Dominating defects in the MOS system: P_band E’ centers

Two types of silicon dangling bond centers play dominating roles in metal=oxide=silicon (MOS) device limitations. Silicon dangling bonds defects at the Si=SiO₂boundary, P_bcenters dominate Si=SiO₂interface trapping. Silicon dangling bond defects called E’ centers dominate deep levels in the oxide. E’ centers can also play dominating roles in the electronic properties of the near Si=SiO₂interface dielectrics, serving as switching traps or border traps (Chapter 7). Under some circumstances, some E0 centers also act as interface traps. Analysis of a combination of electron spin resonance (ESR) and electrical measurements provides a fairly detailed understanding of the relationship between the structure and electronic properties of the P_binterface centers and E0 oxide centers. Straightforward application of the fundamental principles of statistical mechanics provides a partial explanation of the frequently noted correlation between oxide deep level defects and Si=SiO₂interface trap defects. This chapter reviews the spectroscopy, electronic properties, and device relevance of these two families of defects. Since the understanding of the defects has come from ESR, the chapter begins with a brief introduction to this technique. It is important to note that P_band E’ centers are not necessarily the only electrically active point defects in MOS devices. Although many studies have established the dominating roles of these two families of silicon dangling bond centers, the limited precision of ESR measurements as well as that of the relevant electrical measurements precludes concluding with certainty that either defect is entirely responsible for any device limitation. However, they are clearly responsible for the majority of the deep levels in most and perhaps all the phenomena discussed in this chapter. Furthermore, under some circumstances, it is clear that other defects are playing important roles. For example, the addition of nitrogen introduces greater complexity in plasma-nitrided gate oxides. Not surprisingly, several very different defects clearly play important roles in gate stacks based on hafnium oxide=silicon dioxide systems. Several decades of ESR [1] studies of the MOS system have established the roles of these two families of silicon dangling bond defects in MOS device instabilities. At the Si=SiO₂boundary the P_bcenter family dominates interface trapping under many circumstances [2-32]. Largely due to the simplicity of the ESR spectroscopy, most earlier studies focused upon the (111) Si=SiO₂interface, where only one P_bdefect, called simply P_b, appears [2-15].