Introduction.

1. Introduction. • During the last decade the interest in copper passivity significantly increased due to the important role of copper in microelectronic industry. In resent years copper is being evaluated as a replacement for aluminum in integrated circuit interconnects. • One of the main steps in copper technology is chemical mechanical planarization (CMP). Determination of CMP slurry chemical composition, which could provide rapid and strong copper passivity, is an important issue for an efficient CMP. None of Cu CMP commercial slurries fulfills the requirement for rapid passivation. • The main task of our research is to determine the • parameters controlling copper passivity, such as chemical composition of slurry, pH range and the potential region of Cu passivity, which an efficient CMP can be achieved. • Objectives : • To study copper passivity in alkaline solutions composed of • sodium/potassium hydroxide and sodium/potassium carbonate. • To identify the role of pH and different oxidants, such • as, H2O2, KMnO4 and K2CrO4 on Cu passivity. • To evaluate the structure and chemical composition • of the formed passive film . • Experimental: • Electrochemical characteristics of copper was performed in a three electrode electrochemical cell equipped with Pt counter electrode and saturated calomel reference electrode. • Techniques & Methods: • Electrochemical methods: • - Potentiodynamic measurements; • - Potentiostatic measurements. • Surface studies • - HRSEM • - AFM/STM The effect of K2CO3 on Cu I-V profile of in solutions containing 10 g/l Na2SO4 The effect of KOH on Cu I-V profile in a solution containing 10 g/l Na2SO4 a b Increase in potassium carbonate concentration enhances copper passivity breakdown potential in solutions containing10 gr/l Na2SO4 solution. The values of anodic currents remained less than 10-5 A/cm2 in a wide range of potential. Copper repassivation potential in all examined K2CO3 concentrations is ~0.05V Increase in potassium hydroxide content enhances copper passivity breakdown potential. The repassivation potential of copper measured in the back scan was 0.0V for all the KOH concentrations (Fig. b). The effect of K2CO3 on Cu I-V profile Potentiodynamic behavior of copper in solutions containing K2CO3 and KMnO4 as a oxidizer. The effect of K2CO3 on Cu I-V profile of in solutions containing 1 g/l Na2SO4 The effect of reverse scan on Cu I-V profile in 1 gr/l Na2SO4 solution containing 4gr/l K2CO3 (pH 12.6) b a 1 mV/s 1 mV/s The addition of KMnO4 increases the OCP potential of copper in 4 gr/l K2CO3 solution. Increase in KMnO4 concentration shifts the onset of anodic current to more positive potentials. The reverse scan indicates high protection characteristics of the layer which is being formed on copper. Breakdown potential of copper in solutions with K2CO3 concentration above 1 gr/l is ~0.6 V. The values of anodic currents remained less than 10-5 A/cm2 in wide range of potential. Anodic currents obtained from copper in 1 gr/l K2CO3 solution are less than 10-5 A/cm2. Such low anodic currents can be attributed to the formation of a protective layer on the copper surface. Figure b presents reverse scan at different potentials, indicating the strong protective characteristics of the formed layer. The reverse scan indicates that at potential range between-0.1 V and 0.8 V, a protective layer is formed at the copper surface. At potentials above 0.8 V, a breakdown of the protective layer occurs and a further increase in the anodic currents indicates that copper is actively dissolved. AFM images of copper surface exposed at OCP (-0.15 V) in K2CO3 solution. AFM images of copper surface exposed at 0.2V in K2CO3 solution. Conclusions Potentiostatic behavior of copper in K2CO3 solution. • The use of basic solution such as alkaline and carbonate based slurries can provide full a passivity to copper surface. • The use of carbonate solution with the addition of oxidizer allows rapid formation of a compact and thin passive layer. • The passive film formed in carbonate based solution is stable in a wide range of potential (between -0.15 and 1.00 V). • Electrochemical tools in conjugation with in-situ AFM provide a complete understanding of copper passivity. Upon immersion 5 min. exposure Upon immersion 5 min. exposure Without scratching Periodically scratched (scriber) surface Sharp decrease of anodic current was obtained after applying +0.2 V. This indicates high rate of copper passivity K2CO3 solution. High rate of copper surface re-passivation was observed at periodically scratched surface. 60 min. exposure 30 min. exposure 30 min. exposure 60 min. exposure