Poly substrate, fire

Figure 18.15 shows the schematic of the fabrication process. After oxidation of the double-side polished silicon substrate wafer, a first lower poly-Si layer with a thickness of 45 pm is deposited by means of an epi-poly process. In order to remove spikes and obtain a smooth surface, 5 pm of poly-Si has to be removed by poly-Si CMP. This polishing is a two-step process, consisting of a 5 pm bulk removal by means of a fiimed-silica slurry and a subsequent final polish of several 10 nm with a haze-firee slurry. After deposition and stmcturing of some intermediate layers, a second upper poly-Si layer, again with a thickness of 45 pm, is deposited and subsequendy polished with the same two-step poly-Si CMP process. As this will be the surface of the evaporated silver mirror, a smooth as well as flat surface has to be achieved. After a backside silicon etch and the removal of the sacrificial layer, the scanning mirror device is released, see Figure 18.16(a) and (b). 

Superconducting ceramics of Y,Ba2Cu30jj g have been used as substrates for the electrochemical deposition of either poly pyrrole or poly thiophene [87]. Ceramics are typically obtained by firing pressed powders of the oxide compounds. Thus, electrical and mechanical contacts made between the ceramics and wires produced mechanically or by vacuum deposition of metal are often found to be inadequate. Superconductors modified by conducting polymers may help improve the contact area. 

Metal/polymer nanocomposites can have many other important apphcations. For example, nanoparticles embedded into poly(vinylpyrrolidinone) can be used for the electroless plating of polymeric, ceramic, and semiconductor substrates (93-98). These materials have also been used for the preparation of smart systems that experience a reversible alteration of their properties upon exposure to light. They are used as infrared barriers against exposures to intense solar hght or fires (99). 

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