Electrical test structures

Finally, we have proposed a model framework for copper CMP simulation. Characterization methods (masks with physical, electrical test structures) for single- and multi-level pattern-dependencies are also under development, and we are pursuing ways to overcome challenges in model parameter extraction and validation. 

In addition to mechanical test structure it is good practice to include electrical test structures. Simple structures like electrical bond pads that... 

Khmelevaya and Damaskin621 have studied the electrical doublelayer structure at electrochemically polished pc-Sn. Effs0 = -0.63 V (SCE) (corrected by the asymmetrical type of electrolyte) the applicability of the GCSG theory has been tested and the values of /pz and C 0 have been reported. 

To date, only limited work has been reported on models for dishing and erosion in copper structures most work has been experimental in nature and report underlying pattern dependencies [13,33,51]. For example. Pan et al. [32] show experimental data based on electrical and profilometry measurements across a variety of test structures with different density, line width, and line spacing an example plot is shown in Fig. 31 where both dishing and erosion is clearly present. 

FIGURE 15.11 Process flow for thinning to a hurried oxide etch stop, rebonding, and repeating to allow electrical testing of the original structures (from Ref. 49). 

The only way to obtain all necessary parameters is to apply model-based measurement techniques and electrical stimulation during wafer-level tests for each single device or by using test structures designed especially to obtain in-process measurement data (see [28, 29] and Section 5.10). This requires that the sensor s behavior is well understood and the dependencies of the various parameters can be expressed analytically according to Eq. 4.3. 

Concurrently design test structures and develop test models dedicated solely to extracting critical model parameters from electrical precision measurements on the wafer level. Improve fabrication processes using test structures early in the sensor development phase and well in advance of starting production. Eventually, reduce the number of test structures and the wafer space they occupy, optimize testing time and equipment, and then commit a test setup to production. 

It may be desirable to electrically isolate a cathodically protected structure from all other metallic structures, such as connecting lines, pump stations, terminals, etc. If the installation is not isolated, these connections also will be cathodically protected, and current requirements frequently will be excessive. Electrical insulation of pipelines and other structures is accomplished by dielectric isolation. Small lines may be insulated by insulating couplings or unions. If feasible, insulated flanges should be assembled and electrically tested with an ohmmeter before being connected into a line. 

All the mechanical, electrical and electronic equipment to which sodium aerosol had adhered was cleaned (see Fig. 3.4). Visual inspection and electrical testing were carried out as appropriate to ascertain whether any deterioration had occurred. It was found that there had been no damage to mechanical structures as a result of exposure to aerosol. After comprehensive cleaning and rebuilding, the function of electrical and electronic components was found to be unimpaired but this will remain subject to a program of continuing inspection and monitoring. 

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. 

More sophisticated, multisensor test chips contain test structures for the evaluation of thermal resistance, electrical performance, corrosion, and thermomechanical stress effects of packaging technologies (Mathuna, 1992). However, multisensor chips have to be driven by computerized test equipment(Alderman, Tustaniwskyi, and Usell, 1986 Boudreaux et al., 1991) in order to power the chip in a manner that... 

FIGURE 53.3 Typical process defect spectrum for surface-mount assemblies. Process defects marked E" can be detected by electrical tests, those marked M can be detected by mechanical or structural inspection or testing, and those marked by E and M can be detected by either method. 

The final step in the process is to measure the electrical resistance of each of the test structures. Voltage is applied to one of the two electrodes in each test structure and the resistance is obtained by probing the opposite electrode. It has been observed that a single DNA bridge formation results in at least a 1000-fold reduction in resistance on the test structure. 

As described in Chapter 2, the M-Test structures are useful for determining thin film properties as well as testing electrical functionality. By applying increasing voltages to the M-Test structures, they can be optically inspected to determine the voltage that is required for pull-in. These simple test structures enable a rapid assessment to determine quickly if released parts are able to be actuated as expected using electrostatic forces. 

Often the supplier will include one of their own test structures in the customer s layout space. For example the PolyMUMPs die will have a comb-drive resonator added into the layout after the customer turns it in, so long as they have followed the design guidelines that specify leaving a space on the layout for the inclusion of the comb-drive resonator. The comb-drive can be inspected for the fidelity of the patterning since the combs of the comb-drive use the minimum space to achieve the maximum force. The comb-drive can also be driven into electrical resonance by the application of the appropriate biasing conditions [3]. 

---