Cresol-formaldehyde novolac resin

Materials DNQ was synthesized by esterification of o-cresol formaldehyde novolac resin (Mw=900) and of l,2-diazonaphthoquinone-5-sulfonyl chloride. The esterification rate was ca. 0.4. The novolac-based resist used in EB lithography to compare with SPP was... 

Chart 2.2. This DQN system employs a cresol-formaldehyde novolac resin as the matrix material. The resin is rendered photosensitive by addition of a diazonaphthoquinone that undergoes photolysis to produce a ketene intermediate that rapidly reacts with water present in the resin to yield an inde-necarboxylic acid. The lipophilic diazoquinone serves to reduce the solubility of novolac films in aqueous base. Photolysis leads to production of an acidic photoproduct that renders exposed areas of the film soluble in aqueous base. 

Conventional positive photoresists consist of a matrix resin and a photoactive compound. The matrix resin is a cresol-formaldehyde novolac resin (structure 3.1) that is soluble in aqueous base solution, and the photoactive compound is a substituted diazonaphthoquinone (structure 3.2) that functions as a dissolution inhibitor for the matrix resin. As outlined in Scheme 3.1 (20), the photoactive compound undergoes a structural transformation upon UV radiation, known as WolflFrearrangement, foUowed by reaction with water... 

Cresol-formaldehyde, phenol-formaldehyde, and chlorinated cresol-formaldehyde novolac resins all undergo photo-oxidation upon UV-irradiation in air. The change of the carbon core level signals is shown in Fig. 8. The new IR band at about 1720 cm-, corresponding to formation of a carbonyl group, is also found after photo-oxidation of novolac resin. These oxidized layers of the novolac film are limited to a very shallow superficial surface only about 500 A thick, even after long deep UV irradiation, as discussed below in reference to photostabilization of resist images. 

Epoxy novolac resins are produced by glycidation of the low-molecular-weight reaction products of phenol (or cresol) with formaldehyde. Highly cross-linked systems are formed that have superior performance at elevated temperatures. 

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. 

For positive resists, mixtures of 1,2-naphthoquinone diazides with phenolic resins, mainly the polymer from 3-cresol and formaldehyde (Novolac), are used. 

Trimethylsilylmethylphenol and o-cresol were obtained from Petrarch Systems, Inc. and Aldrich Chem. Co. Inc., respectively. Silylated novolac (Sl-novolac) resins were prepared by condensation polymerization of p-trimethylsilylmethyl phenol, o-cresol and formaldehyde. Poly(2-methyl-l-pentene-sulfone) (PMPS) was prepared as described in the literature (12). 

One of the major uses of ortho-cresol is for manufacture of epoxy-cresol-novolac (ECN) resins CAS No. [37382-79-9]. The acidic reaction of less than an equimolar concentration of formaldehyde with o-cresol yields cresol-novolac resins. 

The epoxy-cresol—novolaks resins are prepared by glyci-dylation of o-cresol-formaldehyde condensates in the same manner as phenol-novolak resins, o-cresol-formaldehyde condensates are prepared under acidic conditions with HCHO-o-cresol ratios of less than unity. The o-cresol novolacs of commercial significance possesses degrees of polymerization, n, of 1.7-4.4 and the epoxide functionality of the resultant glycidylated resins varies from 2.7 to 5.4. Softening points (Durrain s) of the products are 35-99°C [31]. 

These resins (Resole or Novolac) are used as curing agents or hardeners for epoxy molding compounds for electronics applications such as computer components. 0-cresol-formaldehyde resins have heen also used to modify phenol-formaldehyde resins, and in laminates. 

Novolac Preparation Novolac resins were prepared by an acid catalyzed condensation of m- and p-cresols with formaldehyde. A three necked flask with a distillation reflux condenser, thermometer and mechanical stirrer was charged with m- and p-cresols, formaldehyde aqueous solution, and cone, hydrochloric acid as a catalyst. The flask was immersed in an oil bath and heated to 90 C and kept for 2 hours while undergoing stirring. After the flask was cooled to room temperature on standing, the supernatant layer of the contents was removed by decantation. Then the volatile components were eliminated by distillation under a nitrogen gas flow and slow heating to 175°C. The molten content was poured into a stainless steel tray to cool. 

The resin most often used with DNQ resists is the reddish-colored novolac (cresol-formaldehyde condensation polymers). The resins adhere well to most metal surfaces and form good films. Additionally, they are soluble in alkaline solutions and many common solvents, and they are capable of coupling with the DNQ sensitizer. The structure of novolac (X) is shown below. °... 

Novolac resins are produced commercially from cresol mixtures that contain amounts of m-cresol and p-cresol isomers in varying proportions, depending on the specific application. The reaction proceeds with both metal cation and acid catalysis (Scheme 1.1) Because of strict guidelines for metallic contaminants in semiconductor grade process materials and chemicals, acid catalysis is employed in the synthesis of novolacs used in photoresist applications. In a typical commercial production process, a mixture of m- and p-cresol isomers, formaldehyde (most often in the form of formalin, a 35-40% aqueous solution of formaldehyde) and an oxalic acid catalyst are reacted, following the description of Pampalone ... 

The cresols are charged into the kettle and heated to 95°C, the catalyst is added and dissolved, and the formaldehyde is added over several hours to complete the exothermic reaction. The kettle is then heated to above 160°C and vacuum is drawn. Water and unreacted p-cresol are stripped off, residual oxalic acid decomposes to carbon dioxide, and only molten novolac resin remains in the kettle. The product is poured onto a cooling belt, and crushed. ... 

As discussed earlier in the secondary structure model, Templeton et al. have shown that the steric arrangement of the methylene links in the novolac resin can have a profound effect on its dissolution rate and on lithographic performance. Using molecular mechanics, these authors have calculated the equilibrium secondary structures of cresol-formaldehyde oligomers. They found that the secondary structure of these molecules determines the relative positions of the hydroxyl groups in the novolac matrix, and hence the possibility of intramolecular hydrogen bonding. ... 

Novolacs produces by cresol-formaldehyde condensation have been the polymers of choice for the DNS photochemistry. These novolac resins are usually synthesized from commercial cresol mixtures, which contain about 60% m-cresol, 30% p-cresol and 10% of various other aromatic phenols. 

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. 

Synonyms ECN Epoxy-cresol-novolac resin Poly ((o-cresyl glycidyl ether)-co-formaldehyde)... 

Thick Resist Lithography, Fig. 2 Example of the structure of a novolac resin and the commercial production route for the polymer that is typically accomplished via the acid-catalyzed polymerization of cresols with formaldehyde... 

Novolac resin Novolac resin Single 7g I was formaldehyde and 13/17/ 70 mol% = p-t-butyl phenol/m-cresol/ -cresol II was formaldehyde and 15/85 mol% = 2-t-butyl phenol/ o-cresol I and II had 0.8-1.6 kg/mol Fahrenhlotz and Kwei (1981)... 

Epoxy NovolaC Resins. Epoxy novolacs are multifunctional epoxies based on phenolic formaldehyde novolacs. Both epoxy phenol novolac resins (EPN) and epoxy cresol novolac resins (ECN) have attained commercial importance (53). The former is made by epoxidation of the phenol-formaldehyde condensates (novolacs) obtained from acid-catalyzed condensation of phenol and formaldehyde (see Phenolic Resins). This produces random ortho- and para-methylene bridges. 

DNQ-Novolac Photoresists. The bulk of the world s semiconductor processing is carried out using DNQ-novolac resin based photoresists and exposure tools equipped with mercury arc lamp illumination sources (producing uv wavelengths of 365 or 436 nm) (21). These photoresists consist of a photoactive DNQ dispersed in a phenolic matrix resin (a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac) (Fig. 3). The phenolic stmc-ture 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, typically by 2-3 orders of magnitude. Photolysis causes the DNQ to undergo a multistep reaction sequence (a photochemical Wolff... 

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