접촉면적 보정을 통한 Polyimide 기판에 증착된 구리박막의 나노경도 측정
Nanohardness Measurement of Cu Thinfilm on Polyimide Substrates with Area Function Calibration
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초록
최근 웨어러블 전자제품 산업의 발전으로 유연소자를 이용하는 분야가 빠르게 확대되고 있어 기계적 신뢰성에 대한 연구가 많이 진행되고 있다. 일반적으로 금속 박막의 특성은 나노압입시험법을 통하여 측정하는데 유연소자는기판의 영향으로 인하여 저평가되는 경향이 있다. 본 연구에서는 접촉면적 함수를 결정하여 유연소자에 증착된 박막의깊이에 따른 나노경도를 측정하였다. PI 시편에 Cu 박막을 스퍼터링으로 1 μm으로 증착하였고, 나노압입실험으로 최대300 nm 까지 압입하였다. Si wafer 기판에 증착된 박막과 기계적 특성과, 동일 하중에 대한 압흔의 크기가 동일하다는 가정 하에 Cu/Si 시편에서 측정한 결과로 Cu/PI 기판에서의 접촉면적 함수를 결정하였다. 깊이에 따른 나노경도를 산출하여 압입깊이별 기판의 영향을 관찰하였고, 유한요소해석을 통하여 박막 및 기판에 걸쳐 나타나는 압입자 하부 응력장의범위를 확인하였다.
Abstract
With the recent advancements in the wearable electronics industry, the field of flexible devices is rapidly expanding, leading to extensive research on their mechanical reliability. Generally, the properties of metal thin films are measured using nanoindentation techniques, but in the case of flexible devices, these properties tend to be underestimated due to the influence of the substrate. In this study, the contact area function was determined to measure the nanohardness as a function of depth for thin films deposited on flexible substrates. Copper (Cu) thin films with a thickness of 1 μm were deposited on polyimide (PI) substrates using sputtering, and nanoindentation experiments were conducted up to a maximum depth of 300 nm. Based on the assumption that the mechanical properties and the size of the indentation under the same load are identical, the contact area function for Cu/PI specimens was determined using results obtained from Cu films deposited on Si wafer substrates. The nanohardness as a function of depth was calculated to observe the substrate's influence at varying indentation depths. Furthermore, finite element analysis was performed to identify the range of stress fields beneath the indenter across the thin film and the substrate.
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