A sub-4 µm via technology of thinfilm polymers using scanning laser ablation

In this paper a new process technology will be discussed which uses a laser scanning ablation process. Laser ablation of polymers is in principle not a new technology. Low speed and high cost was the major barrier for further developments twenty years ago. But the combination of a scanning technology together with a quartz masks has opened this technology to overcome the limitation of the current photo-polymer process. The new technology is described in details and the results of structuring BCB down to less than 4 μm via diameter in a 4 μm thick film has been demonstrated. The via-side wall can be controlled by the fluence of the laser pulse. Basic process parameters for the ablation of BCB have been investigated together with different cleaning techniques. Test structures have been designed and fabricated to demonstrate the electrical resistivity of the vias using a two-layer metallization process. The influence of the laser process on sputtered Al, Cu and plated Cu has been compared by FIB-cuts. An outlook for the combination of structuring the vias together with wiring system is given.