Poly Novolak resins

Alkylated phenol derivatives are used as raw materials for the production of resins, novolaks (alcohol-soluble resins of the phenol—formaldehyde type), herbicides, insecticides, antioxidants, and other chemicals. The synthesis of 2,6-xylenol [576-26-1] h.a.s become commercially important since PPO resin, poly(2,6-dimethyl phenylene oxide), an engineering thermoplastic, was developed (114,115). The demand for (9-cresol and 2,6-xylenol (2,6-dimethylphenol) increased further in the 1980s along with the growing use of epoxy cresol novolak (ECN) in the electronics industries and poly(phenylene ether) resin in the automobile industries. The ECN is derived from o-cresol, and poly(phenylene ether) resin is derived from 2,6-xylenol. 

Apart from multi-level layer resist systems, conventional positive-tone resists can be classified into two categories one-component and two-component systems. Classical examples of the former systems are polyfmethyl methacrylate), and poly (butene-1-sulfone) (2,3). Typical examples of the latter system are AZ-type photoresists, which are mixtures of cresol-formaldehyde-Novolak resins and a photoactive compound acting as a dissolution inhibitor... 

When two polymeric systems are mixed together in a solvent and are spin-coated onto a substrate, phase separation sometimes occurs, as described for the application of poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor for a Novolak resin (4). There are two ways to improve the compatibility of polymer mixtures in addition to using a proper solvent modification of one or both components. The miscibility of poly(olefin sulfones) with Novolak resins is reported to be marginal. To improve miscibility, Fahrenholtz and Kwei prepared several alkyl-substituted phenol-formaldehyde Novolak resins (including 2-n-propylphenol, 2-r-butylphenol, 2-sec-butylphenol, and 2-phenylphenol). They discussed the compatibility in terms of increased specific interactions such as formation of hydrogen bonds between unlike polymers and decreased specific interactions by a bulky substituent, and also in terms of "polarity matches" (18). In these studies, 2-ethoxyethyl acetate was used as a solvent (4,18). Formation of charge transfer complexes between the Novolak resins and the poly (olefin sulfones) is also reported (6). 

Formulation of Resist Solutions. Forty grams of a Novolak resin was mixed with 10 g of the photoactive compound, and dissolved in 100 g of bis-2-methoxy-ethylether. After wafers were spin-coated, the samples were immediately placed on a hot plate at 82 C for 14 min. The formulation procedure of a composite resist of poly (2-methyl-1-pentene sulfone) in the Novolak resin is as follows the polysulfone was mixed with the resin (13 wt% solid), and then dissolved in 2-methoxyethyl acetate the films were spin-coated onto silicon wafers, and then baked at 100°C for 20 min prior to electron beam exposure. 

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. 

For further enhancement of electron beam sensitivity, the chlorinated Novolak resin was studied using poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor. The chlorinated Novolak resin mixed well with the polysulfone, and there was no phase separation observed when the films were spin-coated. With 13 wt% of the polysulfone, the chlorinated Novolak resist cast from a cellosolve acetate solution yielded fully developed images with R/Ra = 9.2 after exposure to 2 / 2. It gave fully developed images with R/R0 = 3.2 at a dose of 1 / 2, as shown in Figure 3. There are some problems with this resist system some cracking of the developed resist images... 

Figure 3. SEM pictures of a composite resist made of poly (2-methyl-1 -pentene sulfone) and o-chloro-m-cresol-formaldehyde Novolak resin after electron beam exposures with doses of (a) 2 /xC/cm2, and (b) 1 fiC/cm2.

Poly(methylmethacrylate) is a well-known single component positive photoresist, whereas a diazoqui-none ester and a phenolic novolak resin is a two component positive photoresist. As anticipated, radiation will render the scission or rupture the main and side chain of the polymer making it soluble in an alkaline developing solution. Hydroxide solutions such as KOH and tetramethylammonium hydroxide are commonly used as the developer for positive photoresist. 

Dry Etch Resistance. Polyvinylnaphthalene and its derivatives were reported to be highly resistant to dry etching ( 9 ). Under Ar ion milling or CCl sputter etching conditions, etch rates for poly(2-vinylnaphthalene) were found to be about two-thirds of those for polystyrene or novolak resin resists. To find relationships between etch resistance and chemical structure, etch rate measurements for various metal-free polymers were made under Ar or C>2 ion beam incidence. It was found that the etch rate under ion bombardment depends linearly on N/(Nc -N0), where N denotes the total number of atoms in a monomer unit, Nc and N0 are the number of carbon atoms and the number of oxygen atoms in a monomer unit, respectively ( ). The dependence on "N/(NC-N0) factor" indicates that... 

Ordinary novolak, as discussed in Sect. 8.2, has a low thermal flow stability. During the bake treatment (120 °C), which is normally applied to developed resist patterns, thermal flow leads to deformation. Although this problem can be solved by hardening the pattern by chemical or physical means (see Sect. 3.2), many phenolic polymers with high T, have been studied as replacements for the novolak resin. For example poly (vinyl phenol) (T 160-180 °C) has been utilized in a commercially available... 

ABSTRACT. Six of poly(organophosphazenes) were prepared the reaction of polydlohlorophosphazene with alkoxldes, phenoxies or amines. Films of these polyphosphazenes were prepared on silicon wafers and were characterized by elllpsometry and ESCA. Detaile studies of plasma stability were conducted with poly(bisanilinophosphazene) which exhibited stabilities similar to novolak resin. 

Poly(olefin sulfone) chart 5.10 Chemical structures of polymeric dissolution inhibitors for novolak resins. 

Heat resistance is an important characteristic of the bond. The strength of typical abrasive stmctures is tested at RT and at 300°C. Flexural strengths are between 24.1 and 34.4 MPa (3500—5000 psi). An unmodified phenoHc resin bond loses about one-third of its room temperature strength at 298°C. Novolak phenoHc resins are used almost exclusively because these offer heat resistance and because the moisture given off during the cure of resole resins results in undesirable porosity. Some novolaks modified with epoxy or poly(vinyl butyral) resin are used for softer grinding action. 

Applications Van der Maeden et al. [646] first used GE-HPLC for the qualitative and quantitative analysis of oligomeric mixtures, such as low-MW resins (epoxy up to 16-mer, o-cresol novolak up to 16-mer, p-cresol novolak up to 13-mer), prepolymers (poly-(2,6-diphenyl-p-phenylene oxide) up to 20-mer), PET (up to 14-mer) and ethoxylated octaphenol surfactants (up to 19-mer). In many GE-HPLC separations of oligomeric mixtures, a compromise has to be found between sample loading, injection volume and compatibility of the sample solvent and the initial phase system. Therefore,... 

Ma C M, Lee C and Wu H (1998), Mechanical properties, thermal stability, and flame retardance of pultruded fiber-reinforced poly(ethylene oxide)-toughened novolak-type phenolic resin , J Appl Polym Sci, 69, 1129-1136. 

For applications, where a high resolution is required, e.g. IC technology and optical recording, resist systems based on novolak (a cresol-formaldehyde resin) or poly(vinyl phenol) are utilized. These resists are developed in aqueous base, which causes no swelling of the polymer and therefore no loss of pattern definition. 

After having discussed the photochemistry involved in a number of photoresists and their technological applications, we will consider in some more detail the role of polymers in photoresist systems. The most familiar polymers in photoresist are poly(vinyl alcohol), poly(vinyl cinnamate), poly(isoprene) and novolak. These resins are manufactured on an industrial scale according to general procedures, but the exact conditions, applied in the production process are mainly proprietary to the manufacturers. 

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