The use of the coulomb meter to measure the excess mobile charge and capacitance of LSI circuits in the charged device model

The conventional charged device model (CDM) test methods for large-scale in tegrated (LSI) circuits have not prescribed the device capacitance; further more, the CDM sensitivity has been represented by the withstand voltage. Al so, a method for measuring;the voltage of small objects such as LSI circuit s has not been established. For these reasons, the failure voltage's obtain ed with every kind of tester have varied, and it could not be judged whethe r the charged LSI circuit would fail or not in CDM events. To solve these p roblems, we defined the failure factor as the excess mobile charge which co uld be measured by the newly developed coulomb meter, In addition, we devel oped a new CDM tester with the coulomb meter and obtained the excess mobile charge and the device capacitance. The CDM tester showed that several logi c MOS LSI circuits failed at their inherent constant charge. However, when the charge in low capacities was measured by the coulomb meter, the interna l circuit showed a step transient response. This problem could be alleviate d considerably by replacing the metal probe with a ceramic one. By using th is coulomb meter, we investigated the basic characteristics of the device c apacitance. Consequently, the device capacitance versus the distance betwee n the LSI circuit and the ground plane and the relationship between each pi n's capacitance and the applied voltage became clear. in conclusion, the ba sic failure factors in the CDM could be made clear; then it could be judged by the coulomb meter whether the charged LSI circuits would fail or not in CDM events.