Papers

ICMCTF2000 Session H4-2: Novel Materials and Processes

Wednesday, April 12, 2000 1:30 PM in Room Sunrise

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		H4-2-1 Transparent Conducting Films of In₂O₃-ZrO₂, ZnO-ZrO₂ and SnO₂-ZrO₂ S.B. Qadri (US Naval Research Laboratory) Indium-tin-oxide (ITO), an alloy of 90 wt. % In2O3 and 10 wt. % SnO 2 which is extensively used, has problems with respect to stability at higher temperatures. In search of an alternative TCO coating which will be stable at high temperature and also erosion resistant, for the first time, we made transparent conducting oxide films consisting of alloys of ZrO2 and In2O3, ZnO and SnO 2. This was done using a pulsed laser deposition technique, which has the advantage of replicating the stoichiometry of the target. The combination of In2O3 -ZrO2, ZnO-ZrO 2 and In 2O 3 -SnO 2 has the distinct advantages over the existing ITO. One of these is due to the chemical inertness and stability of ZrO2 at higher temperatures. The other very important feature of these coatings is their tunability in terms of the electrical and optical properties.
2:10 PM		H4-2-3 Coating of Polymers with Titanium Based Layers by a Novel PACVD-process F.J. Breme, J. Buttstaedt (GfE Metalle und Materialien GmbH, Germany) CVD is an excellent technique to coat complex substrates like fibers or inner surfaces of tubes. But CVD often suffers from high coating temperatures which makes it impossible to coat temperature sensitive materials like polymers e. g. with titanium based layers. At GfE a new PACVD-process has been developed to coat polymers at very low temperatures with different kinds of titanium based layers. The coating temperature could be lowered to about 60 °C (140 F), so that a variety of different polymers can be coated without undesired damaging. In this work, PET, PES, PVC, PE and PP have been used. The very smooth (R_a= 3 nm) and thin (5-100 nm) layers show a very good adherence (> 10 N/mm²) tested by tensile tests. It could be demonstrated that all kind of geometries like tubes, textile structures or containers can be coated. The coating has the huge potential to improve the bio- and bloodcompatibility of polymers for medical devices. This could be shown by a significant higher cell vitality and cells growth on Ti(C,N)-coated polymers compared with uncoated polymers (using fibroblasts and endothelial cells). Moreover the coagulation of blood is less effected if polymers are coated with the Ti(C,N)-layers. It could be demonstrated, that the Ti(C,N)-coating is an effective diffusion barrier to prevent leaching of plasticizers or additives e. g. from PVC which is advantageous for many medical devices as well as for a lot of other applications where PVC is used. Besides the medical applications many other improvements of polymers are possible by this new coating process. Examples are surfaces with a higher wettability, corrosion stability or electrical conductivity.
2:30 PM		H4-2-4 A New Method for Surface Structure Formation in Ion Deposition I.G. Levchenko (Kharkov State Aerospace University KhAI, Ukraine); M. Keidar (University of Michigan) A new method for creating surface structures like a regular surface trench system is proposed. This method is based on using the plasma oscillations for non-uniform film deposition. Two main versions of this method are theoretically and numerically investigated namely using ion flow density modulation when passing through plasma oscillation area and ion precipitation from oscillating plasma by applying alternating substrate voltage. Regular surface trench system may be used for various technical applications such as aerodynamic drag reduction, heat exchange intensification, special tribological environment etc. The possibility to deposit thin films with surface trench system from oscillating plasma was demonstrated theoretically. Appropriate mathematical model was developed. A series of numerical experiments were performed and a number of surface structures were calculated under different conditions of deposition. Some parameters for ensuring surface profile required were calculated. The method was found to be able to create the surface structures of various shapes. Significant advantages are possible in comparison with usual techniques.
2:50 PM		H4-2-5 Coating Adhesion on Ion Implanted Polymer Surfaces L.A. Guzman, A. Miotello, M. Adami (University of Trento, Italy); E. Voltolini (Istituto Trentino di Cultura, Italy) Even though plastics are of great importance in many practical applications, their performance can be further enhanced by surface modification, to improve their hardness, wear and chemical resistance. Metallic coatings, in particular hard Cr, are successfully deposited by various techniques; unfortunately, the low polymer surface tension and the high intrinsic stresses of the coatings give often adhesion problems. The conventional treatment of polymers for further metallization is based on hazardous and pollutive agents like chromic acid and various organic solvants. We have used a combination of ion implantation with vapour deposition (performed in the same treatment chamber) allowing for the production of well adherent Cr coatings on plastics. Mechanical properties of the films were examined as a function of ion beam treatment. Nitrogen ions were implanted at medium-low doses on different polymer substrates. Following ion irradiation, thick chromium films were deposited by evaporation. The implanted substrates were characterized with respect to structure by Laser Raman spectroscopy (LRS) and TOF-SIMS, wettability (by contact angle measurement) and hardness (by nano-indentation).The coatings were characterized with respect to morphology (SEM), adhesion (scratch-test) and hardness (by nano-indentation). It was observed that, without the ion pretreatment, the coatings are poorly adherent. Due to the high level of stresses developed in the Cr films, the deposited layers on unimplanted samples appear broken as expected. On the contrary, the adhesion of the coatings on implanted polymer surfaces is appreciably better for the pre-implanted specimens. This is certainly due to the superior mechanical properties exhibited by the implanted polymers and to the enhanced wettability induced by energetic ion bombardment. Scratch tests show also an optimised tribological behaviour for the doubly treated polymer surfaces.
3:30 PM		H4-2-7 Interface Control in the Chemical Vapor Deposition of Titanium Dioxide on Silicon(100). A.C. Tuan, M. Yoon, V. Medvedev (University of Washington); Y. Ono, Y. Ma (Sharp Labs of America); J.W. Rogers (University of Washington) A novel deposition process has been developed for the deposition of titanium dioxide thin films on p-type Si(100) with high quality interfacial characteristics and the absence of carbon using titanium tetrakis-isopropoxide (TTIP) as the metalorganic precursor. The deposition process occurs in an ultra-high vacuum chamber and consists of three stages. Initially, a buffer layer consisting of a monolayer of titanium is deposited on silicon at a substrate temperature of 650 K using a Ti sublimator. The substrate temperature is then lowered to 300 K and the titanium layer is oxidized using a gas phase oxygen source to form TiO_x. The subsequent TiO₂ thin film is deposited by MOCVD using TTIP at low temperature (below 600 K). Auger electron spectroscopy (AES) analysis at each stage of growth shows no signs of carbon contamination. Furthermore, the absence of both an oxygen signal (before oxidation) and a silicon peak shift (after oxidation) confirm that the titanium layer prevents oxidation of the underlying silicon. Additional AES measurements suggest that at the process temperature, titanium grows on silicon according to the Stranski-Krastanov mode¹, permitting the uniform growth of the titanium layer. In addition, the strong affinity of titanium for oxygen allows it to be easily oxidized so that it may ultimately be incorporated into the TiO₂ thin film. This unique process allows for the production of a high quality titanium dioxide thin film with an abrupt TiO₂/Si interface. ¹T. Ohwaki, K. Aoki, T. Yoshida, S. Hashimoto, Y. Mitsushima, and Y. Taga, Surface Science, 433, 496-500 (1999).
3:50 PM		H4-2-8 Electrical Resistance of Ti-B-Al-O Thin Films Deposited by RF Magnetron Sputtering S.K. Kim, Y.H. Ahn (University of Ulsan, Korea) Ti-B-Al-O thin films were deposited on alumina substrate by rf magnetron sputtering using the composite TiB2-Al2O3 targets produced by the self-propagating high-temperature synthesis method. Effect of power, sputtering temperature and sputtering time on the electrical resistance of Ti-B-Al-O thin films were investigated. Effect of post heat treatment of the films on the electrical resistance was also studied. Microstructure and composition of sputtered thin films was examined by SEM and WDS. Note: Requested an Oral Session.
4:10 PM		H4-2-9 Response Characteristics of Gas Sensitive Tin Dioxide Films J.M. Correia-Pires, J.B. Almeida, V. Teixeira (Universidade do Minho, Portugal) Tin dioxide as good sensitivity to a wide variety of gases. Many research studies have been done in the past years which have permitted to know some of the factors that determine the sensitivity and selectivity of this material too gases. However there is still no means to predict the effects of different film characteristics in the response of produced sensors. In this work we are trying to correlate the reproducibility and the response characteristics of tin dioxide based sensors to the structure and composition of the sensitive films. To study the structure of the films we are using X-ray diffraction techniques, scanning electron microscopy and analysis of the optical transmission spectrum. The chemical composition is being examined by AES and EDX.
4:30 PM		H4-2-10 Impact of Liner Thickness on the Beyond 0.18 µm Generation Devices using Low-k Hydrogen Silsesquioxane as the Interlayer Dielectric. Y.L. Wang (Company, R.O.C.); J.K. Lan, C.G. Chao, Y.L. Wu (University, R.O.C.); S.Y. Chiu (National Chiao - Tung University, Taiwan, R.O.C.); H.C. Liou (Company, R.O.C.) As the minimum geometry in integrated circuits (ICs) continues to shrink to the 0.18-0.25µmm range, the capacitance between metal lines increases dramatically which causes the delay in signal propagation.Low k dielectric materials have to be implemented to reduce the delay, to reduce the line to line cross talk, and to increase the signal propagation speed. Among available low k processes and materials, only spin-on hydrogen silisesquioxane (HSQ) and high-density plasma chemical vapor deposited (HDP-CVD) fluorosilicate glass (FSG) films have been successfully integrated in manufacturing processes. HSQ processes, with k <2.9, offer more potential for better performance than FSG (k~3.5). When integrating HSQ in the interlayer dielectric (ILD) applications, it is a common practice to use SiO₂ layers to form liner/HSQ/cap sandwich structures. Since SiO₂ has a higher dielectric constant than HSQ, the overall capacitance depends on the combinations of HSQ and SiO₂ layers especially for smaller metal gaps in 0.18 µmm devices. Therefore, device wafers with different thickness of SiO₂ liner were processed to explore the impact of liner thickness on overall capacitance and via chain resistance. The experimental data shows that, when compared with SiO₂ ILD materials, there is approx. 20-25% intraline capacitance reduction while only 6-16% reduction is observed for FSG alone at various metal widths and metal spacings. It is observed that wider metal patterns have a higher capacitance than those of smaller metal widths at the same gap spacing due to the fringing capacitance effect. In this paper, the dependence of the capacitance reduction on HSQ, SiO₂/HSQ, and FSG ILD structures will be reported. The impact of these systems on the performance of gap filling, landed via and unlanded via will also be presented.