A Study on Controlling Composition of Si3N4 Thin Film and Forming Deep Trap to Improve Reliability of Flash Memory Devices

Abstract

Excellent retention characteristics were obtained by forming deep traps in Si3N4, which is the charge trap layer of flash memory. Blocking oxide SiO2 was deposited through low-pressure chemical vapor deposition (LPCVD), charge trap layer Si3N4 was deposited through plasma-enhanced atomic layer deposition (PEALD), and tunneling oxide SiO2 was deposited through thermal oxidation. As a comparison, Si-rich LPCVD Si3N4 was manufactured with the same capacitor, and it was confirmed that the N-rich Si3N4 charge trap layer had better retention characteristics than Si-rich Si3N4. The interface and bulk depth profile and thin film properties were analyzed through XPS, TOF-SIMS, and RBS of Si3N4 according to the PEALD process parameters. Compared to Si-rich Si3N4, N-rich Si3N4 thin film showed improved retention characteristics by having a deep trap. Although smaller than the large memory window due to the large trap density of Si-rich Si3N4, an acceptable memory window and better retention characteristics (104s) were achieved. Therefore, deep trap Si3N4 can be considered as a sufficient support for the charge trap layer as a way to increase the reliability of next-generation vertical-NAND flash memory.