AVS 53rd International Symposium
    Nanometer-scale Science and Technology Monday Sessions
       Session NS-MoA

Paper NS-MoA9
Partial Crystallization of HfO2 and Its Application to Nanoscale Flash Memories

Monday, November 13, 2006, 4:40 pm, Room 2016

Session: Nanoscale Structures and Characterization I
Presenter: G. Zhang, National University of Singapore
Authors: G. Zhang, National University of Singapore
W.J. Yoo, Sungkyunkwan University, Korea
Correspondent: Click to Email
The demands for non-volatile memories (NVM) in recent years have increased rapidly due to the growth of mobile device industries. Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) type flash memory layer is extensively studied because of its potential as a high density memory. The high-k dielectric material HfO@sub 2@ is considered as a better trapping layer material than Si@sub 3@N@sub 4@ in SONOS because high k can provide better vertical scalability and data retention property. Amorphous HfO@sub 2@ crystallizes during high-temperature (> 650@super o@C) treatments, which is a drawback of HfO@sub 2@ since the crystallization can induce high leakage current. According to the crystallization result obtained by X-Ray Diffraction (XRD), high intensity peaks of (-1 1 1) and (1 1 1) are observed after the thermal treatment for 5 s in the temperature range of 800@super o@C - 1000@super o@C,. However, conducting-AFM topography image clearly shows that the crystallization across the HfO@sub 2@ film is non-uniform and the grains in the film are formed via partial crystallization. A two dimensional current image of C-AFM confirmed the non-uniform distribution of the grains, where leakage current is significantly higher than amorphous HfO@sub 2@. The z results (contrast in image) are 2nm for topography and 6 pA for current image. We consider that these grains act similarly to nanocrystal dots, which effectively suppress lateral charge migration under the programmed state, via charge localization inside the grains or at the grain boundaries. Excellent 2-bit/cell and 4-level/bit memory properties are achieved by Channel Hot Electron Injection (CHEI) program and outstanding charge retention property is achieved in both room temperature and at 85@super o@C. The novel way of mimicking nanocrystal structure with partially crystallized continuous HfO@sub 2@ trapping layer easily enables multi-bit/cell operation and greatly extend the storage capacity of SONOS type flash memory.