Taku Morisawa

Reduction of line edge roughness in the top surface imaging process

This article presents a novel top surface imaging (TSI) process that is highly sensitive and reduces line edge roughness (LER). We found that LER and residue decreased when we used a chemically amplified (CA) resist, consisting of a base polymer with a high molecular weight and a photo-acid generator producing an acid with a high molecular weight. The top thin silylated layer of the exposed region on the CA resist causes the LER. A breakthrough step in the dry-development process improves the silylation contrast between the exposed and unexposed regions. We then apply a novel step in the dry-development process which involves a predry development bake at a temperature above the glass transition temperature of the silylated polymer. This step is effective in rolling and smoothing the edge of silylated layer by thermal flow. By applying the predry-development bake step above the glass transition temperature, we were able to reduce the LER to less than 6 nm. We have demonstrated a novel TSI process for achie...

Pattern collapse in the top surface imaging process after dry development

In this article the pattern collapse in a 193 nm top surface imaging process after dry development is described. We dry developed the resist with O2 and SO2 plasmas at low temperature in order to replicate a fine pattern profile. Pattern collapse occurred because of stress from neighboring patterns when SO2 was added at low substrate temperatures and the line/space binary pattern was below 0.15 μm. We found, using Auger electron spectroscopy analysis, that a sulfuric compound covered the side walls of the pattern when SO2 was used. We propose a pattern collapsing mechanism caused by the reaction of H2O with the evaporation of water adsorbed by the sulfuric compound on the resist pattern. It is therefore effective to decrease the sulfuric compound on the patterns before the wafer is removed from the etching chamber. Finally, we successfully replicated a sub-0.10 μm line and space pattern without pattern collapse.

Sub-0.1-µm-Pattern Fabrication Using a 193-nm Top Surface Imaging (TSI) Process

This paper presents a 193-nm top surface imaging (TSI) process for the sub-0.10-µm-device rule. The process achieved a 0.07-µm contact hole, 0.04-µm isolated line, and 0.06-µm space pattern without the need for any optical resolution enhancement technique. An exposure latitude of ±10% was obtained for the process with a 0.10-µm contact hole. We can obtain a sufficient depth of focus (DOF) by using an attenuated phase-shifting mask. We resolved a 0.085-µm line-and-space pattern by using an alternative phase-shifting mask, and obtained a 0.8-µm DOF for a 0.09-µm line-and-space pattern, using an alternative phase-shifting mask. We demonstrated the fabrication of sub-0.10-µm line-and-space binary patterns. Sub-0.10-µm patterns were produced by using the TSI process for 193-nm lithography.

Microswelling-free negative resists for ArF excimer laser lithography utilizing acid-catalyzed intramolecular esterification

We have examined alicyclic polymers with a (gamma) -hydroxy acid structure in order to investigate the properties of (gamma) -hydroxy acid and (gamma) -lactone as function groups of ArF negative resist materials. From the viewpoint of transparency and dry-etching resistance, (gamma) -hydroxy acid and (gamma) -lactone structure were found to be suitable for ArF negative resists materials. Surprisingly, the reactivity of the acid-catalyzed reaction of (gamma) -hydroxy acid is affected by the polymer structure. Using ArF excimer laser stepper, 0.20-micrometers line-and-space patterns without micro-swelling distortion were obtained from a negative resist consisting of alicyclic polymer with the (gamma) - hydroxy acid structure and a photoacid generator. Distortion was avoided because the number of carboxyl groups decreased drastically in the exposed area by the acid-catalyzed intramolecular esterification of (gamma) -hydroxy acid to (gamma) -lactone. As a result, (gamma) -hydroxy acid and (gamma) -lactone structure were found to be suitable function groups for ArF negative resist materials.

Theoretical Calculations of Sensitivity of Deprotection Reactions for Acrylic Polymers for 193 nm Lithography II: Protection Groups Containing an Adamantyl Unit.

The reaction energy of deprotection reactions, glass transition temperature, and the dielectric constant were calculated for photoresists having a 2-alkyl-2-adamantyl group. It was found that the lower sensitivity of the polymer with a 2-methyl-2-adamantyl group (compared with the sensitivities of the polymers with a 2-ethyl-2-adamantyl group and a 2-butyl-2-adamantyl group) can be attributed to the smaller exothermic (or greater endothermic) reaction energy of its deprotection reaction. It was also found that the sensitivity difference between the polymers with the 2-ethyl-2-adamantyl and 2-butyl-2-adamantyl groups can be attributed to the difference in the calculated dielectric constant, where a higher dielectric constant leads to a higher sensitivity.

Theoretical calculations of silylation reaction of photoresists

Molecular orbital calculations to predict the activation energy of silylation are performed. The activation energy for polyvinylphenol is predicted to be 19.6 kcal/mol at the MP-2 (the second-order Moller-Plesset perturbation theory) level, and this value is in good agreement with an experimental value of 19.4 kcal/mol. Theoretical values calculated from the Hartree-Fock and nonlocal density functional theories are found to be larger than the experimental value by about 15 kcal/mol and 5 kcal/mol, respectively. Thus, the MP-2 level of calculation is required for a quantitative prediction of the activation energy of silylation. Comparison between the theoretical and experimental values further showed that the rate-determining step of the silylation is the diffusion when pure polyvinylphenol is silylated, whereas it is the reaction when additives are mixed to polyvinylphenol. This result shows that the theoretical calculations become a tool for clarifying the kinetics of silylation, and can be used for designing new materials. The activation energy of silylation for carboxylic acid and alcohol is also predicted, and experiments to silylate polyvinylalcohol are performed. It is shown that the alcohol unit can be silylated with a higher activation energy than that for polyvinylphenol, whereas for carboxylic acid, significant desilylation may occur after the silylation.

Direct Patterning of Spin-on-Glass Materials by ArF Excimer Laser Irradiation and Their New Application to Hard-mask Processes

Several spin-on-glass (SOG) materials were examined as single layer resists for ArF excimer laser lithography, with the goal of directly forming a hard mask from these materials for dry-etching underlying metal films. Perhydro-silazane (PHSN) was found to be photo-reactive at 193 nm wavelength as well as polyphenylmethyl-silsesquioxane (PMSQ) and polyhydroxybenzyl-silsesquioxane (HSQ), which we have reported previously. These materials showed a sufficient resolution performance and sensitivity at 193 nm. The Fourier-transform infrared (FTIR) and X-ray photoelectron spectrometry (XPS) analyses showed that the basic reaction is photo-oxidation, though the imaging mechanism in each material is quite different. The etching resistance of these materials was significantly improved by special treatment after patterning, whereas those without the treatment were insufficient. For example, etching rate of PHSN after baking in steam ambient was comparable to that for CVD SiO 2 in RIE using SF 6 gas. 0.2 μm patterns were transferred into poly-Si films by dry-etching using these materials as hard masks.

Mechanical property of organic resists for ArF lithography

We have investigated the mechanical porperty of ArF resists formed on Si substrate. We measured strength in resist film by introducing the scratch test method. Stress is also evaluated by measuring the curvature of Si wafer coated with resist. The results showed that the mechanical property of resist films mainly depends on the resist polymer structures. A half strength and 5 times large stress of typical ArF resist films comparing with KrF resist explain the observed behaviors of ArF resist such as peering or cracking in lithography process.

Theoretical calculations of sensitivity of deprotection reactions for acrylic polymers for 193 nm lithography

The reaction energy of deprotection reactions, density of the reaction site, glass transition temperature, gas permeability, density and relative permittivity of photoresists of poly(TCDA5–RMA3–MAA2) and poly(TCDMACOOR4–TCDMACOOH6) with various protection groups were calculated. The most-enhanced exothermicity was calculated for protection groups containing an ethoxyethyl group as compared to the other protection groups: tetrahydropyranyl, tricyclodecanyl and tert-butyl. For the ethoxyethyl protection groups, a good correlation was found between the experimental sensitivity and the calculated values of the relative permittivity and the glass transition temperature of the polymers. This indicates that calculating these properties of polymers can provide a quick way to identify polymers having a high sensitivity for ArF lithography.

Recent advantages of bilevel resists based on silsesquioxane for ArF lithography

We evaluated three chemically amplified positive-tone resists which are mainly based on cyclo-hexyl-carboxylic- acid-silsesquioxane. A resist had a good resolution capability of K1 equals 0.435 and a process window of 0.4 micrometers depth of focus at 0.15 micrometers L/S pattern, however its dissolution characteristics was poor. The resist that was improved the resistance to aqueous base developer, had an excellent resolution capability of K1 equals 0.404. It had a permissive sensitivity of 13 mJ/cm2. The bilayer pattern profile dependencies on the transparency of the upper layer resist and the line edge roughness of the resist before and after the dry-development process were also examined. These results showed the applicability of the silsesquioxane based resist to the bilayer resist process for ArF lithography.