Processing of Back Surface of Si Wafers With a Pulsed Nd:YAG Laser

Silicon (Si) is a widely used material by the very-large-scale integration technology addressing manufacturing of integrated electronic circuits. Micromachined Si has also shown its advantages in the fabrication of advanced microelectronic, photonic and micro-electro-mechanical system devices whose continuously decreasing dimensions present growing challenges in packaging. In that context, we have investigated an Nd:YAG laser based process for micromachining of back surface of Si (100) wafers. The application of a laser for micromachining brings the advantage of a selective area processing, while the Nd:YAG laser holds the promise of a cost attractive solution. Our experimental results, consistent with temperature simulations, demonstrate that it is possible to melt the back surface of 380 μm thick Si wafers with 100 μm diameter laser pulses of energy between 2.6 and 3.2 mJ/pulse. Microscopic images and profilometry scans have indicated no measurable modification of the front surface of laser-irradiated wafers. Fourier transform infrared absorption spectroscopy data have indicated formation of a porous Si material on the back surface of irradiated wafers that could be dissolved relatively easily in a potassium hydroxide solution.