In-line advanced process control solution for the fabrication of micro-bumps

Abstract In this paper, Confocal Chromatic Microscopy was investigated to characterize the micro-bump fabrication process. We designed and fabricated in house a new detector that integrates through the same optical chromatic lens two light beams that are reflected into a 2D line scan camera and a spectrometer to obtain on the fly 2D and 3D information while scanning the wafer surface. We inspected 300 mm round wafers hosting arrays of copper micro-bumps down to 10 μm in width and 5 μm in height at post Cu growing and etching step. The 2D inspection revealed the presence of partial μbumps, shifted and missing μbumps. The 3D inspection could recognize shorter and taller bumps and determine the coplanarity of each bump population at die level. This information could be used to classify GOOD and BAD dies over the wafer, so that after dicing only known good dies would be used in the following advanced packaging step. In this way, the risk of shorts and / or missing contact is minimized when stacking dies either on a wafer or on a die.