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In this thesis various degradation mechanisms and characterization meth¬ ods were investigated for metal oxide semiconductor (MOS) devices. The work starts with a survey of some important degradation and failure mechanisms. Degradation takes place at the three main levels of each device: First, on transistor level the thin gate oxide (especially its interface to the channel) is the most sensitive part. Generation of interface traps and oxide charges leads to shifts of the electric characteristics (mainly shifts of threshold voltage, transconductance and saturation current). Ionic contami¬ nation of the interface can have similar effects. Then, on the interconnection level between various transistors the thin metallization lines are threatened by corrosion, electroand Stressmigration and interdiffusion. Finally, on package level thermo-mechanical problems lead to shear stress at interfaces and diffusion through the package results in contamination of the circuit. Degradation on circuit level was studied in two examples: The first was a simple CMOS counter. Here, the power of the Iddq technique for the study of leakage currents due to hot carrier degradation and crystal defects was shown. In the second example old SRAM memories were analyzed. Corro¬ sion and migration problems in the metallization of the circuit were observed. The measurement of input leakage currents and of the standby current is proposed as an efficient reliability test before the reuse of old devices as replacement parts. In chapter 4 some important characterization methods on transistor level were considered. An important point was a deeper understanding of impact ionization: In short channel transistors impact ionization due to hot elec¬ trons occurs at a drain voltage as low as 0.7V. Hence, by a simple reduction of the drain voltage the hot electron problem cannot be resolved. Another important section of this chapter treats Fowler-Nordheim tunneling: The tunneling current was calculated approximately and exactly and current oscillations were measured and compared with the computation. Further¬ more, important measurement techniques such as GIDL, charge pumping or the measurement of the channel effective mobility were reviewed. A focal point of this thesis was the degradation of NMOS transistors. Drain avalanche hot electron and Fowler-Nordheim injection were used to

Characterization of degradation and failure phenomena in MOS devices