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Fiber Textures: application to thin film textures

Fiber Textures: application to thin film textures. 27-750, Spring 2007 A. D. (Tony) Rollett, A. Gungor & K. Barmak. Acknowledgement : the data for these examples were provided by Ali Gungor; extensive discussions with Ali and his advisor, Prof. K. Barmak are gratefully acknowledged.

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Fiber Textures: application to thin film textures

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  1. Fiber Textures: application to thin film textures 27-750, Spring 2007 A. D. (Tony) Rollett, A. Gungor & K. Barmak Acknowledgement: the data for these examples were provided by Ali Gungor; extensive discussions with Ali and his advisor, Prof. K. Barmak are gratefully acknowledged.

  2. Example 1: Interconnect Lifetimes • Thin (1 µm or less) metallic lines used in microcircuitry to connect one part of a circuit with another. • Current densities (~106 A.cm-2) are very high so that electromigration produces significant mass transport. • Failure by void accumulation often associated with grain boundaries Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  3. Interconnects provide a pathway to communicate binary signals from one device or circuit to another. Issues: - Performance - Reliability A MOS transistor (Harper and Rodbell, 1997) Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  4. e- extrusion void vacancy diffusion mass diffusion Reliability: Electromigration Resistance • Promote electromigration • resistance via microstructure • control: • Strong texture • Large grain size • (Vaidya and Sinha, 1981) Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  5. Top view (111) _ _ - (111) (111) e Grain Orientation and Electromigration Voids • Special transport properties on certain lattice planes cause void faceting and spreading • Voids along interconnect direction vs. fatal voids across the linewidth Slide courtesy of X. Chu and C.L. Bauer, 1999. Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  6. Al Interconnect Lifetime Stronger <111> fiber texture gives longer lifetime, i.e. more electromigration resistance H.T. Jeong et al. Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  7. References • H.T. Jeong et al., “A role of texture and orientation clustering on electromigration failure of aluminum interconnects,” ICOTOM-12, Montreal, Canada, p 1369 (1999). • D.B. Knorr, D.P. Tracy and K.P. Rodbell, “Correlation of texture with electromigration behavior in Al metallization”, Appl. Phys. Lett., 59, 3241 (1991). • D.B. Knorr, K.P. Rodbell, “The role of texture in the electromigration behavior of pure Al lines,” J. Appl. Phys., 79, 2409 (1996). • A. Gungor, K. Barmak, A.D. Rollett, C. Cabral Jr. and J.M. E. Harper, “Texture and resistivity of dilute binary Cu(Al), Cu(In), Cu(Ti), Cu(Nb), Cu(Ir) and Cu(W) alloy thin films," J. Vac. Sci. Technology, B 20(6), p 2314-2319 (Nov/Dec 2002). -> YBCO textures Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  8. Lecture Objectives • Give examples of experimental textures of thin copper films; illustrate the OD representation for a simple case. • Explain (some aspects of) a fiber texture. • Show how to calculate volume fractions associated with each fiber component from inverse pole figures (from ODF). • Explain use of high resolution pole plots, and analysis of results. • Give examples of the relevance and importance of textures in thin films, such as metallic interconnects, high temperature superconductors and magnetic thin films. Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  9. Fiber Textures • Common definition of a fiber texture: circular symmetry about some sample axis. • Better definition: there exists an axis of infinite cyclic symmetry, C, (cylindrical symmetry) in either sample coordinates or in crystal coordinates. • Example: fiber texture in two different thin copper films: strong <111> and mixed <111> and <100>. Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  10. Source: research by Ali Gungor, CMU C film substrate 2 copper thin films, vapor deposited:e1992: mixed <100> & <111>; e1997: strong <111> Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  11. Method 1:Experimental Pole Figures: e1992 Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  12. Recalculated Pole Figures: e1992 Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  13. COD: e1992: polar plots:Note rings in each section Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  14. SOD: e1992: polar plots:note similarity of sections Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  15. Crystallite Orientation Distribution:e1992 1. Lines on constant Qcorrespond to rings inpole figure 2. Maxima along top edge = <100>; <111> maxima on Q= 55° (f = 45°) Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  16. Sample Orientation Distribution: e1992 1. Self-similar sections indicate fiber texture:lack of variation withfirst angle (y). 2. Maxima along top edge -> <100>; <111> maxima on Q= 55°, f = 45° Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  17. Experimental Pole Figures: e1997 Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  18. Recalculated Pole Figures: e1997 Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  19. COD: e1997: polar plots:Note rings in 40, 50° sections Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  20. SOD: e1997: polar plots:note similarity of sections Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  21. Crystal Orientation Distribution: e1997 1. Lines on constant Qcorrespond to rings inpole figure 2. <111> maximumon Q= 55° (f = 45°) Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  22. Sample Orientation Distribution: e1997 1. Self-similar sections indicate fiber texture:lack of variation withfirst angle (y). 2. Maxima on <111> on Q= 55°, f = 45°,only! Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  23. Fiber Locations in SOD [Jae-Hyung Cho, 2002] <100>fiber <110>fiber <100>,<111>and<110>fibers <111>fiber Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  24. Inverse Pole Figures: e1997 Slight in-plane anisotropy revealed by theinverse pole figures.Very small fraction of non-<111> fiber. Electromigration Weak Strong IPF VolumeFraction PolePlot Deconvolution

  25. Inverse Pole figures: e1992  <111> <11n> <001> <110> F TransverseDirectionTD NormalDirectionND RollingDirectionRD Electromigration Weak StrongIPF VolumeFraction PolePlot Deconvolution

  26. Method 1: Volume fractions from IPF • Volume fractions can be calculated from an inverse pole figure (IPF). • Step 1: obtain IPF for the sample axis parallel to the C symmetry axis. • Normalize the intensity, I, according to 1 = SI() sin() dd • Partition the IPF according to components of interest. • Integrate intensities over each component area (i.e. choose the range of  and ) and calculate volume fractions:Vi = SiI()sin() dd Electromigration Weak StrongIPF VolumeFraction PolePlot Deconvolution

  27. Method 2: Pole plots • If a perfect fiber exists (C, aligned with the film plane normal) then it is enough to scan over the tilt angle only and make a pole plot. • High resolution is then feasible, compared to standard 5°x5° pole figures, e.g 0.1°. • High resolution inverse PF preferable but not measurable. Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  28. Intensityalong aline fromthe centerof the {001}polefigureto theedge(any azimuth) e1992: <100> & <111> e1997: strong 111 Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  29. High Resolution Pole plots e1997: pure <111>; very small fractions other? e1992: mixture of <100>and <111> ∆tilt = 0.1° Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  30. Volume fractions • Pole plots (1D variation of intensity):If regions in the plot can be identified as being uniquely associated with a particular volume fraction, then an integration can be performed to find an area under the curve. • The volume fraction is then the sum of the associated areas divided by the total area. • Else, deconvolution required. Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  31. Example for thin Cu films <100> <111> Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  32. Log scale for Intensity: e1997 NB: Intensities not normalized Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  33. Area under the Curve • Tilt Angle equivalent to second Eulerangle, q F• Requirement: 1 = S I(q)sin(q) dq; qmeasured in radians. • Intensity as supplied not normalized. • Problem: data only available to 85°: therefore correct for finite range.• Defocusing neglected. Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  34. Extract Random Fraction Mixed <100>and <111>,e1992 Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  35. Normalized Randomcomponentnegligible~ 4% Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  36. Deconvolution • Method is based on identifying each peak in the pole plot, fitting a Gaussian to it, and then checking the sum of the individual components for agreement with the experimental data. • Areas under each peak are calculated. • Corrections must be made for multiplicities. Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  37. {111} Pole Plot <111> <100> <110> A3 A2 A1 q Ai = Si I(qsinq dq Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  38. {111} Pole Plot: Comparison of Experiment with Calculation Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  39. {100} Pole figure: pole multiplicity:6 poles for each grain <100> fiber component <111> fiber component North Pole South Pole 3 poles on each of two rings, at ~55° from NP & SP 4 poles on the equator;1 pole at NP; 1 at SP Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  40. {100} Pole figure: Pole Figure Projection (010) The number of poles present in a pole figure is proportional to the number of grains (-100) (100) (001) (001) (100) (010) (0-10) <100> oriented grain: 1 pole in the center, 4 on the equator <111> oriented grain: 3 poles on the 55° ring. Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  41. {111} Pole figure: pole multiplicity:8 poles for each grain <100> fiber component <111> fiber component 1 pole at NP; 1 at SP3 poles on each of two rings, at ~70° from NP & SP 4 poles on each of two rings, at ~55° from NP & SP Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  42. {111} Pole figure: Pole Figure Projection (-111) (111) (-111) (1-11) (001) (111) (-1-11) (1-11) (-1-11) <100> oriented grain: 4 poles on the 55° ring <111> oriented grain: 1 pole at the center, 3 poles on the 70° ring. Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  43. {111} Pole figure: Pole Plot Areas • After integrating the area under each of the peaks (see slide 35), the multiplicity of each ring must be accounted for. • Therefore, for the <111> oriented material, we have 3A1 = A3;for a volume fraction v100of <100> oriented material compared to a volume fraction v111 of <111> fiber,3A2 / 4A3 = v100 /v111and,A2 / {A1+A3} = v100 /v111 Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  44. Intensities, densities in PFs • Volume fraction = number of grains  total grains. • Number of poles = grains * multiplicity • Multiplicity for {100} = 6; for {111} = 8. • Intensity = number of poles  area • For (unit radius) azimuth, f, and declination (from NP), q, area, dA = sinq dq df. Electromigration Weak StrongIPFVolumeFraction PolePlot Deconvolution

  45. High Temperature Superconductors: an example Theoreticalpole figuresfor c & a 

  46. YBCO (123) on various substrates Various epitaxialrelationshipsapparent fromthe pole figures

  47. Scan with ∆a = 0.5°, ∆b = 0.2° Azimuth, b Tilta

  48. Dependence of film orientation on deposition temperature Ref: Heidelbach, F., H.-R. Wenk, R. E. Muenchausen, R. E. Foltyn, N. Nogar and A. D. Rollett (1996), Textures of laser ablated thin films of YBa2Cu3O7-d as a function of deposition temperature. J. Mater. Res., 7, 549-557. Impact: superconduction occurs in the c-plane;therefore c epitaxy is highly advantageous tothe electrical properties of the film.

  49. Summary: Fiber Textures • Extraction of volume fractions possible provided that fiber texture established. • Fractions from IPF simple but resolution limited by resolution of OD. • Pole plot shows entire texture. • Random fraction can always be extracted. • Specific fiber components may require deconvolution when the peaks overlap. • Calculation of volume fraction from pole figures/plots assumes that all corrections have been correctly applied (background subtraction, defocussing, absorption).

  50. Summary: other issues • If epitaxy of any kind occurs between a film and its substrate, the (inevitable) difference in lattice paramter(s) will lead to residual stresses. Differences in thermal expansion will reinforce this. • Residual stresses broaden diffraction peaks and may distort the unit cell (and lower the crystal symmetry), particularly if a high degree of epitaxy exists. • Mosaic spread, or dispersion in orientation is always of interest. In epitaxial films, one may often assume a Gaussian distribution about an ideal component and measure the standard deviation or full-width-half-maximum (FWHM).

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