Drying process sequences

Fig. 1. Gel—sihca glass process sequence showing the process steps A, mixing B, casting C, gelation D, aging E, drying F, dehydration or stabilization ...

Heat of (exothermic) decomposition A single operational stage of a chemical process sequence - may be purely physical, e.g. distillation or drying A single chemical reaction stage in a process sequence US National Technical Information Service Ultraviolet spectroscopy... 

Crystallization is frequently the initial step in a solida processing sequence, similar to that shown in Fig. 11.1-1, that subeeqnently includes solid-liquid separation and drying equipment. Since product size... 

The subtractive methods practically can only be used to produce single films with lower refractive indices than those of the multicomponent glass substrates. Consequently in optics their use is limited to reflection-reducing films. This limitation does not exist with the additive film formation methods. With additive methods, it is possible to deposit in any sequence low- or non-absorbing compound films with various refractive indices as well as absorbing an highly reflecting metal or alloy films and mixtures of both types of films. It is obvious therefore that the subtractive methods are almost completely superseded by additive ones. The additive film formation methods can be classified into chemical and physical methods and further into wet or dry processes the latter may run at atmosphere or under vacuum. 

Figure 17.10 shows the process sequence of the hydrophilic overlayer (HOL) process. First, a chemically amplified or non-chemically amplified positive-tone photoresist comprising hydrophobic polymer and appropriate PAG is coated to a nominal thickness on an appropriate substrate such as a silicon wafer, followed by a soft bake to dry out the nonaqueous solvent. Next, the photoresist film is exposed to radiation of appropriate wavelength to generate photoacid from the PAG. Then the exposed film is again baked (called PEB) at the standard temperature to enhance the diffusion of the photoacid and thermolysis of the acid-labile protecting groups of the polymers. 

In manual control, expert judgment by the operator is relied upon to judge the endpoint of the drying process. A drya-manual control scheme may be described by the following sequence [2,4]... 

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