Protective overcoat

Fig. 3. Cross-section photomicrograph of a color-negative product showing the film base, the emulsion layer (the black specks are microcrystalline silver hahde grains), and a protective overcoat. The emulsion layer and overcoat are - 3.5 x 10 m thick.

Metal is then deposited into the opened vias (openings) in the oxide layer and over its surface. During the subsequent photolithography process, it is patterned to form the desired electrical interconnections. These two steps are repeated for each succeeding level to produce additional levels of interconnections. Finally, a protective overcoat of oxide/nitride is applied (passivation), and vias are opened so that the wires eonnectlng the IC chip to its carrier package can be bonded to output pads. 

Protective layer, in landfill design, 25 879 Protective overcoat layers, in photography, 19 199... 

Spin coating utilizes centrifugal forces created by a spinning substrate to spread a liquid evenly over its surface. Current applications are in photoresist technology for the microelectronic industry and in the manufacture of protective overcoats and adhesives for the optical storage industry (compact discs and DVDs).5... 

The above three layers form what is collectively referred to as the "ink-receptive formulation". Critical to the success of this product is the COLORCAST technology embodied by the cationic polymer additives called "mordants" that are designed to bind and fix the dye molecules, along the ceramic nanoparticle in the protective overcoat. The exact choice, concentration, and location of the mordants are critical to achieving the best balance of image stabUity across the four main environmental factors hght, heat, humidity, and ozone. Equally important is incorporation of the proprietary ceramic nanoparticles present in the overcoat layer. 

In order for a polyimide to be useful as an interlevel dielectric or protective overcoat (passivant), additional demanding property requirements must be met In the case of the passivant, the material must be an excellent electrical insulator, must adhere well to the substrate, and must provide a barrier for transport of chemical species that could attack the underlying device. It has been demonstrated that polyimide filrns can be excellent bulk barriers to contaminant ion motion (such as sodium) [10], but polyimides do absorb moisture [11,12], and if the absorbed moisture affects adhesion to the substrate, then reliability problems can result at sites where adhesion fails. However, in the absence of adhesion failure, the bulk electrical resistance of the polyimide at ordinary device operating temperatures and voltages appears to be high enough to prevent electrochemical corrosion [13]. 

The nitride layer could alternatively be structured with additional lithography and etching steps in such a way as to leave the protective overcoat only in isolation areas (Fig. 12.20) [33,34]. In this case, planarity is further improved at the expense of the increased process complexity. Using a high-selectivity slurry in combination with a patterned nitride overcoat allows complete elimination of dishing in large isolation areas (Fig. 12.21). 

These films can be used as a protective overcoat to increase the life of many other potentially useful coatings in different applications, for example, the soft Indium-Tin Oxide film used in photovoltaic applications, soft YBaCu Oj superconducting thin films, etc. provided the diamond like overcoat does not alter or influence the basic properties of the underlying soft coating. 

Application of a protective overcoat to seal off airborne contaminants was also a popular approach initially. Although many polymers, lipophilic and hydrophilic, have been evaluated as a topcoat, water-soluble poly[ (meth)acryhc acid] is most commonly employed, which can be cast from a water solution without interfacial mixing with the resist layer and can be removed during aqueous base development. However, it has been reported that a poly(acrylic acid) overcoat allows diffusion of water, which reportedly contaminates a chemical amplification resist [211]. Poly(cx-methylstyrene) has been recommended as a good barrier against both airborne base and water [211]. 

Hydrogenated carbon films have been used in the magnetic recording industry as protective overcoats for both memory disks and pickup sliders for many years now. Recently, the inclusion of nitrogen in these films has become of interest, perhaps primarily because it improves the spreading of lubricants on the overcoats. Raman spectroscopy is currently a major quality control tool for carbon overcoats, especially on computer disks. 

Raman spectroscopy is a powerful tool for monitoring DLC overcoat quality. The technique when used properly can yield more useful information about DLC properties than any other single analysis method. Further to this, Raman spectroscopy is now easy to use and relatively inexpensive. Raman spectroscopy is also used extensively in the disk drive industry for the identification of certain inorganic and organic contaminants down to less than 1 pm in size. The author sees no reason why Raman spectroscopy will not continue to be used extensively throughout the disk drive industry and other industries that use DLC as a protective overcoat. 

An interesting alternative to the use of 1 mm of substrate for providing immunity is a low-birefringence polycarbonate film used as a protective overcoat stretched like a drum skin above a high-performance 14 in optical disc (Kodak Co., Rochester, New York). However, this has not proved to be generally applicable in the marketplace. 

During 1960—1970, an impressive number of heterocycles were engaged in macromolecules without taking into account their processability. At the present time, a few heterocyclic polymers have found general acceptance in the industry as heat-resistant adhesives, dielectric and insulating films, high-modulus fibers, protecting overcoats, and matrices for composites. The... 

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