Optical lithography, alignment

Three main types of optical lithography are used as illustrated in Fig. 4.6. The major differences between these techniques are the position of the mask. The first step in hthography is always the alignment of mask and substrate. 

Deep-W Lithography. The important issues for deep-UV lithography (200-250 nm) are aligner optics and resist materials. Problems in aligner optics stem from the decreased transparency of standard lens materials in this frequency range, which necessitates the use of more-expensive construction materials such as quartz. Typical near-UV positive resists are not useful for deep-UV lithography because of unacceptable absorption at... 

Kostovski G, Chinnasamy U, JayawardhanaS et al (2011) Sub-15 nm optical fiber nanoimprint lithography a parallel, self-aligned and portable approach. Adv Mater 23(4) 531-535... 

For practical use, oti the other hand, more precise fabrication of nanostructures and more precise alignment between the two layers are necessary. Optical nearfield lithography would be one solution for the mass production of large-area nanostructures [29,30]. As for alignment, use of micro electro mechanical systems (MEMS) technologies [31] would be one option to resolve the alignment difficulties. 

---