IMPROVEMENT OF THE THERMAL-STABILITY OF W/C MULTILAYERS

A series of W/C multilayers has been fabricated using a magnetron sputtering device. In order to establish comparison with other multilayers produced by several laboratories, their atomic structure and thermal evolution has been studied by small- and wide-angle x-ray scattering, respectively, and Raman spectroscopy. By plotting the nominal thickness determined by the sputtering speed versus the thickness obtained by simulation of small-angle x-ray scattering spectra the existence has been confirmed of a WC interface compound of about 0.7 nm formed during the multilayer deposition. The multilayers fabricated by the magnetron sputtering device showed higher thermal stability and less period expansion than those produced by different apparatus [Dupuis et al., J. Appl. Phys. 68, 5146 (1990), Jiang et al., J. Appl. Phys. 65, 196 (1989)]. Raman spectra indicated that the carbon in the W/C multilayers is more graphitized than in the previous W/C multilayer. The carbon is further graphitized after annealing at 1000-degrees-C. The graphitization of carbon induced its density to decrease, that is, thickness to increase. Consequently, in the multilayers a smaller expansion of carbon is expected after annealing at 1000-degrees-C since there is more graphitized carbon in the initial as-deposited state than in the previous W/C multilayer. This conclusion agrees very well with the thickness variation measured by x-ray diffraction.