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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.

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 kinetics of a chemically amplified deep ultraviolet (DUV) positive resist, which consists of tert-butoxycarbonyl (t-BOC) protected phenolic resin, benzenesulfonic acid derivative as a photoacid generator (PAG) and an additional dissolution inhibitor, has been investigated by focusing on the polymer structures (t-BOC blocking level, molecular weight and molecular weight dispersion) and photo-acid structures. Based on the analysis of the dissolution rate curve and Arrhenius plots, it was concluded that only one mechanism, namely, the penetration of tetramethylammonium hydroxide (TMAH) developer into hydrophobic t-BOC resin, rules the dissolution kinetics. It was also found that a steep slope of the dissolution rate curve is very effective for improving resolution capability. Moreover, ideal dissolution characteristics which can realize superior resolution capability, were obtained by analyzing both experimental dissolution rate and resist profile simulation.

The relationship between photoacid characteristics and lithographic performance in chemically amplified deep ultraviolet (DUV) resists was investigated. Two types of resist systems which consist of the same resin (tert-butoxycarbonyl (t-BOC) protected polyhydroxystyrene) and different photoacid generators (PAGs) were used. Resist 1 contains PAG 1 which generates aromatic sulfonic acid (acid 1; 2, 4- dimethylbenzensulfonic acid) and resist 2 contains PAG 2 which generates alkyl sulfonic acid (acid 2; cyclohexanesulfonic acid).The sensitivity of resist 1 was about four times higher than that of resist 2, and T-top profile became remarkable in resist 1, while the resolution capability was much the same. In order to clarify the reason of these differences, the photoacid characteristics such as the acid generation efficiency by exposure, the vapor pressure, the acid strength (pKa value), and the acid catalyzed deblocking reaction were investigated, together with the dissolution rate characteristics.Higher sensitivity of resist 1(aromatic sulfonic acid) was originated from larger amount of photogenerated acid (high absorbance), longer diffusion length and higher efficiency of deblocking reaction, as compared with resist 2 (alkyl sulfonic acid). Moreover, it was considered that T-topping profile was due to the evaporation of aromatic sulfonic acid 1.Based on these analysis, it was concluded that moderate absorbance, optimum diffusion length and lower evaporation property can realize ideal acid characteristics, leading to superior resist performance.

The development of a process for contact hole tends to be overdue although priority is generally given to the development of line and space patterns. The size of a contact hole pattern in 45 nm node will be about 60 nm. 157-nm lithography will be applied to 45 nm node. The depth of focus is critical issue. Then we evaluated three types of contact hole shrinkage techniques such as Thermal Flow, SAFIER and RELACS for 157-nm lithography. A resist which was consisted of a polymer with fluoride on a side chain was used. The shrinkage temperature was optimized by applying hole shrinkage processes to patterns formed by 193-nm lithography. It was made clear that Thermal Flow process was not practical in the view point of extremely high shrinkage temperature. On the other hand, hole size was reduced by about 20 nm in the case of SAFIER and RELACS at controllable temperature. It is an advantage of SAFIER process that hole size is changed with shrinkage bake temperature. In RELACS process, small mixing temperature dependence of critical dimension (CD) is advantageous. Also in 157-nm lithography, it was shown that the shrinkage techniques such as SAFIER and RELACS are possible, and the about 75nm hole pattern was formed.

Various resists, which consisted of polymer systems, such as methacrylate, acrylate and cycloolefin/maleic anhydride (COMA), were investigated in the viewpoint of etching resistance, lithographic performance and shelf life. The oxide etching rate was in order of acrylate < methacrylate << COMA. The surface roughness of the acrylate type resist after oxide etching was the smallest among all samples. The methacrylate type resist showed high resolution capability as a line and space resist. On the other hand, pattern collapse was observed in the acrylate type resist, and low resolution was shown in the COMA type resist because of the large resist thickness loss. In the case of contacts, the acrylate type resist showed better linearity. The sensitivity of the acrylate and methacrylate type resists kept at room temperature did not changed in 20 days, while the sensitivity of the COMA type resist changed. It was found that the methacrylate type resist was the most suitable as a line and space resist and the acrylate type resist was the most promising as a contact hole resist.

This paper describes the effects of the blocking level of polymer on both dissolution characteristics and lithographic performance in chemically amplified positive 193 nm resists consisting of a alicyclic methacrylate polymer and a photoacid generator. There were clear relationships between the blocking level and both the dissolution rate characteristics and the lithographic performance. We found that the dissolution contracts and developer selectivity improved as the blocking level of polymer increased, and then the resolution capability was improved. However, the dry-etch resistance and adhesion property of the resist film deteriorated as the blocking level increased, although these were at the same levels as those of conventional i-line novolak resist or polyhydroxystyrene base KrF resists. Therefore, these resist materials show potential for the next generation of LSI devices. Ideal dissolution parameters for improving the resolution capability were obtained by using a resist profile simulator. By using a high-contrast resist incorporating these parameters, and by using a higher numerical aperture lens and annular illumination, the mass production of next-generation devices with a 0.12 micrometers design rule can be achieved.

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 methacrylate 70 -co-tetrahydropyranylcarboxytetracyclododecyl methacrylate 30 ) or the terpolymer, poly(tricyclodecylacrylate 60 -co-tetrahydropyranylmethacrylate 20 -co-methacrylic acid 20 ). 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.

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.

Tetrakis(4-carboxyphenyl)porphine (TCPP), which is well known as a photochemical hole burning(PHB) dye, wasincorporated in amorphous silica materials(a-Si02) by a sol-gel process with using tetramethoxysilane(TMOS) andaminopropyltriethoxysilane(APTES). With using APTES as precursor of silica gel, TCPP was cross-linked to a-Si02matrix through aminopropyl group of APTES. The cross-linkage of TCPP and APTES was confirmed by the FT-IRmeasurement. The TCPP incorporated in a-Si02 matrices showed activity in PHB. In the TCPP cross-linked a-Si02,properties of photochemical hole, such as hole width, quantum efficiency and irreversible broadening under cycleannealing experiment, were improved. A burnt hole at 3.6K was observed after cycle annealing experiment up to 80K inthe TCPP cross-linked a-Si02.Keywords: TCPP, sol-gel process, photochemical hole burning(PHB), aminopropyltriethoxysilane(APTES), FT-IR,cross-link, hole width, quantum efficiency, irreversible broadening 1. INTRODUCTION

Deblocking reaction mechanisms and lithographic performance in chemically amplified positive KrF resist were investigated by analyzing acid concentration and blocking level. The resists consist of tetrahydropyranyl (THP) or tert-butoxycarbonyl (t- BOC) blocked polystyrene as the base resin and 2,4- dimethylbenzenesulfonic acid derivative as a photoacid generator (PAG). The deblocking reaction mechanisms and activation energy of the deblocking reaction were evaluated from Arrhenius plots of the deblocking reaction rate constant kd. It was found that the deblocking reaction is ruled by two rate-determining steps; it is reaction-controlled in the low-temperature region and acid-diffusion-controlled in the high-temperature region. The activation energy of THP blocked resists (THP resists) in the low-temperature region was lower than that of the t-BOC blocked resists (t-BOC resists). The THP groups were deblocked even at room temperature. Then the THP resist was hardly affected by air contamination. This is one of the reasons why the THP resist had good PED stability. Moreover, the linewidth difference between the isolated line and the dense line (iso-dense bias) of the THP resist was much larger than that of the t-BOC resist. It was concluded that the resist with a high deblocking reaction rate at room temperature had a clear advantage for PED stability, and that the activation energy of the deblocking reaction should be high at PEB (post-exposure bake) temperature to reduce iso- dense bias.

The lithographic performance of a chemically amplified resist system very much depends on the photo-generated acid structure. In a previous paper, we reported the molecular structure dependence of two typical photo-generated acids (aromatic sulfonic acid and alkyl sulfonic acid) from the viewpoints of lithographic performance and acid characteristics such as acid generation efficiency, acid diffusion behavior and acid evaporation property. In this paper, we evaluate the effect of the remaining solvent in a resist film on the acid evaporation property. Four types of two-component chemically amplified positive KrF resists were prepared consisting of tert-butoxycarbonyl (t-BOC) protected polyhydroxystyrene and sulfonic acid derivative photo-acid generator (PAG). Here, a different combination of two types of PAGs [2,4-dimethylbenzenesulfonic acid (aromatic sulfonic acid) derivative PAG and cyclohexanesulfonic acid (alkyl sulfonic acid) derivative PAG] and two types of solvents (propylene glycol monomethyl ether acetate; PGMEA and ethyl lactate; EL) were evaluated. The aromatic sulfonic acid was able to evaporate easily during post exposure bake (PEB) treatment, but the alkyl sulfonic acid was not. The higher evaporation property of aromatic sulfonic acid might be due to the higher vapor pressure and the longer acid diffusion length. Furthermore, the amount of aromatic sulfonic acid in the PGMEA resist was reduced by more than that in the EL resist. The amount of acid loss also became smaller at a higher prebake temperature. The concentration of the remaining solvent in the resist film decreased with the increasing prebake temperature. We think that the acid evaporation property was affected by the remaining solvent in the resist, film; the large amount of remaining solvent promoted the acid diffusion and eventually accelerated the acid evaporation from the resist film surface in the PGMEA resist. In summary, the acid evaporation property depends on both the acid structure and the remaining solvent in the resist film. These results can be applied to other chemically amplified resist systems to suppress the T-topping profile and achieve a superior resist performance.

Four Gb dynamic access random memory (DRAM) cell patterns which have a 0.12 μm design rule were demonstrated by using a high contrast chemically amplified 193 nm positive resist and high resolution exposure. All critical layers of 4 Gb DRAM, such as isolation, word line, contact hole, bit line, and storage node, were successfully resolved with suitable focus margin. The dissolution contrast of the resist film and the slope of dissolution rate curve were much higher than those of conventional polyhydroxystyrene based chemically amplified KrF positive resist. Moreover, the dry etch resistance of the resist film for both the polysilicon etch and the oxide etch was better than those of KrF resist. These results indicated that this resist material has enough potential for practical use. Furthermore, the resist profile simulation showed that mass production of 4 Gb DRAMs can be achieved by a combination of a high contrast resist and a higher numerical aperture lens under annular illumination.

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 experimental analysis, the clear relationship among Mw/Mn, dissolution characteristics and acid diffusion behavior in resist film was obtained. Moreover, it was found that lower Mw/Mn has advantage for improving inherent resist performance.

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.

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...