Electron backscatter diffraction (EBSD)

From Semiconductor Spectroscopy and Devices

The acquisition of electron backscattered diffraction (EBSD) (or backscatter Kikuchi diffraction) patterns in the scanning electron microscope is a very powerful method for the microstructural characterisation of crystalline materials. EBSD is presently used predominantly in metallurgy [1], being applied to the measurement of texture, i.e., the mapping of the orientation of individual grains in polycrystalline material [1-2], and for the identification of the phase of crystallites whose composition have been identified previously by x-ray spectrometry [3]. Wilkinson [4] and Troost et al [5] have applied EBSD to the measurement of strain in SiGe epilayers, while Baba-Kishi [6] has used EBSD to investigate crystallographic polarity in zincblende-type structures. Their results make EBSD an attractive technique to adapt for the characterisation of nitride thin films.

Schematic diagram of EBSD system

Our EBSD system is illustrated above. In the present work the SEM is a Cambridge 600S and the EBSD system is home built. The 40 mm diameter phosphor screen is used to intercept the backscattered electrons diffracted from the sample and an EBSD pattern is formed on the phosphor screen. An image of the EBSD pattern is then acquired using a video imaging system interfaced to a PC.

The formation of Kikuchi lines

The EBSD pattern constitutes a number of Kikuchi bands. Each band comprises a pair of parallel Kikuchi lines the formation of which is illustrated above. Backscattered electrons that satisfy Bragg's law for a given plane emanate in diffraction cones from both the front and back surface of the plane. When these cones intersect the phosphor screen the Kikuchi lines are formed. The Kikuchi lines appear as almost straight lines because the cones are very shallow as the Bragg angle θ_D is of order 1° (λ ≈ 0.008 nm for a 25 keV electron beam). Each Kikuchi band is effectively the trace of the plane from which it is formed, the EBSD pattern is therefore a 2-D projection (in fact the gnomic projection) of the crystal structure. Each Kikuchi band subtends an angle of 2θ_D with the sample [5].

The images below show EBSD patterns taken from a gallium nitride sample (left) and from its sapphire substrate (right).

EBSD Patterns from (a) the GaN epilayer and (b) its sapphire substrate

Some of our publications:

1. Carol Trager-Cowan, J-F Treguer, S T F Grimson, I Osborne, M Barisonzi, P G Middleton, S K Manson-Smith, A Mohammed, K P O'Donnell, W Van der Stricht, K Jacobs, I Moerman, P Demeester, M F Wu and A Vantomme, Probing nitride thin films in 3-dimensions using a variable energy electron beam, Electron Microscopy and Analysis 161, 91-94 (1999)

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2. Carol Trager-Cowan, D. McColl, F. Sweeney, S. T. F. Grimson, J-F. Treguer, A. Mohammed, P. G. Middleton, S. K. Manson-Smith, K. P. O'Donnell, W. Van der Stricht, I. Moerman and P. Demeester, M. F. Wu, A. Vantomme, D. Zubia and S. D. Hersee,Probing Nitride Thin Films in 3-Dimensions using a Variable Energy Electron Beam, Mat. Res. Soc. Symp. 595, W5.10 (2000) and MRS Internet J. Nitride Semicond. Res. 5S1, W5.10. (2000)

http://nsr.mij.mrs.org/5S1/W5.10/

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3. C. Trager-Cowan, S.K. Manson-Smith, D.A. Cowan, F. Sweeney, D. McColl, A. Mohammed, R. Timm, P.G. Middleton, K.P. O'Donnell, D. Zubia, and S.D. Hersee, Characterisation of nitride thin films by electron backscattered diffraction, to be published in Materials Science and Engineering B.

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References

[1] D.J. Dingley, V. Randle, Journal of Materials Science 27 (1992) 4545.

[2] V. Randle, Microtexture determination and its applications, The Inst. of Materials, London, 1992.

[3] R.P. Goehner, J.R. Michael, J. Res. Natl. Inst. Stand. Technol. 101 (1996) 301.

[4] Angus J. Wilkinson, Ultramicroscopy 62 (1996) 237.

[5] K.Z. Troost. P. van der Sluis, D.J. Gravesteijn, Appl. Phys. Lett. 62 (1993) 1110.

[6] K.Z. Baba-Kishi, J. Appl. Cryst. 24 (1991) 38.

[7] S. Nakamura, G. Fasol, The Blue Laser Diode, Springer, Berlin, 1997, pp23.

[8] D.J. Dingley, K. Z. Baba-Kishi, V. Randle, Atlas of backscattering Kikuchi diffraction patterns, IOP, Bristol, 1995.

[9] K.W. Andrews, D.J. Dyson, S. R. Keown, Interpretation of Electron Diffraction Patterns, Hilger & Watts Ltd, London, 1967.