| Summary: | 博士 === 國立交通大學 === 電子工程系 === 89 === In this thesis, we proposed an advanced wet chemical one-step cleaning process. A novel one-step cleaning solution had been developed for pre-gate oxide cleaning to replace the conventional RCA two-step cleaning recipe, which used ammonia/hydrogen peroxide/water mixture (or SC-1) and hydrochloric acid/hydrogen peroxide/water mixture (or SC-2) step. The tetraalkylammonium hydroxide with various chain-lengths of hydrocarbon substituents, such as tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH), and ethylenediaminetetraacetic acid (EDTA) are added into the RCA SC-1 cleaning solution to enhance cleaning efficiency. From the experimental results, the particles and metallic contamination on the bare-Si wafer surface could be removed significantly by applying this novel one-step cleaning solution. The effectiveness of various cleaning recipes and their interaction mechanism with silicon surfaces were studied. The surface adsorption and double layer models could explain the surface behavior of tetraalkylammonium-containing solutions. Based on the model, the particle, surface roughness and the metallic contaminants can be realized. It was observed that the electrical properties of MOS capacitors after cleaning with this novel solution were better than these after the conventional RCA cleaning. Hence, this novel one-step cleaning process is very promising for future large-sized silicon wafer cleaning due to the advantages of time-saving, low cost and high performance.
On the other hand, the tetraalkylammonium hydroxide with various chain-length of hydrocarbon substituents, such as TMAH, TEAH, TPAH and TBAH, and chelating agents with various carboxyl acid group (-COOH), such as ethylenediaminetetraacetic acid (EDTA), citric acid and oxalic acid, were developed for post-poly-Si CMP cleaning. These surfactants and other chelating agents were simultaneously added into 3% ammonium hydroxide water-based solutions to enhance the removal of particles and metallic impurities on the poly-Si surface. The effectiveness of various cleaning recipes and their interaction mechanism with poly-Si surfaces were studied. We could explain the surface behavior of various cleaning solutions by the surface adsorption and double layer models of tetraalkylammonium-containing solutions and the different molecular size and charge of chelating agents. Based on the model, the particle, surface roughness and the metallic contaminants can be realized. The co-existance of TMAH with citric acid or oxalic acid in the alkaline cleaning solutions can significantly enhance the electrical property for the capacitor.
Furthermore, we developed a new method to grow robust ultrathin oxynitride (EOT=18 Å) film with effective dielectric constant of 7.15. By NH3-nitridation of Si substrate, grown ultrathin Si3N4 with N2O annealing shows excellent electrical properties in terms of significant lower leakage current, very low bulk trap density and trap generation rate, and high endurance in stressing. In addition, this oxynitride film exhibits relatively weak temperature dependence due to a Fowler-Nordheim (F-N) tunneling mechanism. This dielectric film appears to be promising for future ultralarge scale integrated (ULSI) devices. However, the same method to grow high quality interpolysilicon-oxynitride (interpoly-oxynitride) film is proposed. Samples, nitridized by NH3 with additional N2O annealing and CVD TEOS deposited on poly-oxynitride (poly-I) with RTA N2O oxidation, show excellent electrical properties in terms of very high electric breakdown field, low leakage current, high charge to breakdown, and low electron trapping rate. This novel film is a good candidate for an interpoly dielectric of future high density EEPROM and Flash Memory devices.
Finally, we report for the first time a novel high-k cobalt-titanium oxide (CoTiO3) and nickel-titanium oxide (NiTiO3) were formed by directly oxidizing sputtered Co/Ti and Ni/Ti film. Al/CoTiO3/ Si3N4/Si and Al/NiTiO3/Si3N4/Si capacitor structures were fabricated and measured. The effective dielectric constant (k-value@ 45) with buffer layer for CoTiO3 is a larger than that of NiTiO3. In addition, CoTiO3 depicts excellent electrical properties at the same time. This metal oxide thus appears to be a very promising high-k gate dielectric for future ultralarge scale integrated (ULSI) devices.
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