Establishing Foundation for Next-Generation Semiconductor Lithography Photoresist Development

UNIST researchers have developed design technology that enables the sensitivity and pattern precision of tin-based photoresists used in next-generation extreme ultraviolet (EUV) lithography processes to be controlled according to desired characteristics.

A research team led by Professor Jang Ji-hyun from the Department of Energy and Chemical Engineering at UNIST announced on the 21st that they have developed a technology to control the sensitivity and pattern precision of photoresists by adjusting the ligand characteristics of tin oxo clusters (SnOC).

Photoresist is a photosensitive material that reacts to light or electron beams during semiconductor lithography processes to form circuit patterns. In particular, tin-based photoresists are attracting attention as materials for next-generation semiconductor processes due to their high EUV absorption rate and excellent etch resistance.

The research team varied the bonding structure of tin atoms by applying adamantane-1-carboxylic acid, which has electron-donating characteristics, and diphenylphosphinic acid, which has electron-withdrawing characteristics, as ligands respectively.

As a result, '6-SnOC' employing adamantane-1-carboxylic acid formed a structure with six bonded tin atoms and exhibited high sensitivity. Implementation of fine patterns with a width of approximately 20 nanometers (nm) was possible with minimal electron beam exposure.

Conversely, '3-SnOC' employing diphenylphosphinic acid formed a structure with three bonded tin atoms and, while showing relatively low sensitivity, demonstrated more uniform pattern edges. Line edge roughness (LER) of 1.02nm was recorded for 50nm width patterns.

Through density functional theory (DFT) calculations and electron beam lithography analysis, the research team identified that the electronic characteristics of ligands determine the photosensitive reaction pathway.

The research results confirmed the possibility of applying the 6-SnOC series for processes requiring high sensitivity and the 3-SnOC series for processes where pattern precision is critical.

Professor Jang Ji-hyun stated, "This research clarifies that ligand characteristics are a key factor in determining sensitivity and pattern precision," and explained, "It could serve as a new standard for designing next-generation EUV photoresists."

This research was conducted with support from the National Research Foundation of Korea (NRF), UNIST research funds, and the InnoCORE project of the Ministry of Science and ICT (IITP). The research results have been published in the international academic journal Small.