A study of the thermal behavior of different test patterns used in differential high resolution electromigration measurements

摘要

The differential high-resolution electromigration (EM) measurement technique requires special test patterns since for the implementation of this technique th epresence of two metal lines is necessary, one metal line to be stressed with a high current density (`test' or `stressed' resistor) and a second line (`monitor' or `reference' resistor) to compensate for the thermal instabilities of th estressed one. It is accepted that due to Joule heating the stressed line always acquires higher temperature than the reference line and, therefore, additional resistance changes due to thermaly inuced phenomena, like precipitation of additional elements, will affect the measurement. In order to minimize these unwanted effects, an optimal high-resolution EM test structure should show a minimum temperature difference between the stressed and the reference lines. Based on this requiremtn, in this work we simulated three different test structures being used by various research groups for high-resolution measuremetns and subsequently compared these test structures on account of their thermal behavior. Each test strucure was examined for the case of two different widths of metal lines, 4 and 0.5μm. The results obtained from the simulation of these test patterns demonstrated that the test pattern comprised of two parallel stress and reference lines shows better thermal behavior than the `lined-up'(continuous) metal lines where the stress and reference lines are actually part of the same line. In particular, the test pattern comprised fo two parallel straight lines has slightly better behavio