Polyimide Fine-via Etching and Low-damage Surface-modification Process For High-density Fan-out Wafer Level Package

Abstract

In the last years the number of high performance mobile devices, such as smart phones or tablet PCs, increases widely and accordingly data traffic augments rapidly. Devices for these equipment require high-rate processing capabilities, high-density packaging possibilities and low power consumptions for data-center and servers. Thus the demand for packed semiconductor chips with high density of components is growing. In order to accomplish high-density packaging, miniaturization technology of wiring in heterogeneous Fan-out Wafer Level Packaging (FO-WLP) is needful to multi chip module system fabrication using by the re-distribution layer (RDL) wiring technologies. To obtain the fine vias and line/space in a polyimide film, the PVD sputtering and electro-Cu deposition processes are widely used but there are three major restricting difficulties. The first is that it is difficult to make fine vias and line / space in the FO-WLP process. The second is that PVD sputtering process for high adhesion between Cu and polyimide films is also will be issue by status of surface and surface residue. The third is that surface damage of polyimide by the plasma irradiation (Ions, UV), moisture absorption.In this paper, we report the role of the dry etching to fabricate the RDL. The dry etching has already applied in various RDL fabrication process, such as dry descum process, the surface modification process and so on. Dry descum process is named that the process is the removal of photoresist (PR) residues after photo-lithography. The surface modification process has two major functions. First is the improvement of the interface adhesion of the films. To improve of the adhesion, it is necessary that the change of surface morphology. As one way, the changing of the surface configuration is suggested. To obtain the surface with large roughness, the etching process is recommended that the bombardment characteristics is more effective. As the result, the contact area is increased by the etching, so the adhesion would be improved. Alternatively, the application of the chemical response between films is suggested. To generate the chemical function groups, the etching process is recommended that the chemical response is more effective. These surface morphology is adjusted by dry etching condition. In this study, we focus the control of hydrophilic property using dry etching process. In RDL process, it is important to conduct a pre-treatment of electro-Cu deposition processes. When the polymer surface has hydrophobic characteristic, Cu plating solution would be rejected from the surface of polymer. Then, the plating solution cannot enter the bottom position of channels in polymer films, and the voids may be generated. In the future, these channels would be become reduced in size, therefore the control of hydrophilic property would be focused.