Adhesion enhancement of Cr/polyimide interfaces using RF pre-sputtering of polyimide surfaces

Abstract

The effects of Ar ion RF pre-sputtering of polyimide surfaces on the adhesion of Cr/polyimide interfaces have been examined by TEM, XPS, and peel test. With Ar pre-sputtering, the peel strength of Cu/Cr to polyimide increases remarkably from 1 g/mm to 130 g/mm and 90 g/mm on PMDA-ODA spun on Si and silica substrates, respectively. The negligible change in the polyimide surface morphology by RF sputtering and the little change in the adhesion strength by a long exposure to the air after the sputtering prior to metal deposition eliminate contributions of mechanical interlocking and surface cleaning effects to this adhesion enhancement. Thus, adhesion enhancement by RF pre-sputtering is mainly attributed to chemical changes of the polyimide surface facilitating bonding with the deposited Cr. Such a surface treatment with RF sputtering was also found to be effective for the retardation of the moisture-induced failure of Cr/polyimide interfaces. It has been observed that cracks develop in both Cr and polyimide, and that the size of the cracks varies depending on the RF power density and on the stress state of the polyimide. The cracks at the interface are suggested to be the main path of moisture penetration for the degradation of adhesion strength. © 1990, VSP. All rights reserved.