Yang-koo Lee

ArF pellicle degradation mechanism for resolving CD variation

With the introduction of ArF laser, a binary mask is preferred because a PSM mask is still weak to the crystal defect called as photomask haze although extensive studies trying to resolve the haze impact to a photomask have been performed by various researchers in company and school. However, a new problem was happened after a binary mask introduction that CD variation in an exposure shot is appeared and is gradually increased. And finally, CD variation considerably causes defects in wafer level. It was proven that CD variation is closely related to the change of the reticle transmittance by a lot of researches. In this study, the mechanism of ArF pellicle degradation is focused on because the pellicle degradation affects a reticle transmittance in direct. The components outgassed from a pellicle by the high photon energy of ArF laser, for example carbon or fluorine, are absorbed on the surface of the reticle, so that the transmittance of the reticle is decreased. The phenomena of the pellicle degradation have been studied by the various viewpoints, theoretical background, experiment and results tested in mass production line in this study. Therefore, this study has the important meaning by providing the substantial clues to resolve CD variation problem in a near future.

Nanoimprint template fabrication using wafer pattern for sub-30nm

Patterning of sub-30 nm features using high resolution nano-imprint lithography (NIL) requires use of quartz templates. To this end, various fabrication methods such as e-beam lithography, edge lithography, and focused ion beam lithography were employed for the template formation. Despite significant advances using these methods, NIL template formation process suffers from low throughput and high cost of fabrication when compared with the fabrication of masks used in optical lithography. This is largely owing to a 4X difference in feature sizes involved for the fabrication of NIL template and optical lithography mask. In this paper, we report on a simple, cost-effective method for the fabrication of sub-30 nm NIL templates. Typical fabrication-time required for the formation of sub-30 nm HP templates using conventional Gaussian beam electron beam lithography, runs into several days. Additionally, complicated etch procedures must be employed for pattern transfer onto quartz substrates. Here we propose a low cost, simplified fabrication process for the formation of high resolution NIL templates using wafer pattern replication. We fabricated sub- 30nmHP poly-silicon lines and spaces on silicon wafer using multiple patterning technique. These patterns were subsequently transferred onto quartz substrates using NIL technique. Several types of features were studied to realize a template using the triple patterning technique described above. Results of wafer printing using the said template will be discussed.

Nonoxidative Aqueous Cleaning Solutions for Tungsten Layers

Aqueous cleaning solutions were developed for postetch cleaning of tungsten layers to replace the amine-based organic strippers. They are composed of tetramethylammonium hydroxide, HF, and two additives. Even the cleaning recipes without a strong oxidant, such as hydrogen peroxide, could remove postetch residues formed by reactive ion etching and they also had the same particle removal efficiency compared to ammonium and hydrogen peroxide mixture known as RCA Standard Clean. The concentration of metal ion on the wafer surface after cleaning by them was under 1010 atoms/cm 2 . The effects of the cleaning could be explained by applying Pans double-layer model [J. Electrochem. Soc., 148, G315 (2001)]. In fact, these cleaning solutions made it possible to decrease the resistances of tungsten bit lines and metal contacts and contributed to yield enhancement.

Effects of exposure environment on pellicle degradation in ArF lithography

With the introduction of ArF laser, its high photon energy affects the pellicle degradation in direct. The components outgassed from the damaged pellicle have the effect on the CD variation of reticle. In order to resolve this new inevitable problem, the method of dry gas purge has been proposed among the various solutions recently. Dry gas purge method is generally applied to two applications. It can be applied to a storage environment such as reticle stocker, reticle SMIF pod and reticle library in scanner and to the exposure chamber inside of a scanner during ArF laser exposure phase directly. In this case, it is quite important technologically that which gas is determined as dry purge gas, pure nitrogen or CDA (clean dry air). In this study, the effects of exposure environment on pellicle degradation according to dry purge gas and their mechanism has been investigated to propose strategies and solutions of dry gas purge technology.