Thermal stability, structure, and electrical properties of amorphous metal alloys for electronic applications
Abstract/Contents
- Abstract
- As complementary metal oxide semiconductor (CMOS) transistors continue to scale down, the work function variation (WFV) of the metal gates is becoming a dominant factor of the threshold voltage variation. This is due to the different grain orientations present in polycrystalline metal gates. Replacing these with amorphous or near-amorphous metals can reduce WFV. Furthermore, amorphous materials are known to have superior diffusion barrier properties due to their lack of grain boundaries. This can help prevent work function change due to the diffusion of metals in contact with the gate. In the first part of this thesis, a CoTiN metal alloy is introduced as a potential gate material. Using TiN-based material allows for an easy integration with the current technology as polycrystalline TiN is commonly used as the gate. With the addition of cobalt, thin films of TiN become more amorphous, consisting of nanocrystals in an amorphous matrix. Reducing the nitrogen content further decreases the film's crystallinity. In addition, CoTiN films also exhibit good thermal stability, low resistivity, and low roughness. Even though these materials are not completely amorphous, their small crystal size and an amorphous matrix can potentially reduce WFV and improve the diffusion barrier behavior. The second part focuses on the barrier properties of TiN and CoTiN against the diffusion of metal in contact with the gate. The work function (WF) of the bilayer-metal gate structure (Al/CoTiN/HfO2/SiO2/Si or Al/TiN/HfO2/SiO2/Si) varies with the amount of Al that diffuses to the metal/dielectric interface and is used to measure the diffusion. The WF as a function of the bottom metal layer thicknesses is extracted using capacitance-voltage measurements. A thickness above 15 nm appears to be necessary for maintaining the WF without any effects from the top metal layer. Depending on the reactivity between different elements in different metal layers, an additional barrier may be needed to prevent unwanted diffusion and reaction. Investigating the thermodynamics of different elements within the gate stack is important and can help in choosing appropriate materials. In the last part of the thesis, the diffusion barrier properties of another amorphous metal, TaWSiC, is studied for interconnect application. Copper/barrier/Si structures are annealed at different temperatures and characterized for phase and structural changes. Unlike polycrystalline Ta, 5 nm of TaWSiC is able to prevent Cu reaction with Si up to 550C.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2015 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Wongpiya, Ranida |
|---|---|
| Associated with | Stanford University, Department of Materials Science and Engineering. |
| Primary advisor | Clemens, B. M. (Bruce M.) |
| Thesis advisor | Clemens, B. M. (Bruce M.) |
| Thesis advisor | Deal, Michael D |
| Thesis advisor | Nishi, Yoshio, 1940- |
| Advisor | Deal, Michael D |
| Advisor | Nishi, Yoshio, 1940- |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Ranida Wongpiya. |
|---|---|
| Note | Submitted to the Department of Materials Science and Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2015. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2015 by Ranida Wongpiya
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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