Leveling viscous fluids using ultrasonic waves

In this paper, we propose a method for leveling viscous fluids-photoresist, for example-on substrates using ultrasound. We expect this technology to supersede the spin-coat method, particularly for large substrates. Ultrasonic leveling using standing waves is presented first, followed by a leveling method using traveling waves. The uneven thickness distribution produced through slit nozzle application can be eliminated using the proposed method. The experimental evaluation of these methods was performed, and the results demonstrate the positive effect on the surface nonflatness of a photoresist. In particular, the traveling wave method has an advantage of the freedom of orientation of the slit nozzle movement.