The dataset shows filings rising to a peak of 45 in 2017, then falling to just 2 by the 2022 midpoint and trending to 0 at the 2026 cut-off. This pattern typically means the foundational technical problems — how to keep an immersion fluid stable and transparent, how to raise numerical aperture without introducing defects, how to pattern at higher resolution using multiple exposures — were solved and claimed during an earlier wave, most visibly the 2003-2005 priority filings that still carry the highest citation counts. Later filers had less new ground to stake out, so filing volume naturally thinned. It is worth remembering that publication lags filing by around 18 months, so the very last one or two years in any such chart will always look lower than they eventually turn out to be, but a multi-year decline like this one is a real signal, not just a lag artifact.

The recent-year momentum data names a consistent group of assignees spanning equipment makers, optics suppliers and materials companies, but every one of them shows 0 filings in the latest tracked year, and the equipment leader shows a -100% year-on-year change. The strongest documented collaboration is a co-assignee link between an equipment maker and a projection-optics supplier, filing together 14 times, which reflects how tightly exposure-tool and lens development are coupled in this field. Rather than an active filing race, the current picture is one of established incumbents whose portfolios were built earlier and are not being heavily added to now.

Of 1,789 total records, 1,788 fall under G03F (photolithography and photomechanics), meaning virtually every filing in this space touches core lithographic method or apparatus claims. Secondary classification volume appears in H01L (527, semiconductor devices), G03B (473, photographic apparatus) and G02B (247, optical elements), showing how lithography claims connect outward into device fabrication and imaging systems. Smaller subclasses like C08F (123, resist polymer chemistry) and G03C (86, photosensitive materials) mark narrower but distinct pockets of claim activity in materials rather than optics or apparatus.

US20060154188A1, filed by Tokyo Ohka Kogyo and published 2006-07-13, claims an immersion fluid for liquid immersion lithography that is transparent to the exposure wavelength and comprises a fluorine-based liquid with a boiling point between 70 and 270 degrees Celsius, along with a method of applying that fluid directly onto a resist film or a protective film over it. Anyone formulating an immersion fluid that falls inside that fluorine-based, boiling-point-defined composition and applying it in that manner should review this filing's claim scope closely. Designing around it generally means moving outside that specific boiling-point window, using a non-fluorine-based fluid chemistry, or applying the fluid through a materially different method than direct placement on the resist or protective film.

The dataset shows comparatively thin direct coverage in areas like immersion fluid recovery and recycling systems, defect inspection performed under immersion conditions, multiple-patterning overlay correction techniques, and protective topcoat chemistry tailored to immersion resist stacks. These sit adjacent to the dense core of fluid composition and exposure apparatus claims rather than replacing it. Before committing to any of these branches, it is worth checking whether the apparent gap reflects genuinely open claim space or simply reflects that related work is filed under a different IPC classification or held as a trade secret rather than patented.