Patterning of contact/via is a difficult issue for the optical lithography for each successive generation of LSIs. We examined a number of approaches to obtain a large process window and found that a dry ArF exposure tool with a large depth of focus (DOF) can form 100 nm contact holes. Our experimental results show that enough DOF can be obtained for various layouts by using sub-resolution assist feature (SRAF) technology and a unique illumination technology.
Novel fluoropolymers having partially fluorinated monocyclic (5-membered and 6-membered ring) structure have been synthesized with radical cyclo-polymerization, which have C-F bond in the polymer main chain and also possess fluorocontaining acidic alcohol group. These polymers have excellent transparency lower than 1.0 μm<sup>-1</sup> at 157nm wavelength, a small amount of outgassing, high sensitivity and good adhesion to the wafer. However, this fluoropolymer have lower etching resistance (half of conventional KrF resists) and it must be improved for applying to the single-layer resist. In this paper, we show the new model of the estimation of the dry-etching resistance for designing polymer compositions. It is well known that the model using carbon-atom-density as a parameter is useful for estimating dry-etching resistance. However, these models did not agree with the results of our fluoropolymers. Our new model was focused on the surface area and the volume of the polymer. We succeeded to explain the relationship between the dry-etching resistance and the composition of the fluoropolymer. According to this model, the compositions of fluoropolymer such as protective groups, protective ration and co-polymer units were optimized to improve their etching resistance.
An in-situ quartz crystal microbalance (QCM) method was applied to quantitatively measure the outgassing from F<sub>2</sub> resist materials in real time. The frequency change of quartz crystal coated with resist films was monitored during exposure and the mass desorbed from the resist films was calculated as amounts of outgassing. The sensitivity of the present QCM systems was about 1 ng. The outgassing rate during exposure was strongly dependent on the structure of polymer backbone and blocking unit of resists. VUV light-induced degradation of resist films was investigated using reflection absorption FT-IR spectroscopy and it was confirmed that the outgassing was mainly generated from the photodegradation of acid labile protecting groups in resist films. Outgassing from photoacid generators incorporated in fluorinated cyclopolymers and poly(methacrylonitrile) films was also studied. Outgassing rate for diphenyliodonium triflate and diphenyliodonium nonaflate was slightly higher than those for triphenylsulfonium triflate and triphenylsulfonium nonaflate.
Fluoropolymers are key materials for the single-layer resists used in 157-nm lithography. We have been studying fluoropolymers to determine their potential for use as the base resin and have developed a monocyclic fluorinated polymer with a blocking group of Cyclohexylcyclohexyloxymethyl (CCOM) that has high transmittance (an absorption coefficient of 0.64 μm<sup>-1</sup>) at a 157-nm exposure wavelength and high dry-etching resistance (a dry-etching rate of 1.75 times that of KrF resist) under organic bottom anti-reflective coating/hard mark dry-etching conditions. A resist based on our monocyclic fluoropolymer had high sensitivity. Using it, we were able to resolve a 60-nm line-and-space pattern using a 157-nm laser microstepper (numerical aperture = 0.85) with a resolution enhanced technology of an alternating phase-shifting mask. This polymer was demonstrated to simultaneously enable high transparency, high dry-etching resistance, and good imaging performance.
F<sub>2</sub> laser lithography at 157nm is the most promising candidate of post-ArF excimer laser lithography. A major concern, however, is the deterioration of 157nm optics due to contamination under F<sub>2</sub> laser irradiation. An evaluation of outgassed products of 157nm resist and their effect on optical materials and is therefore indispensable for F<sub>2</sub> laser lithography. Semiconductor Leading Edge Technologies Inc. (Selete) and Komatsu Ltd. designed and constructed a resist outgassing evaluation system in order to develop exposure tools and resists for 157nm lithography. The system determines the negative effects of outgassing resist contaminants on the transmittance of optical materials under F<sub>2</sub> laser irradiation. The system has two units. One unit collects resist outgas and analyzes sampled gas in a gas chromatograph mass spectrometer (GC-MS). The other unit is a resist outgassing adhesion unit, which measures the transmittance change of optical materials due to contamination adhesion in real-time. Our analysis showed that most outgassed products were from the resist protecting groups and photo acid generators (PAG) including small hydrocarbons like isobutene, benzene derivatives and dimethoxymethane. After irradiating a 157nm lithography resist with a total dose of 30J/cm<sup>2</sup> the transmittance of a calcium fluoride (CaF<sub>2</sub>) substrate decreased from initially 90% to 85%. This was due to adhesion contamination as x-ray photoelectron spectroscopy (XPS) analysis showed an organic contamination deposition of over 5nm thickness on the CaF<sub>2</sub> substrate.
We directly measured mass spectra and change in mass spectral intensity as a function of time for outgassed species from fluoropolymers and fluorine-containing resists during 157 nm exposure using quadrupole mass spectrometer at pressure about 4×10<sup>-7</sup> Torr, in order to investigate dependence of outgassing characters on the structure of resist base polymers. We also investigated pressure increase resulting from outgassed species from 157-nm-irradiated fluoropolymers and their resists. The information obtained is as follows: (1) Side-chain-fluorinated polymers produce fluorine-containing outgassed species via scission of side chain. (2) Some fluoropolymers produce HF during 157 nm exposure. Fluorine is suggested to easily dissociate and react with hydrogen to form HF in the exposure of copolymer of tetrafluoroethylene and <i>tert</i>-butyl α-fluoroacrylate. (3) Outgassed species related to deprotection of blocking group originate from some acetal resists during and after exposure at room temperature, although the species were observed only during exposure in the exposure of corresponding base polymer. (5) Regarding base polymers and their resists employed, pressure increase in vacuum chamber becomes smaller in the next order, base polymers with ester groups in their side chains, base polymers having side chains other than ester groups, base polymers without side chains.
Various polymer structures for 157-nm lithography have been vigorously developed for post 193-nm lithography. Polymers with a fluorinated main chain can improve high transparency at the 157-nm wavelength; conversely, norbornene copolymers with fluoride pendant groups do not achieve so high transparency at the 157-nm wavelength. We have developed a novel 157-nm chemically amplified resist. It is composed of a fluorinated monocyclic main-chain polymer, which shows high transparency and can be used for single layer resists. This new resist is referred to as a Small Absorbance Fluorine contAining ResIst (SAFARI). The SAFARI resist exhibited high-resolution patterns of 65-nm line and space patterns using a 0.85 NA microstepper, good sensitivity of 4 mJ/cm<SUP>2</SUP>, and high transparency when applied to 250-nm film thickness.
Novel fluoropolymers having partially fluorinated monocyclic (5-membered and 6-membered ring) structure have been synthesized with radical cyclo-polymerization, which have C- F bond in the polymer main chain and also possess fluorocontaining acidic alcohol group. These polymers have excellent transparency lower than 1.0 μm<sup>-1</sup> at 157nm wave length. The number-average molecular weight (Mn) of the polymers is 4000 to 20000, the glass transition temperature (Tg) is 130 to 155 °C and the decomposition temperature (Td) is about 400 °C. Copolymerization reaction with the other monomers (ex. fluoroolefins,(meth)acrylates and vinyl esters) were also examined. The introduction of protecting group (ex. methoxylmethly, and t-butoxycarbonyl group) to alcohol units of the polymer can be applied before or after polymerization reaction. We also evaluated fundamental resist performances. These have excellent transparency of 0.5 to 1.5 μm<sup>-1</sup>, good solubility in the standard alkaline solution (0.26N N-tetramethylammonium hydroxide aqueous solution) and relatively high sensitivities below than 10mJ/cm<SUP>2</SUP>. The imaging results of the above fluoropolymer based positive- working resists are presented. Under 100-nm line and space pattern are delineated in 200-nm thick film by using the phase shift mask.
Fluoropolymers are key materials for single-layer resists in 157-nm lithography. We investigated main-chain fluorinated polymers and found that the incorporation of fluorine atoms into polymer backbones such as that in tetrafluoroethylene and monocyclic monomers reduced their absorption coefficients to less than 1 micrometers <SUP>-1</SUP> at 157 nm, while side-chain fluorinated polymers had absorption coefficients of 2 to 3 micrometers <SUP>-1</SUP>. The main-chain fluorinated polymers also showed good solubility in a standard alkaline developer and their dry-etching resistance was comparable to that of a ArF resist. Prototype positive-tone resists had good sensitivities of less than 10 mJ/cm<SUP>2</SUP>, and they exhibited fine imaging resolution with 80-nm dense patterns. The resists can be used to obtain 300-nm-thick films.
Fluoropolymers are key materials for single layer resists of 157nm lithography. We have been studying fluoropolymers to identify their potential for base resins of 157nm photoresist. Many fluoropolymers showed high optical transparencies, with absorption coefficients of 0.01micrometers <SUP>-1</SUP> to 2micrometers <SUP>-1 at 157nm, and dry- etching resistance comparable to an ArF resist, and non- swelling solubility in the standard developer. Positive- tone resists were formulated using fluoropolymers that fulfill practical resist requirements. They showed good sensitivities, from 1 mJ/cm(superscript 2</SUP> to 10 mJ/cm<SUP>2</SUP>, and contrast in the sensitivity curves. They were able to be patterned using a F<SUB>2</SUB> laser microstepper.