Enhancement of Adhesion Between Cu Thin Film and Polyimide Modified by Ion Assisted Reaction
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ABSTRACT Polyimide films are modified by ion assisted reaction method using various ion beams in various gases environments. Amount of ion and blown gases rate were changed from 5 x 10 4 to 1 X 1017 and from 0 to 8 sccm, respectively. Wetting angles between water and polyimide films modified by Ar+ ion without oxygen blowing decrease from 670 to 400 and surface free energies increase from 46 to 64 dyne/cm 2 . Wetting angle of polyimide films modified by Ar+ ion in an oxygen environment decreases to 120 and surface free energy increases to 72 dyne/cm 2. The lowest wetting angle was obtained by oxygen ion irradiation in the oxygen gas environment and its value was 70. In the case of polyimide film modified by Ar+ ions in an oxygen environment, the wetting angle increases up to 650 when it kept in air and that increases up to 460 when it kept in water after 5 day. In the case of polyimide film modified by 02+ ion in oxygen environment, however, the wetting angle of polyimide film dose not increase. X-ray photoelectron analysis shows that the chemical bonds between polyimide components are severed by ion irradiation and hydrophilic groups such as CO and C=O are formed by the reaction between newly formed radicals and blown oxygen. It was found that adhesion between Cu and polyimide modified by ion assisted reaction was improved. The main reason of the enhanced adhesion is due to the reaction between Cu and C-O or C=O groups formed by ion assisted reaction on the polyimide surface. INTRODUCTION Polyimide (PI) has been received considerable attention due to its thermal stability, low dielectric constant and good mechanical properties [1 ]. It has been used in application ranging from aerospace to microelectronics. However, one of the drawback is its low adhesion to metals. To improve adhesion between polymers and metals, various methods such as ion beam mixing, insertion of an interlayer, annealing, etc., were studied [2-4]. Though annealing process improves adhesion between PI and metals, it takes place diffusion of a metal layer [5]. Insertion method usually use Cr as a interlayer, but Cr induces pollution problem. While, ion beam modification process, usually performed at room temperature, could avoid these problems. Adhesion between polymers with metals is closely related to wettability [6,7]. To give hydrophilic functionality to polymer, we employ the ion assisted reaction (IAR) techniques, with which we already show remarkable improvement in wettability and adhesion applying to various polymers [8-11]. In this article, we examine the effects of ion assisted reaction in oxygen environment and the relation between hydrophilic groups and adhesion between Cu and PI films. The initial growing stage of Cu film on the IAR treated PI films was investigated by X-ray photoelectron spectroscopy (XPS). Though many studies on interaction between Cu and PI have been done and the results have been published, interaction between Cu and PI films which has hydrophilic surface was not studied. Interaction between Cu and PI films whic
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