The films were deposited within a certain deposition parameter range. The analysis has shown that essentially polymer-like films of amorphous hydrogenated carbon are produced by this CVD technique. The structure depends on the deposition parameters and on the hydrocarbon gas used in the CVD process. The polymeric chains seem to be strongly cross-linked which makes them very stable towards organic solvents. The various structures and the nature of electron energy states are discussed in detail.

Electrical properties of thin carbon films obtained by r.f. methane decomposition on an r.f.-powered negatively self-biased electrode

In this paper the results are presented of an investigation of the electrical properties of polymer-like, diamond-like and graphite-like films obtained on an r.f.-powered electrode in the r.f. discharge of methane. It has been shown that the properties of films obtained by r.f. decomposition of methane depend on the value of the negative self-bias voltage of the r.f.-powered electrode. The changes in resistivity of the films obtained as a function of the changes in the value of the negative self-bias potential of an r.f. electrode are analogous to the changes presented in the literature for films obtained by the ion plating method and by ionized deposition from methane gas.

The behaviour of perfluoropolyether and other vacuum fluids under ion and electron bombardment

A study of perfluoropolyether fluids under electron and ion bombardment has shown them to be well suited for vacuum use in the presence of charged particles. A dc glow discharge was sustained in hydrogen, oxygen, helium, air, argon and Freon 14 between plane electrodes previously smeared with perfluoropolyether. After the discharge both the cathode and the anode surfaces remained visually clean except when hydrogen was used as a discharge gas when a polymer-like film was formed on the cathode and a brown film deposited on the anode. The brown deposit on the anode was a neutral condensate formed independently of electron bombardment. For comparison Apiezon C, Silicone 704, Santovac 5 and Dow Corning FS.1265, were also exposed to argon and hydrogen dc glow discharges, when solid deposits were produced on both anode and cathode. Perfluoropolyether fluid was then smeared in the quartz bottle of an rf ion source and discharges were run in hydrogen and argon; considerable etching was observed on the inside of the bottle. By comparison a smear of Santovac 5 in the bottle did not give rise to etching but left a tarry deposit.

Relay Contact Behavior Under Non-Eroding Circuit Conditions

When palladium or platinum-family metal contacts are operated in an environment which includes organic vapors, the performance of the contacts may be seriously degraded. If the contacts open and close currents, the contact erosion may be increased enormously. On the other hand, if the contacts merely prepare the circuit and do not directly open or close the current flow, no erosion will take place. The contacts may then fail to conduct the circuit current satisfactorily, because of the formation of an insulating polymer-like film. This latter type of failure has been the subject of extensive studies at Bell Telephone Laboratories for the past several years and is the subject of this article. These studies have yielded a new understanding of the contact problem and resulted in certain changes in relay contacts to improve their performance under service conditions.