Phase Stability, Phase Transformations, and Reactive Phase Formation in Electronic Materials XVI: Electronic Interconnection
Sponsored by: TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Shih-kang Lin, National Cheng Kung University; Chao-hong Wang, National Chung Cheng University; Jae-Ho Lee, Hongik University; Ikuo Ohnuma, National Institute for Materials Science (NIMS); Chih-Ming Chen, National Chung Hsing University; Thomas Reichmann, Karlsruhe Institute of Technology; Yu Zhong, Florida International University; Shijo Nagao, Osaka University; Shien Ping Tony Feng, The University of Hong Kong; Yee-wen Yen, National Taiwan Univ of Science & Tech

Tuesday 2:00 PM
February 28, 2017
Room: 25A
Location: San Diego Convention Ctr

Session Chair: Hiroshi Nishikawa, Osaka University; Jenn-Ming Song, National Chung Hsing University

2:00 PM  Invited
Sintering of Nanoparticle-based Interconnections through Chemical and Photonic Means: Jenn-Ming Song1; Tsung-Yun Pai1; Guo-Lung Huang1; Sin-Yong Liang1; 1National Chung Hsing University
    In order to obtain excellent electrical conductivity for nanoparticle deposits, the surfactants have to be removed and the particles should be well linked. This study develops low temperature fabrication of interconnections on polymeric substrates using Ag nano/submicron particles by means of chemical reduction and photonic sintering as well. The reductants for chemical reduction are ascorbic acid and formic acid solutions, while photonic sintering is performed under flash UV light and NIR (near-infrared) light. In addition to ligand desorption during reduction/sintering process as well as the kinetics of particle coalescence, the studying subjects also encompass the effects of residual surfactant/reductant and microstructural characteristics on the electrical resistivity and current stressing reliability. Considering the application for wearable electronics, the electrical performance of the sintered interconnections subject to bending fatigue will also be evaluated.

2:20 PM  
Ultra Thermal Stable Cu-to-Cu Interconnection: Shih-kang Lin1; Che-yu Yeh1; Mei-jun Wang1; Hao-miao Chang1; 1National Cheng Kung University
    Cu-to-Cu interconnection is an essential process for a number of advanced applications in electronic industry, such as three-dimensional integrated circuit (3D IC) and wide band-gap (WBG) device. Conventionally Cu-to-Cu bonding involves micro-bumping by introducing solders. However, intermetallic compounds (IMCs) usually form at solder joints, which are brittle and electrical resistant. Moreover, as 3D IC joints are usually as small as 10 to 20 μm, soldering with conventional solders would result in full IMC joints with poor mechanical and electrical properties. In the presentation, a new Cu-to-Cu bonding concept is proposed. We fabricated fully ductile Cu-to-Cu joints with shear strength greater than 40 MPa and a tensile strength greater than 30 MPa. Furthermore, no strength decay was found after ageing at 300 C for 200 h. Instead, the strength gradually increased against ageing time. We demonstrate the high-reliability Cu-to-Cu joints, which is promising for next generation 3D IC and WBG applications.

2:40 PM  
Ductile and Strong Cu-to-Cu Interconnection Using Ga-based Pastes for Applications on 3D IC and WBG Devices: Che-yu Yeh1; Yi-Kai Kuo1; Shih-kang Lin1; 1National Cheng Kung University
    Direct Cu-to-Cu interconnection is an important process for application in three-dimensional integrated circuit (3D IC) and wide band gap (WBG) device in electronic packaging industry. Cu-to-Cu interconnection can be made using thermo-compression, micro-bumping, or sintering with nano/submicron particles. However, thermo-compression requires high temperature and is time consuming, which makes it an expensive process. Micro-bumping is considered a cheap and fast process, but brittle and electrical resistant intermetallic compounds (IMCs) would form at the joints, which raises significant reliability concerns. Sintering with nano/submicron particles forms porous joints with poor thermal stability, which again does not meet the requirements in electronic industry. In this presentation, we demonstrate new materials and new processes for fabricating ductile and strong Cu-to-Cu joints using Ga-based pastes. This approach opens a door for a new concept for Cu-to-Cu interconnection, which can be applied for applications on 3D IC and WBG devices.

3:00 PM  
Transient Liquid Phase Bonding of Cu/In/Ni and Cu/In/Co and Phase Equilibria of Cu-In-Ni and Co-Cu-In Ternary Systems: Sinn-Wen Chen1; Tsu-Ching Yang1; Ji-Min Lin1; 1National Tsing Hua University
    Improvement of energy usage efficiency via waste heat recovery using thermoelectric modules is a very important topic. Thermoelectric modules are usually composed of arrays of devices, and there are thus many joints in the modules. Indium is ductile and has a low melting point. Transient liquid phase bonding using indium is a potential joining technique for thermoelectric modules which cannot be joined at very high temperatures but need to be operated at relatively high temperatures. The interfacial reactions at the Cu/In/Co and Cu/In/Ni contacts are examined at 200oC and 350oC. At the Cu/In contact, Cu11In9 phase is formed when reacted for 24 hours at 200oC, but Cu2In and Cu7In3 phases were formed at 350oC. A ternary compound is also noticed. Only CoIn3 is formed at the In/Co contact at both 200oC and 350oC. The reaction paths are illustrated using the Co-Cu-In and Cu-In-Ni isothermal sections at both 200oC and 350oC.

3:20 PM  
Oxide Growth Mechanism of (111), (100) and Random Copper Films at Low Temperatures for the Application of Cu-to-Cu Direct Bonding: Chih-Han Tseng1; Chih Chen1; 1National Chiao Tung University
    Cu direct bonding has been implemented in CMOS image sensors by Sony. Prior to the Cu direct bonding, the Cu oxides on the Cu surface need to be removed. However, the surface may get oxidized right after the cleaning process. Thus, the Cu oxidation is an important issue in the study of Cu direct bonding. Our previous study reported that low temperature Cu direct bonding can be achieved by (111)-oriented nanotwinned Cu. However, the oxidation behavior of the nanotwinned Cu is not clear. In this study, we examine the oxidation behavior of highly (111)-, (100)- and randomly-oriented Cu films at temperatures ranging from 250 to 100 C. Because of the oxidation layer is too thin, we use the transmission electron microscopy to observe the oxide thickness. The results shows that the oxidation rate of (111)-oriented nanotwinned Cu possesses the lowest oxidation rate among the three Cu films.

3:40 PM Break

4:00 PM  Invited
Formation and Growth of Intermetallic Compound Layer at the Lead-free Solder/Cu Interface Using Laser Soldering Process: Hiroshi Nishikawa1; Noriya Iwata1; Shinya Kubota1; 1Osaka University
    With the miniaturization of electronic productions and the use of heat sensitive electronic components, a traditional reflow soldering using a furnace often has difficulties. As an alternative soldering process, a laser soldering process has been recently proposed. The laser soldering process brings several advantages in terms of localized heating, and rapid rise and fall in temperature. In this study, the formation and growth of an intermetallic compound (IMC) at the lead-free solder/Cu interface were investigated to clarify the characteristics of the laser soldering process. The results show that the rapid rise and fall in temperature strongly affected the IMC formation at the interface and the IMC thickness for the laser soldering was thinner than that for the traditional reflow soldering. During isothermal aging, the growth rate of IMC layer at the interface for the laser soldering was faster than that for the traditional soldering.

4:20 PM  
Effects of Cu Concentration on the Mechanical Reliability of the Sn-Ag-Cu/Ni Solder Joints–Solid-state Reaction: Cheng-En Ho1; Ming-Kai Lu1; Pei-Tzu Lee1; Wan-Zhen Hsieh1; 1Yuan Ze University
    Tin-sliver-copper (Sn-Ag-Cu) series of alloys with the Ag concentration ranging from 0–4 wt.% and the Cu concentration (x) ranging from 0–1 wt.% has become the most popular solder system in microelectronic packaging applications. In this study, the effects of Cu concentration (x) on the solid-solid reaction between Sn-3Ag-xCu alloy and electrolytic Au/Ni/Cu multilayer and the mechanical reliability were investigated via scanning electron microscopy, electron probe microanalysis, transmission electron microscopy, and high-speed ball shear test. The growth of intermetallic compounds (IMCs), including (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4, and the shear resistance of the Sn-3Ag-xCu/Au/Ni/Cu solder joints strongly depended on x. The residual Cu concentration in the solder played a remarkable role in determining the IMC species and thickness, affecting the mechanical properties of the solder joints. These investigations provided valuable information regarding the Cu concentration effect on the thermal reliability of the Sn-3Ag-xCu/Au/Ni/Cu reaction system.

4:40 PM  
Kinetics of Isothermal Reactive Diffusion between Solid Cu and Liquid Sn-base Alloys: Minho O1; Masanori Kajihara1; 1Tokyo Institute of Technology
    Sn-base solders are widely used in the electronics industry. If a Cu-base conductor is interconnected with the Sn-base solder, Cu-Sn compounds are formed by reactive diffusion at the interconnection during soldering. The growth behavior of the Cu-Sn compounds may be affected by alloying elements in the Sn-base solder. To examine such effects, kinetics of the reactive diffusion between solid Cu and liquid Sn-base alloys was experimentally observed by an isothermal bonding (IB) technique. In the IB technique, the solid and liquid metals are separately preheated at the same temperature as the isothermal annealing temperature in a vacuum. After sufficient preheating, the solid and liquid metals are bonded with each other and then annealed immediately. Thus, unlike immersion and soldering techniques, the temperatures of the solid and liquid metals are equivalent and remain constant during preheating, bonding and annealing in the IB technique.

5:00 PM  
Low Temperature Cu - Cu Direct Bonding for Hermetic Sealing: Po-Fan Lin1; Chih Chen1; 1National Chiao Tung University
    The requirement of performance on electronic devices become higher while their size continues to shrink, which make overheating becomes a serious issue. To solve this problem, heat pipe plays an important role in modern electronic devices to assist heat dissipation. In this study, we perform Cu-Cu direct bonding on silicon wafers for hermetic sealing. Nanotwinned copper is deposited on the silicon wafer with Ti/Cu seed layer. An electropolishing procedure will be applied on the surface of the copper film after the deposition. Next, we perform an etching process on the copper film. A frame like mask layout is designed to pattern the copper films and the seed layers by wet etching process. Finally the bonding process can be carried out below 250 C. Furthermore, we examine the hermeticity by helium leakage test to examine the bonding quality of the Cu – Cu direct bonding.