Takuya Naito

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.

Optimization of a high-performance chemically amplified positive resist for electron-beam lithography

We report on sub-0.1 μm electron-beam (EB) lithography using a new chemically amplified positive resist with a stabilizing additive. Diphenylamine (DPA) was incorporated into the resist formulation as a stabilizing additive. DPA improves the post-exposure delay (PED) stability. Even after a PED of 60 min in a clean-room atmosphere (NH 3 concentration ∼20ppb), no insoluble surface layer was observed for the resist with DPA. High sensitivity and resolution could be achieved by optimizing process conditions such as baking and developer. 0.1 μm lines-and-spaces (L/S) patterns and 0.08 μm hole patterns were obtained using a 50 kV variably shaped beam EB system. The practical sensitivity was 6 μC/cm 2 for L/S patterns. Our resist system also shows good performance as an etching mask. A 0.1 μm diameter hole which was 0.5 μm etched in silicon oxide using a 0.5 μm thick resist could be obtained in this experiment.

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.

Chemically Amplified Resist Using Self‐Solubility Acceleration Effect

A novel three-component chemically amplified positive tone resist system for EB lithography composed of a novolak resin, an acid generator, and a newly synthesized dissolution inhibitor, is investigated. Four 1-(3H)-isobenzofuranone derivatives containing a tert-butoxycarbonyl (t-Boc) group and a lactone ring have been synthesized as dissolution inhibitors. The t-Boc group of these dissolution inhibitors was effectively decomposed by an acid catalyzed thermal reaction. In addition to this decomposition, the lactone ring of the decomposed product was spontaneously cleft in an aqueous base to generate carboxylic acid. Among these synthesized substances, only the t-Boc derivative of o-cresolphtalein showed an excellent solubility in 1-acetoxy-2-ethoxyethane

Effect of base additive on process latitude in chemically amplified electron-beam resists

The stability during the storage between EB exposure and post- exposure bake (PEB) of the chemically amplified resist containing diphenylamine (DPA) was discussed. The large dimension change of 0.15 micrometer L/S pattern with 14 (mu) C/cm2 EB dose was observed within 1 hour in a vacuum due to the deprotection reaction. The stability of the resist properties in an atmosphere before PEB (PED instability) depends on the time during which the exposed resist is stored in a vacuum. Keeping the exposed resist in a vacuum for more than about 20 minutes makes PED instability good. This seems to be caused by a dark reaction for about 20 minutes, which occurs in addition to the deprotection reaction and realizes equilibrium between DPA and acid generated by EB exposure. This mechanism by which DPA acts as a superior stabilizing base additive is supported by the time dependence of surface resistance for the resist in an atmosphere.

Effect of substituent groups of phenol-derivative dissolution inhibitors on inhibition efficiency

This paper focuses on the inhibition efficiency of t-Boc derivatives of bis-phenols. Several t- Boc derivatives of bis-phenols were synthesized and their inhibition effects were evaluated in novolac resin and poly (4-hydroxystyrene) (PHS). When the novolac resin was used as the matrix polymer, the inhibition effects were thought to be governed by both the hydrophobicity and molecular size of the inhibitors. On the other hand, in the case of PHS, the hydrophobicity of the inhibitor molecule was thought to be the dominant factor responsible for decreasing dissolution rates. In addition, the effects of the basic components of the developers were also investigated. Solutions of sodium hydroxide, tetramethylammonium hydroxide and tetraethylammonium hydroxide were employed as developers. The effects of the basic components on the dissolution rates of the resists varied with the matrix polymer of the resist. The dissolution rate of novolac resin was higher in NaOH solution than in the developers consisting of organic bases. However, the dissolution rates of novolac resin samples containing dissolution inhibitors were lower in NaOH solution than in developers consisting of organic bases. This phenomenon may be attributable to the hydrophilic properties of the cation of a developer.

Novel chemical amplification positive-resist material for EB lithography

This paper reports on a novel three-component chemical amplification positive resist system for EB lithography composed of a novolak resin, an acid generator, and a newly synthesized dissolution inhibitor. We synthesized a novel dissolution inhibitor named CP-TBOC (1), which contains a tert-butoxycarbonyl (t-BOC) group and a lactone ring, to obtain resist materials with high sensitivity and high contrast. The t-BOC group of this dissolution inhibitor effectively decomposed by an acid catalyzed thermal reaction as the other conventional dissolution inhibitors. In addition to this decomposition, the lactone ring of the decomposed product was spontaneously cleft in an aqueous base to generate carboxylic acid, further enhancing the solubility to alkaline developers. The subsequent cleavage in an aqueous developer was investigated by UV-visible spectroscopy. The highest EB sensitivity was obtained at a CP-TBOC concentration of approximately 4.7 X 10-4 mol/g.