| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 91 === Metal silicides have been developed as interconnect and contact materials for semiconductor device fabrication. Among different silicides, CoSi2 is the most widely used material for salicide technology recently, since it has immunity to narrow line width effect, lower resistivity and good thermal stability. However, with the continued scaling down of device features, the stress induced by physical structures has noticeable effect on the formation of CoSi2 in deep sub-micron ULSI technology. In this thesis, the formation of CoSi2 affected by the neighboring different physical structures induced stress has been studied in detail.
During the growth of CoSi2, it has been reported that the main diffusing specie is Co atom for the solid phase reaction and volumetric change. We found the diffusion of Co atoms is also affected by the stress, i.e. the compressive stress caused by trench and top trench corner enhances the CoSi2 formation and gains a lower sheet resistance. On the contrary, the tensile stress caused by silicon nitride spacer or impurity dopant retards the CoSi2 formation and a higher sheet resistance.Additionally, the major contribution to the higher sheet resistance is the large tensile stress caused by the silicon nitride spacer on narrow trench. The tensile stress will cause the poor formation of CoSi2.
Furthermore, there is a trend that the TCR (The Temperature Coefficient of Resistance) of the CoSi2 wire is higher with higher compressive stress but is lower for higher tensile stress. Next, the difference in junction leakage is very small with different thickness of lining oxide. Therefore, the stress effect of top trench corner for the formation of CoSi2 is smaller than other physical structures. Finally, the junction leakage of N+/Pwell or P+/Nwell caused by the compressive stress is more significant than that by the tensile one.
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In this thesis, the tungsten plug corrosion induced by the charges on dummy metal surfaces after metal etch process was studied in detail. The tungsten plug corrosion can be induced during polymer strip in solvent and even be almost dissolved by electrochemical reaction. These phenomena were evidenced by in-line inspections with wafer level SEM (Scanning Electron Microscope) scanning at the step of post tungsten CMP (Chemical Mechanical Polish) and found no tungsten plug lifting.
Next, at the discharge step of post over etch or post photoresist ash, the plasmolyzed gases not only can’t release charges on dummy metal surfaces, but also even increase via failure rates. However, an extra added baking in H2O vapor ambient prior to soak in polymer strip solvent is a good approach to improve tungsten plug corrosion.
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