Manufacturing Issues in Extreme Ultraviolet Lithography

Jason Cain
(Professor Costas J. Spanos)

As feature sizes in modern integrated circuits continue to decrease below 100 nm, the physics of conventional deep ultraviolet (DUV) optical lithography impose severe limitations. Past efforts to improve the resolution of lithography systems have been based upon reducing the wavelength of the light source. Current state-of-the-art lithography systems use a source wavelength of 193 nm. However, decreasing the wavelength below this level is problematic because at shorter wavelengths most materials become absorptive. Although much research has been done to develop 157 nm lithography tools, this has proven to be costly and difficult, and progress has been slower than expected.

Therefore, it seems that a "quantum leap" is needed in order to keep up with the relentless progress of Moore's Law. Extreme ultraviolet (EUV) lithography at a wavelength of about 13.5 nm has been proposed as a potential replacement for DUV lithography. In order to minimize problems with absorption, EUV lithography tools rely on reflective optics made of silicon/molybdenum multilayer mirrors instead of the refractive optics found in DUV systems. Early results have been encouraging [1], and this is now an area of active research.

A system for performing static lithographic exposures has been constructed at the Advanced Light Source at the Lawrence Berkeley National Laboratory [2]. This system is currently being used to characterize new high numerical aperture optics and to explore issues related to the future manufacturing possibilities for EUV lithography. These issues include photoresist development, mask fabrication and defect problems, and improved modeling of the EUV exposure process. We wil be exploring these issues with emphasis on control and metrology to characterize and improve the EUV lithography process.

D. A. Tichenor et al., "Performance Upgrades in the EUV Engineering Test Stand," Emerging Lithographic Technologies, Proc. SPIE, Vol. 4688, 2002.
P. P. Naulleau et al., "Static Microfield Printing at the Advanced Light Source with the ETS Set-2 Optic," Emerging Lithographic Technologies, Proc. SPIE, Vol. 4688, 2002.

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