Akira Mori

Micropeak array in the scribe line on a wafer

Small dot matrix marking on a silicon wafer has been performed using an second-harmonic generation (SHG) laser of yttrium aluminum garnet (YAG), liquid-crystal-display (LCD) mask, and projection optics. A marked image was obtained after laser irradiation through the pattern on the LCD mask. The each dot is a square with sides of 3.6micrometers , the pitch of each dot is 4.5micrometers and the height (not the depth) of each dot is approximately 0.5micrometers . The topography of each dot is unique, and features a central peak and peripheral depression. We have named this topography micropeak and have proposed a hypothesis for the micropeak formation mechanism, based on the density of liquid silicon and the congelation of molten silicon. In this report, micropeaks were formed in the scribe line on a wafer covered with oxide layers. Without being torn, these oxide layers were pushed up by micropeak generation and rose. Silicon particle scattering around the laser irradiation area was prevented completely. Clear dot images were observed through the transparent oxide layers. The conditions forc lean marking by laser irradiation greatly depend on the thickness of the oxide layers.