Preparation of Super-Hard Nitride Thin Films for Next Generation by High Density Plasma PVD

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Research on the formation of β-C_3N_4 thin films as one of the most attractive super-hard nitride materials in the next generation has been conducted between 1997 and 1999. The first goal was settled to obtain films with stoichiometric composition for the first by developing a high density helicon-wave excited plasma sputtering source operated at low pressures, in which highly excited radicals and ions could easily be obtained. Results obtained within 3 years project are summarized as follows.1) Using a simple helical coil antenna of several turns a high density plasma with a density reaching to 10^<13> cm^<-3> was obtained in Ar gas of 0.1 - 1 Pa in an external magnetic field with an RF power input of Several 100 W.Even in N_2 gas environment a plasma density of 10^2 cm^<-3> was also obtained easily.2) Developing a sputtering machine based on this plasma, preparation of CN_x films were performed and it was found that increasing nitrogen flux brought an increase of N content in the films and succeeded in obtaining stoichiometric film composition by controlling C and N flux appropriately. Films were composed of mixture of sp^2 and sp^3 phases that increased with N content.3) Micro-hardness of the films was not so high with a value of about 25 GPa in the condition of ion bombardment at a nearly stoichiometric composition. It was considered that softening of films was induced by the existence of graphite phase and impurity atoms such as O and/or H in the films causing polymer-like compound formation.