Immersion defect reduction, part I: analysis of water leaks in an immersion scanner

Abstract

This paper reports the water-leakage mechanism of the immersion hood in an immersion scanner. The proposed static analysis reveals the immersion hood design performance in defect distribution. A dynamic water-leakage model traces the leaked water and identifies its position on the wafer, during exposure. Comparing simulation to experimental results on bare-silicon and resist-coated wafers, the defect type, source of residuals, and critical settings on the immersion system were clearly identified. 1.INTRODUCTIONImmersion lithography is the only viable choice to produce 65-nm and 45-nm half-pitch circuits. Although 193-nm immersion lithography is being developed at an unprecedented pace, it still needs enormous efforts to meet the extremely tight requirements for the 45-nm node. 1,2,3 One of them is defect density. It needs to be as low as 1 defect per wafer pass, especially when many device layers are exposed with immersion scanners.The immersion hood (IH) is an important component of the immersion scanner for supplying, confining, and draining the water during exposure. Unfortunately, the fluid will leak from the IH due to insufficient constrain and the droplets left will produce watermark defects. Besides watermarks, the liquid coupling medium is more likely to carry particulates than the air coupling medium, no matter these particles are from materials, the wafer, or the exposure system itself. The particulates may be left through water leaking from the IH during wafer movement and cause printing and fall-on defects.Hence, preventing water leakage is one of the most critical issues for immersion defect reduction. This paper reports a static residuals analysis to monitor the IH design performance and define the correlation between airflow instability and water leakage in the IH. Furthermore, a dynamic water-leakage model has been setup, basing on the mechanism discussed in Section 3. This dynamic model traces the water-leakage trajectory during exposure routing.

Marching of the microlithography horses: electron, ion, and photon: past, present, and future

“…Immersion lithography is run at single-digit number of defects per wafer, with overlay and yield comparable to those of dry systems in the 90-and 65-nm nodes. Researchers in many disciplines contribute to the success, amongst them: Theological analysis in the early days of immersion lithography in DOF 43 , polarized illumination 44 , image deterioration by bubbles in immersion fluid 45 , and processing parameters for multiple technology nodes 46 ; materials work to reduce defects such as switchable BARC 47 , watermark reduction 48 , and immersion hood cleaning 49 ; process analysis such as algorithm 50 to pinpoint the location of particle leakage on the immersion hood, using super-positioned defect distribution chart, and speedy defect classification 51 . Figure 14 shows a super-positioned defect distribution chart with predicted particle leakage in red and actual particles in black.…”