Charakterisierung galvanisch abgeschiedener Nickel- und Nickel-Wolfram-Schichten für mikrotechnische Anwendungen

Many products in the field of MEMS were realized by the progressive integration of microelectronic circuits and combination with micro mechanical components. Fabrication processes of micro system technology supplement microelectronic components with mechanical microstructures. Sensor and actuator concepts can thus be realized and supporting structures for assembling and mounting technology for micro components can be provided respectively. The micro electroplating process is an additive process suitable to fabricate metallic structures on top of silicon substrates carrying micro electronic circuits. The fabrication of suspending structures providing moveable spring-like elements is possible by application of sacrificial layers. Construction and simulation of micro-springs require detailed knowledge about the behavior of the material under strong mechanical deformation. For microstructures made of electroplated nickel the material behavior in transition from elastically to plastically deformation has been examined only by few investigations yet. Systematic investigations are difficult because many solid state properties of electroplated nickel, as grain size, structure and texture vary in wide spectra. The objective of this work is to find relations between mechanical properties of nickel an parameters used in the micro electroplating process to optimize material for MEMS-application. Examination of solid state properties as well as electrochemical processes of the metal deposition were carried out in this work. In addition the suitability of an electroplated nickel tungsten alloy for fabrication of elastic deflectable microstructures was examined. The alloy was electroplated by an electrolyte developed in this work for application in the micro electroplating process. The influence of the current density and electrolyte composition on the deposited nickel was examined by texture, grain structure and measuring mechanical material data like young´s modulus, yield strength and ultimate tensile strength. Crystallographic an metallographic characterization as well as micro tensile tests, laser-acoustic measurements and mechanical resonance experiments on fabricated micro structures were carried out. Electrochemical phase boundary processes during metal deposition were characterized by means of electrochemical impedance spectroscopy and current-time transients. These examinations show the influence of the substrate on nucleation and growth of deposited nickel layers by comparison of two different substrate materials. The current density used for electrodeposition effects structure and texture of deposited nickel layers strongly. It could be shown that mechanical properties have a close relation to the above mentioned solid state properties. Particular grain structures and textures were found to be typical for individual ranges of current density and are caused by adsorption and desorption phenomena on the growing metal surface which influence nucleation and growth of the deposited metal layer. In addition it was recognized that besides current density further parameters like content of wetting agent or hydrodynamic condition at the phase boundary also effect the examined material properties. A qualitative model has been developed to describe the effect of these parameters on solid state properties of deposited nickel layers. Process parameters were found to deposit nickel layers with the highest possible young´s modulus and high yield strength. A fabrication process for micro-springs made of electroplated nickel could be optimized hence. By means of the developed nickel tungsten alloy process micro structures with clearly enhanced stability against plastically deformation compared to pure electroplated nickel were fabricated. The developed alloy system came out to be a promising alternative to nickel in micro electroplating process for the fabrication of elastically movable microstructures.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2002

Author dc:creator

• Fritz, Thomas Michael

Contributors dc:contributor

• Mokwa, Wilfried

• info:eu-repo/classification/ddc/530
• Physik

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-119109%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:57039