Acid amplifier

A new interesting concept to further increase the sensitivity of chemical amplification resists has been proposed primarily for 193 nm lithography. An acid amplifier in resist film, inert to radiation, produces a large number of acid molecules by its catalytic reaction with a photochemically generated acid (Fig. 10) [93,94]. In many cases only weak sulfonic acids such asp-toluenesul-fonic acid (tosic acid, TsOH) are generated by this mechanism and an aromatic structure incorporated into acid amplifiers to promote acid cleavage increases 193 nm absorption. 

Tri[2-(/>-toluenesulfonyloxy)ethyl]-l,3,5-trioxane has been used as a supply of 3equiv of /<-toluenesulfonic acid, obtainable by acid-catalyzed decomposition <1998CL823>. The released sulfonic acid can be employed in situ as an acid amplifier to enhance the photosensitivity of a chemically amplified photoresistor. 

The components of the copolymers are cycloaliphatic monomers (norbor-nene), and vinyl ether, maleic anhydride, acrylate, and methacrylate. In addition, vinyl sulfonamides have been used as co-monomers in the synthesis of random copolymers capable of functioning as acid-amplified resists. An example is presented in Chart 9.5. A high sensitivity, S = 2mJ cm, was measured for a copolymer (Chart 9.5) with n=0.4 and m=0.6 (resist thickness d=220nm, developer aqueous tetramethylammonium hydroxide solution). Triphenylsulfonium perfluoro-1-butane sulfonate served as acid generator [33]. 

Photoresists employed at 248 nm and 193 nm are too opaque at 157 nm, the wavelength of light emitted by F2 lasers. However, sufficiently transparent fluorocarbon-based polymers containing non-absorbing C-F bonds operate satisfactorily at 157 nm [30, 34]. Therefore, new fluoropolymers, also functioning as acid-amplified resists, were synthesized. Chart 9.6 shows the structures of copolymers containing 4-(2-hydroxy hexafluoro isopropyl) styrene units. 

Three kinds of acid amplifiers liberating sulfonic acids autocatalytically were developed. They include terf-butyl 2-methyl-2-tosyloxyniethyl-3-keto-butanoate, l-phenyl-l-(2-benzenesulfonyloxyethyl)-l,3-dioxolane and ciy-1-hydroxyl-l-phenyl-2-tosyloxycyclohexane. Tliese add-... 

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. 

Photosensitivity Characteristics of Photo polymers Incorporating Acid Amplifiers... 

Figure 5 Photosensitivity curves for poly(ter/-butyl methacrylate) photoactivated by 2 mol% of 8 in the absence (-0-) and in the presence of 5 mol% (- -) 10 niol% (- -) and 15 mol% (-A-) of diol monotosylate (7) as an acid amplifier. Post-exposure bake 100°C for 1 min, development 3 wt% of Me N OH.

Fig. 18. Chemistry of PTBOCST chemically amplified resist. Pattemwise exposure creates small quantities of acid. In a subsequent heating step, pendant TBOC groups are cleaved under acid catalysis. The exposed and unexposed areas can then be differentiated on the basis of solubiUty.

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. 

Fig. 31. An acrylic terpolymer designed for chemically amplified resist applications. The properties each monomer contributes to the final polymeric stmcture are for MMA, PAG solubility, low shrinkage, adhesion and mechanical, strength for TBMA acid-cataly2ed deprotection and for MMA, aqueous...

As the result of high specificity and sensitivity, nucleic acid probes are in direct competition with immunoassay for the analytes of some types of clinical analytes, such as infectious disease testing. Assays are being developed, however, that combine both probe and immunoassay technology. In such hybrid probe—immunoassays, the immunoassay portion detects and amplifies the specific binding of the probe to a nucleic acid. Either the probe per se or probe labeled with a specific compound is detected by the antibody, which in turn is labeled with an enzyme or fluorophore that serves as the basis for detection. 

Berzehus (19) further appHed and amplified the nomenclature introduced by Guyton de Morveau and Lavoisier. It was he who divided the elements into metalloids (nonmetals) and metals according to their electrochemical character, and the compounds of oxygen with positive elements (metals) into suboxides, oxides, and peroxides. His division of the acids according to degree of oxidation has been Httie altered. He introduced the terms anhydride and amphoteric and designated the chlorides in a manner similar to that used for the oxides. 

Other acid gases such as hydrogen chloride and oxides of nitrogen produce similar corrosion problems. The corrosion effects produced by acid condensate are amplified by the motion of the gas stream (typically 20-53 m/s) and erosion effects due to entrained solids and impingement at bends, damper plates, reheaters, etc. 

A linear correlation of log rate coefficient with acidity function HQ was considered to have been obtained in the dedeuteration of deuterobenzene in aqueous sulphuric acid (Table 121) the slope of the plot being given as 1.36461. However, rigorous examination of the data shows the plot to be a curve which is amplified... 

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