High-energy femtosecond pulsed laser micromachining of thin film deposited silicon in self-focused air medium

Abstract

The ultrashort pulsed laser ablation of silicon wafers deposited with 1 m thin film of SiC was performed in air medium using a 1 mJ, 120 fs, 800 nm Ti:sapphire laser, the objective being to determine the self-focusing capability of air to produce nanostructures. The effects of pulse energy, the number of pulses, pulse repetition rate and x-y translation speed on the size, shape, and thermal damage of holes and grooves were evaluated. In addition, a 200 ns pulsed, 1064 nm Nd:yttritiumaluminum-garnet laser was used to process grooves and the results were compared against those processed by the femtosecond pulses. Results show that holes as small as 1 m were produced with femtosecond pulses using the self-action property of air. Despite the capability of air medium to produce tiny holes of a few micron diameters, the shape of the hole is highly asymmetrical due to the beam profile distortion. The critical laser power for nonlinear effects of air to become effective was calculated as 40 MW. However, both the beneficial and deleterious effects of air were not found when the peak power of laser beam was under 2 GW. A comparison of femtosecond pulsed laser ablation with nanosecond pulsed laser ablation demonstrated the advantages of small size, minimal thermal damage and cleanliness for ultrashort pulses.

Femtosecond-pulsed laser micromachining of a 4H–SiC wafer for MEMS pressure sensor diaphragms and via holes

“…These shortcomings have spurred the development of ultrafast (pico and femtosecond pulses) lasers which are proven to be excellent tools for micromachining of metals, semiconductors and dielectrics [26][27][28][29][30][31][32][33][34][35][36]. We have also demonstrated the femtosecond laser's superior edge for etching 3C-SiC thin films [37][38][39][40]. The advantages of ultrafast lasers include negligible collateral thermal damage, fewer processing operations, higher etch rates, insensitivity to crystallographic orientation, ability to form curved features and complex structures, capacity for serial and batch-mode production processing and no major investment required such as large clean-room facilities and expensive process tools.…”