Immersion-related Defects And Strategies Of Defect Reduction

Lithography has been traditionally at the forefront of IC manufacturing technology. In the sub-wavelength era, where the smallest printed features are smaller than the illuminating wavelength, lithography is facing increasingly complex challenges arising from design rule (DR) shrinkage. Immersion lithography is a key enabling technology for the production of critical layers for 45nm and even smaller process. Immersion lithography has water filled in between the front lens and water, forming a water meniscus, this water meniscus moves with the exposure head across the wafer. Defectivity is the most important issue ye to be resolved in order to move immersion lithography into high-volume manufacturing. Typically, unoptimized immersion processes have 4-20% more defects than dry process have.There are three major defect types in 45nm process:big bubble, water mark and printing particle, and we take some action plans for the different defect types. For big bubble defect we clean the immersion hood and use edge speed optimization function; For water mark defect we use new top coating material with bigger contact angle; For printing particle defect we optimized EBR recipe and managed the machine idle time. We also set up defect offline monitor to control the machine defect performance.After optimized the process, immersion defect counts were reduced obviously, and 45nm yield also had a great improvement, meet the critical requirement of modern lithography immersion process.