ICMCTF2001 Session D1-1: Synthesis, Characterization and Applications of Boron Nitride, Carbon Nitride and Fullerene Structures

Monday, April 30, 2001 1:30 PM in Room Royal Palm 4-6

Monday Afternoon

Time Period MoA Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF2001 Schedule

Start Invited? Item
1:30 PM D1-1-1 Ultra-Thin Carbon Films for Hard Disk Drive Applications
C.S. Bhatia (SSD/IBM); W. Fong, D.B. Bogy (Computer Mechanics Laboratory / University of California at Berkeley)
In hard disk drive applications, diamond-like carbon (DLC) films are commonly used as protective overcoats on media and sliders to protect these components from environmental and physical damage. DLC films optimized for this application invariably have good wear "toughness", which may involve high hardness and elastic modulus, coupled with excellent corrosion protection and complementary chemical interaction with the lubricant layer. Typically, these films are sputter-deposited with nitrogen or hydrogen incorporation, but more recently, mono-energetic deposition techniques such as cathodic-arc and ion-beam deposition have been of interest to this community. The driving force for this exploration has been the recent compounded annual growth rates (CAGR) of 100% in areal densities of disk drives - hence, much thinner overcoats are needed to provide a reduction in magnetic spacing between the media and read/write element in the slider. In this forum, we review the DLC films deposited with various techniques and share the latest data on their performance in tribological tests.
2:10 PM D1-1-3 Metal-Containing Amorphous Carbon Films for Hydrophobic Applications
J.S. Chen, S.P. Lau (Nanyang Technological University, Singapore); B.K. Tay (Nanyang Technological University, Singapore,); G.Y. Chen (Nanyang Technological University, Singapore); Z Sun (Nanyang Technological University); J.W. Chai (Institute of Materials Research and Engineering (IMRE))
Metal-containing amorphous carbon (a-C:Me) films including a-C:Fe, a-C:Al and a-C:Ni films were deposited using metal-carbon composite target by filtered cathodic vacuum arc (FCVA) technique. The wettability of the films was examined by the contact angle measurement. Three kinds of liquid with different polarity were used to study the changes in the surface energy including the dispersive and polar component. Micro-Raman spectroscopy and x-ray induced photoelectron spectroscopy were used to characterize the structural and surface properties of the films. Atomic force microscopy (AFM) was used to characterize the morphology and roughness of the films. It is found that the contact angle with the water increases significantly after incorporating the metal into a-C films and the corresponding surface energy become lower. Especially for a-C:Al film, the contact angle with water reaches as high as 105o. Thus a-C:Me films are suitable for hydrophobic applications. The structure and surface analysis show that the surface energy is independent on sp3 or sp2 content of the film. However, the surface adsorption may be responsible for the decrease of the surface energy. In addition, the roughness of the films has no obvious effect on the surface energy.
2:30 PM D1-1-4 On the Preparation of Silicon Carbonitride Compounds
M. Bruns, H. Lutz (Forschungszentrum Karlsruhe GmbH, Germany); E. Theodossiu, H. Baumann (Universitaet Frankfurt, Germany)

Carbonitride as well as Silicon Carbonitride thin films have been the subject of great interest in recent years due to the expected improvement of surface properties for a lot of applications. Various precursor based techniques have been employed to synthezise the pure materials. However, most of these efforts result in amorphous films or tiny crystals embedded in amorphous matrices of deficient nitrogen content and considerable hydrogen and oxygen content, respectively. Very promising approaches to Si-C-N synthesis are R.F. magnetron sputtering and ion implantation providing tailored stoichiometries at high purity. Silicon carbonitrides were reactively sputtered using 15N enriched N2/Ar sputter gas and co-sputter targets with different Si/C areas resulting in defined and reproducible Si/C ratios at constant nitrogen concentrations. Alternatively, surface modification by sequential high fluence implantation of C and N ions into silicon allows for tuning the atomic fraction of all elements over a wide range. Both techniques enable us to synthezise ternary systems of more than 52 at.% nitrogen content, which are stable up to 1000 °C.

The chemical composition of the Si-C-N films was characterized by means of X-ray photoelectron spectroscopy (XPS). In case of the buried implanted layers chemical binding states were attainable after sputter etching using 300 eV Ar ions of a projected range minimized to a negligible part of the XPS information depth. In addition, Auger electron spectroscopy (AES), FTIR spectroscopy, and Raman spectroscopy were used to achieve a comprehensive characterization. For quantification XPS and AES data were calibrated with absolute concentration values from non-Rutherford backscattering spectrometry. Furthermore, both preparation techniques have the advantage that 15N and 13C isotopes can be introduced into the layers enabling non-destructive nuclear reaction analysis for depth profiling.

2:50 PM D1-1-5 Influence of Chemical Sputtering on the Bonding Structure of Carbon Nitride Films
P. Hammer, F. Alvarez (Universidade Estadual de Campinas, Brazil)
The achievement of high N concentration is one necessary condition for the synthesis of crystalline CN compounds. Other demands are the formation of the correct bonding coordination of carbon (sp3) and nitrogen (sp2) and the ability to produce adequate amount of compact continuous crystalline material to allow definitive mechanical testing. For a number of conventional deposition methods like ion beam assisted deposition (IBAD), reactive sputtering etc., the chemical sputtering effect, involving the formation of volatile CN species and N2 during the film growth, is responsible for the limitation of the N content below 40 at.%. For low energy nitrogen irradiation (< 100 eV) using IBAD a critical arrival rate N2+/C ≈ 1.8 was established at which no deposit is formed. Below this limit infrared a X-ray photoelectron spectroscopies show that mixed-phase CNx films are formed. Careful spectral analysis reveals the coexistence of a aromatic and a nonaromatic phase each containing a variety of local bonding environments. The fraction and the particular microstructure of the aromatic phase, which has a strong influence on film properties like hardness, can be adjusted as a function of N content, deposition temperature and nitrogen ion current. Experiments performed by evaporation of azaadenine powder (8-aza-6-aminopurine, C4N6H4) and simultaneous irradiation by low energy nitrogen ions show that CN:H films can be grown with a C/N ratio between 1 and 1.4. Although an amorphous polymer-like phase is obtained an important aspect of this method is that chemical sputtering can be avoided by thermal condensation of a CN precursor resulting in a significant lager nitrogen contents in the deposit.
3:30 PM D1-1-7 Bonding Structure in Amorphous Carbon Nitride : NMR, EELS, XANES and XPS Study
C. Donnet, J.C. Sanchez-Lopez (Ecole Centrale de Lyon, France); F Lefebvre (LCOMS, CPE Lyon, France); C Fernandez-Ramos, A Fernandez (ICM Sevilla, Spain)
Since the prediction about the extraordinary mechanical properties of crystalline beta-C3N4 material, many authors have attempted its synthesis. However, in most cases, the obtained materials result amorphous phases with a very complex bonding structure. Many problems are associated to their characterization particularly due to the absence of a reference compound, the lack of long-range order and poor knowledge about their bonding structure. In this article we present 1H, 13C and 15N nuclear magnetic resonance (NMR) measurements for the determination of type of bonding in amorphous CNx films. NMR measurements does not require long range order and should be able to clearly identify the signals from the sp2 and sp3-bonded phases. The discussion of the spectra obtained by other characterization techniques (IR, XPS, EELS, XANES) on the same sample using the information acquired by NMR will allow to conclude a model structure for the amorphous CNx phase and to revise the classical interpretation found in the literature.
3:50 PM D1-1-8 Growth, Structure, and Deformation Mechanisms of Fullerene-Like CNx Thin Films Synthesized by DC Magnetron Sputtering
J. Neidhardt, Zs. Czigány, I. Brunell, L. Hultman (Linköping University, Sweden)
Fullerene-like CNx films were deposited by dual unbalanced magnetron sputtering of a pyrolythic graphite target in a reactive gas atmosphere. A coupled magnetic field configuration was used in order to give homogenous conditions at the substrate surface. The substrate material used were freshly cleaved NaCl wafers for 50-nm-thick films and polished silicon wafers (001) for 500-nm-thick films. The substrate temperature, ion energy, Ar to N2 partial pressure, total pressure and ion-to-neutral arrival rate ratio were varied in order to investigate their effect upon the microstructure, composition, and growth mechanisms. After deposition on NaCl, the films were immediately floated off and examined by high-resolution TEM. Nanoindentation and insitu AFM performed with a Hysitron Triboindenter on the 500nm thick films in combination with SEM fracture cross sections gave insights as for the mechanical response and deformation mechanisms. The tribological behavior of the films on an atomic scale was studied with the Tribometer as well. The composition and bonding structure was investigated by XPS. The important role of N is to promote the curving of the graphene planes by substituting for C and thus lowering the energy barrier to form pentagons. This curving induces cross-linking with sp3 C between the planes so as to make for fullerene-like solid films. Our results for CNx films composed of nano-onions point to slip or nano-fracture between the onion-like features as a mechanism of deformation, but that the individual graphene planes remain intact after elastic deformation, much like the behavior of a suspended spring.
4:10 PM D1-1-9 On the Structure and Mechanical Properties of Ar Assisted Carbon Nitride Films
L. Valentini, J.M. Kenny (University of Perugia, Italy); H. Haefke (CSEM, Swiss Center for Electronic and Microtechnology, Switzerland); Y. Gerbig (CSEM, Swiss Centre for Electronic and Microtechnology, Switzerland); L. Lozzi, S. Santucci (University of l'Aquila, Italy)
Nitrogen doped amorphous carbon compounds (a-C:H:N) have attracted great attention in recent years, mainly due their interesting properties such as high hardness, low friction coefficients, chemical inertness. These materials can be considered as a metastable phase of carbon; particularly nitrogen doped hard amorphous carbon films are mainly characterized by bond angle disorder and threefold/fourfold coordination atom mixture. It is generally accepted that the intense bombardment of energetic ions during the deposition controls the formation of either sp3 or sp2 bonds. However, only few works investigated the influence of Ar+ plasma assistance bombardment on the properties of a-C:H:N films. To this aim in this work two series of specimen are studied: films deposited with plasma decomposition of CH4/N2 and CH4/N2/Ar mixtures. X-ray photoelectron spectroscopy (XPS) are used for probing the photoelectron core level of the films. Raman spectra and film density are also determined. Then neutron reflectivity technique opportunely combined with X-ray reflectivity is used to give information on the samples structure. The mechanical and tribological properties are investigated by depth sensing indentation, scratch testing and pin on disk configuration. The observed differences suggest that, as argon is introduced in the gas mixture, a progressive graphitization of the films is observed and the mass density decreases. The behavior of the adhesive strength, as a function of nitrogen content, achieved with Ar addition, is of the same order as those reported for CNx. However, at a fixed nitrogen partial pressure, the films obtained without Ar dilution showed a better adhesion and a denser sp3 network. The relationship between mixture composition and measured film properties is rationalized based on previously published models.
4:30 PM D1-1-10 Thermal Stability of CNx Thin Films
N. Hellgren, R. Twesten, J.E. Greene, I. Petrov (University of Illinois); E. Broitman, L. Hultman (Linköping University, Sweden); J.-E. Sundgren (Chalmers Universtiy of Technology, Sweden)
The thermal stability of carbon nitride films, deposited by reactive d.c. magnetron sputtering in N2 discharge, has been studied for post-deposition annealing temperatures TA up to 1000°C. Films were grown at temperatures of 100°C (amorphous structure), and 350 and 550°C (fullerene-like structure) and were analyzed with respect to thickness, composition, microstructure, bonding structure and mechanical properties as a function of TA and annealing time. All properties investigated were found to be stable for annealing up to 300°C for long times (> 48 h). For higher TA, nitrogen is lost from the material and graphitization takes place. At TA = 500°C the graphitization process takes up to 48h while at TA = 900°C it takes less than 2 min. By comparing the evolution of XPS, EELS and Raman spectra during annealing, also important information about the peak assignment can be gained, and the presence of pyridine-like and graphite-like N can be distinguished. For TA > 800°C, preferentially pyridine-like N and nitriles are lost from the films, mainly in the form of molecular N2 and C2N2, while graphite-like N is preserved the longest in the structure. Films deposited at the higher temperature exhibit the best thermal stability, but annealing at temperatures a few hundred °C above the deposition temperature for long times is always detrimental for the mechanical properties of the films.
4:50 PM D1-1-11 On the Conditions for cBN-Growth by Magnetron Sputter Deposition
H. Oechsner, J. Ye (University of Kaiserslautern, Germany)

The conditions for the growth of sp3-coordinated (cubic) boron nitride by r.f. magnetron sputter deposition from hBN - targets have been studied in dependence of the negative r.f. self - biasing voltage at the Si (100) substrates and the substrate temperature. When tracing the growth rate under constant deposition parameters (substrate bias and temperature 200 V and 600°C, respectively,) quite surprisingly a negative growth rate was observed which started at film thicknesses of about 100 nm and caused a thickness shrinking by about 30%. Subsequently the films continued to grow with an again positive growth rate being slightly different from its initial value. The shrinking effect is connected with an onset of the sp3-specific IR-absorbance and the development of a transiently increased surface roughness of the films. Hence, we conclude that the cBN-nucleation starts as an sp 2 - sp 3 - phase transition within the highly ordered"turbostratic" BN-base layer which is formed during the initial stage of the deposition process and becomes clearly visible in our own high resolution TEM images of the respective films.

As soon as the nucleation into cBN has been completed across the entire film surface, the cBN-growth was found to occur at substrate bias voltages down to about 60 V for nitrogen as working gas and down to substrate temperatures around room temperature, even for Ar as working gas. Thus, we propose a two- step deposition process under which at first the required specificly ordered hBN-base layer is formed at elevated bias voltage and temperature. Both quantities can then be reduced to the lower values for which the cBN growth continues after completion of the initial nucleation process.

Time Period MoA Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF2001 Schedule