Jin Nishikawa

Progress of Nikon's F2-exposure tool development

Progress of Nikons F2 tool development is described. Intrinsic birefringence of CaF2 reported in the middle of last year by NIST had large impact on F2 optics designing. However, we believe Nikon has already overcome it, and the imaging performance of our newest design is almost the same level to the performance without the intrinsic birefringence. Several methods to correct the intrinsic birefringence are discussed in this paper. Evaluation software for the intrinsic birefringence is also developed, and simulated performances of the newest optical designs, which correct for the intrinsic birefringence, are shown. Among them, simulated CD uniformity of 35nm width gate is a good measure to evaluate the optical design performance. We have also made a steady progress on gas purging. Purging of 02 and H20 concentration less than O.lppm and lppm respectively has been attained.

Development progress of optics for extreme ultraviolet lithography at Nikon

The full-field extreme ultraviolet (EUV) exposure tool named EUV1 is integrated and exposure experiments are started with a numerical aperture of the projection optics of 0.25, and conventional partial coherent illumination with a coherence factor of 0.8. 32-nm elbow patterns are resolved in a full arc field in static exposure. In a central area, 25-nm line-and-space patterns are resolved. In scanning exposure, 32-nm line-and-space patterns are successfully exposed on a full wafer. Wavefront error of the projection optics is improved to 0.4-nm rms. Flare impact on imaging is clarified, dependent on flare evaluation using the Kirk test. Resolution enhancement technology (RET) fly-eye mirrors and reflection-type spectral purity filters (SPFs) are investigated to increase throughput. High-NA projection optics design is also reviewed.

Nikon F2 exposure tool development

Present status of development of F2 (157nm) exposure tool in Nikon is described. Key points of F2 exposure tool are reported; low aberration projection optics, CaF2 quality, coating durability and gas purging of the pellicle space. We also report the measurement of refractive index inhomogeneity inside CaF2 crystals, which is suspected as the cause of local flare. Characteristics of high NA optics over 0.9 are investigated by imaging simulations for both 193nm and 157nm wavelengths, which are compared NA=0.85 imaging.

Development progress of optics for EUVL at Nikon

Full-field EUV exposure tool named EUV1 integrated and exposure experiments were started with the numerical aperture of the projection optics of 0.25 and conventional partial coherent illumination with the coherence factor of 0.8. 32nm elbow patterns were resolved in full arc field in static exposure. In the central area 25nm line-and-space patterns were resolved. In scanning exposure, 32nm line-and-space patterns were successfully exposed on a full wafer. Wavefront error of the projection optics was improved to 0.4nmRMS. Flare impact on imaging was clarified depend on the flare evaluation using Kirk test. RET flys eye mirrors and reflection-type SPF are investigated to increase throughput. High-NA projection optics design is also reviewed.