Copper/Polyimide Heterojunctions: Controlling Interfacial Structures Through an Additive‐Based, All‐Wet Chemical Process Using Ion‐Doped Precursors

Abstract

Heterojunctions comprising copper thin films and polyimide underlayers are exploited as an important system for generating flexible microelectronic circuit elements. A fully additive‐based chemical method that allows metallization of polyimide films with copper by the in situ reduction of copper ions doped in surface‐modified polyimide precursors is reported. It is shown that dimethylamine borane is a good reducing agent for copper ions initially complexed with carboxylate anions in the hydrolyzed polyimide layers. This reduction allows diffusion of copper ions towards the film surface to form copper thin films, and simultaneously controls the fabrication of interfacial microstructures between the copper and underlying polyimide. The formation of copper thin films and composite layers is elucidated by glow‐discharge optical emission spectrometry depth profiling, scanning electron microscopy, and cross‐sectional transmission electron microscopy studies, and it is shown that the final microstructure at the copper/polyimide interface is dependent upon experimental variables: a larger amount of copper ions incorporated into the modified layers and a higher reduction rate result in the formation of a granular layer containing smaller copper nanoparticles near the film surface. The granular layers thus formed are found to play a critical role in achieving strong adhesion between metal thin films and the substrate, owing to the increased contact area and hence the increased work of adhesion between them. These results have important implications for realizing a novel adhesion scheme between deposited metals and underlying dielectrics based on nanoscale interlocking through metal nanoparticles.

Study of Surface Metallization of Polyimide Film and Interfacial Characterization

“…Metals 2017, 7, 189 2 of 12 [6,13,[24][25][26][27][28]. Sputtering can produce a dense and uniform metallic layer with good adhesion on PI, but the high-vacuum operational environment makes cost-down difficult to achieve.…”

“…In contrast, solution-based electrochemical deposition is a cost-effective method. Prior to electrochemical deposition, the inert PI surface needs to be activated/modified by a base treatment of potassium hydroxide (KOH), ion exchange, and catalyst reduction [4,8,10,[27][28][29][30][31][32][33][34]. Pd is a traditional catalyst due to its superior catalytic activity, but is expensive.…”

Effect of Additional Electrical Current on Adhesion Strength between Copper and Polyimide Films

“…그러나, 폴리이미드(polyimide)를 구성하 고 있는 이미드링(imide ring)의 특성으로 인하여 표 면의 극성이 낮아 다른 고분자 물질, 금속 및 세라 믹 등과의 접합력이 떨어지는 단점을 지니고 있다 1,2) . 폴리이미드와 금속의 접합력을 향상시키기 위하 여 플라즈마 처리 3,4) , 이온빔 5) , 암모니아 처리 6) 등 의 건식 방법과 KOH 7,8) , 아민 수용액 . 그러나 30분간 전 류를 인가한 샘플의 경우 접합력 저하 대비 조도감 소가 적게 나타났으며, 이에 대한 추가적인 분석이 필요할 것으로 판단된다.…”

Aging Effect on Adhesion Strength between Electroless Copper and Polyimide Films

“…1,2) However, low reactivity of polyimide with other substances due to the stable characteristics of imide rings, has resulted in low adhesion strength between coated metal and polyimide films. 1,2) In order to improve the adhesion strength between metal and polyimide films, surface modifications of polyimide have been widely investigated: dry processes such as plasma treatment, 3,4) or ion beam treatment, 5) as well as wet processes using potassium hydroxide 6) or aqueous amine solution. 7) Post processes such as annealing at high temperature and aging in humid environment have also been reported.…”