Novel Zirconium Formamidinate Precursor for the ALD of ZrO 2
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1194-A05-10
Novel Zirconium Formamidinate Precursor for the ALD of ZrO2 Huazhi Li, Deo V. Shenai, and Jean-Sebastien Lehn Dow Electronic Materials, The Dow Chemical Company, 60 Willow Street, North Andover, MA 01845, U.S.A.
ABSTRACT Zirconium tetrakis(N,N’-dimethylformamidinate), Zr-FAMD, was synthesized and evaluated as a precursor for the deposition of zirconium oxide (zirconia) thin films via Atomic Layer Deposition (ALD) technique. Zr-FAMD has a high vapor pressure and displays an exceptionally high thermal stability; it is thus well-suited to be used as a precursor for the deposition of zirconia thin films. Zr-FAMD is a more ideally-suited precursor than tetrakisethylmethylaminozirconium or TEMAZr, which has an equivalent vapor pressure, but is plagued with a rather low thermal stability, limiting its usefulness at high deposition temperatures. Zr-FAMD can be used to deposit zirconia thin films at temperatures as high as 375 ºC without evidence of decomposition.
INTRODUCTION Zirconium oxide (ZrO2), is being widely investigated for alternate gate dielectric and DRAM capacitor applications because of its high dielectric constant (17~30), high breakdown field and excellent thermal stability with Si processing.1,2,3,4 With the transistors and DRAM cells becoming increasingly smaller (sub 45 nm), the atomic layer deposition technique (ALD) is promising to meet the scaling challenges due to its excellent conformity and atomic-scale thickness control.1,2 The ALD technique is a vapor deposition process based on sequential self-limiting surface reactions where the precursors are pulsed into the reactor chamber alternately and the purging gas removes un-reacted precursors from the substrate. This self-limiting growth characteristic allows ALD techniques to deposit thin films with properties such as high uniformities, high conformalities, and a precise thickness control. To fully achieve these benefits, it is very important to select thermally stable and reactive ALD precursors. So far a number of
ALD ZrO2 precursors have been developed and investigated including halides5, alkyls6, alkoxides6, cyclopentadienyls7, alkylamides8 and amidinates9 and combinations thereof. Among them, TEMAZr, one type of alkylamide, has been considered one of the most promising Zr sources due to its characteristics of liquid at room temperature, acceptable vapor pressure, high reactivity and no corrosive by-products8. Additionally, the quality of ALD films using TEMAZr is very high with good electrical characteristics. However, its relatively low thermal stability leads to low temperature process which may result in less dense films with high level of contamination. For these reasons, a more thermally stable and reactive Zr precursor is needed for current DRAM applications. The market has not yet settled on the suitable choice of Zr source that can outperform TEMAZr, and the search for better alternative precursor is still ongoing. Recently Dow Electronic Materials has successfully developed La-FAMD and Hf-FAMD based on the formamidinate p
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