Mask cleaning remains as one of the major challenges in EUV lithography. Without the use of traditional pellicles, EUV masks demand high purity and effective but mild cleaning techniques for protection from defects. Recently, trends towards dilute chemistries and progress in megasonic cleaning have brought renewed interest in gasified DI water. In this paper, we describe the design and development of a point-of-use functional water treatment system, specifically for advanced mask cleaning applications. The system comprises two modules the purification module and the gasification module. The purification module provides treatment features including TOC reduction, sub-micron particle retention, and degassing, as well as thermal and pressure control. The gasification module employs micro-porous PFA membrane contacting technology to deliver ultra clean bubble-free DI water with various gases (O3, N2, H2, CO2, NH3, etc.) over a wide concentration range. The treatment system is also equipped with closed loop process control to maintain and regulate process temperature, pressure and dissolved gas concentration. This active control feature allows precise control and minimal process variations.
22X mask cleaning effects on EUV lithography process and lifetime