Device and method for the electrochemical deposition of chemical compounds and alloys with controlled composition and/or stoichiometry

Abstract

Disclosed is a method for depositing an alloy and / or chemical compounds on a substrate immersed in an electrolyte (1), comprising the steps of: I) applying a first constant or varying potential to the substrate under voltage control for a first time interval (tA); II) applying a second constant or varying current to the substrate under current control for a second time interval (tB); repeating the sequence of steps (I-II). at least twice. Further the use of the method in particular for the deposition of Bi2+xTe3−x is disclosed as well as a specific device for carrying out the above method.

Description

TECHNICAL FIELD[0001]The presented invention relates to a method for depositing an alloy and / or chemical compounds on a substrate immersed in an electrolyte. It furthermore relates to the use of such a method for the deposition in particular of Bi2+xTe3−x coatings and it also relates to a specifically tailored device for the above method.BACKGROUND OF THE INVENTION[0002]Electrochemical deposition (ECD) is a well-known method to electrochemically deposit layers of metals, alloys or chemical substances on the surface or into a surface structure of a substrate to be treated.[0003]Electrochemical deposition is thus generally known and can be achieved by a variety of techniques. A typical electrochemical deposition method comprises the reduction of ions from aqueous, organic or fused salt electrolytes at the electrode-electrolyte interface forming a deposition. This deposition can be achieved in two different ways: a) with an electroless (autocatalytic) deposition process in which the el...

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Benefits of technology

[0030]Our invention allows to reduce the current flow between the working electrode and the counter electrode in a controlled manner, while the potential control between working electrode and reference electrode remains unimpaired and controllable. This current control can for example be achieved by introducing a variable resistance between the working electrode and the counter electrode. With increasing resistivity, a decrease in the deposition rate occurs but also an increase in material homogeneity can be observed. This level of deposition quality could not be reached by only reducing the pulse duration, since short but high current pulses lead to inhomogeneous deposits. According to a preferred embodiment of the invention therefore, control in particular during step I, so in the deposition step, takes place using an adaptable and controllable resistance between the working electrode and the counter electrode, wherein preferably control of this resistance is effected using a feedback loop by current measurement in the path between working electrode and counter electrode. This resistance allows to finely control the current flow (not just determined anymore by the diffusion in the solution) and allows to slow down the deposition process within one pulse without changing the applied voltage, which in turn leads to superior morphology, less grains, better surface roughness.

[0034]The newly proposed method allows the exact control of the stoichiometry and composition, respectively, over the whole duration of the deposition and therefore allows a targeted control over the layer properties and the material properties over the whole thickness of the layer.

[0038]Indeed the voltage controlled deposition period allows to establish the desired electrochemical reduction and allows complete control over the composition and structure and correspondingly over the properties of the deposited material. On the other hand the current controlled relaxation period allows current-free compensation and leveling reactions at the interface between the already deposited material (electrode) and the electrolyte, which leads to a self-regulated resting potential.

[0053]Furthermore the present invention relates to a device for use in a method as outlined above or for a specific use as outlined above. This device comprises a power supply and mixed method control unit to connect to at least one working electrode, at least one counter electrode and (optionally) one or more additional (reference-) electrodes. For the voltage controlled periods the use of a reference electrode allows to have more simple and more accurate control. The mixed method control unit comprises a voltage source for providing a controlled voltage to the electrodes and at least one controllable triggered switch (e.g. mechanical, electromechanical, IC or electrical triggered switch) which allows to connect and disconnect the voltage source from the electrodes for the first time interval and the second time interval, respectively. Such as a device typically further comprises a reference electrode (RE) or a pseudo-reference electrode connected with the working electrode (WE) and an element for measurement and / or control of the voltage between the reference electrode (RE) and the working electrode (WE).

Problems solved by technology

For the deposition of certain alloy and compounds using conventional electrochemical deposition processes may lead to problematic layer properties and material properties like for example insufficient adhesion, internal stress or undesired physical properties etc.

These problems are due to variations in the stoichiometry / composition across the thickness of the layer which in turn are due to lack of control during the deposition process.

This insufficient stoichiometric control during the deposition is inherent to the processes according to the state-of-the-art.

However, during the relaxation period for certain electrochemical systems, e.g. Bi2+xTe3−x the problem of undesired reactions on the deposition electrode occurs, which are caused by shifting of the equilibrium potential.

The current controlled pulsed electrochemical deposition is problematic in the sense that the deposition processes during the deposition period cannot be completely controlled.

Unfortunately few measurements have been made to investigate the stoichiometry across the thickness of electrochemically deposited Bi2Te3 layers.

However discrepancies illustrate the necessity of investigations on the stoichiometric profile and of means to control the deposition process in such a way, that a homogeneous stoichiometry is achieved throughout the entire layer.

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