| Summary: | 碩士 === 國立清華大學 === 工程與系統科學系 === 104 === Ge possesses two times electron mobility and .four times hole mobility compared to Si. Using Ge substrate and high-k material to obtain ultra-thin EOT, to achieve high mobility and drain current. However, using Ge material will face many challenges. It is easy for Ge oxide to be volatilized and hydrolyzed at 400°C. Ge out-diffusion induced gate leakage and Ge oxide quality is our first priority which is needed to be improved immediately. First, Hf film buffer layer can improve the interfacial layer. ZrO with a higher dielectric constant is used to achieve ultra-thin EOT and improve electrical characteristics of Ge MOS devices. At last, different annealing processes is performed to optimize electrical characteristics of Ge MOSFETs.
In this thesis, different high-k materials are deposited by an ALD on Ge substrate to improve the electrical characteristics of MOS device. In the first part, HfON is used as a high-k material. An Hf film buffer layer is deposited between HfON and GeO2, and the change of electrical characteristics is discussed. One can conclude that if HfON with Hf film buffer layer is chosen as a high-k material, 0.7 nm EOT can be achieved, and gate leakage is about 2x10-3 A/cm2. Moreover, it has higher drain current and mobility due to improved interfacial layer. Ge out diffusion into HfON can enhance tetragonal phase, resulting in a higher dielectric constant.
In the second part, ZrO2 and HfON are integrated as high-k dielectric stacks, and the electrical characteristic are discussed as well. The Hf film buffer layer as studied in the first part is also used. HfON/ZrO2 and HfO-ZrO co-deposition exhibit better electrical characteristic than that of single HfON layer. However, it is found that the reliability of single HfON layer is better than that with high-k dielectric stacks.
In the third part, the Hf film buffer layer and HfON/ZrO2 stack are applied to Ge MOSFETs. Difference annealing processes such as sinter, microwave annealing, and laser annealing are compared. In conclusion, laser annealing can improve drain current of Ge MOSFETs. Interface quality can be improved by microwave annealing, and then off current is reduced.
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