Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization technology enables the production of
polymers possessing low polydispersity (PD) in high yield for many applications. RAFT technology also enables control
over polymer architecture. With synthetic control over these polymer characteristics, a variety of polymers can be
designed and manufactured for use in advanced electronic applications. By matching the specific RAFT reagent and
monomer combinations, we can accommodate monomer reactivity and optimize acrylate or methacrylate
polymerizations (193 and 193i photoresist polymers) or optimize styrenic monomer systems (248 nm photoresist
polymers) to yield polymers with PD as low as 1.05. For 193i lithography, we have used RAFT technology to produce
block copolymers comprising of a random "resist" block with composition and size based on conventional dry
photoresist materials and a "low surface energy" block The relative block lengths and compositions may be varied to
tune solution migration behavior, surface energy, contact angles, and solubility in developer. Directed self assembly is
proving to be an interesting and innovative method to make 2- and even 3-dimensional periodic, uniform patterns. Two
keys to acceptable performance of directed self assembly from block copolymers are the uniformity and the purity of the
materials will be discussed.
Immersion lithography at 193 nm has rapidly changed status from a novel technology to the top contender for the 45 nm device node. The likelihood of implementation has raised interest in extending its capabilities. One way to extend immersion lithography would be to develop immersion fluids and resists with higher refractive indices than those currently available (n193 nm = 1.44 for water and n193 nm = 1.7 for typical resists). This work explores methods by which the index of refraction of immersion fluid could be increased to that of calcium fluoride (n193 nm = 1.56) or higher. A survey of the optical properties of various aqueous solutions was performed using spectroscopic ellipsometry. The refractive index of the solutions is measured to identify additives that might increase index while maintaining suitable pH, viscosity and contact angle. Also, ways to increase the index of model resist systems were explored. Higher index resists would help improve contrast in hyper-NA exposure tools.
Immersion lithography has been proposed as a technique to print sub-100nm features using 193nm lithography. The process involves filling the space between the lens fixture of an exposure tool and the photoresist-coated silicon wafer with a liquid. In the case of immersion 193nm lithography, water can serve as that liquid. The immersion option raises questions about how photoresists and water interact. Components of the photoresist could be leached into the water, thus modifying the refractive index of the medium, depositing material on the lens, or altering the solubility switching process of the photoresist. Several phenomena could affect the optical properties of the resist and water and, ultimately, the resolution of the process. To better understand the impact that immersion lithography would have on photoresist performance, a study has been undertaken to measure the amount of resist components that are leached by water from model 193nm photoresists. The components studied were residual casting solvent (propylene glycol methyl ether acetate), the photoacid generator (triphenylsulfonium nonaflate), and the base quencher (triethanolamine). Since it was expected that only a small amount of each material would be leached into the water, 14C-labeled samples of each resist component were synthesized and added to the 193nm resists. Films of the labeled resists were coated onto a silicon wafer and immersed in water. The water was collected and the film was dissolved in casting solvent and collected. The amount of material leached into the water was determined by radiochemical analysis. Spectroscopic ellipsometry was also used to quantify changes in the optical constants of the resists and the water.
Current semiconductor manufacturing utilizes exposure wavelengths from 365 nm to 193 nm, and current research is centered on photoresist development for 157 nm. Our research group discovered the strong inhibition response in the fluorocarbon resins designed for use at 157 nm. We have been investigating dissolution inhibitors (DIs), some of which also serve as photoacid generators (PAGs), that strongly inhibit the dissolution of poly(2-(3,3,3-trifluoro-2-trifuoromethyl-2-hydroxypropyl) bicyclo[2.2.1]heptane-5-ene)(PNBHFA) (1) and the Asahi glass RS001 polymer (2). These inhibiting PAGs, in particular, result in the creation of 2-component resist systems consisting only of the resin polymer and the PAG-DI. This design enables greater ease of formulation, reduces the number of variables present in resist development, and offers improvements in sensitivity and line edge roughness. The synthetic approach has been to design transparent, inhibiting compounds for use at 157 nm. However, during our investigation of these compounds, we found that there is an inherent “backwards compatibility” for these PAGs and DIs at 193 nm, 248 nm and 365 nm. This has created the ability to effectively design dissolution inhibitors, photoactive or otherwise, that span virtually all of the wavelengths used in photolithographic processes today. Here we will present the design, development and imaging of modern dissolution inhibitors suitable for use in a wide range of photolithography technologies.
The focus of 157 nm lithographic research is shifting from materials research to process development. Poly (2-(3,3,3-trifluoro-2-trifuoromethyl-2-hydroxypropyl) bicyclo[2.2.1]heptane-5-ene) (PNBHFA) has received a great deal of attention as a possible base resin for 157 nm lithography. The Asahi Glass RS001 polymer, which was introduced at SPIE in 2002, has also shown promise as a 157 nm base resin due to its low absorbance. Partial protection of either polymer with an acid labile protecting group is a common design for functional photoresists. We previously reported the blending of the carbon monoxide copolymers with PNBHFA copolymers to achieve the critical number of protected sites for optimum imaging performance and contrast. Our group has since studied the use of the unprotected base resin with an additive monomeric dissolution inhibitors (DIs) and a photoacid generator (PAG) to form a three component resist. Surprisingly unprotected PNBHFA was discovered to have dissolution inhibition properties that are far superior to the dissolution inhibition properties of novolac. Several DIs were prepared and tested in PNBHFA to take advantage of the resins dissolution inhibition properties. We have also recently explored the performance of a two-component resist using PAGs that also function as DIs.
Significant progress has been made in 157 nm resist technology. Material development for this emerging field is continuing at a frantic pace. Many new and interesting polymers are surfacing for these studies. Fluorine-containing polymers have become the prominent platform for a variety of research activities within this field and a tremendous amount of progress has been achieved. Since the absorbance of a variety of different organic polymers at 157 nm was first reported, a vast array of fluorine-containing materials has been proposed and designed for photolithography at this wavelength. Free radical polymerizations, metal-catalyzed addition polymerizations and metal-catalyzed copolymerizations with carbon monoxide have produced materials that have yielded positive-tone images with 157 nm exposures. Major progress has been made in decreasing the absorbance of fluoropolymers based on Tetra Fluoro Ethylene (TFE). A number of key monomers have been synthesized based on the learning this project has cataloged over the past 2-½ years. Development of these new and interesting monomers has been done with copolymerizations of TFE taken into consideration. Our project has focused on polymer synthesis efforts, learning how to maximize transparency at 157 nm with consideration to etch resistance and imaging properties of these materials. Vacuum-UV (VUV) studies and variable angle spectroscopic ellipsometry (VASE) data will be shown on numerous fluorinated compounds and synthesized polymers. Our most recent materials have an absorbance of less than 1/μm and etch resistance equal to first generation KrF materials. This paper will provide synthesis, imaging and etch studies that have been completed using a 0.60NA and 0.85NA 157nm micro exposure system.
The design of 157 nm photoresists is a daunting task since air, water, and most organic compounds are opaque at this wavelength. Spectroscopic studies1 led to the observation that fluorinated hydrocarbons offer the best hope for the transparency that is necessary for the design of an effective 157nm photoresist, and these classes of materials have quickly become the prominent platforms for a variety of research activities in this field. Our approach to the design of the resist polymer requires identification of a backbone that tethers the functional substituents and provides basic mechanical properties, an etch barrier that provides RIE resistance, an acidic group that permits solubility in tetramethylammonium hydroxide (TMAH) developer. Fluorocarbon polymers have been identified as promising resist candidates for 157nm material design because of their relatively high transparency at this wavelength. Numerous authors have discussed negative photoresists over the years. There are many uses for such materials at various levels in a semiconductor device. One such use is with complementary phase shift mask thus eliminating the need for a second exposure step. This paper reports our recent progress toward developing a negative 157nm resist materials based on fluoropolymers with crosslinkers that are transparent at 157nm. The authors will report on the synthesis of the polymers used in this work along with the crosslinkers and other additives used in the formulation of the photoresist. Imaging experiments at practical film thicknesses at 157nm with binary and strong phase shifting masks will be shown demonstrating imaging capabilities. Spectroscopic data demonstrating chemical mechanisms and material absorbance will be shown along with other process related information
Fluorocarbon based polymers have been identified as promising resist candidates for 157nm material design because of their relatively high transparency at this wavelength. This paper reports our recent progress toward developing 157nm resist materials based on transparent dissolution inhibitors. These 2 component resist systems have been prepared and preliminary imaging studies at 157nm are described. Several new approaches to incorporating these transparent monomers into functional polymers have been investigated and are described. The lithographic performance of some of these polymers is discussed.
The synthesis and characterization of several new fluoropolymers designed for use in the formulation of photoresists for exposure at 157 nm will be described. The design of these resist platforms is based on learning from previously reported fluorine-containing materials. We have continued to explore anionic polymerizations, free radical polymerizations, metal-catalyzed addition polymerizations and metal-catalyzed copolymerizations with carbon monoxide in theses studies. The monomers were characterized by vacuum-UV (VUV) spectrometry and polymers characterized by variable angle spectroscopic ellipsometry (VASE). Resist formulations based on these polymers were exposed at the 157 nm wavelength to produce high-resolution images. The synthesis and structures of these new materials and the details of their processing will be presented.