Improved thermal stability of sputtered W/C multilayer thin films

摘要

Abstract: Tungsten/carbon (W/C) multilayer thin films prepared by sputtering on unheated Si(100) substrates were encapsulated with various types of layer having low x-ray absorption. Isochronal annealings for 1 hr in the temperature range from 300 to 600$DGR@C and isothermal annealings at 300 and 400$DGR@C were carried out under ambient conditions (in air) on coated and uncoated multilayers. The encapsulated layers are: SiN$-x$/ and SiO$-2$/ prepared by plasma enhanced chemical vapor deposition (PECVD) and SiC, Al$-2$/O$-3$/, C and B$-4$/C prepared by sputtering techniques. Previous studies have shown that unprotected W/C multilayers annealed in air exhibit oxidation at relatively low temperatures (approximately 300$DGR@C). In the present study, we have used Raman scattering (RS), Auger depth profiling and scanning electron microscopy (SEM) to investigate the effects of thermal treatments on the encapsulated W/C multilayers. The results indicate that oxidation of both W and C layers takes place during annealing at temperatures which depend on the type of protective layer. For example, in the isochronal annealing experiments, multilayers coated with C, Al$-2$/O$-3$/ and B$-4$/C suffer oxidation during annealing at 400$DGR@C, whereas multilayers coated with the other three types of protective films prevent multilayers from oxidation at annealing temperatures as high as 600$DGR@C. SEM micrographs show that the formation of pinholes through the protective layer occurred during annealing at the temperatures for which oxidation was first detected. Auger profiling shows the loss of compositional modulation in the region reached by oxygen. A WO$-3$/ phase is identified by RS in the oxidized region, and the loss of the C layers is most likely due to the formation of carbon oxide vapors.!15