Study of droplet spray impact on a photomask surface

Abstract

To overcome the challenge of particle removal without pattern damage, it is important to control and optimize the physical force impact into a narrow energy distribution regime. This can be achieved by gaining in-depth knowledge into the fundamentals of physical cleaning methods as well as the process parameters affecting the performance of these systems. Droplet Spray is considered to be a gentle physical force technique. The droplet size and droplet velocity defines the kinetic energy of a droplet which transfers momentum and pressure onto the substrate surface resulting into particle removal or pattern damage. Droplet pressure is directly influenced by gas and liquid flow rate as well as nozzle design (orifice size, etc.) and process parameters like nozzle distance and scan speed across the substrate surface. In this paper, effect of process and hardware parameters on droplet pressure transfer are presented and related to kinetic energy and momentum as calculated from droplet velocity and size. Effect of these process parameters is also studied on pattern damage and particle removal efficiency. Distance, nozzle hardware, gas and liquid flow rate are found to be independent process parameters which show specific effects on nozzle performance; therefore they all are optimized individually.