Effects of Water Layer on a Through Silicon Via by Using a KrF Excimer Laser

Abstract

We investigated the effect of a water layer on a through silicon via (TSV) by using a KrF excimer laser. When we fabricated the via in air, we found debris and burrs around the via and confirmed by using Raman scattering spectroscopy and X-ray diffraction spectroscopy that those were due to amorphous silicon. Debris around the via surface was effectively reduced when we fabricated the via in the water layer. The fabrication time decreased with increasing pulse energy of the laser in all atmospheres, and a long time was needed to fabricate the via in a 3-mm water layer because of the bubbles near the substrate. In addition, we could fabricate a small-sized via in a water layer because the plasma was concentrated at the surface of the substrate. The size of the via was not influenced by the repetition rate of the laser in any of the atmospheres. Based on those results, we could fabricate an about 170-μm via, which had no debris or burrs, in a thin water layer by using a KrF excimer laser with a pulse energy of 100 mJ and a repetition rate of 12 Hz.