Impurity control in silicon devices

In this paper a brief review is given of how harmful impurities are effectively removed from device regions and of the science underlying it. Illustrations are made mainly on silicon devices since the progress of the technology has been made most drastically on them in connection to the progress of Si-based ULSI. Impurities undesirable for device performance have chances to come into a semiconductor crystals as residual impurities of raw materials, from environment at the time of crystal growth, and due to contamination during device fabrication processing. In a last few decades, a great progress has been achieved in eliminating harmful impurities from electronic devices.The technology of gettering has so far been developed mostly on the basis of experience practically met in device fabrication processing. Not much attention has been paid on the understanding of gettering mechanism. It is certain that a highly advanced gettering technique is achieved on the basis of detailed understanding of the impurity incorporating reactions that occur at various kinds of gettering agents. (author)