Presentation is loading. Please wait.

Presentation is loading. Please wait.

What is the limit of nanolaminate layer thickness in ALD

Similar presentations


Presentation on theme: "What is the limit of nanolaminate layer thickness in ALD"— Presentation transcript:

1 What is the limit of nanolaminate layer thickness in ALD
What is the limit of nanolaminate layer thickness in ALD? Oskari Elomaa, The topic of my presentation:

2 But are there limitations for the layer thickness?
Nanolaminates by ALD: tailored properties & controlled growth! But are there limitations for the layer thickness? Nanolaminates are a perfect material: -tailored properties like hardness on permittivity ALD is perfect technique -monolayer growth -comformal But there are limit to the layer growth, which I will go through here.

3 Contents Nanolaminates: introduction and examples Nanolaminates by ALD
Layer thickness limitations Property related Thick layers Thin layers Process and modelling examples Conclusions References Here are the contents:

4 Nanolaminates: introduction
Multilayer coatings Repeating layers of different materials One or more bilayers in a stack Bilayer thickness from few to tens of nm Growth methods CVD PVD ALD Sol-Gel Cross-sectional TEM image of Al2O3–TiO2 film nanolaminated by alternate ALD growth of 100-cycle Al2O3 and 350-cycle TiO2. [2]  Nanolaminates in simple words: Multilayer films/coatings: -repating 2 or more different materials -bilayers (EXAMPLE IN PICTURE) -individuallayer thicknesses nanometer scale 2-50? Growth methods: -basically anything like CVD, PVD methods -even sol-gel nanolaminates -Magnetron Sputtering for hard coatings -ALD for dielectrics [1-5]

5 Nanolaminates: introduction
Tunable nanocomposites Materials (single layer properties), composition Thickness and number of bilayers Iso-structural vs. non iso-structural bilayers Crystal sructure (polycrystalline, amorphous) Possibility to tailor the properties High strenght and hardness Corrosion/erosion resistance Fracture toughness High film quality (low roughness) High/low thermal/electrical conduction High/low optical refractive index Nanolaminates are more, they can be tailored: properties you want! Tunable thin films, tailoring: -starting material properties, compositions of layers -bilayer thickness, number of etc and copmpostion -Isostructural and non-isostructural BI same crystal structure (super lattice like TiN) or not dislocations move or not -crystalline, polycrystalline, amorphous -interfacial density. Properties: High strenght and hardness, 100 Gpa with titanium nitrides Corrosion/erosion resistance (chemically inert, durable) Fracture toughness (dislocations dont move over layers) High film quality (low roughness) with amorphous High/low thermal/electrical conduction High/low optical refractive index [1-5]

6 Nanolaminates: examples
Hard coatings and high strenght materials TiAlN/VN, TiAlN-CrN, AlN/Si3N4… Machine tooling Thin high-k dielectric layers Al2O3/HfO2, Ta2O5/HfO2, Ta2O5/ZrO2, ZrO2/HfO2... Gate dielectric candidates to replace SiO2, SiON Capasitor dielectrics Other tailored multilayer coatings W/AI2O3… Thermal barrier coatings Optical filters, x-ray mirrors, gas sensors Hard coatings and high strenght materials TiAlN/VN, TiAlNYN-VN, TiAlN-CrN, AlN/Si3N4… titaniumnitrides, aluminum nitrides and combinations Machine tooling , cutting, drills Thin high-k dielectric layers Al2O3/HfO2, Ta2O5/HfO2, Ta2O5/ZrO2, ZrO2/HfO2... Gate oxide candidates to replace Silicon oxide transistor Dielectrics for capasitors Tailored multilayer coatings W/AI2O3…Tungsten/Aluminumoxide Thermal barrier coatings Optical filters, x-ray mirrors Gas sensors [1-15]

7 Nanolaminates by ALD Basic ALD process
Precursors changed after each individual layer to get bilayers 3 or more precursors ALD advantages compared to PVD, CVD... Accurate thickness control Large-scale uniformity Conformal layering Sharp interfaces Diverse sizes and shapes can be coated ALD limitations Speed (slow) Precursors (none, toxic, expensive) Basic ALD process -3 or more precursors needed -first one layer, then the other to bilayers ALD advantages compared to PVD, CVD... Accurate thickness control (up to 1 Å) of the individual nanolayers Large-scale uniformity Conformal layering Sharp interfaces Diverse sizes and shapes can be coated ALD limitations Speed (slow) Precursors, some dont exist, some are expensive, some toxic [1, 5-6]

8 Limits of thickness 1: nanolaminate
Critical thickness Nanolaminate property (mechanical, elecrical etc.) related Optimum bilayer thickness for spesific property AlN/TiN hardness maximum when AlN 2 nm TiO2 amorphous between 2,5 and 9 nm Critical thickness, something that just has to be fulfilled: Nanolaminate property (mechanical, elecrical etc.) related Optimum bilayer thickness for spesific property AlN/TiN hardness maximum when AlN 2 nm TiO2 amorphous between 2,5 and 9 nm [8, 16-17]

9 Limits of thickness 2: thick ALD
Defects and imperfections multiply (in crystalline) Surface roughness increases Unwanted-wanted depending on application Faceting increases layers in the stack not parallel with the substrate Stresses, cracks Some of the problems can be avoided by amorphous layer crystalline/amorphous bilayer nanolaminate see example 1 When thickness increases, problems: -Defects and imperfections multiply in crystalline films -Surface roughness increases -Unwanted in most applications such as optical applications (refractive index) Wanted in gas sensors (large area) -Faceting increases, the case of crystalline layers, the development of faceting will ultimately limit the ability to keep the layers in the stack parallel with the substrate Stresses, cracks These can be avoided by using a thin amorphous layer -Crystalline/amorphous bilayer nanolaminate -see example 1 [1, 5, 8]

10 ALD process: example 1 ZnO2/Al2O3 nanolaminates Process
ZnO polycrystalline electric conductor Al2O3 amorphous insulator Process Diethyl zinc (DEZ), trimethyl aluminum (TMA) and H2O 1-128 bilayers Deposited at 177 C ZnO2/Al2O3 nanolaminates -ZnO conducting, polycrystalline film -rough surface topography, used in gas sensors -Al2O3 insulating, -amorphous film with high conformality Process Diethyl zinc (DEZ), trimethyl aluminum (TMA) and H2O Silicon substrate 1-128 bilayers Deposited at 177 C on silicon substrate [1]

11 ALD process: example 1 Results Speed of growth similar to normal ALD
Surface roughness: from 6 to 0,2 Minimum Al2O3 needed: one monolayer Results Speed of growth similar to normal ALD (2,01 for ZinkOXIDE and 1,29 Å/cycle for ALUOXIDE) Surface roughness: for ZnO up to 6 from 1.45 nm at 1 bilayer to 0.2 nm at 128 bilayers Minimum Al2O3 needed: one monolayer [1]

12 Limits of thickness 3: thin ALD
Basically monolayer by monolayer but: the surface is only gradually converted from into actual film adsorption, limited number of reactive sites, density of reactive sites on substrate and film Nucleation phenomena islands especially in polycrystalline films can affect the growth (unperfect films) W on Al2O3 limits the minimum thickness of a continuous W nanolayer to ~25Å When thickness decreases: problems Basically monolayer by monolayer but reactant molecule will adsorb onto the substrate, and after some time, will react to form the film The outermost surface is gradually converted from pre-deposited substrates into an actual film limited number of reactive sites density of reactive sites on the underlying surface and films surface itself can be different Nucleation phenomena nucleation especially in case of polycrystalline films, islands etc. can critically affect the growth of thin nanolaminates W on Al2O3 limits the minimum thickness of a continuous W nanolayer to ~25Å [5-6,17-18]

13 ALD modelling : example 2
Hypothesis: Reactant adsorption depends on properties of the surface and absorbant The surface changes during the initial deposition from substrate to film Difference between initial stage and the stabilized stage Film thickness is not linearly dependent of cycles during the first few The film thickness becomes linearly dependent After the initial cycles Hypothesis: The probability of reactant adsorption depends on: The properties of the surface and absorbant The surface changes during the initial deposition Substrate to film Thus differences exist between The initial stage and the stabilized stage of ALD The film thickness is not linearly dependent Of deposition cycles during the first few deposition cycles The film thickness becomes linearly dependent After the initial cycles [17-18]

14 ALD modelling : example 2
Results On the left, the results of the proposed modelling, Transient region -starting growths, not linear Converged region -linear On the right model tested in: TiN-ALD using TDMAT and NH3 as the reactant gases. [17-18]

15 Limits of thickness 3: process
Chamber atmosphere Optimum temperature/pressure window for each layer No unwanted growth, thickness control Precursors Temperature, dependence of the substrate self-decomposition and residues need to be avoided Substrates Oxide or stripped affects growth mode Amorphous or crystalline (surface roughness limitations) Speed = time = money ALD is slow to be economical (but batch processing) Typically few nm/min Process parameters are limiting factors for thickness control, compostion crystall structureetc. Chamber atmosphere Optimum temperature/pressure window for each layer (crystal structure) No unwanted growth, thickness control Precursors Temperature, dependence of the substrate self-decomposition and residues need to be avoided Substrates Oxide or stripped affects growth mode Amorphous or crystalline (surface roughness limitations) Speed = time = money ALD is slow to be economical (but batch processing) Typically few nm/min [1, 5, 13-16]

16 Conclusions Nanolaminates by ALD: But layer thickness is limited by:
Tailored properties (mechanical, electrical etc.) Controlled growth, conformality From thin gate oxides to thick tool coatings But layer thickness is limited by: Critical thickness Defects and imperfections Surface roughness and faceting Stresses (thermal, thickness related) Non-linear growth in the beginning Process parameters

17 THANK YOU FOR LISTENING! QUESTIONS?

18 References 1: J.W. Elam, Z.A. Sechrist, S.M. George, ZnO/Al2O3 nanolaminates fabricated by atomic layer deposition: growth and surface roughness measurements, Thin Solid Films 414 (2002) 43–55  2: Yong Shin Kim, Sun Jin Yun, Nanolaminated Al2O3–TiO2 thin films grown by atomic layer deposition, Journal of Crystal Growth 274 (2005) 585–593 3: Philip C. Yashar,William D. Sproul, Nanometer scale multilayered hard coatings, Vacuum 55 (1999) 179}190 4: Lijuan Zhong, Fang Chen, Stephen A. Campbell, and Wayne L. Gladfelter ,Nanolaminates of Zirconia and Silica Using Atomic Layer Deposition, Chem. Mater. 2004, 16, 5: Markku Leskelä, Industrial Applications of Atomic Layer Deposition (ALD), 10th MIICS Conference Mikkeli, March 18, 2010 6: J. M. Jensen, A. B. Oelkers, R. Toivola, and D. C. Johnson, X-ray Reflectivity Characterization of ZnO/Al2O3Multilayers Prepared by Atomic Layer Deposition, Chem. Mater. 2002, 14, 7: R. M. Costescu, D. G. Cahill, F. H. Fabreguette, Z. A. Sechrist, S. M. George, Ultra-Low Thermal Conductivity in W/Al2O3 Nanolaminates, Science 303, 989 (2004) 8:, D.R.G. Mitchell*, D.J. Attard, K.S. Finnie, G. Triani, C.J. Barbe´, C. Depagne, J.R. Bartlett TEM and ellipsometry studies of nanolaminate oxide films prepared using atomic layer deposition, Applied Surface Science 243 (2005) 265–277 9: T.M. Mayer, T.W. Scharf, S.V. Prasad, N.R. Moody, R.S. Goeke, M.T. Dugger, R.K. Grubbs, S. M. George, R.A. Wind, J.M. Jungk, W.W. Gerberich, Atomic Layer Deposition of Highly Conformal Tribological Coatings, SANDIA REPORT 2005 10: Dr. Troy Barbee, Optical applications of nano-laminates, Technology Days in the Government Mirror Development and Related Technologies

19 References  11: Diana Riihelä, Mikko Ritala , Raija Matero, Markku Leskelä, Electronics, Optics and Opto-electronics, Introducing atomic layer epitaxy for the deposition of optical thin films, Thin Solid Films 289 (1996) 12: H. Zhang and R. Solankia, B. Roberds, G. Bai, and I. Banerjee, High permittivity thin film nanolaminates, JOURNAL OF APPLIED PHYSICS 13: Lijuan Zhong, Weston L. Daniel, Zhihong Zhang, Stephen A. Campbell, and Wayne L. Gladfelter , Atomic Layer Deposition, Characterization, and Dielectric Properties of HfO2/SiO2 Nanolaminates and Comparisons with Their Homogeneous Mixtures. Chem. Vap. Deposition 2006, 12, 143–150 14: H. Zhang and R. Solankiz, Atomic Layer Deposition of High Dielectric Constant Nanolaminates, Journal of The Electrochemical Society, 15: Kijung Yong and Joonhee Jeong , Applications of Atomic Layer Chemical Vapor Deposition for the Processing of Nanolaminate Structures, Korean d. Chem. Eng., 19(3), (2002) 16: Steven M. George, Fabrication of Nanolaminates with Ultrathin Nanolayers Using Atomic Layer Deposition: Nucleation & Growth Issues, AFOSR Grant No. FA , Final Report 2009 17: Jung-Wook Lim, Hyung-Sang Park, and Sang-Won Kang, Kinetic Modeling of Film Growth Rate in Atomic Layer Deposition, Journal of The Electrochemical Society, C403-C 18: Jung-Wook Lim, Hyung-Sang Park, and Sang-Won Kang, Analysis of a transient region during the initial stage of atomic layer deposition JOURNAL OF APPLIED PHYSICS 88 (11) 2000


Download ppt "What is the limit of nanolaminate layer thickness in ALD"

Similar presentations


Ads by Google