Reliability and Processing Effects of Bandgap-Engineered SONOS (BE-SONOS) Flash Memory and Study of the Gate-Stack Scaling Capability

In this paper, the reliability properties of bandgap-engineered SONOS (BE-SONOS) devices with various processing methods are extensively studied. BE-SONOS employs a multilayer O1/N1/O2/N2/O3 stack, where O1/N1/O2 serves as a bandgap-engineered tunneling barrier that provides an efficient hole-tunneling erase but eliminates the direct-tunneling leakage. BE-SONOS can overcome the fundamental limitation of the conventional SONOS, for which fast erase speed and good data retention cannot be simultaneously achieved. In this paper, a comprehensive understanding of BE-SONOS reliability is reported, including the processing effects of the critical ONO barrier (O1/N1/O2), the trapping layer (N2), and the top blocking oxide (O3). Moreover, the capability of dielectric scaling is also evaluated. Lower P/E voltages, good P/E cycling endurance, and data retention are maintained when N2 and O3 are further scaled to 60 $\hbox{\rm{\AA}}$. The results in this paper provide design and processing guidelines for optimizing the performance and reliability of BE-SONOS Flash memory devices.