Time dependent dielectric breakdown

A serious potential problem related to the use of high-k gate dielectrics in SiC power MOSEETs can be encountered due to the much smaller (sometimes-negative) conduction band offsets between SiC and high-k metal oxides compared with silicon dioxide (see Table 5.1). Time-dependent dielectric breakdown (TDDB) and hot... 

Thickness and, correspondingly, capacitance variation was less than 2%. The absence of impurity peaks in XPS spectra of silica-coated specimens clearly demonstrates the achieved purity. Yield, defined as the percentage of functioning vs. total measured capacitors, was 100%. Breakdown field strength was in the range 1.1-5.4 MV/cm and leakage current was about lO -lO A/cm at 0.5 MV/cm. Capacitance density was 23-350 nF/cm dependent on thin film thickness and materials. No breakdown was observed after 20 cycles between 0-40 V. Time dependent dielectric breakdown (TDDB) was 185 s at 40 V for ten of the patterned capacitors. 

Time-dependent dielectric breakdown challenges for ULK materials... 

It should be noted that even if there are no shorts detected by electrical testing, the onset of such corrosion induces topography and weakens the interface with the SiCN capping layer, causing reliability problems. Evidence of this is presented by Liniger et al. (2010) in Figure 4.27 through time-dependent dielectric breakdown (TDDB) characterization of the effect of queue time. It can be seen that as queue time is increased, the time required for 50% of the structures to fail with a short under the applied electric field decreases. 

Figure 4.27 Degradation of time-dependant dielectric breakdown (TDDB) characteristics occurs in advanced nodes when wafers are held in air ambient for after damascene Cu CMP is completed (Reprinted with permission from Liniger et al., 2010).

Example 4. An example of mechanism superposition is the relation between two failure mechanism models contributing to Time-Dependent Dielectric Breakdown (TDDB) (McPherson 2010). TDDB can be modeled by two mechanism models, the E-model (equation (9)) and the 1/E-model (equation (10)). 

Unlike the Zener effect in which the breakdown voltage is engineered into the design of the dielectric, many of the above mechanisms are unpredictable and time-dependent, so the chances of breakdown increases with age. 

The electrical properties of materials are important for many of the higher technology applications. Measurements can be made using AC and/or DC. The electrical properties are dependent on voltage and frequency. Important electrical properties include dielectric loss, loss factor, dielectric constant, conductivity, relaxation time, induced dipole moment, electrical resistance, power loss, dissipation factor, and electrical breakdown. Electrical properties are related to polymer structure. Most organic polymers are nonconductors, but some are conductors. 

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