電鍍銅針孔生成機制及其抑制方法

Pinhole Formation Mechanism of Electroplating Cu and Its Mitigation Strategy

李承宇(C.Y. Lee) ； 陳昶志(C.C. Chen) ； 楊政憲(C.H. Yang) ； 李珮慈(P.T. Lee) ； 劉弘晟(H.C. Liu) ； 何政恩(C.E. Ho)

《鑛冶：中國鑛冶工程學會會刊》 63卷1期 (2019/03) Pp. 67-80

https://doi.org/10.30069/MM.201903_63(1).07

摘要

本研究旨在探討電鍍銅填孔製程中，化學蝕刻所造成的針孔（pinholes）問題及其抑制方法。藉由場發射掃描式電子顯微鏡（field-emission scanning electron microscope，FE-SEM）搭配電子背向散射繞射（electron backscatter diffraction，EBSD）分析系統、穿透式電子顯微鏡（transmission electron microscope，TEM）、以及飛行時間二次離子質譜儀（time-of-flight secondary ion mass spectrometer，TOF-SIMS），我們探討電鍍銅於自退火／退火過程中，其內部微結構及雜質分佈的演進情形。研究結果顯示，併入電鍍銅的雜質分佈不均可能引發晶格缺陷（例如：奈米通道、疊錯、雙晶等）及細化銅晶粒，大幅減低電鍍銅的耐腐蝕特性。在後續之面銅薄化的蝕刻製程中，針孔便易於該處產生。有趣的是，在退火過程當中，電鍍銅晶粒將大幅成長，並使其晶格缺陷得以消除。同時，這也驅使雜質向外擴散並排出電鍍銅。晶格缺陷消除及雜質的再分佈促使電鍍銅之耐腐蝕特性得以提升。最後本研究確立了，當電鍍銅之平均晶粒尺寸（D）成長至約2μm時，即可有效抑制針孔的生成。此一知識的建立將可增進吾人對針孔生成機制的認識，同時亦可作為解決針孔生成的方法。

關鍵字

電鍍銅 ； 退火（annealing） ； 針孔（pinhole） ； 奈米通道（nanochannel）

並列摘要

Pinhole formation in electroplating Cu has been a critical reliability issue in developing via-metallization with a thin surface-Cu feature. We investigated the underlying mechanism of pinhole formation and established the mitigation strategy for this undesired phenomenon. The dependences of the pinhole formation behavior on the Cu crystallographic evolution and impurity redistribution in the electroplating Cu during isothermal annealing were characterized via a field-emission scanning electron microscope (FE-SEM) in combination with electron backscatter diffraction (EBSD) analysis system, transmission electron microscope (TEM), and time of flight secondary ion mass spectrometer (TOF-SIMS). We found that the non-uniform distribution of organic impurities might induce crystallographic defects (e.g., nanochannel, stacking faults, twins, and fine grains) in some specific regions, seriously deteriorating the corrosion resistance in such regions, where pinholes might be created in a chemical etching process. Interestingly, Cu grain growth through an isothermal annealing process could eliminate the crystallographic defects and drove the redistribution of the impurities via out-diffusion to the Cu surface, which homogenizes and decreased the impurity content within the Cu platings. Therefore, the pinhole formation could be efficiently alleviated with the Cu grain growth to a grain size (D) of ~2 μm. Finally, the pinhole formation mechanism and its mitigation strategy were established.

並列關鍵字

electroplating Cu ； annealing ； pinhole ； nanochannel