It has long been known that the best lithography can be achieved in theory by considering the design of photomasks as an inverse problem - and then solving the inverse problem to find the optimal photomask, using a rigorous mathematical approach. Inverse Lithography Technology (ILT) has been explored for many years, starting with the pioneering work of B. E. A. Saleh and his students in the 1980s. Although these earlier approaches to ILT often resulted in the design of superior photomasks, they were generally impractical in a production environment: run-times were many orders of magnitude too slow, and the resulting masks were often too complex to manufacture. Luminescent has developed the first commercial ILT solution, suitable for use in a production environment. It can rapidly solve for the optimal manufacturable photomask design, with turn-around times comparable or superior to other mask synthesis solutions such as OPC.

ILT is a methodology that is not limited to simple heuristic modifications of the target pattern; in other words, it explores regions of solution space that are very different from the original pattern. ILT routinely finds unanticipated patterns with superior lithographic results. Because it is inherently pattern independent, no segmentation scripts are required, and the approach is generally not susceptible to the types of errors resulting from unanticipated patterns that are so problematic for OPC. ILT can produce SRAFs ut of thin air, and determine optimal SRAFs simultaneously with the rest of the mask.

By finding optimal mask patterns, ILT enables superior pattern fidelity, larger process windows, and in the end, improved yields.

Level-Set Methods

Our approach to ILT is based on a branch of mathematics invented by Luminescent cofounder Stan Osher (a member of the National Academy of Sciences and winner of the SIAM Pioneer Prize). Commonly known as level-set methods, these techniques have been applied to the solution of inverse problems in a wide range of engineering disciplines, as well as revolutionizing image processing, fluid dynamics, and even CGI (such as the water in the movie Shrek).

Patent Portfolio

Luminescent has filed more than 20 patents covering a range of technologies including mathematical methods, lithography techniques, lithography modeling, and CAD/EDA. Our first patent, 7124394, was awarded Oct 17, 2006, and provides broad coverage on the use of level-set methods in photomask design. Additional patents, both in the U.S. and internationally, are expected to issue soon.

White Paper

For more details on Luminescent unique technology, read our white paper (pdf).