銅薄膜與奈米雙晶銅柱之機械性質與結構分析

Abstract

本論文藉由奈米壓痕儀可以同時精確紀錄不同時間點的壓深和負載重量的特性，用來計算在奈米尺度銅箔膜的硬度、剛性與彈性模數。 再探討常見的故障機制-潛變在對於銅箔膜的影響與結構討論，在不同溫度下的潛變壓痕實驗(30-60 °C, 0.22-0.25熔點溫度)，利用時間-位移曲線計算出高應力指數(n=10.4-27.8)和潛變活化能為4.04 eV，可以推測主要潛變機制為差排潛變；再進一步利用電子顯微鏡對其結構進行分析，在實驗後銅箔膜在壓痕附近出現許多刃狀與環狀差排，與推測的結果一致。 第三部分利用臨場壓痕實驗直接觀測奈米雙晶結構在受應力時產生的形狀與其結構改變，發現雙晶界上差排較易從此缺陷上產生與移動。並且觀測到藉由應力作為驅動力，提供跨越擴散所需要的活化能，使奈米銅柱表面的缺陷減少，此效應稱為”機械退火”。

We investigate mechanical properties of copper thin films, the hardness, stiffness and Young’s modulus, in nano-scale using nano-indentation which records load and displacement accurately and simultaneously. . We discuss the creep on the copper thin films which is a famous breakdown mechanism in material. The nano-indentation creep tests were carried out at different temperatures (30-60 °C, 0.22-0.25 melting temperature). The stress exponent (n = 10.4-27.8) and activation energy (4.04 eV) of creep were calculated. We therefore conclude that it is dislocation creep dominated. The microstructures of the copper thin films were studied using transmission electron microscope, where we observed edge and screw dislocations near the indentation mark at the copper thin film. It is consistent with our results. In-situ nano-indentation for observing the dynamic changes of nano-twinned structures under compressive stress was investigated in transmission electron microscopy. We observed that dislocations were generated from twin boundaries and migrated along twin boundaries. Where the applied stress acted as driving force for dislocation motion. During compression, the defects on the surface of pillars were reduced as the effect of “mechanical annealing”