|Ph.D Student||Esta Abelev|
|Subject||Study of Copper Passivation in Aqueous Solutions|
|Department||Department of Materials Science and Engineering||Supervisor||Full Professor Ein-Eli Yair|
|Full Thesis text|
Copper passivity in aqueous electrolyte solutions was studied for many years. During the last decade the interest in copper passivity significantly increased due to the important role of copper in the microelectronic industry as a metal in integrated circuit interconnects. Copper interconnections are fabricated using dual damascene process. One of the main steps in copper dual damascene technology is Chemical Mechanical Planarization (CMP).
CMP process requires a complete passivation of the planarized metal, while main requirements in passivity of planarized metals are: instantaneous self passivation upon contact with polishing slurry, high protective characteristics of the produced thin passive film, and rapid repassivation of surface sites where oxide film is removed. The goal of this work was to perform a systematic study on different aqueous solutions, which can provide enhanced copper passivity (formation of thin protective films on the copper surface) in a wide potential range.
In this research, the experimental methods applied for corrosion studies are classified into two categories: electrochemical and surface analysis. Repassivation time measurements of copper were performed by the use of slurryjet system, which provides a single particle impact measurement. Surface analysis X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) were used in order to characterize chemical composition of corrosion products formed at different conditions.
The main electrolytic systems which were evaluated during the work were based on potassium carbonate and potassium sorbate solutions. Enhanced copper passivity was obtained in a wide potential range in potassium carbonate and sorbate based solutions. Moreover, potassium sorbate was found to be an efficient copper inhibitor in solutions containing aggressive anions such as; sulfate and chloride. Ultra-short repassivation times characterized both the potassium sorbate and carbonate solutions. XPS spectroscopy demonstrated, that copper surface, subsequent to immersion in carbonate solution, was covered with a protective layer consisting of CuCO3, cupric hydroxide (Cu(OH)2) and cuprous oxide (Cu2O); while after immersion in potassium sorbate solutions the protective film formed at the copper surface was consisted of; Cu2O, Cu(OH)2 and copper(II)-sorbate.
In addition, short chain fatty acid potassium salts were found to be highly efficient inhibiting materials of copper corrosion. By means of FTIR spectroscopy, it was shown that copper binuclear complex with symmetrically bound carboxylate groups having a bridging bidantate divalent structure was formed at the copper surface. This provides enhanced copper passivity in short chain fatty acid potassium salts solutions.