Chemically amplified photoresists

L First manufacturing use of chemically amplified resists Plasma-developed resist first described X-ray proximity lithography demonstrated Bis-azide rubber resists introduced DNO-novolac resist for microelectronics introduced Photoresist technology first applied to transistor fabrication DNO-novolac resist patented by Kalle... 

In the photolithographic process, the functional layer is covered by a photoresist film. State-of-the-art circuits are fabricated with chemically amplified photoresists consisting of a polymer with an acid-labile pendant protection group, photoacid generator molecules (PAG), and additional additives [2], Upon exposure to UV radiation through a patterned mask, the PAG is decomposed generating a low concentration of acid. In a post-exposure bake... 

Chemical nature of photoresists, the chemistries involved in the photolithography, the properties of photoresists are briefly described. The discussion includes diazonaphthoquinone/novolac positive photoresists, polymer-aromatic diazide negative photoresists, photopolymerizable compositions, chalcogenide glass using systems, chemically amplified photoresists, and photoresists with an image formation in a thin layer. 

The problems met by chemically amplified photoresists are a) poor stability to environmental contaminations such as airborne amines b) sensitivity of lithographic parameters to PEB temperature variations c) poor stability during storage both after coating and after exposure d) side-directed diffusion... 

Both the DESIRE and DTSI processes might be good decisions for modern technology, but closely related with either DNQ/novolac or chemically amplified resists. The limited choice of materials to be used as the photoresist component and skin formation is the main drawbacks of the DTSI technology. The problems arisen could be party solved by the TFI approach realization in the form of the selective surface graft-polymerization. 

Vigil, J.C. Barrick, M.W. Grafe, T.H. Contamination control for processing DUV chemically amplified photoresists. Proc. SPIE 1995, 2438, 626-643. 

Typical resists include cyclized polyisoprene with a photosensitive crosslinking agent (ex bisazide) used in many negative photoresists, novolac resins with diazoquinone sensitizers and imidazole catalysts for positive photoresists, poly(oxystyrenes) with photosensitizers for UV resists, polysilanes for UV and X-ray resists, and polymethacrylates and methacrylate-styrenes for electron-beam resists (Clegg and Collyer, 1991). Also note the more recent use of novolac/diazonaphthoquinone photoresists for mid-UV resists for DRAM memory chips and chemically amplified photoacid-catalysed hydroxystyrene and acrylic resists for deep-UV lithography (Choudhury, 1997). 

One of the most important ester-protected polyhydroxystyrene-based resist copolymers, ESCAP (environmentally stable chemically amplified photoresist), developed at IBM, is based on the random copolymerization of 4-hydroxystyrene with tert-butyl acrylate (XXX).On exposure, this resist copolymer is converted to a copolymer of 4-hydroxystyrene with acrylic acid through photoinduced acid-catalyzed deprotection of the tert-butyl group (see Scheme 7.34). Because this resist system can be annealed at temperatures near its Tg in a process that hlls up the free volumes (voids in the resist matrix), thus preventing the out-diffusion of photoacids from the matrix and in-diffusion of airborne bases into the resist, neutralization reactions between the photoacids and bases in the resist matrix (otherwise known as poisoning) are reduced, thus allowing... 

A three-layer model was found by the author to describe adequately a Shipley s phenolic XP-98248 resist, a commercially available environmentally stable chemically amplified photoresist (ESCAP) film, thus suggesting the presence of three distinct layers for each film film-substrate interface layer, bulk layer, and surface layer. This three-layer model is consistent with the results of... 

Figure 17.10 shows the process sequence of the hydrophilic overlayer (HOL) process. First, a chemically amplified or non-chemically amplified positive-tone photoresist comprising hydrophobic polymer and appropriate PAG is coated to a nominal thickness on an appropriate substrate such as a silicon wafer, followed by a soft bake to dry out the nonaqueous solvent. Next, the photoresist film is exposed to radiation of appropriate wavelength to generate photoacid from the PAG. Then the exposed film is again baked (called PEB) at the standard temperature to enhance the diffusion of the photoacid and thermolysis of the acid-labile protecting groups of the polymers. 

D.L. Goldfarb and M. Angelopoulos, Confinement effects on the spatial extent of the reaction front in ultrathin chemically amplified photoresists, J. Vac. Sci. Technol. B 19(6), 2699 (2001). 

ESCAP environmentally stable chemically amplified photoresist... 

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