Application of alternating phase-shifting masks to 200 nm contact holes

The performances of alternating PSM and its modified type(Hybrid PSM:mixed form of alternating and outrigger PSMs) applicable to 200nm contact holes were studied via both simulations and experiments with DUV lithography. We focused on the 1.5 dimensionally arrayed contact holes(X-pitch: Y-pitch= 2: 1) The pitches of Y direction were 320nm, 360nm, 400nm and the pitches of X direction were twice those of Y direction, respectively. To find out optimum NA and sigma, simulations were performed with various conditions (NA = 0.4 similar to 0.8, sigma = 0.3 similar to 0.8). Comparison of aerial images showed optimum conditions depends on the pitch and the type of PSM. Optimum NA ranged 0.5 similar to 0.6 with different pitches, and sigma was kept at 0.3. Experiments were performed with the condition of 0.5NA and 0.3 sigma. We found that the alternating PSM provided benefits in printing highly packed contact holes, but that the pattern fidelities need to be improved for the 1.5 dimensionally arrayed patterns. The hybrid PSM showed its effectiveness for those patterns. In other words, the hybrid PSM has improved both the fidelity and the depth-of-focus. It enabled 180nm hole patterns printing, of 320nm pitch. Therefore, either the alternating or the hybrid PSM may extend the life time of the optical lithography in printing of contact holes.