Numerical investigation of wafer drying induced by the thermal Marangoni effect

Abstract

Marangoni drying induced by organic vapor is an important process in integrated circuit manufacturing to obtain an ultra-clean surface, but its application is limited by the utilization of flammable vapor. Thermal Marangoni drying induced by a temperature gradient is a safe and environmentally friendly technology. However, the regulation of thermal Marangoni-driven flow is complicated, and current understanding of the thermal Marangoni drying mechanism is inadequate. In this work, we present a coupled model of thermal Marangoni drying that combines the two-phase flow, heat transfer, and water vapor transfer in air. The evolution of entrained water film thickness, dynamics of Marangoni-driven flow, and evaporative cooling are numerically simulated. The results show that the achieved minimum residual thickness of the entrained water film is thinned more than tenfold compared with that of the wafer withdrawn without the thermal Marangoni effect. The temperature rise and Marangoni stress grow dramatically in the film and meniscus at the initial time, and then they remain as almost invariant after achieving the dynamic equilibrium between the heating and evaporative cooling. The convective water vapor transfer in air and the reduction of entrained water film thickness improve the evaporative flux, which in turn suppresses the increase in the thermal Marangoni effect until the dynamic equilibrium is attained. Furthermore, the higher heat source, lower wafer thermal conductivity and smaller wafer thickness can enhance drying performance. The investigation of drying dynamics will contribute to a comprehensive understanding of the thermal Marangoni drying process and provide guidance to its industrial applications.