Nanostructured back surface amorphization of silicon with picosecond laser pulses

Laser-based amorphization on the back surface of a 525- μm thick crystalline silicon sample is studied. To deposit sufficient energy for a local change from a crystalline to an amorphous state, laser irradiation at 2- μm wavelength with 25-ps pulse duration is combined with Bessel beam shaping. Deterministic single-site modifications and homogeneous continuous lines of amorphous silicon are demonstrated. Optical and electron microscopy together with Raman spectroscopy measurements highlight the material transformations featuring the formation of subwavelength periodic surface structures. The investigations open up possibilities for processing in-built microelectronic devices.