Laser-induced lattice tensile strain in silicon

Raman scattering measurements have been carried out on Si samples annealed with various energy densities using a free-running pulsed laser with a typical pulse-train length of 0.4 ms. The phonon frequency shifts Δω (relative to unannealed Si) observed up to −2.9 cm−1 are ascribed to the presence of lattice tensile strains in the annealed regions. The maximum lattice tensile strain of 3.9×10−3, inferred from the maximum Δω measured, could be released completely if the annealed regions were to form cracks running parallel to the crystal axes. To explain the data, a new lattice-straining mechanism based on a change in the lattice constant of Si during the crystal regrowth is proposed.