ICMCTF2004 Session B6: Plasma Assisted CVD, Thermochemical Treatments and Duplex Technology

Thursday, April 22, 2004 1:30 PM in Room Golden West

Thursday Afternoon

Start	Invited?	Item
1:30 PM		B6-1 Characterization of TaN Barrier Layers made by Chemical-Enhanced Physical Vapor Deposition (CEPVD) D.N. Ruzic, Ning Li (University of Illinois, Urbana-Champaign) CEPVD TaN is prepared in a modified magnetron sputtering system mainly consisting of a Ta target, a heated substrate, an ICP coil, and a metallorganic precursor (TBTDET) delivery line. The produced film is a comprehensive result of reactive sputtering, precursor decomposition and the enhancement of each other with the aid of a secondary plasma. By controlling the processing parameters and procedures, CEPVD operation is allowed to perform in metallic mode which avoids the organic contamination on target and chamber wall. Experiment results demonstrate that CEPVD TaN film resistivity is close to IPVD TaN resistivity. Increasing the RF power from 260W to 310 W decreases resistivity from 1000©-cm to 370©-cm. Substrate bias voltage has the similar effect and results in a lower resistivity of 510 ©-cm at -60V bias. In addition, CEPVD employs the low sticking coefficient precursors to cover up the trench sidewall area that is inaccessible to IPVD flux and improves the step coverage, for example, from 0% to 11% in a trench with the aspect ratio of 13. Generally, CEPVD films are carbon rich (~ 35%) and polycrystalline. Non-uniformity in this system is caused by the single point source of chemical precursor. Mapping the radial distribution of the film properties include resistivity (by FFP), step coverage (by SEM), elemental composition (by AES), crystalline structure (by XRD) and compositional bondings (by XPS) reveals the respective attribute by reactive sputtering and the chemical decomposition in a certain processing recipe. These properties are also investigated as functions of H2 flow rate, Ar partial pressure and N₂ flow rate, ICP power, substrate bias and substrate temperature. The correlations between film resistivity and other properties are revealed based on the experiment data. A semi-empirical physical model is established for CEPVD process in order to guide the further search for best processing parameters.
1:50 PM		B6-2 Utilizing Bipolar Pulsed PACVD for the Deposition of Alumina Hard Coatings M. Fink, J. Laimer, H Stoeri (Vienna University of Technology, Austria); C. Loecker, C. Mitterer (Montanuniversitaet Leoben, Austria) Due to the outstanding properties of alumina hard coatings at elevated temperatures on air, such coatings have attracted quite some interest in the tool industry. Whereby for some time it was only possible to deposit such coatings by chemical vapour deposition (CVD) at temperatures of about 1000°C, recently it has become possible to lower the needed temperature by activating the process gas by a plasma. First reports have shown that by using bipolar voltage pulses for plasma-assisted chemical vapour deposition (PACVD) of alumina, the insulating nature of this material can be properly dealt with. In the present investigation a commercially available PACVD system suited for the deposition of titanium nitride (TiN) was adapted in order to allow alumina deposition up to substrate temperatures of 800°C. Besides of a modification of the gas supply system, an additional heating system inserted into the reactor was needed. Bipolar voltage pulses were applied to the substrate holder whereas the grounded reactor wall served as counter electrode. In order to achieve a uniform discharge across the substrate holder it was necessary to place an additional grounded counter electrode close to the substrate holder. The alumina deposition was investigated on substrates placed on the substrate holder as well as on the counter electrode. It turned out that the coating thickness decreased strongly with the distance from the central gas inlet. The coatings were analysed by XRD for phase composition, by microhardness indenter for hardness, by XPS for chemical composition and by REM for morphology. In the temperature range of 600 to 800°C only two crystalline modifications of alumina, the Alpha and the Kappa phase, were observed. Microhardness values of up to 18 GPa were measured.
2:10 PM	Invited	B6-4 Production of N, C, O and H Atoms in Flowing Microwave Dishcarges A. Ricard (Université Paul Sabatier, Toulouse, France) Densities of N ,C , O and H atoms are determined in flowing microwave post- discharges , containing N₂ , CH₄ , O₂ , H₂ and H₂O molecular gases. The diagnostics are by NO titration , by spectroscopy of chemiluminescent reactions and by two-photons laser induced fluorescence (TALIF ). The microwave discharges are produced by a surfatron cavity in a quartz tube of 5 mm. int.dia. , at powers of 100 - 200 watts , gas pressures of 2 - 100 Torr and flow rates of 1 - 3 L_N/ min. The discharge tube is connected to a post-discharge chamber where the optical diagnostics are performed. The flowing time between discharge tube and post-discharge chamber is varying between 10^-2 and 10^-1 sec. Production of active atoms is determined in several gas mixtures : Ar-N₂ and Ar-N₂-CH₄ for N and C atoms , Ar-O₂ for O atoms and Ar - H₂ , Ar-H₂O , N₂ - H₂O for H atoms. Variation of atom densities is analysed by varying the discharge parameters as microwave power , gas pressure and gas mixture composition. The effect of H₂O in Ar and N₂ gas mixtures is specially considered. Applications of the flowing post-discharge atom sources are given for steel surface nitrocarburising with N and C atoms and for bacteria sterilisation with N and O atoms.
2:50 PM		B6-6 Laser Beam Surface Hardening of CVD TiN Coated Steels M. Heidkamp, O. Kessler, F. Hoffmann, P. Mayr (IWT Stiftung Institut fuer Werkstofftechnik, Germany) The properties of hard coatings deposited using CVD-processes are usually excellent. However, high deposition temperatures may influence the properties of the steel substrates negatively. Therefore, a subsequent heat treatment is necessary to restore the properties of the steel substrates ready for operation e.g. sheet forming tools in the automotive industry. By the duplex treatment of CVD-coating with laser beam hardening a composite material with flat strength- and hardness gradients from the interface to the core apart from high surface hardness can be implemented. The supporting effect of the laser beam hardened substrate leads to an increase of the wear resistance under high surface contact-pressures and at the same time to an increased material resistance against high mechanical load. Laser beam hardening is applied on CVD TiN-coated 42CrMo 4 (AISI 4140), X100CrMoV5-1 (AISI A2), X153CrMoV12 (AISI D2) substrates. For characterization of the composite materials the chemical composition of the layer and the substrate are analyzed by GDOS (Glow discharge optical spectroscopy). In addition the microstructure and the substrate hardness are examined. To show the characteristic improvements in comparison with the individual processes, scratch tests are executed. The results show great advantages of laser beam surface hardening because only low distortion appears and the properties of the steel substrates are improved without loosing good coating properties.
3:10 PM	Invited	B6-7 Plasma Enhanced Surface Treatments Using Electron Beam-generated Plasmas D. Leonhardt, S.G. Walton (U.S. Naval Research Laboratory); C. Muratore (ASEE/NRL Postodoctoral Research Associate); R.A. Meger (U.S. Naval Research Laboratory) NRL has developed a 'Large Area Plasma Processing System' (LAPPS) utilizing a high energy (~2 keV) electron beam (e-beam) to initiate the plasma ionization. We have demonstrated that this system is (1) efficient at producing plasma in any gas composition; (2) capable of producing low temperature plasma electrons (<0.5 eV) in high densities (10⁹-10¹² cm^-3) and (3) scalable to large area (square meters).¹ This presentation will first discuss the e-beam ionization mechanism and plasma system, which consists of a pulsed, planar plasma distribution generated by a magnetically collimated sheet of electrons injected into a background gas. The majority of the presentation will focus on applications of these systems for improved surface treatments. Presently, etching, thin film deposition, surface nitriding and surface pretreatment methods are being investigated. By combining the high dissociation and ionization rates of LAPPS with the high material throw rates of sputter magnetron sources, systems have been optimized for surface pretreatments of polymers for metallization and thin film deposition of nitrides and oxides. Using LAPPS only, nitride growth has also been investigated for various substrates. For stainless steel, high nitriding rates (5-10 microns/hr) at low temperatures (450 °C) have been established. These systems show a strong positive correlation with large, controllable fluxes of both atomic ions and radicals delivered to the substrate. Complementary time-resolved in situ plasma diagnostics (electrostatic probes, microwave transmission and mass spectrometry) of these modulated plasmas will be presented to illustrate these characteristics. This work was supported by the Office of Naval Research. ¹D. Leonhardt, etal., ICMCTF2003 presentation.
3:50 PM		B6-9 Morphology and Hardness of Mild Steel Treated by Plasma Thermochemical Treatments V.H. Baggio-Scheid (Institute for Advanced Studies, Aerospace Technical Center, Brazil); A.J. Abdalla (Centro Tecnico Aeroespacial, Instituto de Estudos Avancados, Brazil); A. Moreira (Instituto Tecnologico de Aeronautica, Brazil) Plasma thermochemical treatments are widely used to improve corrosion, wear resistance and fatigue strength of engineering steels. Especially interesting are the benefits on the mechanical and chemical properties of low carbon steels, derived from the use of the plasma. In this work we investigate the hardness and morphology of the compound and diffusion layers produced on AISI 1010 and 1020 mild steels by plasma nitriding, nitrocarburizing and nitrocarburizing plus post-oxidation. The samples were treated at temperatures varying from 673 K up to 873 K. The influence of the treatment time, ranging from 10 up to 60 min, and gas concentration on the surface properties was also investigated. The samples were characterized using microhardness testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), and roughness measurements. Decarburization during the plasma cleaning pre-treatment reduces the surface hardness, but this is compensated by further nitriding and nitrocarburizing. An improvement in the hardness was observed with increasing temperature and nitrogen concentration. The microstructure of the compound layer, produced by nitriding just above the Fe-N eutectoid temperature (863 K), leads to the formation of an austenite sublayer, which is located between the nitride surface layer and the diffusion zone. In this situation, hardness higher than 900 HV0.05 has been measured on the top of the nitride layer. The surface roughness, as well as, the improvements in hardness is discussed considering the treatment parameters.
4:10 PM		B6-10 Formation of a Magnetite Overlayer on Nitrocarburized Low Alloy Steel Samples by Plasma Post Oxidation M. Zlatanovic (Faculty of Electrical Engineering, Yugoslavia, Serbia&Montenegro); N. Popovic, Z. Bogdanov (Nuclear Science Institute Vinca, Yugoslavia); S. Zlatanovic (University of California, San Diego) The conventional steam oxidation of salt bath or gas nitrocarburized steel requires an intermediate cleaning process. Polishing is applied on salt bath treated surfaces, while gas nitrocarburized surfaces may be sputter-cleaned before the oxidation in a continuous process. In our experiments the samples made of steel grade AISI 4140 were salt bath or plasma nitrocarburized and then post treated by pulse plasma oxidation process. No intermediate cleaning procedure was applied. The obtained surface structures were analyzed by XRD, SEM and optical microscopy, while Vickers microhardness measurements and calo-test method were used to analyze surface microhardness and microhardness distribution over the sample cross section. The XRD analyses revealed the existence of a superficial oxide layer onto epsilon underlayer beneath with traces of a gamma prime zone in the case of plasma nitrocarburized samples. The post oxidation process parameters were selected to obtain a single-phase magnetite overlayer onto both salt bath and plasma nitrocarburized samples. Phase transformations induced during plasma post-oxidation process were discussed, as well as the role of substrate conditions before oxidation in subsequent phase transformations. It was found that during post-oxidation a hematite layer was formed on previously untreated surfaces simultaneously with single-phase magnetite formation on nitrocarburized layer. The dynamic balance between the oxidation as a source of nitrogen and nitrogen diffusion as the nitrogen atoms drain was discussed. A continuous pulse plasma processing consisting of plasma nitrocarburizing and post-oxidation was found favorable compared to combined salt bath nitrocarburizing and plasma post oxidation process. No intermediate cleaning is required in a continuous pulse plasma treatment in order to obtain an adherent, compact magnetite overlayer onto plasma nitrocarburized specimens.
4:30 PM		B6-11 Influence of Process Parameters on the Properties of Teos-pecvd Grown SiO₂ Films A.M. Mahajan, D.K. Gautam (North Maharashtra University, India) Silicon dioxide (SiO₂) films have been grown by Plasma Enhanced Chemical Vapor Deposition (PECVD) system due to the proven applicability of PECVD grown SiO₂ films in the fabrication of microelectronic and optoelectronics devices. The properties viz-uniform thickness within the substrate and substrate-to-substrate, precisely controlled refractive index, low tensile stress, good stoichiometry and surface morphology etc. have been studied using different characterization techniques like ellipsometery, Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM). The liquid tetraethoxysilane (TEOS) has been used as a source of Si instead of SiH₄ to avoid dangerous handling of SiH₄. In this paper, we intend to study the influence of process parameters viz the variation in Chamber pressure (70 Pa to 240 Pa), Substrate temperature in the range of 473 K to 673K and flow rate ratio (O₂/TEOS) of 2 to 10, one by one on the properties of the deposited SiO₂ films by keeping the other process parameters at their optimized constant values. Ellipsometer (Philips SD1000) has been used to determine thickness, refractive index and film stress. Through FTIR (Shimadzu-8400) spectroscopy, the characteristic peaks of Si-O-Si stretching, bending and rocking have been indicated with the significant intensities in the spectras taken for the SiO₂ films.