Surface Cleaning of Gold Structure by Annealing during Fabrication of Microelectromechanical System Devices

Abstract

We describe a technique for cleaning a gold surface using a dry process during the fabrication of microelectromechanical system (MEMS) devices. After exposure to oxygen plasma for ashing of the organic contaminants or etching of a sacrificial-layer film, the gold surface is oxidized. On such an oxidized surface, there are different incubation periods at different places, which give rise to nonuniform thickness in electroplating as well as in electrodeposition. A surface analysis by X-ray photoelectron spectroscopy (XPS) revealed that annealing at a temperature of over 260 C causes oxygen to desorb from the gold oxide. The application of this cleaning technique before electroplating or electrodeposition leads to uniform growth.

Room-Temperature Gold-Gold Bonding Method Based on Argon and Hydrogen Gas Mixture Atmospheric-Pressure Plasma Treatment for Optoelectronic Device Integration

“…Although Au is most resistant against oxidation in air, even at high temperatures, the plasma oxidation of Au samples has been reported in the literature [18], [24], [25]. It has also been reported that the gold oxide thermally desorbs in two steps (170 and 260…”

“…• C is necessary for the oxide removal [25]. The surface oxide layers impede bonding between Au and Au.…”

Reaction Monitoring of Gold Oxides Prepared by an Oxygen-dc Glow Discharge from Gold Films in Various Aqueous Solutions by a Surface Plasmon Resonance-based Optical Waveguide Sensing System and X-ray Photoelectron Spectroscopy

“…15 The gold oxides that occurred on the gold electrodes of microelectromechanical system (MEMS) devices after the release of organic sacrificial layers caused by exposure to oxygen plasma were also characterized. [16][17][18][19] It has previously been reported that the gold oxides on the gold electrodes of MEMS devices can be removed effectively via treatment with aqueous hydrochloric acid 16,17 or heating. 18,19 Plasma surface treatments using various gases, including oxygen, for bonding with thin gold films and with stub bumps were also compared.…”

“…[16][17][18][19] It has previously been reported that the gold oxides on the gold electrodes of MEMS devices can be removed effectively via treatment with aqueous hydrochloric acid 16,17 or heating. 18,19 Plasma surface treatments using various gases, including oxygen, for bonding with thin gold films and with stub bumps were also compared. 20,21 Gold oxides that were present on gold nanoparticles were also investigated and the results were reported previously.…”

“…X-ray photoelectron spectroscopy (XPS) 27,28 is a useful method for characterization of thin gold oxide layers on gold films. The gold oxides, which were prepared via various methods, all decomposed immediately at higher temperatures, 2,5,[7][8][9]11,13,18,19,21 while they decomposed relatively slowly at room temperature. 9,12 The gold oxides were also found to contain oxygen species other than the gold oxides and these species remained stable at higher temperatures.…”