| Summary: | 碩士 === 國立交通大學 === 工學院半導體材料與製程設備學程 === 102 === To scale-down dynamic random access memories (DRAMs) to the 40-30 nm nodes, it is desirable to have materials of better gap filling and lower resistivity for metal interconnects to meet the design criteria. Titanium nitride (TiN) and tungsten (W) are currently the mostly used barrier layer and plug, respectively, because of the excellent step coverage and good material stability. In this thesis, we discussed the influence of chemical vapor deposition (CVD) conditions of TiN and W thin film on the reduction in the electrical resistivity of the barrier layers and plugs.
We used multi-layer deposition instead of single-layer deposition for the TiN barrier layer fabrication. Titanium tetrachloride (TiCl4) and ammonia (NH3) were used as the precursor for the CVD-TiN deposition. After the CVD deposition, the TiN layer was annealed in NH3 to reduce the chlorine content in the barrier layer. The electrical resistivity of the TiN layer can be significantly reduced by the multi-layer deposition and the NH3 annealing treatment. The resistivity reduction depends on the stacking number of the TiN layer, and the resistivity eventually saturates at a critical stacking number.
In addition to the multi-stacking deposition, the film quality of the TiN barrier layer, including resistivity, stress and roughness, can also be improved by optimizing the NH3 gas flow rate during the CVD deposition and the plasma post treatment using Ar , N2 and H2 as the gas precursors of different gas flow rates.
For the CVD-W deposition, we used B2H6 instead of SiH4, to react with WF6 during the nucleation stage so that large W grains were obtained. Because of the large interface free energy, the heterogeneous growth of W on the polycrystalline TiN layer is retarded and the homogeneous growth of W favors the growth of larger W grains. The larger W grain size results in a less electron scattering in the CVD-W film and, therefore, the resistivity is improved. Combining the CVD-W fabrication with multi-stacking TiN barrier layer, we can reduce the electrical resistivity of the W-plug by 40-50%.
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