Diazo resists

Reiser, Photoactive Polymers The Science and Technology of Resists, p. 45, John Wiley Sons, Hoboken, NJ (1989). 

The chlorinated resin is not water soluble and reacts as a negative resist with an aqueous developer. This resist is widely used in the printing of lithographic plates and for the preparation of silverless negatives. 

In addition to this radiation-induced polarity switch in the diazoresin, crosslinks are also formed on exposure, which helps to make the image mechanically and thermally resistant. This cross-linking occurs at sites where a diazonium ion is located near a secondary amine and where the substitution reaction may produce a quarternary ammonium ion and lead to a cross-link (XXIV). 

Another interesting variation on negative diazo resists involves compositions of aqueous acetic acid solution of 4-dimethylaminophenyldiazonium chloride and zinc chloride in a poly(N-vinyl pyrrolidone) binder this is coated over cresol novolac film on a silicon wafer substrate. The diazonium compound diffuses into the phenolic layer and is eventually partitioned in a uniform layer between the top layer and the phenolic resin. On exposure, the diazonium compound in the top layer bleaches and acts as a contrast-enhancement dye, while in the bottom it decomposes to the nonpolar 4-dimethylaminochlorobenzene, which acts as a dissolution inhibitor of the phenolic resin during development in aqueous-base solution. Line and space feature resolution of 0.5 p-m has been reported for this material. 

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Figure 3.18. Absorbance spectra of Meldrums diazo resist before and after exposure. Reproduced unth permission from reference 37. Copyright 1981 Institute of Electrical and Electronics Engineers.)...

Scheme 6.14 Photochemical transformation of N-iminopyridinium ylides. 6.3.4.S Diazo resists...

The dichromate resists as also the diazo resist systems developed later suffer from limited stability and limited exposure wavelength sensitivity and are very slow photographically. These have therefore been... 

The diazotization of amino derivatives of six-membered heteroaromatic ring systems, particularly that of aminopyridines and aminopyridine oxides, was studied in detail by Kalatzis and coworkers. Diazotization of 3-aminopyridine and its derivatives is similar to that of aromatic amines because of the formation of rather stable diazonium ions. 2- and 4-aminopyridines were considered to resist diazotization or to form mainly the corresponding hydroxy compounds. However, Kalatzis (1967 a) showed that true diazotization of these compounds proceeds in a similar way to that of the aromatic amines in 0,5-4.0 m hydrochloric, sulfuric, or perchloric acid, by mixing the solutions with aqueous sodium nitrite at 0 °C. However, the rapidly formed diazonium ion is hydrolyzed very easily within a few minutes (hydroxy-de-diazonia-tion). The diazonium ion must be used immediately after formation, e. g., for a diazo coupling reaction, or must be stabilized as the diazoate by prompt neutralization (after 45 s) to pH 10-11 with sodium hydroxide-borax buffer. All isomeric aminopyridine-1-oxides can be diazotized in the usual way (Kalatzis and Mastrokalos, 1977). The diazotization of 5-aminopyrimidines results in a complex ring opening and conversion into other heterocyclic systems (see Nemeryuk et al., 1985). 

The stripping of fully developed azoic dyeings can often be carried out using a hot solution of sodium hydroxide (1.5-3 g/1), sodium dithionite (3-5 g/1) and a surfactant addition of anthraquinone (0.5-1 g/1) generally increases the effectiveness of the process. Yellow azoic dyeings are resistant, however, and can only be partially stripped [30]. On the other hand, stripping of naphtholated material before it has been coupled with the diazo component can be done quite effectively in boiling alkali. 

Indolizine is much more basic than indole (p Ta = 3.9 vs. —3.5), and the stability of the cation makes it less reactive and resistant to acid-catalyzed polymerization. Protonation occurs at C-3, although 3-methylindolizine protonates also at C-l. Introduction of methyl groups raises the basicity of indolizines. Electrophilic substitutions such as acylation, Vilsmeyer formylation, and diazo-coupling all take place at C-3. Nitration of 2-methylindolizine under mild conditions results in substitution at C-3, but under strongly acidic conditions it takes place at C-l, presumably via attack on the indolizinium cation. However, the nitration of indolizines often can provoke oxidation processes. 

As recommended laundering temperatures have tended to fall in recent years, a bleach consisting of sodium perborate activated by addition of tetra-acetylethylenediamine (4.110 TAED) has become an important component of household detergent formulations. This system is effective at temperatures as low as 40-50 °C. A recent study of the effects of TAED-activated peroxy bleaching on the colour fastness of azoic dyeings has demonstrated that the sensitivity of these products can be related to their chemical structure. Electron-donating substituents in the diazo component enhance resistance to oxidative attack under these conditions, as do the size and complexity of substituents present in the coupling component [110]. 

Tables 11 and 12 list the currently available non-laked monoazo yellow and orange pigments. Most of them carry a nitro substituent in the diazonium component, usually in ortho position relative to the azo bridge. The more migration-resistant Pigment Yellow 97 lacks a nitro group in its molecule. Seven monoazo yellow pigments are based on 2-nitro-4-chloroaniline or derivatives as a diazo component.

P.O.44 has lost most of its commercial importance and is at present only applied to a limited extent. This is also true for other pigments whose synthetic route involves 3,3 -dimethoxybenzidine as a diazo component. P.O.44 provides a very reddish orange shade, which is much redder than the color of the (3-naphthol pigment P.O.5. Although P.O.44 is more resistant to solvents than P.O.5, the reverse is true for lightfastness. Standardized letterpress proof prints containing P.O.44, for instance, equal step 3 on the Blue Scale, while equally deeply shaded P.O.5 prints equal step 6 on the Blue Scale. 

The formation of olehnic dimerization products as the main product is rare in the decomposition of diazo compounds, whereas formation of ketazine is virtually omnipresent. The authors explained these data by assuming that the hindered diarylcarbenes do not have accessible singlet counterparts, because the singlet would require a smaller carbene angle and incur severe aryl-aryl repulsion. As a result of severe steric hindrance and consequent resistance to external attack by solvent, the... 

The most popular positive resists are referred to as DQN, corresponding to then-photoactive compound (DQ) and base material (N), respectively. DQ stands for diazo-quinone, and N stands for novolac resin. The repeat unit of a novolac resin is shown in Figure 7.47. Novolacs normally dissolve in aqueous solutions, but combinations of... 

Several attempts have been made to redesign the traditional two-component near-UV positive resist systems to make them compatible with the deep-UV. Recall that the major problems associated with deep-UV exposure of conventional resists are related to non-bleaching of the o-quinonediazide sensitizer on exposure because of photoproduct absorbance, and strong absorption of the novolac resin. Willson and coworkers34 attempted to solve this problem using dissolution inhibitors based on 5-diazo Meldrums acid, which undergoes photochemical decomposition as follows ... 

Development of Resist Patterns. Development was done in AZ2401 developer diluted with 2 to 5 times its volume of water AZ2401 is an aqueous solution of KOH with a surfactant. When the resist films were exposed to electron beam doses of 5 iC/cm2 at 25 keV, it usually took 1.5 to 2.0 min for complete development of the images using a diazo-naphthoquinone sensitizer with o-chloro-cresol-formaldehyde Novolak resin in (1 3) AZ2401/water developer. With poly(2-methyl-l-pentene sulfone) the chlorinated Novolak resin exposed to I juC/cm2, it took 2.0 min in (1 4) AZ2401 developer for complete image development. 

Figure 2. SEM pictures of a composite resist made of a diazo-naphthoquinone sensitizer and o-chloro-m-cresol-formaldehyde Novolak resin after various doses (a) 7 , (b) 5 . 2, (c) 5 " 2...

Although the Novolak resin of the w-cresol-benzaldehyde failed to show a marked increase in CF4 plasma etching resistance, the Novolak resins of hydroxy-naphthalene-hydroxybenzaldehyde showed a remarkable increase in the plasma etching resistance. The resist films also yielded excellent patterns when used together with a diazo-naphthoquinone sensitizer almost non-diluted AZ2401 developer had to be used for image development due to the hydrophobic nature of the naphthalene group. 

The existence of an N—N bond in jjrimary nitramines is also proved by the fact that these substances are obtained by the oxidation of diazo compounds. Additional evidence that nitramines contain a nitro and not a nitrite group and hence have a structure different from R—N—ONO is provided by the fact that nitramines are relatively resistant to alkali, whereas nitrous esters are highly unstable. 

The compounds with a quinonoid structure differ from those with a diazo structure by their darker colour and lower chemical stability. They are for example easily decomposed by light and concentrated acids they are less resistant to heat and show a higher sensitiveness to impact, friction and flame than compounds with a diazo structure. 

Many modifications of this basic chemistry have been explored to tailor these resists to deep-UV radiation. For example, changes have been made in the sensitizer so that it bleaches in this wavelength region. Early work in this area was performed on diazo-Meldrum s acid (54) (see structure). This compound functioned as a deep-UV-bleachable dissolution inhibitor however, it was somewhat volatile and, consequently, could be depleted via evaporation during soft bake. More-recent studies have therefore focused on less-volatile sensitizers incorporating heteroatom substitution (55) and on increases in molecular weight (56). 

Treatment of ascorbic acid with p-n i irobenzenediazonium tetrafluor-borate in aqueous phosphate-buffered solution at pH 7 led to the stable 3-0-arenediazoascorbic acid 154, instead of a reaction of electron transfer. The diazo ether derivatives are stable over a wide range of pH and are resistant to nucleophilic displacement.350... 

In the stepwise synthesis of the unsymmetrical complex dye 13 [ 70236-60-1] [10], the azo dye made from diazotized l-amino-2-hydroxy-5-nitrobenzene and 1-phenyl-3-methyl-5-pyrazolone and the 1 1 chromium complex obtained from 6-nitro-l-diazo-2-hydroxynaphthalene-4-sulfonic acid and 2-naphthol are heated together at 80 °C for 5 h. The adduct is salted out with NaCl. A black powder is obtained that dyes wool and leather in dark brown shades. The resulting colors are fast, particularly on shrink-resistant wool. 

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