EUVL

Extreme ultraviolet lithography (also known as EUV or EUVL) is a next-generation lithography technology using an extreme ultraviolet (EUV) wavelength, currently expected to be 13.5 nm. EUV is currently being developed for possible future high volume use in 2020 for Intel's, Globalfoundries' and Samsung's 7 nm node, TSMC's 5 nm node, and SMIC's 14 nm node. The primary EUV tool maker, ASML, projects EUV at 5 nm node to require a higher numerical aperture than currently available and multiple patterning to a greater degree than immersion lithography at 20 nm node. Immersion lithography is still more than 4 times faster than EUV (275 WPH vs. 65 WPH as detailed below), due to source power limitations; hence, multiple patterning with immersion lithography has already been used where EUV had previously been expected to be used. However, it is currently recognized that EUV cannot practically realize 40-50 nm pitch, due to stochastic effects in resist exposure, so even 10 nm node is currently off limits.

While source power is the chief concern due to its impact on productivity, significant changes in EUV mask infrastructure, including blanks, pellicles and inspection, are also under study. Particle contamination would be prohibitive if pellicles were not stable above 200 W, i.e., the targeted power for manufacturing. Without pellicles, particle adders would reduce yield, which has not been an issue for conventional optical lithography with 193 nm light and pellicles. The current lack of any suitable pellicle material, aggravated by the use of hydrogen plasma cleaning in the EUV scanner, is preventing the adoption of EUV lithography for volume production.

Some issues not specific to EUV, such as resist collapse and stochastic effects (including photon shot noise), also currently bar EUV from exceeding the resolution limits of immersion lithography in high volume manufacturing.

Double patterning is expected for EUV for random logic patterns at the 7 nm node (32 nm pitch), due to the need for dipole illumination. The 5 nm node (22 nm pitch) would likewise be expected to use multiple patterning already being developed for immersion lithography.

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