Papers

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

Monday, April 27, 1998 8:30 AM in Room Forum/Senate/Committee

Monday Morning

Start	Invited?	Item
8:30 AM		D1-1 Plenary Lecture
8:50 AM		D1-2 Plenary Lecture
9:30 AM		D1-4 Plenary Lecture
10:10 AM		D1-6 Plenary Lecture
10:30 AM		D1-7 The Dependence of c-BN Film Growth on Ion Energy Distribution in a Low Density, Arcjet-produced Plasma Flow D.H. Berns, M.A. Cappelli (Stanford University) In this presentation we describe the measurement of Ion Energy Distributions at the c-BN film growth surface in a low density arcjet-produced plasma flow. In this flow, ion bombardment of the growth surface is achieved through the application of a negative bias (with respect to the plasma potential) to the substrate. The Ion Energy Distributions are measured by means of a retarding potential probe. The probe consists of a sampling orifice, and a set of electrode/grids that are used to retard and collect the ions; all of which are housed in an independently pumped assembly that is maintained at a pressure of ~ 10 millitorr. The reduced pressure within the probe is necessary to establish a collisionless path between electrodes. The ions are sampled from the substrate at the growth surface, upon which the plasma impinges and creates a stagnation region with pressures in the range of 2-10 Torr. The mean free path in front of the substrate may be smaller than the sheath thickness (created by the DC bias); therefore, the ions may see a collisional environment as they are being accelerated towards the growth surface. It is important to understand the actual spread of ion energies that result from an applied DC bias at the substrate in order to develop a model for c-BN growth in this environment. The Ion Energy Distribution measurements lead to and support a surface growth model which will also be presented.
10:50 AM		D1-8 Evidence for the Formation of Crystalline sp³-Carbon-containing Carbon Nitride Thin Films M.L. Wu, X.W. Lin, Y.W. Chung, V.P. Dravid (Northwestern University) A comprehensive exploration of process parameters in magnetron sputtering demonstrates that crystalline carbon nitride thin films can be grown by pseudomorphic stabilization onto TiN and ZrN templates with strong (111) texture. Relatively thick superlattice films (1-3 micron) can be grown with alternating layers of carbon nitride and TiN/ZrN in a dual-cathode magnetron sputtering system using an argon/nitrogen plasma. The strong (111) texture of metal nitrides can be obtained at low pressures (<10 mTorr) and moderate substrate bias (- 200V) for effective ion bombardment of the growing film. The individual carbon nitride layers must be less than one nm thick to maintain crystallinity. Under these conditions, these CN/ZrN superlattice coatings with 1:2 thickness ratio achieve nanoindentation hardness of 50 GPa. Electron diffraction patterns from these films show extra rings that are consistent with the formation of β-C₃N₄, but do not rule out contributions from graphite. Electron energy loss spectroscopy showed unequivocal evidence that carbon in these films is in the sp³ state, in agreement with the β-C₃N₄ interpretation.
11:10 AM		D1-9 Properties of Carbon Nitride Films Deposited by Magnetron Sputtering Y. Kusano, J.E. Evetts, R.E. Somekh, I.M. Hutchings (University of Cambridge, United Kingdom) Carbon nitride films were deposited by planar balanced magnetron sputtering system under various conditions on to silicon, sodium chloride, and steel substrates. The films were analysed by Rutherford Back-scattering (RBS), electron energy loss spectroscopy (EELS), and Fourier transform infrared (FTIR) spectroscopy. Under all conditions the films were amorphous. Deposition rate increased with nitrogen content in the sputtering gas. The nitrogen content of the film also increased as the nitrogen content in the sputtering gas increased to 50 % and then approached a constant value. Absorption bands at 1250, 1550, and 2200 cm^-1 were detected in FTIR spectra, corresponding to Raman-reactive disordered sp² carbon, graphite-like sp² carbon, and nitrile or isocyanate groups, respectively. Additionally, broad absorption around 1000 - 1200 cm^-1, which may be associated with sp³ hybridised carbon, was observed in films deposited with low nitrogen content in the sputtering gas. The films deposited with more than 70 % nitrogen in the sputtering gas showed higher friction coefficient and lower wear resistance in sliding friction tests than films grown with lower gas nitrogen content, suggesting that the wear resistance of the films was associated with the structure of the films. Other deposition conditions such as chamber pressure, substrate temperature, and power were also varied systematically, and the resulting films were characterised. The results were interpreted in terms of the collision frequency of the sputtered particles with reactive gases in the system.
11:30 AM		D1-10 c-BN Formation by RF Capacitively Coupled PECVD from BCl₃ F. Rossi (European Commission, Joint Research Centre, Italy); L. Thomas (Institut des Matériaux de Perpignan, France); C. Schaffnit (European Commission, Joint Research Centre, Italy) BN thin films have been synthesised by r.f. Plasma Enhanced Chemical Vapour Deposition (PECVD) from BCl₃ / N₂ / H₂ / Ar mixtures. c-BN formation has been studied through correlations between gas phase characterisation (by Optical Emission Spectroscopy, Mass Spectrometry and electrical measurements) and thin film analysis (by Fourier Transformed Infra Red Spectrometry for structure determination). It is shown that atomic hydrogen created in the plasma discharge has a strong influence on the deposition of the BN films.The occurrence of physical and possible chemical mechanisms is studied with the help of post-treatments of as-deposited BN coatings in pure Ar, Ar/H₂ and Ar/Cl₂ plasma mixtures. It is shown that, in addition to the well known ion-induced formation of the cubic phase, a chemical etching also occurs, due to the presence of hydrogen and chlorine species, which leads to a relative increase in the cubic content of the thin film.
11:50 AM		D1-11 Microstructure, Bonding Configurations and Mechanical Properties of Magnetron Sputtered CN_x (0 ≤ x ≤ 0.5) N. Hellgren, M. Johansson, L.I. Johansson, P.-A. Glans, E. Broitman, W.T. Zheng, L.G. Hultman, J.-E. Sundgren (Linköping University, Sweden) Carbon nitride films, deposited by reactive d.c. magnetron sputtering in Ar/N₂ discharges were studied in terms of their electronic structure, microstructure and mechanical properties. CN_x films, with 0 ≤ x ≤ 0.5, were grown onto Si (001) substrates kept at substrate temperatures between ambient and 500°C. The total pressure was kept constant at 2,5 mTorr with the N₂ fraction varied from 0 to 1. The maximum N concentrations in the films were found to be 35 at %. High resolution electron microscopy showed two typical film microstructures depending on the substrate temperature. Films grown at temperatures above 200°C exhibited a turbostratic-like microstructure while films grown at lower temperatures were amorphous. Core level and valance band photoemission spectroscopy, reflection EELS and Raman spectroscopy was used to study the electronic structure of the films. It was found the amount of sp³ coordinated carbon decreases as the temperature increases above 200°C. It was also observed that the nitrogen atoms are bound to both sp² and sp³, as well as sp¹ coordinated carbon with high temperatures favoring sp² and sp¹ configurations. Incorporation of N also favors formation of curved cross-linked planes and thus formation of sp² coordinated neworks. Nanoindentation measurements showed that CN_x grown in pure N₂ discharge and at substrate temperatures > 200 °C had elastic recoveries as high as 90 % and hardness values of 30 - 40 GPa, while the pure carbon films and CN_x films deposited at lower temperatures exhibited lower hardness values and elastic recoveries of 50-60% typical for amorphous diamond like carbon films. The role of N in promoting the formation of hard and elastic three dimensional sp² coordinated networks is discussed.