Contrast enhancement layers

To date, we have exercised these materials in basically three types of multilayer lithographic applications (1) as short wavelength contrast enhancing layers, (2) as imagable 02-RIE resistant materials in bilayer processes and (3) as radiation sensitive materials for multilayer, e-beam processes. 

Contrast enhancement lithography is a clever procedure which uses a bleachable contrast enhancing layer to restore the distorted aerial image of the mask which has been blurred by diffraction effects into a sharp image at the underlying photoresist surface. The process is too complicated to explain in detail here and the interested reader is referred to the cited literature (60,61). Suffice it to say that the large extinction coefficients of most polysilane derivatives coupled with their ready bleachability make them ideally suited for such purposes and we have demonstrated this application at 313 nm (16,18). 

A rapidly increasing number of publications on polysilanes documents current interest in these polymers (JJ. Polysilanes are potentially applicable in microlithography as high resolution UV-resists (2J, imageable etch barriers ), or contrast enhancement layers (4). They have been successfully used as precursors to Si-C fibers (5J and ceramic reinforcing agents ((L). Polysilanes have also initiated polymerization of vinyl monomers (J ). Doping of polysilanes have increased their conductivity to the level of semiconductors (8). Very recently polysilanes were used as photoconductors (9) and non-linear optical materials (10b... 

A number of a-aryl-A-alkyl nitrones and contrast enhancement compositions, which can be used to make contrast enhancement layer photoresist composites (230, 231), and inhibitors of free radical polymerization of monomers in nonexposed regions of the photoresist layer at selective actinic radiation (232). Histidine was used as a catalyst in the synthesis of a, A-diaryl nitrones in situ (233). To study diphenylborate chelates with mono- and bidentate ligands, a series of hydroxyl-containing nitrones have been synthesized (Fig. 2.7) (234-237). 

West PR, Davis GC, Regh KA. Contrast Enhancement Layer Compositions, Alkyl-nitrones, and Use, US Patent No. 5106723, April 21, 1992. 

Contrast-Enhanced Lithography. Contrast-enhanced lithography is a clever technique that uses a thin layer of a bleachable contrast-enhancing layer coated over a conventional photoresist to sharpen the mask image. 

An effective contrast-enhancing layer must possess certain essential characteristics It must be thermally stable, soluble in solvents that permit casting on photoresist layers with no mixing at the interface, strongly absorbing in the desired spectral region, and bleachable upon exposure. In addition, removal of this layer from the exposed photoresist prior to image development is desirable. 

Major Applications Electrphoresis display device, image contrast-enhancing layer,3 photogra-phy,4 Photoelectrographic imaging,5 inks," pamts, toys ... 

The concept of a contrast enhancement layer (CEL) is straightforward. All exposure equipment... 

Figure 14 Schematic of bleaching profile for a contrast enhancement layer...

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