Tony D. Flaim

High-refractive-index polymer coatings for optoelectronics applications

The performance of many solid-state devices including emissive displays, optical sensors, integrated optical circuits, and light-emitting diodes can be improved by applying a transparent high refractive index coating (≥ 1.65) onto the light-emitting or light-sensing portion of the device. Ideally, the coating should combine the excellent durability and easy deposition of a spin-applied polymer coating with the high refractive index and optical clarity of a vacuum deposited metal oxide coating such as titanium dioxide or zirconium oxide. While some success has been achieved in combining these very dissimilar materials to form transparent hybrid coating systems, for example, using sol-gel or nanoparticle dispersion techniques, the resulting coating systems often require complicated manufacturing schemes and have limited storage stability and reliability. We have demonstrated two new approaches to development of high refractive index polymer coatings. In the first approach, an organometallic polymer and a conventional organic polymer are combined to form a compatible coating. When cured at elevated temperatures, the organometallic polymer decomposes to form a highly dispersed metal oxide phase that imparts high index properties to the final hybrid coating. The new coatings are transparent and have refractive indices ranging from 1.6 to as high as 1.9 depending on the metal oxide content. The second approach utilizes our discovery that polyimide materials possess naturally high refractive indices in comparison to most polymer materials. Through careful molecular design, we have developed a new class of polyimide materials having refractive indices ranging from 1.60 to 1.78 at visible wavelengths and exhibiting excellent optical clarity. The new polyimides can be spin-applied to a layer thickness of more than 10 microns in a single coating step and form thermally stable films with good mechanical strength and adhesion to device substrates.

Dyed red, green, and blue photoresist for manufacture of high-resolution color filter arrays for image sensors

We are developing a set of dyed red, green, and blue color filter coatings for the fabrication of high resolution CCD and CMOS image sensor arrays. The resists contain photosensitive polymer binders and various curing agents, soluble organic dyes, and solvents. The new dyed photoresists are sensitive to i-line radiation, primarily at 365 nm, and are negative-working, requiring less than 500 mJ of exposure energy for patterning. The coatings are developed in standard Tetramethylammonium Hydroxide (TMAH) developers. Many dyes were examined in order to achieve the desired spectral properties as well as the meet the solvent solubility and thermal stability requirements. Computer modeling was utilized to determine the correct proportions of dye(s) in each resist, after which the modeling results were verified by actual formulation and testing. Thermal stability of the dyes was determined using isothermal. Thermogravimetric Analysis (TGA) at 200°C for 30 minutes. The dyes were evaluated in both traditional (free radical) and novel polymer systems to see if adequate sensitivity, resolution, and feature quality could be obtained. The studies showed that traditional free radical-based photochemistries are marginal at best for high resolution (1-2 micron) applications. To overcome this limitation, a new polymer system having photodimerizable functional units and acid functional groups was developed to impart photosensitivity and developer solubility, respectively. This system, which does not use free radical-initiated photopolymerization as a mechanism for patterning, shows low exposure dose requirements and is capable of resolving features less than 2 micron in size.

193-nm multilayer imaging systems

This paper highlights the performance of new materials that have been developed for use in 193-nm trilayer microlithography. The products are embedded etch masking layers (EMLs) and bottom antireflective coatings (BARCs). Both coatings are spin applied from organic solvent(s) and then thermoset during a hot plate bake. The EMLs (middle layers) are imaging compatible with JSR, Sumitomo, and TOK 193-nm photoresists. Best-case trilayer film stacks have given 100-nm dense and semi-dense L/S. Plasma etching, selectivities and solution compatibility performance of the EMLs meet or exceed proposed product targets. In addition, the EMLs exhibit both solution and plasma etching properties that should lead to successful rework processes for photoresists. The multiplayer BARCs offer good thick film coating quality and contribute to excellent images when used in trilayer applications. Combining the EMLs, which are nearly optically transparent (k=0.04) at 193-nm, with the new trilayer BARCs results in outstanding Prolith simulated reflectance control. In one modeling example, reflectance is a flat line at 0.5% on five different substrates for BARC thicknesses between 300 and 700-nm.

Thin-film polyetherimides with controlled refractive indices

A series of soluble, fully aromatic polyetherimides were prepared as candidate materials for optical coating applications. Most of the new polymer coatings possessed high transparency in the optical and near-infrared spectral regions at thicknesses ranging from 1 to 10 microns. The refractive indices obtained ranged from 1.60 to 1.80 at visible wavelengths, with the highest values generally being obtained near 400 nm followed by a gentle decline as wavelength increased to 700 nm and beyond. The refractive index values could be controlled by varying the dianhydride and diamine composition. All of the polyimides showed good thermal stability to 400°C and displayed glass transition temperatures above 220°C, making them excellent candidates for device applications where increased refractive index and high optical clarity are desired. The paper will discuss the preparation and physical and optical properties of the polymers and compare them to other high index coating systems.

A lamellar liquid crystal as an in situ surface balance. I. The conformation of 5- (and 6-)carboxy-4-hexyl-2-cyclohexene-1-yl octanoic acid and its monosoap

Abstract The interfacial conformation of a dicarboxylic acid, 5- (and 6-)carboxy-4-hexyl-2-cyclohexene-1-yl octanoic acid, and its monosodium soap was determined from the change of liquid crystal dimensions after introduction of the diacid compounds. The results showed that both functional groups of the monosoap form were present at the interface and that increased water content of the liquid crystal matrix had little effect on the conformation of the monosoap. On the other hand, the results indicated the conformation of the diacid as such to depend on the water content of the matrix. At low water content, the diacid form was in a conformation similar to that found for the monosoap. However, increasing the water content of the matrix resulted in a sharp decrease in the calculated partial molecular areas for the diacid, indicating an extended conformation for the diacid.

Hybrid high refractive index polymer coatings

Thermally curable hybrid high refractive index polymer solutions have been developed. These solutions are stable up to 6 months under room temperature storage conditions and can be easily spin-coated onto a desired substrate. When cured at elevated temperature, the hybrid polymer coating decomposes to form a metal oxide-rich film that has a high refractive index. The resulting films have refractive indices higher than 1.90 in the entire visible region and achieve film thicknesses of 300-900 nm depending on the level of metal oxide loading, cure temperature being used, and number of coatings. The formed films show greater than 90% internal transmission in the visible wavelength (400-700 nm). These hybrid high refractive index films are mechanically robust, are stable upon exposure to both heat and UV radiation, and are currently being investigated for microlithographic patterning potential.

High refractive index photocurable resins

The performance of optoelectronic devices can be increased by incorporating a high refractive index layer into the system. This paper describes several potential high refractive index resin candidates. Our materials include the added advantages over other systems because the new materials are cationically photocurable and free flowing, have low shrinkage upon cure, have no (or little) volatile organic components, are applicable by a variety of methods (dip coating, roller coating, injection molding, or film casting), can be applied in a variety of thicknesses (10-100 m), are fast-curing, and possess robust physical properties. Particular attention focuses on the refractive index in the visible spectrum, light transmission, and formulation viscosity.

A Reversible Separation Method Process Using Nonionic Surfactants

Abstract An extraction method for hydrocarbons based on surfactant association structures is presented. The process utilizes the strong temperature dependence of the micellar association structures in systems of water, hydrocarbons and nonionic surfactants. The extraction is made at the HLB-temperature at which large amounts of water and oil concurrently dissolve to an isotropic solution. Reduction of the temperature (20°C) causes separation of the hydrocarbon; a corresponding increase gives separation of pure water. In this article determinations of the purity of the separated phases are reported.

Conformation of the lecithin molecule with attached water molecules

CNDO/2 studies on the conformation of the α chain of lecithin indicated a strong preference for a gauche-gauche arrangement about the phosphodiester group. Folding the α chain about and α4 was energetically very favorable. Hydration of the same segment revealed three levels of water-binding energies. The ion-dipole interactions of water and the choline moiety were energetically non-substantial. In contrast, binding of water to the unesterified phosphate oxygens produced the highest enthalpies. Attachment of water to the esterified phosphate oxygens or the ester oxygens of the β chain resulted in intermediate binding strengths. By investigating complete incorporation of nine water molecules into a chosen lipid structure, a plausible lecithin-water geometry was deduced for a liquid crystalline system.

W O Microemulsion Studies with Mono- and Dialkyl Amic Acid Surfactants

Abstract A series of new surfactants was prepared by reacting aromatic anhydrides and dianhydrides with long-chain amines to give mono- and bis-(N-alkylamic acids), which was then converted to water-soluble potassium salts. As an example, the reaction product of dodecyl amine and benzophenone tetracarboxylic dianhydride was neutralized with potassium hydroxide to form a surfactant. Two types of surfactants were synthesized and their structures are: The ability of the new surfactants to stabilize water-in-oil ( W O ) microemulsions was examined by determining the pseudoternary component phase behavior of each material in combination with water, pentanol (cosurfactant), and benzene (oil). In general, the monofunctional surfactants could support higher water content microemulsions than those of the corresponding difunctional (bis) surfactants. Microemulsions prepared from the latter materials, however, were more stable to the addition of hydrocarbon. The structure of the parent three-component systems and the four-component microemulsions was probed by measuring the self-diffusion coefficients of water, cosurfactant, and oil at various levels of water and hydrocarbon. The diffusion coefficient measurements were consistent with an inverted to normal micelle transition occurring at high water levels. From inverted micellar solutions, the addition of benzene (up to 50%) formed closed W O structures.