Effect of sputtering parameters on the adhesion force of copper/molybdenum metal on polymer substrate

A pure molybdenum was selected as a copper barrier layer on top of the polyimide substrate because of its good etchability with copper and high thermal stability. The adhesion forces were measured by using a micro-scratch tester and an adhesion improvement mechanism is suggested in terms of thin film microstructure and polymer surface modification. The adhesion force of thin copper film on the polymer substrate is greatly enhanced by variation of deposition conditions such as argon pressure, DC power voltage oxygen plasma pretreatment and annealing treatment. As the sputter dc voltage increased from 500 V to 640 V, the critical adhesion force of the molybdenum on the polyimide film increased from 420 mN to 900 mN. As the argon pressure increased from 5 mTorr to 30 mTorr, the adhesion force slightly decreased from 860 mN to 660 mN. The post-annealing process after the film deposition also yielded an enhanced adhesion force.