Selected trinuclear novolak oligomers

Abstract: A trinuclear novolak oligomer characterized by the formula (I): wherein each X is selected from the group consisting of hydrogen, hydroxyl group and halide group and Y is selected from the group consisting of a lower alkyl group having 1-4 carbon atoms and a halogen atom.

Description: The present invention relates to selected trinuclear novolak oligomers useful as backbones for certain photoactive compounds. Photoresist compositions are used in microlithographic processes for making miniaturized electronic components such as in the fabrication of integrated circuits and printed wiring board circuitry. In these processes, a thin coating or film of a photoresist composition is generally first applied to a substrate material, such as silicon wafers used for making integrated circuits or aluminum or copper plates of printed wiring boards. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure of radiation. This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam, ion beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the coated surface of the substrate. In some processes, it is desirable to bake the imaged resist coating before this developing step. This intermediate step is sometimes called post-exposure bake or PEB. There are two types of photoresist compositions--negative-working and positive-working. When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to a developing solution. Thus, treatment of an exposed negative- working resist with a developer solution causes removal of the non-exposed areas of the resist coating and the creation of a negative image in the photoresist coating, and thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited. On the other hand, when positive-working photoresist compositions are exposed image-wise to radiation, those areas of the resist composition exposed to the radiation become more soluble to the developer solution (e.g. the Wolff rearrangement reaction of the photactive compound occurs) while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working resist with the developer solution causes removal of the exposed areas of the resist coating and the creation of a positive image in the photoresist coating. Again, a desired portion of the underlying substrate surface is uncovered. Positive-working photoresist compositions are currently favored over negative-working resists because the former generally have better resolution capabilities and pattern transfer characteristics. After this development operation, the now partially unprotected substrate may be treated with a substrate-etchant solution or plasma gases and the like. This etchant solution or plasma gases etch the portion of the substrate where the photoresist coating was removed during development. The areas of the substrate are protected where the photoresist coating still remains and, thus, an etched pattern is created in the substrate material which corresponds to the photomask used for the image-wise exposure of the radiation. Later, the remaining areas of the photoresist coating may be removed during a stripping operation, leaving a clean etched substrate surface. In some instances, it is desirable to heat treat the remaining resist layer after the development step and before the etching step to increase its adhesion to the underlying substrate and its resistance to etching solutions. End users of photoresists are demanding photoresist formulations which possess better lithographic properties for the fabrication of smaller microelectronic circuits. The lithographic properties which are critical to these end-users include the following: (1) good resolution capabilities in both the micron and submicron ranges without incomplete development in the exposed areas (i.e. scumming); (2) higher thermal image deformation temperatures (e.g. above 120°C); (3) relatively fast photospeeds; (4) good adhesion to substrate; (5) good developer dissolution rates; (6) good process latitute; (7) near to absolute vertical profiles (or good contrast) between exposed and unexposed photoresist areas after development; (8) good resistance to etching solutions and plasma etching techniques; (9) reduced tendency to form insoluble particulates and (10) mask linearity. FR 2318852 discloses bis (dihydroxyphenylmethyl) chlorophenol preparations. These are used as dip baths for polyester cord for reinforcing rubber. US 4,614,826 discloses polynuclear polyhydricphenols. These are used for adhesives, paints, circuit board and construction laminates, electronics sealants, moulding materials, etc. Generally, in the past efforts to improve one of these lithographic properties have caused significant decreases in one or more of the other lithographic properties of the photoresist. Accordingly, there is a need for improved photoresist formulations which possess all of these desired properties. The present invention is believed to be an answer to that need. In the past, reactions between 2,6-bis(hydroxymethyl)-p-cresol and alkyl monohydric phenols to form novolak oligomers have been known. These novolak oligomers were then reacted with 6-diazo-5,6-dihydro-5-oxo-1-naphthalene-1-sulfonic acid to form a photoactive compound and then used to make a positive-working photoresist. See Japanese Patent Publication (Kokai) No. 62-10646(A) assigned to Kanto Chemical Company and published on January 19, 1987. One of the novolak oligomers taught by this reference has the following formula (PA-I): Separately, reaction between 2,6-bis(hydroxymethyl) -p-cresol and resorcinol to form oligomeric polyhydric phenol novolaks were then reacted with epihalohydrin or the like to form a polyglycidic ether which was combined with curing agent to form a curable epoxy resin composition. See U.S. Patent No. 4,614,826, which issued to Katayama et al on September 30, 1986. The reaction product of 2,6-bis(hydroxymethyl)-p-cresol and resorcinol according to this reference has the following chemical formula (PA II): Accordingly, the present invention is directed to selected trinuclear novolak oligomers of formula (I): wherein each X is selected from the group consisting of hydroxyl group and halogen group (i.e. Cl, Br, I and F); and Y is selected from the group consisting of a lower alkyl group having from 1 to 4 carbon atoms and halogen atom, with the proviso that when Y is lower alkyl and X is hydroxyl, X is in the 3-position. The selected trinuclear novolak oligomers of formula I are made by reacting the corresponding -para-(lower alkyl or halo)-2,6-bis(hydroxymethyl) phenol (preferably 2,6-bis(hydroxymethyl)-p-cresol) with a polyhydroxy phenyl compound (preferably 4-chlororesorcinol and pyrogallol). This reaction is illustrated below in reaction equation (A) wherein X and Y are defined as above: In making this class of novolak oligomers of the present invention, the precursors are preferably present in the reaction vessel in a mole ratio of polyhydroxy phenyl compound or compounds to the 2,6-bis(hydroxymethyl)phenol compound or compounds from about 5:1 to about 20:1, preferably from about 10:1 to about 15:1. The preferred reaction temperature is about 60-100°C for about 2 to 6 hours at atmospheric pressure. Preferably, this reaction occurs in the presence of a solvent and an acid catalyst. The preferred solvent is water. Suitable acid catalysts include those commonly employed in acid condensation-type reaction such as HCl, H 3 PO 4 , H 2 SO 4 , oxalic acid, maleic acid, maleic anhydride and organic sulfonic acids (e.g. p-toluene sulfonic acid). The most preferred acid catalyst is p-toluene sulfonic acid. Excess reaction time may cause undesirable poly- merization of the intended product. The preferred ratio of total solids to water is preferably about 0.1 grams to about 0.5 grams total solids per milliliter of solvent. This condensation reaction will form a mixture of oligomeric novolak species of different molecular weight. When a large molar excess of the polyhydroxy phenyl compound precursor is employed, the major portion by weight of product mixture is the trinuclear novolak oligomer of formula (I). The present invention encompasses both substantially pure trinuclear novolak oligomers of formula (I) as well as mixtures of such trinuclear novolaks with other species formed by this condensation reaction. The intended product may be recovered from the reaction mixture by first cooling to room temperature or less, then diluting the reaction mixture with more solvent (i.e. water) and then isolating the solid product by filtration. This crude product may be washed with water and directly dried or, alternatively, after isolation it may be redissolved in acetone and filtered before solvent evaporation. The preferred novolak oligomers are made from the reaction of 2,6-bis(hydroxymethyl)-p-cresol; with 4-chlororesorcinol (see formula IB); and with pyrogallol (see formula IC); all of which are as follows: Examples of the preparation of Photoactive Compounds using novolak oligomers are disclosed in the parent copending application number EP 90900597.7. The present invention is further described in detail by means of the following Examples. All parts and percentages are by weight unless explicitly stated otherwise. Example 1 Novolak Oligomer A 2.6-bis[(5-chloro-2.4-dihydroxyphenyl) methyl]-4-methylphenol A one liter three-necked reaction flask was fitted with a mechanical stirring apparatus, a Y arm, and a thermometer. To the flask was added 2,6-bis(hydroxymethyl)-p-cresol (recrystallized once from ethanol) (25.25 g, 0.15 mole), 4-chlororesorcinol (216.8g, 1.50 mole), p-toluene sulfonic acid monohydrate (1.0 g), and water (300 mL). The reaction mixture was stirred and heated and to about 80°C and maintained at about 80°C for four hours. The reaction mixture was cooled to room temperature and diluted with water (300 mL). The precipitated product was isolated by filtration and washed with water (3 L). The solid product was air-dried at room temperature, dissolved in acetone (150 mL), filtered, and precipitated into water (2 L). The precipitate was isolated and air-dried at 50 degrees C to leave 50 g solid, 78% of theory. The titled compound's purity and structure were established by its liquid chromatogram and its proton NMR and carbon NMR spectra. The liquid chromatogram was obtained using a 5 micron 4.5 mm X 250 mm C 8 end capped column. The mobile phase used is 45% HISB (high ionic strength buffer) 55% acetonitrile. The high ionic strength buffer is made from trifluoroacetic acid anhydride (1.5 mL), tetramethylammonium hydroxide pentahydrate (1.8 g) and water (1 L). The pH of this solution is adjusted to 3.0 ± 0.1 with sodium hydroxide (0.1N). The flow is 2.5 mL/min. The chromatogram exhibited the following major peaks reported as retention time in minutes and (area percent); 2.1 min. (4.5%), 2.6 min. (67.9%), 4.4 min. (4.5%), 6.3 min. (6.1%). The proton NMR of this oligomer was recorded in acetone d 6 with tetramethylsilane (TMS) as the internal standard. The chemical shifts of the major signals (all singlets) are reported as parts per million (ppm) downfield from TMS; 2.15 ppm, 3.82 ppm, 6.59 ppm, 6.87 ppm, 7.09 ppm. The carbon-13 NMR spectrum of the above solid was recorded in dimethylsulfoxide-d 6 with tetramethylsilane (TMS) as the internal standard. The chemical shifts of the major signals are reported in parts per million (ppm) downfield from the TMS; 20.30 ppm, 28.79 ppm, 103.43 ppm, 109.23 ppm, 119.32 ppm, 127.50 ppm, 127.64 ppm, 128.32 ppm, 130.12 ppm, 149.86 ppm, 151.40 ppm, 154.01 ppm. Comparative Example 2 Novolak Oligomer B 2,6-Bis[(2,4-dihydroxyphenyl)methyl] -4-methylphenol A one liter three-neck flask was fitted a mechanical stirring apparatus, a Y-arm and thermometer. To the flask was added 2,6-bis(hydroxymethyl)-p-cresol(recrystallized once from ethanol) (8.41 g 0.05 mole), resorcinol (82.6 g, 0.75 mole), p-toluene sulfonic acid monohydrate (1.37 g) and water (230 mL). The stirring was begun and the contents of the flask were heated for four hours at 72-95°C. After cooling in an ice bath, the resulting solid was isolated by filtration, washed with water (1.5L) and dried at 40-50°C under vacuum in a nitrogen amosphere. The product weighed 13.3 g, 75% of theory. The titled substance's purity and identity were established from its liquid chromatogram, proton NMR and carbon-13 NMR spectra. The liquid chromatogram was obtained using a 10 cm Apex C 18 column. The mobile phase used is 55% HISB and 45% acetnitrile at a 1 mL/min. The chromatogram exhibited the following major peaks reported as retention time in minutes, and (area percent); 2.64 min. (83.0%), 7.44 min. (15.29%). The proton NMR of the substance was recorded in methanol-d 4 with tetramethylsilane (TMS) as the internal standard. The chemical shifts of the major signals are reported as parts per million (ppm) downfield from TMS; 2.1 ppm, 3.75 ppm, 4.9 ppm, 6.26 ppm (doublet of doublets), 6.33 ppm (doublet), 6.74 ppm, 6.87 ppm (doublet). A carbon-13 spectrum of the substance was recorded in mehanol-d 4 with tetramethylsilane (TMS) as the internal standard. The chemical shifts of the major signals are reported in ppm downfield from TMS; 20.71 ppm, 30.71 ppm, 103.37 ppm, 108.13 ppm, 119.99 ppm, 129.36 ppm, 129.68 ppm, 130.23 ppm, 131.97 ppm, 150.18 ppm, 155.82 ppm, 157.52 ppm. Example 3 Novolak Oligomer C 2,6-Bis-[(2,3,4-trihydroxyphenyl)methyl] -4-methylphenol A one liter, three neck flask was fitted with a mechanical stirring apparatus, a Y-arm and a thermometer. To the flask was added 2,6-bis-(hydroxymethyl)-p-cresol(recrystallized once from ethanol) (18.29 g, 0.1087 mole), pyrogallol (206 g, 1.63 mole), p-toluenesulfonic acid monohydrate (3.36 g), and water (800 mL). The stirring was begun and the mixture was heated to about 65°C and maintained at this temperature for four hours. After cooling in an ice bath, the resulting solid was isolated by filtration and dried under reduced pressure to leave 23 g solid, 55% of theory. The solid was dissolved in boiling water (200 mL), filtered, the solution concentrated to about 150 mL and allowed to recrystallize at room temperature. The solid was isolated by filtration and dried to leave 18.2 g. The titled compound's purity and identity was established by its liquid chromatogram, proton NMR and carbon-13 NMR spectra. The liquid chromatogram was obtained with an end capped C 8 5 micron, 4.5 X 250 mm column. The mobile phase used was 52% HISB and 48% acetonitrile at 1.5 mL/min. The chromatogram's major peaks are expressed as retention time in minutes and (area percent); 3.46 min. (2.9%), 4.02 min., (78.6%), 4.44 min., (6.12%), 5.49 min. (2.12%), 7.18 min. (9.30%). The proton NMR of this substance was recorded in methanol-d 4 with tetramethylsilane (TMS) as the internal standard. The chemical shifts of the major signals are reported in parts per million (ppm) downfield from TMS; 2.1 ppm, 3.8 ppm, 4.85 ppm, 6.3 ppm, 6.48 ppm, 6.75 ppm. The carbon-13 NMR spectrum of this substance was recorded in methanol-d 4 with tetramethylsilane (TMS) as the internal standard. The chemical shifts of the major signals are reported downfield from TMS; 20.71 ppm, 31.09 ppm, 108.34 ppm, 120.83 ppm, 121.28 ppm, 129.49 ppm, 129.72 ppm, 130.43 ppm, 134.17 ppm, 144.12 ppm, 145.29 ppm, 149.90 ppm. Comparative Example 4 Novolak Oligomer D 2,6-Bis[2,4,6-trihydroxyphenyl)methyl]-4-methylphenol] A 3 L three necked flask was fitted with a mechanical stirring apparatus, a Y arm, and a thermometer. To the flask was added 2,6-bis-(hydroxymethyl)-p-cresol (recrystallized once from ethanol) (25.26 g, 0.15 mole), phloroglucinol dihydrate (364.8 g, 2.25 moles), p-toluene sulfonic acid mono-hydrate (6.0 g) and water (2400 mL). Stirring was begun and the mixture was heated to 60°C and maintained at about 60°C for four hours. The reaction mixture was filtered at the end of the heating period and allowed to cool. The solid was isolated by filtration and was extracted with warm (about 45°C) water (3 X 2200 mL). The solid material remaining after extraction was dried in vacuum to leave 13 g of solid. The titled compound's purity and identity were established by its liquid chromatogram, proton NMR and carbon-13 NMR spectra. This substance's liquid chromatogram was obtained using 5 micron 4.5 mm X 250 mm endcapped C 8 column. The mobile phase was 52% HISB and 48% acetonitrile at 1.5 mL/min. The chromatogram exhibited the following major peaks reported as retention time in minutes and (area percent); 3.32 min. (86.13%), 4.43 min. (11.30%). The proton NMR of this substance was recorded in methanol-d 4 with tetramethylsilane (TMS) as the internal standard. The major signals are reported in parts per million (ppm) downfield from the TMS; 2.12 ppm, 3.82 ppm, 4.85 ppm, 5.95 ppm, 6.95 ppm. The carbon-13 NMR of this substance was recorded in methanol-d 4 with tetramethylsilane (TMS) as the internal standard. The major signals are reported in parts per million (ppm) downfield from the TMS; 20.86 ppm, 23.99 ppm, 95.83 ppm, 107.56 ppm, 128.88 ppm, 129.88 ppm, 130.16 ppm, 149.65 ppm, 157.22 ppm, 157.42 ppm.

Claims: A trinuclear novolak oligomer characterized by the formula (I): wherein each X is hydroxyl or a halogen group and Y is a lower alkyl group having 1-4 carbon atoms or a halogen atom, with the proviso that when Y is lower alkyl and X is hydroxyl, X is at the 3-position. The trinuclear novolak oligomer of claim 1 characterized by the formula:

Inventors: BLAKENEY ANDREW J, JEFFRIES ALFRED T III, TOUKHY MEDHAT A, BLAKENEY, ANDREW J., JEFFRIES, ALFRED T. III, TOUKHY, MEDHAT A.
Applicants: OLIN MICROELECTRONIC CHEM INC, OLIN MICROELECTRONIC CHEMICALS, INC.
Application year: 1989
Main classification: C08G8
IPC codes: C08G8, C07C39, G03F7