Akinobu Tanaka

Effect of Acid Diffusion on Resolution of a Chemically Amplified Resist in X-Ray Lithography

The diffusion range of acids in a chemically amplified positive resist (EXP) was quantitatively evaluated using a contact replication method. The acid diffusion range reached a maximum depth of 0.4 µm. The acid diffusion range was diminished, as the temperature of prebaking was raised or the temperature of post-exposure baking (PEB) was reduced. The acid diffusion range also exerted a great influence on changing the replicated pattern width dependence on exposure dose. To clarify the effect of the acid diffusion on the characteristics of the resist, the distribution of the acid-catalyzed reaction in the resist and the acid diffusion range were calculated using the diffusion coefficient of the acid and the acid-catalyzed reaction rate constant determined by experiments. The calculated acid diffusion range coincided rather well with that obtained by the contact replication method.

The Effect of an Organic Base in Chemically Amplified Resist on Patterning Characteristics Using KrF Lithography

A new resist system composed of an SEPR chemically amplified (CA) positive resist and an N-methyl pyrrolidone (NMP) organic base has been developed for KrF excimer laser lithography. Using 0.30-µ m l&s patterns formed with KrF stepper, we studied the effect of contamination from substrate films of plasma chemical vapor deposition silicon dioxide (P-CVD SiO2), low pressure CVD silicon nitride (LP-CVD Si3N4) and reactive sputtered titanium nitride (TiN), and of airborne contamination under the condition of an 8-ppb of ammonia. The results clarify the new resist system reduces the effect of substrate film as well as airborne contamination. The new resist system enables us to form fine patterns on any substrate and attains more than one hour post-exposure delay without overcoat and undercoat films.

Influence of Acid Diffusion on the Lithographic Performance of Chemically Amplified Resists

The distribution of chemical amplification reactions incidental to catalytic acid diffusion is calculated to clarify its influence on the lithographic performance of chemically amplified resists. The distribution of the chemical amplification reaction is less extensive than that of catalytic acid. There exists an optimum diffusion length for maximizing sensitivity without sacrificing resolution. Acid diffusion coefficients in the chemically amplified resist EXP are 15 nm2/s at 55°C and 50 nm2/s at 65°C. A trade-off between sensitivity and resolution is observed in the EXP, which is attributed to acid diffusion. The relation between the variables is formulated by (Resolution)\propt(Sensitivity)-1/2 on the basis of a simple model, and guidelines are proposed for the material design of high-performance chemically amplified resists.

Synthesis of alkali-soluble silicone resin suitable for resist material in microlithography

Abstract An alkali-soluble silicone resin, acetylated phenylsilsesquioxane oligomer (APSQ), was synthesized from phenylsilsesquioxane oligomer by Friedel Crafts acetylation. Silanol groups are simultaneously formed in APSQ through this acetylation. The presence of silanol groups makes APSQ soluble in alkaline aqueous solutions. Silicone-based results composed of APSQ and sensitizers were prepared for ultraviolet (u.v.), deep u.v., electron beam and X-ray lithographies. These resists based on APSQ can be developed with alkaline aqueous solutions and have high resistance to oxygen reactive ion etching.

Resolution characteristics of a novel silicone‐based positive photoresist

A novel silicone‐based positive photoresist (SPP) is developed for a two‐layer resist system. SPP is composed of an alkali‐soluble silicone polymer (APSQ) and a diazonaphthoquinone compound as a sensitizer. APSQ is newly synthesized by means of acetylation of polyphenylsilsesquioxane (PSQ). A fine SPP pattern below 0.5 μm can be fabricated with a g‐line stepper (NA=0.6) using a two‐layer resist system. Moreover, a 0.4 μm line/space pattern is successfully fabricated at a defocus of ±0.4 μm. The high oxygen reactive ion etching (O2RIE) resistance of SPP makes possible the fabrication of a submicron pattern with a high aspect ratio in a two‐layer system. Pattern width loss can be negligible during O2RIE of a 2 μm thick bottom resist when a 0.6 μm thick SPP is used as the top imaging layer.

Metal-free chemically amplified positive resist resolving 0.2 μm in x-ray lithography

A chemically amplified positive resist (EXP) and its processing have been optimized for high resolution in x‐ray lithography. EXP is composed of a novolak resin, 2,2‐bis(t‐butoxycarbonyloxyphenyl)‐propane as a dissolution inhibitor, and bis(p‐t‐butylphenyl)iodonium trifluoromethanesulfonate as an acid generator. Sensitivity and resolution characteristics were greatly influenced by post‐exposure baking (PEB) conditions. Applying PEB at 65 °C for 60 s resulted in the successful fabrication of 0.2‐μm patterns in a 1.3‐μm‐thick EXP film. The pattern width remained virtually unchanged during a three‐hour holding time between x‐ray exposure and PEB. The exposure latitude for ±10% width change for 0.2 μm holes was about 10%.

High‐speed positive x‐ray resist suitable for precise replication of sub‐0.25‐μm features

A high‐speed chemically amplified positive resist based on poly(p‐hydroxystyrene) has been developed for x‐ray lithography. This resist, CANI (meaning chemically amplified resist) by Nippon Telegraph and Telephone Corporation, has a sensitivity of 50–70 mJ/cm2 to soft x rays while maintaining sub‐0.25‐μm resolution and a rather large dose margin of 34%–40%. Another advantage of CANI is that the theoretical weight loss from the removal of t‐butyl protecting groups by chemical amplification reactions is less than 4 wt %. This leads to little volume shrinkage at uv cure and reactive ion etching processes, and thus promises good controllability of pattern feature sizes between lithography and subsequent plasma etching processes.

Theoretical study of latent image formation in chemically amplified resists

Theoretical analysis of chemically amplified resists indicates that a higher reaction order of acid-catalyzed reaction and lower diffusion length of acid enhance image quality. We identified the relation between diffusion length and the number of catalytic acids appropriate for inducing a given amount of acid-catalyzed reactions as a function of the difference between the activation energies of diffusion (E ad) and acid-catalyzed reaction (E ar), and the post-exposure baking (PEB) temperature. When E ad=E ar, the diffusion length required for a certain amount of acid-catalyzed reaction is inversely proportional to the square root of the amount of generated acids, regardless of PEB temperature. When E ad≠E ar, the required diffusion length depends on PEB temperature. When E ad<E ar, the diffusion length is smaller at higher PEB temperatures, and this will be preferable for enhancing the resist resolution.

Characteristics of a Monodisperse PHS-Based Positive Resist (MDPR) in KrF Excimer Laser Lithography

A new chemically amplified monodisperse PHS-based positive resist (MDPR) has been developed for KrF excimer laser lithography. MDPR is an alkali-developable single-layer resist, composed of partially tBOC-protected PHS, a dissolution inhibitor and a photoacid generator. We used nearly monodisperse PHS synthesized by living polymerization and obtained fine patterning. The MDPR has a high contrast value γ of 4, which results in excellent resolution: the MDPR can easily generate l & s patterns down to 0.25 µm in width at 90 mJ/cm2. A higher sensitivity of 45 mJ/cm2 and a contrast value γ of 12 were achieved with a blended MDPR.

Alkali-Developable Silicone-Based Negative Photoresist (SNP) for Deep UV, Electron Beam, and X-Ray Lithographies

A new silicone-based negative photoresist (SNP) developable with alkaline aqueous solutions is prepared. SNP composed of acetylated phenylsilsesquioxane oligomer and azidopyrene is applied to deep UV, electron beam (EB), and X-ray lithographies. SNP slightly swells in alkaline developers, thus exhibiting exceptionally high resolution characteristics for a negative resist. The resistance of SNP to oxygen reactive ion etching is approximately 30 times greater than that of conventional novolac resists.