The W-NCs nonvolatile memory devices were widely investigated in this thesis.
The thick enough capped oxide can be used to prevent the tungsten-oxide out-diffuse, but the lager thermal budget is also needed. In addition, the thicker inner-oxide was also formed after thermal oxidation process. In order to well control the thickness of tunnel oxide, the capped oxide can be replaced by conventional amorphous silicon (a-Si). The reported paper indicated that the a-Si can be used to adjust the W/Si ratio during thermal oxidation process. The volatile tungsten-oxide formation is not easy to form at lower W/Si ratio. For tungsten-silicide layer with high W/Si ratio, the capped a-Si is believed to solve the W out-diffusion effect. However, the thermal oxidized a-Si layer serves as blocking oxide without high enough quality. Hence, the suitable method to improve the quality of the blocking oxide is necessary to be considered, such as steam treatment.
The W-doped silicon-oxide/silicon nitride was also discussed in this contribution.
However, the thermal treatment and the capped oxide are also used in this series
investigated in this thesis. The suitable W/Si ratio can be obtained by tuning the recipe of deposition condition. The W-SiGe is also a potential material serving as nanocrystal self-assembling layer. The silicon-germanium itself is a low thermal-needed material due to the low thermal resistivity. The prior W-Si formation causes the Ge element to nucleate during thermal treatment. The additional charge trapping centers will be generated to cause the memory effect. However, it is reported that the oxide formation depending on the Si/Ge ratio, which directly affect the leaking current and the Ge nanocrystal formation.
In addition, the rapid thermal annealing (RTA) system was not used in this thesis.
It is found that the capped oxide is necessary to prevent the tungsten-oxide out-diffusion. However, the oxidation ability was affect by the 20-nm-thick capped oxide. There was not enough oxidation ability to nucleate the W-NCs. It is believed that the tungsten-silicide layer with lower W/Si ratio can be executed in the RTA system. Due to the rapid thermal treatment process, the thicker inner-oxide may be not occurred.
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