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Copper Oxidation Effect in the EMC/Cu Interfacial Adhesion Improvement for a Novel Copper Interconnection Substrate Application
Keywords: epoxy molding compounds, EMCs, Copper Interconnection Substrate, Copper Oxidation
The epoxy molding compounds (EMCs) / Copper (Cu) interfacial adhesion characterization was considered to improve delamination issue by one key factor of material technology, this factor is linking with bottom-up substrate development, for example copper trace/ interconnection constructed in the EMC. This novel substrate can instead of popular BGA (Ball Grid Array) substrate for low cost concern, moreover, many advanced packaging technology such as WLCSP(Wafer Level Chip Scale Package), fcCSP (Flip Chip-Chip Scale Package), PoP (Package on Package), eWLB (Embedded Wafer Level Ball Grid Array), and SiP (System in Package), etc. In 3D package development, these packages would face many materials properties challenge, these substrate materials should possess high heat dissipation efficiency and high reliability quality to overcome high-density packaging requirement and fine-pitch technology application. Therefore, this kind of copper trace/interconnection constructed in the structure is an attractive solution, however this structure have a weakness of the EMC/Cu adhesion, moreover, the delamination usually happen at EMC/Cu interface, hence, this study is researching an Cu oxidation effect in the EMC/Cu interfacial adhesion improvement as a delamination solution for advanced package [1]. In this study, we utilize Thermo-Gravimetry Analyzer (TA Instruments, The Discovery TGA) under air flow to research Cu foil oxidation rate with temperature to be Arrhenius relationship and to determine Cu foil thermal condition [2-5]. Moreover, we use the EMC molding on Cu foil as a pudding structure and shear testing method [6, 7] to determine the EMC/Cu interfacial adhesion performance for different surface experimental conditions. These experimental conditions of Cu oxidation thickness and the EMC/Cu interfacial observation were measured and analysed by Focus Ion Beam (FEI Helios G4 Dual-Beam System), moreover, we utilize Transmission Electron Microscope (FEI Talos F200X G2 TEM) with Energy dispersive X-ray spectroscopy (EDS) and Electron Energy Loss Spectroscopy (EELS) analyses to identify the Cu oxidation composition and the EMC/Cu interfacial bonding characterization. We have found that Cu oxidation layer have an important surface composition change that is correlating with the EMC/LF adhesion force, moreover, a huge adhesion force is increased with hydrogen plasma treatment after Cu thermal oxidation. An adhesion characterization between the EMC and Cu during the assembly process is the key point, it is necessary to improve the organic compound/metal interfacial bonding force while the EMC/Cu interface has delamination issue. Hence, the process such as copper/interconnection surface treatment would improve the EMC/Cu interfacial bonding force. Copper oxidation have two species, Cu2O of semi-oxidized state (cuprous oxide, Cu+) and CuO of full-oxidized state (cupric oxide, Cu++) oxidized state, different oxidation species would affect the EMC/Cu adhesion characterization due to the copper surface undergo different kinds of high temperature reaction under environmental air[8-11]. Experimental results have shown that a cupric oxide (CuO) possess good adhesion performance due to most of Cu(II)O composition can support the source to form much H-bonding chemical structure on surface modification which the Cu(II)O is under hydrogen plasma treatment. On the contrary of experimental condition without Cu thermal oxidation and hydrogen plasma treatment for traditional process flow, it was shown a void existed at the EMC/Cu interface, it is also reasonable to explain why the bonding force is weaker than the former. Moreover, the conclusion is a Cu(II)O/Cu structure undergo hydrogen plasma surface reduction to obtain the H-bonding formation and enhance the EMC/Cu interfacial bonding force were identified by FIB/TEM analyses. We also clarify that the reaction mechanism of the EMC/Cu interfacial bonding characterization to verify the H-bonding existence for different surface compositions. On the other hand, the activity energies of Cu(II)O and Cu(I)2O species were determined by the TGA with Arrhenius plots under air flow, this result can help to define the surface oxidation temperature and time for adhesion improvement.
Min-Fong Shu, Manager
ASE Group
Taoyuan City, Taiwan, R.O.C.
Taiwan, R.O.C.

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