Light for the Invisible World

Application: Interference Immersion Lithography

Immersion lithography using available 193 nm optics and laser sources provides an attractive near-term path to reducing the printable feature sizes of integrated circuits by using a high-index fluid to reduce the wavelength at the wafer, rather than using light with higher photon energy and shorter vacuum wavelength.  This approach requires the development and characterization of high-performance fluids, photoresists, overlayers, and high-index optics. Interferometric immersion lithography (IIL) allows for rapid testing of these components now, before the general availability of full-blown immersion lithographic tools. A critical component in an interference immersion lithography engineering test-stand is a suitable 193 nm light source. In contrast to the excimer laser sources used in standard lithographic exposure tools, which by design have low spatial and temporal coherence to minimize interference artifacts, IIL requires both very high spatial- and temporal-coherence to allow uniform high-contrast intensity fringes to illuminate a wafer surface over relatively large areas (~ several mm² per exposure site). In addition, the laser should have high power stability and be sufficiently robust to allow extended periods of operation with little maintenance or operator intervention. The result of this IBM/Actinix joint development is a new solid-state 193 nm light source that will address the needs for IIL as well as other critical applications.