The effects of the nitrogen on the electrical and structural properties of the diamond-like carbon (DLC) films M. Guerino a, * , M. Massi a , H.S. Maciel a , C. Otani a , R.D. Mansano b a LPP, Departamento de Fı ´sica, ITA, CTA, Pc ¸. Mal. Eduardo Gomes, 50, 12228-900 S.J. Campos, SP, Brazil b LSI PEE EPUSP, Av. Prof. Luciano Gualberto, trav. 3158, 05508-900 Sa ˜o Paulo, SP, Brazil Abstract Nitrogenated diamond-like carbon (a-C:H:N) films with up to 28 at.% of nitrogen were deposited by reactive d.c. magnetron sputtering with a graphite target in a mixed methane/argon/nitrogen plasma. We have been observed a systematic variation of the properties of these films with the increase in the nitrogen partial pressure. As the nitrogen content in the sputtering gas was increased, the nitrogen content in deposited films increased markedly. Raman analysis was performed to study the chemical bonding structure. Rutherford Backscattering Spectrometry (RBS) was used to investigate the chemical composition. Electrical properties were measured through current – voltage (I – V) curves and related to the composition and structure of the films. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Nitrogenated diamond-like carbon films; Fermi level shift; Single-crystal Si(100) 1. Introduction The unusual combination of electrical, optical, thermal and mechanical properties of the a-C:H:N films have motivated their studies during the last years. In addition, the possibility of growing these films on large-area substrates, at low temperature, has attracted the investi- gation of this material for microelectronic purposes to use them as semiconductor and dielectric materials. The variation of the electrical conductivity due to the Fermi level shift induced by the change in doping concentration is an obvious evidence of a doping effect. Robertson and Davis [1] proposed that electronic doping in these films may be originated from substitutional N in tetrahedral network at low N content, and at high and low N content the substitutional N doping graphitic C by donating p electrons. Meanwhile, the doping effect at low N content remains weak. Robertson and Davis [1] proposed that this occurs due to the coordination environment mechanism governing at the disordered material. The minority of the dopant atoms can self-adjust substitutionally in the tetra- hedral N 4 site and the majority forms non-doping trigonal N o 3 sites. In the highly doped regime, the predominant C – N bonding is a trigonal bond (non-doping pyridine-like bonding, non-doping pyrrole-like and doping N 3p bonding). This can be interpreted as increasing N sites in the C amorphous network cause a reduction of the energy barrier for sp 3 to sp 2 transition to a small value, so the graphitization proceeds around the N site. This result leads to a broadening of the p and p* bands and to narrows the band gap. Nowadays, significant effort has been directed to study usefulness of this film for electrical and other applications. In this paper, we concentrate our attention to the disorder effects on the structure of the a-C:H film caused by N doping and try relate it with the electronic transport properties of this film. 2. Experimental The a-C:H films with a thickness of approximately 160 nm were deposited on p-type, single-crystal Si(100) and glass like carbon substrates by reactive d.c. magnetron sputtering system. The target is a 99,999% pure, 4-inch diameter, graphite plate, located at 53 mm from the substrate. A vacuum system composed of a rotary vane and a turbo-molecular pump was used to attain a residual pressure of 8 £ 10 26 Torr. During deposition, the working pressure was 1.8 mTorr. The Ar þ CH 4 total flow was kept constant at 5 sccm (4.5 sccm Ar and 0.5 sccm CH 4 ) with 0026-2692/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0026-2692(03)00079-X Microelectronics Journal 34 (2003) 639–641 www.elsevier.com/locate/mejo * Corresponding author. Tel.: þ 55-12-39475940; fax: þ 55-12- 39475850. E-mail address: marciel@fis.ita.br (M. Guerino).