Diamond and Related Materials 4 (1995) 499-502 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ RiAMOND RELATED MATERIALS Structural characterization of amorphous hydrogenated carbon and carbon nitride films deposited by plasma-enhanced CVD F.L. Freire Jr. a, G. Mariotto b,*, R.S. Brusa b, A. Zecca b, C.A. Achete ’ a zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Departumento de Fisica, Pontificia Universidade Catdlica do Rio de Janeiro, Caixa Postul38071, 22452- 970 Rio de Janeiro, RJ, Brazil b Dipurtimento di Fisica, Universitri di Trento, Via Sommarive 14, 38050 Povo, TN, Ituly ’ Universidade Federal do Rio de Janeiro, COPPE, PEM M , Caixu Postal 68505, 21945- 970 Rio de Janeiro, RJ, Brazil Abstract Microstructural investigations of a-C:H and a-CN,:H films obtained by plasma-enhanced CVD were performed by means of Raman spectroscopy and positron annihilation spectroscopy (Doppler-broadening technique). Thermal gas evolution analysis has been used to gain insights about the void distribution. The effects of deposition parameters (self-bias voltage and nitrogen partial pressure in the plasma) on the film microstructure were studied. The incorporation of increasing amounts of nitrogen originates an increase in void density as well as a progressive graphitization of a-C:H films. Raman scattering from a-C:H films deposited at self-bias voltages higher than - 800 V reveals a more graphitic structure of these films with respect to those deposited at lower bias. Keywords: Amorphous hydrogenated carbon; Positron annihilation; Raman spectroscopy; Structural characterization 1. Introduction During the last two decades amorphous hydrogenated carbon films (a-C:H) obtained either by plasma decom- position of hydrocarbon gases or by ion-assisted meth- ods have been the target of extensive research owing to their unique mechanical, electrical and chemical proper- ties capable of fulfilling several applications [ 1,2]. Independently of their many potential applications, a- C:H films are materials of considerable interest from an intrinsically physical point of view, since they present both sp2 and sp3 bond hybridizations. In recent years the effects of dopant species incorporated in these films have been intensively studied. Special attention was paid to nitrogen incorporation [3-61, since it was proposed that a hypothetical material, carbon nitride (P-C,N,), isostructural to p-silicon nitride, may be even harder than diamond [7]. Films with up to 15 at.% nitrogen (a-CN,:H) have been obtained by plasma decomposition of nitrogen- methane mixtures [5,6,8]. These films can be as hard as the so-called “diamond-like” films and it was suggested that the nitrogen incorporation causes a significant reduction of their internal stress without any noticeable * Corresponding author. 0925.9635/95/$09.50 0 1995 Elsevier Science S.A. All rights reserved SSDI 0925-9635(94)05211-5 change in their hardness [S]. This is a very important result in view of the employment of carbon films as hard coatings: it is well known that high internal stress is one of the factors that limit the adhesion of a-C:H films. Until now no attempt has been made to correlate the internal stress reduction observed in a-CN, films [8,9] with their microstructure. This paper deals with the results of systematic investi- gations of the microstructure of a-C:H and a-CN,:H films carried out with the help of spectroscopic tools such as Raman scattering and positron annihilation (Doppler-broadening technique). Insights about the void distribution were also obtained by means of thermal gas evolution experiments. The paper focuses on the effects of two deposition parameters, i.e. the self-bias voltage and the nitrogen partial pressure in the plasma. 2. Experimental details Films of a-C:H and a-CN,:H (typically 0.35 pm thick) were deposited on intrinsic single-crystal Si( 100) sub- strates mounted over a water-cooled stainless steel cath- ode of a Varian r.f. (13.56 MHz) diode-sputtering system. The films were obtained by plasma decomposition of CH,-N, mixtures, with the N, partial pressure P,