Session: 12-06-03: Modeling of Nano- and Micro-Scale Phase Change Processes

Paper Number: 165259

Mechanical Modeling of Nano-Structure Collapse in Sublimation Drying 

In accordance with Moore’s law, the continued miniaturization of semiconductor devices has heightened concerns regarding nano-scale pattern collapse, particularly during the drying steps of the manufacturing process. Pattern collapse occurs when adjacent structures come into contact and adhere, largely due to capillary forces arising from residual liquid trapped between nano-structures. Although sublimation drying—which bypasses the liquid phase—has been proposed as a promising method to mitigate these capillary forces, recent reports indicate that collapse is not fully prevented. In some cases, structures were found to have collapsed even after the sublimation agent solidified between patterns. These observations suggest that the solidification process of the sublimation agent plays a critical role in inducing collapse, yet the complex interplay between solidification phenomena and nano-structure collapse remains poorly understood.

This study aims to elucidate the mechanical mechanisms leading to nano-structure collapse by incorporating the solidification behavior of the sublimation agent into a theoretical model. First, collapse modes of pillar-like patterns under sublimation drying were examined, and it was hypothesized that interfacial tension at the solid–liquid interface of sublimation agent is a primary driving force of collapse. The force F acting on the patterns is assumed to be inversely proportional to the nth power of the spacing r, expressed as:

F = A·Δµ / rⁿ , 

where A is a constant and Δµ is the viscosity contrast of the sublimation agent. This viscosity contrast is determined by the difference in viscosity between the liquid and solid phases of sublimation agent at their respective measurement temperatures, and previous studies have suggested a correlation between this contrast and collapse rates. Additionally, the exponent n may vary depending on pattern geometry.

Next, we evaluated seven different sublimation agents on both pillar-like and line-and-space patterns, comparing the maximum stress σ_max calculated from this model with observed collapse rates. Solid-phase viscosities for each sublimation agent were obtained via indentation testing, while liquid-phase viscosities were taken from literature data, allowing for the calculation of Δµ. Parameter A was treated as a constant, independent of the sublimation agent. As a result, a strong correlation was found between σ_max and collapse rates for n = 3~4, suggesting that interfacial tension at the solid–liquid interface is a principal factor in nano-structure collapse and that the interface formed during sublimation-agent solidification imparts significant stress on the patterns.

The findings of this work not only provide practical guidelines for reducing pattern collapse via the selection of sublimation agents with suitable viscosity contrasts and the optimization of solidification conditions, but also offer broader insights into the stress mechanisms associated with sublimation-agent solidification. Moreover, these insights may facilitate the advancement and stabilization of miniaturization technologies in semiconductor manufacturing, particularly as higher aspect ratios become increasingly common.

Presenting Author: Yosuke Hanawa SCREEN Holdings Co., Ltd.

Presenting Author Biography: Yosuke Hanawa is a semiconductor cleaning process researcher at SCREEN Holdings Corporation, where he is working on the development of drying techniques to suppress pattern collapse and the analysis of interfacial phenomena in the wet. He likes to commute by bicycle.

Authors:

Yosuke Hanawa SCREEN Holdings Co., Ltd.
Jianliang Zhang SCREEN Holdings Co., Ltd.
Yuta Sasaki SCREEN Holdings Co., Ltd.
Koichi Sawada SCREEN Holdings Co., Ltd.
Junichi Yoshida SCREEN Holdings Co., Ltd.
Minghan Xu UNIVERSITY OF TORONTO
Mohammaderfan Mohit McGill University
Agus Sasmito McGill University
Atsushi Sakuma Kyoto Institute of Technology