Atomic layer deposition (ALD) of TiO2 thin films using Ti isopropoxide and tetrakis-dimethyl-amido titanium (TDMAT) as two kinds of Ti precursors and water as another reactant was investigated. TiO2 films with high purity can be grown in a self-limited ALD growth mode by using either Ti isopropoxide or TDMAT as Ti precursors. Different growth behaviors as a function of deposition temperature were observed. A typical growth rate curve-increased growth rate per cycle (GPC) with increasing temperatures was observed for the TiO2 film deposited by Ti isopropoxide and H2O, while surprisingly high GPC was observed at low temperatures for the TiO2 film deposited by TDMAT and H2O. An energetic model was proposed to explain the different growth behaviors with different precursors. Density functional theory (DFT) calculation was made. The GPC in the low temperature region is determined by the reaction energy barrier. From the experimental results and DFT calculation, we found that the intermediate product stability after the ligand exchange is determined by the desorption behavior, which has a huge effect on the width of the ALD process window.
Atomic layer deposition ͑ALD͒ of TiO 2 films from tetrakis͑dimethylamido͒ titanium ͑TDMAT͒ or titanium tetraisopropoxide ͑TTIP͒ precursors was investigated. The growth kinetics, chemical composition, and crystallization behavior of the TiO 2 films were compared for combinations of the two precursors with three different sources of oxygen ͓thermal ALD using H 2 O and plasma-enhanced ALD ͑PEALD͒ using H 2 O or O 2 plasma͔. For TDMAT, the growth rate per cycle ͑GPC͒ decreased with increasing temperature; while for TTIP with either water plasma or O 2 plasma, a relatively constant growth rate per cycle was observed as a function of substrate temperature. It was found that the crystallization temperature of the TiO 2 films depends both on film thickness and on the deposition conditions. A correlation was observed between the TiO 2 crystallization temperature and the C impurity concentration in the film. The TiO 2 films grown using a H 2 O plasma exhibit the lowest crystallization temperature and have no detectable C impurities. In situ X-ray diffraction measurements were used to test the diffusion barrier properties of the TiO 2 layers and proved that all TiO 2 films grown using either H 2 O or O 2 plasma are dense and continuous.
Due to its high intrinsic mobility, germanium (Ge) is a promising candidate as a channel material (offering a mobility gain of approximately × 2 for electrons and × 4 for holes when compared to conventional Si channels). However, many issues still need to be addressed before Ge can be implemented in high-performance field-effect-transistor (FET) devices. One of the key issues is to provide a high-quality interfacial layer, which does not lead to substantial drive current degradation in both low equivalent oxide thickness and short channel regime. In recent years, a wide range of materials and processes have been investigated to obtain proper interfacial properties, including different methods for Ge surface passivation, various high-k dielectrics and metal gate materials and deposition methods, and different post-deposition annealing treatments. It is observed that each process step can significantly affect the overall metal-oxide-semiconductor (MOS)-FET device performance. In this review, we describe and compare combinations of the most commonly used Ge surface passivation methods (e.g. epi-Si passivation, surface oxidation and/or nitridation, and S-passivation) with various high-k dielectrics. In particular, plasma-based processes for surface passivation in combination with plasma-enhanced atomic layer deposition for high-k depositions are shown to result in high-quality MOS structures. To further improve properties, the gate stack can be annealed after deposition. The effects of annealing temperature and ambient on the electrical properties of the MOS structure are also discussed.
The properties of ultrathin ruthenium (∼5nm)∕TaN(∼5nm) bilayer as the copper diffusion barrier are studied. Cu, Ru, and TaN thin films are deposited by using the ion beam sputtering technique. The experimental results show that the thermal stability of the Cu∕Ru∕TaN∕Si structure is much more improved than that of the Cu∕Ru∕Si structure, which should be attributed to the insertion of the amorphous TaN interlayer. The microstructure evolution of the Cu∕Ru∕TaN∕Si structure during annealing is also discussed. The results show that the Ru∕TaN bilayer can be a very promising diffusion barrier in the future seedless Cu interconnect technology.
The deposition of Cu seed layers for electrochemical Cu deposition (ECD) via atomic layer deposition (ALD) of copper oxide and subsequent thermal reduction at temperatures between 110 and 120°C was studied on different diffusion barrier systems. While optimization of the process is required on TaN with respect to reduction and plating, promising results were obtained on blanket PVD Ru. The plating results on layers of ALD Cu with underlying Ru even outperformed the ones achieved on PVD Cu seed layers with respect to morphology and resistivity. Applying the processes to via and line patterns gave similar results, suggesting that a combination of ALD Cu with PVD or ALD-grown Ru could significantly improve the ECD Cu growth.
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