AVS2004 Session PS2-TuA: Plasma and Polymers

Tuesday, November 16, 2004 1:20 PM in Room 213B

Tuesday Afternoon

Start	Invited?	Item
1:20 PM	Invited	PS2-TuA-1 Plasmas, Polymers and Plasma-deposited Polymer-like Films: Plasma Diagnostic Studies for SiO₂-like Film Deposition M. Creatore, M.C.M. van de Sanden (Eindhoven University of Technology, The Netherlands) Low temperature plasmas for polymer modification and synthesis of polymer-like films are technologically appealing because of the development of plastic-based applications and the versatility of plasmas as processing tool in engineering the polymer-like film. As plasmas invade hot topics such as flexible electronics and nano-scale devices, the plasma- based technology urgently needs the support of fundamental studies, which can unravel the mechanisms of plasma-polymer interactions and deposition of polymer-like films. A valid example is the deposition of SiO₂ barrier layers on polymers for long-term stability devices, such as plastic windows, polyLEDs and TFTs: here the requirement of water vapor permeability is more demanding that in food packaging. This involves issues, such as the development of an interphase and the generation of defects during film growth, which go beyond the recipe for a stoichiometric, dense SiO₂ layer. Another example is the deposition of SiC_xH_yO_z polymer-like films as low-k dielectrics for ULSI technology. Highlighting the monomer dissociation paths is not only useful in controlling the carbon content in the film and, therefore, the quality of the dielectric, but it is also expected to pave the way towards the engineering of ultra-low-k materials. This contribution describes, through the chosen model system of SiO₂ and SiC_xH_yO_z film deposition, studies performed in an Ar-fed remote expanding thermal plasma where O₂ and hexamethyldisiloxane are injected downstream. The monomer dissociation paths controlled by the (Ar⁺, e^-) flow emanating from the plasma source will be discussed in view of the results obtained by Cavity Ring Down Spectroscopy and Triple Stage Threshold Ionization Mass Spectrometry. Implications of these outcomes on the plasma-deposited film properties will be also addressed.
2:00 PM		PS2-TuA-3 Deposition of SiOx Films from Organosilicone and Oxygen Plasma under Continuous and Pulsed Modes S.R. Kim (Chungju National University, Korea, South Korea) RF plasma enhanced chemical deposition were applied to get SiO_x on polymeric substrates with various processing conditions, such as input power, monomer/oxygen feed ratio, modulated frequency and duty cycle. Organosilicones were used as feed monomer and oxygen was used as mixing gas. Input power was varied from 50 to 300 Watt. Chemical bonding information of deposited film by FTIR-ATR shows that the absortion peak of Si-O near 1032 cm^-1 moved toward 1066 cm^-1 and Si-CH₃ peak was decreased as oxygen amount was increased. I-V curves from Lanmuir Probe was used to measure electron temperature, electron density and plasma potential. Optical Emission Spectroscopy (OES) was used to measure the plasma species and intensity of species and to obtain plasma pathway. Plasma density was of 4 x 10⁸ [cm^-3] and electron temperature of 2.8 eV and maximum deposition rate was 640 Å/min at 150 Watt. Plasma parameters, such as electron temperature, electron density, plasma potential, and plasma species were correlated to the properties of deposited films.
2:20 PM		PS2-TuA-4 Electron Impact Reactions of DVS-BCB Monomer in He Plasma for Low-k Film Deposition K. KINOSHITA, M. SHIMOYAMA, A. NAKANO, J. KAWAHARA, N. KUNIMI, T. KIKKAWA (Mirai, Japan) DVS-BCB (divinylsiloxane-bis-benzocyclobutene) is known as a precursor of a spin-on low-k material with the dielectric constant of 2.7¹. Plasma polymerization process has also been developed to deposit DVS-BCB film from the monomer². Higher thermal stability (400 °C) and very thin (<20 nm) conformal film formation have been achieved by this vapor phase deposition technique. However, reactions of DVS-BCB in the plasma remain unclear. Recently, in-situ quadrupole mass spectrometry (QMS) study of this plasma showed that there were two types of unique reactions which had never been observed in the thermal polymerization process³. These were hydrogen attachment to and methyl group desorption from the DVS-BCB, resulting in different polymer structures from those of thermally polymerized films. This paper reports molecular orbital calculations for these reactions. Total MO energy calculated by the density functional technique with the 6-31G* basis set clearly showed that both the neutral DVS-BCB and ionized DVS-BCB were stabilized by the hydrogen attachment. The attachment energies are about 2 eV and 4 eV for neutral and ionized species, respectively. The methyl group desorption was also analyzed by changing the Si-CH₃ distance. When the Si-CH₃ distance d was stretched from the stable position (d=1.88 Å), there appeared two types of saddle point structures at d=2.38 - 3.88 Å before final dissociation. The total MO energy at this final condition showed a lower value than the transition state. This means, methyl group desorption reaction needs activation to proceeds. The MO calculations well explain the QMS observations. This work was supported by NEDO. ¹ T. M. Stokich, Jr., et al.: Mat. Res. Soc. Symp. Proc., 227, (1991) 103. ² J. Kawahara, et al., Technical Dig. IEDM 2003, 6-2-1, (2003) 143. ³ K. Kinoshita, et al., Proc. Dry Process Symp. 2003, 6-6, (2003) 157.
2:40 PM		PS2-TuA-5 Molecular Dynamics Study of Interactions Between Organic Polymer Surfaces and Hydrogen/Nitrogen Radical Beams H.Y. Yamada (Kyoto University, Japan); S.H. Hamaguchi (Osaka University, Japan) We have studied atomistic scale interactions between organic polymer surfaces and beams obtained from hydrogen/nitrogen plasmas, using classical molecular dynamics (MD) simulations. In typical etching processes of low-dielectric-constant (i.e. low-k) organic polymer layers for semiconductor interconnect applications, hydrogen and nitrogen based plasmas are often employed as their plasma etching sources. To carry out MD calculations of such systems, we have developed a classical interatomic potential model for systems consisting of H, C and N atoms, using interatomic potential data obtained from quantum mechanical calculations. One of the key factors that allow us to appropriately handle various covalent bonds formed among C and N atoms in numerical simulations is an algorithm that we have developed to determine the order of each covalent bond automatically based on local atomic arrangement. In this presentation, we shall discuss details of the newly developed potential model as well as sample MD simulations. As to MD simulations, we have focused on plasma etching of low-k organic polymer surfaces and simulated interactions of such polymer surfaces with energetic radical/cluster beams containing N and/or H atoms. The results obtained from these MD simulations are also compared with recent experimental observations as well as previously obtained MD simulation results for hydrocarbon beam injections into organic polymer surfaces [H. Yamada and S. Hamaguchi, J. Appl. Phys. (2004), submitted.]. We have observed that, as in the case of carbon beam injection simulations, injected N atoms strongly react with the polymer substrate and form bonding networks of C and N atoms on the substrate surface. On the other hand, at similar low injection energies, N2 molecules are less reactive due to their strong covalent bonds. At higher injection energies, however, we have observed that more N molecules can break into N atoms and form bonding networks on the polymer substrate.
3:00 PM		PS2-TuA-6 Computational Investigation of the Role of Polyatomic Ions in Plasma Polymer Deposition I. Jang, W.-D. Hsu, S.B. Sinnott (University of Florida) Fluorocarbon plasmas are widely used to chemically modify surfaces and deposit thin films. It is well-accepted that polyatomic ions and neutrals within low-energy plasmas have a significant effect on the surface chemistry induced by the plasma. For this reason, the deposition of mass selected fluorocarbon ions are useful for isolating the effects specific to polyatomic ions. In this study, the detailed chemical modifications that result from the deposition of beams of polyatomic fluorocarbon ions (C₃F₅⁺ and CF₃⁺) on polystyrene surfaces at experimental fluxes are identified using classical molecular dynamics simulations with many-body empirical potentials. The ions are deposited at incident energies of 50 or 100 eV/ion. For CF₃⁺ deposition, F atoms play the most important role in fluorinating the polystyrene surface, as the majority of F atoms are covalently attached to the polymer chains through replacement of native H atoms or capping the ends of broken chains. CF₂ fragments are also an important long-lived species. In contrast, F atoms are a minor bi-product and CF₂ fragments are the most dominant species for C₃F₅⁺ deposition on polystyrene. Thus the simulations explain the experimental finding that C₃F₅⁺ is more efficient at producing fluorocarbon thin films. In particular, many larger fragments produced by C₃F₅⁺ ion deposition contain more than one C atom, may have more than one active site, and readily react to grow polymer-like structures. In contrast, F atoms, the most dominant fragment in CF₃⁺ deposition, effectively deactivate potential film nucleation sites when they fluorinate the polymer surface. We compare these findings to results for the deposition of comparable hydrocarbon ions (C₃H₅⁺ and CH₃⁺). This work is supported by the National Science Foundation (CHE-0200838).
3:20 PM		PS2-TuA-7 Study of the Selected Effect of Molecules Generated in N₂ and O₂ Plasma for the Surface Modification of HDPE, PVDF and PTFE. N. Vandencasteele (Universite Libre de Bruxelles, Belgium); A. Wagner (Ames National Laboratory); H. Fairbrother (Johns Hopkins University); F. Reniers (Universite Libre de Bruxelles, Belgium) Although plasma treatments of polymers are widely used in today's industry, the surface modification mechanisms remain mostly unknown due to their complexity. The wide variety of the species generated in a plasma, combined with the specificity of a usual polymer surface make such reactions hard to understand. We have undertaken a global systematic study of the individual and synergetic effects of the species generated in a plasma on the surface modification of a series of model polymers: HDPE, PVDF, PTFE, as they illustrate the transition between C-H and C-F bonds. A modified RF plasma allowing to filter out some of the species was used¹, as well as an in situ ion gun and a radical source. N₂ and O₂ plasmas were used, and the selected effect of N₂⁺/N⁺, O₂⁺/O⁺ and O on the polymers was studied. Samples were characterized using water contact angle (WCA), AFM and XPS. The spatial distribution of the plasma species was analysed by OES. In our configuration, most of the particles reaching the polymer are neutrals and electrons. Results show that the nature and amount of the functionalities grafted, the roughness and the WCA strongly depend on the starting polymer, and on the nature of the incident beam. For instance, the functions grafted on HDPE using the plasma neutrals are mostly C=N groups, whereas nitrogen ion treatment leads to a majority of amines. The N₂ plasma treatment of PTFE induces defluorination of the polymer, with rapid increase of the nitrogen content. New chemical functions, and CF₃ groups are evidenced. The decrease of the WCA is directly correlated to the surface amount of nitrogen. On the contrary, exposure of PTFE to N ions leads to no significant grafting. Oxygen treatment of HDPE and PVDF lead to an increase of surface energy, but on PTFE a super-hydrophobic surface is created. ¹ A. Wagner, D.H. Fairbrother, F. Reniers, plasma and polymers, 8 (2003) 119.
3:40 PM		PS2-TuA-8 Deposition of Plasma Polymer Coatings on Stainless Steel A. Mistry, F.R. Jones (University of Sheffield, UK); D.B. Hammond, T.H. English (Corus Plc. Rotherham, UK) Plasma polymerisation is being investigated to produce coatings imparting a specific function on the surface of stainless steels, such as improved cleanability. One approach to this goal is through deposition of inorganic oxide layers that enhance the hydrophilicity of the surface, improve water run-off properties and enhance the surface's dirt shedding properties. Preliminary work with hexamethyldisiloxane (HMDSO) and titanium containing organo-metallic monomers, e.g. titanium (IV) isopropoxide, as the precursor with/without O₂ as a co-reactant for plasma polymerisation onto stainless steel has shown the potential of this approach. The results from XPS indicate that as the concentration of O₂ in the plasma increases, the species deposited on the surface incorporate less carbon. There is also a decrease in the measured contact angle, i.e. the surface becomes more hydrophilic. This change in surface chemistry to a more oxide-like state is shown by an increase in O:Metal ratio. Thus, the surface chemistry can change from organic polymeric-like at high monomer concentration and low power, to inorganic oxide-like at low monomer concentration and high power. The cleaning response of the coated surfaces has been investigated, and copolymerisation of these two monomers to impart other synergistic effects is being carried out.