Advanced Gettering Techniques in ULSI Technology

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 μ m, 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 10 10 cm −2 as the maximum tolerable surface concentration, decreasing to 5 ϗ 10 9 cm −2 by 2004.