Tungsten thin films

The preparation of tungsten thin films is possible by different techniques, such as electrolysis from salt melts, CVD, PVD and plasma spraying, diffusion, plating, electrophoresis, and metallizing. The technically important techniques are only CVD, PVD, and plasma spraying. 

---

Tungsten thin films from W(CO)g for reflectivity control. ]... 

J. of Electro-analytical Chemistry, 471 116- 125 King, F., Quinn, M. J., Litke, C. D., 1995. Oxygen reduction on copper in neutral NaCl solution. Journal of Electro-analytical Chemistry, 385(1) 45 - 55 Kneer, E. A., 1997. Electrochemical measurements during the CMP of Tungsten thin films. J. Electrochem. Soc., 144 3041 - 3049... 

Figure 3 shows the dependence of hardness on load for as-deposited copper, tantalum and tungsten thin films. An increase in the hardness of copper and tungsten films was observed at lower loads, i.e., for lower penetration depths. This is probably due to the presence of an oxide on the film surface and/or surface defects. 

It is to be noted that among other materials, electroless-deposited silver-tungsten thin films were recommended for microelectronics and microelectromechanical systems (MEMS).44,45... 

Figure Al.7.10. STM image (1000 A x 1000 A) of the (111) surface of a tungsten single crystal, after it had been coated with a very thin film of palladium and heated to about 800 K (courtesy of Ted Madey).

Fluorination of tungsten and rhenium produces tungsten hexafluoride, WF, and rhenium hexafluoride [10049-17-9J, ReF, respectively. These volatile metal fluorides are used in the chemical vapor deposition industry to produce metal coatings and intricately shaped components (see Thin films,... 

Molybdenum hexafluoride is used in the manufacture of thin films (qv) for large-scale integrated circuits (qv) commonly known as LSIC systems (3,4), in the manufacture of metallised ceramics (see MetaL-MATRIX COMPOSITES) (5), and chemical vapor deposition of molybdenum and molybdenum—tungsten alloys (see Molybdenumand molybdenum alloys) (6,7). The latter process involves the reduction of gaseous metal fluorides by hydrogen at elevated temperatures to produce metals or their alloys such as molybdenum—tungsten, molybdenum—tungsten—rhenium, or molybdenum—rhenium alloys. 

Members of the ion-insertion/extraction group, as inorganic or organic thin films, especially the former, have attracted the widest interest most recently. Tungsten trioxide was the eadiest exploited inorganic compound (4), even before the mechanism of its electrochromic response was understood (5). It is stiU the best known of the important ion-insertion/extraction group. 

Molybdenum is used for high energy laser mirrors which require water cooling. Corrosive action of the circulating cooling water can be prevented by coating the waterways with a thin film of tungsten by chemical vapour deposition. US Pat Application 308976 (1982). 

Other uses are in thin film technology where coatings are applied by vacuum deposition. Tungsten boats, or coils fabricated from wire are heated by direct resistance heating and used to evaporate Ag, Al, Au, B, Ba, Ce, Cr, Fe, In, Mg, Mn, Ni, Pa, Pt, SiO, Te, V, Zn and Zr. 

Interconnect. Three-dimensional structures require interconnections between the various levels. This is achieved by small, high aspect-ratio holes that provide electrical contact. These holes include the contact fills which connect the semiconductor silicon area of the device to the first-level metal, and the via holes which connect the first level metal to the second and subsequent metal levels (see Fig. 13.1). The interconnect presents a major fabrication challenge since these high-aspect holes, which may be as small as 0.25 im across, must be completely filled with a diffusion barrier material (such as CVD titanium nitride) and a conductor metal such as CVD tungsten. The ability to fill the interconnects is a major factor in selecting a thin-film deposition process. 

Yous, B., Robin, S., Robin, J., and Donnadieu, A., Effects of Structure on the Optical Properties of Thin Films of Tungsten Compounds, Thin Solid Films, 130(3-7) 181-197 (Aug. 1985)... 

Further, tungsten oxysulfide films, WOyS, have shown promising behavior as positive electrodes in microbatteries, unlike WS2 that is not suitable as cathode in lithium cells. Using amorphous thin films of WO1.05S2 and WO1.35S2.2 in the cell Li/LiAsFe, 1 M ethyl-methyl sulfone (EMS)/W03,Sz, Martin-Litas et al. [80] obtained current densities up to 37 xA cm between 1.6 and 3 V. In these cathode materials, 0.6 and 0.8 lithium per formula unit, respectively, could be intercalated and de-intercalated reversibly. 

Figure 23 Photograph of a working tandem device based on a thin film of polycrystalline tungsten trioxide...

---