Kessels, WMM

Potts, SE

Van de Sanden, MCM

English

UCL Discovery

What is CORRAL?A Europe-wide project investigating corrosion protection with perfect atomiclayers.Primary GoalTo develop an efficient corrosion protection system comprising defect-free ultra-thin sealing coatings with excellent barrier properties.CORRAL RequirementsThe current state of the art of films for corrosion protection is ~3 µm. Thecoatings developed in the CORRAL project should be:• Ultra-thin (> 50 nm),• Chemically inert material,• An excellent sealant, which should be defect-free.SubstratesSiliconWith a monolayer of SiO2 (process optimisation)Steel (100Cr6)‘Conventional’ steelStainless Steel (316L)Stainless attribute due to 18-20% chromiumAluminium 2000A standard aluminium alloyPlasma-Enhanced ALD of Al2O3Plasma-enhanced atomic layer deposition was used todeposit 10 and 20 nm of Al2O3 onto the steel and aluminiumsubstrates. The precursors were trimethylaluminium (TMA)and an oxygen plasma (the cycle is shown in Fig. 1). Thetwo half reactions are:1. Al–OH*  +  [Al(CH3)3] (g) →   Al–O–Al(CH3)2*   +   CH4 (g)2. Al–CH3*   +   4 {O} →   Al–OH*   +   CO2 (g) +   H2O (g)* Denotes a surface-bound species.The temperatures investigated were 50, 100 and 150 °C.  A thermal ALD process was also run at 150 °C for comparison.Corrosion ResistanceCorrosion is the result of wear or chemical attack in mechanical moving parts.Forming a thin barrier layer will protect metallic components without dramaticallyaltering their shape. As atomic layer deposition (ALD) affords thin films withexcellent conformality over a large batch area,1 its use as a route to corrosionresistant layers could be crucial.Low TemperaturesALD is a method whereby thin films of a material can be deposited via cycles ofpulsed precursor dosing and purging. The substrate temperatures typically rangefrom 100-450 °C.2 As the mechanical properties of the substrates can be alteredby temperatures greater than 160 °C, the ALD process needs to be optimisedunder these conditions. There are few reports of depositions below 100 °C, themost notable being the ALD of Al2O3 from [Al(CH3)3] and water3 or ozone.4 Weare investigating the use of plasma-enhanced ALD as an alternative to theseroutes to see if high quality films can be obtained at such low temperatures.Corrosion Resistance with Perfect Atomic Layers: An Introduction to CORRALS. E. Potts, M. C. M. van de Sanden and W. M. M. Kessels21st NNV/CPS Symposium, Lunteren, 3-4 March 2009Plasma & Materials Processing Group, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. www.phys.tue.nl/pmp01020304050600 50 100 150 200 250 300 350 400ALD CyclesThinckness (nm)            150 °C100 °C50 °C150 °CthermalFigure 4. FT-IR spectra of the films on Si{100}.  The regions shown are for Al–O, C–O and C–H and O–H respectively.Figure 2. Temperature series of films, showing how the growth rate is dependent on deposition temperature.References 1. R. Matero, M. Ritala, M. Leskelä, T. Salo, J. Aromaa, O. Forsén, J. Phys. IV, 1999, 9, Pr8: 493. 2. J. Niinistö, M. Ritala, M. Leskelä, Mater. Sci. Eng. B, 1996, 41, 23-29.3. M. D. Groner, F. H. Fabreguette, J. W. Elam, S. M. George, Chem. Mater., 2004, 16, 639-645. 4. S. K. Kim, S. W. Lee, C. S. Hwang, Y.-S. Min, J. Y. Won, J. Jong, J. Electrochem. Soc., 2006, 153, F69-F76.SummaryThin films of Al2O3 have been deposited on steel and aluminium substrates at temperatures ≤ 150 °C,which will be tested for corrosion resistance. The impurities in the films decreased with increasingtemperature, as did the growth rate per cycle.400 600 800 1000 120001x10-22x10-23x10-24x10-25x10-2  Absorbance1400 1600 180002x10-34x10-36x10-38x10-31x10-21x10-2   Wavenumber (cm-1) 2500 3000 3500 400002x10-34x10-36x10-38x10-31x10-2   — 25 °C       — 50 °C       — 100 °C       — 150 °C       — 200 °CAl–OSi–OO–C O–HC–H0.120.130.140.150.160.170.180.1940 60 80 100 120 140 160Tsubs (°C)Growth Per Cycle (nm)1.551.561.571.581.59Refractive IndexFigure 3. Variance of growth rate and refractive index with deposition temperature (Tsubs) for 10 nm films.Figure 1. A cycle for plasma-enhanced ALD of Al2O3.ResultsThe growth rate per cycle was highest at lowerdeposition temperatures for the plasma-enhancedprocess (Fig. 2 and 3), due to the formation ofwater in the plasma step. This was confirmed bythe greater intensity of –OH peaks in the FTIRspectra (Fig. 4) at lower temperatures.The thermal process at 150 °C afforded a lowergrowth rate as the reactivity of water at thistemperature is lower than that of the plasma.The refractive index of the films deposited at 50°C was significantly lower than for the othertemperatures, suggesting that these conditionsgive films of a lower density, possibly as a result ofhydroxyl impurities.1 cycle0 1 2 3 4 5 6 7 8 9 10 11 12Oxygen Plasma(150 W)Argon PurgeTMA PrecursorTime (s)

Corrosion Resistance with Perfect Atomic Layers

https://discovery.ucl.ac.uk/10114974/1/Poster_Lunteren_A0_SEPotts.pdf

Corrosion Resistance with Perfect Atomic Layers

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