A new method to statistically monitor active area spread and oxide thinning in real devices

Abstract

ULSI device scaling down continuously requires to improve the control over any key process parameter. In particular, the active dielectric thickness reduction and the use of innovative isolation schemes make it very difficult to have a direct monitor of oxide thickness and active area width at the same time. A new method is presented here which allows one to verify the electrical quality of the thin oxide, giving also information about the active area spread and the dielectric thickness. A standard technique to evaluate the quality of a thin oxide consists of the application of an exponential current stress up to the capacitor breakdown. In this work it is suggested to measure the capacitance and to start the current ramp not above a current density of 1E-5 A/cm/sup 2/ to avoid stress regimes in which the charge trapping heavily influences the measurements. In this way the procedure can be very effective in distinguishing between active area dimension fluctuations and real oxide thinning at the field oxide border, without adding any extra measurements.