銅柱與錐形矽穿孔接合在三維整合製程之研究

Abstract

由於銅具有較低的電阻率以及較高的熱傳導率，銅對銅的熱壓式接合已經得到了深入的研究。然而，銅對銅的接合溫度通常高於300 ºC到400 ºC，可能會導致元件的損壞。此外，較高的接合溫度會因為不同的熱膨脹係數(CTE)造成應力及接合錯位的不良影響。相較於傳統的結構，本實驗室之前的研究中，已經利用銅柱對下凹的結構在低溫下成功的接合。然而此結構需要重分佈線路(RDL)製程連接矽穿孔(TSV)達到垂直連接的特性。 而本研究在基於低溫接合機制下，利用錐形矽穿孔(Tapered TSV)的結構取代下凹的結構，本結構相較於銅柱與下凹接合更加的節省空間，此外，做垂直電性連接時，因為本結構為銅柱與矽穿孔接合直接達到垂直電性的連接，可以比之前的結構少重分佈線路(RDL)製程。亦即本研究除了可以保有原本結構的優點之外，還可以達到三維垂直連接的功用。 在本論文中主要專注在透過Bosch蝕刻和電鍍製程完成錐形矽穿孔最佳化 製程。製作過程中使用光學顯微鏡、掃描式電子顯微鏡、X光斷掃描和能量分佈分析儀以進行材料及製程的分析找到最佳製程參數以達到設計的結構及應用。最後，將會透過電性的分析量測接合後的電阻值，檢驗接合結果的品質。各分析結果也都顯示此結構在未來三維整合的應用上，將具有很好的潛力與發展。

Direct thermo-compression Cu-Cu bonding has been well studied in view of the low resistivity and high thermal conductivity of Cu. However, the corresponding bonding temperature is usually higher than 300-400 ºC, which may lead to the degeneration of device. Moreover, the different coefficients of thermal expansion (CTE) among Cu and Si may result in stress and bonding misalignment. Compared to the conventional structure, copper pillar–concave structure has been successfully developed at low temperature in previous study. However, in order to achieve vertical connection, this structure requires redistribution layer (RDL) process to connect TSV. In this study, tapered copper TSV has been replaced concave structure based on low temperature bonding mechanism. Compared to the pillar–concave structure, this structure can realize to space efficiency. In addition, this structure can be vertical electrical connections since this structure can be directly bonded with tapered copper TSV. Therefore, we can reduce RDL process from the previous structure. In other words, this study can retain the advantages of the original structure, and it can also achieve the vertical connection in 3D integrations. To achieve optimized process, this thesis mainly focuses on the fabrication of tapered copper TSV with Bosch process and electroplating process. After manufacturing process, analyses such as OM, SEM, EDX and X-ray CT analysis are used in order to determine the optimized process parameters to achieve the desired design of structure for future applications. Finally, the quality of bonding results and the resistance of bonded structure from electrical measurements are reported. These findings show a great potential of this bond scheme to be applied in 3D integration.