Ryoko Yamanaka

A New Pupil Filter for Annular Illumination in Optical Lithography

Several super-resolution photolithography techniques are investigated. In annular illumination, both the resolution and depth of focus (DOF) are enhanced most effectively when 0.6<σ<0.7, whether or not contrast enhancement techniques, such as pupil filters or edge-enhancing phase-shift masks (PSMs), are used. Various contrast enhancement techniques are investigated from the viewpoint of spatial frequency characteristics, since flat characteristics are required for good mask-to-image fidelity. We propose a new high-spatial-frequency enhancing filter for annular illumination system which meets this requirement. We also optimize edge-enhancing PSMs for use with annular illumination. It is shown that both methods can improve the resolution/DOF characteristics while maintaining good mask-to-image fidelity. A practical resolution analysis shows that 0.2 (0.3) µm patterns can be delineated with a DOF of ±0.6 (±0.75) µm, if a KrF (i-line) stepper with an NA0.5 lens and high-contrast resist materials are used, with few restrictions on the pattern layout.

Development of Ammonia Adsorption Filter and Its Application to LSI Manufacturing Environment.

Activated carbon treated with a hydrogen salt is found to be effective in suppressing ammonia concentration in LSI cleanrooms. The hydrogen salt which contains neither phosphor nor metals is utilized. Its adsorption capacity is about 1000 mol/m3-carbon. This corresponds to a lifetime of about two years in an ordinary cleanroom. Compared to this, untreated activated carbon adsorbs less than 10 mol/m3, so it cannot be used for more than 10 days. A chemically amplified resist, known to be susceptible to degradation from alkaline gaseous substances in cleanrooms, is shown to maintain its 0.25-µm line and space patterns under hydrogen salt treated carbon filtered air, even when the developing is delayed for 60 min after excimer laser exposure.

Roles of Surface Functional Groups on TiN and SiN Substrates in Resist Pattern Deformations

Resist pattern deformations on a bottom anti-reflective layer (BARL) are a serious problem for deep UV lithography. To clarify the mechanism of these pattern deformations, we analyzed SiN and TiN substrates (candidates of BARL materials) by Auger electron spectroscopy (AES) and thermal desorption (TDS). We also applied N2 annealing and thermal oxidation to the substrates. To examine the reactivity of the substrates to the acid generated in the resist, the potential energy and partial charges of model compounds were calculated using the molecular orbital method. By comparing experimental and calculational results, it was found that the Si–OH group neighboring N atoms on SiN substrates was a stronger base than the Si–OH group neighboring O atoms. We also found that NHx groups can easily react with the acid. The oxidation of SiN, which eliminates NHx and N–Si–OH, prevented pattern deformation. In the case of TiN, on the other hand, oxidation was not effective because Ti–O–Ti can be decomposed by the acid.

Investigation of Resist Pattern Deformation in Chemical Amplification Resists on SiNx Substrates

This paper describes the pattern deformation in chemical amplification resists on SiN x substrates. Pattern deformation was observed not on the Si substrates, but on the SiN x substrates, even for a thin film of 1.2 to 1.5 nm depth. To clarify the resist-substrate interaction, the substrates were analyzed by attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS). From those analyses, the surface Si-OH group was found to be an important factor contributing to pattern deformation. The Si-OH group on Si is not affected by the acid generated in the resist during exposure. However, the protected Si-OH group on SiN x is de-protected by the acid, and the unprotected Si-OH group on SiN x acts as an acid trap. Moreover, Si-OH groups are sites for the resist residue formation. Therefore, the Si-OH group on a SiN x substrate is found to cause the pattern deformation.

Development of high-performance negative-tone resists for 193-nm lithography

We have been developing negative-tone resist systems utilizing an acid-catalyzed intramolecular esterification of γ- and δ-hydroxy acid for ArF phase-shifting lithography. In this paper, α-acryloyloxy-β, β-dimethyl-γ-butyrolactone (DBLA), adamantane lactone acrylate (AdLA), and norbornene lactone acrylate (NLA) were examined as a precursor of hydroxy acid. It was found that AdLA and NLA are not hydrolyzed intro hydroxy acid under an alkali hydrolysis condition. DBLA was found to produce γ-hydroxy acid, which is stable in the resist solution. The γ-hydroxy acid derived from DBLA becomes γ-lactone relatively easily by an acid-catalyzed reaction and can be used to make resists insoluble. Since the variation and the flexibility of the copolymer composition of the base polymer can be increased, the resist properties are controllable and the pattern quality can be improved by utilizing γ-hydroxy acid derived from DBLA.

Suppression of resist pattern deformation on SiON bottom antireflective layer in deep-UV lithography

The interaction between a chemical amplification (CA) resist and a bottom anti-reflective layer (BARL) was clarified to find ways to suppress the resist pattern deformation in the BARL. A SiON film, which is a candidate for use as a BARL material, was analyzed by Fourier transform IR attenuated total reflection spectroscopy, thermal desorption spectroscopy, and x-ray photoelectron spectroscopy (XPS). The Si-NHx, Si-NSi2, Si-OH and Si-OSi groups were identified as the interaction sites on SiON. The effects of those sites on the acid that catalyzes the in-resist reactions were estimated with the partial charge and the at of formation calculated by a molecular-orbital method. The calculation results indicated that the Si-NHx groups completely decompose the acid, and the Si-OH groups decompose it to some extent. The other groups only trap the acid. The strong acid has high affinity and reactivity with those sites. However, a strong acid making a weak bond with the sites on SiON is likely to have a high catalytic ability. This advantage of the strong acid was confirmed by pattern delineation with a resist including onium-salt- generating CF3SO3H.

X-Ray Lithography with a Wet-Silylated and Dry-Developed Resist.

X-ray lithography with a wet-silylated and dry-developed resist has been investigated in order to overcome pattern collapse during wet development and to delineate fine-pitch and high-aspect-ratio patterns. In addition, the applicability to sub-0.1 µ m patterning is discussed. Silylation solution consists of B[DMA]DS (bis(dimethylamino)dimethylsilane) or HMCTS (hexamethylcyclotrisilazane) as the silylating agent, MCA (methyl cellosolve acetate) as the diffusion promoter and a solvent xylene. Silylation characterization and determination of optimum composition of the silylation solution have been performed using Fourier transform infrared spectroscopy (FTIR) measurement. Using the optimal wet-silylation and dry-developed resist system, 0.15 µ m line-and-space patterns of 1 µ m-thick resist (aspect ratio=6.5) and 0.08 µ m line-and-space patterns of 0.5 µ m-thick resist (aspect ratio=6) can be successfully delineated.