Physical mechanisms behind the ion-cut in hydrogen implanted silicon

Hydrogen implanted silicon has been shown to cleave upon annealing, thus facilitating the transfer of thin silicon slices to other substrates, a process known as “ion-cut.” In our experiments 〈100〉 silicon wafers were implanted with 40 keV protons to a variety of ion doses ranging from 1×1016 to 1×1017 cm−2 and subsequently annealed at 600 °C. The samples were studied before and after annealing by a combination of Rutherford backscattering spectroscopy in channeling mode, elastic recoil detection analysis, atomic force microscopy, and electron microscopy. Mechanical stresses in the material, caused by proton irradiation, were determined by measuring changes in curvature of the silicon samples utilizing a laser scanning setup. For H doses of ⩾5×1016 cm−2 ion cutting in the form of “popping off” discrete blisters was obtained. Our analyses of the cleavage mechanisms had shown that the ion-cut location in silicon is largely controlled by the lattice damage that is generated by the H implantation process. At lower H doses, the location of the cut correlates well with the damage peak and can be explained by damage induced in-plane stress and the corresponding elastic out-of-plane strain. However, at higher implantation doses the ion-cut location shifts toward a deeper region, which contains lower damage and a sufficient concentration of H. This effect can be explained by a rapid decrease of the elastic out-of-plane strain coinciding with changing fracture mechanics at high H concentrations in heavily damaged silicon.