Toshikage Asakura

Evaluation of a novel photoacid generator for chemically amplified photoresist with ArF exposure

Recently we have developed a novel non-ionic photoacid generator (PAG), 2-[2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1-(nonafluorobutylsulfonyloxyimino)-heptyl]-fluorene (DNHF), which generates a strong acid (perfluorobutanesulfonic acid) by light irradiation and is applicable to chemically amplified ArF photoresist. The studies on quantum yield of the PAG under 193 nm exposure in an ArF model formulation and in a solution comparing with the ones of ionic PAGs, triphenylsulfonium perfluorobutanesulfonate (TPSPB) and Bis(4-tert-butylphenyl)iodonium perfluorobutanesulfonate (BPIPB) revealed that this compound is superior in photo efficiency to the others. PAG leaching into water from the resist during a model immersion process was investigated in detail. No leaching of DNHF was observed under the immersion process while significant amount of TPSBP was eluted. Dissolution rate of the resist prepared under a model condition of ArF immersion exposure was monitored. No clear difference against dry condition was observed.

Non-ionic photoacid generators for chemically amplified resists: chromophore effect on resist performance

The development of semiconductor chips is making progress with an astonishing speed, enabling electronic apparatus smaller, higher speed, and higher performance. This dynamic advancement is significantly attributable from the development of photolithography technology. At an early era of integrated circuits (IC) manufacturing lithography technique was introduced with light source of g-line wavelength (436 nm). For further miniaturization of IC the wavelength of light source is getting shorter and shorter, i.e., i-line (365 nm), KrF (248 nm) and ArF (193 nm). Currently ArF immersion is actively investigated as the most advanced technology, and EUV (13.5 nm) is discussed as the next generation lithography. Chemically amplified (CA) resist is mainly employed for the study of the advanced lithography. The CA resist is composed of polymer bearing acid-labile groups and photoacid generator (PAG). Photolytic decomposition of PAG during light exposure generates acids in the CA resist. This acid acts as catalyst to facilitate de-protection reaction of ester group or acetal group of polymer, rendering polymer matrix alkaline-soluble. For achieving desired resist performance such as resolution, depth-of-focus, line edge roughness and etching resistance, the acid-labile polymers have been intensively studied first and developed notably. For further improvement of the CA resist, PAG is the key ingredient. We have developed new oxime sulfonate type PAGs releasing strong acid. A series of oxime sulfonate compounds with various chromophors have been synthesized and the application-relevant properties are presented in this paper.

Novel photoacid generators for chemically amplified resists

Recently we have developed new class of non-ionic oxime sulfonate PAG. The compounds generate various kinds of sulfonic acids, such as n-propane, n-octane, camphor and p-toluene sulfonic acid under Deep-UV exposure and are applicable for chemically amplified (CA) photoresists. The application-relevant properties of the compounds such as solubility in propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, ethyl 3-ethoxypropionate, and 2-heptanone, UV absorption, thermal stability with or without poly(4-hydroxystyrene) (PHS), storage stability in a neat form or in PGMEA solution with or without additives, sensitivity in a model resist formulation, dissolution inhibition efficiency during the development process and volatility were evaluated. The compounds exhibit good solubility in PGMEA, high sensitivity in positive tone CA resist formulations, with Deep-UV exposure, and no significant volatility. Especially it was found that the compounds are superior in terms of thermal stability and storage stability, i.e., high thermal stability up to 188 degree(s)C in a phenolic matrix, and no change during storage in PGMEA at 60 degree(s)C for 5 months.

Novel photoacid generators for chemically amplified resists with g-line, i-line, and DUV exposure

A new class of compounds, (5-alkylsulfonyloxyimino-5H-thiophen-2-ylidene)-2-methylphen yl-acetonitriles, characterized as non-ionic and halogen-free photoacid generators (PAGs) was developed. The compounds generate various kinds of sulfonic acids, such as methane, n-propane and camphor sulfonic acid under the g-line (436nm), i-line (365 nm) and Deep UV (DUV, 248 nm or shorter) exposure and are applicable for chemically amplified (CA) photoresists. The application-relevant properties of the compounds such as solubility in propylene glycol monomethyl ether acetate (PGMEA), UV absorption, thermal stability with or without poly(4-hydroxystyrene), storage stability in a neat form, sensitivity in some model resist formulations and dissolution inhibition efficiency during development process were evaluated. The compounds exhibit enough solubility in PGMEA, red-shifted UV absorption (

Non-ionic photoacid generators for chemically amplified resists: evaluation results on the application-relevant properties

lamdamax: 405 nm), good thermal stability up to 140 C in a phenolic matrix, effective acid generation in terms of quantum yield in an acetonitrile solution and high sensitivity in negative tone and positive tone CA resist formulations, such as tert-butyl ester type and t-BOC type formulations, with g-line, i-line and DUV exposure. The photochemical decomposition reaction of the compound was also studied. Additionally a scanning electron microscope (SEM) photography as an application example of microlithography by the CA negative tone resist with the PAG is presented.

Non-ionic photoacid generators for chemically amplified photoresists: structure effect on resist performance

Recently we have developed and reported some novel non-ionic photoacid generators (PAGs) which generate a strong acid (perfluorobutanesulfonic acid) by light irradiation and is applicable to chemically amplified ArF photoresist, such as 2-[2,2,3,3,4,4,5,5-octafluoro-1-(nonafluorobutylsulfonyloxyimino)-pentyl]-fluorene (ONPF), 2- [2,2,3,3,4,4,4-heptafluoro-1-(nonafluorobutylsulfonyloxyimino)-butyl]-fluorene (HNBF) and so on. Here the lithographic property of ONPF in some ArF model formulations was evaluated under 193 nm dry and immersion exposure comparing one of the most typical ionic PAGs, triphenylsulfonium perfluorobutanesulfonate (TPSPB), on lithographic application-relevant properties, e.g. exposure latitude, line edge roughness (LER) and so on, by top-down view SEM observation. 80 nm line and space (L/S) patterning was successfully conducted. Additionally we investigated the striation issue with ONPF when the matrix polymer of resist was changed. It was revealed that ONPF showed better coating property in a copolymer of &ggr;-butyrolactone methacrylate, 2-ethyladamantyl methacrylate and hydroxyladamantyl methacrylate than in a copolymer of &dgr;-methacryloyloxynorbornane butyrolactone in lactone unit.

Novel nonionic photoacid generator releasing strong acid for chemically amplified resists

As reported previously, we developed a novel oxime sulfonate type of photoacid generator (PAG), 2-[2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1-(nonafluorobutylsulfonyloxyimino)-heptyl]-fluorene (DNHF), which generates a strong acid (nonaflic acid) by light irradiation and is applicable to chemically amplified ArF photoresists. Recently we have prepared two DNHF analogues with different fluoroalkyl chains adjacent to the oxime moiety, 2-[2,2,3,3,4,4,4-heptafluoro-1-(nonafluorobutylsulfonyloxyimino)-butyl]-fluorene (HNBF) and 2-[2,2,3,3,4,4,5,5-octafluoro-1-(nonafluorobutylsulfonyloxyimino)-pentyl]-fluorene (ONPF), and investigated the structure effect. The change of the fluoroalkyl chain did not have a strong impact on photo-efficiency and transparency at 193 nm and these PAGs demonstrated superiority to triphenylsulfonium nonaflate (TPSNF) with respect to these criteria. On the other hand, different behaviors were observed in the coating property and contact angle measurement of the photoresists containing these PAGs. The hydrogen atom at the end of the fluoroalkyl chains of DNHF and ONPF was found to have a role in improving the coating property. These non-ionic PAGs were less risky for contamination on the surface of the lens due to insolubility in water. In addition, the effect by these PAGs on increasing hydrophobicity of the photoresist surface was identified. These results suggest that the newly developed non-ionic PAGs are suitable for ArF immersion lithography.

A novel photoacid generator for chemically amplified photoresist with ArF exposure

Recently we have developed a novel non-ionic PAG, which generates a strong acid (perfluorobutanesulfonic acid) by light irradiation, and is applicable for chemically amplified photoresists. Application-relevant properties such as solubility in common organic solvents and water, thermal stability, storage stability in neat form and solution, UV absorption, and sensitivity in model formulations were evaluated. The compound showed good solubility in organic solvents and no solubility in water. Good storage stability was observed in solution, even in the presence of amine, where conventional non-ionic PAGs were not found to be stable. From the evaluation in the model formulation with ArF laser exposure, it was found that this new compound has high transparency at 193 nm and superior photo-efficiency to triphenylsulfonium perfluorobutanesulfonate (TPSPB). In addition, the new compound exhibited significant sensitivities at DUV (254 nm) and i-line (365 nm) wavelengths.

OXIME DERIVATIVES AND THE USE THEREOF AS LATENT ACIDS

Recently a new non-ionic PAG was developed and its performance was evaluated in a model ArF photoresist formulation. The development profile of the photoresist including the new PAG was studied in detail by using dissolution rate measurement (DRM) apparatus and compared with popular PAGs, such as triphenylsulfonium triflate (TPST), bis(p-ter-butylphenyl)iodonium triflate (BTIT) and 5-norbornene-2,3-dicarboximidyl trifluoromethanesulfonate (NDIT). As the consequences, the photoefficiency of the new PAG was higher than BTIT and NDIT and comparable to TPST. From the DRM results, the new PAG showed a high contrast (high tan θ value). In addition, the simulation based on the results of DRM suggested that the new PAG is superior to TPST in terms of resolution and depth of focus (DOF) latitude.