ICMCTF1998 Session D1-2: Synthesis, Characterization, and Applications of c-BN and CN Materials (2)

Monday, April 27, 1998 1:30 PM in Room Forum/Senate/Committee

Monday Afternoon

Start	Invited?	Item
1:30 PM		D1-2-1 The Relationship Between the Mechanical Properties and Chemical Structure of Amorphous Carbon Nitride Thin Films B.C. Holloway, O. Kraft, M.A. Kelly, W. Nix (Stanford University); D.K. Shuh (Lawrence Berkeley National Laboratory); S. Hagstrom, P. Pianetta (Stanford University) Currently, amorphous carbon nitride thin films are being used as wear layer materials for hard disks because of their useful mechanical and tribological properties. However, there is still a lack of understanding about the chemical structure of the films and how the chemical properties and mechanical properties are related. Carbon nitride thin films (CN_x films) were deposited using a magnetron sputter deposition system. Nanoindentation results show that the films have extremely high recovery (≥ 70 %), elastic modulus values in the range of 35 – 55 GPa, and hardness values of at least 6 GPa. Due to inherent error in the calculations of the hardness and elastic modulus, the recovery is a much more accurate and repeatable comparative measure of the mechanical properties. Parametric variations of the substrate growth temperature show that the recovery has a maximum point between 550 and 700 C, which suggests there are changes in film structure with substrate growth temperature. The chemical structure of the CN_x films was analyzed by near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS). NEXAFS shows the presence of two inter-dependent nitrogen π-bonded structures. XPS results suggest that the nitrogen in the system is predominantly in a four-bond configuration. XPS results also show that the nitrogen content of the CN_x films decreases with increasing substrate growth temperature. The chemical structure data presented is consistent with a film structure model based on graphitic sheets with nitrogen incorporated in five-member rings. The incorporation of these five-member rings causes inter-planar bonding due to a buckling of the graphitic sheets. This inter-planar bonding can be used to explain the hardness, elastic modulus, and recovery values measured by nanoindentation. Perturbation of the model by changes in the nitrogen content show that the model is consistent with measured parameteric variations.
1:50 PM		D1-2-2 Vibrational Properties of CN_x film by Raman Spectroscopy A.K.M.S. Chowdhury, D.C. Cameron, M.S.J. Hashmi (Dublin City University, Ireland) Abstract: The Raman spectrum of CN _x films deposited by Penning-type opposed target ^1,2 DC reactive sputtering has been studied to observe the effect of nitrogen concentration on the film bonding structure. Previously Kaufman et al. ³ carried out Raman studies on nitrogen-doped amorphous carbon films with low levels of nitrogen and the work presented here extends the study to nitrogen levels up to 43 at.%. Previous FTIR studies ² have shown that if nitrogen is present at levels >25 at.% the excess above this occurs in an IR invisible bonding structure. The results presented here identify a previously unseen Raman peak which occurs between the commonly found G and D bands of CN _x film. This peak becomes visible at nitrogen content of ~25 at.% and thereafter increases with nitrogen content. XPS results also show that the peak due to nitrogen-nitrogen bonding increases in a similar manner ⁴. Therefore we identify this new Raman peak as being due to nitrogen-nitrogen bonding thus confirms the FTIR findings ². At the same time as nitrogen content in the film increases an overall shifting of the bands occurs to higher wave number due to a change in sp ² domain size ⁵. After annealing the G and D bands become sharper due to graphitisation of the film and the nitrogen-nitrogen peak decreases due to the breaking of the bonds and outdiffusion of nitrogen. ¹ M. J. Murphy, D .C. Cameron, J .Monaghan, A. K. M. S. Chowdhury, M. Tyrrell , R. Walsh, M. Monclus and M. S. J. Hashmi, Int. Conf. on Thin Films and Metallurgical Coatings, San Diego, 22nd-26th April 1996 and submitted to the JVST. ² A .K. M. S. Chowdhury, D. C. Cameron, M. Monclus, M. J. Murphy, N.P. Barradas, J.Gilvarry and M.S.J. Hashmi, Thin Solid Films, 308-309 (1997), 130-134. ³ J. H .Kaufman, S. Metin and D. D. Saperstein, Physical Review B, 39 (18), 13053, 1989. ⁴ A .K.M .S .Chowdhury, D. C. Cameron and M.S.J. Hashmi, presented Asian-European International Conference on Plasma Surface Engineering, Seoul, Korea, October 5-9, 1997. ⁵ H. Seki, International Conference on Metall. Coatings and Thin Films, San Diego, 1988.
2:10 PM		D1-2-3 Preparation of CN_x-Phases Using Plasma-assisted and Hot-filament CVD A. Leonhardt, H. Grueger, D. Selbmann (Institute for Solid State and Materials Research Dresden, Germany) In the work described here, we investigated systematically the binary C-N in a wide range of deposition temperatures. The experiments have been carried out in a RF assisted CVD-apparatus. A hot filament could be positioned between the electrodes to support the generation of activated species and a negative bias could be applied to the substrate to increase their energy. The deposition temperature ranged from 200 °C without hot filament up to 900 °C using hot filament arrangements. Different carbon-precursors and Ar/H₂ gas ratios have been tested in the plasma. The results can be summarized in the following manner. At substrate temperatures up to 250 °C films are prevailing with an amorphous "polymere structure". In the temperature range between 600 - 650 °C "paracyan-like" coatings can be produced. At temperatures higher than 650 °C using hot filament technique with RF-plasma and bias enhancement the deposition rate decreased strongly. On the top of the substrates crystalline deposits are observed. X-ray analysis show, some reflexes are coinciding with those of covalent C₃N₄ phases, but a- or b-Si₃N₄-reflexes could be dedected additionally. Deposition experiments using inert substrates, for example Nickel, have been performed also, but no CN_x phases can be observed, up to date. Therefore in the presentation a discussion have been followed about the existence of superhard, covalent-bounded C₃N₄-phases.
2:30 PM		D1-2-4 Sputtering Process of Carbon Nitride Films by Using a Novel Bio-Molecular C-N Containing Target T.-R. Lu (National Chiao Tung University, ROC); D.M. Bhusari (Academia Sinica, Taiwan); L.C. Chen (National Taiwan University, Taiwan); K.H. Chen (Academia Sinica, Taiwan); T.-M. Chen (National Chiao Tung University, Taiwan); C.-T. Kuo (National Chiao Tung Unversity, Taiwan) In order to reduce the activation energy barrier for formation of carbon nitride, during ion beam sputtering, a novel bio-molecular target material with covalently bonded carbon and nitrogen atoms is successfully developed to deposit the carbon nitride crystalline films, instead of the conventional graphite target that does not contain nitrogen. This novel target material consists of high N/C ratio as well as six-membered ring structure similar to that in various hypothetical C₃N_4. XPS analysis of this films indicate the presence of C and N in the carbon nitride films, with high nitrogen to carbon ratio of 0.58. Both XPS and Raman spectroscopy confirm the chemical bonding between carbon and nitrogen. A broad diffraction peak, attributable to β-C₃N₄, is observed in XRD pattern. This novel target material is expected to be beneficial in further increasing the nitrogen content as well as degree of crystallinity in the carbon nitride films if assisted by atomic nitrogen source during deposition.
3:10 PM		D1-2-6 Structures and Properties of Disordered Boron Carbide Coatings Generated by Magnetron Sputtering T. Hu (The Dow Chemical Company); W. Cermignani, M.G. Robinson (DIAMONDBLACK Technologies, Inc.) Disordered boron carbide coatings with their high hardness, high lubricity, and low surface friction have become the choice of coatings to enhance the wear performance of many existing products. The coatings have been successfully commercialized in a larger scale and trademarked as DIAMONDBLACK^r. The understanding of the effects of the coating process parameters on the structures, the properties, and the performance of the coatings is a key step to the success of this commercialization. FTIR, RAMAN, ESCA, SIMS, SEM, TEM, and X-Ray diffraction were used to study the physical and chemical structures of the coatings. The electrical, optical and tribological properties of the coatings were measured. Performance of the coatings in several real life applications was evaluated.
3:30 PM		D1-2-7 Plasma Substrate Interaction Effects on Compositon and Chemical Structure of Reactively RF Magnetron Sputtered Carbon Nitride Films R. Kaltofen, T. Sebald, J. Schulte, G. Weise (Institute of Solid State and Materials Research, IFF, Germany) The understanding of the carbon nitride film deposition in chemically reactive plasma requires primarily information about physiochemical processes affecting film chemistry and atomic order, from which all other properties are derived. This paper deals with the influence of plasma substrate interactions on the film surface reaction kinetics during rf magnetron sputtering of graphite in N₂ and N₂/He discharges. The neutral and ionic particle fluxes on the substrate were analyzed for various sputtering conditions using energy-resolved mass spectrometry. These data were related to the chemical composition, bonding structure, density and Young's modulus of the deposited CN_x-films studied by several analytic methods. Caused by plasma-induced water desorption, the growing film surface is exposed to significant fluxes of H and H₂ favoring a noticeable nitrogen incorporation via various N-H groups. In hydrogen-free sputter plasmas the chemical kinetics between C and N was found to produce always an N content of about 15 at%, predominatly N-sp²C bonded in aromatic clusters of the amorphous sp²/sp³-hybridized carbon matrix. The ion bombardment during the film growth results in a reduced surface reaction kinetics of H and N due to an enhanced resputtering of N atoms and water contaminants, mainly, however, in changing the matrix from a more graphite-like phase to a disordered carbon structure. These effects were accompanied by increasing densities and Young's moduli of the CN_x films. The obtained results will be presented in detail.
3:50 PM		D1-2-8 Preparation and Characterization of Single-Phase c-BN Coatings I. Konyashin, J. Bill, F. Aldinger (Max Planck Institute for Metals Research, Germany) Single-phase c-BN coatings, that do not contain any interlayers of hexagonal or amorphous BN at the substrate-coating interface, have been obtained by PACVD in a hydrogen-based plasma. They are found to have a good adhesion to various substrates (Si, WC-Co, etc.) and be practically stress-free. The coatings are nano-grained with average grain size of around 50 nm and c-BN grains are well faceted. The c-BN nucleation and growth on various materials are found to be possible without any preliminary seeding of the substrate with diamond or c-BN. Results on the fine structure and composition of the c-BN coatings obtained by HRTEM, HRSEM, AES, XRD, FTIRS, etc. as well as their properties will be presented.
4:10 PM		D1-2-9 The Effect of the Substrate Bias Potentials on the Nucleation and Growth of c-BN Films by Helicon Wave Plasma Chemical Vapor Deposition K.B. Kim, S.H. Kim (Pohang University of Science and Technology, South Korea) Cubic Boron Nitride(c-BN) thin films were deposited on Si(100) substrates at 300°C by low pressure Helicon Wave Plasma Chemical Vapor Deposition(HWPCVD) with a Borazine(B₃N₃H₆) precursor. The effect of the substrate bias potentials on the synthesis of c-BN films have been extensively investigated in terms of nucleation and growth. The bias potentials for the nucleation and growth turns out to be quite different. The critical substrate bias potential for the nucleation of c-BN was found to be significantly higher than that for the growth of c-BN. It was also found that the difference of required substrate bias potentials for the nucleation and growth of c-BN is about two hundred electron volts. This lower bias for the growth of c-BN could possibly improve the adhesion and crystal quality of c-BN.
4:30 PM		D1-2-10 Surface Processes in Cubic Boron Nitride Growth; A Theoretical Study K.M.E. Larsson (University of Uppsala, Sweden) There is a large interest (both theoretically and experimentally) in thin film production of cubic boron nitride (c-BN) due to important industrial and techniccal applications. c-BN exhibits many interesting properties similar to diamond, such as extreme hardness, low dielectric constant, and high thermal conductivity. However, in contrast to diamond, it has proven to be very difficult to deposit thin films of c-BN by Chemical Vapor Deposition methods. The purpose with the present work is to investigate the influence of different type of surface terminating species on the surface processes. The purpose is also to relate different gaseous species regarding the tendency for adsorption and migration on the growing c-BN (111) surface (with B atoms as the uppermost atoms). The Schödinger equations for the models of adsorption and migration were solved using the ab initio molecular orbital (MO) method at the MP2 level of theory. The uppermost atoms in the model, as well as the gaseous species, were described by the more flexible basis set 6-31G**, while the remaining atoms were all represented by the much smaller basis set STO-3G.The atoms described by the former basis set were also allowed to be fully relaxed. The underlayer atoms were kept fixed in order to hold the characteristics of the crystals. Fluorine, F, was found to more efficiently stabilize the c-BN (111) surface.However, the H species was also capable of stabilizing this type of surface. Moreover, the calculated energy of abstraction was found to be appreciable smaller when abstracting a surface-bonded H species with gaseous H (or F) species. Hence, the H species was found to both stabilize the surface well, and to be able to abstract easily, creating surface vacancies to which other growth species may adsorb and further react. The calculated order of energies for the adsorption of the species NH₂, BNH, and NBH to a radical B atom on the c-BN (111) surface was; NBH > BNH > NH₂. Moreover, the barrier of the migration of the more strongly adsorbed NBH and BNH species, respectively, were also the largest obtained ones in the present investigation. The more weakly surface-bonded NH₂ species did also have a large capability for surface migration (low energy barrier). The present investigation will then support a growth process based on an excess of hydrogen in the system (H-terminated surfaces), and with the NH₂ species as a possible growth species if surface migration is a limiting step during CVD growth of c-BN. If not, the NBH species could be regarded as a possible growth species on the uppermost B atoms on the c-BN (111) surface.
4:50 PM		D1-2-11 A Novel Approach to the Formation of Carbon Nitrides on Silicon by ECR-CVD S.L. Sung, C.H. Tseng, X.J. Guo, F.K. Chiang (National Tsing Hua University, Taiwan, ROC); H.C. Shih (National Tsing Hua University, Taiwan ROC) Smooth amorphous carbon nitride film has been synthesized on silicon by using the ECR-CVD system equipped with the d.c. bias in C2H2, N2 and Ar mixtures at 2*10-3 Torr. Through the addition of excess argon together with the application of d.c. bias, the ratio of nitrogen to carbon in the film is up to 41% which is characterized by the XPS. The FTIR spectrum shows the absorption band among 1000 cm-1 to 1600 cm-1 which proves that the nitrogen atoms have been incorporated into the amorphous network. The plasma chemistry of the system was also analyzed by the OES to investigated the active chemical species involved in the formation of carbon nitride. The result indicated that the addition of excess argon (4 times more than nitrogen) could increase the amount of the excited-state nitrogen ions which would promote the concentration of nitrogen in the amorphous carbon nitride film. This finding is likely due to the lower ionization energy of argon (15.8 eV) and its massive weight in comparison with the hydrogen gas as indispensablly being employed in the synthesis or other related materials.