Hardness, elastic modulus, and structure of very hard carbon films produced by cathodic-arc deposition with substrate pulse biasing

Abstract

The hardness, elastic modulus, and structure of several amorphous carbon films on silicon prepared by cathodic-arc deposition with substrate pulse biasing have been examined using nanoindentation, energy loss spectroscopy ͑EELS͒, and cross-sectional transmission electron microscopy. EELS analysis shows that the highest sp 3 contents ͑85%͒ and densities ͑3.00 g/cm 3 ͒ are achieved at incident ion energies of around 120 eV. The hardness and elastic modulus of the films with the highest sp 3 contents are at least 59 and 400 GPa, respectively. These values are conservative lower estimates due to substrate influences on the nanoindentation measurements. The films are predominantly amorphous with a ϳ20 nm surface layer which is structurally different and softer than the bulk. © 1996 American Institute of Physics. ͓S0003-6951͑96͒01105-6͔A cathodic-arc plasma source equipped with a magnetic macroparticle filter is an efficient tool for depositing highquality thin films of metals, alloys, and compounds. To date, the technique has been employed primarily in laboratory settings, but recent advances have led to large units capable of full-scale commercial production. 1 One material which has received a great deal of attention in cathodic-arc processing is amorphous carbon ͑a-C͒. In addition to being chemically inert, electrically insulating, transparent, and having a low coefficient of friction, cathodic-arc carbon is of interest because of its potential as thin coating material with very high hardness. Amorphous carbon has been deposited from a cathodic arc by various groups. [2][3][4][5][6][7][8] Hardness values ranging from 26 GPa to over 60 GPa have been measured by nanoindentation methods. The difficulties of deriving hardness values for such hard, thin films on softer substrates are well recognized. 9 Nevertheless, the high values reported suggest that a-C with very high hardness can be achieved by cathodic-arc deposition.The key to producing high hardness in amorphous carbon films appears to be in promoting high sp 3 bond content through careful control of the energy of incident ions during deposition. 6,10-14 For cathodic-arc deposition, one way to achieve this is by substrate pulse biasing. 15 Pulse biasing has an important advantage compared to dc bias in that, whereas with dc bias electrical breakdown can result with pulsed biasing the applied voltage can be arbitrarily high ͑the voltage is switched off before the high voltage plasma sheath expands to dangerous distances͒.We have investigated the properties of cathodic-arc carbon as a function of biasing conditions and have found a set of conditions which produces very hard films. Here, we report the hardness and elastic modulus of these films measured by nanoindentation methods and the structure of the films determined by transmission electron microscopy ͑TEM͒ and electron energy loss spectroscopy ͑EELS͒.The carbon films were deposited on silicon substrates using a cathodic-arc plasma source combined with a 90°bent magnetic macroparticle filter. The source and f...

Optical and mechanical properties of plasma-beam-deposited amorphous hydrogenated carbon

“…Dekempeneer et al 20 have presented a maximum value of about 14 GPa several years ago but currently they obtain hardnesses of 20 GPa for a-C:H deposited with an rf parallel-plate reactor. Robertson 4 and Pharr et al 24 report a maximum value of 17 GPa. All these hardnesses are obtained at a substrate bias of about 200 V per deposited carbon particle.…”

Engineering Properties of Superhard Films with Ion Energy and Post-Deposition Processing

“…The properties of DLC films prepared by energetic deposition strongly depend on ion energy [5,9,10,14]. Figure 2 shows the correlation between the film density and the carbon ion energy.…”

“…Typically, it has been observed that there is a correlation between the level of stresses and the sp 3 content in these films, which define their diamondlike properties [5,8,9]. Since the as-deposited DLC films with highest sp 3 content have very high levels of intrinsic stresses (as high as 10 GPa), thick films have tendency to delaminate from the substrate.…”

Ultrathin diamond-like carbon films deposited by filtered carbon vacuum arcs

“…For carbon, it is well known that films that are rich in sp 3 (diamond) bonds should be grown in a kinetic mode at low temperature (less than 200°C, preferably room temperature), with film-forming carbon atoms or ions having an energy of about 100 eV. This energy is optimized for subplantation film growth of diamond-like carbon [4][5][6][7][8][9][10]. If the energy is too low, say less than 20 eV, ions do not have the kinetic energy to penetrate the surface; if the energy is too high, thermal spikes and a general enhancement of the temperature will allow the carbon atoms of the film to move to configurations of smaller energy.…”

“…[20,21] There are large variations even within each class of materials, depending on the method and parameters of deposition. Diamond-like carbon films can be synthesized by argon sputter deposition using a graphite target [12,22] [6,16,20,21]. Research over the last years has identified filtered cathodic arc deposition as one of the promising techniques for hard carbon films thinner than 5 nm [28,29].…”