Atomic Layer Chemical Vapor Deposition of Hafnium Oxide Using Anhydrous Hafnium Nitrate Precursor
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Atomic Layer Chemical Vapor Deposition of Hafnium Oxide Using Anhydrous Hafnium Nitrate Precursor J.F. Conley, Jr.,1 Y. Ono,1 D.J. Tweet,1 W. Zhuang, 1 and R. Solanki2 1 2
Sharp Labs of America, Camas, Washington. Oregon Graduate Institute, Department of Electrical and Computer Engineering, Beaverton, Oregon.
ABSTRACT HfO 2 films have been deposited using anhydrous hafnium nitrate (Hf(NO3 )4 ) as a precursor for atomic layer chemical vapor deposition (ALCVD). These films have been characterized using x-ray diffraction, x-ray reflectivity, atomic force microscopy, current vs. voltage, and capacitance vs. voltage measurements. An advantage of this precursor is that it produces smooth and uniform initiation of film deposition on H-terminated silicon surfaces. As deposited films remained amorphous at temperatures below ~700°C. The effective dielectric constant of the film (neglecting quantum effects) for films less than ~15 nm thick, was in the range of κfilm ~ 10-11, while the HfO 2 layer value was estimated to be κHfO2 ~ 12-14. The lower than expected dielectric constant of the film stack is due in part to the presence of an interfacial layer such as HfSiO x . Excess oxygen may play a role in the lower than expected dielectric constant of the HfO 2 layer. Breakdown of HfO 2 films occurred at ~5-7 MV/cm. Leakage current was lower than that of SiO 2 films of comparable equivalent thickness. INTRODUCTION Due to problems such as direct tunneling leakage, boron penetration, reliability, etc., the MOSFET gate SiO 2 can not be scaled much below 1.5 nm. For low power applications, it is projected that a high dielectric constant replacement for SiO 2 will be needed by the 80 nm node in 2005 [1-3]. A relatively new class of materials being considered as replacement dielectrics are metal oxides [1,6-22]. Among these, it has been determined that HfO 2 is an excellent candidate due to high bulk κ, good thermal stability [4], and wide bandgap and offsets with respect to Si [5]. Previous reports on HfO 2 thin films have shown promise [1,6-18]. A technique that has been attracting interest for high κ films is atomic layer chemical vapor deposition (ALCVD or ALD) [1,16-18,23-25]. In ALD, precursors are introduced alternately into the deposition chamber. Reactions take place on the substrate surface and are self- limiting. The desired film is thus built up one monolayer at a time. The self- limiting nature of the process allows for inherent atomic scale interfacial control and excellent conformality. Because an effective thickness < 1.0 nm will be needed, deposition of high- κ directly on H-terminated Si is desirable. Researchers using HfCl4 as a precursor for ALD have reported difficulty initiating deposition of HfO 2 on H-terminated Si and found that a thin layer of SiO 2 was necessary to achieve uniform HfO 2 films [8, 9, 24]. A precursor that has been used recently for CVD of HfO 2 is the anhydrous nitrate of hafnium Hf(NO3 )4 [7, 10-12]. We find that the use of Hf(NO3 )4 as a B2.2.1 Downloaded from https://www.cambridge.org/core
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