Atomic Layer Deposition of High-k Gate Dielectrics Using MO Precursor and Cyclic Plasma Exposure
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Atomic Layer Deposition of High-k Gate Dielectrics Using MO Precursor and Cyclic Plasma Exposure Kazuhiko Endo and Toru Tatsumi Silicon Systems Research Laboratories, NEC Corporation 1120 Shimokuzawa, Sagamihara, Kanagawa 229-1198, Japan ABSTRACT We have successfully achieved an ALD like deposition of ZrO2 or HfO2 by using a MO precursor. The MO precursor used in this study was zirconium tetra-tert-butoxide (ZTB) Zr(t-OC(CH3)3)4 and hafnium tetra-tert-butoxide (HTB) Hf(t-OC(CH3)3)4. Because MO precursors are very sensitive to H2O, we used oxygen plasma as an oxidizer instead of H2O in order to reduce background H2O pressure and suppress the background reaction. As a result, we successfully achieved an ALD-like deposition proved by a self-limiting adsorption of MO precursor. The carbon content in the films was suppressed due to highly reactive oxygen plasma. The leakage current of the film with plasma oxidation is much lower than that of film with H2O oxidation. Thus, MO-ALD using a plasma oxidation is a promising candidate for the high-k gate deposition process. INTRODUCTION An exponential increase in leakage current with decreasing thickness of a gate dielectric of complementary metal oxide semiconductor (COMS) devices sets a fundamental limit on the scaling of gate dielectric1,2. To further scale the gate dielectric without increasing tunneling leakage current, high-k dielectrics are potential replacements. Al2O3, ZrO2, HfO2 and lanthanide dioxide are currently being considered as they are thermodynamically stable with Si3,4. The atomic layer deposition (ALD) method is a promising candidate for a production of high-k gated dielectrics because of its superb uniformity, precise thickness controllability, and conformal deposition5. Metal chlorides such as ZrCl4 are widely used as precursors for ALD6,7, however, introduction of these precursors are technically difficult due to an overly high evaporation temperature above 300°C. In addition, a lack of a variety of these chloride precursors prevents scalability of the ALD process to widespread CMOS generations. We also felt some concern over the corrosion of the deposition chamber and deposited film due to chlorine. On the other hand, there are several metal-organic (MO) precursors with higher vapor pressure, no chlorine, and a wide array of metal selections. Our motivation in this work was then to study a new ALD process
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by using MO precursors. EXPERIMENT The MO precursors used in this study was zirconium tetra-tert-butoxide (ZTB) Zr(t-OC(CH3)3)4 and hafnium tetra-tert-butoxide (HTB) Hf(t-OC(CH3)3)4. We vaporized them around 70-80°C and we used mass flow controller to introduce them into an ALD chamber as they have higher vapor pressures of around 1 Torr at 100°C, We also used trimethylaluminum (TMA) to deposit Al2O3 for comparisons. The ALD chamber was evacuated with a turbo molecular pump to less than 10-6 Torr. The irradiation pressure was typically 10-3 Torr. 6-in. Si wafers with 1 nm Si-oxide were used as substrates. Because MO precursors are ver
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