Analyzing electrical effects of RTA-driven local anneal temperature variation

Abstract

Suppresing device leakage while maximizing drive current is the prime focus of semiconductor industry. Rapid Thermal Annealing (RTA) drives process development on this front by enabling fabrication steps such as shallow juction formation that require a low thermal budget. However, decrease in junction anneal time for more aggresive device scaling has reduced the characteristic thermal length to dimensions less than the typical die size. Also, the amount of heat transferred, and hence the local anneal temperature, is affected by the layout pattern dependence of optical properties in a region. This variation in local anneal temperature causes a variation in performance and leakage across the chip by affecting the threshold voltage (Vth) and extrinsic transistor resistance (Rext). In this work, we propose a new local anneal temperature variation aware analysis framework which incorporates the effect of RTA induced temperature variation into timing and leakage analysis. We solve for chip level anneal temperature distribution, and employ TCAD based device level models for drive current (Ion) and leakage current (Ioff) dependence on anneal temperature variation, to capture the variation in device performance and leakage based on its position in the layout. Experimental results based on a 45nm experimental test chip show anneal temperature variation of up to ∼10.5°C, which results in ∼6.8% variation in device performance and ∼2.45X variation in device leakage across the chip. The corresponding variation in inverter delay was found to be ∼7.3%. The temperature variation for a 65nm test chip was found to be ∼8.65°C.