Microlithography

In general there are two lithographic processes used in computer-circuit fabrication -photolithography and radiation (X-ray, laser, electron-beam and deep-UV (248- and 193-nm wavelength)) lithography. The principal difference is the radiation source and wavelength, which in turn define the feature size which can be achieved. 

Resist deposition deposition of the resist (material) film from dilute-solution spinning and baking onto a substrate. 

Pattern exposure a pattern is generated by a mask or controlled radiation-beam steering, where the exposed material is degraded, chemically modified or crosslinked. 

Pattern development the pattern is developed by solvent interaction to form a positive (irradiated material is removed) or negative (non-irradiated material is removed) and then baked. 

Transfer of pattern to substrate exposure of the patterned substrate to an etchant or gas plasma allows features to be transferred to the substrate. 

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Barraud A, Rosilio C and Ruaudel-Teixier A 1980 Polymerized monomolecular layers a new class of ultrathin resins for microlithography Thin Soiid Fiims 68 91-8... 

I ovolac Synthesis and Properties. Novolac resins used in DNQ-based photoresists are the most complex, the best-studied, the most highly engineered, and the most widely used polymers in microlithography. Novolacs are condensation products of phenoHc monomers (typically cresols or other alkylated phenols) and formaldehyde, formed under acid catalysis. Figure 13 shows the polymerization chemistry and polymer stmcture formed in the step growth polymerization (31) of novolac resins. 

In the following sections the properties of photogenerators of strong Bronsted acids and their use in microlithography are summarized. 

Acid-C t lyzed Chemistry. Acid-catalyzed reactions form the basis for essentially all chemically amplified resist systems for microlithography appHcations (61). These reactions can be generally classified as either cross-linking (photopolymerization) or deprotection reactions. The latter are used to unmask acidic functionality such as phenohc or pendent carboxyhc acid groups, and thus lend themselves to positive tone resist apphcations. Acid-catalyzed polymer cross-linking and photopolymerization reactions, on the other hand, find appHcation in negative tone resist systems. Representative examples of each type of chemistry are Hsted below. 

Rai-Choundhury, P. ed.. Handbook of Microlithography, Micromachining and Microfabrication. Vol. 1 microlithography, SPIE Optical Engineering Press, Washington,... 

A number of possible uses of radiation grafting are being explored for microlithography, diazo printing, and various copying and printing processes. 

Miller RD, Hofer D, McKean DR, Willson CG, West R, Trefonas P (1984) in Materials for Microlithography, Thomson L, Willson CG, Frechet JMJ (eds), ACS Symposium Series 266, American Chemical Society, Washington, DC... 

It has also been recently employed to investigate NEMCA by Imbihl and coworkers.28 Both porous Pt paste films and evaporated microstructured Pt electrodes prepared by microlithography were investigated. These microstructured electrodes were typically 500 A thick. 

HANDBOOKOF VLSI MICROLITHOGRAPHY edited byWilliamB.GIendinning and John N. Helbert... 

Horn, M. W., Antireflection Layers and Planarization for Microlithography, Solid State Technology, pp. 57-62 (Nov. 1991)... 

An outline of these two possible processes of microlithography is shown in Figure 8.1. 

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... 

Polysilylenes have been widely investigated in the past decade because of their potential applications in the field of materials science [1], Recent applications of polysilylenes in SiC precursors [2], microlithography [3], photoinitiators [4], and reprography [5] show that polysilylenes are very promising as advanced materials for high technology of the next generation. 

Childs, W. R. Nuzzo, R. G. 2002. Decal transfer microlithography A new soft-lithographic patterning method. J. Amer. Chem. Soc. 124 13583-13596. 

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