Dynamic deformation and fracture of single crystal silicon: Fracture modes, damage laws, and anisotropy

• Published in: Acta materialia 2016-08, Vol.114 (C), p.136-145
• Main Authors: Huang, J.Y., E, J.C., Huang, J.W., Sun, T., Fezzaa, K., Xu, S.L., Luo, S.N.
• Format: Article
• Language: English
• Subjects: Cleavage; Cracking (fracturing); Damage; Diffraction; Dynamic fracture; Fracture mechanics; Imaging; Laue diffraction; MATERIALS SCIENCE; Semiconductors; Silicon; Single crystals; Single-crystal Si; X-ray imaging
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2016.05.022

Impact fracture of single-crystal Si is critical to long-term reliability of electronic devices and solar cells for its wide use as components or substrates in semiconductor industry. Single-crystal Si is loaded along two different crystallographic directions with a split Hopkinson pressure bar integrated with an in situ x-ray imaging and diffraction system. Bulk stress histories are measured, simultaneously with x-ray phase contrast imaging (XPCI) and Laue diffraction. Damage evolution is quantified with grayscale maps from XPCI. Single-crystal Si exhibits pronounced anisotropy in fracture modes, and thus fracture strengths and damage evolution. For loading along [11¯ 0] and viewing along [001], (1¯1¯0)[11¯ 0] cleavage is activated and induces horizontal primary cracks followed by perpendicular wing cracks. However, for loading along [011¯] and viewing along [111], random nucleation and growth of shear and tensile-splitting crack networks lead to catastrophic failure of materials with no cleavage. The primary-wing crack mode leads to a lower characteristic fracture strength due to predamage, but a more concentrated strength distribution, i.e., a higher Weibull modulus, compared to the second loading case. Moreover, the sequential primary cracking, wing cracking and wing-crack coalescence processes result in a gradual increase of damage with time, deviating from theoretical predictions. Particle size and aspect ratios of fragments are discussed with postmortem fragment analysis, which verifies fracture modes observed in XPCI. [Display omitted]