Solutions, formaldehyde Resistivity

The workhorse of the VLSI industry today is a composite novolac-diazonaphthoquinone photoresist that evolved from similar materials developed for the manufacture of photoplates used in the printing industry in the early 1900 s (23). The novolac matrix resin is a condensation polymer of a substituted phenol and formaldehyde that is rendered insoluble in aqueous base through addition of 10-20 wt% of a diazonaphthoquinone photoactive dissolution inhibitor (PAC). Upon irradiation, the PAC undergoes a Wolff rearrangement followed by hydrolysis to afford a base-soluble indene carboxylic acid. This reaction renders the exposed regions of the composite films soluble in aqueous base, and allows image formation. A schematic representation of the chemistry of this solution inhibition resist is shown in Figure 6. 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

Aqueous formaldehyde is corrosive to carbon steel, but formaldehyde in the vapor phase is not. AH parts of the manufacturing equipment exposed to hot formaldehyde solutions must be a corrosion-resistant alloy such as type-316 stainless steel. Theoretically, the reactor and upstream equipment can be carbon steel, but in practice alloys are required in this part of the plant to protect the sensitive silver catalyst from metal contamination. 

A Methylolhydantoins. l,3-Bis(hydroxymethyl)-5,5-dimethyIhydantoia [6440-58-0] is used extensively as a preservative in cosmetic and industrial appHcations, and carries EPA registration for the industrial segment. It is available in soHd and in aqueous solution forms, including low free formaldehyde versions of the latter. A related derivative, l,3-bis(hydroxyethyl)-5,5-dimethyIhydantoia [26850-24-8] is used in the manufacture of high temperature polyesters, polyurethanes, and coatings, offering improved heat resistance, uv stabiUty, flexibiUty, and adhesion. 

Their performance falls short of most present finishes, particularly in durabiUty, resistance to chlorine-containing bleaches, and formaldehyde release, and they are not used much today. Both urea and formaldehyde are relatively inexpensive, and manufacture is simple ie, 1 —2 mol of formaldehyde as an aqueous solution reacts with 1 mol of urea under mildly alkaline conditions at slightly elevated temperatures. 

Textiles. Sorbitol sequesters iron and copper ions in strongly alkaline textile bleaching or scouring solutions (see Textiles). In compositions for conferring permanent wash-and-wear properties on cotton fabrics, sorbitol is a scavenger for unreacted formaldehyde (252) and a plasticizer in sod-resistant and sod-release finishes (253). 

The chemical resistance of the mouldings depends on the type of filler and resin used. Simple phenol-formaldehyde materials are readily attacked by aqueous sodium hydroxide solution but eresol- and xylenol-based resins are more resistant. Provided the filler used is also resistant, phenolic mouldings are resistant to acids except 50% sulphurie aeid, formic acid and oxidising acids. The resins are stable up to 200°C. Some reeently developed grades of moulding compounds are claimed to be capable of exposure to 300°C for short periods. 

Phenolic coatings Phenolic is reacted with formaldehyde under heat to form a completely insoluble material. They are usually applied in an alcohol solution by spray, dip or roller. During their curing, they release water, which must be removed. They have maximum chemical and solvent resistance but poor alkaline resistance. 

When samples of about 1 cm were taken from a single cast film of 100 X 200 mm of a number of paint and varnish films, their resistances varied with the concentration of potassium chloride solution in one of two ways (Fig. 14.2). Either the resistance increased with increasing concentration of the electrolyte (inverse or / conduction) or the resistance of the film followed that of the solution in which it was immersed (direct or D conduction). The percentage of / and D samples taken from different castings varied, but average values for a number of castings were 50% D for the pentaerythritol alkyd and the tung oil phenol formaldehyde varnishes, 57% for urethane alkyd, 76% for epoxypolyamide and 78% for polyurethane varnishes... 

Cured phenol-formaldehydes are resistant to attack by most chemicals. Organic solvents and water have no effect on them, though they will swell in boiling phenols. Simple resins are readily attacked by sodium hydroxide solutions, but resins based on phenol derivatives, such as cresol, tend to be less affected by such solutions. Simple phenol-formaldehyde polymers are resistant to most acids, though formic and nitric acids will tend to attack them. Again, cresol-based polymers have resistance to such attack. 

Vinyl substituted cyclic hemlamidals 2 and their Interconvertible acetal precursors (eg. acrylamldo-butyraldehyde dimethyl acetal 1) were Incorporated as latent crosslinkers and substrate reactive functional comonomers In solution and emulsion copolymers. Some use and applications data for copolymers prepared with these new monomers are presented. They show low energy cure potential, long shelf life and high catalyzed pot stability In solvent and aqueous media, good substrate reactivity and adhesion, and good product water and solvent resistance. They lack volatile or extractable aldehyde (eg. formaldehyde) components and show enhanced reactivity and hydrolytic stability with amines and diol functional substrates. 

A dip technique in which metallic Ag films were converted into Ag2Se was described [95]. The Ag film was made by successive dipping of glass substrates in a AgNOs solution, followed by dipping in a solution of formaldehyde, and was converted to the sulphide by treatment with a solution of Se02. The films were rough and apparently poorly adherent. The resistivity of the films was ca. 10 H-cm. 

The structural variations of Novolak resins also influence how well they mix or form solid solutions with a dissolution inhibitor when resist films are cast onto substrates. This is a crucial problem for resist formulation. Usually, cresol-formaldehyde Novolak resins mix well with photoactive compounds like a... 

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. 

A procedure based on condensation with phenol and paraform (used as formaldehyde source) was developed to convert spent UNEX solvent (CCD, PEG-400, Ph2-CMPO, and FS-13) into a solid infusible resin for disposal. The resulting material is insoluble in aqueous alkali and acidic solutions and organic solvents. Incorporation of FS-13 in the cross-linked polymer was confirmed by physicochemical methods. Resistance of the cured resin to high temperatures was proven by thermogravimetry... 

Sterilization of a membrane system is also required to control bacterial growth. For cellulose acetate membranes, chlorination of the feed water is sufficient to control bacteria. Feed water to polyamide or interfacial composite membranes need not be sterile, because these membranes are usually fairly resistant to biological attack. Periodic shock disinfection using formaldehyde, peroxide or peracetic acid solutions as part of a regular cleaning schedule is usually enough to prevent biofouling. 

Fire-retardant chemicals used by the commercial wood-treating industry are limited almost exclusively to mono- and diammonium phosphate, ammonium sulfate, borax, boric acid, and zinc chloride (4,8). It is believed that some use is also made of the liquid ammonium polyphosphates (9). Some additives such as sodium dichromate as a corrosion inhibitor are also used. Aqueous fire-retardant treatment solutions are usually formulated from two or more of these chemicals to obtain the desired properties and cost advantages For leach-resistant type treatments, the literature shows that some or all of the following are used urea, melamine, dicyandiamide, phosphoric acid, and formaldehyde (10-12) ... 

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