Abstract
In copper interconnects of integrated circuit process technology, chemical mechanical polish (CMP) is the most important step to remove overburden material and planarize surface of metallization. However, the slurry adopted in CMP may introduce corrosion issue. Chemical and galvanic corrosions of copper interconnects during processing may cause the failure of device. Therefore, it is crucial to find a way to increase the corrosion resistance of copper interconnects. Nanotwinned copper has received broad attention recently due to its high mechanical strength, reasonably low electrical resistivity, and better electromigration resistance. However, its corrosion resistance is yet to be investigated. In this thesis, the corrosion resistance of nanotwinned copper prepared by pulsed electrodeposition technique is studied. Benzotriazole (BTA) is widely applied as a corrosion inhibitor in CMP and an electrodeposition additive as a brightener. But there is only limited literatures addressing the corrosion resistance of copper films deposited with BTA. In this study, the corrosion resistance of copper films electrodeposited with BTA is investigated. From the results by electrochemical polarization, scanning electron microscope and atomic force microscopy, it was found that copper films prepared by pulsed electrodeposition technique as well as with BTA in electrolyte have better corrosion resistance than those deposited by direct current deposition and without BTA in the electrolyte. Surface roughness, crystal orientation, and grain size are known to affect the rate of corrosion. In this study, the former two are controlled in all specimens to minimize their influence on corrosion behaviors. Moreover, the grain size effect is unable to explain the observed corrosion properties of the copper films prepared by different methods. The existence of twin structures, confirmed by transmission electron microscopy, is thought to be associated with the increase of corrosion resistance. Twinning induced grain boundary segment transformation is speculated to be held responsible for better corrosion resistance. X-ray diffractions results indicate that copper films deposited with BTA have poor crystallinity due to BTA incorporation in the electrodeposited films. The incorporation of BTA was found to increase corrosion resistance of the electrodeposited copper films.