Poly(t-BOC-styrene sulfone)-based chemically amplified resists for deep-UV lithography

The unique ability of the tert-butoxycarbonyl protecting group (t-BOC) to be removed by a catalytic amount of strong acid has intensified the search towards new chemically amplified resist systems based on this chemistry. A series of new copolymers of t-BOC-styrene and sulfur dioxide have been prepared by free radical polymerization. These polysulfones function as chemical amplification positive resists for deep-UV lithography when mixed with either 2,6-dinitrobenzyl tosylate or triarylsulfonium salt acid precursors. The lithographic characteristics of 2:1 and 3:1 polysulfones have been evaluated. The new positive deep-UV photoresists are aqueous base developed and are capable of 0.5 μm resolution. Even though the photoresists containing 2,6-dinitrobenzyl tosylate are less sensitive than the onium salt formulations, they displayed greater contrast values. For example the poly(t-BOC-styrene sulfone) (2:1) 15 wt % tosylate resist formulation exhibits a sensitivity of 26 mJ/cm² and a contrast of ～20.     

Factors affecting the sensitivity of e-beam resists

In order to determine the effects of chemical structure on electron beam resist sensitivities, a series of polymers with different reactive components and additives has been investigated. The results, based on a larger number of exposures varying over five orders of magnitude, point out several interesting facts. The data indicate that the sensitivity of negative resists is not a linear function of molecular weight as previously supposed. Also, the negative electron resists tend to be more sensitive and cover a broader range of sensitivities than positive resists. The results further show that olefin and epoxy groups greatly enhance the crosslinking rate of these exposed polymers. However, additives, which are good energy transferring type sensitizers, have little effect on resist sensitivity. This last result is not surprising considering the nonselectivity of the exciting electrons.     

Acid-catalyzed photoaromatization of poly(cyclohexadiene-1,2-diol) derivatives into polyphenylene

Summary Substituted poly(cyclohexene)s, used as poly(phenylene) precursors, have been prepared by radical polymerization of cyclohexadiene-1,2-diol derivatives containing various leaving groups. The precursors were converted into poly(phenylene) either by curing at elevated temperatures or by deep-UV exposure in the presence of a photoacid generator. These reactions were investigated by both IR and UV analysis. Our results with the conversion of precursors into poly(phenylene) via photoaromatization suggest that polyphenylene precursors can be imaged by deep-UV microlithography (as a new class of photoimageable thermally stable polymers).     

Effect of post-exposure delay in positive acting chemically amplified resists: An analytical study

The lithographic performance of chemically amplified positive resists depends on controlling the delay time between the exposure and post-exposure bake (PEB) process steps. The effect of post-exposure delay (PED) was investigated in poly(t-butoxycarbonyloxystyrene-sulfone) formulated with photoacid generators (PAG) by a variety of analytical techniques including Rutherford backscattering, infrared, X-ray photoelectron and laser ablation microprobe mass spectrometry. The results indicate that the base-insoluble residue formed during PED is primarily a surface phenomenon and is a result of incomplete deprotection at the resist surface. It was determined that ppb levels of basic vapors present in the resist processing environment affect process performance profoundly by reacting with the photogenerated acids during PED. Isolation of resist surface from the immediate environment by means of a thin, acidic, and base-soluble overcoat (covercoat) material dramatically alleviates the environmental effects by quenching basic airborne contaminants and improves PED latitude.     

BIOARTIFICIAL POLYMER MATERIALS BASED ON PVC/NATURAL POLYMER BLENDS: BINARY PVC/HYDROLYZED COLLAGEN BLENDSv

Compatibility and biocompatibility of the binary blends of plasticized poly (vinyl chloride) and hydrolyzed collagen have been studied. The following investigation methods have been used: differential scanning calorimetry, thermogravimetry, contact angle measurements, and to assess the biocompatibility, “in vitro” cell growth test. The results indicate that these materials behave as relatively homogeneous systems and that the surface polarity increases by collagen incorporation. Polyvinyl chloride interacts with hydrolyzed collagen through either hydrogen or chemical bonds. A better substrate for cell growth in comparison with pure components has been obtained.

The main effects of the combination of these polymers are, on the one hand, the improvement of hydrophylicity and thermal stability of PVC, and on the other hand, the rapid dissolution is avoided of the collagen-based materials when in contact with biological fluids, which means a better biological stability in terms of resistance to enzymatic digestion.     

Recent resist developments in Japan—a review

Several kinds of resist materials for microlithography have been developed in Japan. Poly(4-vinyl phenol) sensitized with 3,3′-diazidodiphenyl sulfone has been proved to be a high resolution negative deep UV resist with high sensitivity and good resistance to dry etching. The use of this resist enables a 1:1 projection printer to replicate fine patterns with 1 micrometer (μm) minimum feature size at the rate of 90 wafers per hour. Poly(methyl isopropenyl ketone) (PMIPK) has been investigated as a positive deep UV resist. Several resists composed of PMIPK with or without sensitizers are commercially available. Dry-developable photo- and deep UV resists comprising PMIPK and aromatic bisazides have been developed. Poly(glycidyl methacrylate) having the sensitivity of 0.4 micro Coulomb (μC)/per square centimeter (cm²) is now being routinely used as a negative electron beam resist in the fabrication of chromium masks. Recently, aromatic polymers such as chloromethylated polystyrene, iodinated polystyrene, chloromethylated poly(α-methylstyrene), poly(vinylnaphthalene) and its copolymers have been investigated as dry-etching resistant electron beam resists.     

Dry-developed organosilicon resists for 193-nm excimer laser lithography

Irradiation of certain organosilicon polymers with a 193-nm excimer laser forms a latent image that contains increased amounts of oxygen. Patterning is achieved by dry development in an HBr plasma, where the oxidized polymer etches more slowly than the unexposed areas. With these polymers as the top layer in a bilayer resist scheme, 0.2 μm resolution has been demonsrated and resist sensitivities less than 50 mJ/cm² have been achieved. Three classes of organosilicon layers have been investigated: polysilynes; polysilanes, in particular poly(phenylmethyl) silane; and a plasma-deposited polymer derived from tetramethylsilane (PPTMS). The PPTMS, when used with plasma-deposited planarizing layers, opens the possibility of an all-dry, cluster-tool-compatible lithographic cycle.     

Thermal analysis of poly(1,3,4-oxadiazole-2,5 diyl-1,2-ethenediyl) and poly(1,4-phenylene-1,3,4-oxadiazole-2,5 diyl-1,2 ethendiyl)

Poly(1,3,4-oxadiazole-2,5-diyl-1,2-ethendiyl) and poly(1,4-phenylene-1,3,4-oxadiazole-2,5 diyl-1,2-ethenediyl) have been prepared by condensation polymerization using fuming sulfuric acid and different quantities of terephthalic acid (T), fumaric acid (F), and hydrazine sulfate (HS). Homopolymers of F and T and various copolymers of F:T have been prepared. The polymer structure was investigated by IR and visible-range spectra and elemental analysis. The existence of poly(1,3,4-oxadiazole-diylphenylene) and poly(hydrazoterephthaloyl) structures was revealed by these studies. These polymers were thermally stable, and most of them did not show a weight loss below 350°C. The relative thermal stabilities of the various polymers have been evaluated by “integral procedural decomposition temperature” and activation energy measurements.     

Modulus reinforcement in elastomer composites. II. Polymeric fillers

Blends were prepared with high-modulus “filler polymers,” polystyrene, polyamide, and poly(methyl methacrylate) dispersed in a low modulus matrix of ethylene/vinyl acetate copolymer. The modified Kerner equation was applied to dynamic mechanical data obtained on these blends, which may be considered to be model systems for thermoplastic elastomer block polymers. The implication of the interaction parameter, B, in terms of the reinforcing capability of each polymer as well as its optimum volume fraction in the blend, is discussed.     

Nano-adsorbents control surface properties of polyurethane

Additives are minor but critical components that polymers need for processing and applications. However, these additives may also have adverse effects, e.g. for polymeric biomaterials, leaching additives can change surface properties, and may lead to poor biocompatibility. How to use additives yet keep them from detrimental behaviors is a challenging issue. Diffusion barriers may be used to slow down the additive migration but difficult to stop it. In this paper, we introduce the concept of “nano-adsorbents” in polymers. These nano-adsorbents confined the additives within the polymers by thermodynamically interacting with them. While the additives are still present in polymers to provide intended functions, they are thermodynamically constrained from free migration to the surface. Nano sized-fillers were selected due to their high surface to volume ratio. This new usage of nano-fillers for polymers was demonstrated with a biomedical polyurethane and a surface coated nanoclay that thermodynamically attracts the additive in the polyurethane.     

Tetrahydropyranyl- and furanyl-protected polyhydroxystyrene in chemical amplification systems

Tetrahydropyranyl- (THP) and furanyl- (THF) protected polyhydroxystyrene (PHS) polymers have been investigated for their potential use in conjunction with onium salt acid precursors to yield high-sensitivity resist systems. The synthesized polymers have high transmittance at 248 nm (the wavelength used in next-generation excimer laser, KrF exposure tools). At 248 nm the transmittance for a 1-μm thick film is ～ 80% (Abs = 0.097 μm^?1). The acid sensitivity of the acetal functionality at room temperature is high, requiring careful handling of all materials to prevent any premature deprotection of the hydroxy group. The highest lithographic sensitivities obtained so far with a system consisting of poly(p-tetrahydropyranyl-oxy-styrene) base resin and 1 mol % of bis (p-tert-butyl phenyl) iodinium triflate (TBIT) was ～ 2 mJ / cm². High-resolution line and space patterns (0.35 μm) were obtained with a system comprising PHS-p-THP and an acid precursor, using an excimer laser step and repeat exposure at 248 nm.     

Permeability of semicrystalline polymers to toluene/methanol mixture

In this article, we analyze the effect of the alcohol content in gasoline on the permeability of four semicrystalline polymers used in automobile fuel systems. More specifically, we are interested in the methanol/toluene mixture as a “binary” model of a complex gasoline to understand the selectivity brought about, in front of these solvents, by the nature of the polymer. We developed a permeation cell coupled to a chromatograph to analyze the composition of escaping toluene and methanol. These experiments allow us to demonstrate the strong “positive synergy” that exists between the flows of the methanol and the toluene when they are mixed, compared to the flows of these solvents on their own. This phenomenon is notably highlighted on polymers of very different kinds (PA12, PVDF, HDPE, EVOH) and, in light of recent theoretical developments, we can consider that this property is general, because this “positive synergy” is a consequence of the evolution of the solubility of the mixture of solvents in the polymer film, and more particularly, of the highly positive value of the Flory‐Huggins interaction coefficient between methanol and toluene. These experimental data allow one to better understand and predict the permeability behavior of the polymers in front of complex gasolines. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2727–2733, 2003     

Permeability of semicrystalline polymers to toluene/methanol mixture

In this article, we analyze the effect of the alcohol content in gasoline on the permeability of four semicrystalline polymers used in automobile fuel systems. More specifically, we are interested in the methanol/toluene mixture as a “binary” model of a complex gasoline to understand the selectivity brought about, in front of these solvents, by the nature of the polymer. We developed a permeation cell coupled to a chromatograph to analyze the composition of escaping toluene and methanol. These experiments allow us to demonstrate the strong “positive synergy” that exists between the flows of the methanol and the toluene when they are mixed, compared to the flows of these solvents on their own. This phenomenon is notably highlighted on polymers of very different kinds (PA12, PVDF, HDPE, EVOH) and, in light of recent theoretical developments, we can consider that this property is general, because this “positive synergy” is a consequence of the evolution of the solubility of the mixture of solvents in the polymer film, and more particularly, of the highly positive value of the Flory‐Huggins interaction coefficient between methanol and toluene. These experimental data allow one to better understand and predict the permeability behavior of the polymers in front of complex gasolines. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 676–682, 2004     

Aqueous lubricating properties of charged (ABC) and neutral (ABA) triblock copolymer chains

Application of charged polymer chains as additives for lubricating neutral surfaces in aqueous environment, especially via polymer physisorption, is generally impeded by the electrostatic repulsion between adjacent polymers on the surface. In this study, we have investigated the adsorption and aqueous lubricating properties of an amphiphilic triblock copolymer, comprised of a neutral poly(ethylene glycol) (PEG) block, a hydrophobic poly(2-methoxyethyl acrylate) (PMEA) block, and a charged poly(methacrylic acid) (PMAA) block, namely PEG-b-PMEA-b-PMAA. After adsorption onto a nonpolar hydrophobic surface from aqueous solution, an equal and homogeneous mixture of neutral PEG and charged PMAA chains is formed on the surface, with an adsorbed polymer mass comparable to its fully neutral counterpart, PEG-b-PMEA-b-PEG. The lubricity of PEG-b-PMEA-b-PMAA showed significant improvement compared to fully charged polymer chains, e.g. poly(acrylic acid)-block-poly(2-methoxyethyl acrylate) (PAA-b-PMEA), which is attributed to dilution of charged moieties on the surface and subsequent improvement of the lubricating film stability.     

Die „Inverse Gaschromatographie”︁ zur Charakterisierung von Polymeren,Polymergemischen und Copolymeren I. Zur Charakterisierung synthetischer Polymerer durch Retentionsindices

Relative retention data, as e.g. the retention index, can be determined much easier and more accurately than absolute retention values. For polystyrene, poly(vinyl acetate) and poly(ethy1ene oxide) as stationary phases the retention indices have been measured for benzene, ethanol, methylethylketone, nitromethane and pyridine as polar test molecules. Based on these data the significance of the index in the framework of “Inverse gas-chroma-tography” is discussed. The mobile/stationary-phase interaction-and therefore the reten-tion-is usually the result of a superposition of different sorption mechanisms, where adsorption at different interfaces (gas-support, gas-polymer, polymer-support, polymer-polymer) and absorption into the polymer-bulk phase have to be considered. It is shown, that the different sorption behavior of polar and nonpolar (n-alkanes) test molecules at the polymer surface must lead to systematic index-variations with different amounts of polymer coating. For polymers however, investigated at temperatures Sufficiently above the glass transition and melting point and at high liquid loadings on inert support materials, mainly the bulk phase solution of the test molecule will be relevant for the index value. Under these conditions it seems to be possible to characterize the “polarity” of a polymer by application of test molecules whose functional groups reflect characteristic interaction forces. The method proposed by Rohrschneider is discussed with respect to this problem.     

Studies of polymeric systems for absorbing airborne sound

Sound absorption properties of polymer systems were investigated as functions of temperature, frequency, and chemical composition. Viscoelastic polymers were mixed with rigid polymers to obtain improved acoustical performance. In the case of foamed polymers, it was found that the chemical nature of the polymer is the most important factor controlling sound attenuation if the thin membranes of the closed-cell foams are “acoustically transparent.” Polyurethane-based polymer foams have been developed which possess excellent sound absorption characteristics. The foams are closed-cell, leathery, and “dead,” and can absorb as much as 96% of the normal incident sound energy at 1250 Hz (foam thickness 25 mm). The temperature-dependent acoustical properties of various polymer systems are discussed in terms of viscoelastic theory of polymers.     

X-ray photochemistry: ω-Chloro olefin sulfones

To be efficacious as an x-ray resist, a material must efficiently undergo a desirable chemical change upon being irradiated with x-rays. The probability of such a change taking place is given by the product of the fractional x-ray absorption and the “inherent sensitivity,” which we define as the yield per unit energy absorbed. Increasing the absorption of the polymer, as, for example, by chlorinating an olefin sulfone thereby increasing the absorption at wavelengths just below the chlorine absorption edge will result in improved usefulness if, and only if, this increased energy absorbed can be used by the polymer to enhance the desired chemical reaction. The “usefulness” of chlorinating is thus dependent on the efficiency of intramolecular energy transfer. We have studied the efficiency of this transfer by monitoring the loss of SO₂ from the main-chain backbone as a function of absorbed x-ray energy, using x-ray wavelengths both abov and below the chlorine absorption edge. The polymers studied were 1-olefin sulfones, with and without the chlorine atom in the ω-position. Through the use of this series of polymers it was hoped to observe an effect due to the changing separation of the chlorine atom from the backbone. The experiments indicate that (a) the inherent sensitivity is independent of irradiating wavelength, for both the chlorine-containing and the non-chlorine-containing polymers; (b) the hexene polymers are considerably more sensitive than the lower members of the series (which exhibit a sensitivity which is approximately independent of the side chain length); and (c) the chlorine-containing polymers are less sensitive than the non-chlorine-containing species. At this time the explanation for these observations is speculative.     

Prediction of plasticizer solvency using hansen solubility parameters

The solvating strength of a plasticizer for poly(vinyl chloride) resin is a measure of the interactive forces between these two materials. Hansen's three-dimensional solubility parameters provide a quantitative measure of these interactive forces. By using CO-ACT^SM service, a computer program designed for solvent systems with various resins, plasticizers were found to lie near the edge of the solvency “sphere” of PVC. The relative positions of various plasticizer structures are in the expected order, while known solvents show strong association and lubricating additives fall outside the solvency sphere of PVC.     

Temperature effects on positive electron resists irradiated with electron beam and deep-UV light

The exposure characteristics of poly(methyl methacrylate) (PMMA) and poly(methyl isopropenyl ketone) (PMIPK) were studied with electron beam and deep-UV light irradiation at different temperatures (20–160°C). The sensitivities and γ(contrast) values for electron beam irradiation show small temprature effects, but those for deep-UV light irradiation revel relatively large temperature effects. The result in which γ (contrast) values for the electron beam irradiation as a whole are significantly larger than for the deep-UV light irradiation is related to the molecular weight dispersity of irradiated resists. The result in which γ(contrast) for PMMA is larger than that for PMIPK at given development conditions is also related to the molecular weight ratios of the original and irradiated resists. The thickness reduction and negative inversion (crosslinking) compete under a large dose of electron beam irradiation, but the latter is scarcely apparent under deep-UV irradiation. The PMMA sensitivity for deep-UV irradiation diminishes in O₂ gas flow compared with the irradiation in N₂ gas flow, but PMIPK sensitivity is not influenced by O₂. From these results, the different decomposition mechanisms are discussed.     

Rheology of solvent-cast polymer films

This paper describes and analyzes the results of an experiment where various thin polymeric films are continuously sheared between smooth glass substrates. The shear force per unit area has been measured as a function of mean uniaxial stress and temperature using representative “good” and “poor” casting solvents followed by a range of heat treatments. The polymers studied include high density polyethylene, polybisphenol-A–carbonate, poly(ethylene terephthalate), atactic polystyrene, isotactic polystyrene, atactic poly(methyl methacrylate), isotactic poly(methyl methacrylate), poly(vinyl acetate), poly(vinyl alcohol), poly(vinyl pyrrolidone), poly(vinyl chloride), and polytetrafluoroethylene. The results indicate that the casting solvent has a very pronounced influence upon the rheology of the film. The casting solvents may apparently confer either ductile or brittle failure in the film and also influence the nature of the temperature and pressure dependence of the shear stress. The data have been analyzed using Eyring theory and also by reference to relevant published literature on the influence of solvent and thermal treatments on the morphology and deformation behavior of polymers. “Good” solvents generally tend to promote a brittle mode of failure with little temperature dependence. The same type of solvents also produced films which have higher shear strengths and show greater increases in shear strength with pressure. These data are adequately rationalized using free volume and entanglement notions.