In situ surface modification and growth of ultrasmooth amorphous carbon films by direct carbon ion-beam deposition
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In situ surface modification and growth of ultrasmooth amorphous carbon films by direct carbon ion-beam deposition M. H. Sohn and S. I. Kim SKION Corporation, 50 Harrison Street, Hoboken, New Jersey 07030 (Received 21 January 1998; accepted 26 February 1999)
Very thin s,100 nmd amorphous carbon films were grown on silicon substrates by unfiltered and filtered direct carbon ion beams. In situ surface modification was performed using C2 energies in the range of 300–500 eV prior to the growth of the film. By lowering the energy of the C2 beam to 150 eV, an amorphous carbon film was continuously grown after the surface modification. High-resolution electron microscopy showed that the film/substrate interface was damaged by 400 and 500 eV C2 beams. The carbon composition profile at the interface investigated by electron energy-loss spectroscopy illustrated that the 500 eV C2 beam generated a 30 nm thick carbon/silicon mixing layer at the interface. The damage and mixing layers were not observed at 300 eV modification. Wear testing found that strong adhesion occurred in samples modified at 400 and 500 eV. However, at 300 eV, modified samples exhibited delamination failure, which indicated inferior adhesion of the films. Surface roughness evolution of 30, 60, and 90 nm thick films was investigated by atomic force microscopy. The film surface roughness decrease as a function of film thickness was much faster when the films were grown by the filtered C2 beam. I. INTRODUCTION
The interactions of energetic particles with a solid surface are strongly dependent on the kinetic energy of the incident bombarding particles. The interactions can be categorized by the kinetic energy of the particles: film deposition (1 to a few hundred eV), sputtering (300 eV–1 KeV), shallow implantation (0.5–5 KeV), and implantation (more than 10 KeV).1 Direct ion-beam deposition (DIBD) is a very promising technique, which can produce controlled properties for amorphous carbon films. In this technique, the ion beam energy can be controlled independently to optimize the process. The kinetic energy of the ion beam can be varied from 1 to 500 eV. The DIBD technique has been proved to control the sp 3ysp 2 ratio of the carbon film by controlling the incident C2 ion beam energy.2 A rectilinear direct ion beam source has been developed by SKION. The rectilinear negative carbon ion beam, 4 in. long and 0.5 in. wide, can deposit uniform amorphous carbon films on 4 in. silicon wafers. It has been reported earlier that very hard s.50 GPad and ultrasmooth s,1 nm Rad amorphous carbon films could be obtained.3 Unlike cathodic arc or laser ablation, the beam produces no particulates on the film, and the beam energy can be controlled precisely. In this work, in situ surface modification and ultrasmooth amorphous carbon film growth are performed using unfiltered and filtered direct carbon ion beams. In situ surface modification is done using carbon ion energies of 300–500 eV during the initial deposition stage. In this
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