High temperature tolerance silicones

If a plasma is used to generate ions or radicals that recombine to give the desired film, the process is plasma-enhanced CVD (PEC VD). In PECVD it is possible to use much lower substrate temperatures because the plasma provides energy for the reaction to proceed. A major commercial application of PECVD is the formation of silicon nitride films for passivation and encapsulation of semiconductor devices. At this stage of the fabrication process the device caimot tolerate temperatures much above 300°C. High temperatures would still be required if crystalline or epitactic films were required. Many nitrides have been prepared in thin-film form by PECVD, including AIN, GaN, TiN, and BN. A more complete list of films deposited by PECVD is given in Table 28.3. 

The CVD growth technique was the first used to grow carbon nanotube networks for sensing applications. SWNT networks are typically grown on silicon wafer substrates due to this substrates tolerance to high temperatures. The CVD has proved to be an excellent way to grow randomly oriented networks of carbon nanotubes. Various conditions such as catalysts, temperature, and growth of time may be varied in order to achieve desired network properties. 

The silicon device layer is metallized with gold (500 nm Au/20 nm Cr) and patterned with the PAD METAL mask using a photolithographic lift-off process that is capable of defining 3 pm lines and spaces with a 3 pm alignment tolerance. This metal layer is exposed to high temperatures during the subsequent process steps, so it does not provide an optical quality surface for mirrors like the second metallization that is patterned with the BLANKET METAL mask. Any metal features that are defined in the first metal deposition will be in electrical contact unless they are separated by a trench etched in the device layer since the surface of the device layer is heavily doped with phosphorus. 

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