Thin HfO 2 Films Deposited via Alternating Pulses of Hf(NO 3 ) 4 and HfCl 4
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Thin HfO2 Films Deposited via Alternating Pulses of Hf(NO 3)4 and HfCl4 J.F. Conley, Jr.,1 Y. Ono,1 R. Solanki,2 and D.J. Tweet1 1 IC Process Technology Laboratory, Sharp Labs of America, Camas, WA, 98607 2 Oregon Graduate Institute, Department of Electrical and Computer Engineering, Beaverton, OR ABSTRACT A novel technique for deposition of metal oxide films is demonstrated in which alternating pulses of metal-nitrate and metal-chloride precursors are used. The metal nitrate, Hf(NO3) 4, acts as the oxidizing agent, avoiding the use of a separate oxidizing species such as H 2O. This method results in greater than one monolayer per cycle deposition rate of HfO 2 films compared to the use of a single precursor and enables deposition directly on H-terminated Si due to the reactivity of Hf(NO3) 4. It was found that performing a short in-situ anneal after every deposition cycle increases film density and improves electrical characteristics. Films are characterized via capacitance vs. voltage, current vs. voltage, spectroscopic ellipsometry, and x-ray diffraction and reflectivity. INTRODUCTION High dielectric constant metal oxide thin films (HfO 2, ZrO2, La 2O3, HfAlOx, etc.) are currently under intense investigation as potential replacements for SiO2 as the gate oxide in metal/oxide/semiconductor field-effect-transistors (MOSFETs). One of the most promising techniques for deposition of these films is atomic layer deposition (ALD). The most widely used ALD precursor for metal oxides are the metal chlorides (MCl x, where x = the valence of metal). Although it has been shown that use of metal chlorides allows deposition of high quality films with good electrical characteristics [1], it has been found that these precursors do not allow smooth initial deposition directly on hydrogen terminated Si [2]. Recent work has demonstrated that a thin initial layer of chemical SiO2 (~0.7 nm) is necessary to achieve smooth initiation.[2] Since an equivalent electrical thickness of less than 1 nm will be required of a high-k gate oxide stack, the requirement of a few initial monolayers of low k material is a serious disadvantage of metal chloride precursors. Recently, CVD [3] and ALD [4-7] of metal oxides directly on H-terminated Si have been demonstrated using a class of precursors known as metal nitrates (M(NO 3) x). However, there are also disadvantages of using nitrates such as the traditional difficulties associated with solid precursors (Hf(NO3) 4 is a solid at room temperature). Also, the density and refractive index of HfO2 films deposited using Hf(NO3)4 are not quite as high as those reported for films deposited using HfCl 4 (see table 1), suggesting that the electrical properties may not be quite as good. In this paper, a novel technique is introduced aimed at exploiting the advantages of each precursor while minimizing the disadvantages. Deposition of high quality HfO2 films is achieved using alternating pulses of Hf(NO 3)4 and HfCl 4. In this deposition method, Hf(NO 3)4 plays the role of oxidizing agent. The use of a
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