Methodology for Word Line-Contact Dielectric Characterization in Flash Normemories

Aim of this work is to study the reliability of the dielectric between cell control gate and drain contact. Conduction characteristics and reliability under high field stress are investigated. The large spread in this dielectric thickness because of mask misalignment makes the usual reliability procedures very difficult to be applied. Results relative to fast and long reliability measurements are discussed, proposing a method for the evaluation of the spread between control gate and drain contact. Moreover, this methodology allows a screening of the structures with a too critical mask misalignment, or with a poor dielectric quality which could cause memory failures during cycling