Energy filtered convergent beam electron diffraction was used to
investigate localized strain in aluminum interconnects. By analyzing
the position of higher order Laue zone lines, it is possible to measure
the three-dimensional lattice strain with high accuracy
(∼10−4) and high spatial resolution (10 to 100 nm).
In the present article, important details of the strain analysis procedure
are outlined. Subsequently, results of measurements of the local variation
of thermal strains in narrow, free-standing interconnects are presented.
The strain development in single grains during thermal cycling between
−170°C and +100°C was measured in situ and local
stress variations along the interconnect were investigated. The interconnects
show reversible elastic behavior over the whole temperature range, leading to
large stresses at low temperatures. The strain state varies locally within
single grains, as well as from grain to grain, by as much as 50% in
both types of samples. By comparing the experimental findings with
elastic finite element modeling, a detailed understanding of the
triaxial strain state could be achieved.
