Handling of multi-reflections in wafer bump 3D reconstruction

In advanced electronic manufacturing that involves say die-to-die bonding, microscopic surfaces like solder bumps on wafers have to be inspected in 3D. However, because the bumps are of hemispherical shape, light projected onto the bumps could be reflected and illuminate other regions. Such multi-reflections could greatly disturb the intensity distribution in the image data and limit the use of gray level intensities for accurate 3D reconstruction of the bumps. In a previous work, we described a new solution mechanism that was based upon the concept of binary pattern projection, but unlike the traditional mechanisms which use an array of light sources it uses only a single light source. The light source in combination with a binary fringe grating could induce binary pattern on the target surface to be imaged, and the displacements of the binary fringe grating could allow the binary pattern to be varied. In this work, we describe under that solution framework how multi-reflections could be detected and the correct binary signals could be restored. Experimental results on solder bumps validate the feasibility of the proposed approach.