Yasuhide Kawaguchi

Synthesis of novel fluoropolymers for 157-nm photoresists by cyclopolymerization

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-1 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-1, good solubility in the standard alkaline solution (0.26N N-tetramethylammonium hydroxide aqueous solution) and relatively high sensitivities below than 10mJ/cm2. 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.

Imprinted 50 nm Features Fabricated by Step and Stamp UV Imprinting

We fabricated features down to 50 nm by UV step and stamp imprint lithography (UV-SSIL). This method enables fast sequential imprinting for large areas operating at room temperature with a low-viscosity material. This allows the patterning of both large micron-scale and submicron-scale structures simultaneously. A low-viscosity polymer allows pattern transfer at moderate pressures, thereby reducing mechanical stress on the stamp and substrate. Processing at room temperature helps to maintain the alignment and to prevent the distortion of the features caused by the thermal expansion of the mold and substrate. A UV-SSIL experiment with a novel photosensitive polymer was performed using a prototype of currently commercially available machines used for both thermal and UV step and stamp imprintings. As a master, we used a transparent quartz stamp (with features down to 50 nm) patterned by electron-beam lithography. The polymer was dispensed on a 100 mm silicon substrate using a syringe-type dispensing system. The results were analyzed by atomic force microscopy and a scanning electron microscopy. The fabricated structures exhibited good lateral and vertical feature replication fidelities.

Dry-etching resistance of fluoropolymers for 157-nm single-layer resists

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-1 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.

Performances of resists for 157-nm lithography based on monocyclic fluoropolymers

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-1) 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.

Evaluation of UV roller imprinting using replicated fluorinated film molds

In this study, a fluorinated UV-curable resin was replicated by UV imprinting and used as a film mold. The film mold was fabricated by anti-sticking process (ACP). A remarkable advantage of the application for easy mold fabrication is expected, because it uses only UV imprinting. We evaluated two types of the pattern replications, directions between the stage movement and line and space (L&S) patterns in perpendicular as well as in parallel. The results of replication tests show obvious difference between UV roller imprinting and UV roller press imprinting. In addition, Vickers hardness is measured to evaluate the thermal property of UV roller imprinting. The results indicate that temperature is effective not only to improve pattern replication, but also to accelerate UV curing.

157-nm single-layer resist based on novel monocyclic fluorinated polymer

Fluorinated polymers are key materials for single-layer resists used in 157-nm lithography. We have been studying fluorinated polymers to determine their potential for use as the base resin and have developed a new monocyclic fluorinated polymer that has high transmittance (an absorption coefficient of 0.1 μm-1) at a 157-nm exposure wavelength and high dry-etching resistance (a dry-etching rate of 1.86 times that of a KrF resist) under hard mask dry-etching conditions. Moreover, it has a high dissolution rate in standard aqueous tetramethylammoniumhydroxide developer (a dissolution rate of more than 600 nm/s). Using this polymer with adamanthylmethoxymethyl as a protecting group, we were able to resolve a 60-nm line-and-space pattern using a 0.90 numerical aperture 157-nm laser micro-stepper along with a resolution-enhancement alternating phase-shift mask technique. This polymer has enabled both high dry-etching resistance (a dry-etching rate equal to 1.43 times that of a KrF resist) and good imaging performance.

Fluoropolymers for 157-nm single-layer resists developed using a new etching rate estimation model (KI-Model)

For 157-nm single-layer resists, dry etching resistance is an important issue because of the difficulty of striking a balance between 157-nm transparency and an acceptable level of dry etching resistance. To achieve an acceptable trade-off, the fluorine atom can be introduced into the resist polymer structure to obtain higher transparency, despite the fluorine atom’s high reactivity in the plasma etching process. We recently proposed a model for estimating dry-etching-resistance (the KI-model) and have shown that it can be effectively applied to the design of new fluoropolymer structures. Through simulation based on the KI-model, we were able to develop a new fluoropolymer with good dry etching resistance and high transparency. We found that a new protective group, 2-cyclohexylcyclohexanoxymethyl (CCOM), improved the characteristics of our novel fluoropolymer, compared with use of a MOM group, when used in the base resin of the resist. In this paper, we report on the usefulness of the KI-model for developing new fluorinated protective groups and new base polymers. Moreover, we have developed a new base fluoropolymer which has higher transparency and a similar degree of dry etching resistance as a monocyclic fluoropolymer with a CCOM protective group.