The Nikon eReview

After ArF immersion, Extreme Ultra-Violet Lithography (EUVL) is the front-running technology for next-generation lithography. Therefore, in addition to the highly successful immersion scanner integration and double patterning programs, Nikon is aggressively engaged in developing EUVL systems for sub 32 nm applications. Nikon EUV1 systems, with a numerical aperture (NA) of 0.25 and 1/4x reduction are already being used by customers for early process development. At the SPIE Advanced Lithography conference earlier this year, Ichiro Mori, Selete Director and General Manager of Lithography Research shared data from the Nikon EUV1 system demonstrating successful resolution of 30 nm L/S and 30 nm contact holes.

EUVL imaging utilizes fully reflective optics with three roughness parameters critical to the associated polishing processes. These include low spatial frequency roughness (LSFR), which mainly determines the optical aberrations, mid spatial frequency roughness (MSFR)—specifying the system’s imaging flare level, and high spatial frequency roughness (HSFR), which affects surface reflectivity. Ongoing improvements in Nikon polishing techniques have resulted in MSFR performance well below EUV1 program targets, ensuring flare levels below 7% can be achieved for high-volume manufacturing EUV systems.

Improved polishing techniques have resulted in MSFR performance well below EUV1 program targets, ensuring flare levels below 7% can be achieved for high-volume manufacturing EUV systems.

Multiple EUV projection lenses have been completed with wavefront error achieving world-class levels. At the Nikon LithoVision symposium earlier this year, Katsuhiko Murakami, Nikon Development Section Manager responsible for optics development and General Research Manager for EUVA, shared 33 point measurement data using an exposure field size of 26 mm x 2 mm on the wafer, demonstrating an average wavefront error of 0.6 nm RMS. The wavefront error at all points was less than 1 nm RMS, with some measurements as low as 0.3 nm RMS. Murakami also announced that EUV1 projection optics performance had met all objectives. Static exposures were started early this year, with Selete already successfully resolving features below 30 nm.

Thirty-three point measurement data using an exposure field size of 26 mm x 2 mm on the wafer demonstrated an average wavefront error of 0.6 nm RMS.

Given the high cost of lithography equipment, it is not cost-effective to use a toolset for only a single process generation. Therefore, one of the main motivations for the transition to EUV lithography is its potential for application at multiple process shrinks. The next-generation Nikon EUV2 system will maintain the same 0.25 numerical aperture as EUV1. However, it will enable sub 32 nm development with 30% lower flare, significant overlay enhancements, and increased throughput. To further enhance imaging capabilities, a numerical aperture greater than 0.30 is then planned for EUV3 systems. The higher NA will be coupled with further improvements to overlay and flare with throughput targeted at 100 wafers per hour. Murakami shared the Nikon EUV system provisional performance details below at LithoVision.

The Nikon EUV program is right on track with EUV1 tools currently being used by customers for early process development. EUV1 systems will be followed by EUV2 tools for sub 32 nm device development, and production tool verification in 2010. EUV3 systems are targeted for release in 2012 for sub 32 nm volume applications—fully aligned with IC manufacturers’ requirements.

Selete Achieves Resolution of 30 nm Features Using Nikon EUV1 System