Usefulness of SAMs in Lithography

For this reason, the study on the application of organic ultrathin films of several nanometers thickness to resist materials has been advanced as one of the technologies which makes much finer lithography possible [32-36], Moreover, the trials to fabricate molecular devices have begun to unfold by immobilizing functional molecules, such as DNA and proteins, selectively at fine-structured SAMs which have reactive terminated groups like NH3-, COOH- and Cl- [37-42], 

Thick organic polymer resist films are used for the conventional lithography. Their thicknesses are dozens to hundreds of nanometers. When a processing size becomes small and enters nanometer order in electron beam lithography, scattering of electrons in a resist causes various problems, such as the proximity effect. The variation in molecular mass of each molecule which forms the resist also reduces the resolution. If the ultrathin resist film of several nanometers thickness will be realized, the lithography of higher resolution will become possible. 

The thicknesses of SAMs are 1-2 nm, depending on the length of molecules comprising the monolayer. Moreover, the SAMs consist of molecules of the same kind, and there is no variation in molecular mass in SAMs, which is in contrast to the polymer films. Therefore, SAMs are highly promising as high-resolution resists. The uniform coating of SAMs is also possible onto substrates with three-dimensional complex shapes, fine-structured substrates and inner surfaces of tubes. 

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