AVS2004 Session TF2-TuM: ALD and Applications

Tuesday, November 16, 2004 10:20 AM in Room 303C

Tuesday Morning

Start	Invited?	Item
10:20 AM		TF2-TuM-7 Atomic Layer Deposition of Tungsten Disulphide Solid Lubricant Coatings T.M. Mayer, T.W. Scharf, S.V. Prasad, R.S. Goeke, M.T. Dugger (Sandia National Laboratories) We have developed a new process for the deposition of polycrystalline tungsten disulphide (WS₂) solid lubricant coatings with monolayer precision by atomic layer deposition. Sequential reactions of WF₆ and H₂S in a viscous flow reactor at 1 to 2 torr and 300 to 400°C lead to growth rates of 0.1 to 0.2 nm/cycle. Nucleation of WS₂ is impeded on SiO₂ substrates such that no growth is observed even after 200 cycles. However nucleation occurs readily on ZnO and ZnS substrates and growth catalyzed by the presence of small quantities of Zn, which segregates to the surface of the growing film. SEM with EDS, and Raman spectroscopy determined the coating morphology, composition, and crystallinity, respectively. The friction coefficient was determined to be approx. 0.12 as deposited and decreased to approx. 0.04 when the coating was annealed, well within the acceptable range of other solid lubricant coatings like sputtered MoS₂ and pulsed laser deposited WS₂, making this material and process attractive for applications in micromachine technology.
10:40 AM		TF2-TuM-8 Molybdenum Atomic Layer Deposition Using MoF₆ and Si₂H₆ G.B. Rayner, Jr., S.M. George (University of Colorado) Although many binary materials have been grown using atomic layer deposition (ALD) techniques, the growth of most single-element metals has been difficult. Tungsten (W) ALD has been demonstrated earlier using WF₆ and Si₂H₆ as reactants. In this study, we extend a similar surface chemistry strategy for Mo ALD. Auger electron spectroscopy (AES) was used to monitor the nucleation and growth during Mo ALD on thin SiO₂ films thermally grown on Si(100) substrates. Using MoF₆ exposures of 8 x 10⁵ L and Si₂H₆ exposures of 4 x 10⁶ L at 200°C, the Mo ALD was observed by the attenuation of the O(KLL) AES signal and growth of the Mo(MNN) AES signal. Mo ALD nucleation on SiO₂ required 10-15 MoF₆/Si₂H₆ reactant cycles. The Si(LMM) AES signal oscillated dramatically during the sequential MoF₆ and Si₂H₆ exposures. No Si(LMM) AES signal was observed following the MoF₆ exposures that deposit MoF_x surface species. Large Si(LMM) AES signals were monitored after the Si₂H₆ exposures that strip off the fluorine and deposit SiH_yF_z surface species on the growing Mo surface. Mo ALD may be important for the fabrication of Mo/Si Bragg mirrors for extended ultraviolet (EUV) lithography.
11:00 AM		TF2-TuM-9 Atomic Layer Deposition for the Conformal Coating of Nanoporous Materials J.W. Elam, G. Xiong, C.Y. Han, J.P. Birrell, G.A. Willing, H.H. Wang, J.N. Hryn, M.J. Pellin (Argonne National Laboratory) Atomic layer deposition (ALD) utilizes a binary reaction sequence of self-saturating chemical reactions between gaseous precursor molecules and a solid surface to deposit films in a layer-by-layer fashion. These attributes make ALD an ideal method for applying very precise, conformal coatings over porous materials. In this presentation, we describe recent work exploring the ALD coating of two porous solids: anodic aluminum oxide (AAO) and silica aerogels. The AAO and silica aerogels have been successfully coated by ALD with a variety of oxide films including Al₂O₃, ZnO, TiO₂, Y₂O₃ and V₂O₅ as well as several metals. These materials were characterized with a host of analytical techniques including SEM, TEM, EDX, AFM, XRD and BET surface area measurements. The ALD coated AAO materials are being employed as mesoporous catalytic membranes as well as size-specific separations membranes. To fabricate the catalytic membranes from the AAO templates, the pore diameter of the AAO membranes is first reduced to the 5-10 nm regime using Al₂O₃ ALD. Next, TiO₂ ALD is used to deposit several monolayers of catalytic support material. Finally, the active V₂O₅ catalyst is deposited by ALD. The resulting nanostructured catalytic membranes show remarkable selectivity in the oxidative dehydrogenation of cyclohexane when compared to conventional powder catalysts. Silica aerogels have the lowest density and highest surface area of any solid material. Consequently, these materials serve as an excellent substrate for fabricating catalytic materials by ALD. In addition to their use as catalysts, the ALD modified aerogel materials have applications in hydrogen storage and production, chemical sensing, and optics. In this study, both thin film and monolithic aerogels were coated by ALD and the coating process was investigated as a function of the reactant exposures.
11:20 AM		TF2-TuM-10 High Reflectivity X-Ray Mirrors from W/Al₂O₃ Nanolaminates Fabricated by Atomic Layer Deposition F.H. Fabreguette, Z.A. Sechrist, R.A. Wind, S.M. George (University of Colorado) Nanolaminates can display novel optical, thermal, electrical or mechanical properties. In this study, atomic layer deposition (ALD) was used to fabricate W/Al₂O₃ nanolaminates for x-ray mirrors. High x-ray reflectivity depends on precise thickness control, minimal interfacial roughness and high density contrast between the absorber (W) and spacer (Al₂O₃) layers in the superlattice that defines the Bragg mirror. The sequential, self-limiting ALD surface reactions allow for atomic control of each layer thickness. Al₂O₃ ALD films are amorphous, whereas W ALD films are polycrystalline. To minimize the surface roughness, the W ALD growth temperature was decreased from 177°C to 125°C. This temperature reduction lowered the surface roughness and also changed the tungsten crystalline phase from the α-phase with some β-phase to the pure α-phase. This transformation is desirable because the α-phase has a higher density than the β-phase. Quartz crystal microbalance (QCM) was used as an in-situ probe to optimize the nucleation of Al₂O₃ ALD on W and W ALD on Al₂O₃ at 125°C. Atomic force microscopy (AFM) studies revealed that smoother films resulted from nanolaminates that had shorter nucleation periods. The optimized W/Al₂O₃ nanolaminate growth parameters were used to grow W/Al₂O₃ x-ray mirrors. These Bragg mirrors were fabricated with variable bilayer thickness, D, spacer-to-absorber ratio, γ, and number of bilayers, N. The measured x-ray reflectivities were compared with the predicted x-ray reflectivities from the Fresnel equations. Reflectivities as high as 70-80% were obtained using the best set of D, γ and N parameters. These results demonstrate that the W/Al₂O₃ nanolaminates fabricated by ALD are competitive with commercial x-ray mirrors prepared using sputtering techniques.
11:40 AM		TF2-TuM-11 Atomic Layer Deposition of Nickel Oxide Films Using Ni(dmamp)₂ and Water T.S. Yang, W. Cho, M. Kim, K.-S. An, T.-M. Chung, C.G. Kim, Y. Kim (Korea Research Institute of Chemical Technology) A novel precursor synthesized for the chemical vapor deposition of metallic nickel, Ni(dmamp)₂ (dmamp = 1-dimethylamino-2-methyl-2-propanolate), has been tested for its use as a nickel source for the atomic layer deposition of nickel oxide (NiO) using water (H₂O) as the oxygen source. The precursor is a solid at room temperature, but readily sublimes at 90 °C. The ALD temperature window for this precursor is between 90 °C and 150 °C. The NiO films deposited on Si(001) at 120 °C were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The growth rate of the films was found to be ~0.8 Å/cycle by ellipsometry. The XRD pattern showed no distinct peaks for NiO, indicating that the films deposited at this temperature were amorphous. XPS analysis showed the films to be stoichiometric with some carbon impurities. For a film with the thickness of 820 Å (with 1000 cycles) the rms surface roughness was only ~4 Å as measured by AFM. To elucidate the ALD mechanism of the Ni precursor with water, a quadrupole mass analyzer was employed using D₂O in lieu of H₂O. It was found that after a Ni precursor pulse no reaction seemed to take place, however, after a D₂O pulse, decomposition of the precursor was detected. It is speculated that when the precursor is sent to the substrate (or growing film) it is coordinated to the surface OH groups and when water is introduced, it undergoes a decomposition process to produce a hydroxylated nickel oxide surface. At present, an effort is being made to reduce the amount of carbon impurities. We are also trying to devise a method to deposit metallic nickel using this precursor.