Evaluation of the Role of Deep Trap State Using Analytical Model in the Program/Erase Cycling of NAND Flash Memory and Its Process Dependence
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 (<inline-formula> <tex-math notation="LaTeX">$\text{E}_{\text {trap}}$ </tex-math></inline-formula>) is more than 3.5 eV. Furthermore, the as-grown trap state density (<inline-formula> <tex-math notation="LaTeX">${\text{N}}_{e}$ </tex-math></inline-formula>), the trapping capture cross section (<inline-formula> <tex-math notation="LaTeX">$\sigma $ </tex-math></inline-formula>), and the number of trapped positive charges can also be extracted to explain the tunneling current modulation and the <inline-formula> <tex-math notation="LaTeX">$\text{V}_{\text {T}}$ </tex-math></inline-formula> 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 <inline-formula> <tex-math notation="LaTeX">$\sigma $ </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">$\sim {4} \times {10}^{ {-17}}$ </tex-math></inline-formula> cm<sup>2</sup>). However, 30% reduction of <inline-formula> <tex-math notation="LaTeX">${\text{N}}_{e}$ </tex-math></inline-formula> is shown in plasma oxidation (<inline-formula> <tex-math notation="LaTeX">$\sim {1.25} \times {10}^{ {19}}$ </tex-math></inline-formula> cm<sup>−3</sup>) when compared with thermal dry oxidation (<inline-formula> <tex-math notation="LaTeX">$\sim {1.88} \times {10}^{ {19}}$ </tex-math></inline-formula> cm<sup>−3</sup>).