RAPID FORMATION OF INTERMETALLIC COMPOUNDS BY INTERDIFFUSION IN THE CU-SN AND NI-SN SYSTEMS

Fundamental investigations were carried out to examine a new interconnection technology which is based on the rapid formation of intermetallic compounds composed of a high melting component (e.g. Cu or Ni) and a low melting component (e.g. Sn) between two layers of the high melting component at temperatures just above the melting point of Sn. This reaction is known as isothermal solidification. The growth of the intermetallic compounds of the Cu-Sn and Ni-Sn systems were studied in thin films at temperatures from 513 to 673 K. At the beginning of interdiffusion, the Sn-rich intermetallic compounds eta (Cu6Sn5) and Ni3Sn4 grow fastest with a non-parabolic time dependence. The Cu3Sn phase grows parabolically, however, not the Ni3Sn2 phase. The Ni3Sn phase does not nucleate below 623 K in specimens with clean Ni/Sn interfaces. Far the first time, the influence of the small grain size of the Cu or Ni thin films were studied by performing similar experiments with Cu or Ni single crystals. In the Cu-Sn system the interdiffusion coefficients for Cu3Sn obtained from the thin film experiments are twice those obtained from the single crystal experiments. In the Ni-Sn system there are no differences between thin him and single crystal results.