Tohru Ushirogouchi

Effect of basic additives on sensitivity and diffusion of acid in chemical amplification resists

The effect of amine additives in chemical amplification resists is discussed. Phenolic amines such as 4-aminophenol and 2-(4-aminophenyl)-2-(4-hydroxyphenyl) propane were investigated as model compounds from the viewpoint of sensitivity, diffusion and resolution. Equal molar amounts of acid and amine deactivated at the very beginning of post-exposure bake, and could not participate in decomposing the inhibitor as a catalyst. Only the acid which survived from the deactivation diffuses in the resist, decomposing the inhibitors from the middle to late stage of PEB. The basic additives reduce the diffusion range of the acid, especially for long-range diffusion, resulting in higher contrast at the interfaces between the exposed and unexposed areas. In addition, the amine concentration required is found to be less than the concentration which causes the resist sensitivity to start decreasing.

Mechanism of amine additive in chemically amplified resist visualized by using Monte Carlo simulation

A novel simulator using the Monte-Carlo method, which simulates molecular-like movements and reactions in chemically amplified resist systems, has been developed in order to clarify the mechanism of amine additive. The simulation program simulates diffusion phenomena with random-walked acids and amine molecules, and reactions of deactivation (neutralization) and inhibitor cleavage in every movement of the molecules. It was found that the amine in the exposed area was rapidly deactivated, and the concentration profile of the remaining amine was rapidly changed to an inversely shaped profile of that of the acid. This means that the remaining amine prevents diffusion of acids outside the exposed area by functioning as a barrier during almost the whole period of post-exposure bake (PEB). These concentration profiles lead to an enhancement of stability of pattern sizes and reduction of edge roughness of the pattern. Environmental stability was also calculated, and amine additive was also found to prevent contamination from the environment in the initial period of the PEB.

Highly transparent chemically amplified ArF excimer laser resists by absorption band shift for 193 nm wavelength

Naphthalene-containing chemically amplified resists for ArF excimer laser exposure are proposed, based on the concept of the absorption band shift by conjugation extension. Newly developed ArF excimer resists show a high transparency at 193 nm wavelength, a high sensitivity and a high contrast. The sensitivity of the resist is 150 mJ/cm2, which is 20 times greater than that of poly(methylmethacrylate) (PMMA). Furthermore, a 0.16 µ m pattern could be successfully fabricated by an ArF excimer laser stepper with 0.55 numerical aperture (NA) projection lens.

A new positive electron-beam resist material composed of catechol derivatives

Abstract A catechol derivative, hexahydroxycyclotribenzylene protected with p - t -butoxycarbonylmethyl group (HCB-BCM), was synthesized. We found that the photoresist containing HCB-BCM could be dissolved in water, after EB-exposure and post-exposure bake. It showed a high sensitivity and contrast, and high durability to CF 4 plasma etching. At 10 μC/cm 2 under 50-keV electron beam, 90-nm space pattern could be obtained.

Advanced materials for 193-nm resists

Acrylate monomers containing alicyclic side chains featuring a series of polar substituent groups were assumed to be model compounds. Solubility parameters were calculated for the corresponding acrylate polymers. These acrylate monomers were synthesized using a novel aerobic oxidation reaction employing N-hydroxyphtalimide (NHPI) as a catalyst, and then polymerized. These reactions were confirmed to be applicable for the mass-production of those compounds. The calculation results agreed with the hydrophilic parameters measured experimentally. Moreover, the relationship between the resist performance and the above-mentioned solubility parameter has been studied. As a result, a correlation between the resist performance and the calculated solubility parameter was observed. Finally, resolution of 0.13-micron patterns, based on the 1G DRAM design rule, could be successfully fabricated by optimizing the solubility parameter and the resist composition.

Effect of remaining solvent on sensitivity, diffusion of acid, and resolution in chemical amplification resists

The effect of the remaining solvent on the diffusion of the catalytically active acid within the chemical amplification resists is discussed. A range of solvents was investigated from the viewpoint of sensitivity, diffusion, and resolution. The solvent remaining after the coating and baking processes is thought to one of the most probable factors among the several possible causes in the determination of the performance of the resists. It is also considered to result in the environmental instability which is currently one of the most serious problems in the use of the resists of this type. The remaining solvent drastically enhances the thermal diffusion of acid generated from photo‐acid generators upon photoanalysis. The log of the diffusion range of the acid is found to be proportional to the concentration of the remaining solvent. This phenomenon may be described by a theory which combines the hole theory of liquids and the free volume theory of polymers and was also found to be the correlation energy be...

Resist profile simulation for photoresist composition optimization

Monte Carlo dissolution simulation and dissolution properties related to resist composition were studied. Using these results, a composition assembling resist profile simulator (CARPS) has been developed. This simulator makes it possible to optimize the resist composition.

Chemically amplified ArF resists based on cleavable alicyclic group and the absorption band shift method

Recent advances in the single-layer resist for forming finer patterns have led us to a search for new resist materials for the ArF excimer laser. We describe a novel, environmentally friendly, single-layer resist based on a menthyl acrylate copolymer protected with a cleavable alicyclic group and the absorption band shift method.

Chemically ampilified ArF excimer laser resists using the absorption band shift method

The VUV-absorption spectrum of aromatic compounds can be red-shifted toward longer wavelengths to make the window of absorption align with 193 nm by extending the conjugation length of the double bonds. Based on this observation, the new concept of absorption band shifting is proposed as a way to increase the transparency of resist components for 193 nm ArF excimer laser exposure. A chemically amplified single-layer ArF excimer laser resist consisting of naphthalene-containing photoacid generator, a dissolution inhibitor, and base polymer has been newly developed. Using this resist, a 0.17 micrometers line/space pattern with a vertical resist profile was resolved by a prototype 0.55 NA projection lens for ArF excimer laser exposure, and a resolution limit of 0.16 micrometers was achieved.

Quantum chemical studies of chemically amplified resist materials for electron-beam and ArF excimer laser

Quantum chemical calculation is applied to investigate the reaction mechanism of sulfonyl acid generator and the transparency of the resist material. We have found that electron absorbed dimethylsulfone can be easily decomposed by relatively low energy (2.95 Kcal/mol), reaching to the decomposed status of methyl radical and methyl sulfonyl anion. This was thought to be an initial step in the electron acid generation reaction of the sulfonyl compounds. The total molecular energy of dimethyl sulfone anion was found to be higher than that of the neutral dimethylsulfone. On the other hand, sulfone derivatives with electron-withdrawing groups, such as methyl sulfonyl acetonitrile, usually have higher energy (about 41 kcal/mol) than those for their anion. This suggests that the electron withdrawing groups enhance the electron affinity of the sulfone compounds, which are also considered to increase the efficiency of acid generation. Additionally, another quantum chemical study was carried out in order to improve transparency of the aromatic species in resist for ArF excimer laser. Using configuration interaction (CI) methods of molecular orbital theory, the substituent effects of UV absorption in the aromatic compounds were investigated. As a result, significant red sifts in Amax were observed in the conjugated aromatic rings, which increases the transparency at 193 nm wavelength region.