Experimental and Theoretical Investigation of Electrochemical Pattern Etching
Deligianni, Hariklia
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Permalink
https://hdl.handle.net/2142/69797
Description
Title
Experimental and Theoretical Investigation of Electrochemical Pattern Etching
Author(s)
Deligianni, Hariklia
Issue Date
1988
Doctoral Committee Chair(s)
Alkire, Richard C.
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Engineering, Electronics and Electrical
Abstract
Manufacturing of Integrated Circuits and Printed Circuit Boards involves a series of processing steps such as, lithography deposition and etching. The reliability of micro-electronic devices relies mainly on the ability to retain pattern fidelity during etching.
Wet chemical etching in the presence of a flow field is useful for generating patterns in relatively thick metal films (max 250 microns), since the flow imparts a variable degree of directionality to the process. Fresh etchant is rapidly and constantly supplied to the reaction site while the products are continuously removed. The use of electrolytic current as a reducing agent solves the problem of choosing an appropriate oxidant and permits accurate control of the reaction rate (current density).
From a fundamental point of view, electrochemical etching is a process which involves the interaction of transport and reaction phenomena in microscale recesses which change shape during the course of etching. Electrochemical etching of copper under the influence of a transverse flow field was investigated experimentally and optimum conditions to obtain anisotropic patterns were identified. Anisotropy was found to be associated with formation of a salt film at the edges of the cavities while the rest of the cavity bottom surface would dissolve actively. The presence of the salt layer would tend to suppress dissolution in the corner region, and therefore would enhance anisotropy.
A theoretical model was developed which accounted for the effects of potential field, mass transfer, surface reaction and fluid flow in microscale cavities. Theoretical predictions were tested using experimental shape change results for active, mass transfer limited and mixed controlled etch rate. The model although based on fundamental principles, predicted conditions of externally applied flow rate and current density for which patterns will be anisotropic or will result in beveled sidewalls.
Furthermore, a moving boundary scheme was employed to study the shape evolution of an etched cavity. The metal surface was assumed to dissolve under diffusion controlled conditions in a stagnant medium. A model experimental system was used to compare with theoretical predictions and existing literature.
Finally, a simplified model was developed to guide strategies for the design and operation of wet etching systems.
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