Metal oxide nanoparticle resists are promising materials for highly-resolving high-throughput patterning. However, their performance is still inadequate for the application to the production of semiconductor devices. In this study, the dependence of the relationship between chemical gradient and line width roughness (LWR) on the pattern duty, acid generator, and developer was investigated using a zirconia (ZrO2) nanoparticle resist. The line-and-space patterns of ZrO2 nanoparticle resists were analyzed on the basis of the EUV sensitization mechanism. LWR was roughly inversely proportional to the chemical gradient. The proportionality constant decreased with the increase of the ratio of nominal space width to the nominal line width. The proportionality constant for n-butyl acetate was smaller than that for an alternative developer with a high polarity. The proportionality constant decreased by the addition of an acid generator. The improvement of dissolution process and the suppression of secondary electron migration are essential to the suppression of LWR in the ZrO2 nanoparticle resist.
The performance of chemically amplified resist is approaching its physical limit with the reduction of feature sizes due to the acid diffusion needed for the solubility change of resist polymer. The line edge roughness (LER) of chemically amplified resists rapidly increases in the sub-10-nm-half-pitch region when the half-pitch is decreased. Also, the stochastic defect (pinching and bridges) generation is a significant concern for the high resolution patterning with high throughput. To solve these problems, the increase of the density of resist films is an important strategy. Metal oxide nanoparticle resists have attracted much attention as the next generation resist used for the high-volume production of semiconductor devices because of their high density property. However, the sensitization mechanism of the metal oxide nanoparticle resists is unknown. Understanding the sensitization mechanism is important for the efficient development of resist materials. In the previous study, the numbers of electron-hole pairs required for the solubility change of the resist films were estimated for a zirconia nanoparticle and a ligand shell, respectively. In this study, the pattern formation mechanism of zirconia nanoparticle resist was investigated. The elementary reactions possibly induced in the zirconia nanoparticle resist were investigated using a pulse radiolysis method. The pulse radiolysis is a powerful method to directly observe the kinetics of short-lived intermediates produced by an ionizing radiation. The pattern formation mechanism was assumed by integrating the elementary reactions. The resist patterns fabricated using an EUV exposure tool were analyzed on the basis of the assumed pattern formation mechanism. In the material design of metal oxide nanoparticle resists, it is important to efficiently use the electron-hole pairs generated in nanoparticles for the chemical change of ligand molecules.
This work was partially supported by Ministry of Economy, Trade and Industry (METI) and the New Energy and Industrial Technology Development Organization (NEDO).
 T. Kozawa, J. J. Santillan, and T. Itani, “Electron–hole pairs generated in ZrO2 nanoparticle resist upon exposure to extreme ultraviolet radiation”, Jpn. J. Appl. Phys. 57, 026501 (2018).