Electrical activity of iron and copper in Si, SiGe and Ge

Abstract

The main reason for the interest in metal impurities in semiconductors is their electrical activity, resulting in device performance and yield degradation (to be discussed in Chap. 7). In this chapter, the electrical properties of the 3d transition metals iron and copper will be discussed in detail. First, the different configuration of the two metals will be outlined, i.e., whether they occur in substitutional or interstitial form, their interaction with other point defects to form pairs and complexes and, finally, the precipitation behavior. Besides homogeneous nucleation which results in the formation of silicon-rich silicides for the case of Fe and metal-rich Cu3Si for copper, there can also be heterogeneous precipitation/decoration on extended defects in the interior of a wafer. The wafer surface may also be a preferential precipitation site. Next, the electrical activity, i.e., the deep levels, associated with Fe (Cu) will be described in detail, both in Si and (Si)Ge. An overview of the deep-level parameters of the different point and extended defects will be given. Also the activation of pre-existing extended defects will be discussed. Finally, dedicated, mainly lifetime-based analysis techniques will be reviewed to identify Fe (Cu) in silicon and, whenever possible, to perform in-line wafer-based mapping. Most of these techniques have recently been developed for the case of mc-silicon wafers but can be extended for in-line process monitoring.