  Here we report the evolution of Ni stress in electroplated Ni films and
investigate its origins as a function of electroplating time. First, low stress
200-nm-thick Ti / 200-nm thick Ni seed layers are deposited onto Si (100)
wafers via electron-beam evaporator.Then, Ni films are electroplated onto the
seeded Si (100) wafers in an All-Chloride bath. We observe that Ni grains
nucleate prominently in the [111] direction aligning with Si[100]. Using
optical curvature measurements, scanning electron microscopy (SEM), and X-ray
diffraction (XRD) measurements, we quantify the electroplated Ni stress and
investigate its evolution as a function of electroplated Ni thickness, grain
size, crystal orientation, crystallite size, lattice spacing, and dislocation
density. Particularly, when averaged electroplated Ni thickness was increased
from 2.1 um to 5.9 um, Ni tensile stress reduced from 604.8+-137.9 MPa to
339.8+-74.7 MPa as (1) average Ni grain size increased by 40.9+-1.3 % (Ni
lattice constant expanded by 0.19+-0.03 % in the [220] in-plane direction and
shrunk by 0.22+-0.04 % along normal [111] direction), (2) Ni grain growth along
Ni [110] was inhibited and that along Ni [100], [111], and [311] were promoted,
(3) Ni crystallite size improved by 26.3+-6.2%, and (4) Ni dislocation density
reduced by 42.7+-10.0%. Overall, Ni stress is shown to be strongly correlated
with the Ni structure, which is a function of electroplating time, and both can
be quantified through optical and structural characterization techniques.
