"From Guesswork to Calculation": KAIST Measures Droplet Movement in Semiconductor Processes

by Jeong Ilwoong

Published 02 Dec.2025 08:17(KST)

It has become possible to precisely observe the movement of droplets at the nanoscale in semiconductor processes.

During semiconductor manufacturing, the uniformity with which water or liquid spreads on a surface and the speed at which it dries are critical factors that determine quality. However, directly observing such "wettability" at the nanoscale has been technically nearly impossible, forcing most researchers to rely on assumptions.

A domestic research team has addressed this issue by developing a next-generation research platform technology that overcomes the limitations of conventional surface analysis techniques. For the first time, they have succeeded in directly observing and measuring the process by which nanoscale droplets interact with surfaces.

(From left) Jung Eechang, PhD student in the Department of New Materials Engineering, Professor Hong Seungbum. Provided by KAIST

KAIST announced on December 2 that Professor Hong Seungbum's research team in the Department of New Materials Engineering, in collaboration with Professor Lim Jongwoo's team at Seoul National University, has developed a technology that uses atomic force microscopy (AFM) to directly observe nanoscale droplets in real time and calculate the contact angle based on the droplet's shape.

The technology developed by the joint research team allows for direct visual confirmation of actual nanoscale droplets and enables precise analysis of how well droplets adhere to and detach from surfaces. This advancement is expected to be immediately applicable not only to semiconductor processes but also to advanced technology fields such as hydrogen production catalysts, fuel cells, and batteries, where the movement of liquids determines performance.

The analysis of wettability is increasingly focused on precise measurements at the nanoscale. Traditional methods involved using large droplets, several millimeters in size, to determine hydrophilicity (how well water spreads) or hydrophobicity (how poorly water spreads) of surfaces. However, at the nanoscale, droplets are so small that it has been difficult to directly observe their shape.

To address this, the joint research team gently cooled the surface to a temperature where water vapor in the air would condense but not freeze, naturally forming nanoscale droplets. They then used the non-contact mode of AFM to observe and capture the original shape of these droplets. This was made possible by creating a precisely controlled environment that accounts for the high sensitivity of nanoscale droplets, which can deform even with the slightest touch of the probe.

Applying this technology to the ferroelectric material lithium tantalate (LiTaO₃), the team was able to confirm for the first time that the contact angle of nanoscale droplets changes depending on the material's electrical orientation (polarization). This difference, which is not observed with larger droplets, demonstrates that nanoscale droplets are extremely sensitive to the electrical state of the surface.

Schematic diagram of the process of visualizing nano-sized droplets in non-contact mode. Provided by KAIST

In particular, the joint research team also applied this technology to a water electrolysis catalyst (NiFeLDH) used in hydrogen production, successfully observing individual nanoscale droplets. This enabled them to understand how water reacts on the catalyst surface and to analyze catalyst performance, such as how easily bubbles detach.

Professor Hong stated, "This study is an important example demonstrating that atomic force microscopy can be used to directly visualize nanoscale droplets and even measure their contact angles. The technology developed by the joint research team enables real-time observation of droplet behavior in the nanoscale world, which was previously difficult to confirm visually, and can serve as a core analytical tool for developing next-generation energy and electronic materials."

Meanwhile, Jung Eechang, a PhD student in the Department of New Materials Engineering at KAIST, participated as the first author of this study. The research results (paper) were recently published in 'ACS Applied Materials and Interfaces,' a journal in the field of new materials and chemical engineering published by the American Chemical Society (ACS).