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 ( $\text{E}_{\text {trap}}$ ) is more than 3.5 eV. Furthermore, the as-grown trap state density ( ${\text{N}}_{e}$ ), 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 $\text{V}_{\text {T}}$ shift by oxide-trapped charges under the P/E stress. The trapped electrons are mainly distributed in the center of tunnel oxide, 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 $ ( $\sim {4} \times {10}^{ {-17}}$ cm2). However, 30% reduction of ${\text{N}}_{e}$ is shown in plasma oxidation ( $\sim {1.25} \times {10}^{ {19}}$ cm−3) when compared with thermal dry oxidation ( $\sim {1.88} \times {10}^{ {19}}$ cm−3).