Alkaline Development

A further variant of silver staining of proteins resulting in some other color of protein bands has been described by Heukeshoven and Dernick. 

A 10% (v/v) acetic acid, 30% (v/v) ethanol in H2O B 6.8 g sodium acetate, 0.2 g Na2S203 5H2O (fixing salt) dissolved in 60 ml ddH20, then 0.5 ml 25% glutareddehyde is added. 30 ml of ethanol are followed and ddH20 is filled up to 100 ml. 

25% AgNOs (w/v) in ddH20, supplemented with 4 pi 37% formaldehyde per 10 ml immediately before use. 

After electrophoresis, the gel is fixed in Soln. A for 30 min, then it is equilibrated at least for 30 min or overnight in Soln. B. Next the gel is washed with ddH20 three times for 5 min and agitated in Soln. C 

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The process by which a solubility differential between exposed and unexposed areas occurs is well known (74). Photodegradation products of the naphthoquinone diazide sensitizer, eg, a l,2-naphthoquinonediazide-5-sulfonic acid ester (11), where Ar is an aryl group, to an indene carboxylic acid confers much increased solubility in aqueous alkaline developer solutions. 

The most widely used positive resists are those that operate on the basis of a dissolution inhibition mechanism. Such resists are generally two-component materials consisting of an alkali soluble matrix resin that is rendered insoluble in aqueous alkaline solutions through addition of a hydrophobic, radiation-sensitive material. Upon irradiation, the hydrophobic moiety may be either removed or converted to an alkali soluble species, allowing selective removal of the irradiated portions of the resist by an alkaline developer. 

A photosensitive composition, consisting of an aromatic azide compound (4,4 -diazidodi-phenyl methane) and a resin matrix (poly (styrene-co-maleic acid half ester)), has been developed and evaluated as a negative deep UV resist for high resolution KrF excimer laser lithography. Solubility of this resist in aqueous alkaline developer decreases upon exposure to KrF excimer laser irradiation. The alkaline developer removes the unexposed areas of this resist. 

We have found the combination of the azide compound and the styrene resin is well suited for achieving high resolution and high aspect ratio patterns using KrF excimer laser stepper system, because of the absence of swelling-induced pattern deformation during alkaline development and the suitable optical density at 248 nm in terms of sensitivity. 

In order to determine the appropriate development conditions, we examined dissolution characteristics for resist films in the aqueous alkaline developers by measuring film thickness as a function of development time. In Figure 7, dissolution characteristics for the new resist before and after exposure to KrF excimer laser are compared with those for the styrene resin matrix. 

This indicates that the thermally or photochemically decomposed azide (Figure 4) inhibits the dissolution of the styrene resin into the alkaline developer. The inhibition may be due to the increase of the molecular weight of the styrene resin in the presence of the decomposed azide. Hydrogen abstraction from the polymer by nitrene of the decomposed azide and subsequent polymer radical recombination result in a increase in the molecular weight of the polymer (17). 

Bulky AlkyllAryl Substituted Phenol-Formaldehyde Novolak Resins. Low molecular weight cresol-formaldehyde Novolak resins tend to have high solubility rates in alkaline developers. To increase developer resistance, Novolak resins containing a hydrophobic chain incorporated on a portion of the phenol group were synthesized, as shown below (17). As the number of alkyl... 

Figure 1 shows the exposure characteristics of atactic and isotactic poly(a,a-dimethylbenzyl methacrylate) resists with CH3ONa development together with those of the poly (methyl methacrylate) resist with MIBK/IPA development. Poly(a,a-dimethylbenzyl methacrylate) s showed high sensitivity and very good contrast between exposed and unexposed areas. The atactic polymer with alkaline development was improved in the sensitivity and 7-value by a factor of more than three over poly(methyl methacrylate) with MIBK/IPA development. 

Table VII the electron-beam exposure characteristics are given for the soluble poly (triphenylmethyl methacrylate-co-methyl methacrylate)s. The sensitivity on alkaline development was strongly influenced by the copolymer composition. The highest sensitivity was obtained on the copolymer containing 93.7 mol% methyl methacrylate. The copolymer of highest sensitivity showed the 7-value of 6.3, which was nearly twice as large as that for poly(methyl methacrylate). Formation of methacrylic acid units on exposure is obvious from the infrared spectrum. However, the mechanism of the occurrence should be different from the case of the a,a-dimethylbenzyl methacrylate polymer since there are no /3-hydrogen atoms in the triphenylmethyl group, and may be similar to the case of poly (methyl methacrylate). This will be explored in the near future.

From this result on MRS, we expected that a combination of phenolic-resin-based resist and aqueous alkaline developer would lead to etching-type dissolution and non-swelling resist patterns. In this paper, we report on a new non-swelling negative electron beam resist consisting of an epoxy novolac, azide compound and phenolic resin matrix (EAP) and discuss the radiation chemistry of this resist. 

A resin which enhances a solubility of the resin in an alkaline developer by an action of an acid, and... 

Two types of material have been employed. In a so-called one-component system the material essentially comprises the diazonium salt, with the coupler incorporated into the alkaline developing solution. Alternatively, a two-component material contains both the diazonium salt and the coupler in the coated layer. 

An advantage of this alkali is the almost proportionate change in developer activity with varying alkali concentration, permitting precise adjustments of the activity of a moderately alkaline developer. 

Uses As a restrainer in alkaline development used in several copper toning baths. 

NOTE A white scum of calcium sulfite may occur on films processed in high-sulfite, low-alkalinity developers. This scum is soluble in acid stop baths and in fresh acid fixing baths, especially if the film is well agitated. It is slowly soluble in water and may also be wiped or sponged off wet film, although light deposits may not be noticed until the film is dry. Kodak SB-5 Non-swelling Acid Rinse Bath is recommended for its removal. 

Fig. 3. Exposure characteristics of MRS obtained by aqueous alkaline development. O molecular weight MRS (Mw=7.4x10 ). standard molecular weight MRS (Mw=6.7x10 ).

Fig. 7. SEM photographs of MRS patterns during alkaline development. Patterns 0.4 ym line and space. Dose 40 yC/cm. Developer 0.72 wt.% TMA solution.

Reichmanis et al. (38, 40), Wilkins et al. (39), and Chandross et al. (41) redesigned both the dissolution inhibitor and the matrix resin. They evaluated a variety of o-nitrobenzylcholates (structure 3.6) that are initially insoluble in alkaline developer but are cleaved upon UV radiation to form base-soluble species. As shown in Scheme 3.3, irradiation of the o-nitro-benzyl ester results in rearrangement and degradation to generate a carboxylic acid and o-nitrosobenzaldehyde (R = H in Scheme 3.3) (42). The matrix resin chosen is a copolymer of methyl acrylate and methacrylic acid that is far more transparent in the DUV than novolac resins and is soluble... 

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