Resist materials for 157-nm microlithography: an update

Fluorocarbon polymers and siloxane-based polymers have been identified as promising resist candidates for 157 nm material design because of their relatively high transparency at this wavelength. This paper reports our recent progress toward developing 157 nm resist materials based on the first of these two polymer systems. In addition to the 2-hydroxyhexafluoropropyl group, (alpha) -trifluoromethyl carboxylic acids have been identified as surprisingly transparent acidic functional groups. Polymers based on these groups have been prepared and preliminary imaging studies at 157 nm are described. 2-Trifluoromethyl-bicyclo[2,2,1] heptane-2-carboxylic acid methyl ester derived from methyl 2-(trifluoromethyl)acrylate was also prepared and gas-phase VUV measurements showed substantially improved transparency over norbornane. This appears to be a general characteristic of norbornane-bearing geminal electron-withdrawing substituents on the 2 carbon bridge. Unfortunately, neither the NiII nor PdII catalysts polymerize these transparent norbornene monomers by vinyl addition. However, several new approaches to incorporating these transparent monomers into functional polymers have been investigated. The first involved the synthesis of tricyclononene (TCN) monomers that move the bulky electron withdrawing groups further away from the site of addition. The hydrogenated geminally substituted TCN monomer still has far better transparency at 157 nm than norbornane. The second approach involved copolymerizing the norbornene monomers with carbon monoxide. The third approach involved free-radical polymerization of norbornene monomers with tetrafluoroethylene and/or other electron-deficient comonomers. All these approaches provided new materials with encouraging absorbance at 157 nm. The lithographic performance of some of these polymers is discussed

Resist materials for 157-nm microlithography: an update

Fluorocarbon polymers and siloxane-based polymers have been identified as promising resist candidates for 157 nm material design because of their relatively high transparency at this wavelength. This paper reports our recent progress toward developing 157 nm resist materials based on the first of these two polymer systems. In addition to the 2-hydroxyhexafluoropropyl group, (alpha) -trifluoromethyl carboxylic acids have been identified as surprisingly transparent acidic functional groups. Polymers based on these groups have been prepared and preliminary imaging studies at 157 nm are described. 2-Trifluoromethyl-bicyclo[2,2,1] heptane-2-carboxylic acid methyl ester derived from methyl 2-(trifluoromethyl)acrylate was also prepared and gas-phase VUV measurements showed substantially improved transparency over norbornane. This appears to be a general characteristic of norbornane-bearing geminal electron-withdrawing substituents on the 2 carbon bridge. Unfortunately, neither the NiII nor PdII catalysts polymerize these transparent norbornene monomers by vinyl addition. However, several new approaches to incorporating these transparent monomers into functional polymers have been investigated. The first involved the synthesis of tricyclononene (TCN) monomers that move the bulky electron withdrawing groups further away from the site of addition. The hydrogenated geminally substituted TCN monomer still has far better transparency at 157 nm than norbornane. The second approach involved copolymerizing the norbornene monomers with carbon monoxide. The third approach involved free-radical polymerization of norbornene monomers with tetrafluoroethylene and/or other electron-deficient comonomers. All these approaches provided new materials with encouraging absorbance at 157 nm. The lithographic performance of some of these polymers is discussed

Synthesis, copolymerization studies and 157 nm photolithography applications of 2-trifluoromethylacrylates

textAdvances in microelectronic devices have relied heavily on improved photolithographic imaging capabilities. The resolution limit of optical lithography can be improved by lowering the wavelength of exposure light. The latest reduction in exposure wavelength is from 193 nm to 157 nm. The focus of this work is the synthesis, copolymerization studies and lithographic imaging capabilities of 2-trifluoromethylacrylates. Model calculations and gas phase absorbance measurements of model compounds first suggested that these materials would provide suitable transparency at the 157 nm wavelength. Methyl 2-trifluoromethylacrylate was synthesized and aniocically polymerized and variable angle spectroscopic ellipsometry showed that this material had an absorbance that was 1,000 times more transparent than its non-fluorinated analogue. A variety of relatively transparent resist materials based on a 2- trifluoromethylacrylate backbone were synthesized by anionic polymerization, and these materials were successfully imaged at 157 nm. While 2- trifluoromethylacrylates do not undergo homopolymerization with radical initiators, they do radically copolymerize with various norbornenes. Interestingly, these materials exhibit a 2:1 (2-trifluromethacrylate:norbornene) monomer incorporation. This phenomenon was exploited to produce a number of relatively transparent materials that produced positive-tone structures when imaged at the 157 nm wavelength. Kinetic studies were performed to show that the copolymerizations of 2-trifluormethacrylates and norbornene derivatives deviate from the terminal model and follow the penultimate model. Competitive reaction studies using the “mercury method” were performed to demonstrate that substitution of a trifluoromethyl group can indeed effect the reactivity of a propagating radical, lending support to the proposed penultimate model. The structure of the 2-trifluoromethylacrylate propagating radical will also be investigated by electron spin resonance spectroscopy.Chemistry and BiochemistryChemistr

Metal-Catalyzed Vinyl Addition Polymers for 157 nm Resist Applications. 2. Fluorinated Norbornenes: Synthesis, Polymerization, and Initial Imaging Results

Three metal-catalyzed vinyl addition copolymers derived from partially fluorinated norbornenes and tricyclononenes have been synthesized and evaluated for use in formulating photoresists for 157 nm lithography imaging. The transparency of these polymers at 157 nm, as measured by variable angle spectroscopic ellipsometry (VASE), is greatly improved over their nonfluorinated counterparts. The results of preliminary lithographic evaluations of resists formulated from these polymers alone and with the addition of several new fluorinated dissolution inhibitors are presented. Images as small as 70 nm have been printed in some formulations