Sn/Cu互连体系界面和金属间化合物层Kirkendall空洞演化和生长动力学的晶体相场法模拟

PHASE-FIELD CRYSTAL SIMULATION ON EVOLUTION AND GROWTH KINETICS OF KIRKENDALL VOIDS IN INTERFACE AND INTERMETALLIC COMPOUND LAYER IN Sn/Cu SOLDERING SYSTEM

采用二元合金晶体相场模型模拟研究了Sn/Cu互连体系Cu/Cu3Sn界面及金属间化合物层中Kirkendall空洞形成和形貌演化及长大过程,对Kirkendall空洞生长的微观机制进行了剖析,同时还模拟和分析了界面Cu3Sn层厚度和杂质含量对Kirkendall空洞形貌和生长动力学的影响.研究表明,Kirkendall空洞的生长过程由4个阶段组成:Cu/Cu3Sn界面形成大量原子错配区,原子错配区迅速成长为空洞,空洞的长大及随后的空洞合并生长.Kirkendall空洞优先在Cu/Cu3Sn界面处形核,其尺寸随时效时间的延长而增大,并在时效后期空洞的生长伴随有空洞的合并.Cu3Sn层厚度增加和杂质含量增多均使得Kirkendall空洞数量和生长指数增加以及尺寸增大,并且2种情况下空洞数量随时间的变化均呈现先增后减的规律.

With the development of electronic products towards further miniaturization, multifunction and high- reliability, the packaging density has been increasing and the dimension of solder joints has been scaling down. In electronic packaging, during the soldering process of Sn/Cu system, an intermetallic compound（IMC）layer is formed at the interface between the molten solder and pad（substrate）, the interfacial microstructure plays an important role in the reliability of solder interconnects. Generally, during the reflow soldering and subsequent aging process, a large number of Kirkendall voids may form at the Cu/Cu3 Sn interface and in the Cu3 Sn layer. The existence of Kirkendall voids may increase the potential for brittle interfacial fracture of solder interconnects and reduce the thermal conductivity. Thus, characterization of formation and growth of Kirkendall voids is very important for the evaluation of performance and reliability of solder interconnects. In this work, the formation and growth of Kirkendall voids at the Cu/Cu3 Sn interface and in the Cu3 Sn layer of Sn/Cu solder system have been investigated by means of phase field crystal modeling. The growth mechanism of Kirkendall voids was analyzed.The effects of thickness of Cu3 Sn layer and impurity particles in the Cu3 Sn layer on the growth of Kirkendall voids were discussed. Phase field simulation results show that the growth of Kirkendall voids exhibits four stages during the thermal aging, including the formation of atomic mismatch areas at the Cu/Cu3 Sn interface, the rapid growth of the atomic mismatch areas leading to the formation of Kirkendall voids, the growth of Kirkendall voids and the subsequent coalescence of Kirkendall voids. Kirkendall voids nucleate preferentially at the Cu/Cu3 Sn interface and their sizes increase with the aging time, and the coalescence of the voids can be observed obviously in the later stage of thermal aging. It has also been shown that the increase of the Cu3 Sn layer thickness and the amount of impurity particles lead to an increase in both number and size of Kirkendall voids, as well as an increased growth exponent; and the number of Kirkendall voids increases initially and then decreases with the aging time.