Chemically amplified photoresist

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... 

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

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... 

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... 

Major concern of this paper is to review the nature and the reactivity of acid amplifiers and to apply them to the enhancement of photosensitivity of chemically amplified photoresist systems. 

It was found that the addition of these add amplifiers to conventional chemically amplified photoresist systems results in marked enhancement of photosensitivity characteristics. A photoresist based on a ternary system consisting of pBOCSt, the acetoacetate-type add amplifier (2a) and PAG exhibited enhanced deprotection during post-exposure bake irrespective of the nature of PAG. Marked improvemoit in photosensitivity was observed when the ketal-sulfonate-type add amplifier (3) or the diol monotosylated-type add amplifier (7) is embedded in a thin film of poly(ter/-butyl... 

Practical additive effect of an add amplifier was verified by evaluating photolithographic characteristics of a chemically amplified photoresist for 193 nm photomicropatteming both photosensitivity and pattern profiles were improved. The optimization of the chemical structure of the add amplifier and of its combination with a suitable dissolution inhibitor should be a promising way to give high performance photoresists for microphotopatteming. 

Fluorescence techniques are being used increasingly in wide range of research fields including biochemical, medical and chemical research, due primarily to the inherent sensitivity of the technique and the favorable time scale of the phenomenon of fluorescence (4). Some fluorophores have dramatically different emission characteristics for their protonated and unprotonated forms. Using this phenomenon, the photo-acid concentrations generated within chemically amplified photoresist systems can be monitored (5-7). 

Advanced photoresists, such as 193 and 248 nm photoresists, are based on chemical amplification concept [7,8]. These chemically amplified photoresists generally consist of a base polymer, a photo-sensitive compound called photoacid generator (PAG), and sometimes a cross-linking... 

The metal-containing onium salts are generally not preferred in modem photoresists as they will contaminate the device fabrication processes. Instead organic onium salts are preferred in chemically amplified photoresist formulations. Table 57.15 shows extinction coefficients at 248 nm, 254 nm, and the absorption maxima as well as thermal stability of some organic onium salts [43]. 

Correlation of the Reaction Front with Roughness in Chemically Amplified Photoresists... 

Deprotection of the t-Boc groups is achieved by reaction with an acid, HX (Scheme 13.6). The acid is generated from photochemical decomposition of iod-onium (R2r X ) or sulfonium (R3S X ) [17]. Deprotection of the t-Boc groups results in the formation of a styrene polymer with soluble phenolic side-chain groups. Thus the photoinduced creation of a soluble polymer from an insoluble one constitutes a positive chemically amplified photoresist. 

Postnikov SV, Stewart MD, Tran HV et al (1999) Study of resolution limits due to intrinsic bias in chemically amplified photoresists. J Vac Sci Technol B Microelectron Nanometer Struct 17 3335... 

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