Papers

AVS2004 Session AS-ThM: High-k Dielectrics

Thursday, November 18, 2004 8:20 AM in Room 210A

Thursday Morning

Start	Invited?	Item
8:20 AM		AS-ThM-1 Physical and Chemical Characterization of MOCVD Zirconia Films Deposited on Hydrogen-Terminated and Native Oxide Si Surfaces B.R. Rogers (Vanderbilt Universirty); Z. Song, R.D. Geil, R.A. Weller (Vanderbilt University); M.O. Bloomfield, T.S. Cale (Rensselaer Polytechnic Institute) Successful replacement of silicon dioxide-based MOSFET gate dielectrics by a high-permittivity (high-k) dielectric is a critical step in the continued drive to build the smaller, faster, lower-power, more-integrated circuits that society is demanding. Our group has been studying zirconia films deposited via MOCVD on hydrogen terminated silicon and silicon native oxide surfaces. Process pressures on the order of 10^-5 torr were used along with substrate temperatures between 300 and 450 °C. Films were characterized using AFM, TEM, AES, spectroscopic ellipsometry, time-of -flight medium energy backscattering, and XRD. Results show that films deposited on hydrogen-terminated silicon are rougher, and have a mainly tetragonal microstructure. In contrast, films deposited onto silicon native oxide are much smoother and have a mixture of tetragonal and monoclinic microstructure, the ratio of the two microstructures depended on the deposition temperature. In addition, grain sizes in films of similar thickness also depended on the surface on which the films were deposited. In situ spectroscopic ellipsometry analyses show that depositions on hydrogen-terminated silicon begin with and induction period (where no deposition occurs) followed by a linear growth. Depositions on silicon native oxide have no induction period, initiating immediately into linear growth. Results from additional analysis techniques, along with simulation of the nucleation/growth process provide insight into the reason why films of different properties are deposited onto the two surfaces. This work is supported by the National Science Foundation grant # CTS-0092792.
8:40 AM		AS-ThM-2 Challenges for the Characterization and Integration of High-k Dielectrics R.M. Wallace (University of Texas at Dallas) The integration of advanced gate dielectric materials into CMOS technology presents several significant challenges.^1,2 Moreover, the introduction of these materials is expected to occur at an unprecedented pace to meet industry technology forecasts. Although recent research has focused on the search for a material that yields a suitable (higher) dielectric constant than the industry benchmark SiO₂, a more important problem is the actual integration of any new dielectric material in existing CMOS flows in a cost-effective manner. These integration issues include etching, constituent stability, control of phase segregation and crystallization, dopant penetration, as well as gate electrode compatibility, which influence the resultant electrical properties. The study of these issues require substantial efforts in physical and electrical characterization. This talk will examine several of these integration issues in view of recent characterization studies and the associated challenges that must be addressed for successful high-k gate dielectric integration. This work is supported by the Texas Advanced Technology Program. ¹G.D.Wilk, R.M.Wallace and J.M.Anthony, J. Appl. Phys., 89, 5243 (2001). ²R.M.Wallace and G.D.Wilk, Crit. Rev. in Sol. State Mat. Sci, 28, 231 (2003).
9:20 AM		AS-ThM-4 Engineering the Properties of Hf-based Gate Dielectrics: Role of Initial Surface Preparation and Post Deposition Annealing R. Puthenkovilakam, Y.-S. Lin, J.P. Chang (University of California, Los Angeles) Alternative gate dielectrics such as HfO₂ or HfO_xN_y are required in the future generations of MOSFET devices to enable their rapid down-scaling. However, the material and electrical properties of these materials are not fully understood or optimized. In this work, we investigate the material and electrical properties of ultra thin HfO₂ and HfO_xN_y films on Si, deposited by an atomic layer controlled deposition process involving alternate pulses of Hf-t-butoxide precursor and oxygen (or NH₃). Post deposition annealing was performed in-situ in O₂, N₂, N₂O, NH₃ and ex-situ in H₂/D₂. X-ray photoelectron spectroscopy (XPS) measurements indicated the formation of interfacial layer and its structural changes upon post-deposition will be addressed. Extended x-ray absorption fine structure (EXAFS) measurements indicated that the short-range order in the as-deposited HfO₂ films resembled to that of the monoclinic phase HfO₂ and showed signs of crystallization upon annealing, while N incorporation seems to change the short-range order in the films and increase the crystallization temperature. Capacitance-voltage (C-V) measurements were performed on MOS devices to extract the dielectric constants (k), flat band voltage shifts, and interface state density. The as-deposited samples yielded k-values from 15-23 and their leakage currents were significantly less than that of SiO₂ films at the same equivalent oxide thickness (EOT). Temperature dependent current-voltage (I-V) measurements were performed to elucidate the conduction mechanisms in these ultra thin films. Substrate injection resulted in Schottky-like current transport while the gate injection showed a tunneling mechanism. The effect post-deposition annealing on the electrical performance will also be addressed in this talk in detail.
9:40 AM		AS-ThM-5 Applications of ARXPS to Semiconductor Fabrication and Characterization P. Mack, M. Shakespeare, A. Wright, R.G. White (Thermo Electron Corporation, UK) In modern semiconductor fabrication, two trends are clear. Layers are becoming thinner and the materials are becoming chemically more complex. For these reasons, XPS is becoming increasingly important as a characterisation tool. It is well known that XPS provides chemical state information from the near surface region and commercial tools exist to handle wafers of up to 300 mm. Now that the thickness many of the layers used in semiconductor technology are less than the escape depth of the photoelectrons, the technique can be used to characterise the layers and their interface with the substrate. If angular resolution is combined with the XPS technique (angle resolved XPS or ARXPS) it becomes possible to measure the thickness of layers, and the distribution of the materials and chemical states within the layer non-destructively. For example, not only can ARXPS measure the thickness of an oxynitride layer but it can also determine the way in which nitrogen is distributed through the layer. The nitrogen distribution affects both the electrical properties and the accuracy of dose measurements. In the case of high-k dielectrics, the nature and thickness of both the high-k layer and any intermediate silicon dioxide or silicate layer can be determined. The combined electrical properties of these layers determine the integrity of the dielectric stack. By using the technique of parallel ARXPS it becomes possible to make all of these measurements from intact 300 mm wafers. ARXPS can produce depth profiles without the need for sputtering. This means that ARXPS has the potential to be applied to shallow implants, such as arsenic in silicon. This has the advantage over SIMS profiles that it does not suffer from near-surface sensitivity artefacts. Examples of materials characterisation from a range of semiconductor thin films will be shown.
10:00 AM		AS-ThM-6 ALD and MOCVD Growth of High K Dielectric Al and Hf Films Studied by Parallel Angle Resolved XPS (PARXPS) R.K. Champaneria, P. Mack, J. Wolstenholme, R.G. White (Thermo Electron Corporation, UK) XPS has been identified as being a suitable technique for the characterisation of surfaces and ultra thin layers encountered in semiconductor device fabrication. The extension of this technique to angle resolved XPS, ARXPS allows quantification of elemental and chemical state concentrations in the region of 5 to 10nm, a thickness that is well matched with the gate dielectric thickness currently used. By using maximum entropy calculations it is possible to generate non-destructive atomic concentration depth distribution plots from ARXPS data. These plots show the integrity of a film as well as the behaviour of interfacial layers. This paper looks at Al and Hf films grown by ALD and MOCVD processes. It shows differences in the state of the grown or deposited film as well as changes to the interfacial layer depending on how the film is grown and the thickness of the film. In addition, surface pre-treatment is also found to have a dramatic affect on the nature and role of the interfacial layer For Al and Hf multilayer films the integrity, thickness, preferential growth and the role of the interfacial layer are also investigated.
10:20 AM		AS-ThM-7 Comparative Study of Metal Oxy-Nitride Films by Electron Spectroscopy P.M. Mrozek, D.F.A. Allgeyer, B.C. Carlson, K.B. Beaman, H.K. Krasinski (Micron Technology, Inc.) X-ray photoelectron spectroscopy (XPS) was used extensively to provide information regarding the chemical composition and chemical states of the nitrogen in silicon, hafnium, and other oxy-nitride films grown on silicon or tungsten substrates. Different substrates were investigated in order to minimize differential charging effects. Nitride and ON-like states were identified in different films, and their depth distributions were found to vary from film to film. Nondestructive angle-resolved XPS analysis was applied to reconstruct elemental distributions in films and showed a nitridization depth of ~4nm for SiON and below 2nm for HfON. These results were compared with activation enthalpy for nitridization for different systems.
10:40 AM		AS-ThM-8 Development of Reference Thin Films for Gate Oxide Thickness Determination and Ultra Shallow Junction Profiling D.W. Moon (KRISS, Korea) With the continued scaling down of CMOS devices beyond 50 nm, accurate and precise measurements of gate dielectric layer thickness and dopant profiles in ultra shallow junctions are no more simple and straightforward even with sophisticated techniques. In this presentation, the current status and remaining issues in analytical methodology for gate oxides and ultra shallow junctions are summarized and discussed. For accurate measurement of nm gate oxides thickness with sub atomic layer thickness precision, the thickness that each technique generates can be different and the difference should be understood in a complementary nature. Compared and discussed are the differences between high resolution transmission electron microscopy, grazing incidence X-ray reflectivity, medium energy ion scattering spectrometry, X-ray photoelectron spectroscopy, ellipsometry for accurate and precise determination of gate oxides down to sub nm thickness. For ultra shallow junction depth profiling, details of the sputtering processes in low energy secondary ion mass spectrometry are investigated regarding to the damage profiles and surface transient sputtering effect. Development of multiple delta layer reference thin films for ultra shallow junction profiling is reported on the growth and the application for sputtering rate calibration including the surface transient effect. Relevant activities of ISO TC 201 Surface Chemical Analysis and CCQM Surface and Micro/Nano Analysis WG and the present status and issues of reference thin films for gate oxide thickness determination and ultra shallow junction profiling will be briefly discussed.
11:20 AM		AS-ThM-10 XPS and SIMS Analysis of HfSiON Films S. Miwa, S. Kusanagi, Y. Murakami, H. Kobayashi (Sony EMCS Corp., Japan) Nitrided Hafnium-silicate (HfSiON) is one of the promising materials for high-k gate dielectrics in advanced CMOS LSI. This material is so new that we have to investigate not only its electrical performance but also its chemical and physical properties. X-ray Photoelectron Spectroscopy (XPS) is the conventional technique for analyzing the chemical composition of thin films. We have found that XPS can also confirm the presence of phase separation in HfSiON films from the peak shift of the O1s signal. Secondary Ion Mass spectrometry (SIMS) is the most frequently used method to detect impurities in thin films and semiconductor substrates. In the case of high-k films grown by atomic-layer deposition or metal-organic chemical vapor deposition, it is necessary to use SIMS to determine whether H or C from precursor has been incorporated. SIMS can also be used N distribution in HfSiON films. However, it is difficult for conventional SIMS to observe the diffusion of Hf from HfSiON film to the Si substrate. Hf is moved from the film to the Si substrate by the probe ion beam, so we have employed backside-SIMS to observe Hf diffusion and obtain the precise Hf distribution near the HfSiON/Si interface.
11:40 AM		AS-ThM-11 Nitridation of Hf Silicate Layers for Advanced CMOS Gate Oxides : A Core Level and Valence Band Study by Photoelectron Spectroscopy O. Renault (CEA-DRT-LETI, France); N. Barrett, F. Calvat (CEA-DSM-DRECAM, France); Y. Le Tiec (CEA-DRT-LETI, France); P. Besson (ST-Microelectronics, France); F. Martin (CEA-DRT-LETI, France) The nitridation of high-k materials is widely investigated for sub-65nm CMOS technology nodes¹.In this contribution, we will present recent results of a core-level and valence band study by photoelectron spectroscopy, using both synchrotron and AlKa radiation, of nitrided Hf-silicate films for advanced gate oxides. Hf-silicate layers (3.5 nm-thick) were grown onto thin oxidized Si surfaces and then nitrided in an NH3 ambient. The valence band study at 80 eV photon energy reveals the introduction, upon nitridation, of localized N2p electronic states in the band gap of the silicate, thus confirming recent theoretical predictions². The core-level analysis (Hf4f, N1s, Si2p) of as-grown, partially and totally etched silicate layers indicates that nitridation creates Hf-N bonds with a gradient from the surface to the interface depending on the nitridation temperature. Spectra recorded using synchrotron radiation with enhanced surface sensitivity and photon energy tunability will be presented and highlighted emphasizing the possibility to isolate the Si bonding states from the silicate layer itself. ¹ M. Koike et al., extended abstracts, IEDM, 107 (2003). ² G. Shang, P. W. Peacock, J. Robertson, Appl. Phys. Lett. 84, 106 (2004).