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

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.

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).

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 (R_a 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).

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.