The temperature dependence of grain boundary (GB) self-diffusion in Cu
polycrystals was systematically investigated using the Cu-64 radiotra
cer and the serial sectioning technique. Two different high-purity Cu
materials were used: 99.9998% Cu and 99.999% Cu. The difference in imp
urity content was checked by time-of-flight secondary-ion mass spectro
metry (SIMS). The two materials were studied in the temperature ranges
1066-720 K (99.9998% Cu) and 973-784K (99.999% Cu). A significant dep
endence of the GB self-diffusion on the material purity was observed,
resulting in a different Arrhenius behaviour of the diffusivity delta
D-GB where delta is the GB width and D-GB is the GB diffusion coeffici
ent. The Arrhenius parameters are 3.89 x 10(-16) m(3)/s and 72.47 kJ/m
ol for the highest purity material, and 1.16 x 10(-15) m(3)/s and 84.7
5 kJ/mol for the high purity material. The differences in GB diffusion
coefficients and activation enthalpies are explained in terms of stro
ng impurity-Cu atom bonds in the boundary. In the present investigatio
n sulphur is the dominant impurity. Remarks are made relating the impu
rity segregation and the reduction of the GB diffusivity to the lifeti
mes of thin film metallic interconnects determined by electromigration
effects in GBs. Using a semi-empirical relation of Borisov ct al. the
GB energy, gamma(GB), of large angle boundaries and its temperature d
ependence were determined from the self-diffusion data of Cu. The resu
lting values of gamma(GB) (e.g. 650 mJ/m(2) at 1000 K) are in good agr
eement with GB energy measurements and model calculations for Cu. (C)
1997 Acta Metallurgica Inc.