OndaSonics - Sensor Arrays

Wet photomask cleaning relies on megasonic agitation to enhance the process, but there are many challenges to reliably control performance in terms of particle removal efficiency (PRE) and damage. With the shift to pellicle-free EUV masks, photomask processes are more vulnerable to contamination. This gap exists largely because of the unavailability of appropriate measurement of the acoustic field. Typically all that is specified about the acoustic output is the driving frequency and the electric power delivered to a transducer. The complexity of the actual cleaning process should account for other important process variables (e.g., frequency, power, chemistry, transducer orientation, flow rate, etc.), which demands an in-situ measurement. Understanding how the acoustic waves interact with the substrate is essential to optimize cleaning, and this knowledge is becoming accessible with the development of sensor arrays.