AVS 50th International Symposium
    Nanometer Structures Monday Sessions
       Session NS-MoM

Paper NS-MoM11
Investigation of Nucleation and Growth of Si(Ge) Nanocrystals Embedded in HfO@sub 2@ as Floating Gate for Flash Memory Devices

Monday, November 3, 2003, 11:40 am, Room 316

Session: Quantum Dots and Nanoscale Devices
Presenter: R. Gupta, National University of Singapore
Authors: R. Gupta, National University of Singapore
L.K. Bera, Institute of Microelectronics, Singapore
W.J. Yoo, National University of Singapore
D.S.H. Chan, National University of Singapore
N. Balasubramanian, Institute of Microrelectronics, Singapore
Correspondent: Click to Email
Charge storage in semiconductor nanocrystals is a very critical property to determine electrical performance of non-volatile memory devices. Nanocrystals embedded in high dielectric constant materials are not only effective to scale down the device size but also to enhance the programming and retention properties. Also, it is known that Si(Ge) nanocrystals of size @<=@ 10nm can have much better charge storage capability at room temperature than Si nanocrystals. This study is focused on understanding mechanisms to control shape, size, and composition of Si(Ge) nanocrystals that will be used for improving device properties of non-volatile memories. The Si(Ge) nanocrystals were deposited using Silane & Germane at the pressures of 0.5Torr - 5Torr and at the temperatures of 500°C-600°C on 40Å of either thermally grown SiO@sub 2@ or MOCVD HfO@sub 2@. The deposition time was varied from 5 seconds to 70 seconds at different flow rates of Silane & Germane. It was found that the evolution of size and density of Si(Ge) nanocrystals was dependent on pressure, deposition time, and substrate material. We found, as the deposition pressure decreased from 5 Torr to 0.5 Torr, the minimum size of Si(Ge) nanocrystal on SiO@sub 2@ decreased from 50 nm to 2 nm while density increased from 10@super 8@/cm@super 2@ to 10@super 11@/cm@super 2@. We observed that nanocrystal size increased in early stages but agglomeration took over with the further increase of deposition time. For SiO@sub 2@, we found that Ge atomic percent decreased from 18.4% to 14.6% as the deposition time increased from 5 seconds to 15 seconds at 5 Torr. However, Ge atomic percent on HfO@sub 2@ at same conditions at 5 seconds was lower at 12.3 %, showing significant difference in kinetics of the Si(Ge) nanocrystal formation between HfO@sub 2@ and SiO@sub 2@ substrates. Details on nucleation, growth, and electrical results on charge storage of Si(Ge) nanocrystals on HfO@sub 2@ will be presented.