Internal Stress in Nitrogen Doped Diamond-Like a-C:H Films
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INTERNAL STRESS IN NITROGEN DOPED DIAMOND-LIKE a-C:H FILMS D. Franceschini*, C. Achete*, F. Freire Jr.**, G. Mariotto *** *COPPE, Universidade Federal do Rio de Janeiro, Cx. Postal 68505, Rio de Janeiro, Rj, Brazil **Pontifice Universidade Cat6lica do Rio de Janeiro, Brazil ***Dipartimento de Fisica, Universita di Trento, Povo, Italy ABSTRACT: Results of a study on internal stress, hardness and structure of nitrogen doped amorphous hydrogenated hard carbon films deposited by r.f. glow discharge on silicon are presented. Films obtained for different bias voltage (Vb), N2 partial pressure and total gas pressure were characterized by Nuclear Reaction (NR), Elastic Recoil Detection (ERD), Rutherford Back-Scattering (RBS), Infrared Spectroscopy (IR) and Raman Scattering. The elemental composition, density and structure are correlated with Vickers hardness, and internal stress values obtained by the substrate bending method. It has been observed that internal stress considerably decreases with increasing nitrogen content, contrary to the behavior shown by hardness, structure and hydrogen concentration, which remain unchanged. 1-INTRODUCTION Amorphous hydrogenated (a-C:H) films deposited by plasma decomposition of hydrocarbon gases can be quite hard, electrically insulating and resistant against corrosion. These properties make hard a-C:H films a candidate for several applications, especially as protective coatings. The structure and properties of these films, mainly those deposited by selfbias glow-discharge have been extensively studied under a wide range of deposition parameters [1,2]. Recently, there have been several reports on the effect of nitrogen incorporation into aC:H films. It has been shown that nitrogen incorporation causes the reduction of the electrical resistivity and of the optical band-gap width (ref.3-5]. However, these previous works do not present any measured values for the mechanical properties of the films. In this work we report on the structure, composition and mechanical properties of nitrogen-incorporated a-C:H films. The films were deposited by RF self-bias glow discharge in CH4 -N 2 atmosphere , under several conditions of total pressure, measured self-bias and N2 partial pressure. 2-EXPERIMENTAL The nitrogen doped a-C:H films were deposited on intrinsic silicon single-crystal Si(100) substrates, which were mounted over a water cooled stainless steel cathode of a Varian RF (13.56 MHz)-diode sputtering system. Three sets of films were produced. The first two sets were deposited at a constant self-bias (Vb) of -370 V, with the N2 partial pressure ranging from 0% to 50%, at deposition pressures of 0.8 and 8 Pa. The third set was produced at a deposition pressure of 8 Pa with Mat. Res. Soc. Symp. Proc. Vol. 270. @1992 Materials Research Society
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25% of N2 partial pressure, while varying the self-bias from 200 to -950 V. Chemical analysis of the films was performed by ion beam techniques. Hydrogen content was determined by Elastic Recoil Detection, using a 2.2 MeV 4 He÷ incident beam. Nitro
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