Analysis of Failure Mechanisms based on 3D TCAD Simulation and Measurement in NAND Flash memory cell

Abstract

As the device of NAND Flash memory has been extremely scaled down (sub-30nm), many reliability issues related to the device characteristics have appeared. Particularly, the retention characteristics cannot be explained anymore by the conventional lifetime evaluation method (Arrhenius model) because there are various failure mechanisms contributing to the charge loss of device. To estimate the accurate prediction of lifetime, we previously proposed a new lifetime evaluation method (proposed method) which is superposition of the behaviors of three dominant failure mechanisms (detrapping, trap-assisted tunneling (TAT), and interface trap (Nit) recovery mechanism). From the proposed method, we separated the amount of charge loss of each failure mechanism (ΔVTH,Detrap, ΔVTH,TAT, and ΔVTH,Nit) from total charge loss (ΔVTH,TOTAL) in test element group (TEG) cells of the advanced NAND Flash memory for different generations (A, B, and C). In this paper, we investigated the behavior of Arrhenius plot for lifetime estimation in NAND Flash memory using 3D TCAD simulation, where the number of failure mechanisms and the criterion determining failure data (ΔVTH,FAIL), the percentage of total charge loss (ΔVTH,TOTAL) at specific temperature, are considered. When detrapping and trap-assisted tunneling (TAT) mechanism are applied to retention simulation together, abnormal behavior of Arrhenius plot was observed and explained by mechanism separation with the proposed method. In addition, as TAT mechanism proportion is larger than detrapping mechanism proportion in ΔVTH,TOTAL, abnormal characteristics of Arrhenius plot was obviously observed. Finally, two experiments which are charge pumping (CP) and 1/f noise analysis were conducted to verify the 3rd mechanism extracted on generation A, B, and C in previous work. Relative Nit extracted by two experiments showed perfect correlation with the amount of charge loss of 3rd mechanism (ΔVTH,Nit). As a result, the 3rd mechanism was verified as Nit recovery mechanism.