WLR test structure design - Discussion group summary

The test structure design group discussed the general requirements for test structure designs for wafer level reliability tests. These discussions used specific test structures as examples for extracting general requirements for designs. The first conclusion was that the structures must be customized for each process. Changes in layer resistivity, minimum design rules and oxide layer thickness can make significant changes in the appearance of test structures for specific purposes. This is especially true for the self heated test structures which depend on power dissipation and heat flow characteristics of various layers. Thus general descriptions of these test structures must be specified in terms of power density and thermal conductivity rather than in microns. The discussions also pointed out the requirements for an in-depth understanding of the trarget failure mechanism in order to prepare a design optimized to test this mechanism. It was pointed out that the highly accelerated tests are very prone to anomalous failure mechanisms. A brief discussion was also conducted in the measurement of the TCR of a metal line and the use of a metal line as a thermometer. Difficulties introduced by the change of resistance of a line subjected to a temperature cycle as well as annealing effects and alloy effects were noted.