Improvement of adhesion between dielectric layer for high density package substrate and sputter-deposited metal electrode seed layer

Abstract

Recently, the package industry has experienced rapid technical changes in keeping pace with the development of the Internet of Things (IoT) technology. Ajinomoto build-up film (ABF) is especially useful dielectric material which is used as the insulating layer of the interposer substrate interconnecting the chips in a field of packaging technology. Cu / Ti deposited by the sputtering method for the seed layer are investigated to improve the adhesion of the ABF film and on the seed layer using Ar plasma pretreatment. The feasibility testing of Ar plasma treatment was evaluated according to the plasma generation power, the plasma source method and the kind of gases for plasma generation. In order to form a seed layer demanded by highly reliable copper circuit, Radio Frequency (RF) plasma and Induce Coupled Plasma (ICP) pretreatment were performed using a high vacuum sputtering machine. RF and ICP plasma using Ar pretreatment of the ABF film resulted in three-fold increase of the peel-off strength compared to the untreated sample. Ar plasma treatment produced a nanoscale surface roughness that was responsible for the improvement of adhesion of the Ti seed layer while O2 plasma treatment produced a clean sharp interface, weakening the seed layer adhesion. Examination of the fractured surfaces revealed that the increased adhesion strength between the Ti seed layer and the ABF after the plasma pretreatment exceeded the intrinsic strength of the ABF so that the fracture proceeded through the bulk of the ABF film when plasma treated. To further improve the adhesion of the Ti seed layer, it is advisable that the interface between the SiO2 filler and the ABF matrix needs to be considered through surface modification of the SiO2 filler.