The role of additives on direct copper electrodeposition on barriers

The impact of bath composition and additives on copper nucleation on barrier materials was investigated. The effect of bath composition and additives on the initial stages of copper electrodeposition onto Ru substrates is presented in chapter 2. Surface pretreatment on Ru surface enhances the adhesion between Cu and Ru. The impact of additives and bulk cupric sulfate concentration is reported for both potentiostatic and galvanostatic operation. The presence of chloride ions and polyethylene glycol (PEG) leads to an increase of particle density, while bis (3-sulfopropyl) disulfide (SPS) leads to a decrease in particle density.;Numerical simulations are used to study the electrochemical nucleation and growth on barrier materials, and results are presented in chapter 3. The impact of reactant depletion on nucleation rate is considered by introduction of a concentration-dependent rate law. The effect is only important for progressive nucleation, when nucleation rates are comparable to or slower than the growth rate. For instantaneous nucleation, the impact of surface concentration depletion was not essential, because copper nucleation occurs before surface depletion is significant. A concentration-dependent nucleation rate may have a relatively small impact on the predicted current transient, but may have a significant: effect on particle density and size distribution.;The influence of the bulk concentration of cupric sulfate on copper nucleation on Ti and Ta was investigated, and results are presented in chapter 4. Both chronoamperometry and SEM suggest that an increase in bulk concentration cause an increase of particle density in dilute electrolyte, while the particle density does not increase with increasing concentration in the higher concentration range. The bulk concentration cupric sulfate is observed to have a significant impact on current transients. Results of pulsed electrodeposition are also shown, and simulation results get qualitatively agreement with experimental results.;Results for the electrochemical nucleation of Cu on Ru, Ta and glassy carbon are given in chapter 5. Additives are observed to have an impact on the microstructure of the copper film deposited on barrier materials. Similar trends are seen on Ru, Ta and glassy carbon. The presence of chloride ions (Cl-) and PEG increases the particle density minimally. The addition of SPS decreases particle density and increases particle size when results are compared at the same potential, and its acceleration effect still exists after copper coalesced on Ru. The behavior of additives also remains the same in both dilute electrolyte and concentrated electrolyte. The impact of additives on particle density is observed to be signifcant on Ru than on Ta and glassy carbon.