Both stress and atomic force microscopy (AFM) measurements were carried out in situ during potentiostatic electrodeposition of copper on gold in 0.05moldm−3 CuSO4 in 0.1moldm−3 H2SO4 with and without additives. With no additives, compressive stress generally developed initially and films subsequently underwent a compressive-to-tensile (C-T) transition. With increasing negative potential, the time for the C-T transition decreased rapidly as the rate of coalescence of nuclei (measured by AFM) increased rapidly. This is consistent with models that attribute the C-T transition to increasing tensile stress due to coalescence of nuclei. Furthermore, at a potential of −75mV (Cu∕Cu2+), where AFM showed very little coalescence of nuclei, no C-T transition was observed, again consistent with these models. The nucleation density measured by AFM increased from 2.7×107cm−2 at −75mVto2.5×109cm−2 at −300mV. Stress measurements with a combination of three additives [1×10−3moldm−3 Cl−, 8.82×10−5moldm−3 polyethylene glycol, and 1×10−5moldm−3 3-mercapto-1-propanesulfonic acid sodium salt (MPSA)] also showed that compressive stress generally developed initially and its magnitude was greater than in additive-free electrolyte. At less negative potentials, even though the rate of coalescence of nuclei was rapid, as observed by AFM, the stress continued to evolve in the compressive direction. At intermediate potentials (−90to−150mV), classical compressive-tensile-compressive (C-T-C) behavior was observed, while at more negative potentials the stress continued to evolve in the tensile direction. Similar results were obtained with a combination of two additives (1×10−3moldm−3 Cl− and 1×10−5moldm−3 MPSA), but in that case the compressive stress appeared to be greater, and consequently the T-C transition was observed even at −500mV. The results are consistent with enhancement of a compressive component of stress in the presence of additives.
Stress was measured in situ during electrodeposition of copper nanofilms. Grain size was measured using both in-situ AFM and exsitu SEM imaging and showed that grain size increased with time for about the first 10 depositions and thereafter became approximately constant. Films deposited at low growth rates had compressive stress while films deposited at higher growth rates had tensile stress. The transition from compressive to tensile stress occurred at a growth rate of ~1 nm s -1 , in reasonable agreement with the literature. Our data supports Chason's model for stress development during thin film deposition. Addition of chloride gives decreased stress, a rougher surface and larger grains. Addition of PEG alone has very little effect on the stress in the deposit. The reduction in stress due to chloride is still observed when PEG is also added and this greatly reduces the surface roughness which occurs with the addition of chloride alone.
In-situ stress measurements and in-situ AFM imaging were employed to study stress evolution during the electrodeposition of copper nanofilms from acidic copper sulphate electrolyte, at overpotentials of 125-200 mV and to compare the observed stress and morphology changes with theoretical predictions. As the films grew, tensile stress initially increased, corresponding to grain coalescence as observed by AFM, and reached a plateau value when significant GB volume had occurred. The time evolution of stress was examined during interruption of deposition. Generally, when deposition was interrupted, tensile stress decreased as predicted by Chason's model 13 for low mobility deposits. At all potentials, upon resuming deposition stress recovered to its pre-interrupted state. Stress increased with increasing overpotential as expected from theory. Cl -was found to directly reduce stress and resulted in a rougher surface than was observed without additives.
Both atomic force microscopy (AFM) imaging and stress measurements were carried out in situ during potentiostatic electrodeposition of copper on gold in 0.05 mol dm-3 CuSO4 in 0.1 mol dm-3 H2SO4 with and without chloride ion (Cl-) and polyethylene glycol (PEG) additives. Our in-situ stress measurement technique allowed us to develop an accurate and reliable method of determining local stress in newly deposited copper films. Stress increases in the tensile direction with thickness and eventually reaches a plateau value. We attribute the initial increase in tension to the coalescence of previously isolated islands and the associated formation of grain boundaries. Stress was observed to be higher at higher overpotentials. The addition of 3 ppm Cl- reduced stress significantly but had very little effect on deposition rate. The addition of 5 ppm PEG with the Cl- enhanced stress reduction.
In-situ stress measurements and in-situ AFM imaging were employed to study time evolution of stress during interruption of the room-temperature electrodeposition of copper nanofilms. Generally, when deposition was interrupted, tensile stress decreased as predicted by Chason's model for low mobility deposits. At all potentials, upon resuming deposition stress recovered to its pre-interrupted state. The relative reduction in stress during interruption increased with increasing overpotential.
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