Selective tungsten thin films

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. 

Oxides are normally stable at the operating temperatures necessary to enhance the interaction between their surface and the gas phase, much more stable compared to organic materials. They are normally operated between 500 and 800 K where the conduction is electronic and oxygen vacancies are doubly ionized. Different oxides have been proposed for conductometric chemical sensors, the most studied is by far tin dioxide that has also been commercialized in form of thick film sensors. Other oxides studied are titanium oxide, tungsten oxide, zinc oxide, indium oxide and iron oxide, first in form of thick and then in form of thin films. Furthermore, the use of mixed oxides, as well as the addition of noble metals, has been studied to improve not only selectivity but also stability. 

If the subsequent assembly process calls for thermocompression or thermosonic wire bonding, plated copper under the wire-bond sites should be avoided. This can be accomplished by selectively plating the copper. When the adhesion layer is Nichrome or titanium-tungsten, then precision-deposited thin-film resistors can be fabricated. 

This section focuses on the low temperature synthesis ofhighly oriented (Sr,Ba)Nb206 (SBN)-based thin films of tungsten bronze structure. The crystallographic phase, the mechanism of orientation on properly selected substrates and the characteristic... 

See, for example, Carlsson, Jan-Otto and HSrsta, Anders, Thermodynamic investigation of selective tungsten chemical vapour deposition Influence of growth conditions and gas additives on the selectivity in the fluoride process. Thin Solid Films, 1988 158 107-122. 

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