ICMCTF2012 Session GP: Symposium G Poster Session

Diamond-like carbon (DLC) films are generally synthesized at low pressure less than 10 Pa, but high cost for vacuum devices, long deposition time and a limited synthetic area have been pointed out as fundamental problems. Based on above reasons, DLC films synthesized under atmospheric pressure (AP-DLC) have attracted much attention in many fields . In our previous study, AP-DLC films were generally inferior to those synthesized at low pressure in surface smoothness and hardness.

In this study, we synthesized DLC films using C₂H₂ gas diluted with N₂ gas under atmospheric pressure and investigated the effect of applied pulse frequency of electric source on the physical properties. Changing the pulse frequencies at 2, 4, 6, 8, 10 kHz, the pulse width and applied voltage were fixed at 5 μs and 18 kV, respectively. The surface roughness and hardness were analyzed by atomic force microscope (AFM) and tribo scope nano-mechanical indentation tester, respectively. As the pulse frequency decreased from 10 to 2 kHz, the surface roughness decreased from 32.5 to 1.76 nm, and finally, the hardness increased from 0.5 to 1.2 GPa.

Recent studies indicated that the deposition process parameters exhibit strong dependence on crystal growth and stoichiometry of sputtered MoS₂. All the studies are focused on building highly oriented coatings without columnar crystal growth. There is a wide consensus that these films can be achieved mainly by low process pressures. Considering the different characteristics (mass) of the two species and models of film growth in which the energy flux is a main influence factor, the question arises how process parameters like working gas pressure affect the kinetic energy and the composition of particles arriving at the substrate.

In general, the sputter deposition process can be separated into three steps. The first one is the vaporization of the target caused by collision cascades of impacting ions. The second one is the transport of sputtered particles through the gas phase and the last one is film growth on the substrate. In this paper, results of a Monte Carlo simulation with TRIM considering the first two steps are presented. Within the first step the energy and angular distribution of the sputtered molybdenum and sulfur atoms where calculated when argon ions with varying kinetic energies impact the MoS₂ target perpendicularly. The varying argon ion energy represents different acceleration and cathode voltages respectively. To simplify matters, energy and angular distribution of the impacting argon ions where neglected.

Within the second step the transport through the gas phase in the vacuum chamber is calculated. The calculation is based on sputtered particles from the first step with equal angles and energies. In this step the pressure of the working gas, argon in this case, was varied. Finally, energy distribution and amount of particles are analyzed at different distances from the target. This enables to determine the effect of three process parameters namely cathode voltage, working gas pressure and distance to target on energy and amount of particles. To visualize the mutual interactions of parameters in response surface diagrams design of experiment methods where applied.

In short, this study gives a fundamental understanding for the sputtering process of MoS₂ and the energy distributions and composition of sputtered particles.

Atomic diffusion, and later formation of intermetallic compounds, can become a serious problem in electronic joints. The growing of intermetallic compounds at the interface can affect the structural integrity of the joints, due the formation of cracks. This process hinders the use of some lead-free solders like Zn-Sn alloys. This alloy system is a good candidate to substitute high temperature solders based on lead. The joint failure between Zn-Sn and Cu comes from the formation of CuZn5 and Cu5Zn8 intermetallic compounds .The use of a conductor thin film as a diffusional barrier coating can inhibit the formation of intermetallic compounds and consequently maintain the structural integrity of the joint.

In this work the atomic diffusion between Zn-Sn alloy into Cu and Si substrates was studied. Two different diffusional barrier coatings were used: tantalum - tantalum nitride and tantalum - tantalum nitride + 5% wt Silicon. The Ta/TaN thin film was deposited using a DC sputtering under Argon / Nitrogen atmosphere. The Ta/TaN+Si film was deposited under an Ar/Ni atmosphere, using two separate magnetrons, the first with a RF source and a Si target, and the second with DC source and a Ta target.

Standard XRD diffraction patterns were obtained from the coatings (using a grazing configuration), in order to analyze a structural change due the addition of Si. Samples were annealed at 423 K a different times, to evaluate the performance of the DBCs as a diffusion barrier coating. The elemental diffusion was obtained from EDX spectra (line scan), showing marginal Zn content into the coatings. The interfaces and epitaxies between coatings and substrates were discussed based on the observations made through FIB, SEM and TEM.

The main effort in the development of a new generation of metal –oxide-semiconductors (MOS) devices is toward the reduction of their dimension down to submicron values. The actual technology node is undergoing below 35 nm and became critical the oxide deposition technique and its effective characterization. Spin-on-Dielectric (SOD) materials have generated much interest for gap filling as alternative to chemical vapour deposition (CVD) and high density plasma deposited materials (HDP). In high aspect ratio (HAR) structures CVD technologies have difficulties in gap filling where SOD conversion to silicon oxide could be inhibited inside the pattern structure and by the presence of thin film barriers. In this direction the effects of the SOD conversion temperature as well as the different chemical composition of the amorphous liner, deposited between the Silicon wafer and the SOD layer, are studied on unpatterned wafers. Silicon oxide and silicon nitride liners via furnace and CVD deposition technique are provided.

Intrinsic stress induced on silicon wafer was studied and analysed by means of the Stoney’s formula. Fourier Transform Infrared Spectroscopy (FTIR) was performed to compare SOD conversion degree. The quality of silicon oxide obtained was correlated to the presence of 4-fold and 4/6-fold Si-O bonds that is an index of sub-stoichiometry of the bulk. This fact indicates a better amorphous conversion of SOD in presence of silicon oxide liners instead of silicon nitride or bare-silicon.

Polymer materials such as polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET) are widely used as food packaging materials due to their lightness, low cost, and optical transparency. However, most of the polymer materials have low gas barrier property which may cause a great damage on the quality of food products. Thus the improvement of the low gas barrier property is widely desired.

Recently, thin solid coatings by diamond-like carbon (DLC) and silicon oxide (SiOx) based on plasma technology have been prominent methods. Several researches have been reported on the gas barrier properties of polymers coated with DLC, eventually improving the gas barrier properties of certain types of polymers. However, most plasma systems used for the syntheses of DLC and SiOx are operated under low pressure and, therefore, require an expensive and complicated vacuum system.

As a new thin coating method, silane coupling treatment was investigated. The silane coupling agent is a common adhesion promoter and is widely used in polymeric composites. In addition, the silane coupling agent possesses high transparency, and it can easily spread over polymer films since it is in a liquid state. Furthermore, the silane coupling treatment can solidify itself through hydrolysis, which can be an easier and faster way to produce a high gas barrier coating.

For fabrication of thin film using microwave plasma CVD, mode-conversion type microwave plasma is expected to improve the deposition area and growth rate . By converting the TE₁₀ mode to the TM₀₁ mode for microwave, electric field component is changed from vertical direction of the rectangular waveguide into the circumference direction of the circular waveguide . And then, uniform electric field distribution can be obtained. So, larger deposition area and higher growth rate may be perform ed. Moreover, quality of deposits is improved because of the higher microwave density . On the other hand, carbon materials such as diamond and diamond like carbon (DLC) can be obtained by using microwave plasma CVD . So, investigation was carried out on the manufacturing of mode-conversion type microwave plasma CVD apparatus and applying for synthesis of carbon materials.

Different wavelength s microwave of 2.45 GHz and 915 MHz were applied to experimental apparatus. The mode of microwave was converted by using of mode convertor. It is important to discharge plasma at higher microwave density and higher pressure to obtain higher growth rate and high qualities for diamond growth.

Diamond synthesis using the apparatus applied 2.45 GHz microwave, CH₄-H₂ mixture gas system was used as the reaction gas. The flow rate of CH₄ and H₂ were set at 1 to 10 and 100, respectively. Pressure, microwave power and reaction time were unified at 20.0 kPa, 1.5 kW, and 3h, respectively. Si wafers scratched by diamond powders were used as substrates. The deposits were characterized by a scanning electron microscopy (SEM) for surface observation, and Raman spectroscopy was used for estimation of quality of deposits.

Results of the surface observation by SEM, deposits which has clear crystalline shape were observed in all the conditions. In addition, in the estimation of quality of deposits by Raman spectroscopy, diamond peak at 1333 cm^-1 was observed in their Raman spectra of all samples, and DLC peak at 1550 c m^-1 was ob serv ed.

In the case of the apparatus applied 915 MHz microwave, 915 MHz microwave apparatus is tried to set up the similar configuration . The deposition area will be larger by applying 915 MHz microwave because of longer wavelength.

In conclusion, diamond was synthesized from CH₄-H₂ reaction gas system using mode-conversion type microwave plasma CVD apparatus applied 2.45 GHz microwave.

A novel technique to suppress self sputtering of radio-frequency electrode in capacitively-coupled glow discharge

Xiubo Tian¹, Yinghe Ma¹, Chunzhi Gong¹, Shiqin Yang¹, Paul. K. Chu²

¹State Key lab of Advanced Welding & Joining, Harbin Institute of Technology, Harbin, China

²Department of Physics & Materials Science, City University of Hong Kong

The capacitively-coupled Radio-frequency discharge (CCP) has been widely utilized in industry. The self-sputtering effect induced by self bias on the radio-frequency electrode inherently exists. This may produce the metal contamination to the generated plasmas. Although some measures including quartz covering have been taken and the sputtering effect was weakened, the self-bias does not be eliminated. In this paper we proposed a novel technique to decrease the self-bias and resultant self-sputtering effect. An external circuit was added into the radio frequency discharge circuit. The self bias on radio frequency electrode may be counteracted by external energy. Our experimental results have demonstrated that the self-bias on the electrode may effectively be eliminated. The positive and negative waveform of radio fervency current seems to be symmetric. The electrical circuit to weaken the self-bias is described and the waveform before and after the external circuit is coupled is compared and suppression effect of self sputtering is experimentally demonstrated.

Recently, there have been many research for higher deposition rate (DR) and good uniformity of μc-Si:H film in large-area discharge. Two factors should be the most important issues in the fabrication of the thin film solar cell. In order to solve these issues, several dicahrge conditions, including large area electrode (more than 1.1 mx1.3 m), higher pressure (more than 1 Torr), and very high-frequency RF power (more than 40 MHz), have attracted. But, in the case of large-area capacitive discharges (CCP) driven at high frequencies, the effect caused by the standing wave should be important limitation. Furthermore, the ion damage on the thin film layer by the high sheath voltage can cause the defects, which degrade the film quality.

The ever increasing demand for higher productivity in manufacturing gears requires advanced hard coatings and new substrate materials. Up to now in this field of gear manufacturing two different substrate materials are availed for single-piece hobs: powder metallurgy high-speed steel (PM-HSS) and cemented carbide. Today PM-HSS has a market share around 70% offering limited cutting speeds for wet and dry conditions on labile machine conditions. On the other hand cemented carbide offers from the technical point of view strong performance related features like high cutting speeds up to 400 m/s on stable machine conditions. .

But due to the fact, that hobs have a typical life cycle time of 10-15 recondition cycles– hobs are often demounted – packed and shipped – decoated- regrinded and coated again- could cause small handling or production damages that result in a shorter tool life time and less reliability of the production process. Additionally using cemented carbide hobs required often new hob machines with stable machine conditions.

To fill this gap, a new generation of substrate material was developed based on intermetallic phases. This cutting material offers compared to conventional PM-HSS higher hot hardness and as result from this higher cutting speeds. In fact today hobs are coated and e.g. dry gear cutting is only possible with coated tools due to the prevention of chip welding.

Today hob coatings that are available on the commercial market mainly based on TiAlN system applied by AIP and Sputter PVD processes.

Properties of coating are correlated with plasma characteristics. Barrier properties are determined concerning oxygen permeation. The composition of the coatings regarding carbon and hydrogen content is analyzed by means of Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). Good oxygen barriers are observed as carbon content in the film is reduced. Atomic oxygen etching of the coated substrate visualizes coating defects responsible for a residual permeation. Crack formation mechanisms are studied in-situ by means of atomic force microscopy (AFM) using an AFM-stage to apply a desired strain. In addition, the evaluation of water up-take in barrier films was performed. The results show how process parameters such as gas composition and substrate bias have an impact on properties of permeation barrier coatings.

The authors gratefully acknowledge the support provided by the Deutsche Forschungsgemeinschaft (DFG) within the framework of SFB-TR 87, the Ruhr-University Research School, Aurion Anlagentechnik Seligenstadt and the Center for Plasma Science and Technology – CPST (Ruhr-Universität Bochum).

In the present paper, Fluidized Bed Machining (FBM) of thermally sprayed coatings is proposed. In particular, aluminium cylindrical components coated by High Velocity Oxy Fuel (HVOF) with Stellite 6 (cobalt-chromium alloy) and by Atmospheric Plasma Spraying (APS) with chromium oxide were exposed to the impact of suspended abrasives, while rotating at high speed within the fluidization column. The interaction between Al₂O₃ abrasive media and surfaces of the thermally sprayed coatings was studied, identifying the effect of the main process parameters, such as machining time, abrasive mesh size and rotational speed. The change in surface morphology as a function of the process parameters was evaluated by Field Emission Gun – Scanning Electron Microscopy (FEG-SEM) and contact gauge prof ilometry. The change in the size of the machined parts was measured by Coordinate Measuring Machine (CMM). The experimental findings emphasize an improvement in the finishing as well as in the dimensional accuracy of the processed surfaces was achieved whatever the setting of the operational parameters, showing FBM as a very promising technique in the reprocessing of thermally sprayed coatings.

Key words: Fluidized Bed; Abrasive; Grinding; Thermally Sprayed Coatings; Morphology; Dimensional Tolerance.