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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 breakout 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 threefold symmetry for Berkovich indents and fourfold symmetry for Vickers indents. X-ray diffraction imaging (XRDI) of indents does not reveal this underlying symmetry and the images exhibit a very substantial degree of variation in their extent. This arises because the XRDI contrast is sensitive to the long-range strain field around the indent and breakout reduces the extent of this long-range strain field. Breakout is also detected in the loss of symmetry in the short-range strain field imaged by scanning micro-Raman spectroscopy. Weak fourfold 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 subsurface cracks, and the presence of extensive lateral cracks is a prerequisite for material breakout at indenter loads above 200 mN. The overall crack shape agrees with that predicted from simulation. [ABSTRACT FROM AUTHOR]

The geometry of fracture associated with the propagation of cracks originating at the edges of (001) oriented, 200 mm diameter silicon wafers has been investigated under two regimes of high temperature processing. Under spike annealing, fracture did not occur on low index planes and all except one wafer exhibited crack patterns that started initially to run radially, but after a distance of typically 20-30 mm, turned and ran almost tangentially. Wafers subjected to plateau annealing, with a 60 s dwell time at high temperature, predominantly fractured through radial cracks running along $$\langle 110\rangle $$ directions. X-ray diffraction imaging reveals substantial slip in all wafers subjected to plateau annealing. We demonstrate using finite element (FE) modelling that the change in fracture geometry is associated with this plastic deformation, which changes the stress distribution during the cooling phase of the rapid thermal annealing cycle. FE simulations without plastic relaxation show that the radial component of the thermal stress distribution is compressive in the centre of the wafer, causing the crack to run tangentially. Simulations incorporating temperature dependent plasticity showed that the equivalent stress becomes tensile when the plateau anneal allows time for significant plastic relaxation, permitting the crack to continue propagating linearly. [ABSTRACT FROM AUTHOR]

The apparatus for X-ray diffraction imaging (XRDI) of 450-mm wafers, is now placed at the ANKA synchrotron radiation source in Karlsruhe, is described in the context of the drive to inspect wafers for plastic deformation or mechanical damage. It is shown that full wafer maps at high resolution can be expected to take a few hours to record. However, we show from experiments on 200-, 300-, and 450-mm wafers that a perimeter-scan on a 450-mm wafer, to pick up edge damage and edge-originated slip sources, can be achieved in just over 10 min. Experiments at the Diamond Light Source, on wafers still in their cassettes, suggest that clean-room conditions may not be necessary for such characterization. We conclude that scaling up of the 300-mm format Jordan Valley tools, together with the existing facility at ANKA, provides satisfactory capability for future XRDI analysis of 450-mm wafers. [ABSTRACT FROM PUBLISHER]

The article discusses a study of the thermal slip sources (TSS) at the extremity and bevel edge of a silicon wafer (SW). The authors performed rapid thermal annealing (RTA) on a 200-millimeter SW, which showed no edge defects either under optical inspection or X-ray diffraction imaging. They found that the dislocation velocity is constant during slip-band nucleation. They also observed that the majority of TSS appear at the extremity of the SW and are not suppressed by the RTA apparatus.

We show that x-ray diffraction imaging (topography) and finite-element modelling can determine accurately the probability of propagation of individual cracks in brittle single crystal materials. The x-ray image of the crack provides a critical parameter for crack propagation which informs a predictive model, enabling us to identify critical defects that lead to catastrophic shattering of silicon wafers during high temperature thermal processing. Wafers fracture on cooling and finite element modelling shows that, during cooling, the tangential stress at the wafer edge is tensile and results in crack propagation. The predicted fracture geometry agrees extremely well with that observed experimentally. [ABSTRACT FROM AUTHOR]

Abstract: White beam X-ray diffraction imaging (topography) with an optimised CCD-detector system is used to monitor in-situ and in real time the nucleation, growth and movement of dislocations in silicon at high temperatures. It can be shown, that damage like microcracks and the surrounding strain fields in a wafer act as sources for dislocation loops, which end in slip bands far away from the source. The dislocations are arranged in channels of parallel {111} glide planes, which become visible as bands of parallel surface steps when the dislocations slip out on the back or front sides of the wafer. The width of such a channel or band depend on the dimensions of the damaged volume where the dislocations nucleate. This can be explained with a simple geometrical model. [Copyright &y& Elsevier]