Photosensitive polymer reliability for fine pitch RDL applications

Abstract

We present the reliability results obtained on a two-metal level copper RDL patterned on a photosensitive polymer with a target pitch below 4 μm. Our polymer has been submitted to high temperature storage at 150 °C and to temperature humidity stress at 85 °C/85 %RH for 1000 hours. A thermal cycling stress between -50 °C and 125 °C for 1000 cycles was also performed on these samples.

Collected electrical data indicate an increase in the copper wires resistivity and via resistance after 1000 hours at 150 °C. Failure analyses performed on the stressed samples reveal the formation of a copper oxide layer on top of the metal lines and at the bottom of the vias resulting from the presence of water at the interface metal/polymer. The presence of moisture inside the polymer is further confirmed by Fourier-transform infrared spectroscopy (FTIR) measurements. These results emphasize the need of a capping layer on top of the metal lines and reiterate the need of a continuous Ti barrier for a reliable process