利用原位追蹤方式探討電鍍銅的自退火行為

In-situ Self-annealing Behavior of Electroplated Copper

陳昶志(C.C. Chen) ； 呂名凱(M.K. Lu) ； 楊政憲(C.H. Yang) ； 吳映璇(Y.S. Wu) ； 何政恩(C.E. Ho)

《鑛冶：中國鑛冶工程學會會刊》 61卷1期 (2017/03) Pp. 62-74

https://doi.org/10.30069/MM.201703_61(1).0006

摘要

銅(copper)的低電阻率、高抗電遷移(electromigration)能力、和極佳的機械、化學、導熱等特性，使其被廣泛使用於各類電子零組件上，例如印刷電路板(printed circuit boards, PCBs)之銅線路。近來許多研究報導指出，電鍍銅於室溫下的再結晶行為（俗稱“自退火”）會改變其微結構/晶體特徵、機械、物化等特性，進而影響電子產品的可靠度。然而，過去有關電鍍銅自退火行為的研究幾乎都著重於較薄之電鍍銅膜(＜ 5 μm)，而PCB製程中所用之銅膜厚度大多超過10 μm。因此，本研究特以原位追蹤(in-situ)方式，探討較厚之電鍍銅膜(≈20 μm)之自退火行為。透過XRD、殘餘應力分析儀、及TOFSIMS等一系列的分析結果顯示，電鍍銅的內應力會隨銅的再結晶而逐漸釋放。此期間，電鍍銅之內部雜質將被排至鍍層表面，而得以重新分佈。EBSD分析結果進一步顯示，在自退火過程中，銅晶粒會從奈米級之晶粒尺度成長至數個微米大小。同時，其晶體取向(crystallographic orientation)也將伴隨雙晶(twin)結構的產生，並以[111]作為電鍍銅的擇優沉積方向。值得一提的是，提高電流密度(j)將會加速上述現象的演進。此一知識的建立將可增進吾人對金屬再結晶機制的認識，同時亦可作為後續PCB製程再精進的重要參考依據。

關鍵字

電鍍銅 ； 自退火 ； 內應力/應變 ； 晶體取向 ； 雙晶

並列摘要

Copper (Cu) has been used in various printed circuit boards (PCBs) for its low electrical resistivity, high electromigration resistance, and good mechanical, chemical, and thermodynamical properties. Self-annealing of electroplated Cu at room temperature might cause remarkable microstructure evolution and significant transitions of physical/chemical characteristics that might affect the Cu conducting lines less reliable. In the literature, there was limited information regarding the Cu self-annealing behavior in a Cu film (δ_(Cu)), especially for δ_(Cu) ＞ 5 μm. In this study, we conducted an in-situ investigation on the Cu self-annealing behavior in a PCB scale (δ_(Cu) ≈ 20 μm) using XRD, EBSD, a cantilever method, and TOF-SIMS. The XRD, cantilever, and TOFSIMS analyses showed that the Cu recrystallization accompanied by the stress relaxation towards tensile direction and the redistribution of impurities (Cl, S, C, and O) towards the surface of Cu films in the self-annealing process. The Cu recrystallization and stress relaxation could be greatly accelerated by increasing plating current density (j). EBSD analyses revealed that a considerable Cu grain growth from approximately 100 nanometers to several micrometers accompanied by an increase of twin structure and a decrease of grain orientation spread (GOS) agreeing well with XRD, the stress relaxation via the cantilever method, and impurity redistribution via TOFSIMS analyses showed the same observations. We also observed a preferred orientation of [111] ∥electrodeposition direction developed during self-annealing. This study provided a better understanding of self-annealing behavior of a thick Cu film (δ_(Cu) ≈ 20 μm).

並列關鍵字

electroplated Cu ； self-annealing ； internal stress/strain ； crystallographic orientation ； twin