ABSTRACT
In this chapter we review chemical, photochemical, and electrochemical forming.* In chemical forming, chemical reactions create features by forming new compounds. The energy source at the work piece in this additive process is chemical. The method is extremely broad and covers fabrication with metals, ceramics, and polymers. Reactions are induced by combining different reagents and are often aided by
heat and/or catalysts and also may be accompanied by a shape-forming step using, for example, a spraying nozzle, a mold, or a template. Almost all manufacturing processes include one or more chemical forming steps and can be part of lithographyor nonlithography-based schemes. Chemical and thermal forming processes are difficult to distin guish because they are almost always intertwined. Some chemical forming processes involve an exothermic reaction, and such processes we classify as purely chemical (they do not require the application of external heat). This is the case, for example, in re action injection molding (RIM; see Chapter 10) and for selfassembled monolayers (SAMs; see page 523 below). Other chemical forming processes are endo thermic and require a significant increase in temperature for the reaction to initiate such as in the oxidation of Si (see Volume I, Chapter 4) or chemical vapor deposition of polycrystalline Si (CVD; see Chapter 7). The distinction between chemical and thermal forming is somewhat arbi trary, and in this chapter we cover as additional chemical forming methods those low temperature material deposition techniques that are used in chemical and biological sensor manufacture, often arranged in some type of an array configuration. The additional chemical forming methods covered are sol-gel deposition from alkoxide-based precursors, organic film spin coating, polymer dry film lamination, polymer dip coating, polymer spraying, polymer casting, organic film doctor’s blade (also called knife coating), glow dis charge polymerization, low temperature silk screening of organics, Langmuir-Blodgett deposition, and SAMs. Some of the chemical forming processes discussed here involve self-assembly such as in the case of SAMs, in which case one refers to bottom-up manufacturing. Whereas top-down nanofabrication is principally based on lithography and traditional mechanical machining, etching, and grinding, bottom-up manufacturing, which we also call nanochemistry in this book, is based in chemical synthesis, self-assembly, and positional assembly (see Volume III, Chapter 3). Arraying of low temperature materials (often organics) for sensor arrays may be accomplished by lithography, digital mirror deposition (a type of lithography as well), ink-jetting, mechanical microspotting, and
microcontact printing. Some of the same additive methods discussed in this section will reappear in Chapter 9 on thermal forming where they involve the manufacture of ceramics in which heat application is more essential.
