Microstructural Effect of Electrodeposited Copper on Direct Bonding for Microelectronic Assembly

近年來隨著3D-IC發展成主流趨勢，大量新穎電子產品接連問世，在電子元件的製程中，常見的填入銅導線製程為電鍍法，利於晶片進行縱向矽穿孔堆疊(Through Si via, TSV)。電鍍銅因配方與製程的不同，在硬度、成長方位、晶粒徑與雙晶比例可顯現相當大的差異。本實驗中使用直流電與脈衝電流以及硬銅的添加劑等，製備出三種具不同晶粒特徵電鍍銅膜，於250oC、10MPa進行銅/銅直接壓合，探討組織效應與光照效果。實驗結果顯示，細晶粒、高雙晶比例與表面壓縮殘留應力均有助於直接接合效果。但接點強度仍不如銅表面具伸張殘留應力但晶粒徑小至0.08μm2之濺鍍銅。各種銅試片含電鍍、濺鍍製備者，經Xenon flash表面改質，接合強度均可提升約60%。本研究亦提出以脈衝電鍍製程加上後續光照處理，電鍍銅試片接合強度可較商業配方、具粗大等軸晶者高出129%。In order to allow conductance between stacked ICs, jointing by metallic connections is necessary. Cu-to-Cu direct bonding is ideal to form required interconnections because copper possesses many advantages, e.g., excellent electrical conductivity, low cost and high electromigration resistance. Electroplating is commonly used to deposit Cu into TSV. Due to ingredient and processing variations, electroplated Cu with differences in hardness, growth orientation, grain size as well as twin boundary fraction can be prepared. In this study, three kinds of electroplated Cu films with various hardnesses and crystal characteristics are deposited and a comparison with sputtered Cu is made. Effects of microstructure and Xenon pulses on directly bonded joint strength are investigated. Experimental results reveal that fine grains, high twin boundary fraction and compressive surface residual stresses are beneficial to thermal compression bonding. However, sputtered Cu with ultra-fine grain (grain size of 0.08 m2) possessed greater joint strength even though the surface stresses are tensile. It is found that subjected to a proper flash pulse exposure, the directly bonded joint strength all kinds of Cu films can be raised by 60%. An optimal process design for electroplated Cu can also be proposed. With pulsed electroplating and following flash irradiation, the joint strength obtained is 129% higher than that of Cu films with coarse equiaxed grains prepared using commercial ingredients.摘要 i Abstract ii 目錄 iii 表目錄 v 圖目錄 vi 第一章 前言 1 第二章 文獻回顧 3 2.1 Cu-Cu接合技術簡介 3 2.2 提升接合效果方法 4 2.2.1 表面活化 4 2.2.2 以機械方式產生缺陷 6 2.2.3 以電鍍方式控制銅結晶取向 6 2.2.4 超音波接合 6 2.2.5 利用電遷移促進接合 8 2.2.6 改變表面殘留應力促進接合 8 2.3電鍍銅 9 2.3.1直流電鍍銅原理 9 2.3.2脈衝電鍍 10 2.3.3奈米雙晶電鍍銅 11 2.3.4 電鍍雙晶銅熱處理行為 11 第三章 實驗步驟 34 3.1 電鍍銅試片製作 34 3.1.1 微影製程 34 3.1.2 電鍍製程 35 3.1.3 CMP表面平坦化處理 35 3.1.4 Flash表面預處理 36 3.2 接合預處理後之銅表面分析 36 3.2.1 表面粗糙度分析 36 3.2.2 奈米壓痕分析 36 3.2.3 表面殘留應力分析 36 3.2.4 XRD織構分析 37 3.2.5 EBSD晶粒性質分析 37 3.3 熱壓接合及接點剪力強度測試 38 3.3.1 Cu/Cu電鍍銅熱壓接合 38 3.3.2 接合介面分析 38 3.3.3 接合試片剪力測試 38 第四章 結果與討論 46 4.1 電鍍銅與濺鍍銅晶粒微結構分析 46 4.1.1 FIB 銅薄膜微結構分析 46 4.1.2 XRD 織構分析 46 4.1.3 EBSD分析 46 4.2 電鍍銅經Flash照射效應 47 4.2.1 表面粗糙度 47 4.2.2 表面硬度 48 4.2.3 表面殘留應力分析 48 4.3 電鍍銅Cu/Cu接點分析 49 4.4 光照射於銅表面影響之探討 49 第五章 結論 66 參考文獻 6