共濺鍍銅鈦薄膜之相分離演化機制與其對機械性質於3DIC接合的影響;Effect of Phase Separation Evolution on Mechanical Strength of Co-sputtering Cu(Ti) Thin Film in 3DIC Bonding

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Title:	共濺鍍銅鈦薄膜之相分離演化機制與其對機械性質於3DIC接合的影響;Effect of Phase Separation Evolution on Mechanical Strength of Co-sputtering Cu(Ti) Thin Film in 3DIC Bonding
Authors:	林柏丞;Lin, Po-Chen
Contributors:	化學工程與材料工程學系
Keywords:	共濺鍍銅鈦;推力測試;銅銅接合;相分離
Date:	2017-01-11
Issue Date:	2017-05-05 17:10:22 (UTC+8)
Publisher:	國立中央大學
Abstract:	近年來，三維積體電路在半導體封裝製程中受到廣大的討論，除了有可能突破莫爾定律的限制，並且有著降低能源損耗，縮小元件體積，以及提高元件效能等優點。然而在尺寸越來越小的趨勢之下，封裝及接合的可靠度將越來越受重視。晶圓接合就成為3D-IC技術中的關鍵步驟。在眾多不同種的晶圓接合技術中，近年來以銅對銅熱壓接合技術為3D-IC的主流，不外乎是因為它的製程簡易以及成本較低的兩個原因。本研究中將使用簡易的共濺鍍技術將鈦加入銅中鍍製薄膜，研究其退火後反應以及應用於晶圓接合的影響。第一部分中，以討論單一銅鈦薄膜退火400 oC後之特性改變為主。藉由ESCA的縱深分布可發現含有不同鈦含量的銅鈦薄膜會有不同程度的相分離現象。由結果可得在四種不同鈦含量中，以15%鈦的相分離現象最為明顯，並且擁有150nm的銅層於表面。相分離現象在眾多分析中皆可被證實，包括截面分析由高解析電子顯微鏡影像，以及其元素線掃描和面掃描可得，並且從場發電子維探儀中了解相分離後的表面形貌。實驗中，相分離後的試片其結晶特性與片電阻可由X-ray繞射分析及四點探針得知。本論文中所提相分離現象可由熱力學與動力學計算所證明。從動力學可得鈦擁有比銅大10倍的擴散速率，以及從熱力學來說，鈦有較傾向氧的能力相較於銅和矽。因此，本論文推斷鈦是主要的擴散因子，並且會朝向氧化矽基板方向擴散，同時銅會被推向往表面擴散，並且隨著時間增長形成一層無氧的純銅層。接著將鍍有銅鈦薄膜的基板採用面對面熱壓的方式接合，以觀察相分離對接合的影響。結果可得，利用含有15%鈦的銅鈦薄膜熱壓60分鐘可得到無孔洞的接合介面。接合介面的強度利用推力測試來檢測，其中發現接合時間越長以及相分離程度越明顯皆有助於接合強度的提升。最後，本論文也提出相分離以及其接合的演化機制。並且可得知銅與鈦在共濺鍍銅鈦薄膜中相分離的結果提供了一個形成高品質銅接合的好方法。 ;In recent years, three-dimension integration technology has been widely discussed in regard to the packaging industry. Because of its many advantages such as reductions in power and device size, an increase in efficiency, and the miniaturization of electronic devices, the reliability of bonding in packaging is becoming gradually more evident. Wafer-level bonding is a key aspect of three-dimension integrated circuits, and Cu-Cu thermocompression bonding has become main stream because of its low cost and simple processes. In this study, a simple co-sputter technology was used to add Ti into Cu to deposit Cu(Ti) films. First, the characteristics of a single Cu(Ti) film after annealing at 400 oC were investigated. We obtained samples with various Ti concentrations, and through in-depth profile analysis we determined that the samples exhibited different levels of phase separation. The results showed that the Cu(Ti) alloy films with 15% Ti contained approximately 150 nm of pure Cu near their sample surfaces. Evidence for phase separation was obtained from a cross section of high-resolution transmission electron microscopy images, line-scan images, and mapping images. Moreover, the morphology of the sample plane view was observed through electron probe microanalysis images and mapping. In the experiment, the crystal characteristics and sheet resistance were detected through grazing incidence X-ray diffraction and a four-point probe. Theoretically, the calculation of the diffusivity of Ti in Cu is one order of magnitude smaller than that of Cu in Cu. Both calculations prove thermodynamically and kinetically that Ti is a dominant diffusing species that is segregated near SiO2, whereas Cu atoms are pushed toward the surface. In this study, the films were bonded through thermocompression. A Cu(Ti) film containing 15 at% Ti with a bonding time of 60 min at 400 oC exhibited the highest bonding strength with no void caused by phase separation. The relationships between bonding strength and the samples with various Ti concentrations were measured over different bonding times through shear testing. Finally, the evolution of phase separation and bonding were proposed. From the results, we know that phase separation of Cu and Ti in co-sputtered Cu(Ti) films provides a innovative method for forming high-quality Cu bonds.
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