Conventional Novolak Research Articles

Novolak Type Phenol Formaldehyde Resin from Waste Brown-Rotted Wood

The waste brown-rotted wood was liquefied in phenol with phosphoric acid as a catalyst and the resulting liquefied products were condensed with formaldehyde to yield novolak liquefied wood-based phenol formaldehyde resin (LWF). The results showed that brown-rotted wood could be almost completely liquefied within 0.5 h at phenol to wood (P/W) ratio 2. An increase in P/W ratio from 2 to 3 slightly improved the flow property of LWF, but accompanied by decreasing the product yield from approximately 140 to 120 %. The increase of liquefaction time from 30 min to 60 min did not have a significant influence on the resulting LWF. The thermofluidity of LWF were compared to that of the commercial novolak PF resin, and could be used to make moldings with similar thermal property and mechanical properties to those obtained from the conventional novolak PF resin.

Linesize effects on ultraviolet reflectance spectra

We have investigated the effect of resist thickness, linewidth, and pitch on UV reflectance spectra. This technique exploits the property that conventional novolak resists are very absorptive from 200 to 300 nm, while substrates are significantly more reflective. For line-space developed resist features of constant pitch, we observe that the reflectance in this wavelength range varies periodically with ? and increases linearly with decreasing linesize. The dominant factor in wavelength dependence is the constructive/destructive interference of the measurement light from the air-resist and air-substrate interfaces. The linesize dependence at constant pitch and resist thickness is predominantly controlled (within proper boundary-condition regimes) by the percentage of the substrate exposed. The gross periodicity of the deep UV (DUV) reflection spectra for patterned films is correlated with resist thickness in a manner similar to the resist-thickness dependence of UV reflection spectra for unpatterned films. Simulation of DUV reflectance from patterned films showed semiquantitative agreement with experimental results.

Physical and mechanical characterization of near-zero shrinkage polybenzoxazines

A new class of phenolic-like thermosetting resins has been developed that is based on the ring-opening polymerization of a benzoxazine precursor. These new materials were developed to combine the thermal properties and flame retardance of phenolics with the mechanical performance and molecular design flexibility of advanced epoxy systems. The polybenzoxazines overcome many of the traditional shortcomings of conventional novolak and resoletype phenolic resins, while retaining their benefits. The physical and mechanical properties of these new polybenzoxazines are investigated and are shown to compare very favorably with those of conventional phenolic and epoxy resins. The ring-opening polymerization of these new materials occurs with either near-zero shrinkage or even a slight expansion upon cure. Dynamic mechanical analysis reveals that these candidates for composite applications possess high moduli and glass transition temperatures, but low crosslink densities. Long-term immersion studies indicate that these materials have a low rate of water absorption and low saturation content. Impact, tensile, and flexural properties are also studied. Results of the dielectric analysis on these polybenzoxazines demonstrate the suitability of these materials for electrical applications. © 1996 John Wiley & Sons, Inc.

Nanometer-scale imaging characteristics of novolak resin-based chemical amplification negative resist systems and molecular weight distribution effects of the resin matrix

Molecular weight distribution effects of novolak resin-based chemical amplification negative resist systems are investigated for electron-beam lithography. The resist systems investigated consist of onium salts as an acid generator, a methoxymethyl melamine crosslinker, and a conventional/fractionated novolak resin matrix. Delineated patterns of both types of resist systems are compared to evaluate submicron-scale resolution. The conventional novolak resin-based system shows higher contrast than the fractionated one. High aspect ratio patterns are resolved for the conventional novolak-based resist, whereas poor results are obtained for the fractionated resin-based one on the submicron scale. Very thin films (30 nm) of both resist systems are delineated with a finely focused electron beam (diameter: approximately 2 nm at 5 kV) from a scanning electron microscope. Nanometer-scale edge roughness (nanoedge roughness) is observed for the conventional novolak resin-based resist. On the contrary, the degree of nanoedge roughness is greatly reduced for the fractionated one.

Preparation and characterization of high molecular weight novolak resins

High molecular weight novolak resins were prepared from phenol and paraformaldehyde in organic solvents, e.g., 2-propanol, ethyl propionate, 2-methoxyethanol, 4-methyl-2-pentanone, dioxane and acetic acid. The molecular weights were estimated by gel permeation chromatography (GPC) and solution viscosity measurement and it was confirmed that high molecular weight resins were formed in organic solvents. The structure was determined by13C-NMR measurements, and it was found that the resin obtained in organic solvent was a random novolak with higher molecular weight than a conventional novolak.

Silicon stencil masks for lithography below 0.25 μm by ion-projection exposure

Large-area silicon stencil masks for demagnifying ion-projection lithography have been fabricated and characterized. The masks were made by patterning silicon membranes 120 mm in diameter and 2.5 μm in thickness. The membranes, prepared on 150 mm host wafers using a p/n-junction electrochemical etch stop, were designed with low tensile stress (10 MPa) to obtain minimum pattern distortion. Mask blanks were made by field bonding the membrane-containing host wafers to pyrex rings. The blanks were patterned by e-beam lithography over a 60×60-mm field in a conventional novolak resist. The resist patterns were transferred into the silicon membranes in a magnetically enhanced reactive ion etcher using molecular bromine. The intermediate pattern-transfer layer was low-stress chemical vapor deposition silicon dioxide. Mask openings as small as 0.5 μm were achieved. The sidewalls of the openings were smooth and had positive tapers no more than 3° from vertical. The linewidth uniformity across the mask was <±10%, and linewidth bias was small, nearly constant, and uniform across the mask. Mask pattern distortion measurements indicated a pattern-placement deviation of less than 0.2 μm (3σ).

An organosilicon photoresist for use in excimer laser lithography

An investigation of an organosilicon resist for use in deep UV excimer laser lithography was performed. The resist is based on the poly(vinylphennol) resin, and was found to exhibit transparency at 248 nm comparable to the transparency of g-line light in conventional novolak resists, making single-layer resist processing possible. The results of single-layer patterning on an excimer laser contact printer are presented. Results are also presented for a bilayer resist process using oxygen RIE etch for transfer of the top layer pattern into a thick underlying novolak layer.

Phenol-Crotonaldehyde Resins. II. Effect of Crotonaldehyde Purity on Resin Properties

Acid-catalyzed polycondensation of phenol and crotonaldehyde results in soluble thermoplastic resins over a broad range of compositions. The thermal and curing behavior of the resins are found to vary markedly with the phenol to crotonaldehyde mole ratio and the purity of crotonaldehyde. Infrared analysis of the resins and their fractions separated by column chromatography indicates that all the resins are structurally similar. The number-average molecular weights of the resins fall in the range of 400 to 600. The resins from distilled crotonaldehyde exhibit higher molecular weights than those from crude crotonaldehyde. The thermal properties of the resins are comparable to the Novolak-type phenol-formaldehyde resins. The thermoplastic nature is retained even at higher fraction of crotonaldehyde, unlike for the conventional Novolak resins.

Conventional novolak resists for storage ring x-ray lithography

This paper describes the lithographic processing of several positive novolak‐based resists exposed on the IBM x‐ray lithography system at the Brookhaven National Laboratory 750 MeV storage ring. One of the advantages of the storage ring exposure system has been the ability to use resist development processes which are the same as the corresponding optical or e‐beam processes. The exposure system and the x‐ray mask used for resist evaluation are described elsewhere in this symposium. Determining the best process conditions requires consideration of mask contrast as well as the desired linewidth and profile control, particularly in the presence of topography. Data will be presented and compared with results obtained using other lithographic systems (i.e., e‐beam and conventional source x‐ray). In particular, the relationship of mask absorber thickness to process window will be presented using a simple model of the development process. Using the process window defined by this model, we have exposed test patterns and typical device patterns in 1 to 2 μm thick conventional positive novolak resists. Linewidth control data as a function of dose and development time were determined for one resist at doses in the 100–200 mJ/cm2 range and compared with corresponding results using electron beam exposure. The x‐ray exposures compared favorably with the electron beam exposures in the dosage ranges considered.