Novolac resins properties

I ovolac Synthesis and Properties. Novolac resins used in DNQ-based photoresists are the most complex, the best-studied, the most highly engineered, and the most widely used polymers in microlithography. Novolacs are condensation products of phenoHc monomers (typically cresols or other alkylated phenols) and formaldehyde, formed under acid catalysis. Figure 13 shows the polymerization chemistry and polymer stmcture formed in the step growth polymerization (31) of novolac resins. 

The polyglycol diepoxies are used primarily as flexibilizers and reactive diluents. Commercial products are available where n varies from 2 to 7. Generally, these are used in the range of 10 to 30 percent by weight with DGEBA or epoxy novolac resins to improve flexibility without a significant loss in physical properties. 

Epoxy novolac resins are polyglycidyl ethers of a novolac resin. They are prepared by reacting epichlorohydrin with a novolac resin (see Chap. 2). The most common epoxy novolacs are based on medium-MW molecules with phenol and o-cresol novolacs. They generally have significantly different properties from DGEB A epoxies because of the presence of the phenolic structure. 

This property has been widely utilized, and many kinds of silicon-containing resists have been reported as a result. Most of the new resists developed use silicon containing novolac resins with a sensitizer(4)(5). 

Table 59 Preparation Conditions and Properties of Novolac Resin (15)...

The thermoplastic phenolic resin in the above Eqs. (7)-(9) could be a novolac resin.Similarly, the commercial polyparaalkyl phenol, Xylok, has been used in Diels-Alder reactions with diimides. These systems have good processing properties, good mechanical properties, and superior thermal properties. 

Special considerations cobalt salts reduce UV and thermal stability steel fiber and acrylic fiber give the best wear retention to brake pads composites containing graphite have much better flame retarding properties than composites containing aramid or glass fiber glass fiber slows down the cure rates of novolac resins ... 

For an injection and extrusion molding application a poly(ester-imide) was patent protected, where the polyol is a novolac resin [45]. The product was claimed to have having improved char forming properties. 

The role of the novolac resin is not as minor as it may seem as a base-soluble binder. While the aromatic nature of the resin provides high dry etch resistance, the novolac structures and properties such as the ratio of o-cresol to m-cresol, the ratio of ortho to para backbone linkages, the molecular weight, and molecular weight distribution all affect the dissolution behavior, thermal flow resistance, and lithographic performance. The optimization of the novolac and diazonaphthoquinone properties in conjunction with the improvement of the i-line step-and-repeat exposure tools has pushed the resolution limit of photolithography to a sub-0.5-pm regime [4]. 

These novolac resins have exhibited enough balance in the needed binder properties mentioned above that they are now exclusively used in all commercial... 

Attempts have been made over time to improve the physical properties of novolacs. The use of phenol formaldehyde resins prepared in alkaline medium in photoresist compositions is mentioned in a Kalle Co. AG patent. The use of polyvinyl ethers in combination with novolacs to impart stickiness and plasticization action to the latter was patented by Christensen. Steinhoff, Isaacson, and Roelants of the Shipley Company mention the use of vinyl ethers in a patent on roller coating. Lower alkyl polyvinyl ethers, such as methyl, ethyl, butyl, and isobutyl, are added to novolac resins to improve coating flexibility and adhesion to metal surfaces as well as to improve resistance to mildly alkaline solutions. The use of styrene, methyl styrene, and styrene-maleic anhydride copolymers in combination with novolac was mentioned in several patents of both Shipley and Kalle Co. AG. When novolac is copolymerized with maleic anhydride, a resin that is readily soluble in alkaline solutions is obtained. ... 

One of the main advantages of DNQ/novolac resists over the bis-azide/rubber resist system that was responsible for the former superseding the latter is the fact that novolac does not swell during development and is therefore suitable for the printing of high-resolution patterns. Additionally, novolac resin is reasonably resistant to plasma, a very important property in semiconductor device fabrication. However, the thermal and mechanical properties of novolac are not outstanding its plastic flow temperature is around 120°C. Even here, the effects of isomer composition... 

The soft bake process can affect the solubility properties of some resists in the developing solvent. For instance, in DNQ/novolac resists, the solubility of the exposed resist as a function of prebake temperatures shows a maximum at around 120°C (Fig. 11.16). Four zones can be distinguished in this plot (i) a no-bake zone where residual solvent and dissolution rates are high, (ii) a low-temperature zone (up to 80°C) where the dissolution rate shows an appreciable decrease due to solvent removal, (iii) a mid-temperature zone (80-110°C) where the DNQ is thermally and preferentially converted to indene carboxylic acid, leading to an increase in dissolution rate, and (iv) a high-temperature zone (>120°C) where the film densification takes place, DNQ is thermally decomposed, the film is depleted of water, and the novolac resin is cross-linked, resulting in dramatic dissolution inhibition. ... 

Expanded materials with excellent high-temperature properties are obtained when cresol novolacs are used as hardeners. A typical formulation is based on mixtures of bisphenol A resins and epoxy novolac resins which are cured by cresol novolacs and accelerated by suitable nitrogen-containing agents. 

The novolacs are another class of epoxy resins. They are produced by reacting a novolac resin, usually formed by the reaction of o-cresol or phenol and formaldehyde with epichlorohydrin. Figure 3.5 shows the general structure. These materials are used as transfer molding powders, electrical laminates, and parts where superior thermal properties and high resistance to solvents and chemicals are required. 

Chem. Descrip. Bisphenol F-based epoxy novolac resin Uses Epoxy for high-solids and solv.-free industrial maintenance coatings, chem.-resist. flooring, groufs, and high-temp, adhesives and laminates inc. crosslink dens, and chem. resist, of ambient cured systems Properties Gardner 1 iiq. sp.gr, 1.19 dens. 9.9 Ih/gal vise. 16,000cps EEW 175 100% solids Epotuf 91-263 [Reichhold]... 

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