ALD of Lanthanum Aluminate Using Lanthanum Formamidinate Precursor
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1036-M04-18
ALD of Lanthanum Aluminate Using Lanthanum Formamidinate Precursor Huazhi Li1, Deodatta Vinayak Shenai*1, Ralph Pugh1, and Jiyoung Kim2 1 Advanced Thin-Film Technologies, Rohm and Haas Electronic Materials LLC, 60 Willow Street, North Andover, MA, 01845 2 Materials Science and Engineering, University of Texas at Dallas, Richardson, TX, 75083 ABSTRACT The physical and electrical characteristics of La2O3 and LaAlO3 films, deposited by atomic layer deposition (ALD) and using a new La formamidinate precursor (La-FAMD), were investigated. The La-FAMD precursor has superior thermal stability and is also the most volatile La source available today. The vapor pressure of La-FAMD, maintained at 100 ºC, is approximately 60 times higher than the commercial available source La-THD (THD = tetramethylheptanedionate).
INTRODUCTION Recently, La-incorporated HfO2 and HfSiOx have been reported for tuning the work function of metal gate to near Si conduction band edge. Also La incorporation in HfO2 and HfSiOx films has improved the electrical performance 1,2 of these films. La2O3 itself is also a promising dielectric material in transistor at 45 nm node and beyond, because of its higher dielectric constant, excellent thermal stability and compatibility with Si processing 3. Atomic layer deposition (ALD) technique is particularly suitable for depositing gate dielectrics as well as Dynamic Random Access Memory (DRAM) dielectric due to the excellent conformity, appropriate thermal budget, excellent step coverage, and digital thickness uniformity it offers vis-à-vis chemical vapor deposition (CVD). To fully utilize the potential and benefits of ALD, it is imperative to select the most appropriate ALD source for La. So far βdiketonates of lanthanum such as Lanthanum tetramethylheptane dionate (La-THD), and amidinates of lanthanum such as lanthanum di-isopropyl acetamaidinate (La-AMD) have primarily been used as preferred La sources 4,5,6 in ALD. Comparative evaluation of these two platforms and sources have successfully demonstrated earlier5 that the ALD process based on La-AMD generates higher quality lanthanum oxide film with significantly lower carbon contamination (0.2%) in the films. To further improve the volatility and vaporization characteristics of the La amidinate source while maintaining the superior quality and electrical properties of the resultant film, we have designed and developed a new precursor using metal amidinate product platform. In this report, we describe the successful deposition of La2O3 and LaAlO3 films for the first time using this new source, lanthanum 1,3-di-isopropylformamidinate (La-FAMD).
EXPERIMENTAL The synthesis of lanthanum 1,3-di-iso-propylformamidinate (La-FAMD) was carried out as follows. The adduct of lanthanum (III) chloride with tetrahydrofuran, LaCl3(THF)2, was suspended in tetrahydrofuran, and reacted with freshly prepared tetrahydrofuran solution of lithium 1,3-di-iso-propylformamidinate in stoichiometric quantities. The reaction mixture was stirred for 12 hours. The product was
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