ALD Tutorial

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  • Taking out cost / availability from the equation, the Must be thermally stable;Volatile / Reactive; Compatibility with substrate / manufacturing
  • Taking out cost / availability from the equation, the Must be thermally stable;Volatile / Reactive; Compatibility with substrate / manufacturing
  • MgCp2 – shows decomposition above 300C, high carbon contamination below 200
  • ALD Tutorial

    1. 1. July 2011<br />Cambridge NanoTech ALD Tutorial<br />
    2. 2. ALD Applications<br />Other applications<br />Roll to rollInternal tube linersNano-glueBiocompatibleMagnetic<br />Chemical<br />CatalysisFuel cells<br />Semi / Nanoelectronics<br />Flexible electronics<br />Gate dielectricsGate electrodesMetal InterconnectsDiffusion barriersDRAMMultilayer-capacitorsRead heads<br />MEMS<br />Etch resistanceHydrophobic / antistiction<br />Optical<br />AntireflectionOptical filtersOLED layersPhotonic crystalsTransparent conductorsElectroluminescenceSolar cellsLasersIntegrated opticsUV blockingColored coatings<br />Nanostructures<br />Inside poresNanotubesAround particlesAFM tips<br />Wear resistant<br />Blade edgesMolds and diesSolid lubricantsAnti corrosion<br />Cambridge NanoTech Inc. Confidential<br />
    3. 3. ALD Films<br />- ALD films deposited with digital control of thickness; “built layer-by layer”<br /> - Each film has a characteristic growth rate for a particular temperature<br />Common ALD Materials<br />ALD Deposition Rates at 250°C<br />Oxides<br />Al2O3, HfO2, La2O3, SiO2, TiO2, ZnO, ZrO2, Ta2O5, In2O3, SnO2, ITO, FeOx, NiO2, MnOx, Nb2O5, MgO, NiO, Er2O3<br />Nitrides<br />WN, Hf3N4, Zr3N4, AIN, TiN, TaN, NbNx<br />Metals<br />Ru, Pt, W, Ni, Co<br />Sulphides<br />ZnS<br />1.26 Å<br />1.08 Å<br />0.38 Å<br />Cambridge NanoTech Inc. Confidential<br />
    4. 4. Benefits of ALD<br />Perfect films<br />Digital control of film thickness<br />Excellent repeatability<br />100% film density<br />Amorphous or crystalline films<br />Conformal Coating<br />Excellent 3D conformality<br />Ultra high aspect ratio (>2,000:1)<br />Large area thickness uniformity<br />Atomically flat and smooth coating<br />Challenging Substrates<br />Gentle deposition process for sensitive substrates<br />Low temperature and low stress<br />Excellent adhesion<br />Coats challenging substrates – even teflon<br />Cambridge NanoTech Inc. Confidential<br />
    5. 5. ALD Reaction Sequence<br />ALD is based on the spatial separation of precursors<br />A single ALD cycle consists of the following steps:<br />1) Exposure of the first precursor<br />2) Purge or evacuation of the reaction chamber to remove the non-reacted precursors and the gaseous reaction by-products<br />3) Exposure of the second precursor – or another treatment to activate the surface again for the reaction of the first precursor<br />4) Purge or evacuation of the reaction chamber<br />Single Cycle<br />Precursor A<br />Purge<br />Precursor B<br />Purge<br />Time<br />Cambridge NanoTech Inc. Confidential<br />
    6. 6. ALD Example Cycle for Al2O3 Deposition <br />Tri-methyl<br />aluminum<br />Al(CH3)3(g)<br />Methyl group<br />(CH3)<br />Al<br />H<br />C<br />H<br />H<br />H<br />O<br />Substrate surface (e.g. Si)<br />In air H2O vapor is adsorbed on most surfaces, forming a hydroxyl group. <br />With silicon this forms: Si-O-H (s)<br />After placing the substrate in the reactor, Trimethyl Aluminum (TMA) is pulsed into the reaction chamber.<br />Cambridge NanoTech Inc. Confidential<br />
    7. 7. Methane reaction<br />product CH4<br />H<br />Reaction of<br />TMA with OH<br />H<br />C<br />H<br />H<br />H<br />H<br />C<br />C<br />H<br />H<br />H<br />Al<br />O<br />Substrate surface (e.g. Si)<br />Al(CH3)3 (g) + : Si-O-H (s) :Si-O-Al(CH3)2(s) + CH4<br />ALD Cycle for Al2O3<br />Trimethylaluminum(TMA) reacts with the adsorbed hydroxyl groups,<br />producing methane as the reaction product<br />Cambridge NanoTech Inc. Confidential<br />
    8. 8. ALD Cycle for Al2O3<br />Methane reaction<br />product CH4<br />Excess TMA<br />H<br />H<br />C<br />C<br />H<br />H<br />Al<br />O<br />Substrate surface (e.g. Si)<br />Trimethyl Aluminum (TMA) reacts with the adsorbed hydroxyl groups,<br />until the surface is passivated. TMA does not react with itself, terminating the reaction to one layer. This causes the perfect uniformity of ALD.<br />The excess TMA is pumped away with the methane reaction product.<br />Cambridge NanoTech Inc. Confidential<br />
    9. 9. ALD Cycle for Al2O3<br />H2O<br />O<br />H<br />H<br />H<br />H<br />C<br />C<br />H<br />H<br />Al<br />O<br />After the TMA and methane reaction product is pumped away, water vapor (H2O) is pulsed into the reaction chamber.<br />Cambridge NanoTech Inc. Confidential<br />
    10. 10. 2 H2O (g) + :Si-O-Al(CH3)2(s) :Si-O-Al(OH)2(s) + 2 CH4<br />ALD Cycle for Al2O3<br />Methane reaction product<br />New hydroxyl group<br />Methane reaction <br />product<br />Oxygen bridges<br />H<br />O<br />O<br />Al<br />Al<br />Al<br />O<br />H2O reacts with the dangling methyl groups on the new surface forming aluminum-oxygen (Al-O) bridges and hydroxyl surface groups, waiting for a new TMA pulse. Again metane is the reaction product. <br />Cambridge NanoTech Inc. Confidential<br />
    11. 11. ALD Cycle for Al2O3<br />H<br />O<br />O<br />O<br />Al<br />Al<br />Al<br />O<br />The reaction product methane is pumped away. Excess H2O vapor does not react with the hydroxyl surface groups, again causing perfect passivation to one atomic layer.<br />Cambridge NanoTech Inc. Confidential<br />
    12. 12. H<br />H<br />H<br />O<br />O<br />O<br />O<br />O<br />Al<br />Al<br />Al<br />O<br />O<br />O<br />O<br />O<br />Al<br />Al<br />Al<br />O<br />O<br />O<br />O<br />O<br />Al<br />Al<br />Al<br />O<br />O<br />O<br />Al(CH3)3 (g) + :Al-O-H (s) :Al-O-Al(CH3)2(s) + CH4<br />ALD Cycle for Al2O3<br />One TMA and one H2O vapor pulse form one cycle. Here three cycles are shown, with approximately 1 Angstrom per cycle. <br />Two reaction steps in each cycle:<br /> 2 H2O (g) + :O-Al(CH3)2(s) :Al-O-Al(OH)2(s) + 2 CH4<br />Cambridge NanoTech Inc. Confidential<br />
    13. 13. ALD Deposition Characteristics<br />ALD is insensitive to dose after saturation is achieved<br />Deposition rate remains unchanged with increasing dose<br />MgO Saturation Curve at 250°C<br />Linear MgO Deposition<br />Cambridge NanoTech Inc. Confidential<br />
    14. 14. ALD “Window”<br /><ul><li>Each ALD process has an ideal process “window” in which growth is saturated
    15. 15. Process parameters inside the ALD window allowfor reliable and repeatable results
    16. 16. The ALD window is defined by the precursor volatility / stability</li></ul>Decomposition limited<br />Condensation limited<br />Growth Rate<br />Å/cycle<br />ALD<br />Window<br />Saturation<br />Level<br />Temperature<br />Desorption limited<br />Activation energy limited<br />Cambridge NanoTech Inc. Confidential<br />
    17. 17. ALD Reaction Temperatures<br />ALD is a chemistry driven process<br />Based on precursor volatility/reactivity<br />Most ALD Processes<br />Reactor Temp<br />>400°C<br />250°C<br />300°C<br />150°C<br />150°C<br />Room T<br />200°C<br />100°C<br />350°C<br />High precursor volatility, lower thermal stability of precursors<br />Lower precursor volatility, Slow desorption of precursors<br />Cambridge NanoTech Inc. Confidential<br />
    18. 18. High Aspect Ratio Coatings<br />ALD is uniquely suited to coat ultrahigh aspect ratio structures enabling precise control of the coatings thickness and composition. <br />Cambridge NanoTech’s research systems offer deposition modes for ultra high aspect ratio (>2,000:1)<br />“Capillary tube”<br />Cross Sectional SEM<br />AAO template*<br />*Image courtesy of the University of Maryland<br />Cambridge NanoTech Inc. Confidential<br />
    19. 19. Compositional Uniformity<br />Refractive Index – Ellipsometry<br />Cross sectional EDX <br />2.104<br />2.103<br />2.101<br />2.101<br />2.105<br />2.102<br />2.104<br />2.104<br />2.101<br />2.103<br />2.103<br />2.103<br />2.099<br />2.101<br />2.104<br />Al2O3 Silica aerogel foam<br />Ta2O5 - 500Å film<br />Cambridge NanoTech Inc. Confidential<br />
    20. 20. ALD Precursors <br />Good ALD precursors need to have the following characteristics: <br />Volatility <br />Vapor pressure (> 0.1Torr at T < 200°C) without decomposition <br />Stability <br />No thermal decomposition in the reactor or on the substrate <br />Reactivity <br /> Able to quickly react with substrate in a self-limiting fashion (most precursors are air-sensitive) <br />Byproducts <br /> Should not etch growing film and/or compete for surface sites <br />Availability <br />Precursor cylinders<br />Cambridge NanoTech Inc. Confidential<br />
    21. 21. Plasma Enhanced (PE)ALD<br /><ul><li>Remote Plasma as a reactant
    22. 22. Expands ALD window for materials by decreasing activation energy
    23. 23. Lower temperature possible: avoids precursor decomposition
    24. 24. Faster deposition cycle times
    25. 25. Fewer contaminates in films</li></ul>Single Cycle<br />Fiji PE-ALD chamber<br />Precursor A<br />Purge<br />Plasma On<br />Plasma Purge<br />Time<br />Cambridge NanoTech Inc. Confidential<br />
    26. 26. Plasma Enhanced (PE)ALD<br />Plasma ALD processes are used for a variety of oxides, nitrides, and metals, including titanium nitride, platinum, and other materials, allowing for low resistivity of titanium nitride, and significantly lower temperatures for depositing platinum. <br />Cambridge NanoTech Fiji Manifold<br />Cambridge NanoTech Fiji Chamber<br />Cambridge NanoTech Inc. Confidential<br />
    27. 27. Variety of Material Types Possible<br />ALD allows for the fabrication of different types of materials, all in the same deposition chamber, without the need for different hardware configurations. <br />Doped films: single “layers” of dopant film in between bulk<br /><ul><li>Doped films do not require “activation” by annealing</li></ul>(B) Nanolaminate Films: stacks of alternating layers<br />(C) Graded films: composition slowly changes from material A to material B<br />M1<br />Cambridge NanoTech Inc. Confidential<br />
    28. 28. Low Temperature ALD<br />Some ALD processes can deposit films < 150°C: Al2O3, HfO2, SiO2, TiO2, ZnO, ZrO2, Ta2O5, SnO2, Nb2O5, MgO<br />Ideal for merging organics with inorganics<br />Compatible with photoresist, plastics, biomaterials<br />Cambridge NanoTech Inc. Confidential<br />
    29. 29. Product Portfolio<br />Cambridge NanoTech ALD systems are engineered for a wide variety of applications from research to high-volume manufacturing. These systems deposit precise, conformal and ultra-thin films on multiple substrates. Their simplified system designs yield low startup and operating costs. <br />Savannah <br />Fiji<br />Phoenix<br />Tahiti<br />Compact, cost-effective system for research <br />Plasma system for research<br />Batch manufacturing system<br />Large area manufacturing system<br />Production<br />Research<br />Cambridge NanoTech Inc. Confidential<br />

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