Mitsuharu Yamana

A study of acid diffusion in chemically amplified deep ultraviolet resist

Postexposure bake (PEB) dependence of photogenerated acid diffusion was investigated in a chemically amplified deep ultraviolet positive resist. The resist consisted of a tert‐butoxycarbonyl protected polystyrene as base resin and 2,4‐dimethylbenzenesulfonic acid derivative as photoacid generator. The diffusion length of photoacid increased with increasing PEB temperature or its time. Moreover, the activation energy of acid diffusion reaction within the resist film became smaller, with increased exposure dose. It is considered that hydrophilic OH sites of the base resin generated by the deprotection of hydrophobic protecting groups has a role as one of the diffusion paths in the polymer matrix. Furthermore, it was found that the diffusion coefficient under high PEB conditions was affected by the acid reduction. Based on the analysis of diffusion characteristics, clear correlation between acid diffusion in the resist film and PEB conditions was obtained. These results are useful for improving both resoluti...

Polymer structure effect on dissolution characteristics and acid diffusion in chemically amplified deep ultraviolet resists

The role of molecular weight dispersion (Mw/Mn) of base phenolic resin was investigated in chemically amplified positive KrF resists. The resists consisted of tert-butoxycarbonyl (t-BOC) blocked polystyrene as base resin and 2,4-dimethylbenzenesulfonic acid derivative as photoacid generator, and the Mw/Mn value was changed as 1.2, 4.0, and 9.0. Not only dissolution rate contrast, but also the slope m of log(dissolution rate)-log(exposure dose) plots increased with decreasing Mw/Mn. In the case of low Mw/Mn, the molecular structure becomes more homogeneous, so resist film could be dissolved uniformly via constant developer penetration into film. This uniform dissolution characteristics may be attributable to the origin of dispersion effects mentioned above. Furthermore, higher acid diffusion property and smooth pattern side wall were obtained without side wall roughness in lower Mw/Mn. This fact indicates that acid diffusion length is also uniform within resist film in the case of low Mw/Mn. Based on the e...

Relationship between Remaining Solvent and Acid Diffusion in Chemically Amplified Deep Ultraviolet Resists

For clarification of the diffusion path of photogenerated acid in the resist film, the prebake temperature dependence and tert-butoxycarbonyl ( t-BOC) blocking level dependence on acid diffusion were investigated for chemically amplified deep ultraviolet (DUV) positive resists. The resists consisted of a t-BOC protected polystyrene base resin and a 2,4-dimethylbenzenesulfonic acid derivative as a photoacid generator (PAG). The concentration of remaining solvent in the resist film decreased as the prebake temperature or t-BOC blocking level increased. The acid diffusion coefficient was almost independent of exposure dose; however, it decreased with increasing prebake temperature or blocking level. Therefore, it was considered that the concentration of remaining solvent in the resist film corresponds to one of the acid diffusion paths. Moreover, hydrophilic OH sites, whose concentration was the reciprocal of the blocking level, were also considered to correspond to a diffusion path in the polymer matrix, based on the fact that the acid diffusion length increased gradually with decreasing t-BOC blocking level, even when the solvent concentration remained constant. Based on the experimental analysis results, the existence of two diffusion paths, as well as of explicit relationships among the remaining solvent, t-BOC blocking level and acid diffusion length was confirmed.

A study of dissolution characteristics and acid diffusion in chemically amplified DUV resist

The effects of dissolution characteristics and acid diffusion behavior on lithographic performance were evaluated in tert-butoxycarbonyl (t-BOC)-protected chemically amplified positive deep-ultraviolet (DUV) resists. The resists consisted of t-BOC-protected polyhydroxystyrene as a base resin and 2,4-dimethylbenzenesulfonic acid derivative as a photoacid generator (PAG). In particular, the line width difference between an isolated line and a dense line (iso/dense bias) was investigated by changing the post-exposure bake (PEB) temperature. As a result, clear relationships among dissolution characteristics, acid diffusion length, and iso/dense bias were obtained. Moreover, suitable dissolution characteristics and acid diffusion length for reducing iso/dense bias were clarified.

Acid and base diffusion in chemically amplified DUV resists

Abstract In order to clarify the photogenerated acid diffusion in resist film, the diffusion behavior of acid, as well as the role of additional base component was investigated in tert-butoxycarbonyl (t-BOC) protected type chemically amplified positive deep ultraviolet (DUV) resists. The resists consisted of t-BOC protected polystyrene as a base resin, 2,4-dimethylbenzene sulfonic acid derivative as a photoacid generator (PAG) and N-methyl-pyrrolidone (NMP) as an additional base component. Acid diffusion coefficient was suppressed by the addition of base component. Moreover, the change of base concentration corresponded directly to the lithographic performance, such as sensitivity, resolution capability and resist profile, especially T-topping formation. Based on the experimental analysis, the clear relationship between acid diffusion length and additional base was obtained.

Dissolution characteristics of chemically amplified 193 nm resists

The dissolution kinetics of two types of chemically amplified positive 193 nm resists were investigated; a ter-polymer resist consisting of poly(tricyclodecylacrylate-co-tetrahydrodpyranyl-methacrylate-co-methacrylic acid) and triphenylsulfonium triflate as a photoacid generator, and a copolymer resist consisting of poly(carboxytetracyclododecylmethacrylate-co-tetrahydro-pyranyloxy-carbonyl-tetracyclododecylmethacrylate) and triphenylsulfonium triflate as a photoacid generator. The dissolution rate contrast was higher and the slope of dissolution rate curve was steeper for the ter-polymer resist than those for the copolymer resist. However, the Arrhenius plots of the dissolution rates were straight lines for both resists irrespective of the exposure doses. This indicates that only one mechanism determines the dissolution of both resists, and it is believed that the dominant rate-determining step in both resists is the tetramethylammoniumhydroxide penetration into the resist films. The resolution capabilit...

Deblocking reaction of chemically amplified ArF positive resists

Deblocking reaction mechanisms and lithographic performance in chemically amplified positive ArF resists were investigated by analyzing acid concentration and blocking level. The resists consisted of triphenylsulfonium triflate as a acid generator and either the copolymer, poly(carboxy- tetracyclododecyl methacrylate70-co- tetrahydropyranylcarboxy-tetracyclododecyl methacrylate30) or the terpolymer, poly(tricyclodecylacrylate60- co-tetrahydropyranylmethacrylate20-co-methacrylic acid20). The deblocking reaction mechanisms were evaluated from Arrhenius plots of the deblocking reaction rate constant. It was found that the deblocking reaction of both resists is ruled by two rate-determining steps, i.e., reaction-controlled in the low-temperature region and acid- diffusion-controlled in the high-temperature region. Furthermore, the copolymer resist had better post-exposure- delay (PED) stability. To clarify this result, acid loss caused by air-born contamination effect on deblocking reaction was investigated. The change of amount of blocking group by acid loss was small for the copolymer. Therefore the copolymer resist had better PED stability. Furthermore, the post-exposure bake (PEB) sensitivity of linewidth of the copolymer resist was smaller than that of the terpolymer resist. Both deblocking reaction rate constant and reverse reaction rate constant of the copolymer resist increased with PEB temperature. As a result, equilibrium constant of the copolymer was not valuable with temperature. This is the reason why the copolymer resist has low PEB sensitivity. It is concluded that small acid loss effect on deblocking reaction induces better PED stability. A resist with reverse reaction has an advantage for PEB temperature sensitivity.

Compatibility of chemically amplified photoresists with bottom antireflective coatings

The effects of acid structures and blocking groups in chemically amplified resists on compatibility with bottom anti-reflective coatings (BARCs), were investigated. The resists consisted of tert-butoxy carbonyl (t-BOC) or acetal blocked polyhydroxystyrene with three types of photoacid generators (PAGs) which generate trifluoromethanesulfonic acid (acid 1), 2,4-dimethyl benzensulfonic acid (acid 2) and cyclohexanesulfonic acid (acid 3). Three types of commercially available BARCs, Brewer Science CD9, DUV11 and DUV18 were used for this study. CD9 was decomposed by exposure and generated an acid substance, which induced the necking at the bottom of the resist films. In the case of DUV11, the generated acid from the PAG was neutralized, and footing was observed in t-BOC type resists. Acetal type resists had no footing on DUV11 because the deblocking reaction progressed without post-exposure baking. DUV18 had good compatibility with most of the resist materials because of its neutral acidity. From the viewpoint of resist materials, it was found that the acetal type resists tended to have necking, because the deblocking reaction occurred at lower acid concentration compared with t-BOC type resists. Moreover, the tendency to have a necking profile, in increasing order, was acid 3 > acid 2 > acid 1. This order corresponded with the reverse order of the efficiency of the deblocking reaction. A weak acid might be greatly affected by some substance diffused from a BARC. The acetal type resist with acid 1 had excellent compatibility with various BARCs. However, the resolution capability of the acetal type resist with acid 1 was lower than that of the acetal type resist with acid 3, because the acid diffusion length of acid 1 was larger than that of acid 3. It was concluded that good compatibility of the resist with the BARC is achieved by the high deblocking reaction efficiency and moderate diffusion length of acid in acetal type resists.

Preparation and optical properties of amorphous silica doped with porphins (TCPP)

Tetrakis(4-carboxyphenyl)porphine (TCPP), which is well known as a photochemical hole burning (PHB) dye, was incorporated in amorphous silica materials (a-SiO2) by a sol-gel process with using tetramethoxysilane (TMOS) and aminopropyltriethoxysilane (APTES). With using APTES as precursor of silica gel, TCPP was cross-linked to a-SiO2 matrix through aminopropyl group of APTES. The cross-linkage of TCPP and APTES was confirmed by the FT-IR measurement. The TCPP incorporated in a-SiO2 matrices showed activity in PHB. In the TCPP cross-linked a-SiO2, properties of photochemical hole, such as hole width, quantum efficiency and irreversible broadening under cycle annealing experiment, were improved. A burnt hole at 3.6 K was observed after cycle annealing experiment up to 80 K in the TCPP cross-linked a- SiO2.

Investigation of environment stability in chemically amplified resists

Abstract This paper describes the environmental stability in chemically amplified resists, especially post exposure delay stability depending on NH 3 concentration in the atmosphere around resists, and substrate sensitivity. The environmentally stable chemically amplified resists, ARCH2 and KRF L7G, exhibited high resistance to both airborne contamination and substrate contamination. These resists may be used without chemical filters, which removes base contamination in the air. However, the resist footing caused by the low light strength at the bottom of the resist film, were not eased even in these resists, because acid diffusion was restrained in these resists.