J. E. Klemberg-Sapieha

Transparent barrier coatings on polyethylene terephthalate by single- and dual-frequency plasma-enhanced chemical vapor deposition

Transparent barrier coatings on polymers are receiving much attention in industry, for pharmaceutical, food and beverage packaging applications. Plasma-enhanced chemical vapor deposition (PECVD) is among several competing techniques which can produce thin layers of inorganic glassy barrier materials. In this article we describe the performance of silicon compounds (SiO2 and Si3N4) on 13 μm polyethylene terephthalate (PET) substrates, the barrier coatings being deposited in a dual-frequency (microwave/radio frequency) pilot-scale PECVD reactor for continuously moving flexible webs up to 30 cm in width. The volatile silicon compound used for SiO2 deposition is HMDSO (C6H18Si2O), while SiH4 serves to deposit Si3N4. Coating thicknesses, d, in the range 8 nm⩽d⩽200 nm, are measured using a variety of techniques, namely stylus profilometry, continuous wavelength optical interferometry, x-ray fluorescence, variable angle spectroscopic ellipsometry, and transmission electron microscopy, while film compositions are...

Critical ion energy and ion flux in the growth of films by plasma‐enhanced chemical‐vapor deposition

Dual‐mode microwave/radio frequency plasma‐enhanced chemical‐vapor deposition allows one to decouple ion bombardment effects from processes in the discharge volume. This approach has been used to deposit three types of hydrogenated amorphous films at low substrate temperature and high deposition rate (∼10–20 A/s): SiNx, SiO2, and a‐C:H. For each of these materials, we have determined critical values of the negative bias potential, VB,C, of the average ion energy, Ei,c, and of the ion/condensing‐atom flux ratio (φi/φn)c, which characterize the transition from a porous to a densely packed microstructure. The evaluations are based on measurements of the films’ resistivity, dielectric loss tangent, microhardness, density, and stress. The Ei,c, (φi/φn)c values found are: 170 eV, 0.60 for SiNx; 70 eV; 0.26 for SiO2; and 80 eV, 0.28 for a‐C:H. Ion bombardment at energies above Ei,c has been found to account for a large portion of hydrogen in the films which is not chemically bonded. The results are interprete...

Optical properties and microstructure of plasma deposited Ta2O5 and Nb2O5 films

Advanced optical filter applications require an appropriate control of the optical constants, as well as of other suitable film properties such as mechanical performance, thermal and environmental stability, absence of refractive index inhomogeneities, and others. In the present work we studied the characteristics of two high index optical materials, namely amorphous tantalum pentoxide (Ta2O5) and niobium pentoxide (Nb2O5) prepared by plasma enhanced chemical vapor deposition, using penta-ethoxy tantalum Ta(OC2H5)5 and penta-ethoxy niobium, Nb(OC2H5)5, precursors. We particularly investigated the effect of energetic conditions on the film growth by using different modes of plasma excitation, namely rf, microwave, and dual-mode microwave/radio frequency discharges. Under sufficient ion bombardment, controlled by the rf-induced negative substrate bias, the dense Ta2O5 and Nb2O5 films exhibited a refractive index of 2.16 and 2.26 (at 550nm), respectively, while the extinction coefficient was below 10−5, as d...

Deposition and properties of diamondlike carbon films produced in microwave and radio‐frequency plasma

Hard a‐C:H films were grown in a dual frequency plasma sustained simultaneously by microwave and radio‐frequency power. ‘‘Optimum’’ growth conditions, namely those leading to the most pronounced sp3 structural features in the films, depend very strongly on the methane feed gas flow rate and on the argon concentration, in the case of CH4/Ar mixtures. These optimum conditions have been found to correspond to maximum values of ion flux at the growing film surface, and high concentrations of precursor species such as CH, C2, C3, and atomic hydrogen in the plasma, as revealed by optical emission spectroscopy. Films grown under optimum conditions have very high microhardness (∼50 GPa), high density (1.8 g/cm−3), and low internal stress (0.5 GPa). Addition of argon to the methane is shown to enhance the gas phase fragmentation and to raise the microhardness, but argon atoms trapped in the films’ structure increase the internal stress.

Argon plasma treatment of polycarbonate: In situ spectroellipsometry study and polymer characterizations

The influence of argon plasma on polycarbonate (PC) was studied in terms of structural changes, reaction mechanisms, and adhesion. In situ ultraviolet‐visible ellipsometry reveals formation of a surface layer with a higher refractive index than the untreated polymer. The increase in the refractive index is attributed to polymer densification, which in turn is attributed to crosslinking. However a decrease in the average molecular weight is also observed, and two populations of macromolecules of different sizes are detected by light scattering measurements, revealing a competition between crosslinking and degradation. The reaction mechanisms are investigated using nuclear magnetic resonance and in situ infrared ellipsometry. Degradation is caused by carbonate bond breaking, whereas crosslinking seems to be related to a decrease in methyl groups. In addition, an increase in surface acidity is detected by contact angle measurements and is attributed to photo‐Fries rearrangements producing phenolic groups. Th...

Structure-property relationships in dual-frequency plasma deposited hard a-C : H films

Abstract Films of amorphous hydrogenated carbon (a-C:H) which are hard (30–50 GPa), dense (1.7-1.8 g cm-3), and low in stress (0.5 GPa), were deposited in a dual-frequency (microwave (MW)-r.f.) plasma system, where the substrates are placed on an r.f. powered electrode while simultaneously being exposed to a microwave discharge in CH4, or CH4-Ar mixtures. This MW-r.f. deposition mode, and/or the addition of argon to the hydrocarbon feed gas, result in highly efficient monomer fragmentation in the gas phase and in the creation of species which contribute to enhanced sp3 features in the deposits. Film properties such as microhardness, density, hydrogen content, and refractive index are related to microstructure and composition, which are determined by Fourier transform IR spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and elastic recoil detection. The MW-r.f. films exhibit a systematically lower stress, and a higher density than their r.f. counterparts. It is shown that the observed structure - property relationships can be interpreted if we distinguish three categories of a-C:H films with diamond-like properties, namely (a) hard carbon with bonded hydrogen, (b) hydrogen-doped (unbonded) carbon, and (c) hard, polymer-like material.

Pulsed radio frequency plasma deposition of a-SiNx:H alloys: Film properties, growth mechanism, and applications

In this work, we propose a fabrication process of a-SiNx:H alloys by pulsing the radio frequency (rf) signal in a low pressure plasma-enhanced chemical vapor deposition (PECVD) system. The characteristics of the films can be controlled simply by adjusting the duty cycle of the pulsed rf power, while keeping the N2∕SiH4 gas mixture constant. Spectroscopic ellipsometry analysis in the ultraviolet-visible-near infrared and far infrared ranges, atomic force microscopy, and elastic recoil detection reveal strong variations in the optical properties (1.88⩽n⩽2.75, 10−4⩽k⩽5×10−2 at 550nm), optical gap (4.01eV⩽Eg⩽1.95eV), microstructural characteristics (1.3nm⩽surfaceroughness⩽8.3nm), and chemical composition (0.47⩽x⩽1.35) of the coatings as a function of duty cycle. This behavior is interpreted in terms of radical concentration changes in the gas phase, as well as variation in the average ion bombardment energy at the film surface, leading to modifications of both chemical and physical mechanisms that sustain the...

Plasmas and polymers: From laboratory to large scale commercialization

The use of low-pressure plasmas for materials processing, pioneered by the semiconductor industry since the 1960s, is now also a commercial reality in technologies which make extensive use of plastics (automotive, aerospace, packaging, pharmaceutical, and other industries). On hand of examples from our own experience, we show how research on plasma surface modification of polymers and plasma coating of polymers has progressed from the university laboratory, via pilot-scale operations, to full-scale commercial implementation.

Plasma deposition of low stress electret films for electroacoustic and solar cell applications

We studied electric charge retention and internal stress in low‐pressure plasma‐deposited silicon‐compound films (silicon nitride, oxide, and oxynitrides), prepared from SiH4/NH3/N2O mixtures in a dual‐mode microwave/radio frequency (2.45 GHz/13.56 MHz) plasma at low (∼30 °C) substrate temperature. The internal stress is found to vary from tensile (∼+150 MPa) to compressive (∼−100 to −500 MPa) when the bombarding ion energy is increased. Minimum stress values occur for the substrate bias voltage of about −100 V, which also results in a high charge stability on the film surface. Further improvement of the electret properties is achieved by postdeposition annealing, by exposure to organosilicone vapors, and by using oxynitride layers. This is confirmed by the presence of deeper charge traps, as determined by the measurement of thermally stimulated discharge currents, and by chemical stabilization of the film surfaces, as revealed by x‐ray photoelectron spectroscopy. The films are considered for novel miniat...

Plasma treatment of porous SiNx:H films for the fabrication of porous-dense multilayer optical filters with tailored interfaces

Porous and dense silicon nitride films with low (1.58) and high (1.88) refractive indices were prepared by using successively microwave and radio frequency (rf) plasma-enhanced chemical vapor deposition. Surface treatments were performed on porous layers using argon and nitrogen rf plasmas in order to densify and flatten their surface, and hence to obtain an abrupt transition between porous and dense films. The processes during deposition and interface treatment were studied by in situ real-time spectroscopic ellipsometry as well as by other characterization techniques. We show that besides the densification effect, preferential sputtering and annealing phenomena occur during plasma treatments at high bias (∣VBtreat∣>400V), leading to silicon enrichment at the film surface and chemical stabilization of the film bulk. Using atomic force microscopy, we observed a significant reduction of the thickness of the surface roughness layer after treatment for single layers (≈70% reduction) and multilayer stacks (≈6...