| Summary: | 碩士 === 國立中興大學 === 化學工程學系所 === 105 === Nowadays, development of microelectronic products follows the trend of miniaturization with the progress of technology. Therefore, the size of the solder joints shrinks and the reliability issue can not be avoided in semiconductor industry. One main reliability issue is the joint structure due to the formation of brittle intermetallic compounds (IMCs) resulting from the solder/metallization reactions. Also, the current density through the solder joints increases rapidly. The joints are not only affected by electromigration but also attacked by the thermal effect caused by current.
The electroplating technique is commonly used in fabricating the Cu metallization in the solder joints. Previous studies indicated that some impurities originated from the additives of electroplating solution. The impurities were incorporated in the Cu deposit and caused severe void formation at the solder/Cu interface during thermal aging. In this study, we investigate the effect of additives on the properties of electroplated copper. Moreover, the solder/electroplated copper interfacial reaction was observed and the reliability of solder joints was discussed.
The IMCs of the Cu/Sn reaction for all copper electroplating formulas grow at a faster rate at higher temperatures during thermal aging. The Sn/Cu interfaces prepared with CS (Cl-+SPS), PCS (PEG+Cl-+SPS), Cu foil are void-free. We find the IMCs formed at the Sn/Cu interface prepared with PC (PEG+Cl-) will easily break at low temperature and exhibit a multi-layer structure at high temperature. Kinetic analysis indicates the bulk-diffusion at high temperature. The four-point probe measurement shows that the Cu deposit prepared by the CS formula has the lowest resistivity.
Focused Ion Beam system (FIB) images show the voids accumulated at the Cu/Cu3Sn interface at low-temperature heat treatment which means that the mechanical strength of the joint prepared by the PC formula is the weakest at low temperature aging. Conversely, the voids distribute in IMC and interface at high temperature and the gray-dark substance appears around the periphery of the voids. Time-of-Flight Secondary Ion Mass Spectrometer (TOF-SIMS) results show the impurity concentration is similar.
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