Simple electrochemical method for monitoring the time-dependent dissolution behavior of layers deposited by atomic layer deposition

Abstract

Spectroscopic and microscopic techniques are not suitable for the rapid monitoring of time-dependent dissolution behavior (particularly, pinhole changes) of a layer deposited by atomic layer deposition (ALD). Here, we present a simple electrochemical method that provides information on the dissolution mechanism including pinhole generation and thickness change. Because indium tin oxide (ITO) electrodes exhibit flat capacitive currents and good (electro)chemical stability, they are selected as ideal underlying substrates for the electrochemical monitoring of the ALD layers even under harsh conditions. Two ALD layers (Al 2 O 3 and TiO 2 layers) that exhibit opposite dissolution behaviors are chosen as model layers because the as-deposited Al 2 O 3 layers are pinhole-free but unstable in aqueous solutions, whereas the as-deposited TiO 2 layers are not pinhole-free but stable in aqueous solutions. The combination of capacitive current level (in an electrolyte solution containing no redox-active species) and electrochemical blocking behavior (in an electrolyte solution containing a redox-active species such as Ru(NH 3 ) 6 3+ and ferrocenemethanol) obtained from cyclic voltammograms enables us to verify whether the dissolution of an ALD layer occurs, to evaluate the dissolution rate, and to identify the plausible dissolution mechanism. The electrochemical results reveal that the Al 2 O 3 layers are dissolved in biological buffers, along with pinhole generation, and that the TiO 2 layers are stable with no pinhole generation. The difference in electrochemical blocking behavior between Ru(NH 3 ) 6 3+ and ferrocenemethanol provides information on the approximate size of the pinholes. The present method is appealing for practical use because even an ALD layer with a thickness of only a few nanometers can be tested to monitor the dissolution behavior and because any ALD layer that can be readily deposited on ITO electrodes can be easily examined using this method. • Stability comparison of Al 2 O 3 and TiO 2 layers deposited by atomic layer deposition. • Indium tin oxide electrodes are ideal underlying substrates for the comparison. • The combination of capacitive current level and electrochemical blocking behavior allows for evaluating dissolution. • Al 2 O 3 layers are dissolved in biological buffers, along with pinhole generation.