Multilayer resist systems processes

Multilayer resist systems can improve the performance of optical, electron beam. X-ray, and ion beam lithography (83,86). Whereas these schemes increase processing complexity, they appear to be gaining popularity and are currently used in several manufacturing areas. Both DUV blanket-ex-posure-PCM and DUV imaging and RIE-PCM schemes are strong candidates for submicrometer lithography. 

The three main approaches to multilayer resist imaging systems (see Chapter 16 for details) include (i) hard mask (HM) processes, (ii) top surface imaging (TSI) processes requiring latent image formation only near the surface of the resist, thus circumventing any transparency requirements, and (iii) bilayer resist (BLR)... 

Since in multilayer interference systems, denser layers can be deposited, improved abrasion resistance is expected compared to porous coatings. Multilayer AR films can readily be deposited from traditional polymeric sols, and low temperature post-treatments allow processing such films on polymer substrates. For instance, multicomponent AR coatings have been applied on PC and acrylate substrates by hydrolysis and condensation of silanes and various metal alkoxides (Ashley, 1986). However, it seems that low temperature... 

X-ray lithography also takes advantage of the increased resist sensitivity due to the thinner imaging films of multilayer systems. Thinner imaging films further improve X-ray resolution by minimizing the penumbra effect, a problem associated with an uncollimated X-ray beam. Consequently, the oblique exposure of features near pattern edges are minimized by multilevel resist processes, thereby restoring the desired profile. 

If multilayer systems are to be manufactured, suitable bonding methods are needed. Attention must be paid not only to the mechanical stability of the bond but also to its resistance to chemicals and changes of temperature. Bonding by means of modern glues is not impossible but is rarely used in the construction of microreactors. The prerequisite for tension-free bonding is similar coefficients of linear thermal expansion. The following bonding processes are of importance ... 

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