Papers

ICMCTF2003 Session D1-1: Carbon Nitride, Boron Nitride and Ternary Phase Materials

Monday, April 28, 2003 10:30 AM in Room Royal Palm 1-3

Monday Morning

Start	Invited?	Item
10:30 AM		D1-1-1 Role of Ion Energy on the Growth Mechanism of Cubic Boron Nitride Films C. Ronning (Universität of Göttingen, Germany) Recent studies of several groups worldwide show that micrometer thick cubic boron nitride (c-BN) films can be grown with a variety of deposition techniques. This break-through was achieved using both chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques. In both cases, it is well accepted that ion bombardment is crucial in order to archive c-BN growth, but the understanding of the role of the ion energy on the growth mechanism is still under controversial discussion. The growth of the cubic phase occurs in a large ion energy window, from as low as 50 eV up to at least 27 keV, as shown by mass selected ion beam deposition (MSIBD). The observed low energy threshold for the growth of c-BN is lower than to the c-BN nucleation threshold and fits well with the cylindrical spike model as well as with recent literature. However, on the high-energy side, c-BN growth can be realized using 20 keV nitrogen and 27 keV boron ions. Therefore, if a transition back to sp²-bonded BN growth for high ion energies exists, as predicted by the cylindrical spike mode, such a transition must definitively lie beyond 20/27 keV. Furthermore, c-BN remains stable for ion irradiation with fluences up to about 10¹⁷ cm^-2 for nitrogen and argon ions with energies between 10 and 30 keV, as observed with TEM and FTIR. Therefore, cubic boron nitride is extreme stable upon ion impact, in contrast to recent studies in literature. However, if the c-BN/t-BN interface is irradiated, a complete transition to sp²-bonded BN already takes place at low ion fluence of 10¹⁶ cm^-2. These results will be discussed in respect to existing growth models for c-BN.
11:10 AM		D1-1-3 In Situ Measurement of Instantaneous Stress during Magnetron Sputter Deposition of cBN B. Abendroth, R. Gago, A. Kolitsch, W. Möller (Forschungszentrum Rossendorf, Germany) Dynamic in situ analysis of stress and film thickness provide fast and more physical information on growth and stress evolution in cBN layers than integrating (ex situ) methods. Especially features of the layered structure of boron nitride films, like the evolution of instantaneous stress and growth rates during deposition can be resolved by in situ methods. This work is concerned with dynamic in-situ stress measurement by means of cantilever bending during magnetron sputter deposition of cBN thin films. Laser deflection in combination with in situ ellipsometry is used to determine the instantaneous stress of the films. The results show, in agreement with results that were obtained previously from IBAD, that the tBN and cBN layers exhibit different levels of stress under constant deposition conditions. The stress increases from less than -4 GPa to very high values (-9 GPa) after the coalescence of the cBN nuclei. It is therefore possible to establish the point of cBN nucleation instantly. As has been shown for IBAD^1,2, a simultaneous medium energy ion bombardment could be a promising way of relaxing stress also in magnetron sputtering and thus offering the possibility for the deposition of thick cubic boron nitride. A modified substrate bias voltage is used to enable an ion bombardment in the energy range between 2 and 8 keV. In this way, cBN films with a stress as low as -1 GPa can be produced. ¹C. Fitz, A. Kolitsch, W. Möller, W. Fukarek, Appl. Phys. Lett. 80 (2002) 55 ² H.-G. Boyen, P. Widmayer, D. Schwertberger, N. Deyneka, P. Ziemann, Appl. Phys. Lett. 76 (2000) 709.
11:30 AM		D1-1-4 Preparation and Properties of Ion-assisted Pulsed Laser Deposited Cubic Boron Nitride Films G. Reisse, S. Weissmantel, D. Rost (University of Applied Sciences Mittweida, Germany) Cubic boron nitride films were prepared by ion-beam-assisted pulsed laser deposition (IAPLD) using a KrF excimer laser and pyrolytic h-BN targets for ablation. C-BN growth rates up to 100 nm/min were achieved at relatively low substrate temperatures of 250°C by using high laser fluences of more than 30 J/cm². The main advantage of IAPLD for the deposition of c-BN films is that at high laser fluences of 30 to 60 J/cm² the ratio of ions from the ion beam to ablated atoms and ions necessary for cubic film growth can be reduced strongly, since the ablated boron and nitrogen species themselves have high mean kinetic energies of 130 to 180 eV. The mechanical stresses in those films were investigated both ex-situ and in-situ in dependence of the deposition parameters. It will be shown that the stress of our c-BN films is governed by the mean kinetic energy of the ablated species and the ion-to-ablated-species ratio. The stresses can be lowered by annealing the films after deposition. In-situ stress measurements showed a gradual increase of the stresses during the c-BN nucleation process if the films were deposited directly on the substrate and a steep increase if the c-BN film was nucleated on top of an h-BN adhesion layer. Stress peaks during nucleation were not observed. The adherence of our c-BN films on Si and WC hard metal substrates was investigated by scratch testing in dependence on preparation conditions. Critical loads up to 50 N were achieved by using special h-BN interlayers. Depending on deposition parameters the Vickers microhardness of the c-BN films is in the range of 30 to 45 GPa, the Young`s modulus was measured to be in the range of 430 to 590 GPa, and the density is between 3.0 and 3.3 g/cm². The results of wear resistance measurements will be presented.
11:50 AM		D1-1-5 Effect of Ion Bombardment on the Evolution of Microstructure and Residual Stress of Boron Nitride Films by Sputtering with Ar Ions H.S. Kim, Y.-J. Baik (Korea Institute of Science and Technology, South Korea) We investigated the possibility of Ar incorporation in the BN films during the deposition according to its energy and its effect on the residual stress. The bombarding Ar ions can penetrate into the deposited films as interstitials, which will change the stress state of the film. We tried to investigate the relation of Ar incorporation with the residual stress generation as well as microstructure variation. BN films were deposited on (100) Si wafer by using radio-frequency (RF) unbalanced magnetron sputtering source. Hexagonal boron nitride disk (99.9% in purity) was used as a sputter target. The BN films were deposited at 400 W of target radio-frequency (13.56 MHz) electric power and with various substrate bias voltages (200 kHz high-frequency). The chamber was evacuated to a pressure less than 1.0X10^-5 Torr and then filled with argon - 10% nitrogen mixed gas up to 1.3 mTorr. During the precleaning and deposition process, a substrate holder (100 mm in diameter) was not heated additionally. The stress of the film is measured in situ during sputter deposition at various substrate bias voltages. The variation of the stress with increasing film thickness follows that of Ar concentration profile in the films along the growth direction. This result reveals that the interstitial Ar atoms induce the evolution of the compressive residual stress in the tBN film. Cross-sectional transmission electron microscopic images of the films are examined to explain the penetration behavior of Ar ions during the deposition.