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 mu m thick Si wafers with 100 mu m 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.