Energy considerations in crack deflection phenomenon in single crystal silicon

Abstract

Crack deflection in single-crystal brittle occurs when a crack, propagating on one cleavage plane, 'chooses', from energy considerations, to continue propagating on another cleavage plane. This phenomenon was identified during dynamic crack propagation experiments of thin, rectangular [0 0 1] single-crystal (SC) silicon specimens subjected to three-point bending (3PB). Specimens with long pre-cracks (hence propagating at a 'low' energy and velocity) cleave along the vertical (1 1 0) plane, while the same specimens but with short pre-cracks (and therefore with higher propagation energy and velocity) cleave along the inclined (1 1 1) plane. The same specimens with intermediate pre-crack length show that the crack first propagates on the (1 1 0) plane and then deflects to the (1 1 1) plane. We show that the deflection is due to variations of the material property that resists cracking, , the dynamic cleavage energy, with velocity and crystallographic orientation. We propose selection criteria to explain the deflection: The crack will deflect to the plane with the lowest dynamic cleavage energy. We further suggest that crack deflection is the basic mechanism controlling the way the crack consumes energy while propagating and is the main cause of surface perturbations.The spatial temporal fracture energy along the (1 1 0) cleavage plane is evaluated.

Bifurcation and Deviation of Cleavage Paths at Through-Thickness Grain Boundaries

“…Because cleavage cracking in silicon can take place on both {111} and {110} planes and the surface free energies of them are only slightly different, [7,8] within the same crystal, the crack surface may shift among cleavage facets that are of similar orientations, resulting in relatively wavy flanks. Once the crack front reaches a grain boundary, if the orientations of the two grains are considerably different, especially when the twist misorientation angle is relatively large, the crack must overcome a significant barrier effect to enter into the next grain.…”

Cracks observed to propagate discontinuously on the millisecond timescale

“…, many orders of magnitude below that described by Sherman (2006). However, the images show that the crack moves in a series of jumps in which the crack moves at a speed greater than the 6 m s À1 resolution limit, followed by a stop time of between 1 and 2 ms.…”

“…The result is that the larger surface area of the {111} planes increases the cleavage energy by a factor of 1.225, making fracture on the {110} planes favourable, as is observed during the fabrication of semiconductor device die and microelectromechanical sensor (MEMS) devices. This {110} cleavage occurs for low crack velocities (below about 1500 m s À1 ), but when the crack velocity becomes high, (above about 3000 m s À1 ), propagation entirely on the {111} planes is observed (Sherman, 2006). At intermediate velocities, propagation starts on the {110} planes but then switches to {111}, driven, it is suggested, by the energetics of phonon emission.…”

An initiative to develop a new approach for fracture characterization of silicon die crack

“…[7,8]. Furthermore, many theoretical studies have also shown that when Si is subjected to mechanical stresses at ambient temperature, it will cleave in the planes with the low bond densities into {111} as the most preferred cleavage plane before propagating in the <110> or <112> directions [9][10][11]. Therefore, the different fracture planes will have different bond densities, resulting in different fracture strength.…”