Studies On Copper And Ruthenium Electrochemical Mechanical Polishing And Their Characteristics

In the manufacturing field of large scale integrated circuit, damascene process is applied to form multi-layer copper interconnections, and electrochemical mechanical polishing of Cu and Ru are the two independent key processes. Since feature size of copper interconnections becomes thinner and thinner, and device structures become more and more mini and complex, Cu/low-k interconnects integration technology provides the direction as well as the challenges in the fabrication of integrated circuits wafers. Electrochemical mechanical polishing and their characteristics of Cu and Ru were investigated in this paper.The optimization of electrolytes and the characterization of passive film at different pH including1-hydroxyethyl-lidene-1,1-diphosphonic acid,5-methyl-1h-benzotriazole, ammonium citrate tribasic were investigated by electrochemical techniques, nano-scratch tests, atomic force microscope measurements and X-ray photoelectron spectroscope analysis. Synergistic inhibition capability of5-methyl-lh-benzotriazole and chloride ion was also investigated in this work. The experimental results show that the planarization efficiency and the surface quality after electrochemical mechanical polishing obtained in alkali-based solutions are superior to that in acidic-based solutions. The main factor affecting the thickness of the oxide layer formed during electrochemical mechanical polishing process is the applied potential. X-ray photoelectron spectroscope analysis reveals that copper(Ⅱ) is present in the passive film, no copper(Ⅰ) is detected.The effect of electrochemical action on mechanical abrasion was investigated by using nano-scratch tests and atomic force microscope measurements. A mathematic model based on the nano-scratch tests using Berkovich indenter was proposed to calculate the thickness of passive film. To mitigate undesirable scratches caused by the softer pad asperities during electrochemical mechanical polishing, a critical equation among the normal pressure on the pad, hardness of pad and the frictional coefficient was proposed to predict the initiation of scratching by the combination of nano-scratch tests and finite element simulation.The optimation of electrolytes suiting Cu/Ru electrochemical mechanical polishing were investigated by electrochemical techniques. The formula of electrolyte was investigated including1-hydroxyethyl-lidene-1,1-diphosphonic acid,5-methyl-1h-benzotriazole, benzotriazole, and ascorbic acid. Benzotriazole and ascorbic acid were chosen as selective anodic and cathodic inhibitors for Cu and Ru, respectively. The performance of Ru electrochemical mechanical polishing and the galvanic corrosion between Cu and Ru were investigated by linear sweep voltammetry, open circuit potential, electrical impedance spectroscopy, scanning electron microscope, and X-ray photoelectron spectroscope. The results show that the combination of benzotriazole and ascorbic acid can effectively mitigate the galvanic corrosion of Cu and Ru. The main factor affecting the thickness and characteristics of the oxide layer formed during Ru electrochemical mechanical polishing process is the applied potential. From experiments it is also interesting to note that the thickness of passive film increases with the rotating speeds. With the increase of the rotating speeds under the same load, the thickness of Ru oxide layer increases and the friction coefficient measured decreases. With an increased load at the same speed, the thickness of Ru oxide layer decreases and the corrosion potential increases.