Microlithography exposure

FIGURE 15. Bilayer polysilane photoresist after exposure, development and oxygen plasma etching. Conversion of the polysilane surface to Si02 is evident. By courtesy of IBM Almaden Research Laboratories. Reprinted with permission from Materials for Microlithography, Am. Chem. Soc., Symposium Series. Copyright (1984) American Chemical Society... 

C.A. Mack, Photoresist optimization, in KTI Microlithography Seminar Proc., pp. 153 167 (1987) P. Trefonas and C. A. Mack, Exposure dose optimization for a positive resist containing poly functional photoactive compound, Proc. SPIE 1466, 117 131 (1991). 

Polymers which undergo radiation degradation on exposure to radiation are also important commercially. The best-known example is the group of polymers used as positive resist materials in electron beam microlithography. These include aliphatic poly(sulfone)s and poly(methacrylate)s. Finally, an understanding of the radiation chemistry of polymers is essential for their application in environments where they are exposed to high doses of ionizing radiation, for example in the nuclear and space industries. 

An electron beam is of much shorter wavelength than the radiation used in standard microlithography and, therefore, provides greater resolution possibilities. For resist exposure a beam of electrons can be used whose position is controlled by a computer-driven beam deflector, thus obviating the need for a mask. Both positive- and negative-working resists are used for electron beam lithography. 

The dissolution behavior of copolymers in aqueous base is of primary importance in photoresist performance. As microlithography continues to decrease in exposure wavelength and the minimum feature size required from photoresist compositions decreases below 0.20 pm, control of macromolecular architecture will play an increasingly significant role. That is, how does the random, alternating or "blocky nature of the matrix polymer effect its solubility in aqueous base. It has been well documented for novolac based photoresists that the molecular weight distribution... 

Specific types of polymer micropatterns were made of crosslinked and uncrosslinked poly(methacrylic acid) and poly(N-isopropyl acrylamide) or polyNI-PAM. Also, the spacer material between the Si wafers was adjusted to hundreds of micrometers, allowing for a single-exposure high aspect ratio microlithography of theses polymers. Also, since these polymers under go LCST behavior during polymerization conditions, they are suitable as thermoreversible gels during application. 

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