Potential of solid immersion lithography using I-line and KrF light source

ArF technology is currently being used for 80nm resolution in the photo-lithography field, and ArF wet immersion technology is expected to be used for high resolution systems down to 50nm. Between ArF wet immersion technology and EUV technology, there is no proper technology that can cover the resolution range from 50nm to 30nm. In this paper, a new lithography technology using a Solid Immersion Lens (SIL) is introduced as an idea for very high resolution, and its resolution achievement is estimated through simulation. SIL technology is a near-field optics technology that achieves high resolution. A SIL is a hemispherical lens, and the incident beam is normal with respect to the surface of the lens. Because a high refractive index material is used for the SIL, very high numerical aperture provides high resolution. The resolution limit is estimated by calculating the vector irradiance inside the thin-film stack composed of the SIL, air gap, photoresist, anti-reflection layer and substrate. Feature size is estimated over reasonable exposure latitude at 20nm depth in the resist. Results show that, using a 365nm wavelength source, 70nm resolution is expected, and 50nm resolution is expected with a 248nm wavelength source. With a shorter wavelength light source and a proper SIL material of high refractive index for the wavelength, higher resolution can be achieved.