Tetrahedral amorphous carbon films prepared by magnetron sputtering and dc ion plating

Abstract

Highly tetrahedral, dense amorphous carbon (ta-C) films have been deposited using rf sputtering of graphite by an unbalanced magnetron with intense dc Ar-ion plating at low temperatures (<70 °C). The ratio of the argon ion flux to neutral carbon flux Φi/Φn is about 5. The film density and compressive stress are found to pass through a maximum of 2.7 g/cm3 and 16 GPa, respectively, at an ion plating energy of about 100 eV. Experiments with higher ion flux ratios of Φi/Φn=10 show that it is possible to deposit carbon films with densities up to 3.1 g/cm3 and sp3 contents up to 87%. Deposition of ta-C in this experiment when the energetic species is Ar appears to require a minimum stress of 14 GPa to create significant sp3 bonding, which contrasts with the continuous increase in sp3 content with stress when the energetic species is C ions themselves. These results are used to discuss possible deposition mechanisms.

Stress-induced formation of high-density amorphous carbon thin films

“…The energy dependence of the microdensity for the flux ratios of 5 and 10 was published elsewhere. 18 The results show that for flux ratios of 5, 8, and 10 a maximum in the microdensity is found. For a flux ratio of three no significant densification of the carbon films can be observed as a function of the ion plating energy.…”

“…18 In our experiment, the neutral sputtered carbon ata͒ Present address: SAP AG Postfach 1461, D-69185 Walldorf, Germany; author to whom all correspondence should be addressed.…”

“…18 In our experiment, the neutral sputtered carbon at- oms are deposited on crystalline silicon substrates and are hit by argon ions originating from the substrate side of the plasma. As a result of the Ar ϩ collisions, the carbon atoms at the surface of the film are forced into the film.…”

“…Nevertheless, at such impact energies several thousand vibrations are involved for a time period of the order of 10 Ϫ12 s. 14 Dense and highly tetrahedral amorphous carbon films have also been deposited by the laser ablation technique, 15,16 by dual ion beam technique, 17 and recently by magnetron sputtering together with intense ion plating ͑MS/IP͒. 18,19 This MS/IP technique differs from other techniques since the film forming particles are low energy neutral carbon atoms ͑sput-tered from a graphite target͒, and the necessary energy for densification of the film is transferred by the argon ion plating process.…”

“…Nevertheless, at such impact energies several thousand vibrations are involved for a time period of the order of 10 Ϫ12 s. 14 Dense and highly tetrahedral amorphous carbon films have also been deposited by the laser ablation technique, 15,16 by dual ion beam technique, 17 and recently by magnetron sputtering together with intense ion plating ͑MS/IP͒. 18,19 This MS/IP technique differs from other techniques since the film forming particles are low energy neutral carbon atoms ͑sput-tered from a graphite target͒, and the necessary energy for densification of the film is transferred by the argon ion plating process.In this article evidence as to the influence of stress on the deposition of highly tetrahedral amorphous carbon ͑ta-C͒ films by MS/IP is discussed using new experimental results. The relaxation or migration of implanted carbon atoms to the film surface at high plating energies is shown not necessarily to be due to a thermal spike ͓of Seitz and Koehler ͑Ref.…”