Polymers in photolithography

The lithographic process that is widely used to generate microstructures, especially in the context of the fabrication of microdevices, is shown schematically in Fig. 9.1. It is based on the interaction of electromagnetic or particle radiation with matter. Since direct irradiation of the substrate (e.g., silicon wafers) does 

In applying the process depicted in Fig. 9.1, the mask may either be placed directly onto the wafer (contact printing) or may be positioned a short distance in front of the wafer (proximity printing). In either case, the minimum feature size amounts to a couple of micrometers, and thus does not satisfy toda/s industrial demands. However, fine-line features down to the sub-micrometer range can be obtained with projection techniques, as described in the next subsection. 

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In addition to conventional photoresist polymers, Langmuir-Blodgett (LB) films and SAMs [79-81] have been used as resists in photolithography. In such applications, photochemical oxidation, cross-linking, or generation of reactive groups are used to transfer micropatterns from the photomask into the mono-layers [82-84]. 

FIGURE 2.14 Electron micrograph of a turn in the channel fabricated in a PDMS chip, created by casting the polymer against a positive relief, which is made of photoresist patterned on a glass substrate. The roughness in the side wall arises from the limited resolution of the transparency used as a photomask in photolithography [1033]. Reprinted with permission from the American Chemical Society. 

CHART 12.5 Structures of monomers and polymers employed in photolithography in 193 nm optical lithography. Most polymers are co-, ter-, and AVra-polymers of norbomenes bearing various substituents, /er Abutoxy ac ry I ales, adamantane, and maleimide. 

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