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

Amethod 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 (N_e), the trapping capture cross section (σ ), and the number of trapped positive charges can also be extracted to explain the tunneling current modulation and the VT shift by oxide-Trapped charges under the P/E stress. The trapped electronsaremainly distributedin the centerof 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 thesame value of σ (∼4×10^-17 cm²).However,30% reduction of N5_e is shown in plasma oxidation (∼1.25×10¹⁹ cm^-3) when compared with thermal dry oxidation (∼1.88×10¹⁹ cm^-3).