계면 접착 특성에 따른 구리 배선의 피로 거동 및 신뢰성 평가
Reliability of Fatigue Deformation for Flexible Cu Interconnect Varying Interfacial Adhesion
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초록
현대 전자기기는 반복적인 기계적 변형을 견딜 수 있는 유연한 형태로 발전하고 있다. 이로 인해 전자기기 내부에서 금속 배선의 기계적 안정성을 유지하면서 장기적인 신뢰성을 확보하는 것이 중요한 과제로 여겨진다. 본 연구에서는 구리(Cu) 박막과 폴리이미드(Polyimide) 기판 간 접착력을 향상시키고, 인장변형 하에서 기존의 피로 실험(USliding) 과 달리 유연 전자기기의 실제 사용되고 있는 환경을 모사한 U 자 모양의 굽힘(U-folding) 피로 거동을 분석하였다. 폴리이미드 기판과 구리 박막의 접착력을 향상시키기 위해 크롬(Cr) 접착층 도입과 산소 플라즈마 처리를 비교 분석하였으며, 이러한 계면처리법이 피로 변형 거동에 미치는 영향을 평가하였다. 나노스크래치 테스트를 통해 접착력을 정량적으로 평가하였으며, 전기저항 측정과 미세구조 분석을 통해 피로 파괴 메커니즘을 규명하였다. 연구 결과, 1.0% 변형률에서 크롬 접착층을 도입한 경우가 가장 우수한 접착력을 보였으며, 피로 시험에서도 가장 향상된 피로 저항성을 나타냈다. 본 연구는 유연 전자기기의 실제 사용 환경에 적합한 피로 저항성 개선방안을 제시하였으며, 전자기기의 장기 신뢰성 향상을 위한 설계 지침을 제공할 것으로 기대된다.
Abstract
Modern electronic devices have evolved to be mechanically flexible, capable of withstanding repetitive deformation. This advancement necessitates ensuring the long-term reliability of metal interconnects, which are essential components in flexible electronic devices. In this study, we analyzed the fatigue behavior of U-shaped structures under tensile conditions, focusing on modifications at the interface between copper (Cu) films and polyimide (PI) substrates. The U-folding fatigue method, which involves complete flattening and bending of the sample compared to U-sliding fatigue, better simulates the actual fatigue deformation occurring during flexible device usage. We compared two adhesion enhancement methods: oxygen plasma treatment and chromium (Cr) adhesion layer introduction. The interfacial adhesion was quantitatively evaluated through nanoscratch tests, while fatigue failure mechanisms were investigated using electrical resistance measurements and microstructural analysis. Our findings revealed that under fatigue strain of 1.0%, the Cr adhesion layer exhibited the highest adhesion strength and showed significant improvement in fatigue resistance. This research provides essential guidance for enhancing the long-term reliability of flexible electronic devices by suggesting effective methods to improve fatigue resistance under practical usage conditions.
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