Laser Assisted SiC Wafering Using COLD SPLIT

Kerf-free wafering techniques hold the potential to drastically reduce material losses in semiconductor manufacturing processes. Spalling processes use externally applied stresses to separate crystalline materials along crystal planes with well-defined thickness. Spalled substrates, however, exhibit striations from crack propagation along the crystal, a pattern called Wallner lines. Here, we demonstrate a wafering process that scales favorably for SiC substrates starting from 1 inch in diameter. To eliminate the Wallner line pattern, we use a laser-conditioning process with high numerical aperture at photon energies below the material bandgap energy, using multi-photon effects. The process leads to SiC surfaces with a roughness after spalling of Ra< 4μm.

Stress Waves and Fracture Surfaces

Surface markings observed in the brittle fracture of certain frozen rubbers display striking, wavelike characteristics. They have been identified as “Wallner” lines, caused by the interaction of the fracture front with stress waves emanating from the region of the fracture front itself. These oscillations are possibly caused by the supply of excess energy to the fracture tip. A value of approximately 1:2 is obtained for the ratio of fracture velocity to wave velocity.