Papers

AVS2004 Session DI+PS-TuM: High-k Dielectrics: Growth and Processing

Tuesday, November 16, 2004 8:20 AM in Room 304C

Tuesday Morning

Start	Invited?	Item
8:20 AM		DI+PS-TuM-1 Inductively Coupled Remote Nitrogen Plasma Treatment of Hf Based Gate Dielectrics for Improved Interface Stability on Si(100) T. Klein (University of Alabama) HfO₂ is a leading candidate for replacement of SiO₂ in CMOS field effect transistors. Past work has shown this material has a tendency to interdiffuse and react with the substrate forming a less-than-ideal abrupt interface. In this paper, HfO₂ thin film stability results for a remote plasma nitrification process is reported in which the Si substrate is exposed to a N₂/He plasma then annealed in vacuum before the gate oxide deposition process. The nitrided surface and subsequently deposited films were studied using ellipsometry and x-ray photoelectron spectroscopy before and after annealing treatments. This method is compared to other procedures for the addition of nitrogen developed in our laboratory including the plasma enhanced deposition of HfO₂ using N₂O and N₂ plasmas, and post deposition treatment of the films with a remote N₂ plasma. Nitrogen plasma treated substrates showed a nitride layer approximately 16 Å thick which was sufficient to prevent significant film/substrate interdiffusion and thickness growth for 2 min., 800°C anneals in Ar.
9:00 AM		DI+PS-TuM-3 In Situ Infrared Spectroscopy of High-k Dielectric Growth on Si (100) R.T. Brewer, M.-T. Ho, L. Ghoncharova (Rutgers University); M.P. Boleslawski (Aldrich Chemical Co.); T. Gustafsson, E. Garfunkel, Y.J. Chabal (Rutgers University) We have used in situ, transmission infrared (IR) spectroscopy and ex-situ Medium Energy Ion Scattering (MEIS) to investigate the growth mechanisms of atomic layer deposition (ALD) of Al₂O₃ and HfO₂ on Si (100). The high-k materials were deposited by alternating exposures of organometallic precursors (trimethylaluminum for Al₂O₃ and tetrakis(ethylmethylamido)hafnium for HfO₂) and D₂O at ~300°C. IR spectroscopy makes it possible to identify the adsorbed precursor products, the growth of the high-k films, and the formation of an interfacial layer, such as SiO₂. For ALD directly on hydrogen terminated Si (100) we observe the formation of interfacial SiO₂; moreover, several ALD exposure cycles are required before the high-k film can nucleate on the surface and begin to grow. Functionalizing the surface with a pretreatment of NH₃ results in high-k film growth from the first cycle exposure, and reduces the formation of interfacial SiO₂ by acting as a barrier and providing a nucleation layer for the high-k growth. In this talk, we will compare HfO₂ and Al₂O₃ growth.
9:20 AM		DI+PS-TuM-4 DFT Study of the Initial ALD Reactions of Hf(N(CH3)2)4 on the SiO2 and Si-H Surfaces: Mechanism, Kinetics, Vibrational Spectra and Interface Structure J.G. Han, C.B. Musgrave (Stanford University); M.J. Kelley, G.N. Parsons (North Carolina State University) Atomic layer deposition is ideally capable of depositing uniform thin films of materials one atomic layer at a time. In practice, the initial coverage of active sites on the starting substrate determines the initial growth rate, which is typically below the steady state growth rate. Furthermore, the initial reactions on the starting substrate are important in defining the atomic structure of the interface between the deposited film and the substrate. Because the electronic properties of advanced CMOS are highly sensitive to the electronic structure and thus the atomic structure of this interface, it is essential to gain control over the structure of the interface through the chemistry of the ALD process on the starting substrate. We have used ab initio electronic structure theory to calculate mechanisms leading to various interface structures for the reaction of a tetrakis(dimethylamido) hafnium precursor with Si-H and Si-OH terminated substrates and the resulting interface bonding. We also calculate the vibrational spectra for some possible surface species and compare these with those measured by FTIR. Our calculations show that the adsorbed metal precursor activates neighboring Si-H sites enabling subsequent reactions with water and the ALD metal precursor.
9:40 AM		DI+PS-TuM-5 Development of Post Etching Process for Hf Based High-K Gate Dielectric W.S. Hwang, J.H. Chen, W.J. Yoo, D.S.H. Chan (National University of Singapore, Singapore); D.-L. Kwong (University of Texas at Austin) For successful integration of high-K dielectrics into CMOS process, a technique to selectively remove high-K films and interfacial layers with minimum consumption of both Si substrate and shallow trench isolation SiO₂ needs to be developed. In this work, we studied the wet etching properties of Hf based high-K dielectrics using 1% HF (DHF) for HfO₂, HfSiO, and HfAlO deposited by atomic layer deposition or sputtering. Effects of anneal, plasma oxidation and nitridation are discussed. Results show that before anneal, all these films can be removed completely by DHF with etch rates higher than 12nm/min. After 700°C anneal, etch rate of HfAlO does not change, whereas etch rate of HfSiO decreases ~ 50%, leaving ~ 1nm thick densified HfSiO interfacial layer unremoved. Furthermore, HfO₂ cannot be etched by DHF after anneal: after etching for 24 hours, no thickness change was observed. By applying the room temperature plasma oxidation treatment, HfSiO interfacial layer can be removed in 10s in DHF, but 3-6nm thick SiO₂ grows underneath HfSiO interfacial layer, resulting in significant recess into Si substrate. However, 2 nm thick HfO₂ can be removed in 10s in DHF without noticeable recess into Si substrate, by applying the room temperature plasma nitridation treatment. Surface analysis using X-ray photoelectron spectroscopy shows that Hf-N bonds are formed on the surface of HfO₂ after plasma nitridation. High etch rate of HfN of 1000Å/min in DHF can explain the increase of the etch rate by the incorporation of N. HfSiO interfacial layer was also removed in 10s after plasma nitridation. By the plasma nitridation aided DHF cleaning process, very little recess of both Si substrate and STI SiO₂ was achieved, and furthermore low contact NiSi sheet resistance of 4-5Ω/sq was achieved.
10:00 AM		DI+PS-TuM-6 Plasma-Enhanced Atomic Layer Deposition for Compositionally Controlled Metal Oxide Thin Films S.X. Lao, R.M. Martin, J.P. Chang (University of California, Los Angeles) The need to replace SiO₂ by a higher dielectric constant material in fabricating smaller and faster metal-oxide-semiconductor (MOS) transistors is well recognized by the National Technology Roadmap for Semiconductors. Atomic layer deposition emerges as a viable chemical processing technique to enable the deposition of ultra-thin and highly conformal thin films, and the use of plasma allows greater flexibility and higher processing yield. In this work, ZrO₂ and HfO₂ films were deposited using zirconium and hafnium tetra-tert butoxides as the metal precursors and oxygen radicals generated from oxygen plasma as the oxidant, introduced in alternating, cyclical sequence. The thicknesses of the films scaled linearly with the number of deposition cycles as determined by both ellipsometry and x-ray photoelectron spectroscopy (XPS) measurements. Optical emission spectroscopy (OES) was utilized to identify and quantify the gas phase atomic radicals. It was found that the OES intensity of oxygen radicals varies inversely with that of hydrogen radicals originating from the precursor. The presence of oxygen and hydrogen radicals in the gas phase resulted in the formation of surface hydroxyl groups, an important surface functional group for the chemisorption of precursors. As measured by the Fourier transform infrared spectroscopy (FTIR), the -OH integrated absorption intensities increased linearly with the number of deposition cycles and decreased upon annealing. Atomic force microscopy (AFM) analysis showed fairly smooth films with an RMS roughness of 1.7 Å after 5 deposition cycles. MOS capacitors were fabricated with the PEALD deposited films. The capacitance-voltage (C-V) and current-voltage (I-V) measurements showed that the PEALD HfO₂ films had the highest dielectric constant of 25 with an equivalent oxide thickness (EOT) of 12.5-15 Å. The leakage currents were several orders of magnitude less than that of SiO₂ films at the same EOT.
10:20 AM		DI+PS-TuM-7 DFT Investigation of Initial HfO₂ Atomic Layer Deposition on Nitrided Silicon Surface Y. Xu, C.B. Musgrave (Stanford University) The atomistic mechanism of the initial atomic layer deposition (ALD) reactions of hafnium oxide on a nitrided silicon surface was investigated using density functional theory (DFT). Reactions involving two different metal precursors are explored: Tetrakis-dimethylamido-hafnium (Hf[N(CH₃)₂]₄) and hafnium tetra chloride (HfCl₄). Hf[N(CH₃)₂]₄ forms no adsorbed complex on the nitrided Si substrate. The ALD ligand exchange reaction requires a barrier of 0.63eV and is exothermic by 0.22 eV. The adsorbed precursor state is not formed because the Hf atom of the precursor state has full s and d-shells and the amines are doubly bonded to Hf. Furthermore, the lone pair of nitrogen on the nitrided silicon surface is somewhat delocalized, reducing its ability to form dative bonds. Reaction between HfCl₄ and the nitrided silicon surface results in adsorbed HfCl₄ complex with an adsorption energy of 0.66 eV. The ligand exchange barrier is 1.33eV relative to the complex structure and the overall reaction is endothermic by 0.50 eV. Consequently, the alkylamide precursor is both kinetically and thermodynamically superior to HfCl₄ for the initial ALD reactions on the nitrided surface. We previously showed that for ALD of HfO₂, Hf[N(CH₃)₂]₄ appears to be a better choice than HfCl₄ both thermodynamically and kinetically. Thus Hf[N(CH₃)₂]₄ precursor performs better for both the initial reaction on the nitrided silicon surface and subsequent ALD of the HfO₂.
10:40 AM		DI+PS-TuM-8 Oxygen Transport Properties in Hafnium Silicate Films D. Starodub, L. Goncharova, E. Garfunkel, T. Gustafsson (Rutgers University); G. Bersuker, B. Foran, P. Lysaght (International Sematech) Developing an understanding of the kinetics and thermodynamics of film growth during fabrication of CMOS high-K gate stacks is thought to be critical in enabling control of interfacial layers, defects and other film properties. In this presentation we present new results on the oxygen transport mechanisms and kinetics in hafnium silicate films as a function of composition, structure and annealing conditions. The silicate films were grown on Si(001) substrates with and without nitride incorporation. To study oxygen transport, incorporation and interfacial growth, reoxidation of as grown and annealed films was performed in isotopically labeled oxygen-18. Oxygen isotopic distributions were then measured using high-resolution medium energy ion scattering. With a nitride layer present, the interface oxidation was minimized, and reaction with oxygen was limited to exchange with network oxygen in the silicate film. This exchange saturated with time and appeared to be enhanced after film recrystallization, perhaps due to an increase in grain boundaries. The films directly grown on H-terminated substrates exhibited additional oxygen incorporation at the interface with SiO₂ formation. This process increases with increasing film crystallinity, opening more permeable diffusive pathways via crystallite grain boundaries. We also explore PDA effects on oxygen permeability of the silicate films.
11:00 AM		DI+PS-TuM-9 Investigation of the Roles of Oxygen Plasma and Solvent in the Pulsed-Liquid Injection PE-MOCVD Deposition of Y₂O₃ High-κ Materials in MIM Structures C. Vallee, C. Durand, M. Derivaz, M. Kahn, M. Bonvalot (CNRS, France) CMOS scaling and Metal-insulator-Metal (MIM) capacitance density improvement will require use of new high-κ dielectric material in a near future. We have focused our work on the elaboration of Y2O3 thin films at low thermal budget (350°C) by pulsed-liquid injection Plasma Enhanced MOCVD for MIM capacitors (TiN-Y2O3-TiN). In this technique, dissolved Yttrium β-diketonate Y(tmhd)₃ precursors (in cyclohexane and octane) are sequentially injected into an evaporator, with accurate reproducibility in the amount of precursors delivered to a low frequency (380 KHz) plasma chamber, where a O₂ plasma is applied to induce precursor decomposition and surface reactivity. The respective roles of oxygen plasma and solvent composition in the Y2O3 high-κ materials characteristics and interface properties have been investigated. The plasma is monitored by optical emission spectroscopy (OES) while films and interfaces are mainly characterized by X-rays Photoelectron Spectroscopy (XPS). Electrical characterizations are also performed in order to obtain capacitance density, voltage linearity and electrical breakdown properties. We have shown that a low plasma power and a high pressure limit carbon contamination while a high injection frequency limits interface reactions (as observed on SiO2/Si substrates). With this technique a capacitance density up to 6 fF/µm² has been obtained. We have also investigated the effects of two solvents, cyclohexane and octane, in this study : it has been observed that deposition rate is strongly influenced by solvent nature. In addition, we also studied the effect of nitrogen plasma before, during and after deposition. Chemical bonding, concentration, and distribution of N in Y-oxide films after deposition and after high-temperature annealings are also characterized. The N concentration distribution in high-k dielectrics is likely to be an important factor to achieve optimal electrical performances.
11:20 AM		DI+PS-TuM-10 UV Activated Surface Preparation of Silicon for High-k Dielectric Deposition C.C. Finstad, A.J. Muscat (University of Arizona) High-k gate materials, such as HfO₂, are unstable on silicon, readily forming a low permittivity interfacial oxide when heated. A single layer of silicon nitride grown prior to gate dielectric deposition could serve as a diffusion barrier to prevent oxide formation. Moreover the SiN layer should promote nucleation of the dielectric film, thereby acting as both a barrier and a seed layer. A monolayer film of surface amine groups will be chemically similar to the hydrogen atoms of surface hydroxyl groups; therefore a pin-hole free monolayer of amine groups should simultaneously serve as both a diffusion barrier and a seed layer. This study aims to deposit a thin, continuous layer of surface amines at low temperatures (<100°C) using atomic layer deposition (ALD). UV-Cl₂ exposures (0.1-100 Torr Cl₂ at 25-150°C, 2-10 min, 1000 W Xe lamp) were used to terminate Si with Cl atoms. Exposure to NH₃ (0.05-1000 Torr, 75°C, 5-20 min) replaced Cl atoms with amine groups. Cl atoms served as reactive leaving groups, lowering the overall activation energy barrier for nitridation; HCl formed as a by-product and desorbed from the surface. By providing a more reactive surface, ALD of silicon nitride occurs at lower temperatures (<100°C) and with better initial deposition rates compared to deposition on H-terminated Si.¹ As measured by XPS, the amine surface coverage saturated at 0.35 monolayer (ML) at a NH₃ pressure of 10 Torr. Cl coverage decreased, but the surface reaction did not go to completion. Significant oxygen was observed due to competition by H₂O contamination. Alternatively, UV photons with energy >5.8 eV can photodissociate NH₃ molecules to yield NH₂ photofragments that react with H-terminated Si surfaces. With UV activation, N coverage increased with time and saturated at 1.7 ML. ¹A. Nakajima et al., Appl. Phys. Lett. 80 (7), 1252 (2002).
11:40 AM		DI+PS-TuM-11 Annealing of Hafnium Oxide Grown on Silicon by Atomic Layer Deposition: Changes in Interfacial Structure A. Deshpande (University of Illinois at Chicago); R. Inman, G. Jursich (American Air Liquide); C. Takoudis (University of Illinois at Chicago) Thin films of hafnium oxide are deposited on Si(100) substrates by means of atomic layer deposition (ALD) using tetrakis(diethylamino)hafnium as the hafnium precursor and subsequently annealed at various temperatures (600-1000 C) under Ar atmosphere. The resulting composition and purity of the films are determined at different substrate temperatures using x-ray photoelectron and Fourier transform infrared (FTIR) spectroscopies. The chemical and physical structure of the film/interfacial regions are analyzed using a combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope. Depth profiling of film/interfacial regions were obtained using high-resolution angle resolved x-ray photoelectron spectroscopy (XPS). The pre-annealed films showed presence of a very thin silicon oxide at the film/substrate interface that originated from the residual surface oxide resulting from the wet chemical surface cleaning procedure used. Thus, no growth of interfacial region is observed from deposition alone. However, the post annealed films show increase in interfacial silicon oxide thickness coupled with formation of silicate-like structure as the annealing temperature is increased. This is evident from independent sets of data of FTIR spectroscopy and XPS. At the highest annealing temperature used (i.e., 1000 ÂºC), formation of silicide is observed at the interface. From these measurements detail information on the interfacial changes incurring from thermal annealing are obtained when there is a very thin layer of silicon oxide present on the silicon substrate. These results will be discussed in view of the intermediate SiO2 in terms of HfO2:SiO2 inter-diffusion and the formation of silicate-like structure.