MICRO: Ultrapure Gas Delivery - Karwacki (February 2001)

Eugene J. Karwacki Jr., Kerry R. Berger, Ronald M. Pearlstein, and Robert J. Haney, A study investigates the effects of fluorine on gas delivery systems used to supply excimer lasers and develops methods for passivating stainless steel with fluorine to reduce damaging impurities . With the increasing demand in the semiconductor industry for critical line dimensions below 250 nm, microlithography has taken on greater importance, representing almost one-third of an IC's total production cost. The microlithography process, which produces highly accurate microscopic, two-dimensional patterns in photosensitive resist material, relies on deep-ultraviolet (DUV) steppers and scanners to achieve linewidth reductions. In turn, these new-generation tools derive their light from a type of gas laser known as excimer (short for ), which uses fluorine and rare-gas mixtures to produce wavelengths of light between 248 and 157 nm. For example, exciting a blend of fluorine and krypton within a neon buffer produces light at 248 nm. Since microlithography is essential to semiconductor manufacturing and excimer lasers are crucial to microlithography, optimizing the use of fluorine and rare gases in excimer lasers is critical to the industry. While the actual amount of fluorine fueling a laser is typically <0.2% by volume, it is usually delivered to the laser at concentrations between 1 and 5% and then diluted at the point of use by rare gases such as krypton or argon in neon. Although gas costs are a very small component of the overall microlithography cost of ownership (COO), their contribution can be magnified many times if gaseous impurities or insufficient fluorine are delivered to the laser. For example, the "poisoning" of a laser with gaseous impurities can lead to days of downtime if the lasing chamber must be replaced. It is estimated that this worst-case scenario could cost a semiconductor manufacturer more than $100,000 per