Despite superior efficiency, Japanese four-mirror EUV setup unlikely to make waves

Japanese engineer Tsumoru Shintake of the Okinawa Institute of Science & Technology has come up with a low-NA EUV mirror system that’s over ten times more efficient than the one currently used in ASML’s scanners. Reducing the number of mirrors from ten to four, the design would reduce the power needed to generate EUV light by 92 percent as well as improve manufacturing and maintenance cost. Nonetheless, the setup is unlikely to ever see commercial application.

The most interesting part of Shintake’s design is the projector optics module, which consists of only two in-line mirrors, each with a tiny hole in the center (see illustration below). One of them is even used dual-sided. Another innovation is the dual-line field illumination, which irradiates a flat mirror photomask with EUV light from the front without interfering with the optical path. This eliminates shadowing effects from the mask.

The performance of his mirror configuration “has been verified using Optalix optical simulation software and it is guaranteed to be sufficient for the production of advanced semiconductors,” says Shintake. “It may seem impossible at first glance, but once solved, it becomes very simple.”

As it turns out, however, EUV monopolist ASML and its optics suppliers Zeiss have already considered similar setups. “Zeiss has several designs available with similar/better performance than the Shintake design,” an ASML spokesperson told Bits&Chips. So far, these haven’t generated chipmakers’ interest due to the reduced resolution and smaller field size of the design. Should this change in the future, “we will explore whether one of Zeiss’ systems makes sense.”