Semiconductors protective coatings

Because of the high functional values that polyimides can provide, a small-scale custom synthesis by users or toU producers is often economically viable despite high cost, especially for aerospace and microelectronic appHcations. For the majority of iudustrial appHcations, the yellow color generally associated with polyimides is quite acceptable. However, transparency or low absorbance is an essential requirement iu some appHcations such as multilayer thermal iusulation blankets for satellites and protective coatings for solar cells and other space components (93). For iutedayer dielectric appHcations iu semiconductor devices, polyimides having low and controlled thermal expansion coefficients are required to match those of substrate materials such as metals, ceramics, and semiconductors usediu those devices (94). 

Such a dilemma can be overcome by using semiconductor electrodes coated with sparsely scattered, extremely small (nanometer-sized) metal dots,42 45) such as shown schematically in Fig. 4.9 with n-Si used as a semiconductor. The naked Si surface is covered with naturally grown thin Si02 layer and passivated. The photocurrent flows through the metal dots. The photocurrent can be stable in aqueous redox electrolyte because the Si surface is covered and protected by coating with metal dots and Si02. 

Semiconductor microchip processing often involves chemical vapor deposition (CVD) of thin layers. The material being deposited needs to have certain desirable properties. For instance, to overlay on aluminum or other bases, a phosphorus pentoxide-doped silicon dioxide coating is deposited as passivation (protective) coating, by the simultaneous reactions... 

The twenty chapters included in this volume can be conveniently divided into the following groups review plasma polymerization of hydrocarbons plasma polymerization of fluorocarbons plasma polymerization of organometallic systems plasma-initiated polymerization and applications of plasma polymerization. Though the emphasis of this Symposium is on the fundamental aspects of plasma polymerization, we should not lose sight of the fact that it is the potential applications of this technique that has stimulated the efforts in basic research. Potential applications for plasma-polymerized films include membranes for reverse osmosis, protective coatings for optical components, and insulating layers for semiconductors. 

Protective coatings are used extensively on metal or semiconductor surfaces to isolate them or limit access of an aggressive environment (17,18). Frequently these coatings are multilayered and complex in structure, as for example in automobile paints. In this case, the innermost coating is either hot-dipped or electrodeposited zinc ("galvanizing"), over which a zinc-rich polymer-chromate undercoat is placed. The decorative top coat provides a physical barrier to the transport of water and ionic species. It is important to note, however, that protection is achieved electrochemically by the galvanic action of zinc on steel and by the inhibiting action of chromate toward oxidation. 

The combination of an optimized protective coating and an inherent underlying stability in the semiconductor material itself can lead to an extended lifetime in operation, because a breach in the protective layer would not be fatal to the device. 

Progress in development of protective coatings for semiconductor photoelectrodes was bound with making use of materials other than metals, with "metallic" conductivity, namely, silicides (of platinum, or ruthenium), or degenerate semiconductors (Sn02 Sb, Sn02 - In203 BP, and others) [43 - 45]. 

Also, fluorine-carbon composites were investigated as functional coating materials in a wide variety of applications coating materials for construction under low temperature environments [139], protective coating for computer hard disks [140], automotive components [141], semiconductor in opto-electronic devices [142, 143], and biomedical implants [144]. Those applications follow outstanding physicochemical, electrical and mechanical properties of these materials, (i.e., hardness, friction, water repellency, chemical... 

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