| Summary: | 碩士 === 國立交通大學 === 工學院碩士在職專班半導體材料與製程設備組 === 98 === In recent years, nonvolatile memory with nanocrystals cell have been widely studied to overcome difficulties occurring to of operation and reliability of conventional floating gate memory. Desirable electrical characteristics of memory devices include the following criteria : low power consumption, high-speed operation, good endurance, and long retention time. Nonvolatile memory devices, using metal nanocrystals cells have received extensive search because of many advantages, such as a high density of states around the Fermi level, stronger coupling with the conduction channel, a wide range of available work functions and a smaller energy perturbation due to carrier confinement, and become a potential candidate for future flash memory devices. Because tungsten has many attractive material properties, such as a high work function (4.6eV), an ultra high melting point(3411°C), being chemically stable with silicon oxide and being compatible with VLSI technology nowadays, it is widely used for the fabrication of the metal nanocrystals in nanocrystal nonvolatile memory devices.
Most methods applied for the nanocrystals fabrication need thermal treatments at high temperatures and a long duration which cause high energy consumptions and impurity redistribution. In this thesis, a new rapid thermal wet oxidation technology called “In-Situ Steam Generation (ISSG)”, is adopted for the tungsten nanocrystal fabrication to reduce the thermal budget and prevent impurity redistribution. In addition, during the ISSG oxidation process, hydrogen is introduced into the reaction chamber, thereby increasing the concentration of oxygen radicals. Oxygen radicals present in the ISSG process can reduce intrinsic defects in the oxide layer. ISSG oxides have much better reliability than conventional furnace oxides.
We fabricated tungsten nanocrystals under various ISSG process conditions, including the oxidation temperature, the process time and the hydrogen concentration, and studied material and electrical characteristics of the tungsten nanocrystal nonvolatile memory devices.
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