VSS-induced NiSi 2 Nanocrystal Memory
- PDF / 148,175 Bytes
- 5 Pages / 595 x 842 pts (A4) Page_size
- 11 Downloads / 177 Views
1160-H01-09
VSS-induced NiSi2 Nanocrystal Memory Bei Li and Jianlin Liu Quantum Structures Laboratory, Department of Electrical Engineering, University of California, Riverside, California 92521 ABSTRACT NiSi2 nanocrystals were synthesized and used as the floating gate for nonvolatile memory application. Vapor-solid-solid mechanism was employed to grow the NiSi2 nanocrystals by introducing SiH4 onto the Ni catalysts-covered SiO2/Si substrate at 600˚C. The average size and density of the NiSi2 nanocrystals are 7~10nm and 3 × 1011 cm-2, respectively. Metal-oxidesemiconductor field-effect-transistor memory with NiSi2 nanocrystals was fabricated and characterized. Programming/erasing, retention and endurance measurements were carried out and good performances were demonstrated. INTRODUCTION Silicide nanocrystals are believed as one of the promising candidates to replace traditional Si as the floating gates in nonvolatile memory. The time-voltage dilemma prevents conventional Si memory scale beyond 32nm technology node. Using silicide nanocrystals may extend this scale limit by enhancing the device retention without compromising the program efficiency. Because silicides are metallic materials, the strong coupling between the channel and floating gates helps improve the programming speed and deeper quantum well formed between the metals (those Fermi-levels within the energy band gap of Si), and Si substrate elongates the retention time. The storage capability can also be improved using silicide nanocrystals due to their high density of states. The large memory window makes it possible for the device to be used for multi-bit applications. Another advantage for silicide materials is their thermal stability. The current long retention reported in Si nanocrystal memory is mainly due to the charging on the defect levels within Si, which is not thermally robust. Various silicide nanocrystals [1-5] have been reported showing good memory performance. The methods include ebeam evaporation, sputtering with post rapid thermal annealing (RTA). In this work, we use a novel method, i.e., Vapor-Solid-Solid (VSS), which is mainly used for nanowires growth [6-8], to synthesize silicide nanocrystals. EXPERIMENT A thin layer of metal Ni was deposited by ebeam evaporation on a 5nm thermally grown SiO2 covered p-Si (100) substrate. In-situ annealing in N2 at 900 for 30s was carried out to release the stress and densify the oxide film. The wafer was then transferred to a low vapor chemical vapor deposition (LPCVD) furnace for silicide synthesis. As the furnace temperature increases to the growth temperature, ~600 Ni nanocrystals were formed, then Si precursor (SiH4) was introduced to diffuse into/react with Ni to form silicide. The growth time was calibrated and the SiH4 gas was shut off at the time when no Si nanowires growth underneath the catalysts. Control oxide of 25nm was deposited on the nanocrystals followed by 350nm
℃
℃,
polysilicon gate formation. Phosphorous was implanted to make heavily doped source/drain/gate regions. Aluminu
