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X-ray asterism and the structure of cracks from indentations in silicon

DOI: 10.1107/S1600576715024620 DOI Help

Authors: B. K Tanner (University of Durham) , J. Garagorri (CEIT Technun (University of Navarra)) , E. Gorostegui-colinas (Universidad de Navarra Education CEIT) , M. R. Elizalde (University of Navarra) , D. Allen (Dublin City University) , P. J. Mcnally (Dublin City University) , J. Wittge (University of Freiburg) , C. Ehlers (University of Freiburg) , A. N. Danilewsky (Albert-Ludwigs-Universit├Ąt)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Journal Of Applied Crystallography , VOL 49 , PAGES 250 - 259

State: Published (Approved)
Published: February 2016
Diamond Proposal Number(s): 7634

Abstract: The asterism observed in white radiation X-ray diffraction images (topographs) of extended cracks in silicon is investigated and found to be associated with material that is close to break-out and surrounded by extensive cracking. It is a measure of the mechanical damage occurring when the fracture planes do not follow the low index cleavage planes associated with the crystal structure. It is not related to a propensity for some cracked wafers to shatter during subsequent high temperature processing. There is no correlation between crack morphology and alignment of an indenter with respect to the orientation of a silicon wafer, the cracks being generated from the apices of the indenter and having three-fold symmetry for Berkovich indents and four-fold symmetry for Vickers indents. X-ray diffraction images (XRDI) of indents do not reveal this underlying symmetry and exhibit a very substantial degree of variation in their extent. These arise because the XRDI contrast is sensitive to the long range strain field around the indent and break-out reduces the extent of this long rage strain field. Break-out is also detected in the loss of symmetry in the short range strain field imaged by scanning micro-Raman spectroscopy. Weak four-fold symmetric features at the extremes of the images, and lying along <110> directions, are discussed in the context of slip generated below the room-temperature indents. Scanning electron microscopy imaging of the region around an indent during focused ion beam milling has permitted the three dimensional reconstruction of the crack morphology. The surface-breaking Palmqvist cracks are found to be directly connected to the median sub-surface cracks and the presence of extensive lateral cracks is a prerequisite for material break-out at indenter loads above 200 mN. The overall crack shape agrees with that predicted from simulation.

Journal Keywords: X-ray diffraction imaging; X-ray asterism; cracks; silicon; indentation

Subject Areas: Materials, Physics

Instruments: B16-Test Beamline

Other Facilities: ANKA, Karlsruhe