Planarizing coatings

A widely used glass is phosphosilicate (PSG), which is used extensively in semiconductor devices as a passivation and planarization coating for silicon wafers. It is deposited by CVD by the reaction of tetraethyl orthosilicate (TEOS) (C2H50)4Si, and trimethylphosphate PO(OCH3)3, in a molecular ratio corresponding to a concentration of 5 to 7% P. Deposition temperature is usually 700°C and pressure is 1 atm. 

In demanding applications, for example barriers for OLED displays, control of polymer smoothness and cleanliness by the routes mentioned above may not be sufficient. In such circumstances it is necessary to lay down a further coating under clean-room conditions which acts both as a planarizing coating and as a hard coat to prevent scratching on subsequent processing. This has been discussed elsewhere [6, 12, 13]. 

Baked coatings of novolac-based resists have been observed to produce the most planar coatings because they flow before they are cross-linked by the thermolysis of the multifunctional NDS compounds that are present in the resist. The resulting networks are not degraded by UV exposures and thus cannot be used in the PCM scheme however, they are thermally stable enough to allow the deposition of the refractory oxides necessary for the etch barriers in the trilayer scheme. 

Figure Bl.17.8. Iron oxide particles coated with 4 nm of Pt in an m-planar magnetron sputter coater (Hennann and Mtiller 1991). Micrographs were taken in a Hitachi S-900 in-lens field emission SEM at 30,000 primary magnification and an acceleration voltage of 30 kV. Image width is 2163 nm.

Curing of Coatings with Electron Beams, y-Ray, X-Ray, and Planar Cathodes... 

Ellipsometry can be sensitive to layers of matter only one atom thick. For example, oxidation of freshly cleaved single-crystal graphite can be monitored from the first monolayer and up. The best thicknesses for the ellipsometric study of thin films are between about 1 nm and 1000 nm. Although the spectra become complicated, films thicker than even 1 pm can be studied. Flat planar materials are optimum, but surface and interfacial roughness can be quantitatively determined if the roughness scale is smaller than about 100 nm. Thus ellipsometry is ideal for the investigation of interfacial surfaces in optical coatings and semiconductor struc-... 

Currem field characteristics measured wiih conjugated polymers sandwiched between an indium-tin oxide (ITO) anode and an aluminum cathode are usually hole dominated and are, consequently, appropriate for testing injection/lransport models for the case of unipolar current How. Data shown in Figure 12-1 refer to injection-limited currents recorded on typically 100 nm thick spin-coated films of derivatives of poly(y d/"fi-phenylenevinylene) (PPV) and a planarized poly(/ /" -pheny-leue) employing a Keilhley source measure unit. The polymers were ... 

Figure 20. I U) curves for Cg-Au (left) and Gal-Au (right) in H2O as a function of pH (adjusted with phosphate buffer). The numbers 1—4 in the Gal-Au data identify voltage plateaus. Cartoons of the experimental arrangements for measuring curves of individual nanoclusters in solution are shown at the top of each data column. The insulated STM tip, ligand-capped Au nanocluster and an octanethiol-coated planar Au substrate are shown. Length and shapes are not to scale. (Reprinted with permission from Ref. [35], 1998, American Chemical Society.)...

Modem planar chromatography is suitable not only for qualitative and quantitative analysis but also for preparative purposes. The separation efficiency of a thin-layer chromatographic system is independent of this intended purpose and is mainly determined by the quahty of the stationary phase, that is to say, by the applied coated layer. Therefore, progress in modem planar chromatography can be attributed not only to the development of the efficiency of the instmments but also to a large extent to the availability of high-quahty precoated layers. And today, as in the past, bulk sorbents for self production, especially of preparative layer chromatography (PLC) layers, are widely used. 

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