Gettering mechanisms in silicon

Abstract

Various procedures for heavy metal gettering in silicon p-n junctions have been compared in order to test the effectiveness of dopants and extended defects as getter sites; the role of silicon interstitials in the gettering process has also been studied. It has been found that only phosphorus and boron atoms are effective getter sites, while arsenic and antimony are not; such gettering effectiveness is independent of the presence of extended defects in the heavily doped regions. During a moderate temperature annealing (segregation annealing) dissolved metal impurities diffuse from the space-charge region of the devices and segregate at getter sites. Extended defects generated by oxygen precipitation and stacking fault backside damage have some ability to capture metal impurities, but electrical tests show that they do not provide a satisfactory gettering technique. The role of self-interstitials consists of increasing the dissolution rate of metal precipitates with subcritical radii, so that the segregation of metal impurities into getter sites is made easier; however, a complete gettering process requires three steps, that is: (1) the creation of effective getter sites; (2) the dissolution of metal precipitates; (3) the segregation of dissolved metal impurities at getter sites. Some of these steps may be activated simultaneously.