Advanced Gettering Techniques in ULSI Technology

Abstract

Progress in silicon technology has been phenomenal since the invention of the transistor some 50 years ago. Device performance has improved by at least a factor of a million in every respect. As the minimum feature size on chips decreases toward 0.1 μm, which should be reached on a mass-production scale in a few years, the device yield is becoming ever more sensitive to defects and impurities. Transition metals, particularly iron, nickel, and copper, are the most common and most detrimental contaminants on a process line, and they can be unintentionally introduced in nearly every process step, including ingot growth, wafer handling, ion implantation, wet-chemical cleaning, high-temperature anneals, or oxidation. To avoid yield losses, the silicon industry has to be very strict with respect to metal-contamination levels on the production line. For instance, for iron, the Semiconductor Industry Association (SIA) Roadmap presently specifies 2.5 ϗ 1010 cm−2 as the maximum tolerable surface concentration, decreasing to 5 ϗ 109 cm−2 by 2004.