Wafer level tunnel oxide reliability evaluation by means of the Exponentially Ramped Current Stress method

Abstract The Exponentially Ramped Current Stress method (ERCS) is an accelerated test for wafer-level tunnel oxide evaluation and screening. In this work the technique is described and its advantages are discussed, with special attention to the comparison with the most widely used constant current test. In the ERCS the dielectric is stressed by an exponentially increasing current flow until breakdown occurs. In a short measurement time a wide current density range is explored, so that both defectivity and intrinsic oxide properties can be monitored. The intrinsic charge-to-breakdown dependence on capacitor area and on current density under constant current stress have also been investigated, both for gate and for substrate charge injection. A simple algorithm is proposed in order to correlate the two techniques, allowing for the projection of the results obtained with the ERCS method to constant current stress conditions. The self-consistency of such an algorithm has been verified on the base of independent experimental results. It is concluded that the Exponentially Ramped Current Stress is suitable both as an efficient tool in Research and Development and as a routine control in production; in fact, the method shows several desirable qualities, such as the short measurement time, the good sensitivity in charge to breakdown determination over a wide range, the good correlation with constant current stress results, as well as the possibility of other electrical parameter extraction (i.e. Fowler-Nordheim characteristics, breakdown electric field, Time Dependent Dielectric Breakdown).