An Overview About the Excimer Laser Ablation of Different Polymers and Their Application for Wafer and Panel Level Packaging

The demands for packaging for either wafer or panel respectively heterogeneous integration in general are rising. New materials and technologies are needed to address the challenges resulting from that demands like better dielectric properties or higher resolution just to name two examples. The excimer laser ablation is able to meet that needs and process the new materials, which are not always photosensitive anymore. The system used for this paper is a combination of a projection stepper platform combined with an excimer laser. The field of application for this system is quite wide. It can be used for laser de-bonding of supporting substrates or the seed layer removal after galvanic. The main application, however, is the ablation of all types of polymers to generate VIAs for example. In contrast to already known PCB lasers, it is also possible to ablate complex structures in parallel, as it is a mask-based technology. Due to that, it is possible to generate trenches and VIAs within one step. This enables a technology already known from the front end of line (FEOL) to be transferred to the back end of line (BEOL): the dual damascene process. Within this paper, all the mentioned applications and the experience with a broad variety of polymer materials such as Polyimide, PBO, BCB, ABF, Dry Films are going to be presented. It is going to be shown that the excimer laser system can overcome the limitations of common polymers in terms of resolution and that the laser dual damascene approach can meet the needs for the overall demand towards 2um lines and space for packaging. Additionally some reliability data is presented that prove that the laser ablation can replace the today common lithography processes without any drawbacks.