CHEM-E5205 : Advanced FunctionalMaterials Atomic Layer Deposition (ALD)

Transcription

1 CHEM-E5205 : Advanced FunctionalMaterials Atomic Layer Deposition (ALD) Saima Ali

2 Contents Atomic Layer Deposition (ALD) history ALD process ALD surface chemistry Plama enhanced atomic layer deposition (PEALD) ALD examples PEALD of AlN X-ray Reflectivity X-ray Diffraction 2

3 Atomic Layer Deposition (ALD) Thin film deposition process Coatings obtained in nm range Precise thickness control Microelectronics and semiconductor technology Dr. Tuomo Suntola,1974 in Finland develop the process under the name of "atomic layer epitaxy (ALE) for electroluminescent displays. The name Atomic layer deposition (ALD) comes from work in 1990 s "Molecular Layering" in the 1960s by Soviet Union Japanese researchers work with the name of "Molecular layer epitaxy (MLE) " Ref: Riikka L. Puurunen, A Short History of Atomic Layer Deposition: Tuomo Suntola s Atomic Layer Epitaxy, Chem. Vap. Deposition 2014, 20,

4 ALD Applications High k dielectrics Insulation Metal barriers Moisture barriers Passivation/Protection Conductive coatings Optical coatings (NIR filters, anti-reflective coatings, LEDs) Anti tarnish coatings (Kalevala jewelry for silver) Decorative coatings Ref: ( ) 4

5 ALD Process Cycle Precursors introduced in the form of gas/vapors Self terminating reactions with introduction of precursors Chemisorption Sequential process Uniform thickness coatings Fig: ALD one complete reaction cycle Ref: Riikka L. Puurunen, Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process (2005) Journal of Applied Physics 97:

6 ALD Cycle Self terminating reaction by first reactant Purging Self terminating reaction by second reactant Evacuation/Purge Growth per cycle (GPC) Ref_fig: ( ) 6

7 Atomic Layer Deposition Cycle Ref: J.L. Lu, J.W. Elam, P.C. Stair, Synthesis and Stabilization of Supported Metal Catalysts by Atomic Layer Deposition (2013) Acc. Chem. Res.46:

8 ALD Example of Al 2 O 3 deposition Al C H o Silicon wafer ALD half cycle M-OH* + Al(CH 3 ) 3 M-O-Al(CH 3 ) 2 * + CH 4 ALD complete cycle M-O-Al(CH 3 ) 2 * + H 2 O M-O-Al(OH) 2 ) + 2CH 4 Ref_fig: C. Detavernier et al. Tailoring nanoporous materials by atomic layer deposition (2011) Chem. Soc. Rev. 40,

9 ALD Process Examples Al 2 O 3 example TiO 2 example from TiCl 4 and H 2 O 9

10 ALD Reactors Fig: Picosun ALD reactor R-200 advanced Fig: Beneq TFS 500 ALD reactor ( ) ( ) 10

11 ALD Materials Ref: Riikka L. Puurunen, Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process (2005) Journal of Applied Physics 97:

12 ALD window Fig: ALD window is the region of nearly ideal ALD behaviour ( o C) Ref: Steven M. George, Atomic Layer Deposition: An Overview (2010) Chem. Rev, 110:

13 ALD surface chemistry Adsorption Chemisorption (irreversible) Physisorption (reversible) Fig: ALD Monolayers (a) Chemisorbed (b) physisorbed (c) ALD grown material Ref: Riikka L. Puurunen, Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process (2005) Journal of Applied Physics 97:

14 ALD surface chemistry Chemisorption Ligand exchange Dissociation Association Fig: Chemisorption mechanism Ref: S. Heil, Plasma-Assisted Atomic Layer Deposition of Metal Oxides and Nitrides PhD Thesis, 2008 doi: 14

15 ALD surface chemistry Adsorption rate and coverage Pressure Temperature Time Fig: Chemisorption coverage as a function of time Ref: Riikka L. Puurunen, Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process (2005) Journal of Applied Physics 97:

16 ALD surface chemistry Saturation factors Number of reactive surface sites Steric hinderance of the ligands GPC increases by decreasing adsorbate size Fig: Factors effecting saturation (a) Steric hinderance (b) Available reactive sites Ref: Riikka L. Puurunen, Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process (2005) Journal of Applied Physics 97:

17 Growth Per Cycle: temperature Reactive sites/ Reaction mechanism Steric hinderance Overcome Energy barriers Incomplete Reactions or Affected reactive sites Fig: Effect of temperature on GPC in ALD window Ref: Riikka L. Puurunen, Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process (2005) Journal of Applied Physics 97:

18 GPC: Number of cycles Fig: No of cycles effect on GPC (a) linear growth (b) substrate enhanced growth (c) substrate-inhibited growth Type 1, (d) substrate-inhibited growth Type 2, island growth Ref: Riikka L. Puurunen, Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process (2005) Journal of Applied Physics 97:

19 Plasma Enhanced Atomic Layer Deposition (PEALD) High reactive radicals and ions Fig: Thermal ALD and PEALD Ref: H. B. Profijt et al. Plasma-assisted ALD (2011) J. Vac. Sci. Technol. A, 29:

20 Example of Al 2 O 3 deposition Fig: Deposition of alumina by thermal and plasma ALD Ref: S. Heil, Plasma-Assisted Atomic Layer Deposition of Metal Oxides and Nitrides PhD Thesis, 2008 doi: 20

21 PEALD reactors Fig : Plasma ALD reactors (a) radical enhanced ALD (b) Direct plasma (c) remote plasma-assisted reactor (d) direct plasma with mesh Ref_fig : H. B. Profijt et al. Plasma-assisted ALD (2011) J. Vac. Sci. Technol. A, 29,

22 PEALD Advantages High film density Low impurities and improved electronic properties Film deposition at low temperature Polymer coating Increased choice of materials Increased growth rate Nice control on film composition Substrate pretreatment (oxidation, nitridation) Cleaning and post deposition treatments Ref: H. B. Profijt, S. E. Potts, M. C. M. van de Sanden, and W. M. M. Kessels, Plasma-assisted ALD, J. Vac. Sci. Technol. A, Vol. 29, No. 5c 22

23 PEALD Challenges Reduce conformality on high aspect ratio substrates and porous materials Recombination probability Deposition material Type of radicals used Ref_fig:X. Ming et al. Atomic Layer Deposition of Silicon Nitride Thin Films: A Review of Recent Progress, Challenges, and Outlooks (2016) Materials 9(12), Ref: H. B. Profijt, S. E. Potts, M. C. M. van de Sanden, and W. M. M. Kessels, Plasma-assisted ALD (2011) J. Vac. Sci. Technol. A, Vol. 29, No. 5c 23

24 PEALD Challenges Undesired oxidation and nitridation of substrate top due to high reactivity of plasma Defects on material and interfaces mostly in case of direct plasma reactor Bond-breaking, displacement of atoms and charge accumulation Properties of films vary with plasma reactor type Complex reactors required for industrial purposes Fig: TEM of 20 nm Al 2 O 3 film on Si substrate, oxide layer is also present between film and substrate Ref_fig: S. Heil, Plasma-Assisted Atomic Layer Deposition of Metal Oxides and Nitrides PhD Thesis, 2008 doi: Ref: H. B. Profijt, S. E. Potts, M. C. M. van de Sanden, and W. M. M. Kessels, Plasma-assisted ALD (2011) J. Vac. Sci. Technol. A, Vol. 29, No. 5c 24

25 PEALD of AlN AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH 3 ) enhanced by N 2 plasma Less impurities Fig: AlN thickness as a function of ALD cycles and temperatures Fig: Atomic concentration as a function of growth temperature Ref: Markus Bosund et al. Properties of AlN grown by plasma enhanced atomic layer deposition (2011) Applied Surface Science 257 (2011)

26 PEALD of AlN (a) (c) (b) Fig: (a) Atomic concentration as function of plasma pulse time (b) ALN thickness and thickness variation as a function of plasma pulse time (c) density, roughness and growth rate dependence with deposition temperature Ref: Markus Bosund et al. Properties of AlN grown by plasma enhanced atomic layer deposition (2011) Applied Surface Science 257 (2011)

27 Conformal ALD films on high aspect ratio structures More reactant exposure time ALD on anodic alumium oxide (AAO) DRAM capacitors MEMS Photonic crystals Fig: 300 nm thick ALD alumina film on a Si wafer with a trench structure Ref: Steven M. George, Atomic Layer Deposition: An Overview (2010) Chem. Rev, 110:

28 ALD Coatings For different applications ALD method has been used for coating Substrates Particles Polymers Nanotubes (CNT and TNT) Fig: TiO 2 Nanotubes coated with Al 2 O 3 by ALD Ref: Raul Zazpe et al. Atomic Layer Deposition for Coating of High Aspect Ratio TiO 2 Nanotube Layers (2016) Langmuir 2016, 32,

29 ALD on polymers Polyethylmethacrylate (PMMA) Polypropylene Polystyrene Polyethylene polyvinylchloride Fig: Al 2 O 3 ALD on polymer films Ref: Steven M. George, Atomic Layer Deposition: An Overview (2010) Chem. Rev, 110:

30 Nanotubes From ALD Fig (a): TEM image of ZrO 2 nanotubes fabricated on polycarbonate templates Fig (b): TiO 2 nanotubes fabricated on Al 2 O 3 templates Ref_fig (a): Steven M. George, Atomic Layer Deposition: An Overview (2010) Chem. Rev, 110: Ref_fig (b): M. S. Sander et al. Template-Assisted Fabrication of Dense, Aligned Arrays of Titania Nanotubes with Well-Controlled Dimensions on Substrates (2004) Adv. Mater. 16:

31 Nanolaminates by ALD Al 2 O 3 /W Al 2 O 3 /TiO 2 W/Se Au/Si Dielectric oxides (SiO 2 /Y 2 O 3, SiO 2 /Cr 2 O 3, and SiO 2 /Al 2 O 3 ) Bi 2 Te 3 /Sb 2 Te 3 TiN/TaN Organoclay nanolaminates Inorganic organic hybrids Fig: TEM image of a 16-bilayer Al 2 O 3 /W superlattice HfO 2 /Al 2 O 3 Ref_fig: Steven M. George, Atomic Layer Deposition: An Overview (2010) Chem. Rev, 110: Ref: S Ali et al. Thermal conductivity of amorphous Al 2 O 3 /TiO 2 nanolaminates deposited by atomic layer deposition (2016) Nanotechnology

32 ALD Advantages Precise thickness control Conformal deposition Self-terminating growth Uniformity Excellent step coverage on complex and high aspect ratio structures High film density Pinhole free films Excellent adhesion Coating of senstive substrates such as polymers and biomaterials Disadvantages Materials limitation Slow process Expensive 32

33 Feedback 33

34 XRR and XRD

35 X-ray characterization X-ray tube Incident beam optics Goniometer Diffracted beam optics Fig: Philips X Pert Pro Diffractometer 35

36 X-Ray Reflectivity (XRR) Non destructive method Amorphous, single crystalline and polycrystalline materials Opaque films Single and multilayer films Reflection at surface and film interfaces due to different electron densities. Film parameters Film density Film thickness Roughness 36

37 XRR data Fig: X-ray reflectivity data Ref_fig: () 37

38 X-Ray Reflectivity (XRR) The x-ray intensity analytically described by Parrat s (recursive) equations The recursive reflection coefficient for the amplitude of the electric field of the (j-1)th layer (t j is the layer thickness and the F is Fresnel factor ) δ is known factor known as scattering factor that is material dependent parameter also β is associated with absorption r e = Bohr radius; N a = Avogadro number; Z j =average atomic number ; A j = average atomic mass for the jth layer; Δf j and f j = material specific dispersion correction coefficients and ρ j is the mass density of the layer. Ref: L.G. Parrat. Surface studies of solids by total reflection of X-Rays (1954) Phys. Rev., 95(2),

39 XRR of films Fig: XRR of methycelloluse films with increasing thicknesses Ref_fig: Vallerie Ann Innis-Samson, and Kenji Sakurai Hydrophobic switching nature of methylcellulose ultra-thin films: thickness and annealing effects (2011) Condens. Matter 23:

40 XRR of films Fig: XRR of W films deposited at different parameters Ref_fig: K Salamon et.al Structure and morphology of magnetron sputtered W films studied by x-ray methods (2013) J. Phys. D: Appl. Phys. 46:

41 XRR Characterization of Nanolaminate Al 2 O 3 /TiO 2 Nanolaminates with varied bilayer thicknesses Total thickness = 100nm Silicon substrate Picosun TM R-150 ALD reactor used for deposition from Me 3 Al,TiCl 4 and H 2 O precursors Deposition temperature = 200 o C Fig: Schematic View of Nanolaminate Structure Ref: S. Sintonen et al. X-ray reflectivity characterization of atomic layer deposition Al 2 O 3 /TiO 2 nanolaminates with ultrathin bilayers (2014) J. Vac. Sci. Technol. A 32, 01A111 41

42 XRR Measurement Results Fig: XRR measurements results for (a)50nm (b)20nm (c)10nm (d)5nm (e)2nm and (f)1nm bilayers. Red lines shows the simulated curves while blue ones shows the actual measured data Ref: S. Sintonen et al. X-ray reflectivity characterization of atomic layer deposition Al 2 O 3 /TiO 2 nanolaminates with ultrathin bilayers (2014) J. Vac. Sci. Technol. A 32, 01A111 42

43 Nanolaminate Results Nanolaminate characterised with bilayer thickness from 0.1 to 50nm Layered structures preserved with invidual layer thickness of 0.38nm, below which the samples decomposes to single layers Ti x Al y O z Layers were uniform 43

44 X-ray diffraction Non destructive technique Diffraction from atoms, constructive interference occurs when Bragg s law is satisfied Used to determine Crystallinity Phase identification and crystallite orientation Crystallite size Lattice constants, strain and composition of single crystals d sin 2 hkl Fig: Conditions required for Bragg diffraction to occur for X-ray Diffraction Ref_fig: ( ) 44

45 X-ray diffraction Powder diffraction Crystallites assumed to be oriented randomly Incident and exit angles are kept equal during measurement Measured peak positions correspond to atomic plane distances and phases are identified Grazing incidence XRD (GIXRD) Fixed incident angle allows large volume probing of a thin film Suppresses substrate contribution 45

46 GIXRD of Al 2 O 3 /TiO 2 Nanolaminates Fig: GIXRD of pure TiO 2 films deposited at different temperatures Ref: S Ali et al. Thermal Conductivity of Amorphous Al 2 O 3 /TiO 2 Nanolaminates Deposited by Atomic Layer Deposition (2016) Nanotechnology, 27:

47 XRD data Peak position and intensity Phase identification Lattice constant Residual stress Peak width Crystal quality Lattice strain Crystallite size Fig: anatase and rutile phase of titania Ref_fig: ( ) 47

48 Crystallite Size The crystallite size is found by the Scherrer equation as stated below. B is the FWHM of the peak profile D is volume average of crystal thickness K is constant of proportionality Θ is diffraction angle of λ is the wavelength Fig: FWHM of peak Ref_ fig: ( ) 48

49 XRD results Fig(a): XRD pattern of ALN (002) deposited by ALD Fig(b): GIXRD pattern of TiO 2 deposited by ALD Ref_fig(a): H.A. Bui et al. Initial growth, refractive index, and crystallinity of thermal and plasma-enhanced atomic layer deposition AlN films, (2015) J. Vac. Sci. Technol. A 33(1). Ref_fig(b): Viljami Pore et al. H 2 S modified atomic layer deposition process for photocatalytic TiO 2 thin films, (2007) J. Mater. Chem.17,

50 Crystallinity Deposition temperature Thickness of the film TiO 2 thin film crystallizes at 200 o C Thinner films have less peaks Ref: Jussi Lyytinen, Xuwen Liu, Oili M.E. Ylivaara, Sakari Sintonen, Ajai Iyer, Saima Ali, Jaakko Julin, Harri Lipsanen, Timo Sajavaara, Riikka L. Puurunen, Jari Koskinen (2015) Nanotribological, nanomechanical and interfacial characterization of atomic layer deposited TiO 2 on a silicon substrate, Wear, Vol :

51 Home reading What ALD materials are used for mentioned applications? 51