THREE-DIMENSIONAL MODIFICATION IN SILICON WITH INFRARED NANOSECOND LASER

Motivated by previous work on three-dimensional (3D) fabrication inside dielectrics, we report experimental results of 3D modification inside intrinsic silicon wafers using laser pulses with 1.55 gm wavelength and 3.5 ns pulse duration. Permanent modification in the form of lines is generated inside silicon by tightly focusing and continuously scanning the laser beam inside samples, without introducing surface damage. Cross sections of these lines are observed after cleaving the samples, and are further analyzed after mechanical polishing followed by chemical etching. With the objective lens corrected for spherical aberration, tight focusing inside silicon is achieved and the optimal focal depth is identified. The laser-induced modification has a triangular shape and appears in front of the geometrical focus, suggesting significant absorption in those regions and resulting in reduced energy density. The morphology of modified regions is found to be dependent on the laser polarization.