26 June 2003 Water immersion optical lithography for 45-nm node
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It is possible to extend optical lithography by using immersion imaging methods. Historically, the application of immersion optics to microlithography has not been seriously pursued because of the alternative solutions available. As the challenges of shorter wavelength become increasingly difficult, immersion imaging becomes more feasible. We present results from research into 193nm excimer laser immersion lithography at extreme propagation angles (such as those produces with strong OAI and PSM). This is being carried out in a fluid that is most compatible in a manufacturable process, namely water. By designing a system around the optical properties of water, we are able to image with wavelengths down to 193nm. Measured absorption is below 0.50 cm-1 at 185nm and below 0.05 cm-1 at 193nm. Furthermore, through the development of oblique angle imaging, numerical apertures approaching 1.0 in air and 1.44 in water are feasible. The refractive index of water at 193nm (1.44) allows for exploration of the following: 1. k1 values approaching 0.17 and optical lithography approaching 35nm. 2. Polarization effects at oblique angles (extreme NA). 3. Immersion and photoresist interactions with polarization. 4. Immersion fluid composition, temperature, flow, and micro-bubble influence on optical properties (index, absorption, aberration, birefringence). 5. Mechanical requirements for imaging, scanning, and wafer transport in a water media. 6. Synthesizing conventional projection imaging via interferometric imaging.
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Bruce W. Smith, Bruce W. Smith, Hoyoung Kang, Hoyoung Kang, Anatoly Bourov, Anatoly Bourov, Frank Cropanese, Frank Cropanese, Yongfa Fan, Yongfa Fan, } "Water immersion optical lithography for 45-nm node", Proc. SPIE 5040, Optical Microlithography XVI, (26 June 2003); doi: 10.1117/12.485489; https://doi.org/10.1117/12.485489

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