Abstract
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.
Highlights
Wafer breakage during high temperature processing is a multi-million dollar problem in semiconductor manufacturing lines, the prime cost being in loss of product during the time taken to stop the line, recover the broken wafer, clean and restart the affected tool
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
We show that the two different fracture modes are related to plastic relaxation occurring, or not occurring, during the dwell time at high temperature
Summary
Wafer breakage during high temperature processing is a multi-million dollar problem in semiconductor manufacturing lines, the prime cost being in loss of product during the time taken to stop the line, recover the broken wafer, clean and restart the affected tool. Rather than rely on statistical approaches (Cook 2006; Brun and Melkote 2009), we have developed an X-ray diffraction imaging (XRDI) technique for assessing the probability that individual cracks will propagate (Tanner et al 2012). This methodology underpins commercial XRDI products on the market. We show that the two different fracture modes are related to plastic relaxation occurring, or not occurring, during the dwell time at high temperature
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