Ultra-Thin Zirconium Silicate Filmsc With Good Physical And Electrical Properties For Gate Dielectric Applications
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ULTRA-THIN ZIRCONIUM SILICATE FILMS WITH GOOD PHYSICAL AND ELECTRICAL PROPERTIES FOR GATE DIELECTRIC APPLICATIONS Easwar Dharmarajan, Wen-Jie Qi, Renee Nieh, Laegu Kang, Katsunori Onishi and Jack C. Lee Microelectronics Research Center, The University of Texas at Austin, Austin, TX 78758 ABSTRACT The need for alternative gate dielectrics to replace conventional SiO 2 is increasing to facilitate further CMOS scaling. One of the most promising materials for use as an alternative gate dielectric is Zr silicate due to its thermodynamic stability on Si and its good interface quality with Si. In this study, ultra-thin Zr silicate films (45 – 60 Å thick) with different Zr compositions have been deposited on Si using magnetron reactive cosputtering. The Zr composition was kept below the stoichiometric value of about 16% to prevent precipitation of ZrO 2 and to have Si rich films for better interface quality. Films were rapid thermal annealed in N2 ambient up to 9000 C and Pt was used as the gate electrode. Electrical characterization of these films was done using HP 4156 and HP 4194 parameter analyzers. Based on these studies, we demonstrate Zr silicate films with equivalent oxide thickness (EOT) of less than 14 Å with gate leakage significantly lower than SiO 2 of similar thickness and hysteresis of < 20mV ( in a sweep from –3 to 3 V). The films exhibit good thermal stability on Si even after 900 0 C annealing as shown by a minimal increase in EOT with annealing. TEM and XPS analyses show high quality Zr silicate films that remain stable and amorphous even at 900 0 C.
INTRODUCTION The need to scale down the gate oxide in CMOS devices has led to the search for new alternative gate dielectrics to replace conventional thermal oxide in order to minimize the gate leakage and also improve reliability of the ultra-thin dielectric. These gate dielectrics with a higher dielectric constant (k) allow a physically thicker oxide to be used to reduce the gate leakage and also achieve a lower equivalent oxide thickness. Several gate dielectrics like Ta2 O5 [1], TiO 2 [2], ZrO 2 [3], SrTiO 3 [4] are being studied as potential candidates. But some of these dielectrics are not thermodynamically stable on contact with Si and require a barrier layer to prevent any adverse reaction with Si. On the other hand, Zr silicate films are thermodynamically stable on contact with Si and possess extremely good thermal stability even at very high processing temperatures. Russak et al [5] showed that even a small amount of SiO 2 (10 at %) can stabilize the mixed film of ZrO2 and SiO 2 in an amorphous phase. Wilk et al [6] reported Zr and Hf silicate films with equivalent oxide thicknesses of 21 Å and 18 Å respectively, with low gate leakage and C-V hysteresis. In this paper, we present the physical and electrical characteristics of ultra-thin Zr silicate films deposited by DC magnetron reactive co-sputtering technique directly on Si. These films exhibit low leakage and good thermal stability up to 9000 C.
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EXPERIMENT Experiments were carried ou
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