Papers

AVS1996 Session PS+BI-ThM: Deposition II - Biomaterials and Organics

Thursday, October 17, 1996 8:20 AM in Room 201B

Thursday Morning

Start	Invited?	Item
8:20 AM		PS+BI-ThM-1 Plasma Processing in Medical Device Manufacturing M. Dalvie, E. Vogler, A. Liebmann-Vinson, L. Wainwright, D. Montgomery, D. Martin (Becton Dickinson Research Center) A convenient categorization of plasma processing in the manufacture of biomedical devices is (i) control/optimization of the biological response to surfaces, (ii) improvement of tribological properties, and (iii) deposition of thin films onto formed biomedical devices. Historically, surface modification is probably the first significant application of plasma processing in the biomedical industry. Biomaterials surface science research has demonstrated that surface and interfacial chemistry/energy affect protein adsorption which, in turn, controls the biological response to medical devices. Thus, surface modification has been applied to disposable products such as blood collection tubes, catheters, and tissue culture labware; as well as in-dwelling medical devices including pace-makers, vascular grafts, and prostheses. A useful application of plasma processing in the tribology category is control of lubricity. An example is oxygen plasma cross linking of silicone-based lubricants to eliminate "stick-slip" behavior in ordinary syringes. Finally, thin film deposition applications are found in packaging technology and in the fabrication of solid state biological sensors. We will focus on current applications in barrier coatings to control gas and water permeation. Where transparency requirements preclude metallization, sub-micron inorganic oxide layers (e.g., AlOx, SiOx) have been used. Low-temperature PECVD has been demonstrated as a viable process for barrier deposition onto polymeric medical devices. We will review recent literature in the PECVD of barrier materials with emphasis on the need for better metrology and on processing of 3D objects.
9:00 AM		PS+BI-ThM-3 Plasma Treatment of Polymers: The Effects of Energy Transfer from an Argon Plasma on the Surface Chemistries of Polystyrene, Low Density Polyethyene, Polypropylene and Polyethylene Terephthalate R. France, R. Short (University of Sheffield, United Kingdom) Argon plasma treatment and subsequent exposure to atmospheric oxygen has been used to introduce new carbon- oxygen functionalities to polymer surfaces. We report on the treatment of polystyrene (PS), low density polyethylene (LDPE), polypropylene (PP) and polyethylene terephthalate (PET). Attention has been paid to the level and stability of oxygen incorporation and the selectivity towards new functionalities. Argon plasma-treated polymer surfaces exhibit a 'saturation' level and a 'stable' level of oxygen incorporation. The former is the maximum amount of oxygen which can be introduced into the surface. The latter is the maximum level of oxygen incorporation at which the surface is stable to both washing with a polymer non solvent, and ageing with time. PS exhibits the greatest level of stable oxygen incorporation followed by LDPE and PP. PET displays very little stable oxygen incorporation. Stable surfaces are characterised by a high selectivity towards C-O functionalities (\>\70% for PS at O/C ratio \=\ 0.2). Approximately 40\%\ of these functionalities have been shown to be hydroxyls, through chemical derivatisation. We consider the inert gas plasma to impart reactivity to a surface through an energy transfer process. Paying attention to the molecular structure of the polymers, the results are rationalised on the bond breakages which occur after energy transfer.
9:20 AM		PS+BI-ThM-4 Novel CVD of "Teflon-like" Insulating Biomaterials S. Limb, C. Labelle, E. Gleason (Massachusetts Institute of Technology); D. Edell (Harvard University); K. Gleason (Massachusetts Institute of Technology) Two chemical vapor deposition (CVD) methods have been developed for growing fluorocarbon films that chemically resemble bulk tetrafluoroethylene [ (-CF\sub 2\-)\sub n\, Teflon\super TM\: pulsed plasma-enhanced CVD (PECVD) and thermal CVD. The resulting films have F/C ratios >1.9 and dielectric constants of < 2.0. Thicknesses of > 10 microns have been achieved. For both CVD techniques, the relationship of reactor kinetics to film properties will be discussed. These two CVD methods produce less ion-bombardment of the growing film surface than traditional continuous PECVD. Reducing ion bombardment lowers the concentration of dangling bonds and crosslinks. Dangling bonds are undesirable because they lead to aging of the film properties over time and have been implicated in dielectric loss. The low crosslink density of the pulsed PECVD films results in a flexible coating which maintains their integrity under physical stress. In contrast, traditional continuous PECVD fluorocarbon wire coatings have F/C ratios of ~1.6 and shatter when flexed. Films deposited on silicon dioxide have retained good electrical characteristics under saline soak testing for several months. CVD enables the coating of three-dimensional topography having micron-scale dimensions such as neural probes from the Huntington Medical Research Institute and silicon micro-ribbon cable made at the University of Michigan. The deposition can be controlled so that only selective regions of the structure are coated. Alternatively, the entire structure can be covered. In addition, the CVD process allows the micro-ribbon cable to retain bends of up to 90 degrees.
10:00 AM		PS+BI-ThM-6 RF Inductively Coupled Plasma with Internal Antenna for Deposition of HMDSO-based Barrier Coatings A. Wendt, K. Blobaum, J. Jacobs, M. Varialle, F. Denes (University of Wisconsin, Madison) Plasma-polymerized hexamethyldisiloxane (PPPHMDSO) films deposited using RF, capacitively-coupled discharges have been demonstrated by others as effective barrier coatings for several applications. Such coatings are of great interest as barriers against permeation of oxygen and water through plastic containers for food and other perishable products to prevent spoilage, as well as barriers to protect metal films from corrosion. Viable industrial processes require not only high deposition rates, but also uniform coating of large and irregularly shaped substrates of various types, some of which have low melting temperatures. For this reason, we believe that ICP discharges may be more suitable than capacitively coupled discharges for some applications, and we report here on a large ICP reactor with an internal induction antenna operating at 13.56 MHz. Discharge operating characteristics and deposited film properties will be described for O\sub 2\/HMDSO and Ar/HMDSO gas mixtures and a range of operating powers and pressures. Film deposition rate and chemical structure are characterized through ellipsometry and FTIR and will be compared to published characteristics of films deposited using conventional techniques. The role of energetic ion bombardment during film formation will also be addressed by applying bias voltages to the substrates. This work supported in part by NSF Grant #EEC8721545
10:20 AM		PS+BI-ThM-7 Alkyl Ketenes as Gas-Phase Precursors of Photoluminescence Chromophores in Plasma Polymerized Films Y. Pan, E. Augustyniak, D. Denton (University of Wisconsin, Madison) The gas-phase chemistry of methyl methacrylate (MMA) and other \alpha\,\beta\-unsaturated esters plasmas has been studied with in situ Fourier Transform Infrared (FTIR) Spectroscopy. The formation of alkyl ketenes in the plasma gas-phase is shown to be critical to the photoluminescence (PL) properties of the plasma polymerized films. Different monomers are utilized to generate various alkyl ketenes in the plasmas, such as dimethylketene, ethylketene, etc. PL of plasma polymerized films appears to be affected by the different ketene neutrals in the plasmas. Our results with methyl crotonate (MC) suggest a very similar plasma chemistry to that of MMA. The gas-phase FTIR diagnostic reveals similar by-products in MC and MMA plasmas. Plasma polymerized MC films exhibit PL as well with the PL wavelength blueshifted relative to that of plasma polymerized MMA films. The data indicate that a class of \alpha\,\beta\-unsaturated esters, including MMA and MC, generate ketene species in the plasmas via a common gas-phase pathway. The presence of ketenes is particularly relevant to the formation of PL chromophores and unsaturation in the plasma polymer films. Plasma polymerization of additional \alpha\,\beta\-unsaturated esters, such as ethyl methacrylate and vinyl acetate, is under investigation to characterize the plasma gas-phase (particularly the presence of ketene neutrals) and to characterize the plasma polymerized film properties, e.g. PL and film functional groups.
10:40 AM		PS+BI-ThM-8 Plasma Chemistry in Methane rf Glow Discharges J. Doyle, D. Dagel, C. Mallouris (Macalester College) The chemical and film growth kinetics of methane rf glow discharges are studied as a function of discharge power including conditions suitable for diamond-like carbon deposition. Mass spectrometry is used to monitor the partial pressures of ethane, ethylene, acetylene, and various three-carbon gases. Both flowing and static configurations are studied, and the discharge production as well as depletion rates of these gases are deduced from the measurements. The data are modeled using known gas phase reaction kinetics for C\subm\H\sub n\ radical species. The CH\sub 3\ densities inferred from the model are in very good agreement with threshold ionization results reported in the literature. The model further implies that film growth results primarily from C\sub 2\H\sub n\ and C\sub 3\H\sub n\ species resulting from the depletion of the discharge-produced ethane, ethylene,and acetylene, instead of one-carbon radical species such as CH\sub 3\ and CH\sub 2\
11:00 AM		PS+BI-ThM-9 Fast Deposition of a-C:H: Increasing Quality with Increasing Growth Rate J. Gielen, W. Kessels, A. de Graaf, J. Longueville, M. Sanden, D. Schram (Eindhoven University of Technology, The Netherlands) An expanding thermal arc plasma is used to deposit amorphous hydrogenated carbon films. The thermal arc is operated in argon and the carbon containing gas C\sub 2\H\sub 2\ is injected downstream in the expanding plasma beam. The substrate can be biased separately by means of an RF bias. The substrate temperature can be controlled in the range -100 up to 250 \super 0\C. The ion energy can be controlled by a separate RF bias in the range 2 up to 100 eV. By means of arc current (Iarc = 25-90 A) and C\sub 2\H\sub 2\ flow variation (0.5-20 scc/s) films with different characteristics are deposited at different temperatures. Other plasma settings, chamber pressure and Ar flow were kept constant (at 0.2 mbar and 100 scc/s respectively). The plasma is characterized using Langmuir probe measurements and emission spectroscopy. The films are deposited on glass and silicon substrates, and in situ ellipsometry is used to determine the growth rate. The films are characterized using various techniques. ERDA and RBS are used to determine the carbon and hydrogen density. The bonding structure, refractive index, and band gap are obtained by UV/VIS transmission-reflection and infrared absorption measurements. The hardness and Young's modulus are measured by micro-indention measurements. It is observed that the quality in terms of hardness increases with growth rate (a maximum growth rate of 50 nm/s is achieved). From the emission spectroscopy in combination with the Langmuir probe measurements the dominant radical and ion fluxes are obtained. The temperature dependence and the dependence on ion energy indicate that the deposition is radical dominated, presumably the C\sub 2\H radical. The radical and ion fluxes are used as input parameters in the deposition model. The influence of ion energy and substrate temperature on hardness and other film properties is discussed.