Zhao N, Zhong Y, Huang M L, Ma H T, Dong W
School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China.
Sci Rep. 2015 Aug 27;5:13491. doi: 10.1038/srep13491.
The growth behavior of intermetallic compounds (IMCs) at the liquid-solid interfaces in Cu/Sn/Cu interconnects during reflow at 250 °C and 280 °C on a hot plate was investigated. Being different from the symmetrical growth during isothermal aging, the interfacial IMCs showed clearly asymmetrical growth during reflow, i.e., the growth of Cu6Sn5 IMC at the cold end was significantly enhanced while that of Cu3Sn IMC was hindered especially at the hot end. It was found that the temperature gradient had caused the mass migration of Cu atoms from the hot end toward the cold end, resulting in sufficient Cu atomic flux for interfacial reaction at the cold end while inadequate Cu atomic flux at the hot end. The growth mechanism was considered as reaction/thermomigration-controlled at the cold end and grain boundary diffusion/thermomigration-controlled at the hot end. A growth model was established to explain the growth kinetics of the Cu6Sn5 IMC at both cold and hot ends. The molar heat of transport of Cu atoms in molten Sn was calculated as + 11.12 kJ/mol at 250 °C and + 14.65 kJ/mol at 280 °C. The corresponding driving force of thermomigration in molten Sn was estimated as 4.82 × 10(-19) N and 6.80 × 10(-19) N.
研究了在250°C和280°C热板回流过程中，Cu/Sn/Cu互连结构液固界面处金属间化合物（IMC）的生长行为。与等温时效期间的对称生长不同，回流期间界面IMC呈现明显的不对称生长，即冷端Cu6Sn5 IMC的生长显著增强，而Cu3Sn IMC的生长受到阻碍，尤其是在热端。研究发现，温度梯度导致Cu原子从热端向冷端发生质量迁移，使得冷端有足够的Cu原子通量用于界面反应，而热端的Cu原子通量不足。生长机制被认为在冷端是反应/热迁移控制，在热端是晶界扩散/热迁移控制。建立了一个生长模型来解释冷端和热端Cu6Sn5 IMC的生长动力学。计算得出在250°C时，Cu原子在熔融Sn中的迁移摩尔热为 +11.12 kJ/mol，在280°C时为 +14.65 kJ/mol。在熔融Sn中热迁移的相应驱动力估计为4.82×10(-19) N和6.80×10(-19) N。
