Characteristics of hafnium oxide grown on silicon by atomic-layer deposition using tetrakis(ethylmethylamino)hafnium and
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The growth of HfO2 thin films on a HF-dipped p-Si(100) substrate at 200 °C by atomic-layer deposition (ALD) using Hf[N(C2H5)(CH3)]4 and H2O vapor as precursors is demonstrated. Uniform HfO2 thin films are obtained on a 4-in. silicon wafer, and the energy-band gap and band offset are determined by x-ray photoelectron spectroscopy analysis. The as-deposited HfO2 thin film is amorphous and able to crystallize at 500 ∼ 600 °C with only the monoclinic phase. As for the electrical performance of Au–Ti–HfO2–Si metal oxide semiconductor capacitors, a dielectric constant of ∼17.8 and an equivalent oxide thickness value of ∼1.39 nm are obtained from the 40-cycle ALD film after annealing at 500 °C. In addition, the breakdown field is in the range of 5 ∼ 5.5 MV/cm, and the fixed charge density is on the order of 1012 cm−2, depending on the annealing temperatures. The interface quality of HfO2 thin films on silicon is satisfactory with an interface-trap charge density of ∼3.7 × 1011 cm−2 eV−1.
I. INTRODUCTION
As the complementary metal oxide semiconductor (MOS) device continues to be scaled down, high- oxide thin films are attracting great interest as a replacement for SiO2 or SiON gate oxides.1–3 Among the high- candidates, hafnium oxide (HfO2) has attracted much attention due to its relatively high dielectric constant, large band gap, and the thermodynamic compatibility of interface with silicon.4–7 There are numerous techniques that have been used to deposit HfO2 thin films. Among them, atomic-layer deposition (ALD) is the most important method due to its excellent thickness and uniformity control, as well as its low-temperature deposition ability.8 The selection of the precursor for the ALD of HfO2 is essential. Halogen precursors such as HfCl4 and HfI4 have often been used for ALD HfO2 deposition.9,10 However, the use of these precursors results in halogen contamination, which causes serious problems in microelectronic applications. Besides, a relatively high process temperature is required because the halogen precursors are solids with low vapor pressure at room temperature. For depositing HfO2 at low temperature by ALD, the metallora)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0242 J. Mater. Res., Vol. 22, No. 7, Jul 2007
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ganic precursors such as alkoxides [e.g., Hf(OtBu)411 and Hf(mmp) 4 12 ] and amides [e.g., Hf(NEt 2 ) 4 , 13 Hf(NMe2)4,14 and Hf(NMeEt)415] are preferred. Among them, metal oxides deposited by ALD using amides contain fewer carbon residuals than those using alkoxides,16 which could provide higher film density and better dielectric properties. Therefore, in this work, the preparation and characteristics of HfO2 thin films on a p-type Si (100) substrate by ALD using an amide liquid of Hf [N(CH3)(C2H5)]4 composition and H2O vapor as precursors were investigated. II. EXPERIMENTAL PROCEDURES
The HfO2 thin films were grown at 200 °C on a p-type (the Si water is doped with boron) (100) Si substrate
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