銅單晶與多晶濺鍍銅奈米孿晶薄膜及其低溫接合研究

Abstract

電子產品的微縮化為製程帶來了精密度的考驗，例如奈米尺寸下銅應用於內連線的可靠度，而透過奈米孿晶銅膜的優勢能提升機械強度、抗電遷移與熱穩定度，因此成為重視的研究之一。 奈米孿晶擁有非常良好的熱穩定性與機械性質，而且強化時晶體並不會失去延展性，因此含有越多奈米孿晶比例的銅膜為本研究的目標。本研究透過改變基板的濺鍍偏壓與基板種類，以能期找到良好品質的銅奈米孿晶薄膜，並透過熱處理以觀察微結構變化，證實其穩定性。銅為面心立方金屬(FCC)，最密堆積平面族為{111}，由於擁有最小的表面能而促使奈米孿晶以平行於表面的{111}平面生長，因此{111}被視為奈米孿晶多寡的衡量指標，藉由X射線繞射分析、電子背向式散射繞射技術(EBSD)、聚焦離子束影像分析(FIB)，可以間接與直接得到奈米孿晶銅膜的機械性質與微結構變化。 優良的奈米孿晶薄膜可以應用在輔助銅-銅的低溫接合，奈米孿晶薄膜高比例的<111>優選方向其擴散速率較快，意即降低接合溫度，較低的溫度能降低預算，或是應用於對溫度敏感的晶片時，大幅提升良率。本研究針對不同試片作低溫接合，觀察接合溫度和接合壓力對孔隙率之影響，並以推力測試測其接合強度。

With the shrinkage of the electric device, there is also a challenge come to the reliability of the process such as applying Cu on interconnects in nanoscale. Today, it’s popular for elevating mechanical strength, great resistivity of migration, and excellent thermal stability. Film with nanotwins have great thermal stability and excellent mechanical property yet not losing great ductility. In this study, we changed the substrates and the sputtering bias to obtain densely nano-twinned film, annealing the thin film to confirm the microstructure of nanotwins would not change at high temperature. Cu belongs to Face Centered Cubic metal, which possess closest packing plane {111}. Due to the smallest surface energy, the nanotwins grow in the {111} plane parallel to the surface, {111} is regarded as a measure of the amount of nanotwins. X-Ray Diffraction (XRD), Electron Back-Scattered Diffraction (EBSD), and Focused Ion Beam image analysis (FIB) can indirectly and directly obtain the mechanical properties and microstructural changes of nanotwinned copper films. Excellent nano-twinned films can be used to assist low-temperature bonding of copper-copper. The high proportion of nano-twinned films in the preferred direction of <111> has a faster diffusion rate, which means lower bonding temperature. Lower temperature can reduce the budget, or when applied to temperature-sensitive chips, the yield can be greatly improved. In this study, different test pieces were bonded at low temperature, the effects of bonding temperature and bonding pressure on porosity were observed, and the bonding strength was measured by thrust test.