Thermo-Elastic-Plastic Analysis on Internal Processing Phenomena of Single-Crystal Silicon by Nanosecond Laser

When a nanosecond pulse laser is irradiated into a single crystal silicon, a local area near the focal point is melted and solidified, and internal cracks develop from this modified layer to the surrounding single crystal layer. This processing is applied to a dicing of silicon wafer, which is called stealth dicing (SD) and attracts attention in industries of semiconductor. A light of 1064 nm penetrates usually through a single crystal silicon. When a pulsed laser of this wavelength with high pulse energy is focused up to near the diffraction limit inside the silicon, however, strong absorption occurs near the focal point. This phenomenon depends on not only increase of beam intensity by focusing but also the temperature dependence of absorption coefficient. We conducted the thermo-elastic-plastic analysis by the finite element method, and calculated the stress intensity factor. As a result, the stress intensity factor exceeds the fracture toughness of a silicon. This result suggests the possibility of crack development from the modified layer to the surrounding single crystal layer.