Showing papers by "Ludvik Martinu published in 1994"
TL;DR: In this paper, the negative bias potential, VB,C, of the average ion energy, Ei,c, and of the ion/condensing atom flux ratio (φi/φn)c were determined for three types of hydrogenated amorphous films at low substrate temperature and high deposition rate.
Abstract: 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...
112 citations
TL;DR: In this article, it was shown that Cu reacts with both oxygen and nitrogen to form, respectively, Cu-O and Cu-N bonds at the interface but no reaction occurs with carbon and fluorine.
Abstract: Adhesion of evaporated Cu to Teflon PFA (polytetrafluoroethylene-co-perfluoroalkoxy vinyl ether) was greatly enhanced by plasma pretreatment. The efficiency of the treatment decreased in the following order: N2 > O2 > (N2 + H2) > (O2 + H2) > H2. X-ray photoelectron spectroscopy (XPS) showed the loss of fluorine and the incorporation of oxygen and nitrogen at the polymer surface. Among the gases, H2 was found to be the most efficient for fluorine elimination, and (N2 + H2) for surface functionalization. Based on this investigation, it is proposed that Cu reacts with both oxygen and nitrogen to form, respectively, Cu-O and Cu-N bonds at the interface but no reaction occurs with carbon and fluorine. While greater enhancement in polymer surface wettability and stronger interfacial reactions can account for the higher performance of N2 over O2 in improving adhesion, these effects cannot explain the lower efficiency of H2. Several possibilities are discussed, including surface cleaning, oxygen incorporation and...
59 citations
TL;DR: In situ x-ray photoelectron spectroscopy revealed that Cr deposition leads to defluorination and the formation of fluoride and carbide species as discussed by the authors, slowly at the initial stages of deposition but more rapidly afterwards.
Abstract: Cr and Al were evaporated onto Teflon PFA (polytetrafluoroethylene−co‐perfluoroalkoxy vinyl ether) substrates by electron beam evaporation. In situ x‐ray photoelectron spectroscopy revealed that Cr deposition leads to defluorination and the formation of fluoride and carbide species. The concentrations of fluoride and carbide increased with deposited Cr thickness, slowly at the initial stages of deposition but more rapidly afterwards. Al deposition was qualitatively similar to that of Cr, although the concentrations of fluoride and carbide formed were much lower. The sticking coefficients of both metals, low at the outset of metal deposition, were enhanced after initial deposition, with simultaneous increases in interfacial reactions. Oxygen contaminants in the form of metal oxides were observed, particularly in the case of Al.
38 citations
TL;DR: In this article, the effect of x-ray irradiation on the metal/polymer interfaces was studied using in situ X-ray photoelectron spectroscopy (XPS) and mass spectrometry.
Abstract: Interaction of Cr, Ti, Al, Ag, Au, and Cu with Teflon PFA (polytetrafluoroethylene‐ co‐perfluoroalkoxy vinyl ether) and FEP (fluoroethylene propylene), and the effect of x‐ray irradiation on the metal/polymer interfaces, were studied using in situ x‐ray photoelectron spectroscopy (XPS) and mass spectrometry. Cr, Ti, and Al were found to react with both PFA and FEP, leading to polymer surface graphitization and formation of carbide and fluoride species, which are enhanced at higher metal thicknesses. On the other hand, evaporation of Au, Ag and Cu causes only a slight loss of fluorine, but no chemical interaction occurs. Post‐deposition x‐ray irradiation does not promote metal–polymer interactions, but it leads, in the case of reactive metals, to a pronounced increase of the C–CFn peak intensity, which rises with the metal thickness. A mechanism based on radical recombination reaction and accumulation of the small fragments, inside the metal film and/or near the metal/polymer interface, is proposed to explain this behavior. The metal XPS signal decreases upon x‐ray exposure, which is interpreted by diffusion of metals into the polymer matrix. The relative change in XPS signal is enhanced at longer x‐ray irradiations, but decreases at a higher metal thickness. This effect is most pronounced for Cu, Cr, and FEP.
27 citations
TL;DR: In this paper, the effect of the kinetic energy of the depositing metal atoms on the metal/polymer interaction was examined using x-ray photoelectron spectroscopy.
Abstract: Ti, Ag, and Au were evaporated onto Teflon PFA (polytetrafluoroethylene‐co‐perfluoroalkoxy vinyl ether) surfaces by electron beam evaporation Au was also sputtered onto PFA, in order to examine the effect of the kinetic energy of the depositing metal atoms on the metal/polymer interaction The evolution of metal/polymer interfacial structures with increasing deposited metal thickness was followed using x‐ray photoelectron spectroscopy It was found that Ti deposition leads to defluorination and the formation of fluoride and carbide species The reactions increased with deposited Ti thickness, slowly in the initial stages of deposition but more rapidly afterwards The effects of evaporated Ag and Au were very similar, both resulting in slight losses of fluorine: No formation of new species was detected Compared to evaporated Au, sputtered Au increased polymer surface modification, indicated by the formation of –CF3, –CF–, and –C– species; an enhanced chemical reactivity was manifested by the appearance of Au fluorides After deposition of the first several A of metal, the rate of deposition onto the PFA was enhanced for evaporation but decreased for sputtering, due to the action of subsequently sputtered species
22 citations
28 Jul 1994
TL;DR: In this article, the authors present the characteristics of plasma-polymerized tetrafluoroethylene layers with a refractive index of approximately 1.4, and also spin-coated Teflon AF films with a low pressure plasma.
Abstract: Amorphous fluorocarbon polymers are attractive materials for optical applications because of their high transparency at wavelengths up to 3 micrometers because of the absence of C-H bonds. since 1989 DuPont's amorphous fluoropolymer Teflon AF is available, films of which can be fabricated by means of spin, spray, or dip coating from solution or by use of compression or injection molding from the melt. An alternative and promissing route for processing fluorocarbon films is the use of a low- pressure plasma: This technique can be employed for plasma polymerization of suitable fluorocarbon monomers and for controlled etching of fluorocarbon materials. In the present work, we present the characteristics of plasma-polymerized tetrafluoroethylene layers with a refractive index of approximately 1.4. Reactive ion etching in an N2O plasma is used for patterning these layers, and also the spin-coated Teflon AF films with a refractive index of around 1.3. Possibilities of fabricating passive and active polymer waveguide devices from flurocarbon polymers are discussed, and estimates of the expected waveguide performance are presented.
9 citations
TL;DR: In this article, the growth of diamond in a dualmode microwave/radio frequency plasma was studied and the effect of the thickness of predeposited hydrogenated amorphous carbon (a•C:H) films and of ion bombardment on the nucleation process and on the crystal quality.
Abstract: In the present work we study the growth of diamond in a dual‐mode microwave/radio frequency plasma We investigate the effect of the thickness of predeposited hydrogenated amorphous carbon (a‐C:H) films and of ion bombardment on the nucleation process and on the crystal quality The deposits are characterized by x‐ray photoelectron spectroscopy (XPS) and by scanning electron microscopy The XPS spectra of the C(1s) carbon peak and of the plasmon features confirm the presence of an amorphous, carbonaceous phase and of silicon carbide on the surface Radio frequency biasing during the initial stage of diamond growth leads to a lower crystal quality, but to a higher nucleation density (ND) Without biasing, good quality, predominantly (100) oriented diamond crystals are obtained on a Si(100) surface The ND values are found to increase with the thickness of the predeposited a‐C:H layer Evolution of the nucleus size distributions indicates that the a‐C:H film contributes to the carbon supply, enhancing the n
9 citations
07 Sep 1994
TL;DR: In this paper, a micromachined electret condenser microphone with SiO/sub 2/Si/sub 3/N/sub 4/ single and double layers and SiON layers are investigated in terms of chargeability and long-term charge-stability.
Abstract: Silicon dioxide and nitride based materials are interesting inorganic electrets for applications in the field of micromechanics and sensor technologies since they are compatible to the silicon technology. It was the motivation for this work to find new suitable electret materials with good mechanical properties for the application in a micromachined electret condenser microphone. SiO/sub 2/, Si/sub 3/N/sub 4/ single and double layers and SiON layers are investigated in terms of chargeability and long-term charge-stability. The main emphasis is put on the miniaturization of electret layers. The lateral dimensions of the electrets are reduced down to 2 mm and the characteristics under different environmental conditions are described.
7 citations
07 Sep 1994
TL;DR: In this paper, the applicability of spin-coated Teflon AF electrets to MIS-solar cells is discussed, and it is shown that the I-V-characteristic drastically depends on the polarity and density of the electret space charge.
Abstract: Novel thin film materials, namely cold plasma-deposited SiO/sub 2/ and spin-coated Teflon AF have recently been identified as useful electrets; the present paper briefly summarises preparation conditions and material characteristics, the main attention being focused on the applicability of these electrets to MIS-solar cells (Metal Insulator Semiconductor). As a functional coating, the electret passivates the surface and generates a permanent electric field which induces an inversion zone at the silicon surface between the metal lines of the front electrode. It is shown that the I-V-characteristic drastically depends on the polarity and density of the electret space charge. Hence, electrets in solar cell technology can be an important means to increase the device efficiency, and to study silicon-insulator interfaces.
4 citations
03 Jul 1994
TL;DR: In this article, the critical average ion energy (E~/sub i/ ) and critical ion flux (I flux) were determined for four types of amorphous dielectric films: SiN/sub 1.3, SiO/sub 2, a-C:H, and plasma-polymerized hexamethyldisiloxane (PP-HMDSO).
Abstract: Dual-mode microwave/radiofrequency PECVD processes have been used for the fabrication of four types of amorphous dielectric films: SiN/sub 1.3/, SiO/sub 2/, a-C:H, and plasma-polymerized hexamethyldisiloxane (PP-HMDSO). For each of these materials, we have determined values of the critical average ion energy E~/sub i/ (between about 70 and 170 eV) and of the critical ion flux, which characterize the transition from a porous to a densely packed microstructure, at low (/spl sim/25/spl deg/C) substrate temperature T/sub s/ and high deposition rates (between 20 and 120 /spl Aring//s). When E~/sub i/ values are optimized, the d.c. resistivity and the dielectric loss tangent values for all of these dielectrics are found to be about 10/sup 16/ /spl Omega/ cm and 10/sup -3/, respectively. We present evidence which shows that E~/sub i/ and T/sub s/ can be considered as interchangeable process parameters. Large area scale-up and continuous deposition onto flexible substrate materials are also discussed. >
2 citations
07 Sep 1994
TL;DR: The photo-isomerization of azo-chromophores in a nonlinear optical sidechain polymer permits the orientation of the dipoles under an applied electric field even well below the glass transition temperature of the polymer as discussed by the authors.
Abstract: The photo-isomerization of azo-chromophores in a nonlinear optical side-chain polymer permits the orientation of the dipoles under an applied electric field even well below the glass-transition temperature of the polymer. As the dipoles become orientable only within the penetration depth of the pump light, the technique is especially suitable for the preparation of poling patterns across the thickness of the polymer. Pyroelectrical investigations allow for an in-situ examination of the photo-induced poling process and for an analysis of the resulting nonuniform dipole-orientation patterns. For long-time exposures to the short-wavelength pump light, a photo-induced degradation of the chromophore molecules (photo-bleaching) is observed, which is analyzed by pyroelectrical (thermal) analysis, optical techniques and X-ray photoelectron spectroscopy.