Evaluation of the Role of Deep Trap State Using Analytical Model in the Program/Erase Cycling of NAND Flash Memory and Its Process Dependence

Abstract

A method to analyze the kinetics of the charge accumulation in the tunnel oxide by the nand flash memory program and erase (P/E) cycling is proposed. Both electron trapping and detrapping processes are required to be considered owing to the oxide high electric field during P/E cycles. Consequently, the electron trapping in the deep trap state is concluded, whose trap energy (E-trap) is more than 3.5 eV. Furthermore, the as-grown trap state density (Ne), the trapping capture cross section (sigma), and the number of trapped positive charges can also be extracted to explain the tunneling current modulation and the V-T shift by oxide-trapped charges under the P/E stress. The trapped electrons are mainly distributed in the center of tunneloxide, and the distributed area extends as the P/E bias increases. In addition, the dependence of oxidation process is also shown. Both thermal dry and plasma oxidation have almost the same value of sigma (similar to 4x10(-17) cm(2)). However, 30% reduction of Ne is shown in plasma oxidation (similar to 1.25x10(19) cm(-3)) when compared with thermal dry oxidation (similar to 1.88 x 10(19) cm(-3)).