ICMCTF2005 Session D1-1: Carbon Nitride, Boron Nitride and Group-III (Al, Ga, In) Nitride Materials

Wednesday, May 4, 2005 8:30 AM in Room Royal Palm 1-3

Wednesday Morning

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8:30 AM D1-1-1 Ion Bombardment for Stress Release in Cubic Boron Nitride Thin Films
W. Möller, B. Abendroth (Forschungszentrum Rossendorf, Germany); R. Gago (Forschungszentrum Rossendorf, Germany and Universidad Autonoma de Madrid, Spain); A. Kolitsch (Forschungszentrum Rossendorf, Germany)

Low-temperature growth of cubic boron nitride requires ion bombardment for nucleation and growth of the cubic phase. However, simultaneously the ion bombardment creates extremely high compressive stress, which is a major obstacle for the deposition of sufficiently thick films, which might, e.g., be applied for tribological purposes.

The paper will demonstrate that, on the other hand, keV ion bombardment during growth may be employed to reduce the internal stress significantly, for the processes of both ion-beam assisted deposition and magnetron sputtering. In the latter case, pulsed keV substrate bias is applied at a duty cycle in the order of 1%. In-situ diagnostics using cantilever stress measurements and spectroscopic ellipsometry are required for the correct timing of the keV bias, as the h-BN/c-BN interface is unstable against keV bombardment. The stress release scales with the stationary damage introduced during film growth. Below a certain critical damage, the cubic phase is not significantly affected. Possible mechanisms of the stress release will be discussed in connection with XRD, TEM and XANES results.

Film thicknesses close to one micrometer have been achieved, still being limited by the presence of interface stresses. An outlook will be given on corresponding possibilities of interface engineering.

9:10 AM D1-1-3 Microstructure Evolution of Turbostratic Boron Nitride Thin Film Deposited by Sputtering with Ion Bombardment Energy
J.-H. Jeong, J.-K. Park, Y.-J. Baik (Korea Institute of Science and Technology, South Korea)
During ion bombardment, cubic boron nitride (cBN) is always preceded by amorphous BN (aBN) and then aligned turbostratic BN (tBN), except two reports using high temperature process on diamond thin film. The ion bombardment and resulting compressive stress have been so far considered as basic requirements for the cubic boron nitride (cBN) formation, but its exact mechanism is still controversial. In this study, instead of the stress-induced-formation perspective, a threshold energy-transfer concept for changing surface bonding nature was introduced to describe the evolution of tBN microstructure with thickness. Along with a curled structure of tBN which was recently found, its microstructural evolution plays a key role in a nucleation of cBN. In the bias range of -30 ~ -60 V, the aligned tBN is changed into a curled structure after a (bias-dependent) threshold thickness, which is possibly due to stress-assisted surface interaction, and at a higher bias of -70 ~ -100 V cBN starts to nucleate over the curled surface, with its bond changed into sp3. Even at higher bias, the cBN forms over the aligned tBN without a curling transition. This energy-wise evolution shows that there exists a threshold energy level for each event and is mostly related to how the tBN structure responds to the ion bombardment. That is, alignment and curling of tBN moderate the energy amount transferred into the BN surface, thereby promoting or hindering cBN formation. Here, the effect of pressure and bias on the tBN microstructure and cBN formation was investigated and discussed in terms of momentum transfer into surface atoms. For verifying the argument, two sets of two-step experiments were performed for sequential bias increase and switching pressure, all of which showed that high compressive stress is not a requisite of cBN formation. The results suggested a possibility of facilitating cBN formation by tailoring the tBN structure.
9:30 AM D1-1-4 In Situ Deposition of B4C / BCN / c-BN Multilayered Thin Films by r.f. Magnetron Sputtering
G. Bejarano (SENA, Colombia); J.M. Caicedo, G. Zambrano, E. Baca, O. Moran, P. Prieto (Universidad del Valle, Colombia)

Thin films of cubic Boron Nitride (c-BN) and B4C /BCN/c-BN multilayers, were deposited "in situ" by r.f. ( 13.56 MHz) multitarget magnetron sputtering from high purity (99.99 %) h-BN and (99.5%) B4C targets, respectively. Films were grown onto silicon substrates with (100) and (111) orientations heated to 300-900 °C in an Ar (90%) / N2 (10%) gas mixture. The r.f power density was about 24 W/cm2. To obtain the highest fraction of the c-BN phase, an r. f. substrate bias voltage between 100 and 300 V was applied during the initial nucleation process and a voltage between 50 to 100 V during film growth. Other films of B4C and BCN were deposited and analyzed individually. In order to improve the adhesion of the films to the substrates, thin films of B4C/BCN/c-BN multilayers were deposited onto silicon (100) and AISI M2 steel substrates. The films were characterized by X-ray Diffraction (XRD), Fourier Transformed Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Raman Spectroscopy. The X-ray diffraction patterns evidence the presence of c-BN (111) and h-BN phases. FTIR spectroscopy measurements show peaks at 780 cm-1, 1100 cm-1 and 1400 cm-1, corresponding to the "out-of-plane" h-BN vibration mode, c-BN TO mode and the "in plane" vibration mode of the h-BN, respectively. Under confirmed assumption that the h-BN "in plane" peak near 1400 cm-1has the same absorption coefficient as that of the c-BN TO-peak near 1100 cm-1, the cubic fraction phase in the films can be derived using the absorption strength obtained by a Lorentz fitting of both peaks. BN films, deposited "in situ" at 300 °C, at a pressure of 4.0 Pa and nucleation RF bias of 250 V, applied for 35 minutes, presented the highest c-BN fraction, namely 85%.

This work was supported by COLCIENCIAS, Colombia under the 1106-05-12406 research project (contract 395-2002).

9:50 AM D1-1-5 Boron Carbide and Boron Carbonitride Thin Films As Protective Coatings in Ultra-High Density Hard Disk Drives
Y.F. Chen, Y.W. Chung, S.Y. Li (Northwestern University)
Boron carbide (B4C) and boron carbon nitride (BxCyNz) thin films were synthesized by pulsed DC magnetron sputtering. Effects of target power, target pulse frequency, substrate bias and pulse frequency on surface roughness were studied by AFM over sampling areas of 20 micron*20 micron. For B4C, the combination of target power of 75 W/ 50 kHz and substrate bias of -100 V/ 2 kHz results in smallest surface roughness. Compressive stress in these films is around 2.5 GPa. These B4C films have hardness of 30 GPa and reduced modulus of 250 GPa. Nitrogen incorporation into B4C films, which gives BxCyNz thin film, has a beneficial effect. When deposited under similar conditions with substrate bias pulsed at ?"100V/50 kHz, the root-mean-square surface roughness decreases to 0.19 nm, compared with 0.28 nm for B4C. The hardness of BxCyNz is 20 GPa, and reduced modulus is 210 GPa. Auger electron spectroscopy was used to characterize the film composition. High-resolution cross-sectioned TEM images and diffraction show that both films are amorphous and that BxCyNz film appears to be more uniform than B4C. Corrosion studies indicate that BxCyNz is a better protective coating for hard disk substrates than B4C and CNx films. This is attributed mainly to the smoother morphology of BxCyNz films.
10:10 AM D1-1-6 The Deposition and Characteristics evaluation of BCN Films by Cathodic Arc Evaporation
P.C. Tsai (National Huwei University of Science and Technology, Taiwan); K.H. Chen (Academic Sinica, Taiwan)
This abstract is a summary of the deposition of Boron carbon nitride (BCN) thin films by using cathodic arc plasma deposition (CAPD) technique. The depositions were conducted with B, C containing target in an Ar/N2 mixture. The portion of N2 in the gas was varied with the substrate at different floating bias levels. The characteristics of the films were investigated using a Raman spectroscopy, an atomic force microscope (AFM) and a nanoindentation tester. The microstructures of the films were evaluated using field emission scanning electron microscopy (FEGSEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffractometry (XRD). X-ray photoelectron spectroscopy (XPS) and Fourier-transformed infrared spectroscopy were used to analyze the bonding structure of the films. In this study, a workable B, C containing target were developed. The results showed that the BCN films were synthesized successfully and adhered well on the silicon substrate. The FEGSEM and HRTEM showed that the films reveal an amorphous cauliflower-like columnar structure. The Raman spectra showed that the wavenumber ranging from 900 to 1800cm-1 consists of D and G bands, similar to that of cathodic arc plasma deposited DLC. The nanohardness of the films raging 1-3 Gpa, Er value raging 30-108 Gpa. The surface roughness of the films are high, RMS value are about 25-60 nm. The effects of processing parameters on the deposition rate, film morphology and the bonding structure will also be evaluated.
10:30 AM D1-1-7 Boron Based and cBN Combination Coatings - Characterization and Application Tests
M. Keunecke, K. Bewilogua (Fraunhofer IST, Germany); E. Wiemann (Institute for Machine Tools and Factory Management, Germany); K. Weigel, R. Wittorf, H. Thomsen (Fraunhofer IST, Germany)
Wear protection coatings are well established in many applications of industrial production. Especially requirements to tool coatings increase. In many cases progress could be achieved with combination coatings. The broad range of mechanical properties of coatings in the B-C-N and Ti-B-N ternary systems, from very soft, e.g. hexagonal boron nitride, to very hard, e.g. titanium diboride or especially the superhard cubic boron nitride (cBN) is very desirable as a high potential tool coating. Combination coatings were prepared with PVD techniques with different materials and phases in one coating or in a sequence of different layers. Especially the second method leads to the possibility to deposit 3 µm m thick coating systems with a 0.5 to 1 µm m thick cBN layer onto cutting inserts. Further combination coatings will be introduced, with different application areas in production engineering. The coatings were characterized with respect to hardness, friction coefficient and abrasive wear rate. The correlation between properties and composition was revealed. Results of application tests under production near conditions will be reported. Especially turning tests with cBN layer system coated cemented carbides cutting inserts will be discussed.
10:50 AM D1-1-8 Reactive Magnetron Sputtering of Hard Si-B-C-N Films and Their Properties
J. Vlcek, S. Potocky, J. Houska, P. Zeman, Z. Soukup (University of West Bohemia, Czech Republic); V. Perina, J. Zemek (Academy of Sciences, Czech Republic); L. Martinu (Ecole Polytechnique de Montreal, Canada)

Based on the results obtained for C-N [1] and Si-C-N [2] films, a systematic investigation of reactive magnetron sputtering of hard quaternary Si-B-C-N materials has been carried out. The Si-B-C-N films were deposited on p-type Si (100) substrates by dc magnetron co-sputtering using a single C-Si-B target (at a fixed 20% boron fraction in the erosion target area) in nitrogen-argon gas mixtures. Elemental compositions of the films, their bonding structure, and mechanical, tribological and optical properties, together with their oxidation resistance in air, were controlled by the Si fraction (5-75%) in the magnetron erosion target area, by the Ar fraction (0-75%) in the gas mixture, by the rf induced negative substrate bias voltage (from a floating potential to -500V) and by the substrate temperature (180-350°C). The total pressure and the discharge current on the magnetron target were held constant at 0.5Pa and 1A, respectively. The energy and flux of ions bombarding the growing films were determined on the basis of the discharge characteristics measured for the rf discharge dominating in the deposition zone. Mass spectroscopy was used to explain differences between sputtering of carbon, boron and silicon from the composed targets in nitrogen-argon discharges. The films, typically 1-7µm thick, possessing a density around 2.4gcm-3, were found to be amorphous with a very smooth surface (Ra less than 1nm) and good adhesion to substrates at a compressive stress less than 1.2GPa. They exhibited high hardness (up to 50GPa) and elastic recovery (up to 90%), very high oxidation resistance (up to a 1350°C substrate limit) and optical transparency (at high Si and low C contents), and promising tribological properties.

[1] J. Vlcek, K. Rusnak, V. Hajek, L. Martinu, J. Appl. Phys. 86, 3646 (1999).

[2] J. Vlcek, M. Kormunda, J. Cizek, Z. Soukup, V. Perina, J. Zemek, Diamond Relat. Mater. 12, 1287 (2003).

11:10 AM D1-1-9 Synthesis and Properties of CNx Films Deposited by Magnetron Sputtering Amplified by RF Inductive Plasma
P.-Y. Tessier, B. Angleraud (University Nantes, France); H.F. Hildebrand (Ecole Nationale Supérieure de Mécanique et d’Aérotechniques, France); P. Villechaise (Faculté de Médecine, France); M.P. Besland, A. Djouadi (University Nantes, France)

Carbon and carbon nitride films are prepared using a non conventional magnetron sputtering reactor. In this process, a built in radiofrequency (rf) coil generates a high inductively coupled plasma in the region between the graphite target and the substrate. This technique has been used for microelectronics applications to ionize atoms vapour coming from metal target but very few results have been presented on carbon film deposition.

The effect of the rf power injected into the magnetron source and the coil, the effect of the nitrogen composition in the Ar/N2 plasma, and the influence of the substrate bias are studied. The high density plasma generated by the coil can greatly modify the deposition kinetics of sputtered carbon films. Particularly, a very high increase of the deposition rate with the rf power injected in the coil is observed. The rf plasma can be generated independently of the plasma generated by the magnetron source. This opportunity allows developing in situ substrate cleaning procedure before deposition by controlling the rf coil power and the substrate bias. Moreover, a selective area carbon deposition can be performed by this way. Optical emission spectroscopy is used to characterize the plasma. A systematic XPS analysis and SEM morphology is carried out on films. Film evaluation for biomedical, mechanical and microtechnology applications are presented.

11:50 AM D1-1-11 Nanoindentation Response of High Performance Fullerene-Like CNx
J.F. Palacio, S.J. Bull (University of Newcastle, United Kingdom); J. Neidhardt, L. Hultman (Linköping University, Sweden)
Amorphous carbon nitride (CNx) coatings are now being used as a protective top layer for hard disks and, due to their biocompatibility, as a coating to reduce the friction between synthetic joints in the human body. The purpose of this work is to assess the mechanical properties of the latest generation of fullerene-like CNx deposited on different substrates in order to expand the number of potential applications. Samples of CNx on four different substrates have been studied using quasistatic nanoindentation in a wide range of loads, from 500 µN to 500 mN and dynamic nanoindentation for loads from 100 µN to up to 10 mN. Improved deposition techniques generate samples with extremely high values of Hardness/Young's Modulus; in some cases greater than 0.4 which is not achieved by any other material. Adhesion and fracture toughness were also studied and compared to traditional high hardness coatings, such as SiC and TiN. Interesting results were obtained for the sample of CNx on titanium. The differences in hardness and Young's modulus at low loads, where the influence of the substrate is negligible and only the coating is tested, result from the fact that Ti from the substrate has diffused into the coating in the deposition process creating a sort of C-N-Ti high hardness coating which has some advantages of both the fullerene-like and traditional hard coating systems. This paper will discuss the potential applications of this material.
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