Dynamic Stress Analysis at Solid Electrodes

Wafer curvature and cantilever bending techniques have been used by the electrochemical community to examine stress development during electrochemical processing. Surface stress changes as low as 10 N/m can typically be resolved from cantilever electrodes immersed in solution and under potential control. Such resolution makes this measurement useful for examining virtually all aspects of electrochemistry; i.e., electrocapillarity, adsorption processes, underpotential deposition, electrodeposition, battery reactions, and metal hydride formation. Often these processes occur either simultaneously or in rapid succession and we are often limited to measuring the influence of the dominant process in the time-scale of the experiment. Electrochemical impedance spectroscopy (EIS) is a technique in which one measures the impedance of an electrochemical system over a range of frequencies, revealing information about the reaction mechanisms: different reaction steps will dominate at frequencies dictated by their relaxation times. Whereas traditional EIS determines the transfer function of the current in response to potential modulation, we are interested in determining the transfer function of the stress (as measured from cantilever curvature) to the same potential modulation. This will provide us with the time constants for the stress response that might enable us to directly link the stress to specific electrochemical phenomena.