Tunable Droplet Momentum and Cavitation Process for Damage-free Cleaning of Challenging Particles

摘要

Particle removal without damage has been demonstrated for < 60nm photomask sub-resolution assist features with droplet momentum cleaning technology that employs NanoDroplet™ mixed-fluid jet nozzle. Although 99%+ particle removal efficiency can be achieved for standard Si_3N_4 particles with broad size distribution, there are some cleaning challenges with small (< 100nm) and large contact area (> 500nm) particles. It was found that tunable uniform cavitation can provide the additional physical assist force needed to improve cleaning efficiency of these challenging particles while meeting the damage-fee cleaning requirement. An integrated cleaning process was developed that combines both droplet momentum and damage-free cavitation technology. Cleaning tests were performed with different types of challenging particles. The results showed 5-8% particle removal efficiency improvement as compared to momentum based only cleaning. All masks were processed using the Terra™ mask cleaning tool configured with NanoDroplet™ mixed fluid jet technology and full face megasonics.