Tracer study of diffusion and electromigration in thin tin films

Abstract

A comprehensive study of lateral self-diffusion and electromigration in evaporated thin Sn films over the temperature range −50 to 198 °C is reported. Sn119m atoms were deposited over a central portion of thin Sn film stripes and the subsequent diffusional spreading and migration of the tracer distribution were evaluated by a high-resolution autoradiographic technique. Activation energies suggestive of grain boundary transport processes were obtained. At low temperatures the ionic drift velocity in grain boundaries Vb is measured to be VbT/j=3.4×10−2 exp[−(8710±360 cal/mol)/RT] cm3 K/A s, while the low-temperature grain boundary diffusivity Db is given by Db=4.9 exp[−(11 700±840 cal/mol)/RT] cm2/s. At higher temperatures (i.e., >80 °C) transport measurements were conducted employing Sn films of two different grain sizes, and apparent drift velocities and diffusivities were obtained. Application of the Hart model enabled the extraction of grain-size independent values of the grain boundary ionic drift velocity and diffusivity given by VbT/j=3.3×10−2 exp[−(8980 cal/mol)/RT] cm3 K/A s and Db=8.3×10−2 exp[−(9790 cal/mol)/RT] cm2/s. The effective valence Z* in the grain boundaries was calculated over the complete temperature range using the Db and VbT/j values obtained in the present investigation. A rapid rise in Z* at low temperatures, similar to that previously reported in Au films, was observed, suggesting that at low temperatures the Z* in the grain boundaries is greater than in the lattice. Electromigration in Sn is anode directed at all temperatures.

Effect of Constant and Cyclic Current Stressing on the Evolution of Intermetallic Compound Layers

“…A current density of 10 4 A/cm 2 is generally regarded as the threshold above which bulk materials start to melt. 14,17 Thus, if solder interconnections in the experiments carried out, for example, in Refs. 2, 8-10 locally melt, it is quite understandable why IMCs can ''migrate'' from the cathode to the anode.…”

“…In addition, it has been experimentally determined that the effective valence (Z * ) of Sn is negative. [13][14][15] This means that Sn should always be driven towards the anode. 13 Furthermore, it is known that Cu can diffuse interstitially in Sn 16,17 and has also a negative effective valence (Z * ).…”

Measuring the Stress Dependence of Nucleation and Growth Processes in Sn Whisker Formation

“…The activation energy from the slope is 0.37 eV, similar to the activation energy for grain boundary diffusion in Sn. 38,39 This is not surprising because it is known that Sn diffuses over a long range to feed whisker/ hillock growth. We want to emphasize that the analysis above is based only on the average stress and temperature.…”

Deformation of solder joint under current stressing and numerical simulation––I

“…The grain boundary diffusivity given by Singh and Ohring (1984) by assuming a grain boundary width of 0.5 nm is: D gb ¼ ð4:9 þ15:6 À3:7 Þ exp½Àð11; 700 AE 840 cal=molÞ=RT cm 2 =s…”

“…Sun and Ohring (1976) developed a tracer-scanning technique to study self-diffusion and electromigration in evaporated thin Sn films at 142-213°C. Singh and Ohring (1984) conducted the self-diffusion and electromigration experiment in evaporated thin Sn films at )50 to +198°C. Their measurements of grain boundary diffusivity in pure tin are shown in Fig.…”