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Thin film electrodes of the perovskite oxide (Ba,Sr)RuO3 (BSR) were deposited on 4 inch ptype Si wafers by metal organic chemical vapor deposition (MOCVD) for the practical (Ba,Sr)TiO3 (BST) capacitor application using a new single cocktail source. The source materials used for the MOCVD BSR process were Ba(METHD)2, Sr(METHD)2 and Ru(METHD)3 and these were dissolved in n-butyl acetate. The source-feeding rate was precisely controlled by liquid mass flow controllers (LMFC). As-deposited BSR films possessed a (110)-oriented structure, with good uniformity and adherence on bare Si wafer. The phase formation was strongly affected by the oxygen flow rate and the input source rate. As the oxygen flow rate increased, the Ru/(Ba+Sr) composition ratio in the film decreased, while the Ba/(Ba+Sr) ratio was almost independent of the oxygen flow rate. The dielectric constants of BST capacitors fabricated using these electrodes was greater than 500.
A novel concept of field aided lateral crystallization (FALC) and the effects of Cu on FALC of amorphous silicon (a-Si) were investigated. Cu was found to induce the lateral crystallization toward a metal-free region as well as the crystallization of a-Si in contact with Cu. In particular, the lateral crystallization caused by Cu was noticeably accelerated at the negative electrode side in every pattern with an aid of electric field, while it was retarded at the positive electrode side. The occurrence of Cu-FALC phenomenon was interpreted in terms of dominant diffusing species (DDS) in the reaction between metal and Si. The FALC velocity increased with the applied field intensity and the annealing temperature. The crystallization of a-Si was achieved at temperatures as low as 375°C when the annealing time increased in the presence of high electric field, above 30V/cm. Therefore, we could demonstrate the possibility of low temperature (<500°C) polycrystalline silicon (poly-Si) crystallization using Cu as a mediator in FALC technology.
The junction depth should be less than 0.05 microns to fabricate sub 0.1 micron devices. This requires implanting boron with energy of less than 1 keV. One drawback in a low energy ion source is low throughput due to low ion beam current. At present, boron known for a major p-type dopant for PMOSFET has problem to easily diffuse into Si wafer even in rapid thermal processing by high diffusivity. To resolve this problem, decaborane (B10H14) molecules are implanted to make p+/n junction on n-type Si wafers for low-energy boron dopant source. Ionized decaborane is accelerated at 1∼10 kV and implanted up to dosages from 1×1012/cm2 to 5×1013/cm2. Afterwards, Decaborane implanted Si wafers were post-annealed for 10 sec at 800, 900 and 1000°C, respectively. From RBS results on as-implanted n-type Si wafer implanted at 5 kV, it is observed there are amorphous Si layers with 4 nm in depth and boron ions are implanted up to 1∼5 nm in depth from SIMS analysis. The electrical properties of these p-n junctions are 127∼130 ω/sq. as sheet resistance, +0.3 V turn-on voltage and −1.1 V breakdown voltage obtained from I-V measurement.
Selection of a proper electrode for high dielectric material such as (Ba, Sr)TiO3 is a great concern because the deposition of BST requires a high temperature and an oxidizing atmosphere. In this study, we suggested the perovskite-type electrodes, which provide a structural match with the BST dielectric material, under the recognition that the high leakage current is associated with the structural mismatch between BST and the electrode. We studied the (Ca,Sr)RuO3 electrode of which the lattice parameter can be tuned to fit into BST by changing the Ca/Sr ratio. We also studied (Ba,Sr)RuO3 electrode which is not only structurally identical but also chemically similar to BST. In addition, the effect of doping in the BSR electrode was investigated to minimize the leakage current by proper modulation of the barrier height. The electrodes were directly deposited on an Si substrate and all the films in the experiments were deposited by RF magnetron sputtering technique. Electrical properties were measured from MIM structure. The main focus was to address the effect of Ca/Sr and Ba/Sr ratio variations in the electrodes on the resulting dielectric constant and the leakage current. The interface characteristics between the BST film and the electrode were examined in order to interpret the electrical properties of BST films.
There have been many reports on the low temperature crystallization of amorphous silicon films by introducing a trace amount of metal impurity for low temperature poly-Si TFTs applications. MIC (Metal Induced Crystallization) uses various metals, to lower crystallization temperature. In this study, a new crystallization method called FALC (Field Aided Lateral Crystallization) in which an electric field is applied during the crystallization was explored. Among possible alloying elements with Si, Ni and Al were selected to compare the effects of these impurities on the FALC.
A trace of Ni lowered the crystallization temperature of a-Si down to 5001C and induced lateral crystal growth along the electric field into the metal free region. But Al exhibited no such effect. A new crystallization method, FALC, showed considerably enhanced speed of lateral crystallization and a strong preferred orientation in crystallized Si-films.
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